Symposium Organizers
Dawn Bonnell University of Pennsylvania
Sergei V. Kalinin Oak Ridge National Laboratory
Sidney R. Cohen Weizmann Institute of Science
Richard E. Palmer University of Birmingham
B1: Scanning Probe Microscopies at the Limits of Resolution
Session Chairs
Ricardo Garcia
Charles Sykes
Monday PM, November 26, 2007
Back Bay A (Sheraton)
9:15 AM - B1.1
A Single-molecule Investigation of Ferroelectrics in a Simple Organic Monolayer System.
Ashleigh Baber 1 , Stephen Jensen 1 , E. Charles Sykes 1
1 Department of Chemistry, Tufts University, Medford, Massachusetts, United States
Show AbstractBy studying styrene, a simple hydrocarbon with a weak dipole moment we have investigated ferroelectric ordering and ferroelectric transitions at the single-molecule level. Low-temperature scanning tunneling microscopy imaging of individual styrene molecules reveals their internal structure, and hence the orientation of their dipole moment parallel to the Au{111} surface. At near monolayer coverages, both local ferroelectric ordering of the molecules and long-range antiferroelectric ordering of the domains are observed, and the dipole-dipole interaction energies quantified. A piezoelectric transition from ferroelectric to paraelectric ordering is observed upon further increase of the coverage. The effect of the STM tip in randomizing ordered domains is also discussed. This work demonstrates that important ferroelectric properties such as spontaneous polarization, long-range ordering and piezoelectricity can be achieved in nanoscale domains of a weakly polar molecule on a metal surface.
9:30 AM - **B1.2
Tracing Forces Between Individual Atoms by Atomic Force Microscopy.
Franz Giessibl 1
1 Physics, University of Regensburg, Regensburg Germany
Show AbstractThe invention of AFM by Binnig was triggered by his observations of force effects that occur when performing scanning tunneling microscopy experiments. The publication of first experiments with an “atomic force microscope” and the possibility of once obtaining atomic resolution by AFM1 lead to a surge in global research activities. However, it turned out that the road to an atom resolving force microscope was a long and winding one, a road that initially led away from STM. Measuring spring deflections through tunneling, the pivotal trick that promised great force resolution in AFM, proved to be impractical and it turned out that long-range interactions that are unimportant in STM are important in AFM. Almost a decade had passed before atomic resolution on silicon – STM’s early feat that captured the imagination of surface scientists – could be repeated by AFM in 1994. In these AFM experiments, cantilevers made from silicon with spring constants of about 20 N/m were used in the frequency-modulation mode (FM-AFM).2 In FM-AFM the cantilever is driven at a constant amplitude and forces acting between tip and sample are reflected in frequency changes. Intuitively, one would think that small oscillation amplitudes would be optimal in FM-AFM, because that would maximize the effects of the tip-sample forces on the cantilevers motion. However, amplitudes of about 10 nm were required when using silicon cantilevers with a stiffness of 20 N/m. Large amplitude operation has a disadvantage because it is strongly susceptible to long-range forces. To minimize the magnitude of long-range forces, sharp tips that were machined on the ends of silicon cantilevers had to be used. The introduction of force sensors that are about two orders of magnitude stiffer than usual silicon cantilevers has allowed stable small-amplitude operation and brought the AFM closer to a tool that focuses on chemical short-range forces.3 The qPlus sensor, an implementation of a self-sensing cantilever based on a quartz tuning fork, that is particularly simple to implement in STMs is now used in several laboratories4,5,6 at room temperature and low temperatures. In particular at low temperatures, measurements of chemical bonding forces at high-precision are now possible.7 Perspectives about the merits of adding AFM capabilities to previously pure STM experiments will be discussed. 1.G. Binnig, C. F. Quate, Ch. Gerber, Phys. Rev. Lett. 56, 930 (1986). 2.T. Albrecht, P. Grutter, H. K. Horne, and D. Rugar, J. Appl. Phys. 69, 668 (1991).3.Franz J. Giessibl, “AFM’s path to atomic resolution”, Materials Today 8, 32 (2005).4.M. Maier, Pico Nr. I 2006 , page 4 (Omicron newsletter, http://www.omicron.de).5.M. Ternes, C. P. Lutz, A. Heinrich et al., unpublished.6.M. Heyde et al., Appl. Phys. Lett. 89, 263107 (2006).7.Sugimoto, Y. et al. Nature 446, 64–67 (2007).
10:00 AM - **B1.3
Molecular Manipulation and Energy Transfer by STM.
Maki Kawai 2 1
2 Department of Advanced Materials Science, University of Tokyo, Kashiwa-shi Japan, 1 , RIKEN, wako-shi Japan
Show AbstractSpecial and state selective chemistry on individual molecules is nowadays being driven by inelastically tunneled electrons from an STM tip. Molecules adsorbed on substrates such as metals or semiconductors have been some good examples. Such molecular manipulation is often coupled with the excitation of vibrational modes. Vibrational spectrum of a single molecule provides useful information not only for the chemical identification of the molecule [1] but also for investigating how molecular vibration can couple with the relevant dynamical processes [2]. The response of vibrationally mediated molecular motion to applied bias voltage, namely an “action spectrum”, can reveal vibrational modes that excited through STM inelastic tunneling processes, because the molecular motion is induced only via the inelastic tunneling processes [3]. Thus, the action spectrum would be a candidate for detecting which vibrational mode is actually excited and associated with molecular motions. The mechanism to excite vibrational modes of molecules is revealed to be a resonant mechanism. Examples are given for dissociation of dimethyl disulfide to methylthiolates on Cu(111) and also hopping of the reaction product, methylthiolate, on the same surface [4-6]. Action spectra observed for both cases are well explained by accepting a resonant-excitation model i.e. the electronic state accepting electron via the transfer between the tip and the molecule acts as an resonant state to perturb the vibrational states to be excited. The coupling between vibrational states plays an important role on whether reaction coordinated can be perturbed when a certain vibrational state is excited. The key is the rate of anharmonic coupling between the vibrational modes of interest. At the symposium, we will discuss also on the dynamics of the coupling. References [1] Y. Kim, T. Komeda, and M. Kawai, Phys. Rev. Lett. 89, 126104 (2002). S. Katano, M. Trenary, Y. Kim and M. Kawai, Science in press (2007).[2] T. Komeda, Y. Kim, M. Kawai, et al., Science 295, 2055 (2002).[3] Y. Sainoo, Y. Kim, T. Okawa, et al., Phys. Rev. Lett. 95, 246102 (2005).[4] M. Ohara, Y. Kim and M. Kawai, Langmuir 21, 4779 (2005)[5] M. Ohara, Y. Kim and M. Kawai, Chem. Phys. Lett. 426, 357 (2006).[6] M. Ohara, Y. Kim and M. Kawai, submitted for publication.
11:00 AM - B1.4
Scanning Probe Energy Loss Spectroscopy.
Richard Palmer 1 , Adriano Pulisciano 1
1 Nanoscale Physics Research Laboratory, University of Birmingham, Birmingham United Kingdom
Show AbstractScanning Probe Energy Loss Spectroscopy (SPELS) is a new technique [1-3] that can be viewed as a hybrid between scanning tunneling microscopy (STM) and electron energy loss spectroscopy (EELS). Typical tip voltages of 50 to 200 V are used to produce an incident beam of electrons via field emission from the tip. The electrons are scattered at the surface and then detected by an energy analyser to reveal energy loss and secondary electron data. The fundamental advantage of SPELS is the potential to provide local, 10 nm-scale spectroscopic and therefore chemical/electronic information from surfaces. SPELS can access plasmon excitations, molecular electronic excitations, interband transitions and local secondary electron spectra [4].Here we present SPELS spectra taken at tip-surface distances of less than 100nm, an important development in attempts to achieve the highest possible spatial resolution. A working distance of 50 nm with respect to a graphite surface was achieved by producing tips which generated adequate signal intensities at voltages of only 30 to 60 V. The characteristic graphite π and σ plasmon modes were detected along with local secondary electron emission band structure features. We differentiate secondary electron peaks, occurring at fixed kinetic energy, from energy loss plasmon peaks.A SPELS study of thin films based on gold and silver is also presented. The surface plasmons of both noble metals are identified along with the tip voltage dependence of the interband transition background that exists in both cases. The Au surface plasmon was measured by SPELS for the first time and compared with (the first) conventional high resolution EELS measurements of the system. Results from a sputter coated gold surface indicate how the surface plasmon excitation, normally recorded at 2.5 eV for gold, can be shifted to an energy as high as 3.3 eV depending on the local positioning of the tip. In the case of a striped, micropatterned gold and silver surface, we measure both gold and silver plasmon modes and explore the possibility of coupling near the boundaries. [1] B.J. Eves, F. Festy, K. Svensson, and R.E. Palmer, Applied Physics Letters, 77, 2000, 4223.[2] R.E. Palmer, B.J. Eves, F. Festy, K. Svensson, Surface Science, 502, 2002, 224.[3] F. Festy and R.E. Palmer, Applied Physics Letters, 85, 2004, 5034.[4] J. Yin, A. Pulisciano and R.E. Palmer, Small, 2, 2006, 744.
11:15 AM - B1.5
Atomic Dipole Moment Distributions on Semiconductor and Insulator Surfaces Studied using Non-contact Scanning Nonlinear Dielectric Microscopy.
Yasuo Cho 1 , Ryusuke Hirose 1
1 Research Institue of Electrical Communication, Tohoku Univ., Sendai Japan
Show AbstractBroadly speaking, two types of scanning probe microscopy technologies have been reported to be capable of resolving real space topography with atomic resolution: i) scanning tunneling microscopy and ii) atomic force microscopy. Although these techniques have real atomic resolution, they cannot directly distinguish the atomic species making up the specimen to be measured without using other relative speculation. In recent years, we have developed and reported the use of scanning nonlinear dielectric microscopy (SNDM) for the measurement of the microscopic distribution of dielectric polarization. Thus, since the technique can sense the dielectric polarity of the specimen, if we can resolve a single electric dipole moment of an atom, we can expect to be able to directly distinguish atomic species. Most recently, we have succeeded in observing the Si(111)7×7 atomic structure using newly developed non-contact scanning nonlinear dielectric microscopy (NC-SNDM).[1] This is the first successful demonstration of the achievement of atomic resolution in a capacitance microscopy . Unfortunately, the quality of the image in Ref. [1] falls far short of clearly distinguishing the sign of a single-atom electric dipole moment. Nevertheless, advances in the resolution of SNDM have been expected to enable improved characterization of the single dipole moment at the atomic level.In this paper, we clearly resolve the electric dipole moment distribution of Si atoms on Si(111)7x7 surface by NC-SNDM under ultrahigh vacuum conditions. The dc-bias voltage dependence of the atomic dipole moment on Si(111)7x7 surface was measured and the directions and the magnitudes of dipole moments of Si atoms on the surface were revealed.Since the technique is applicable not only to semiconductors but also to both polar and non-polar dielectric insulator materials, SrTiO3 (STO) surface was also observed by NC-SNDM and we succeeded to resolve the surface atomic structure of STO . These results mean that SNDM will open new possibilities for SPM to distinguish the atomic species making up condensed matter without using speculative methods.[1]R. Hirose, K. Ohara. and Y. Cho, Nanotechnology 18, 084014 -1-5 (2007).
11:30 AM - B1.6
Electrochemical Imaging of Surfaces and Adsorbates at the Atomic-Scale.
Erin Iski 1 , Mahnaz El-Kouedi 2 , E. Charles Sykes 1
1 Chemistry, Tufts University, Medford, Massachusetts, United States, 2 Chemistry, University of North Carolina at Charlotte, Charlotte, North Carolina, United States
Show AbstractElectrochemical Scanning Tunneling Microscopy (EC-STM) is a useful technique as it operates under ambient conditions while providing atomic and molecular resolution of a surface. The pressure and temperature gaps can be bridged because in an electrochemical cell, the sample voltage can be cycled allowing for surface cleanliness at the atomic-level. Once the surface is clean, it is possible to add molecules to the electrolyte and then image the resultant surface assembly. Chiral molecule adsorption on achiral surfaces, like Au(111), is of particular interest as one can turn a flat achiral surface into a chiral one by molecular templating. In addition, the deposition of metal to create metal alloys on the surface can be used to alter the electronic state of the surface. This allows one to convert an inert surface like Au(111) into a more catalytically active surface without the problems associated with working with large reactive metal electrodes. The underpotential deposition of Ag on a Au(111) surface is of particular interest.
11:45 AM - B1.7
Templating Molecular Adsorbates with an Indium Nanocluster Surface.
Alfred Weymouth 1 , Alastair McLean 1
1 Physics, Queen's University, Kingston, Ontario, Canada
Show AbstractThe assembly of single atoms and molecules into more complex structures with tailored properties using bottom-up assembly processes is one of the central foci of nanoscience. The goal of this work is to develop a method in which molecules can be patterned in an array on a surface with sub-nanometer precision. Control over the properties of these molecules (optical, magnetic) would produce a functional molecular array. A material with regular spacing of magnetic moments, for example, could be of interest for magnetic storage.Previous studies in our group, using scanning tunneling microscopy (STM), have examined the assembly of metal nanoclusters on silicon and germanium surfaces. [1] It has recently been demonstrated that by carefully controlling the deposition of indium, arrays of identical six-atom clusters can be grown on Si(111) surfaces. [2] The large Si(111)-7x7 unit cell acts as a template for cluster growth and is preserved upon adsorption of the indium. At low coverage, isolated clusters form preferentially in the faulted half unit cell. As the coverage increases, the faulted half unit cells saturate with indium, creating a cluster surface. One half of the unit cells is thus saturated with indium and the other has exposed dangling bonds of silicon. In this study, we investigate thiophene (C4H4S – an aromatic heterocycle) on an indium cluster surface. Thiophene is an interesting candidate because it bonds differently to metals (via the sulfur atom) and silicon (via the carbon atoms). Previous results show that thiophene bonds to silicon readily at room temperature [3] but desorbs from bulk metals below room temperature [4]. Our preliminary results are in agreement with the literature, indicating thiophene bonding to the exposed unfaulted half unit cell. I will present what is known about the properties of cluster arrays and contrast our work to that done on a copper cluster surface where thiophene was observed bonding to the copper [5]. Our results, as well as possible mechanisms for this observed preferential bonding, will be discussed.[1] MacLeod et al. PRB 73, 241306(R). (2006)[2] Li et al. PRL 88, 066101. (2002) [3] Cao et al. JACS 122, 1812. (2000)[4] Sexton, Surf. Sci. 163, 99. (1985) [5] Zhang et al. APL 85, 2926. (2004)
12:00 PM - **B1.8
Imaging Functionality at the Nano-scale.
E. Ward Plummer 1 2
1 Physics and Astronomy, University of Tennessee, Knoxville , Tennessee, United States, 2 Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show Abstract12:30 PM - B1.9
4a×4a Electronic Charge Order and Nanoscale Electronic Inhomogeneity in the Pseudogap State of High-Tc Superconductor.
Ying-hao Liu 1 , K. Takeyama 1 , T. Kurosawa 1 , N. Momono 2 , M. Oda 1 , M. Ido 1
1 Department of Physics, Hokkaido University, Sapporo 060-0810 Japan, 2 Department of Materials Science and Engineering, Muroran Institute of Technology, Muroran 050-8585 Japan
Show AbstractElectronic inhomogeneity was revealed in the superconducting state of underdoped Bi2Sr2CaCu2O8 recently by scanning tunneling microscopy and spectroscopy (STM/STS) [1, 2] and attracted much attention in both theoretical and experimental aspects. But, its origin remains unclear until today. In this presentation, we report the experimental observations of the electronic inhomogeneity in the pseudogap and superconducting states of underdoped Bi2Sr2CaCu2O8 by STM/STS. We found that for the sample exhibiting the electronic inhomogeneity on the nanometer scale in the superconducting state, the pseudogap state is also inhomogeneous, while for the sample exhibiting a homogeneous superconducting state the pseudogap state is homogeneous on the nanometer scale. These observations seem to suggest that the electronic inhomogeneity in the superconducting state observed previously [1, 2] comes from that in the pseudogap state. In other words, the nanoscale electronic inhomogneity in the pseudogap state can persist into the superconducting state. We will also report that the static charge modulations, i.e. 4a×4a charge order (a, lattice constant), is strongly correlated with the electronic inhomogneity, implying that they will originate from the same electronic states. ___________________________________________________________ References[1] S. H. Pan, J. P. O’Neal, R. L. Badzey, C. Chamon, H. Ding, J. R. Engelbrecht, Z. Wang, H. Eisaki, S. Uchida, A. K. Gupta, K. W. Ng, E. W. Hudson, K. M. Lang, and J. C. Davis, Nature (London) 413, 282 (2001).[2]C. Howald, P. Fournier, and A. Kapitunik, Phys. Rev. B 64, 100504(R) (2001).
12:45 PM - B1.10
STM Tip Induced Reversible Local Melting of Charge Ordering in Pr0.63Ca0.37MnO3 Single Crystal.
Arup Raychaudhuri 1 2 , Sohini Kar 2
1 , S. N. Bose National Centre for Basic Sciences, Kolkata India, 2 Physics, Indian Institute of Science, Bangalore India
Show AbstractWe report the destabilization of the charge-ordered (CO) state in a localized region of Pr0.63Ca0.37MnO3(PCMO) single crystal by current injection using a scanning tunneling microscope (STM) tip. Destabilization of the CO state by a current in bulk crystal of PCMO is known. However, for the first time such an experiment has been done using an STM. The region where the charge ordered state is “molten”, is conducting and can have nanometric dimensions. The charge ordering transition leads to creation of an insulating state with a gap in the charge excitation spectra. This gap can be determined from tunneling spectroscopy. It was found that the gap collapses to a small value as the tunnel current is increased beyond a certain value. The effect occurs at temperatures below the charge ordering temperature, TCO = 235K, of PCMO. The collapse of the charge ordering gap is expected to create regions that have metallic conductance and hence a higher tunneling conductance. Simultaneous local conductance mapping (LCMAP), which measures the local tunneling conductance at a given bias as a function of position, show that a region being scanned by a high tunnel current is driven to an enhanced conductance state which persists even after reducing the scanning current to lower values. The creation of localized regions of high conductance by current injection, in a matrix that is insulating, gives rise to the possibility of “writing” with the STM tip. We showed that one can create or “write” regions of high local conductance of size ~20nm with a tunnel current of only ± 5nA. The region so created is stable and can be imaged (“read”) by using LCMAP with tunneling current limited to ± 1nA. The conducting region so created persists till the sample is heated above the TCO. Interestingly, the original conductance state can be restored or “erased” by using a tunnel current of same magnitude but of opposite polarity . Using this observation, we are able to “write” isolated metallic regions in an insulating background by controlling the tunnel current and we can subsequently “erase” these metallic regions by reversing the tunnel current. We find that the “Write-Read-Erase” process can be taken through repeated current cycles.
B2: Novel SPM Methods I
Session Chairs
Monday PM, November 26, 2007
Back Bay A (Sheraton)
2:30 PM - B2.1
Inner-shell Charging of Multiwalled Carbon Nanotubes.
Thierry Melin 1 , Mariusz Zdrojek 1 2 , Thomas Heim 4 , David Brunel 1 , Alexandre Mayer 3
1 ISEN, Institut d'Electronique de Microélectronique et de Nanotechnologie, IEMN-CNRS, Villeneuve d'Ascq France, 2 , Faculty of Physics, Warsaw University of Technology, Warsaw Poland, 4 , Interdisciplinary Research Institute, Villeneuve d'Ascq France, 3 , Laboratoire de Physique du Solide, Facultés Universitaires Notre-Dame de la Paix, Namur Belgium
Show Abstract2:45 PM - B2.2
Torsional Resonance Atomic Force Microscopy in Air and Liquid.
Nic Mullin 1 , Jamie Hobbs 1 2
1 Department of Physics & Astronomy, University of Sheffield, Sheffield United Kingdom, 2 Department of Chemistry, University of Sheffield, Sheffield United Kingdom
Show AbstractTorsional Resonance (TR) AFM is a dynamic AFM imaging technique in which the cantilever is oscillated about its long axis, yielding a nano or angstrom scale dithering motion at the tip. The resonant frequency, amplitude and phase of the dithering motion are sensitive to forces in the plane of the sample; hence this technique has attracted interest from the area of nanotribology. As the cantilever remains in the same position in the non-linear force gradient normal to the sample during imaging, it is possible to obtain analytical solutions to the equation of motion of the cantilever and extract quantitative data concerning the nature of the tip-sample interaction. It is also possible to monitor the normal deflection of the cantilever during force spectroscopy experiments, allowing the nature of the in-plane tip sample interaction to be studied as a function of separation. In the work presented here, an AFM capable of TR measurements in both air and liquid has been constructed and used to explore this tip-sample interaction. Novel aspects of the instrument are discussed, together with quantitative analysis of approach curves to shed light upon the image formation mechanism both in air and liquid. It is possible to image the topography and phase of delicate samples with high resolution in both environments. This work is of interest not only to the emerging field of TR AFM, but also to the well established Shear-Force Microscopy, where the difficulty of measuring the normal force has led to much debate in the literature concerning the mechanics of the tip-sample interaction.
3:00 PM - B2.3
Scanning Probe Recognition Microscopy.
Yuan Fan 1 , Q. Chen 1 , L. Udpa 1 , V. Ayres 1 , A. Rice 2
1 ECE, MSU, East Lansing, Michigan, United States, 2 , Veeco Metrology Group, Santa Barbara, California, United States
Show AbstractScanning Probe Microscopy(SPM) is one of the ideal techniques for nanoscale science in biology and medicine. Its great advantages are its direct investigative capability and its inherent resolution which easily and reliably reaches the nanometer level. But SPM has limitations in several aspects. One of them is the speed of imaging. Our group designed and developed a new SPM-based technique, Scanning Probe Recognition Microscopy(SPRM), in partnership with Veeco Instruments, which gives SPM system itself the ability to auto-focus on regions of interest through incorporation of recognition–based motion control. It will not only save the operation time dramatically, but also provide more reliable data and dynamic information.The recognition capability is realized using algorithms and techniques in pattern recognition and image processing fields. Adaptive learning and prediction are also implemented to make detection and recognition procedure quicker and more reliable. Scanning Probe Recognition Microscopy can operate in both offline and online modes. In the offline mode, the SPRM will auto-zoom the region of interest. An example of cell-sorting will be given and comparison with other auto-segmentation imaging techniques used for biological and semiconductor applications will be made. In the online mode, SPRM is able to auto-focus on either a single region of interest or multiple regions of interest. Examples of single and multiple region of interest SPRM will be presented from two points of view. One is from the point of view of saving time. Coarse and auto-focused fine scanning of cells and single molecules(the regions of interest) separated by large regions of empty substrate will be presented to demonstrate this aspect. The other is from the point of view of enabling investigations that cannot be done using raster-scan based SPM. Combined multiple properties investigations along individual nanofiber in a tissue scaffold will be used as one example of this aspect. Greatly increased data collection, sufficient to recognize patterns within the collected values is one new contribution that SPRM brings to this application. Another advantage is the ability to combine SPRM with deconvolution algorithm to achieve accurate measurements. SPRM applied to nanowire-based nanocircuits will be presented as another example of newly enabled capability in a different application area, thus demonstrating the universality of the technique. In this example, SPRM will be used to first track along the nanocircuit, including right-angle bends, and then to maintain auto-focus over the critical metal-nanowire contact region for electronic properties investigations.All these application examples discussed here show the power and universality of SPRM, which will be an outstanding assistant tool in the multiple research fields that need to be investigated with SPM techniques.Acknowledgments: The support of National Science Foundation DMI0400298 is gratefully acknowledged.
3:15 PM - B2.4
The Band Excitation Method for Energy Dissipation Measurements by SPM.
Stephen Jesse 1 , Brian Rodriguez 1 , Sergei Kalinin 1
1 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractQuantitative energy dissipation measurements in force-based SPM are key to understanding fundamental mechanisms of energy transformations on the nanoscale, molecular, and atomic levels. To date, these measurements are invariably based on either phase and amplitude detection in constant frequency mode, or amplitude detection in frequency tracking mode. The analysis in both cases assumes that amplitude is inversely proportional to the Q-factor - an assumption which is inapplicable when the driving force is position dependent, as is the case for virtually all SPM measurements. This limitation follows from the fact that currently available SPM's sample only a single frequency in the Fourier domain of the system. Thus, only two out of three parameters (amplitude, resonance, and Q) describing resonance can be determined independently. Here, we developed and implemented a new approach for SPM detection based on the excitation and detection of a signal having a specified amplitude over a band of frequencies that allows the simultaneous determination of all three parameters. This band excitation method allows acquisition of the pixel-by-pixel spectral response at a rates compatible with fast imaging (~10ms/pixel) and is illustrated for electromechanical and mechanical imaging, magnetic force microscopy, and force-distance spectroscopy. The BE method thus represents a broad reaching capability in SPM going beyond traditional single-frequency excitation.Research supported by the ORNL SEED program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC
3:30 PM - **B2.5
Optical Detection of Single Nonfluorescent Nanoparticles.
Vahid Sandoghdar 1
1 Laboratory of Physical Chemistry, ETH Zurich, Zurich Switzerland
Show AbstractThe advent of various single molecule detection techniques in the 1990s has pushed fluorescence microscopy to its limit, where a single dye molecule is used to visualize the location, translation or rotation of nanoscopic biological entities such as proteins. At the single emitter level, however, all fluorescent systems confront the problem of limited photostability. We show that an interferometric microscopy method can be used to detect nonfluorescent nanoparticles such as gold particles down to a diameter of 5 nm [1], microtubules [2] or single viruses on membranes [3] can be detected directly. Furthermore, we shall show that the modification of the fluorescence lifetime of an emitter close to a gold nanoparticle can be used as a measure for changes in the separation between the two [4, 5]. This method extends the range of fluorescence resonant energy transfer (FRET) as a nanoscopic ruler to 10-40 nm. If time permits, we will also discuss the design of plasmonic nanostructures (nano-antennae) for achieving very large modifications of the spontaneous emission rate and thus improvement of the quantum efficiency of poor emitters [6].[1] K. Lindfors, T. Kalkbrenner, P. Stoller, V. Sandoghdar, Phys. Rev. Lett. 93, 037401 (2004).[2] V. Jacobsen, P. Stoller, C. Brunner, V. Vogel, V. Sandoghdar, Optics Express 14, 405 (2006). [3] H. Ewers, V. Jacobsen, E. Klotzsch, A. E. Smith, A. Helenius, V. Sandoghdar, Nano Lett., to appear. [4] S. Kühn, U. Hakånson, L. Rogobete, and V. Sandoghdar, Phys. Rev. Lett. 97, 017402 (2006); see also the Supplementary Materials.[5] J. Seelig, K. Leslie, A. Renn, S. Kühn, V. Jacobsen, M. van de Corput, C. Wyman, V. Sandoghdar, Nano Lett. 7, 685 (2007).[6] L. Rogobete, F. Kaminski, M. Agio, V. Sandoghdar, Opt. Lett. 32, 1623 (2007).
B3: Novel SPM Methods II
Session Chairs
Monday PM, November 26, 2007
Back Bay A (Sheraton)
4:30 PM - **B3.1
Novel AFM Probes for Fast Imaging and Quantitative Material Characterization.
Levent Degertekin 1 , Guclu Onaran 1 , Mujdat Balantekin 1 , Hamdi Torun 1
1 G.W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractNovel AFM probe structures called the force-sensing integrated readout and active tip (FIRAT), are described and results on fast imaging, quantitative material characterization at nanoscale, and single biomolecular mechanics measurements are presented. FIRAT combines a micromachined integrated electrostatic actuator to move the tip and an integrated optical interferometric displacement detector in a microscale volume. Current implementation of the probe uses surface micromachined membrane and clamped-clamped beam structures on quartz substrates as the mechanical force sensing/actuation structure and provides tip motion normal to the sample surface. The probe tips are fabricated by focused ion beam assisted deposition. Tip displacement detection with interferometric sensitivity is achieved by monitoring the reflected diffraction pattern generated when the diffraction grating shaped actuator electrode is illuminated by a laser. Using several gratings, the tip motion in multiple directions can be detected and the detection range can be extended beyond the quarter wavelength - the typical limit in Michelson type optical interferometers. This robust interferometer structure has been shown to provide detection levels of 10fm/√Hz down to 3Hz, operating close to the shot noise level. These probes are already integrated to several commercial AFM systems for imaging and material characterization experiments. The results indicate the potential to increase the tapping mode imaging speed more than an order of magnitude as compared to commercial AFM systems. This is achieved by specially designed FIRAT structures with 1MHz resonance frequency, 40N/m spring constant and low quality factors (~5-10). FIRAT probes also enable measurement of transient tip-sample interaction forces with a broad bandwidth. When used in this time resolved interaction force (TRIF) mode, the probe provides quantitative information such as surface adhesion and elasticity through model based inversion, while simultaneously imaging the topography. TRIF mode data and images of adhesion energy, elastic modulus and viscosity have been obtained on various polymer and carbon nanotube samples. Finally, FIRAT probes fabricated for in-liquid, biological applications are described and initial results on single molecule force spectroscopy are presented.
5:00 PM - B3.2
Simultaneous Observation of Magnetic Domain Structure and Topography of Fe70Co30 Using Scanning Lorentz Force Microscopy.
Seiichi Suzuki 1 , Yasuo Azuma 1 , Yutaka Majima 1
1 Department of Physical Electronics, Tokyo Institute of Technology, Tokyo Japan
Show AbstractMagnetic imaging and analysis techniques have greatly contributed to the development of magnetic recording media such as hard disk drives. Various magnetic imaging methods employing scanning probes have been developed, such as magnetic force microscopy (MFM), spin-polarized scanning tunneling microscopy, scanning Hall probe microscopy, or scanning magnetoresistance microscopy.[1] MFM is one of the most widely used techniques to obtain stray magnetic field distribution; however, careful measurement is necessary in the MFM study under an external magnetic field because of the magnetization of the probe tip.[2] We have proposed scanning Lorentz force microscopy (SLFM) as a new technique to obtain magnetic images using a scanning probe.[3] SLFM is based on contact mode atomic force microscopy (AFM), and in this technique, a conductive cantilever is employed instead of a magnetic-coated tip. The main advantage of SLFM is that it is essentially possible to observe magnetic domain behaviors when an external magnetic field is applied because the SLFM cantilever does not need to contain magnetic materials. AC voltage is applied to the conductive cantilever, which is in contact with the sample, to make current flow through the tip. The tip current and a lateral stray magnetic flux density from a magnetic sample generate the Lorentz force which twists the cantilever in accordance with Fleming’s left hand rule. This Lorentz force causes the cantilever to undergo a lateral torsion since the direction of the Lorentz force is in the plain of the cantilever. Meanwhile, the surface topography corresponds to the vertical deflection of the cantilever. Here, we demonstrate the SLFM images of the magnetic domain of the Fe70Co30 sample along with its topography by using a boron-doped diamond-coated cantilever.[4] We discuss the effect of the surface roughness and friction force in the SLFM image as well as the repeatability of SLFM imaging by taking the raster scans in directions of 90° apart.[1] A. Hubert and R. Shäfer, Magnetic Domains (Springer, New York, 1998).[2] X. Zhu and P. Grutter, IEEE Trans. Magn. 39, 3420 (2003).[3] A. Okuda, J. Ichihara, and Y. Majima, Appl. Phys. Lett., 81, 2872 (2002).[4] S. Suzuki, Y. Azuma, and Y. Majima, Appl. Phys. Lett., 90, 053110 (2007).
5:15 PM - B3.3
Real time AFM for the Investigation of Viral and Cellular Materials and Processes.
Georg Fantner 1 , Paul Hansma 2 , Angela Belcher 1
1 Department of Materials Science and Engineering, Massachusets Institut of Technology, Cambridge, Massachusetts, United States, 2 Physics, University of California Santa Barbara, Santa Barbara, California, United States
Show AbstractObserving dynamic behavior at the nanometer scale is essential for understanding mechanisms underlying self assembly of materials or biological structures. Many of such processes occur in less than seconds and require observation in ambient or liquid conditions. Atomic force microscopy (AFM) has proven invaluable for the investigation of materials on the nanometer scale at these conditions. However, the low image acquisition speed has limited the use of AFM to investigation of samples that are not changing over time. AFMs with increased acquisition speeds are required for imaging dynamic processes. Successful attempts have been made to build high speed AFMs with small scan ranges (100s of nm) for investigations of single molecules and protein motors. In our work, we have designed an AFM to extend high speed AFM capability to larger samples in materials science and cell biology. The instrument uses a new flexure based scanner and cantilevers that are a factor of 10 smaller in all dimensions than conventional cantilevers. This way we achieve high detection speeds of several images per second and 12um scan range. We use this instrument to observe M13 bacteriophage viruses and the protein induced nucleation of nanoparticles on the virus. M13 bacteriophage is a rod shaped virus that can be genetically modified to express a variety of proteins at its end and at outer coat. These proteins have been selected to nucleate a variety of metals or semiconductor nano-crystals, creating interconnected nano-wires of the material. In our experiments we investigate the nucleation kinetics of the nano crystals and the arrangement of the virus into the desired network.
5:30 PM - B3.4
High Speed Surface Property Mapping: Continuous AFM Image Acquisition with Nanoscale Resolution in 1 Second or Less .
Ramesh Premnath 1 , Nicholas Polomoff 1 , Kate Bagnoli 1 , David Shuman 1 , Minhua Zhao 1 , Bryan Huey 1
1 Institute of Materials Science, University of Connecticut, Storrs, Connecticut, United States
Show AbstractA new variation of Atomic Force Microscopy (AFM) has been developed to address limitations on imaging speeds with modern AFM hardware. High Speed Surface Property Mapping (HSSPM) uniquely provides maps of electronic, mechanical, magnetic, piezoelectric, and other surface properties in seconds or less, compared with many minutes for traditional AFM imaging. In this manner, entire movies of hundreds of consecutive images are acquired, yet still maintaining the familiar nanoscale resolution of typical AFM. This allows unique and previously impractical studies of sample dynamics as well as efficient large area imaging. Furthermore, by varying external stimuli in a frame by frame manner, 4d-SPM is achieved (eg. as a function of in-situ biasing, temperature variations, applied force, etc.). Most importantly, the method is applicable to legacy AFM systems with the simple addition of moderate commercial test and measurement equipment. Examples of HSSPM applied to ferroelectrics, semiconductor masks, IC metal lines, block co-polymers, magnetic thin films, and biomolecular structures are provided. Finally, individual images with more than 128x128 pixels are acquired in as fast as 1/10th of a second with this widely applicable technique.
5:45 PM - B3.5
Detection of Magnetic Nanoparticles inside Liquid by Magnetic Force Microscopy.
Monalisa Mazumder 1 , Arup Purkayastha 2 , Suvranu De 3 , Theodorian Borca-Tasciuc 3
1 Department of Chemical & Biological Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States, 2 Department of Materials Science & Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States, 3 Department of Mechanical, Aerospace & Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States
Show AbstractDetection of nanoparticles suspended in liquids with nanoscale spatial resolution can have a wide range of applications from nano/microfluidics engineering and science to biological and medical fields. In the present work we report imaging of liquid droplets by atomic force microscopy (AFM) and then detection of magnetic nanoparticles inside those droplets by the magnetic force microscopy (MFM). To predict the sensitivity of the magnetic signal to various sample and cantilever configurations a theoretical model is developed. The model show detection is possible. The AFM topographic images were obtained in the tapping mode whereas the MFM images were taken by “lift mode” whereby a lift offset is applied to the preceding topographic scan using a magnetic tip. The challenge to image liquid surface comes from the wetting of an AFM cantilever by the liquid and formation of a capillary neck between the tip and the (liquid) sample. The strong capillary forces of the liquid bridge prevent stable imaging of the droplet surface. In this talk we will discuss our approach to overcome the aforesaid challenges and tune the tapping forces to obtain imaging condition stable enough for imaging not only the liquid surface but also capture the long range magnetic interaction between the AFM cantilever tip and the magnetic nanoparticles suspended in the liquid droplets. Such detection of nanoparticles inside liquid would be instrumental in understanding key aspects of nanoscale fluidic transport in different systems.
Symposium Organizers
Dawn Bonnell University of Pennsylvania
Sergei V. Kalinin Oak Ridge National Laboratory
Sidney R. Cohen Weizmann Institute of Science
Richard E. Palmer University of Birmingham
B4: SPM in Biology and Soft Condensed Matter
Session Chairs
Salim Elhadj
Paula Vilarinho
Tuesday AM, November 27, 2007
Back Bay A (Sheraton)
9:00 AM - B4.1
Combining High Aspect Ratio Carbon Nanotube AFM Probes with Attractive Mode Imaging for High Resolution Surface Potential Mapping.
Minhua Zhao 1 , Vaneet Sharma 2 , Sang-Yong Ju 2 , Fotios Papadimitrakopoulos 2 , Bryan Huey 2
1 Associateship NIH/NIST Programs, National Research Council, Washington, District of Columbia, United States, 2 Institute of Materials Science, University of Connecticut, Storrs, Connecticut, United States
Show AbstractThe resolution of Scanning Surface Potential Microscopy (SSPM) is partly limited by non-local electrostatic interactions due to the finite probe size. Here we present high resolution surface potential imaging on IC chip structures and bacteria membrane fragments via high aspect ratio carbon nanotube (CNT) AFM probes (Figure 1), which are homemade using AC dielectrophoresis. The unique features of the prepared CNT AFM probes are both high aspect ratio (CNT bundle typical length ~5 micron meters, diameter ~200 nano meters) and ultra-sharp at the end of CNT bundle (radius < 10nm). In the meantime, AFM probe contamination is a common issue in SSPM imaging, especially for soft biological samples. We approach this challenge by employing attractive instead of repulsive amplitude modulation for the first topographic scan, effectively eliminating probe contamination as well as damage to the sample surface. Accordingly, an enhanced contrast of surface potential is reported on IC interconnects compared to that derived by standard conducting AFM probes (Figure 2). In addition, ultra-high resolution surface potential images of bacteriorhodopsin on HOPG substrates are also achieved (Figure 3). High resolution in surface potential measurement is due to reduction of non-local capacitance coupling by high aspect ratio CNT AFM probes, discussed in terms of three electrode model.
9:15 AM - B4.2
Interaction Between Dibucaine and Supported Lipid Bilayers: Structural and Elastic Properties.
Gabriela Lorite 1 , Thatyane Nobre 2 , Maria Elisabete Zaniquelli 2 , Eneida de Paula 3 , Monica Cotta 1
1 Departamento de Física Aplicada, Instituto de Física Gleb Wataghin - UNICAMP, Campinas, SP, Brazil, 2 Departamento de Química, Faculdade de Filosofia Ciências e Letras de Ribeirão Preto - USP, Ribeirão Preto, SP, Brazil, 3 Departamento de Bioquímica, Instituto de Biologia - UNICAMP, Campinas, SP, Brazil
Show AbstractUnderstanding anesthetics-biomembrane interactions at high resolution is a key issue in current biophysical research. In this work we report on the interaction effects of the local anesthetic (LA) dibucaine (DBC) with lipids domains in model membranes by Atomic Force Microscopy (AFM). We have also used adsorption kinetics and elasticity measurements to complement the AFM analysis. Supported lipid bilayers are widely used as models to investigate the properties of biological membranes and associated processes such as molecular recognition, enzymatic catalysis, cell adhesion and membrane fusion. On the other hand, LA effects on structural and dynamic properties of the membrane lipid region could be the key to understand its mechanisms of action. Supported egg phosphatidylcholine (EPC) and dimyristoylphosphatidylcholine (DMPC) bilayers were formed on mica using the vesicle fusion method. Topography and phase images were acquired on the lipid membrane in the absence or presence of DBC. The AFM images show irregularly distributed and sized EPC domains on mica. On the other hand, DMPC formation presents extensive bilayer regions where multi-bilayer domains can be observed. For EPC bilayers, we have observed a progressive decrease in size of the original EPC domains with increasing DBC concentration. At higher concentrations (5mM), the DBC effect was more drastic, causing disruption of the EPC bilayer. For the DMPC bilayer, at 5mM DBC concentration, we observed a progressive disruption of the domains with time, but more slowly than in the EPC case. In both cases, phase images show the formation of small structures on the bilayer surface, which are associated to 0.05-0.2nm height variations in topography images. These results suggest an effect on the elastic properties of the bilayers when DBC is present. Adsorption kinetics and elasticity measurements of EPC and DMPC monolayers in the presence of DBC by pendant drop method confirm this hypothesis. The curve of lipid monolayer elasticity versus DBC concentration, for both cases (EPC or DMPC), shows a maximum for the elasticity modulus at the same DBC concentration where we observed the disruption of the bilayers by AFM. These results indicate that at this point the disruption of the monolayers occur and new aggregates (lipids and DBC) are formed. Our results suggest that changes of the local curvature of the bilayer in the presence of DBC could be a possible mechanism for the anesthetic action in membranes.
9:30 AM - **B4.3
In vitro High-resolution Architecture and Structural Dynamics of Single Pathogens.
Marco Plomp 1 , Terrance Leighton 2 , Katherine Wheeler 2 , Bert Vogelstein 3 , Hoi-Ying Holman 4 , Alexander Malkin 1
1 Chemistry, Materials, and Life Sciences, Lawrence Livermore National Laboratory, Livermore, California, United States, 2 , Children's Hospital Oakland Research Institute, Oalkand, California, United States, 3 , The Johns Hopkins Kimmel Cancer Center, Baltimore, Maryland, United States, 4 , Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractElucidating the molecular architecture of pathogen surfaces and its structural dynamics is essential to understanding mechanisms of pathogenesis, immune response, physicochemical interactions, environmental resistance and development of countermeasures against bioterrorist agents. I will discuss the application of in vitro AFM for studies of high-resolution architecture, assembly and structural dynamics of several microbial systems, including bacteria and bacterial spores. We have demonstrated that strikingly different species-dependent high-resolution structures of the spore coat appear to be a consequence of crystallization mechanisms that regulate the assembly of the spore coat (1,2). In case of Clostridium novyi-NT spores (3), coat layers were found to exhibit screw dislocations typically observed on inorganic and macromolecular crystals. This presents the first case of non-mineral crystal growth patterns being revealed for a biological organism. The similarities in the mechanisms controlling the assembly of spore coat structures and the growth of minerals and macromolecular crystals provides an unexpected example of nature exploiting fundamental materials science mechanisms for the morphogenetic control of biological ultrastructures. I will present data on the direct visualization of the high-resolution structural dynamics of single Bacillus atrophaeus spores germinating under native conditions (4). Here we show that AFM reveals previously unrecognized germination-induced alterations in spore coat architecture and topology as well as the disassembly of outer spore coat rodlet structures. These results suggest that the spore coat rodlets are structurally similar to amyloid fibrils, which have been historically associated with neural degenerative diseases. The in vitro AFM imaging also revealed the porous fibrous cell wall structure of newly emerging and mature vegetative cells, consisting of a network of nanometer-wide peptidoglycan fibers. I will also present data on the direct visualization of stress-induced environmental response of metal-resistant Arthrobacter oxydans bacteria to Cr (VI) exposure. These studies demonstrate that in vitro AFM can probe microbial surface architecture, environmental dynamics and the life cycle of pathogens at near-molecular resolution under physiological conditions. This work was performed under the auspices of the U.S.DOE at LLNL under contract number W-7405-ENG-48.1. M.Plomp, T.J. Leighton, K.E. Wheeler and A.J. Malkin (2005). Biophys. J., 88, 603-608. 2. M.Plomp, T.J. Leighton, K.E. Wheeler and A.J. Malkin (2005). Langmuir, 23, 10710. 3. M. Plomp, J. M. McCaffery, I. Cheong, X. Huang, C. Bettegowda, K. W Kinzler, S. Zhou, B. Vogelstein and A. J. Malkin (2007). J. Bacteriology, in press. 4. M. Plomp, T. J. Leighton, K.E. Wheeler, H. D. Hill and A. J. Malkin (2007). bacterial spores. PNAS, 104 (23), 9644.
10:00 AM - B4.4
Sub-molecular Resolution Imaging of Bacteriorhodopsin in Liquids by Frequency Modulation Atomic Force Microscopy.
Takashi Horiuchi 1 , Kenjiro Kimura 1 2 , Kei Kobayashi 2 3 , Kazumi Matsushige 1 , Yoshiki Hirata 4 , Hirofumi Yamada 1 2
1 Department of Electronic Science and Engineering, Kyoto University, Kyoto Japan, 2 Advanced Measurements and Analysis, Japan Science and Technology Agency, Kyoto Japan, 3 International Innovation Center, Kyoto University, Kyoto Japan, 4 , National Institute of Advanced Industrial Science and Technology, Tsukuba Japan
Show AbstractHigh-resolution atomic force microscopy (AFM) imaging in liquids is severely hindered by the extreme reduction of the Q-factor due to the hydrodynamic interaction between the cantilever and the liquids. We recently found that the use of the small amplitude mode (less than 1 nm) brought great progress in frequency modulation atomic force microscopy (FM-AFM) imaging in liquids [1]. The force sensitivity is increased by FM detection with small amplitude oscillation because of the increase in the duration of the proximity interactions. Note that the small amplitude mode can be used only when the noise in the deflection sensor is sufficiently reduced to a level of the thermal fluctuation of the cantilever. In this presentation our recent investigations of individual protein molecules in liquids by high-resolution FM-AFM are reported. The sample used in this study was a purple membrane deposited on a cleaved mica surface. The membrane contains arrays of the protein molecules functioning as proton pumps (bacteriorhodopsin: bR). We successfully imaged each individual monomer molecule in the trimer structure. The difference in structure between the cytoplasmic and the extracellular sides of the membrane was clearly observed. We also found that the images of the internal structure of the single protein strongly depend on the frequency shift, which can be interpreted as the deformation of the protruded loops. [1] T. Fukuma, K. Kobayashi, K. Matsushige and H. Yamada, Appl. Phys. Lett., 87, 034101 (2005) [2] H. Yamada, T. Kajita, T. Horiuchi, K. Kobayashi, Y. Hirata, International Conference on Nanoscience and Technology, Basel, Switzerland (2006).
10:15 AM - B4.5
Electromechanical Probing of Cellular and Biomolecular Systems on the Nanoscale.
Brian Rodriguez 1 2 , Gary Thompson 3 , S. Jesse 1 , K. Seal 2 , Roger Proksch 4 , Sophia Hohlbauch 4 , Irene Revenko 4 , Alexey Vertegel 3 , S. Kalinin 1 2
1 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 The Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 3 Department of Bioengineering, Clemson University, Clemson, South Carolina, United States, 4 , Asylum Research, Santa Barbara, California, United States
Show AbstractElectromechanical coupling is ubiquitous in biological systems with examples ranging from simple piezoelectricity in calcified and connective tissues to voltage-gated ion channels, energy storage in mitochondria, and electromechanical activity in cardiac myocytes and outer hair cell stereocilia. Piezoresponse force microscopy (PFM) originally emerged as a technique to study electromechanical phenomena in ferroelectric materials, and in recent years, has been employed to study a broad range of non-ferroelectric polar materials, including piezoelectric biomaterials. At the same time, the technique has been extended from ambient to liquid imaging on model ferroelectric systems. Here, we present results on local electromechanical probing of several model cellular and biomolecular systems, including breast adenocarcinoma cells, yeast, and red blood cells. The specific features of PFM operation in liquid are delineated and bottlenecks on the route towards nanometer-resolution electromechanical imaging of biological systems are identified. An intermittent-contact version of PFM is also discussed. In air, this mode is dominated by electrostatic forces, which are screened in solution, allowing the electromechanical signal to dominate. The pathway for molecular resolution electromechanical imaging is illustrated using model bacteriorhodopsin membranes in a liquid environment.Research sponsored in part by the Division of Materials Sciences and Engineering ORNL LDRD funding (BJR, SJ, and SVK) through the Office of Basic Energy Sciences, U.S. Department of Energy, at ORNL managed and operated by UT-Battelle, LLC. Research was also supported through CNMS user proposals #2005-075 and #2006-049, and NSF #CMS-0619739 (GLT and AAV). The authors (BJR, SVK, GLT) are also grateful for financial support from Asylum Research and for the use of their imaging facilities.
11:00 AM - **B4.6
Topography in Protein Micropatterned Substrates.
Jan Hoh 1 , William Heinz 1 , Jonas Rundqvist 2 , Devrim Pesen 2 , Jeffrey Werbin 1 , Beatriz Mendoza 2 , Christopher Lemmon 1 , Lewis Romer 1 , David Haviland 2
1 , Johns Hopkins School of Medicine, Baltimore, Maryland, United States, 2 , Royal Institute of Technology, Stockholm Sweden
Show AbstractMicropatterns of proteins and other biomolecules are emerging as powerful tools for studying how cells interpret signals in the local microenvironment. Living cells interact with their environment through signals mediated by proteins and other signaling molecules. Some of these molecules are soluble and can act at large distances, but many signaling molecules are immobilized and require a direct physical contact with the cell. These direct contacts can, for example, be in the form of a cell-cell contact or a cell-extracellular matrix contact. Micropatterning offers the ability to experimentally control the composition and spatial organization of molecules in cell culture systems. A wide range of patterning methods are being developed for these types studies, and one issue that emerges is the degree of topographic coupling. That is to what extent does the chemical patterning also introduce a topographic feature? Cells are well known to respond to topographic cues in the microenvironment, and therefore it is important to know the how much changing of the local biochemistry also changes the topography. Atomic force microscopy is an excellent tool for measuring small height variations in features with lateral dimensions of nanometers to micrometers. We are establishing a collection of methods for pattering in order to study how cells interpret spatially variant biochemical cues, and here report on the AFM characterization of patterns made by various methods. For example, electron beam lithography has been used to patterned proteins by highly localized functional inactivation. In this patterning approach a conducting substrate such as doped silicon is coated with a protein monolayer, and pattern features <100 nm are produced by exposure to the electron beam. AFM imaging shows that these patterns have no detectable topography, although when labeled with an antibody the pattern is topographically clearly visible. An alternate patterning approach based on a laser microplasma has also been developed. In this approach a substrate such a glass coverslip is coated with a monolayer of a protein, and the protein is removed in a predetermined pattern by scanning the laser across the surface. Here, the physical removal of the protein produces a clear topographic feature, although interestingly the functional inactivation appears to extend beyond the topographic change. Results from other methods will also be presented, including microfluidic patterning using the Nano Enabler (Bioforce Nanosciences).
11:30 AM - B4.7
Electrophoretic Deposition of Proteins Using Atomic Force Control.
Aaron Lewis 1 2 , Yulia Lovsky 2 1 , Chaim Sukenik 3 , Eli Grushka 4
1 , Nanonics Imaging Ltd., Jerusalem Israel, 2 Applied Physics, Hebrew University of Jerusalem, Jerusalem Israel, 3 Inorganic & Analytical Chemistry, Hebrew University of Jerusalem, Jerusalem Israel, 4 Chemistry, Bar Ilan University, Ramat Gan Israel
Show AbstractCapillary electrophoresis (CE) is a rapid and efficient technique for separation of a variety of compounds including proteins and other bio-molecules. Research in our laboratory has shown that cantilevered quartz nanopipettes can be used for Fountain Pen NanoLithography (FPN) with atomic force controlled delivery of liquid phase chemicals such as etchants [1], proteins [2] etc. By combining these two techniques we can achieve the correlation of the separation of chemicals in time with spatially controlled nanodeposition to obtain Atomic Force Controlled Capillary Electrophoresis or ACCE. Here we demonstrate electrophoretic delivery of Bovine Serum Albumin (BSA) upon mirrorepoxy substrate, using atomic force microscopic (AFM) techniques. The electric field is applied between two electrodes that are positioned on the nanopipette itself. This allows the use of variety of substrates for different applications. A cantilevered nanopipette with 0.1-0.5 micron aperture sizes is filled with a solution of BSA in pH 8 buffer where the protein is negatively charged. Positive polarity of the applied voltage causes the protein to migrate to the substrate while negative polarity reverses the flow direction of the protein and moves it away from the substrate. Additional mechanisms of the voltage control of deposition are also described including electroosmotic flow (EOF). The detection of the protein on the substrate is achieved by reflection fluorescence near field imaging (NSOM) techniques. 1.A. Lewis, Y. Kheifetz, E. Shambrodt, A. Radko, E. Khatchatryan And C. Sukenik, Appl. Phys. Lett 75, 2689-2691 (1999).2.H. Taha , R. Marks , L. Gheber , I. Rousso and J. Newman, C. Sukenik and A. Lewis, Applied Physics Letters 83, 1041-1043 (2003)
11:45 AM - B4.8
Probing Microsprayed Polymer-Drug Coatings with Novel Environmental AFM: Morphology, Segregation and Crystallization.
Greg Haugstad 1 , Klaus Wormuth 2
1 Institute of Technology Characterization Facility, University of Minnesota, Minneapolis, Minnesota, United States, 2 , Surmodics, Inc., Eden Prairie, Minnesota, United States
Show AbstractThe formulation of drug eluting coatings remains a challenge because coatings must be thin, conformal, and mechanically stable to deformations during medical device insertion; yet have chemical and morphological characteristics conducive to controlled elution of drug. Structure is critical, with phenomena such as segregation of ingredients (across coatings and surface/interior) and nano-to-microscale crystallization strongly impacting the ultimate drug release kinetics. Thus a probe that reveals not only morphology down to the nanoscale but also the distribution of specific ingredients, and moreover mechanical behavior, is of high interest. A large part of our effort in this arena has been in developing advanced scanning probe microscopy (SPM) methodologies. We present environmental Digital Pulsed Force Mode atomic force microscopy (AFM) of poly n-alkyl methacrylate blend coatings incorporating the drug dexamethasone, spray-deposited as microdroplets on silanated-glass (a commercial deposition process for stent coatings). These results are complemented by confocal Raman microscopy to characterize 3D chemical distribution at submicron spatial resolution, and time-of-flight secondary ion mass spectrometry in full-imaging mode (mass spectrum per pixel location).Our implementation of Digital Pulsed Force Mode AFM acquires force-distance cycles at each image location (up to 512x512 pixel, GB-regime data files) under variable ultimate load, relative humidity and sample temperature. Images of tip-sample adhesion, mechanical stiffness and viscoelastic loss angle, as well as details of the tip-sample separation dynamics at sub-microsecond time resolution, elucidate the micro-to-nanoscale segregation of polymer phases and drug. Differences in viscoelastic memory were examined by varying the maximum load (set point) achieved during force-distance cycles. We identify a significant correlation of ingredient concentration with crater or wheel-and-spoke morphologies of impacted microdroplets, apparently deriving from the deposition process. Relative humidity was controlled via a custom, feedback-driven system to provide a range of specific values; sample temperature was controlled using the commercial SPM system. On poly(butyl/laurel methacrylate) coatings containing dexamethasone, one goal was a targeted softening of PBMA domains (glassy at room temperature) to differentiate from dexamethasone. Another goal was the “careful” mobilization of drug (i.e., compared to liquid immersion) to induce crystallization and thereby help to identify non-crystalline manifestations of drug initially present. The discovery of rampant crystallization within a subpopulation of microdroplets, while largely absent in others (also utilizing light microscopy), is a phenomenon of ongoing investigation.
12:00 PM - **B4.9
Force Spectroscopy: from Forced Unfolding of Single Proteins to Forced Unfolding within Cells.
Dennis Discher 1
1 , University of Pennsylvania, Philadelphia, Pennsylvania, United States
Show AbstractUnlike synthetic polymers, proteins generally fold into ordered conformations that are biologically functional. ‘Cytoskeletal’ proteins fold and have mechanical and signaling functions in cells, but the stresses sustained by the cytoskeleton have raised questions of whether proteins unfold under force and whether forced unfolding is part of function. Force spectroscopy methods emerged about a decade ago, primarily AFM methods, and it is now clear that many purified cytoskeletal proteins can unfold under force in a rate dependent fashion. Our own AFM studies have demonstrated the surprisingly strong dependence on temperatures near body temperature (37 C), which softens folded proteins, and we have also demonstrated coupling of forced unfolding to single molecule chemical reactions. Both studies paved the way to our latest in-cell studies of forced unfolding. Most recently, in order to identify cytoskeletal proteins that change conformation or assembly in stressed versus static cells, in situ labeling of sterically shielded cysteines in proteins with fluorophores was analyzed by fluorescence imaging, quantitative mass spectrometry, and sequential multi-dye labeling. Shotgun labeling of blood cells and stem cells shows that shielded cysteines in the cytoskeletal proteins spectrin and filamin are increasingly labeled as a function of shear stress and time, indicative of forced unfolding of specific domains. These in-cell systems are now being investigated by coupled AFM(T)-Fluorescence to better understand the molecular forces in cells, but forced unfolding of at least some proteins within cells seems clear from our multi-pronged approach.
12:30 PM - B4.10
Nanoscale Forces at the Heart of Staphylococcus Infections.
Ruchirej Yongsunthon 1 2 , Francis Vellano 2 , Brian Lower 3 , Vance Fowler 4 , Emily Alexander 4 , Steven Lower 2
1 , Corning Incorporated, Corning, New York, United States, 2 , Ohio State University, Columbus, Ohio, United States, 3 , Pacific Northwest National Laboratory, Richland, Washington, United States, 4 , Duke University, Durham, North Carolina, United States
Show Abstract Implanted cardiac devices (e.g., prosthetic heart valves) that improve a patient’s quality of life paradoxically also place the patient at increased risk for life-threatening infection by Staphylococcus aureus. Blood proteins, such as fibronectin, adsorb onto the implanted device surface and provide anchoring sites for bacterial cell wall adhesins called MSCRAMMs (microbial surface components that recognize adhesive matrix molecules). Once attached, S. aureus may proliferate and form device-related biofilms. These biofilm-associated infections are difficult to combat with antibiotics and often require complicated surgical removal for cure. Clinical studies have highlighted the impact of S. aureus biofilms on human health and separate laboratory studies have probed the nanoscale forces between S. aureus and a material surface. This work begins to bridge the long-standing gap between macroscopic, clinical investigations and phenomena occurring at the nanometer scale by presenting a strong correlation between the clinical outcome of patients with prosthetic devices and the forces ultimately responsible for S. aureus biofilms in vivo. Atomic force microscopy was used to “fish” for binding reactions between a fibronectin-coated probe (i.e., substrate simulating an implant device) and each of 15 different strains of S. aureus which produce MSCRAMMs such as fibronectin binding protein. These clinical bacterial strains were isolated from either patients with infected cardiac prosthesis (invasive group) or healthy human subjects (control group). Preliminary analysis of 30,000+ force-distance profiles established a strong distinction in the binding force signature observed for the invasive vs. control populations, established a correlation spanning 7 orders of magnitude between the nanoscale forces of interaction and macroscopic, clinical infections occurring in humans. This observation suggests that a microorganism’s “force taxonomy” may provide a fundamental and practical indicator of the risk that bacterial infections pose to patients with implanted medical devices. Additionally, exploration of these interaction forces may enhance understanding of bacterial binding mechanisms and provide a novel perspective for preventing biofilm infections in humans.
12:45 PM - B4.11
Poly (L-lactic) Acid for Biomedical Application - Assessment of Piezoelectric Properties and Protein Adsorption Mechanism by Scanning Probe Microscopy.
Nathalie Barroca 1 , Ana Daniel-da-Silva 1 , Aiying Wu 1 , Maria Fernandes 1 , Paula Vilarinho 1 , Alexei Gruverman 2
1 Department of Ceramics and Glass Engineering, University of Aveiro, Aveiro Portugal, 2 Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina, United States
Show AbstractThe piezoelectric properties of bone have been implicated as a regulatory mechanism of local remodelling and mineral deposition. Thus, piezoelectric materials such as BaTiO3, PVDF, Teflon, natural collagen, modified collagen and poly (L-lactic) acid (PLLA) have been investigated to be used as bone substitutes and have shown to accelerate bone regeneration [1,2]. However, the responsible mechanisms have not been fully evaluated and are still unclear. A limiting factor to this understanding has been the lack of tools to access at a nanoscale the regeneration process. However the recent developed piezoforce microscopy opens the possibility for nanoscale characterization of materials particularly the piezoelectric properties, by using electrical interactions between the probing tip and the surface.In this work atomic force microscopy (AFM) is used for the first time for the investigation of piezoelectric properties of PLLA spin-coated thin films at the nanoscale level by piezoresponse force microscopy (PFM) and AFM non – contact mode to study protein adsorption mechanism in poled and non poled PLLA samples. PLLA, a semi-crystalline polymer, due to its unique property of being both piezoelectric and biodegradable is an interesting candidate to be used as a piezoelectric bone graft scaffold. As the piezoelectric properties are related to the crystalline character, PLLA thin films were prepared with different crystalline characteristics. For that different post melting isothermal annealings were conducted at varied temperatures near the glass transition and crystallization temperatures to induce both nucleation and crystal growth. Piezoelectric activity was detected in the prepared films, piezoresponse was imaged and local piezoelectric hysteresis loops were measured. The results clearly show an improvement of the local piezoelectric properties with increasing crystallinity. PLLA thin films were also submitted to local poling by a DC field application through PFM tip and dipole motion and switching were demonstrated and imaged. Additionally, it is known that when a biomaterial is implanted in the body, the first biological event that happens is the protein adsorption and later cells adhesion and proliferation. Thus, protein adsorption assays were conducted on poled and unpoled PLLA thin films for different immersion times in simulated body fluid (SBF) to analyse the effect of the polarization on the protein adsorption kinetics. Human serum fibronectin, as the first protein to be adsorbed in vivo, was used in SBF in the same concentration as in the human blood plasma. Non-contact mode was then used to image protein adsorption in air and also in liquid to allow imaging in an environment closer to the protein native one.1. Tsutomu Ochiai, Eiichi Fukada, Jpn. J. Appl. Phys. Vol. 37 3374-3376 (1998). 3. C. Halperin, S. Mutchnik, A. Agronin, M. Molotskii, P. Urenski, M. Salai, and G. Rosenman, NanoLetters Vol. 4, No. 7. 1253-1256 (2004)
B5: NSOM and Nanooptics
Session Chairs
Tuesday PM, November 27, 2007
Back Bay A (Sheraton)
2:30 PM - **B5.1
Nanoscale Spectroscopy with Optical Antennas.
Lukas Novotny 1 , Palash Bharadwaj 1 , Neil Anderson 1 , Matthias Danckwerts 1
1 The Institute of Optics, University of Rochester, Rochester, New York, United States
Show AbstractAntennas are devices that efficiently convert localized energy to free propagating radiation, and vice versa. They are a key enabling technology in the microwave and radiowave regime but their optical counterpart is greatly unexplored.In order to understand antenna-coupled light emission and absorption we use a single molecule as an elementary light emitting device. With an optical antenna in the form of a simple gold particle we are able to increase the emission efficiency by more than a factor of 10. However, for very short distances between particle and molecule the fluorescence yield drops drastically because of nonradiative energy transfer. A simple gold particle is not an efficient optical antenna and it can be expected that favorably designed nanoplasmonic structures will yield much higher enhancement. Optical antennas can be employed as light sources for high-resolution optical microscopy and spectroscopy. We demonstrate vibrational (Raman scattering) and nonlinear imaging with spatial resolutions down to 10nm.
3:00 PM - B5.2
STM and SNOM Type of Scanning Probe Microscopes in the Same Unit: Towards Electrical Modification and Optical Characterization at Nanoscale.
Ilya Sychugov 1 , Hiroo Omi 1 , Tooru Murashita 2 , Yoshihiro Kobayashi 1
1 NTT Basic Research Labs, NTT Corporation, Atsugi, Kanagawa, Japan, 2 NTT Photonics Laboratories, NTT Corporation, Atsugi, Kanagawa, Japan
Show AbstractOptical and electrical properties of nanostructures can be addressed using radiation or electrical current as a probe. In general, a near-field type of electromagnetic interaction is necessary for an optical probe to enter nanoscale regime in the spatial resolution domain by overcoming the optical diffraction limit (~ 1 um). A typical scanning near-field optical microscope (aperture-SNOM) provides such an opportunity both for the excitation and collection of light for spectroscopy applications. However, this instrument utilizes a dielectric fiber tip as an aperture, which makes it unsuitable for electrical measurements. On the other hand, a scanning tunneling microscope (STM), capable of atomic-resolution measurements by electrical current, can also cause luminescence of materials. Here, in order to realize both electrical and optical probing at nanoscale, we combine these two kinds of instruments into a single unit. An STM-luminescence (STML) instrument with a conductive and transparent tip, featuring ~ 10 nm spatial resolution, was reported previously. We have complemented it with a beamsplitter unit in a configuration typical for the fluorescent microscopy. The excitation light is guided from lasers through a beamsplitter unit to the indium tin oxide (ITO) coated tip and the signal is collected via the same fiber transmission line at the beamsplitter output. Variation of the excitation wavelength was realized using various beamsplitter units with different optical design for the UV-line of a He-Cd laser (325 nm) and the green line of the second-harmonic Nd:YAG laser (532 nm). The signal can be collected in a spectroscopy mode or in a photon mapping regime. The proof-of-the-concept experiments were performed on luminescent Si nanocrystals and GaAs quantum wells.The influence of tip geometry on collection efficiency and spatial resolution as well as inherent limitations of such an instrument are discussed. This approach may find its niche not only where all-optical measurements with subwavelength resolution are required in addition to STM and STML characterization, but also where electrical modification with subsequent in situ optical probing is desirable.
3:15 PM - B5.3
Study of Photoinduced Charging Effects in Hybrid CdSe-Au Nanodumbbells Using Electrostatic Force Microscopy (EFM).
Ronny Costi 1 2 , Uri Banin 1 2
1 Department of Physical Chemistry, The Hebrew University of Jerusalem, Jerusalem Israel, 2 The Center for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem, Jerusalem Israel
Show AbstractPhotoinduced charge separation has been studied extensively in different systems due to the potential in using these effects for photocatalysis, photochemical reactions and alternative energy production. Charge separation via light absorbance can be used to transform solar energy to a more available form of energy e.g. chemical energy. The ability to create a well defined nanometric structure with control over the charge separation should allows us the degrees of freedom in designing functional systems with light induced activity. Nanodumbbells (NDBs) are hybrid nanocrystals consisting of a semiconducting CdSe nanorod body with selectively grown gold tips. These metal tipped nano-structures provide a unique model for a metal-semiconductor interface on the nanometer scale. The metal-semiconductor nanometric interface introduces new electronic effects to the nano-structure, such as a light induced charge separation. We use electrostatic force microscopy (EFM) to study the charging effects in hybrid nanodumbbells. EFM is an atomic force microscopy based method that allows the sensing of long range electrostatic forces. The EFM method we use enables the separation of the electrostatic force into two different components – forces derived from the polarizability of the material and forces derived from charges within the sample. By following the charge component of the electrostatic force it is possible to image and quantify the amount of charges within a single nanoparticle. This method is sensitive enough as to detect a single charge within the sample. We have studied the charging effects of CdSe-Au hybrid nanodumbbells and of its separate components – CdSe nanorods and gold nanoparticles. We were able to show that hybrid nanodumbbells exhibit slight negative charging whereas its components exhibit no charging effects. During illumination of the sample an accumulation of negative charge was seen, indicating that the charging effect is a light induced effect. The experimental results were modeled using different theoretical and mathematical proximities to quantify the amount of charges per particle.
3:30 PM - **B5.4
Ultrafast Evolution of Photonic Eigenstates Investigated in Real and K-space.
Laurens Kuipers 1
1 Center for Nanophotonics, FOM Institute AMOLF, Amsterdam Netherlands
Show AbstractThe optical properties of nanophotonic structures are governed by their photonic eigenstates and the coupling between them. Periodic nanostructures can exert a huge influence on the propagating light, which in the structure has to obey Bloch's theorem just like electrons in an atomic lattice have to. In nanophotonics this leads to exciting phenomena like slow light in photonic crystal waveguides [1] or extraordinary transmission through periodic subwavelength hole arrays [2]. Small variations in the geometry of the structure, intentional or not, can break the crystal symmetry and result in huge variations in optical properties.Investigations of nanophotonic structures "from the outside" typically yield only limited information concerning the photonic eigenstates. Near-field visualization of the light propagation allows the propagation of light inside the structure to be tracked. In reciprocal space (k-space) the photonic eigenstates can really be identified. By the tracking ultrafast dynamics of photonic eigenstates in k-space, we are able to follow their evolution and their mutual coupling even when they are co-located in real space [3].[1]H. Gersen, et al., Phys. Rev. Lett. 94, 073903 (2005).[2]T.W. Ebbesen, et al., Nature 391, 667 (1998).[3]R.J.P. Engelen, Nature Physics, 3, 401 (2007).
B6: Nanofabrication and Manipulation
Session Chairs
Tuesday PM, November 27, 2007
Back Bay A (Sheraton)
4:30 PM - B6.1
Patterned Polymer Brushes Grafted from Chemically Active Surface Templates.
Stephanie Hoeppener 1 , Claudia Haensch 1 , Remzi Becer 1 , Ulrich Schubert 1 2
1 Laboratory of Macromolecular Chemistry and Nanoscience, Eindhoven University of Technology, Eindhoven Netherlands, 2 Laboratory of Organic and Macromolecular Chemistry, Friedrich-Schiller-University , Jena Germany
Show AbstractPatterned polymer brushes have attracted significant interest in recent research because of their versatile abilities to tailor the mechanical, optical, electrical and chemical properties of surfaces. They can also be used to render surface biocompatible or bioresistive, depending on the grafted polymers. Different approaches can be used to tether polymer brushes to surfaces. We introduce an approach that allows the patterned grafting of polystyrene from the surface by using a primary bromine to initiate the polymerization. These initiation group is provided e.g. by 11-bromo undecyltrichlorosilane, which can be selectively assembled on surface templates, produced by electro-oxidative nanolithography. This structuring approach allows the fabrication of micro- and nanometer dimension, chemically active surface areas, generated by the local electro-chemical oxidation of a self-assembled monolayer of n-octadecyltrichlorosilane (OTS). These areas can be selectively functionalized with the initiator molecule in a subsequent self-assembly step and be used in the atomic transfer radical polymerization (ATRP). We demonstrate the formation of laterally well defined polymer brush structure and demonstrate the possibility to introduce the three-dimensional organization of copolymer systems.
4:45 PM - B6.2
Fabrication of Novel Nanopillar Scanning Electrochemical Microscpy – Atomic Force Microscopy Probes.
D. Comstock 1 , J. Elam 2 , J. Hiller 2 , M. Pellin 2 , M. Hersam 1
1 Materials Science and Engineering, Northwestern University, Evanston, Illinois, United States, 2 , Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractThe integration of scanning electrochemical microscopy and atomic force microscopy (SECM-AFM) provides a powerful tool for characterizing both electrochemical and biological processes, such as localized corrosion and membrane transport. SECM-AFM differs from conventional SECM in that it utilizes a nanoelectrode integrated within a conventional AFM tip and cantilever, providing the advantage of independent topographic and electrochemical characterization. In this work, a novel SECM-AFM probe has been developed using electron beam induced deposition (EBID) and atomic layer deposition (ALD). Beginning with a conventional silicon AFM tip, focused ion beam (FIB) milling is used to flatten the tip apex to serve as a platform for subsequent EBID, and the probe is coated with a gold film to provide a conductive path from the apex to the probe body. A thin tungsten nanopillar, 60 nm in diameter and 1 μm tall, is then deposited by EBID onto the flattened tip apex. In order to encapsulate the probe and eliminate background currents when operating in liquid environments, a 50 nm thick aluminum oxide film is deposited by ALD. This encapsulating film is deposited by ALD as it allows for the controlled deposition of thin, pinhole-free, and conformal films onto both the probe body and the high aspect ratio nanopillar. Lastly, the encapsulated nanopillar is FIB milled in cross-section to reveal a 60 nm diameter nanoelectrode embedded within the 160 nm overall diameter tip apex. While the overall tip apex is larger than conventional AFM probes, it is substantially smaller than many SECM-AFM probe designs previously reported in the literature. Additionally, the nanopillar geometry provides the advantage of a high aspect ratio, allowing for the investigation of recessed features such as trenches and pores. In order to demonstrate these properties, the fabricated probes were used to image the diffusion of redox mediators through silicon nitride membranes containing 1 μm diameter pores. The pores were readily resolved in simultaneous topographic and electrochemical current imaging. Additionally, the current was highly localized over the pores, which is consistent with both the small dimensions of the tip nanoelectrode and the localized diffusion of redox species.
5:00 PM - B6.3
Fabrication of a Single Metal Nanowire Connected with Dissimilar Metal Electrodes and its Application to Chemical Sensing.
Hsin-Yu Lin 1 , Hsiang-An Chen 1 , Heh-Nan Lin 1
1 Materials Science and Engineering, National Tsing Hua University, Hsinchu Taiwan
Show AbstractThe study reports a convenient method for the fabrication of a single metal nanowire connected with dissimilar metal electrodes based on a combination of atomic force microscopy nanomachining and conventional photolithography and its application to chemical sensing. A metal nanowire with a length of 16 μm, a width of around 70 nm, a thickness of 20 nm is first created on a substrate by atomic force microscopy nanoscratching on a polymer resist, metal deposition and lift-off. A pair of metal electrodes of same or dissimilar metal is then patterned by photolithography onto the two ends of the nanowire. A single metal nanowire (Ti or Au) connected with same metal electrodes is fabricated and the obtained resistivities are comparable to our previous results and those reported in the literature. Single metal nanowires (Au) connected with dissimilar metal electrodes (Ti) are also fabricated and confirmed by the linear I-V curve relationship. Furthermore, the chemical sensing capability of the fabricated nanowires is demonstrated by the selective binding of a self-assembled monolayer onto a single Au nanowire connected with Ti electrodes. It is found that the resistance increases by 1-2 % and 5-7 % after the binding of two kinds of molecules, 1-dodecanethiol (DT) and 1-octadodecanethiol (ODT), respectively. The increase is believed to originate from enhanced surface and/or grain-boundary scattering effects after the adsorption of the monolayer. Due to the extent of molecule coverage on the nanowire, the relationship between the resistance change and various ODT concentrations is also obtained.
5:15 PM - B6.4
Guided Nanoscale Remodeling of Soluble Surfaces using a Novel Probe-based Method.
Selim Elhadj 1 , Alex Chernov 1 , James Deyoreo 1
1 CMLS, LLNL, Livermore, California, United States
Show AbstractA methodology for remodeling surfaces at nanometer length scales would enable the mitigation of defect or damage sites in a broad range of technologically relevant materials, such as optics used in high-fluence lasers. Here we describe a novel probe-based method to guide the remodeling of KDP (KH2PO4) surfaces that exploits two phenomenon occurring at nm lengthscales: 1) the unique physical chemistry that occurs in the region surrounding a nanoscale tip-surface contact, and 2) the natural driving force for elimination of regions of high curvature. This method takes advantage of the meniscus that forms through condensation at a tip-surface contact in a humid environment. Surrounding this meniscus is a naturally occurring ultrathin aqueous film on the crystal surface. Our experimental model consists of two parts: 1) repair of a groove etched into the KDP surface by hard contact with an atomic force microscope (AFM) tip and 2) creation of pillars and beams by tip-induced overgrowth on a smooth KDP surface.We find that the wet micro-environment formed by the meniscus, combined with tip rastering during AFM scanning over a groove site, results in local surface smoothing and filling-in of the groove such that groove depth decreases with time. We present in-situ AFM measurements of the kinetics of this surface remodeling process. Control of relative humidity above the surface is essential and systematically increases the rate of remodeling over un-treated surfaces. Starting with the Gibbs-Thompson relation, which describes the dependence of the chemical potential of the crystal surface on local curvature, we present a quantitative physical analysis of damage site remodeling. With the controlling parameters in the model constrained by independent measurements, we find that the predictions are in good agreement with experimental results.We also find that pillars and beams can be grown on flat KDP surfaces by keeping the tip in contact over some period of time. The lateral dimension of the overgrowth features is controlled by the size of the meniscus through the applied humidity. Because both the mitigation method and the over-growth technique rely only on the Kelvin effect and a finite substrate solubility, they can in principle be applied to any material that is soluble in water or other solvents, either for repair of damaged and defective surfaces or for construction of complex surface features at nanometer scale resolution.This work was performed under the auspices of the U. S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48.
5:30 PM - B6.5
Electronic Structure in Self-assembled Semiconductor Nanocrystal Arrays.
Oded Millo 1 , Dov Steiner 1 , Assaf Aharoni 2 , Uri Banin 2
1 Racah Institute of Physics, The Hebrew University of Jerusalem, Jerusalem Israel, 2 Department of Physical Chemistry, The Hebrew University of Jerusalem, Jerusalem Israel
Show AbstractThe electronic level structure of colloidal InAs quantum dots (QDs) in two-dimensional arrays, forming a QD-solid system, was probed using scanning tunneling spectroscopy (STS). The band gap is found to reduce compared to that of the corresponding isolated QDs. Typically, the electron ('conduction-band') ground state red shifts more than the hole ('valence-band') ground state. This is assigned to the much smaller effective mass of the electrons, resulting in stronger electron delocalization and larger coupling between electron states of neighboring QDs compared to the holes. This is corroborated by comparing these results with those for InAs and CdSe nanorod assemblies, manifesting the effects of the electron effective mass and arrangement of nearest neighbors on the band gap reduction. In addition, in InAs QD arrays, the levels are broadened, and in some cases their discrete level structure was nearly washed out completely and the tunneling spectra exhibited a signature of two-dimensional density of states. The latter observation suggests an emergence of collective array levels. Our results for the above 'semiconductor-semiconductor proximity effects' will be compared with our previous STS investigations of proximity effects in metal-semiconductor nanojunctions [D. Steiner, T. Mokari, U. Banin, O. Millo, Phys. Rev. Lett. 95, 56805 (2005)]. We shall also briefly describe our new method for achieving nanorod arrays having long-range order.
5:45 PM - B6.6
Novel Chemistries in High Field Scanning Probe Lithography for Tone Reversal and High Speed (cm/s) Patterning.
Marco Rolandi 1 2 , Itai Suez 1 , Andreas Scholl 3 , Jean Frechet 1 2
1 College of Chemistry, University of California, Berkeley , Berkeley, California, United States, 2 Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 3 Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractHigh field degradation and cross linking of common organic solvents with a biased atomic force microscope probe generates etch resistant carbonaceous nano-patterns in the range of a few nanometers. We have investigated novel chemistries for tone reversal and patterning at cm/s velocities. Scanning probe lithography (SPL) in hexadecane results in substrate oxidation or amorphous carbon deposition depending on surface hydrophilicity. Immersion of the patterns in fluorinated etchants transfers the oxide in the positive tone and the carbonaceous structures in the negative tone. SPL in perfluorooctane enables the use of really fast writing speeds (1 cm/s) for fluorocarbon features with excellent dry etch resistance. Structures comprising hundreds of 50 nm wide and 20 nm tall lines spanning a surface of 100 μm2 were fabricated after 15 seconds SPL and SF6 plasma. This is several folds faster than state of the art e-beam lithography. Rate increase is likely due to higher propagation speed for streamer discharge and dielectric breakdown in the perfluorinated solvent. Amorphous carbon and fluorocarbon nano-patterns were extensively characterized by photoemission electron microscopy and secondary ion mass spectroscopy.
B7: Poster Session I
Session Chairs
Wednesday AM, November 28, 2007
Exhibition Hall D (Hynes)
9:00 PM - B7.1
Study of Gold Thin Films Evaporated on Polyethylene Naphthalate Films toward the Fabrication of Quantum Cross Devices.
Hideo Kaiju 1 , Akito Ono 1 , Nobuyoshi Kawaguchi 1 , Akira Ishibashi 1
1 Research Institute for Electronic Science , Hokkaido University, Sapporo Japan
Show AbstractMolecular electronics devices continue to be pursued as a technology that offers the prospect of scaling device dimensions down to a few nanometers and also promote a practical introduction for high-density memory applications. One of several molecular devices is a cross-bar memory device fabricated by nanoimprint lithography process, which has achieved the production of 30-nm half-pitch patterning. However, today’s production procedures such as nanoimprint lithography, optical lithography, and electron-beam lithography, do not allow for the resolution to achieve sub-10-nm line-width structures. Recently we have proposed a double nano-"baumkuchen" (DNB) structure, composed of two thin slices of alternating metal/insulator nano-"baumkuchen" as a lithography-free nano-structure fabrication technology. The DNB has potential application in a high-density memory device, the cross point of which can scale down to ultimately a few nanometers feature sizes because the pattering resolution is determined by the metal-deposition rate, ranging from 0.01 nm/s to the order of 0.1 nm/s. One element of the DNB structure is called a quantum cross (QC) device that consists of two metal nano-ribbons having edge-to-edge configuration. In the area of edge-to-edge QC devices there has been no experimental reports, meanwhile face-to-face devices such as cross-bar devices and spin tunneling devices, have been widely studied both theoretically and experimentally. In our present work, as the first experimental attempt toward the fabrication of QC devices, we have studied gold thin films evaporated on polyethylene naphtalate (PEN) organic films, which can be a candidate of metal/insulator part used for QC devices, by using the atomic force microscope (AFM).Au thin films were thermally evaporated on PEN films in the high vacuum chamber including the film-rolled-up system. The Au thickness was measured by a mechanical method using the stylus surface profiler and an optical method using the diode pumped solid state (DPSS) green laser. Surface morphologies of Au thin films on PEN films were analyzed by the AFM at room temperature. As the thickness of Au films evaporated on PEN films decreases from 20 nm to 5 nm, the AFM surface roughness is reduced from 4.8 nm down to 1.5 nm in the scanning area of 500×500 nm2. The Au grain size is 28.0±4.6 nm for 5-nm-thick Au films and 45.8±5.8 nm for 10-nm-thick Au films, respectively. As a result of the scaling investigation of the surface roughness, the surface roughness of 5-nm-thick Au films is 0.22 nm, corresponding to one atomic size, in the scanning scale of 5 nm. These experimental results indicate that Au thin films on PEN films are suitable as a candidate of metal/insulator(organic films) hybrid materials used for QC devices, and may open up a noble research field to clarify the electric characterization of QC devices using a few atoms or molecules leading to high-density memories.
9:00 PM - B7.10
Time-Dependent-Surface Properties of a Piezoelectric Polymer.
Ke Wang 1 , Hyungoo Lee 3 , Rodrigo Cooper 2 , Hong Liang 2 3
1 Department of Physics , Texas A&M University, College Station, Texas, United States, 3 Materials Science and Engineering, Texas A&M University , College Station, Texas, United States, 2 Department of Mechanical Engineering , Texas A&M University , College Station, Texas, United States
Show AbstractWe investigate the time dependence of the surface property and microstructure of Polyvinyldifluoride (PVDF) under influence of an external electrical field and a mechanical force. The surface properties include morphology, surface forces (adhesion), and nature of phases (microstructure). Approaches include using an atomic force microscope (AFM), a scanning tunneling microscope (STM), and a scanning electron microscope (SEM). Use those techniques, we were able to observe surface and near surface structural change in situ under different electrical and mechanical conditions. In this presentation, we discuss the relaxation behavior associated with electron structures of PVDF.
9:00 PM - B7.11
Nano-scale Observation Technology of Si Trench Sidewall Surface Morphology by AFM.
Reiko Hiruta 1 , Hitoshi Kuribayashi 1 , Ryosuke Shimizu 2
1 , Fuji Electric Device Technology Co. Ltd., Matsumoto Japan, 2 , Fuji Electric Advanced Technology Co. Ltd., Hino Japan
Show AbstractControllability of shape and surface morphology of microstructures is essential for developments of a wide range of devices, such as semiconductor devices, micro electro-mechanical systems (MEMS), photonic crystals, and various kinds of nano-devices. Especially in three-dimensional Si devices, such as trench metal-oxide-semiconductor field-effect-transistor (MOSFET) [1], fin-FET [2] and Si-MEMS [3], atomic-level flatness has been recently strongly required for their constituent surfaces with the progressive downscaling of the device structures.Atomic force microscopy (AFM) is a powerful tool for the study of physical morphology of nano-scale surfaces of Si. We have developed an observation technique with which Si trench sidewall surface is able to be scanned with the tip of cantilever and to be investigated its morphological evolution. An array of 0.7 mm wide and 3.0 mm deep trenches was formed on Si (100) substrates by a standard silicon process. The longitudinal direction of the trenches was chosen to be parallel to the [0-11] direction, and thus, on the trench sidewalls {011} planes appeared. The samples were annealed in hydrogen gas ambient using a lamp furnace. By developing a novel technique of cleaving the substrate at the center of a micron-sized trench along its longitudinal direction, the sidewall nano-scale morphologies of the trenches could be observed with AFM technique.On the standpoint of the image resolution we also investigated the difference between Si and carbon nanotube (CNT) tips for the AFM observations. As the result, the CNT tip is proved to show a superior signal-to-noise (S/N) ratio compared with the Si tip.Combination of both technologies mentioned above enables us to investigate the dependence of the nano-scale root-mean-square (RMS) roughness of the trench sidewall surface on hydrogen gas pressure. And it also enables us to observe the morphological evolution of the sidewalls of micron-sized trench structures in the various phase of hydrogen annealing [4-6]. In the presentation, we will also show some application results of the AFM technology in the fields other than the hydrogen annealing.[1] N. Fujishima et al.: IEDM Tech. Dig. (1997) p.359, [2] Y.-K. Choi et al., IEDM Tech. Dig. (2002) p.259, [3] M-C M Lee et al., Proc. 18th IEEE Int. Conf. on Micro Electro Mechanical Systems (2005) p. 596, [4] R. Hiruta et al., Appl. Surf. Sci. 237, 63 (2004), [5] R. Hiruta et al., Appl. Surf. Sci. 252, 5279 (2006), [6] R. Hiruta et al., M.R.S. Symp. Proc. Vol.958 (2007).
9:00 PM - B7.12
Limitations for the Determination of Piezoelectric Constants with Piezoresponse Force Microscopy.
Tobias Jungk 1 , Akos Hoffmann 1 , Elisabeth Soergel 1
1 Institute of Physics, University of Bonn, Bonn Germany
Show AbstractAt first sight piezoresponse force microscopy (PFM) seems an ideal technique for the determination of piezoelectric coefficients thus making use of its ultra-high vertical resolution (< 0.1 pm/V). Christman et al. first used PFM for this purpose [1]. Their experiments, however, yielded only reasonable results of unsatisfactory accuracy. Those difficulties basically originate from two different features of the PFM setup: the inherent PFM background [2] and mechanical clamping of the samples [3]. In principle the background influences all PFM experiments but particularly the measurements on materials with low piezoelectric constants. In addition the inhomogeneous electric field, which reaches values up to 108 V/m, leads to internal clamping of the material, thus reducing the deformation as compared to the theoretically expected value. In this contribution a reliable calibration procedure is given followed by an analysis of the encounted difficulties determining piezoelectric constants with PFM. We point out approaches for their solution and expose why, without an extensive effort, those difficulties can not be circumvented [4].[1] J. A. Christman, J. R. R. Woolcott, A. I. Kingon, and R. J. Nemanich, Appl. Phys. Lett. 73, 3851-3853 (1998).[2] T. Jungk, Á. Hoffmann, and E. Soergel, Appl. Phys. Lett. 89, 163507 (2006).[3] T. Jungk, Á. Hoffmann, and E. Soergel, Appl. Phys. A 86, 353-355 (2007).[4] T. Jungk, Á. Hoffmann, and E. Soergel, arXiv:cond-mat 0703402 (2007).Acknowledgments:We thank D. Scrymgeour for helpful discussions. Financial support of the DFG research unit 557 and of the Deutsche Telekom AG is gratefully acknowledged.
9:00 PM - B7.13
Beryllium Diffusion Mechanisms in SiGe Systems.
Otso Koskelo 1 , Petteri Pusa 4 , Iiro Riihimaki 2 , Ulli Koster 3 , Jyrki Raisanen 1
1 , University of Helsinki, Helsinki Finland, 4 , University of Liverpool, Liverpool United Kingdom, 2 , University of Jyväskylä, Jyväskylä Finland, 3 , CERN, Geneva Switzerland
Show AbstractWhile beryllium doped SiGe shows interesting optical properties, the diffusion properties of beryllium in Si, Ge and SiGe are not well understood and only limited amount of data is available.We have studied the diffusion of beryllium in Si(1-x)Ge(x) (x=0.2, 0.65, 1.0) using modified radiotracer technique. In this technique radioactive 7Be isotopes were deployed into the materials by ion implantation. Samples were then annealed at temperatures ranging from 450°C to 720°C followed by serial sectioning in nanometer scale using low energy ion beam sputtering. Sputtered material was collected to foils and the depth profiles were then constructed by measuring the activity of the foils.Our results show a clear change in diffusion mechanism at about x=0.6. The mechanisms are suggested to be vacancy dominated diffusion in germanium rich materials and interstitialcy/kick-out mechanism in silicon rich materials in accordance with previous findings for group III, IV and V elements in SiGe. However, the Be diffusion behavior in silicon rich materials differs significantly from the earlier results in SiGe as it is relatively much faster. The causes of this feature are discussed.
9:00 PM - B7.14
Molecular States on Semiconductor Surfaces and Supported Thin Film Insulators.
Yurie Fukuma 1 , Mathieu Lastapis 1 , John Boland 1
1 CRANN, Trinity College Dublin, Dublin Ireland
Show AbstractThere is considerable interest in the potential use of single molecules as molecular electronic and electro-mechanical devices [1,2]. Scanning tunneling microscopy (STM) is a powerful tool to investigate single atoms and molecules since it can directly image the electronic states of these systems with sub 100 pm resolution. However, the electronic states of atoms and molecules, which are adsorbed on conductive substrates, are necessarily perturbed by coupling with the states of the substrate. Recently, successful isolation of the atomic and molecular states from the substrate states has been demonstrated using ultrathin insulating films formed on metal substrates [3]. For the study of molecular functional devices, it is desirable to examine the molecular states on Si substrates and here in this work we investigate ultrathin CaF films formed on Si(111) surfaces. We study the formation of atomically flat CaF bilayer films in which several kinds of defect are observed. Inelastic tunneling electron spectroscopy (IETS) showed the instability of some kinds of defects. We present an analysis of the stability and dynamics of these defects, and the adsorption of 3,4,5,6-Tetraphenyl-2,2’-bipyridine molecules adsorbed on Si(111) substrates and on the CaF bilayer structure. [1] A. Aviram and M. A. Ratner, Chem. Phys. Lett. 29, 277 (1974).[2] A. Stabel et al., Angew. Chem. Int. Ed. Engl. 34, 303 (1995).[3] J. Repp et al., Science 312, 1196 (2006)
9:00 PM - B7.15
Local Electronic Charge Transport Properties of Carbon Nanotube Networks.
Pio Nirmalraj 1 , Jonathan Coleman 1 , John Boland 1
1 Chemistry, Trinity College Dublin, Dublin Ireland
Show AbstractWe report on the local electronic properties of single walled carbon nanotube (SWCNT) networks probed using conductance imaging atomic force microscope (CI-AFM) to simultaneously record the local structure and the conductivity. SWCNTs solubilised in N-methyl pyrrolidone (NMP) were sprayed onto silicon dioxide substrates to form conducting networks. Using CI-AFM we have analysed the local electronic properties of the SWCNTs at junction points and also along the tubes. We observed an increase in the resistance at the intertube junctions when compared to the resistance along the tubes. Also certain junctions are found to be more resistive, this feature can be attributed to the fact that they are junctions between metallic and semiconducting tubes acting as Schottky barriers. Backgating experiments were also perfomed where we observed that regions connected by semiconducting tubes are switched off and only metallic tubes are visible in the current map with positive gate voltage. By switching off the gate voltage the semiconducting tubes were restored again. Through this method we were able to identify the semiconducting pathways in the network. We have also analysed the voltage drops at junction points by applying a bias voltage to the tip. Further we investigated the dependence of resistance of the tubes as a function of distance from the electrode for films ranging from a few microns in thickness down to films which are just a few monolayers thick. Electronic properties of SWCNTs treated with bromine and functionalised tubes cross linked with linker molecules were also studied
9:00 PM - B7.16
The Physical and Chemical Surface Properties of Caffeine Cocrystals.
Andrew Cassidy 1 , Catherine Gardner 1 , William Jones 1 , Evgenyi Shalaev 2
1 , Cambridge University, Cambridge United Kingdom, 2 Pfizer Global R&D, Pfizer Ltd, Groton, Connecticut, United States
Show AbstractThe engineering of caffeine/dicarboxylic acid cocrystals to circumvent the tendency of caffeine to form hydrates at high humidity has been considered in previous work.1 These previous studies, based primarily on PXRD patterns and IR spectra, have shown that the cocrystals are stable to 90 % RH for up to 7 weeks, and also to suspension in water. That work, however, focused on the bulk stability of the cocrystals to humidity. We now demonstrate that atomic force microscope (AFM) imaging confirms that surface changes occur in reportedly stable cocrystals, over short time periods, on exposure to different relative humidity environments. In this poster, the effect of water moisture on the chemical and physical properties of caffeine/oxalic acid and caffeine/malonic acid cocrystals will be considered in detail. These results may have implications in the area of API/excipient incompatibility where surface reactivity could be of importance in determining the nature of the interactions between particles.1. Andrew V. Trask, W. D. Sam Motherwell, William Jones, Cryst. Growth and Design, 2005, vol 5 1013
9:00 PM - B7.17
Young’s Modulus Measurement of Boron Nanowires with Frequency-modulation Atomic Force Microscopy.
Xiaoxia Wu 1 , Terry Xu 1
1 Mechanical Engineering and Engineering Science, The University of North Carolina at Charlotte, Charlotte, North Carolina, United States
Show Abstract Frequency-modulation atomic force microscopy (FM-AFM) utilizes the resonance frequency shifts of the AFM cantilever induced by the tip-sample interaction to image or measure force interactions between the tip and sample. The technique has been used for mechanical properties measurement of thin films on flat substrates. Recently, few research groups are attempting to use FM-AFM to study the mechanical properties of one-dimensional nanostructures (e.g., nanotubes and nanowires). Compared with static atomic force microscopy, FM-AFM is superior because of its stability, attenuation of the long-range force effect and low noise. In this presentation, we report our recent progress on quantitative study of mechanical properties of boron nanowires using FM-AFM. Unlike the conventional “sample-substrate” configuration for FM-AFM where samples are on a flat solid substrate, the nanowires are placed on a silicon substrate with trenches. The individual nanowires spanning over trenches are pinned down at two ends using electron beam induced deposition, followed by the FM-AFM testing at different points along the nanowire. For this “nanowire-over-trench” experimental configuration, a new analytical model based on the energy principle is developed to correlate the experimentally measured frequency to the mechanical property of the nanowire. To eliminate the uncertainty induced by boundary conditions, the experimental frequency profile is compared to the analytical ones employing three different boundary conditions: (i) two fixed ends, (ii) two simply support ends, and (iii) one simply supported end with one fixed end. The analytical frequency profile which matches closest to the experimental one is used to calculate the Young’s modulus. Since the 1D nanostructures are suspended over trenches, the common substrate effect observed in FM-AFM is eliminated. The current technique can be readily extended to study the mechanical property of other one-dimensional nanostructures and stand-alone thin films.
9:00 PM - B7.18
Evolution of Alumina Surface Facets.
Jessica Riesterer 1 2 , C. Carter 1
1 Chemical, Materials Science & Biomolecular Engineering, University of Connecticut, Storrs, Connecticut, United States, 2 Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota, United States
Show AbstractSurface faceting of crystalline materials has been extensively studied, primarily from the point of view of how equilibrium structures are determined by surface energies. Understanding surface energy and the resulting surface reconstruction behavior is necessary in surface, thin-film and nanopatterning research, especially for ceramic substrates. The present study examines the kinetics of this process and aims to relate this to the actual mechanism of the process. The same surface region has been monitored from the initial polished surface through a series of thermal treatments until a well developed topology is formed on the initially unstable the m-plane of alumina (α−Al2O3). This study shows that the surface parallel to the m-plane develops individual facet pairs which then undergo a nano-scale step-bunching before the final facet formation. Once facets have formed, a hill-and-valley morphology develops which consists of a “simple” and “complex” surface. The m-plane Al2O3 surface is first marked with fiducial markers using a Buehler gravity-loaded hardness tester. These markers allow the same region to be returned to between thermal treatments for monitoring. Surfaces have been subjected to thermal treatment at 1400oC in ambient conditions from 10 min to 8 hrs and air quenched in an attempt to preserve the high-temperature behavior. Contact-mode atomic force microscopy (AFM) have been used to monitor the evolution of the marked area after each thermal treatment.
9:00 PM - B7.19
The Interfacial Force Microscope at the NRC National Institute for Nanotechnology.
David Munoz-Paniagua 1 , Mark McDermott 1 3 , Peter Norton 2 , Leighton Coatsworth 2
1 , National Institute for Nanotechnology, Edmonton, Alberta, Canada, 3 Chemistry, University of Alberta, Edmonton, Alberta, Canada, 2 Chemistry, The University of Western Ontario, London, Ontario, Canada
Show AbstractThe NRC National Institute for Nanotechnology (NINT) is an integrated, multi-disciplinary institution involving researchers in physics, chemistry, engineering, biology, informatics, pharmacy and medicine. The focus of NINT's research program is the combination of separate nano-scale devices and materials into complex nanosystems that are connected to the outside world. In order to pursue this goal, NINT is interested in the development of quantitative imaging and characterization techniques that support nanotechnology research.
The Interfacial Force Microscope (IFM) was first proposed in 1991 by J. E. Houston and S. A. Joyce from Sandia National Laboratories. In their design, the interaction between the sample and probe is constantly monitored and compensated for, making it possible to trace the interaction forces between between the probe and the sample at the interface. This ability makes the IFM ideally suited as a tool to support NINT's nanotechnology research.
This poster will showcase the capabilities of the Interfacial Force Microscope recently built by NINT in collaboration with P. R. Norton's research group at The University of Western Ontario.
9:00 PM - B7.2
Enzymatic Control of DNA-b-PPO Diblockcopolymer Micelles Directly Visualized by Atomic Force Microscopy.
Jie Wang 1 , Fikri Alemdaroglu 1 , Andreas Herrmann 1 , Ruediger Berger 1
1 , Max Planck Institute for Polymer Research, Mainz Germany
Show AbstractEnzymatic processes are efficient ways to realize activities of biological entities in nature as well as in laboratories. Atomic force microscopy (AFM) can be used to study and follow enzymatic processes in-situ owing to its capability of imaging in near-physiological environments. In our studies, pure terminal deoxynucleotidyl transferase (TdT) particles and DNA-b-PPO micelles were imaged with AFM, respectively, and the growths of DNA-b-PPO micelles on mica surface in buffer solution induced by TdT were directly observed in real time measurements. The height of micelles increased after the temperature reached 37 °C when all the components for the reaction were present in the mixture. It also increased after 2’-deoxythymidine 5’-triphosphate (dTTP) monomers were added while all the other components already existed at 37 °C. Statistical analysis showed that, in both cases, the height of micelles reached a plateau after about 1 hour and the distribution of height of micelles reached a maximum during the reaction. We proposed possible reasons and explanations for these phenomena.
9:00 PM - B7.20
The Adsorption Structures and Molecular Behavior of Vinylferrocene on Ge(100).
Young Bin Kim 1 , Soon Jung Jung 1 , Sehun Kim 1
1 Department of Chemistry, Korea Advanced Institute of Science and Technology, Deajeon Korea (the Republic of)
Show Abstract9:00 PM - B7.3
Fluorescence Enhancement in Hot Spots of Laterally Arranged Single Gold Nanoparticle Dimers.
Alpan Bek 1 , Reiner Jansen 1 , Sergiy Mayilo 1 , Thomas Klar 1 , Jochen Feldmann 1
1 Physics, LMU Munich, Photonics and Optoelectronics Group, Munich Germany
Show AbstractSpontaneous emission can be modified by resonant coupling to the external electromagnetic environment. Resonant cavities, planar metal surfaces or metallic nanoparticles are examples of modified electromagnetic environment. Rough metal film surfaces are observed to enhance Raman scattering, resonant Raman scattering, and fluorescence from adsorbed molecules. Plasmonic metal nanoparticles also enhance local electromagnetic fields. The luminescence of fluorophores change when they are positioned in the close vicinity of gold nanoparticles. Nanoscale gaps between two spherical metal nanoparticles produce significant field enhancement and the enhancement factor is maximized if the excitation polarization lies in the center-to-center direction. In this talk I report on the enhancement of fluorescence from a single fluorescent sphere, which is sandwiched in the hot spot of strong field enhancement in between two individual gold nanoparticles. The fluorescence enhancing hot spot is produced by assembling a plasmonic gold nanoparticle pair with an atomic force microscope cantilever. The fluorescence intensity is monitored while the separation between the two gold nanoparticles is reduced by gradually pushing the gold nanoparticles closer to the fluorescent sphere. The enhancement is maximal when the distance between the two gold nanoparticles is smallest, the excitation polarization is parallel to the axis of the sandwich, and when the fluorescent sphere is positioned exactly on the axis connecting the two gold nanoparticles.
9:00 PM - B7.4
Electrostatic Force Microscopy Studies of Boron-doped Diamond Films for Electrochemical Applications.
Sanju Gupta 1 , O. Williams 2 , E. Bohannan 3
1 Electrical and Computer Engineering Department, University of Missouri, Columbia, Missouri, United States, 2 Hasselt University, Institute for Materials Research, Dienpenbeek Belgium, 3 Chemistry, University of Missouri, Rolla, Missouri, United States
Show AbstractMuch has been learned from electrochemical properties of boron-doped diamond (BDD) thin films synthesized using microwave plasma-assisted chemical vapor deposition about factors influencing electrochemical activity, but they still possess some characteristics that are not entirely understood such as its electrical conductivity in relation with microscale structure. Therefore, in order to effectively utilizing these materials, understanding both the microscopic structure and physical (electrical, in particular) properties become indispensable. In addition to topography using atomic force microscopy, electrostatic force microscopy (EFM) in the phase mode measuring long-range electrostatic force gradients, help to map the electrical conductivity heterogeneity of boron-doped micro-/nanocrystalline diamond surfaces. The mapping of electrical conductivity on boron doping and bias voltage is investigated. The experimental results showed that the BDD films’ surfaces were partially rougher with contrast of conductive regions (areas much less than 1 micrometer^2 in diameter) which were uniformly distributed. Usually, the EFM signal is a convolution of topography and electrostatic force and the phase contrast was increased with boron doping. At the highest boron doping level, the conductive regions exhibited quasi metallic electrical properties. Moreover, the presence of “positive-negative-positive” phase shift along the line section indicates the presence of “insulating-conducting-insulating” phases, albeit qualitative. Furthermore, the electrical properties such as capacitance and dielectric constants at operating frequency were quantitatively evaluated through modeling the bias dependent phase measurements using simple and approximate geometries. It was found that decreasing grain size (or increasing boron-concentration) lowers the dielectric constant which is attributed to the change in the crystal field caused by surface bond contraction of the nanosized crystallites. These findings are complemented and validated with scanning electron microscopy, X-ray diffraction and visible Raman spectroscopy revealing their morphology, structure and carbon bonding configuration (sp3 versus sp2), respectively. These results are significant in the development of electrochemical nano-/microelectrodes and diamond-based electronics. The author (SG) acknowledges Dr. R. Giedd (CASE, Director) for providing AFM equipment and Mr. R. Patel for EFM measurements, both are from Springfield, MO.
9:00 PM - B7.5
Efficient Large area AFM Imaging.
James Bosse 1 , Ali Langston 1 , Bryan Huey 1
1 Institute of Materials Science, University of Connecticut, Storrs, Connecticut, United States
Show AbstractHigh Speed Surface Property Mapping (HSSPM) is a newly developed variation of Atomic Force Microscopy (AFM) that increases image acquisition by as much as two orders of magnitude. Combined with automated sample manipulation, this allows previously impractical large area AFM scanning while maintaining nanoscale spatial resolution. Specifically, high precision step and repeat functionality is employed to efficiently image up to 100um on a side with sub-10-nm pixel resolution throughout. Imaging rates up to 100Hz/line are maintained. Ferroelectric domains as well as metal lines lithographically deposited on semiconductors are imaged in this manner in this undergraduate research project.
9:00 PM - B7.6
Visualization of Charges Localized in the Thin Gate Film of Metal-Oxide-Nitride-Oxide-Semiconductor Type Flash Memory using the Scanning Nonlinear Dielectric Microscopy - Detecting the Higher Order Nonlinear Dielectric Constant.
Koichiro Honda 1 , Yasuo Cho 2
1 , Fujitsu Laboratories Ltd., Atsugi Japan, 2 , Tohoku University, Sendai Japan
Show AbstractIn the downsizing the Metal-SiO2-SiN-SiO2-Semiconductor (MONOS) type Flash memory, charges are stored in further localized area of the cell transistor. Then, a high-resolution evaluation measurement is necessary to detect such localized charges. The charges stored in the gate dielectric thin film induce a permittivity change in the film. We have succeeded in clarifying the position where electrons/holes are located in the gate thin SiO2-SiN-SiO2 (ONO)film of the MONOS memory. Following our previous work (MRS2003 Fall Meeting GG4.2, 2005 Fall Meeting NN12.6), we succeeded in visualizing the charge distribution to measure a higher-order nonlinear dielectric constant by using Scanning Nonlinear Dielectric Microscopy (SNDM). SNDM is one of the microwave microscopy measurement techniques using an AFM where a ring electrode is used in conjugation with a cantilever. Alternating electric field Ecoswp is biased between this electrode and the sample, the capacitance variation of the surface region of the sample is detected. The capacitance variation ΔCs(t) is, ΔCs(t)/Cs0 ∼ ε333/ε33Ecosωp+ε3333/4ε33E2cos2ωp+higher order. In this formula, ε33 is a linear dielectric constant, ε333 is the lowest-order and ε3333 is 2nd order nonlinear dielectric constant. The ε333/ε33 and ε3333/ε33 can be obtained by detecting cosωp(ωp),and cos2ωp (2ωp) components of SNDM signals, respectively. From the higher order signal, we can obtain higher-resolution SNDM image, because the electric field of higher order dump faster than that of lower order, then it penetrates into limited area.The SNDM images of electrons/holes in a MONOS memory can be interpreted as that of the capacitance variation (dC/dV) of the polarization of the electron-hole pair, which dC/dV is determined from the ωp component. On the other hand, in the higher-order SNDM image, it is deferent from ωp case. The 2ωp component contains d2C/dV2 and higher orders non-linear dielectric constant of the ONO film. The higher order SNDM image shows the polarization of the electron-hole pair, since d2C/dV2 is not 0 due to the flat band voltage shift of the electron-hole pair system. Therefore the stored charge in ONO film can be visible in high resolution. As mentioned above, SNDM is a powerful method for visualizing charge spatial location in a dielectric thin film.
9:00 PM - B7.7
Gas Nanosensors by Local Anodic Oxidation.
Braulio Archanjo 1 , Alem-mar Goncalves 1 , Rodrigo Lacerda 1 , Bernardo Neves 1
1 Physics, UFMG, Belo Horizonte Brazil
Show AbstractMetallic-oxide-based devices have attracted enormous attention of the scientific community, as they are widely applicable to gas sensing. Furthermore, the recent advances in nanoscience and microfabrication brought the possibility of fabrication and integration of metallic oxide sensors. A well known example is the large amount of published studies about growth and manipulation of metallic oxide nanowires and their use as gas sensors.In this work, a new fabrication methodology of metallic oxide nanosensors is proposed, which uses a Scanning Probe Microscopy technique known as Local Anodic Oxidation – LAO. LAO is basically an anodic oxidation process due to an applied bias between tip and sample. Since the tip is very small, the applied bias produces a strong electric field, which, in the presence of a contamination layer (which works as an electrochemical environment), oxidizes the sample surface.The whole nanosensor fabrication process can be summarized in two steps. The first one uses optical lithography to define a microscopic metallic track. The second step uses the LAO technique to oxidize the center of the track creating a nanometer-scale metallic oxide which constitutes the active region of the sensor. The remaining parts of the metallic track serve as electrical contacts to such nanosensor. Therefore, with this technique, the technological challenge of electrically connecting nanodevices is already solved as the nanosensor is directly created onto its pre-existing metallic contact. Two processes of LAO were investigated for nanosensor definition: a “slow” process and a “fast” one. The “slow” process is accomplished by oxidizing, point by point, the metallic track applying a bias between 1 and 10 volts. The “fast” process is made trough application of a bias pulse, as high as 100V, at one point and oxidizing the center of the track.Two metals have been tested: Ti and Ni, with their respective oxides as the active regions of the sensors. The functionality of such devices has been tested with success for the presence of the following test gases: NH3 and H2. Both DC and AC techniques were used to monitor the nanosensor response. Finally, each sensor is being investigated in terms of selectivity, stability, sensibility, response and recovery times.
9:00 PM - B7.8
Charge Injection on Insulators: Towards Data Storage Devices.
Elisangela Silva-Pinto 1 , Bernardo Neves 1
1 Physics, UFMG, Belo Horizonte Brazil
Show AbstractCharge distributions on insulators are of great interest, both scientifically and technologically, in areas such as tribocharging, piezo- and pyroelectric polymers, electrets, and electrophotography. The seminal work of Stern and co-workers, proposing Electric Force Microscopy (EFM), showed that it is possible to inject and quantify charges on insulators at a sub-micrometer scale almost two decades ago [1]. Since then, the spatial resolution of both charge injection and its quantification has increased towards the nanometer scale and several sub-sequent works tried to explore this simple idea of contact electrification and its measurement to develop nano-scale memory (data storage) devices. Even though the “write” and “read” processes are relatively easy to accomplish through biased-AFM and EFM techniques, respectively, controlling both “storage time” and “erasing” still is a significant challenge. In other words, it is easy to inject charge (“write” different patterns on the surface) and to visualize it (“read”). However, keeping such pattern for long times (“storage time”) and controlling the discharge of this surface region (“erase”) is trickier. In the present work, a careful investigation of charge injection and manipulation on different insulators has been carried out. Thin polymer films (PMMA - poly(methyl methacrylate) and PMMA-MAA – poly(methyl methacrylate-co-metacrylic acid)) deposited on conducting substrates and functionalized silicon dioxide on doped silicon substrates were employed as test samples. The charge is injected when a biased AFM tip is brought into contact with the sample (“writing”) and it is monitored by EFM (“reading”), also used to characterize both charging and discharging process. Several experimental parameters were investigated in order to optimize charge injection and manipulation: bias voltage, insulator layer thickness, ambient conditions and others. A simple, yet effective, process of controlling “storage time” and “erasure” is explored: application of a proper bias at the conductive substrate. It has been observed that when a bias with opposite polarity from the injected charge is applied, charge on the sample is kept for longer times (increasing “storage time”), achieving indefinitely long storage times for some conditions. If a bias with the same polarity is applied on the substrate, the discharging process is fast (enabling a quick “erasure”). An alternative method of fast and selective discharging (“erasure”) is to apply a pulse of opposite bias on the sample surface with the AFM tip. In conclusion, this work suggests a complete route for data storage, showing simple and effective ways to write (inject the charge with an AFM tip), to read (detect the charge with EFM), to store (keep the charge on the sample applying an opposite bias on the substrate) and to erase the information (make the discharging process faster). References:[1] – J.E. Stern et al., Appl. Phys. Lett. 53, 2717 (1988).
9:00 PM - B7.9
Lateral Resolution in Piezoresponse Force Microscopy.
Tobias Jungk 1 , Akos Hoffmann 1 , Elisabeth Soergel 1
1 Institute of Physics, University of Bonn, Bonn Germany
Show AbstractAmong the methods for visualization of ferroelectric domains [1] piezoresponse force microscopy (PFM) has become a very common technique mainly due to its high lateral resolution without any need for specific sample preparation. Although domain structures are easily imaged with this method, the lateral resolution and thus the observed domain wall width is still under discussion. The reported values for the width of 180° domain walls – even in comparable material systems – scatter noticeably. These inconsistencies can be explained by the PFM background inherent to the experimental setup [2] that can broaden the observed domain wall widths [3]. In this contribution, we present a quantitative study of the resolution in PFM depending on the tip radius, the type of sample and the thickness of the sample [4]. For bulk single crystals the measured linear dependency of the width of the domain wall on the tip radius using PFM is validated by a simple theoretical model. Independent on the crystal type (BaTiO3, KNbO3, KTiOPO4, LiNbO3, LiTaO3, Pb5Ge3O11 and Sr0.61Ba0.39Nb2O6) the same lateral resolution was measured. Using a Ti-Pt-coated tip with a nominal radius of 15 nm the so far highest lateral resolution in bulk ferroelectric crystals of only 17 nm was obtained.[1] E. Soergel, Appl. Phys. B 81, 729-752 (2005).[2] T. Jungk, Á. Hoffmann, and E. Soergel, Appl. Phys. Lett. 89, 163507 (2006).[3] T. Jungk, Á. Hoffmann, and E. Soergel, J. Microsc.-Oxford 227, 76-82 (2007).[4] T. Jungk, Á. Hoffmann, and E. Soergel, arXiv:cond-mat 0703819 (2007).Acknowledgments:We thank L. Tian and V. Gopalan for fruitful discussions. Financial support of the DFG research unit 557 and of the Deutsche Telekom AG is gratefully acknowledged.
Symposium Organizers
Dawn Bonnell University of Pennsylvania
Sergei V. Kalinin Oak Ridge National Laboratory
Sidney R. Cohen Weizmann Institute of Science
Richard E. Palmer University of Birmingham
B8: Nanomechanics and Tribology
Session Chairs
Sidney Cohen
Maxim Nikiforov
Wednesday AM, November 28, 2007
Back Bay A (Sheraton)
9:30 AM - B8.1
The Viscoelastic Properties of the Liquid-like Water Layer on Ice.
Jack Houston 1
1 Surface and Interface Sciences, Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractThere has been considerable debate about the so called liquid-like (L-L) water layer on the surface of ice and its behavior as a function of temperature, a debate often aimed at the long-standing controversy over just why ice is so slippery. Here, we present the results of detailed relaxation measurements, using the Interfacial Force Microscope (IFM), in order to map the viscoelastic behavior of the L-L layer as a function of temperature from -5 to -40 °C. In these measurements, the tip approaches the surface in a series of 20 Å steps separated by pauses sufficient to allow the resulting force to relax as the liquid “drains” from the interfacial space. These measurements permit the quantitative determination of both the L-L layer thickness and its complex shear modulus both as a function of temperature and the separation between the tip and ice surface. The results indicate L-L layer thickness first by the point at which the “meniscus” initially nucleates, i.e., contact between the tip and L-L layer. Just below the freezing point, this contact appears as a sudden increase in attractive force. However, at lower temperatures the level of the increases diminishes indicating the nucleation of a “frustrated” capillary due to the increase in viscosity of the L-L layer, making it more difficult for the meniscus to spontaneously grow after initial contact. The attractive force accelerates as the tip is forced into the L-L layer until contact is made with the ice surface, where the force rapidly turns repulsive. From the details of the relaxation behavior, as the tip “steps” toward the surface, it is found that at a given temperature the viscosity increases only slightly as the tip approaches the surface after meniscus contact. In addition, after tip-ice contact, the tip is not stable and slowly creeps into the ice surface with a speed that depends on the level of the repulsive force and the temperature. The results will outline the detailed viscoelastic behavior as a function of both the temperature and the tip/ice-surface separation. In addition, they are contrasted with the behavior of the friction force, measured by dithering the tip laterally by about 20 Å at 100 Hz and detecting the lateral-force signal synchronously. These overall results give the first comprehensive picture of the L-L layer properties as a function of temperature.Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy’s National Nuclear Security Administration under Contract DE-AC04-94AL85000.
9:45 AM - B8.2
Confined Polymers: Forces Between Solid Surfaces Across Polymer Melts.
Jijun Wang 1 , Hans-Juergen Butt 1
1 , Max-Plank-Institute for Polymer Research, Mainz Germany
Show Abstract10:00 AM - **B8.3
The Study of Nanocarbon Films by and for Atomic Force Microscopy.
Robert Carpick 1
1 Mechanical Engineering and Applied Mechanics, University of Pennsylvania, Philadelphia, Pennsylvania, United States
Show AbstractNanostructured carbon-based materials, such as nanocrystalline diamond and atomically smooth, nanometer-thick diamondlike carbon films, have outstanding and in many cases unrivalled tribo-mechanical properties. We will show explicitly how the atomic and nanoscale structure of the surfaces critically affects nano-scale friction and adhesion. Particular attention will be paid to the effects of surface termination (chemisorption)
1, local crystal orientation
2, crystalline structure, annealing, environment, and nanoscale roughness
3. Each of these topics involves special consideration of the AFM techniques used, as well as the use of surface spectroscopic techniques to complement the AFM measurements. We will then discuss leveraging these properties at the nanoscale for advanced scanning probe applications, and will discuss the advantages of using tips composed of or coated with nanocarbon films.
1. A. V. Sumant, D. S. Grierson, J. E. Gerbi, J. Birrell, U. D. Lanke, O. Auciello, J. A. Carlisle & R. W. Carpick. "Toward the ultimate tribological interface: Surface chemistry and nanotribology of ultrananocrystalline diamond". Adv. Mater. 17, 1039-45 (2005).
http://dx.doi.org/10.1002/adma.200401264
2. G. T. Gao, R. J. Cannara, R. W. Carpick & J. A. Harrison. "Atomic-scale friction on diamond: A comparison of different sliding directions on (001) and (111) surfaces using MD and AFM". Langmuir 23, 5394-405 (2007).
http://dx.doi.org/10.1021/la062254p
3. R. J. Cannara, M. J. Brukman & R. W. Carpick. "Cantilever tilt compensation for variable-load atomic force microscopy". Rev. Sci. Instrum. 76, 53706 (2005).
http://dx.doi.org/10.1063/1.1896624
This work was supported by the Air Force Office of Scientific Research, the Department of Energy, and the National Science Foundation.
10:30 AM - **B8.4
The Nanomechanics of Compositional Mapping in Amplitude Modulation AFM.
Ricardo Garcia 1
1 , Consejo Superior Investigaciones Científicas (CSIC), Tres Cantos Spain
Show Abstract11:30 AM - B8.5
Iterative Control Approach to High-Speed Force-Distance Curve Measurement Using AFM: Time Dependent Response of PDMS.
Qingze Zou 1 , Kyongsoo Kim 1 , Zhiqun Lin 2 , Pranav Shrotriya 1 , Sriram Sundararajan 1
1 Mechanical Engineering, Iowa State University, Ames, Iowa, United States, 2 Materials Science and Engineering, Iowa State University, Ames, Iowa, United States
Show Abstract11:45 AM - B8.6
Measuring Poisson's Ratio with Contact-Resonance Atomic Force Microscopy.
D. Hurley 1 , J. Turner 2
1 Materials Reliability Division, NIST, Boulder, Colorado, United States, 2 Dept. of Engineering Mechanics, Univ. of Nebraska-Lincoln, Lincoln, Nebraska, United States
Show AbstractThe superb spatial resolution and imaging capability of atomic force microscopy (AFM) make it ideally suited for investigating nanoscale mechanical properties. Previous work has demonstrated the ability of contact-resonance AFM to determine quantitative elastic properties. In contact-resonance AFM, the frequencies of the cantilever's resonant vibrational modes are measured while the tip is in contact with the sample. Such measurements yield values for the indentation or plane strain modulus M. However, M depends on two separate elastic properties, Young's modulus E and Poisson's ratio ν. In some cases, it is desirable to determine the individual elastic properties separately. We describe new contact-resonance AFM methods to quantitatively measure shear properties such as Poisson's ratio ν or shear modulus G. By simultaneously measuring the contact-resonance frequencies of both flexural and torsional modes, ν or G can be determined separately from E. Analysis methods are presented to relate the contact-resonance frequencies to the tip-sample contact stiffness, which in turn determines the sample's elastic properties. Experimental results are presented for a glass specimen with fused silica used as a reference material. The agreement between our contact-resonance AFM measurements and values obtained from other means demonstrates the validity of the basic method.
12:00 PM - B8.7
Modelling of Nanoindentation Measurements using an AFM or Nanoindenter for Compliant Layers on Stiffer Substrates.
Charles Clifford 1 , Martin Seah 1
1 Surface and Nano-Analysis, National Physical Laboratory, Teddington United Kingdom
Show AbstractAtomic force microscopy (AFM) or nanoindentation can be used to measure the modulus of surface and near-surface regions [1]. For the analysis of inhomogeneous materials and coated systems, when imaging and when performing force-indentation experiments, an understanding of the depth of the tip-sample interaction is needed. Here, finite element analysis (FEA) is used to model the nanoindentation process of a rigid, spherically shaped tip acting on an elastic two-phase system exampled by an elastic layer that is more compliant than the underlying elastic substrate. A review of current analytical equations to model this process is made and compared to FEA [2]. We show a universal curve can be developed that describes the indentation of this system that is independent of the moduli and Poisson's ratio values, thickness of layer or radius of indenter tip. We present a new, simple, analytical equation based on a power law function that can be used to model this general layered system. This function can then easily be used to extract the modulus of the layer.The alternative approach to measure the layer modulus is to indent to shallow enough depth so that only the layer and not the substrate underneath is detected by the tip. A well-known rule of thumb suggests that this depth limit is 10% of the thickness of the layer [3]. We investigate this using FEA and our new analytical equation. We show that this rule is invalid for many situations at the nanoscale. A new rule is developed, which depends on layer thickness and indenter radius. This determines that to keep the uncertainty in the measured layer modulus to better than 10% at 10% of the layer thickness depth, the thickness of the layer should be 8.2 times the radius of the tip.References[1] Clifford C A and Seah M P 2005 Appl Surf Sci, 252, 1915.[2] Clifford C A and Seah M P 2006 Nanotechnology, 17 5283[3] Bückle H 1961 VDI Berichte 41 14.
12:15 PM - B8.8
Active Friction Modulation of Self-Assembled Monolayer Films using External Electric Fields.
Kanaga Karuppiah Kanaga Subramanian 1 , Angela Bruck 1 , Sriram Sundararajan 1
1 Mechanical Engineering, Iowa State University, Ames, Iowa, United States
Show Abstract12:30 PM - B8.9
Micromechanical Properties of Self-Assembled Supramolecular Structures of Chiral Phospholipids.
Yue Zhao 1 , Jiyu Fang 1
1 Advanced Materials Processing and Analysis Center, University of Central Florida, Orlando, Florida, United States
Show AbstractSelf-assembled lipid tubules represent promising hollow cylindrical supramolecular structures. The tunable size and unique surface properties make lipid tubules valuable as biomaterials for applications as a nanoreactor for biosensors and a controlled release system for drug/gene delivery. Using the tip of an atomic force microscope as a nanoindentation, we studied the radial deformation of lipid tubules of 1,2-bis(tricosa-10,12-diynoyl)-sn-glycero-3-phosphocholine on glass substrates. There was a reversible linear regime that persisted up to indentations of 25% of the tubule diameter; it was followed by a steep drop in force that is associated with irreversible deformation. We established finite elements model to calculate Young’s modulus of the lipid tubules. The Young's modulus increased with the decreasing outer diameter (when the inner diameter of the lipid tubule varied within the range of ±0.6%). An understanding of the mechanical properties of lipid tubules was critical in developing their applications and also suggested design principals for nanotechnology.
12:45 PM - B8.10
Confinement Effects of Hard Disk Lubricant Investigation by Atomic Force Microscopy.
George Caia 1 , Cynthia Buenviaje-Coggins 1 , Nicole Munoz 1 , Doru Florescu 1 , SungChang Lee 2
1 , Park Systems, Santa Clara, California, United States, 2 , Samsung Information Systems America, San Jose, California, United States
Show AbstractAs the critical design requirements decrease, we need to understand how confinement affects the performance of the materials we use. For example, the lubricant used on magnetic recording disks to reduce wear between the disk and head reader during unexpected intermittent contact is a good candidate to evaluate. Lubricants used in hard drives need to have sufficient reflow and redistribution properties, which are stable in a wide range of temperatures experienced in today’s hard drive applications. Since the materials properties of the confined system often differ from the bulk properties, tools to properly investigate these systems need to be developed and understood. In this study, we utilized atomic force microscopy (AFM) techniques to study the confinement effects on lubricant stability with temperature. Our studies have demonstrated distinct changes in adhesion force with changes in the thickness of the confining substrate layer. As adhesion is a component of friction, these changes in adhesion are directly related to lubricant performance and its ability to reduce wear between disk and reader.In summary, our experiments include a set of measurements performed on three samples (denoted A, B, and C) carrying the same type of lubricant of different thicknesses. The temperature of the lubricant – substrate system were varied in the 20÷70 0C range using an external thermo-couple stage. The dependence of the force distance (F-d curve) on temperature was measured for multiple surface locations. With every measurement, the probe was re-engaged and a new F-d curve was acquired. For each temperature the system was left to reach thermodynamic equilibrium for approximately 5 minutes. Each of the F-d curves were fitted by a first order polynomial in the linear regions and the parameters associated with the elasticity constant as well as the adhesion were extracted. The resulting data point is an average of the curves assuming that there is ideal isotropy/homogeneity of the lubricant on the substrate. This procedure was repeated for all the temperature values and for the three different samples. These preliminary studies show that sample A and C do not show a significant properties dependence on the temperature while sample B exhibits a very strong correlation, on both analyzed parameters (elasticity and adhesion), with the increase in temperature and a critical point around 45 0C where a sudden jump is observed. These studies highlight the feasibility of using an AFM technique to quantitative estimate the confinement effects on lubricant stability with temperature. Additional details will be discussed.
B9: Electromechanics on the Nanoscale
Session Chairs
Wednesday PM, November 28, 2007
Back Bay A (Sheraton)
2:30 PM - B9.1
High Speed Piezo Force Microscopy for Novel Studies of Dynamic Ferroelectric Domain Switching
Nicholas Polomoff 1 , Ramesh Nath 1 , Ying-Hao Chu 2 , Ramamoorthy Ramesh 2 , Bryan Huey 1
1 Chemical, Materials and Biomolecular Engineering, University of Connecticut, Storrs, Connecticut, United States, 2 Materials Science and Engineering, University of California, Berkeley, Berkeley, California, United States
Show AbstractHigh speed Piezo Force Microscopy (PFM) is used to uniquely observe domain switching dynamics with epitaxial strained PbZr0.2Ti0.8O3 films deposited onto (100) SrTiO3 and DyScO3 substrates. Piezo Force Microscopy is commonly used for such nanoscale domain studies, but practical limitations on imaging speeds limit its application for dynamic studies. In this work, a high speed variation of PFM is applied that maintains <20 nm resolution but provides an enhancement in imaging speeds of up to 2 orders of magnitude. Domain nucleation and growth are thus uniquely accessed for 30 nm, epitaxial, PbZr0.2Ti0.8O3 thin films grown on SrTiO3 and DyScO3 substrates. The lattice mismatch between the PZT film and the two substrates creates distinct stress fields in the films, compressive and tensile, respectively. This difference is shown to profoundly influence the ferroelectric domain switching dynamics. Measurements to probe these differences include movies of domain stability as a function of time for various DC offsets near and far from the coercive field. Spatial maps of switching hysteresis are also performed, where the applied bias is incremented in a frame by frame fashion allowing nucleation and growth to be uniquely visualized. Finally, the domain orientation is repeatedly cycled to monitor the extent to which domain nucleation sites are influenced by the number of switching events. This presentation will therefore demonstrate the potential of applying newly developed high speed imaging methods for previously inaccessible insight into the dynamic properties of functional materials.
2:45 PM - B9.2
Nanoscale Observation of Charge Retention Behaviors on (Bi,Nd)4Ti3O12 and PMN-PT Thin Films by Scanning Force Microscopy.
Ji Hye Lee 1 , William Jo 1
1 Physics, Ewha Womans University, Seoul Korea (the Republic of)
Show AbstractWe report charge retention in highly (117)/(100) oriented and preferentially c-axis oriented ferroelectric Bi3.15Nd0.85Ti3O12 (BNT) thin films on Pt/Ti/SiO2/Si substrates by scanning force microscopy. The surface charge density of the BLT films was observed as a function of time in a selected area which consists of a single-poled region and a reverse-poled region. Charge retention behaviors of the regions are basically categorized into two types: extended exponential decay states and retained states. The highly (117)/(100) oriented film shows the extended exponential decay with characteristic scaling exponents, n = 1.5 ~ 1.6. On the other hand, the preferentially c-axis oriented films show a remarkable retained behavior regardless of the poling procedure. Decay and retention mechanisms of the regions are explained by space-charge redistribution and trapping of defects in the films.Piezoelectrics are used in a variety of applications for sensors ans actuators due to their unique properties. Pb(Mg1/3Nb2/3)O3-PbTiO3(PMN-PT) is well-known that they have very large piezoelectric responses and unique dielectric behavior. In this report, we aim to address anisotropic properties of the piezoelectrics, the need for epitaxial growth for large d33 values, formation of Schottky barriers at the interface by forming epitaxial oxide-oxide heterostructures. We control the interface between epitaxially-grown PMN-PT/SrRuO3 heterostructures on SrTiO3(001) crystal substrates. PMN-PT were grown on conducting SrRuO3 electrodes on (001) SrTiO3 substrates by sol-gel method. The SrRuO3 as a bottom electrode was grown by pulsed laser deposition. Crystalline orientation and phase formation of the heterostructures were measured by x-ray diffraction. The surface roughness and morphology were studied by piezoelectric force microscopy. Piezoelectric responses were measured in a number of regions on the films with subsequent statistical analysis of the obtained data. In addition, we also produced an epitaxial conducting film using the ion beam texturization at nucleation (ItaN) method, and we consequently discovered a significant decrease in surface roughness for the SrRuO3. We obtained a higher piezoelectric coefficient (d33) value of the thin film. Our proposed architecture is promising for practical piezoelectric sensor applications since piezoresponse is highly anisotropic; it is therefore important to make epitaxial thin films of PMN-PT in order to maximize the piezoeffects. In particular, scanning force microscopic techniques are used to study the surface morphology and the local electrical properties.
3:00 PM - B9.3
Domain Specific Reactions on Ferroelectric Oxides.
Dongbo Li 1 , John Garra 1 , Alexie Kolpak 2 , Andrew Rappe 2 , Dawn Bonnell 1
1 Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States, 2 Department of Chemistry , University of Pennsylvania, Philadelphia, Pennsylvania, United States
Show AbstractDomain specific chemical reactivity has been demonstrated for ferroelectric surfaces in ambient and aqueous environments. To understand the factors that affect polarization dependent adsorption on ferroelectric surfaces, in situ studies in UHV were carried out on BaTiO3 and lead zirconate titanate (PZT) surfaces. Polarization was oriented in situ with a metal coated scanning probe microscope (SPM) tip, surfaces were exposed to CO2 at various dosages, and adsorption was monitored through its effect on local surface potential. Using SPM, we poled the ferroelectric substrates such that sub-micron meter sized out-of-plane domains terminate the surfaces. Surface potentials of these positive and negative domains were then measured by frequency modulation scanning surface potential microscopy (FM-SSPM). The influence of domain polarization on molecular adsorption was examined by comparing surface potential variation as a function of CO2 dosages. Positive and negative domains exhibited quantitatively different variations in surface potential. The differences are discussed in terms of possible adsorption mechanisms. The effect of the magnitude of the polarization is examined by comparing results on PZT and BaTiO3 with first principles calculations of surface relaxations and associated adsorption energies. The effect of defects is examined by comparing results on BaTiO3 single crystals before and after UHV annealing to produce oxygen vacancies.
3:15 PM - **B9.4
Nanoscale Structure of a Ferroelectric Domain Wall using Scanning Probe Microscopy.
Lili Tian 1 , Sergei Kalinin 4 , Eugene Eliseev 2 , Anna Mozorovska 3 , Nozomi Odagawa 5 , Yasuo Cho 5 , Venkatraman Gopalan 1
1 Materials Science and Engineering, Pennsylvania State University, University Park, PA, Pennsylvania, United States, 4 Center for Naophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Institute for Problems of Materials Science, National Academy of Science of Ukraine, Kiev Ukraine, 3 Institute of Physics, National Academy of Science of Ukraine, Kiev Ukraine, 5 Research Institute of Electrical Communication, Tohoku University, Sendai Japan
Show AbstractAn antiparallel ferroelectric domain wall is ideally considered only a few unit cells wide (<0.5nm). Extracting information on that length scale is a considerable challenge. Piezoelectric force microscopy is used extensively to study the domain walls, but rigorous quantitative interpretation of the images, including resolution limits, tip-sample interaction geometry, and realistic numerical and analytical simulations of the images is becoming possible only now. I will discuss these issues in detail, and show evidence for finite broadening of ferroelectric domain walls on 5-50nm scale. The dramatic consequences of such broadening on ferroelectric properties will also be presented.This work was funded by the National Science Foundation
3:45 PM - B9.5
Anomalous Polarization Inversion in Ferroelectric Materials.
Andrei Kholkin 1 , I. Bdikin 1 , N. Pertsev 2
1 Department of Ceramics & Glass Engineering, EICECO, University of Aveiro, Aveiro Portugal, 2 RAS, A.F. Ioffe Physico-Technical Institute, St. Petersburg Russian Federation
Show AbstractFerroelectric domains are aligned in the direction of applied electric field if the external field exceeds the coercive one. We will show in this presentation that ferroelectric polarization can be oriented antiparallel to the external field and remain stable for an infinitely long time if poling is done by the sharp conducting tip of the scanning probe microscope (SPM). The experimental results are obtained here on bulk ferroelectrics (single crystals of relaxor-ferroelectric solid solutions) [1] and confirm earlier reports on ferroelectric thick films [2]. The formation of antiparallel domains is attested to the inversion of the space-charge internal bias field induced by the injected mobile charge carriers and their subsequent drift and trapping beneath the SPM tip. The poling voltage and poling time dependencies of the size of anomalous domain are correctly described by the proposed mechanism. The implications of such inversion for memory applications will be discussed along with the new possibilities of domain wall engineering in ferroelectric materials. It will be shown that the growth of the inverse domains with time can be used for the local determination of drift mobility of charge carriers in ferroelectrics and related materials.[1] A. L. Kholkin, I. K. Bdikin, V. V. Shvartsman, N. A. Pertsev, Nanotechnology 18, 095502 (2007). [2] M. Abplanalp, J. Fousek, P. Gunter, Phys. Rev. Lett. 86, 5799 (2001).
4:00 PM - B9.6
Liquid Piezoresponse force Microscopy of Living Myoblasts.
Gary Thompson 1 , Sophia Hohlbauch 2 , Brian Rodriguez 3 4 , Roger Proksch 2 , Sergei Kalinin 3 4 , Alexey Vertegel 1
1 Department of Bioengineering, Clemson University, Clemson, South Carolina, United States, 2 , Asylum Research, Santa Barbara, California, United States, 3 Materials Sciences and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 4 The Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractPiezoelectricity was demonstrated in biological systems at the tissue level (e.g., bone and wood) about 50 years ago, and using solution Piezoresponse Force Microscopy (PFM), we have recently shown piezoelectricity occurring at the molecular level with protein fibrils [Kalinin et. al., Nanotechnology 2007, accepted]. Here we investigate electromechanical coupling of the fundamental living units, cells, using liquid PFM. PFM utilizes the inverse piezoeffect to image local polarization orientation. In PFM, a local oscillatory electric field is generated by applying an ac voltage to a conducting tip in contact with a sample, and the deformation due to the piezoelectric effect is detected. Previously, living breast adenocarcinoma cells have been imaged using liquid PFM. The response signals were weak with only cell boundaries being resolved, suggesting a strong elastic contribution to the PFM signal. Much stronger response signals may be expected from cells that are electromechanically active in vivo, such as muscle cells. L8 myoblasts from rat skeletal muscle were cultured to about 60% confluence and then transferred onto ITO-coated glass coverslips. The myoblasts were grown on the ITO until they had just begun to line up to form muscle fibers, but before they had fused. Liquid PFM imaging was performed in the growth media using an Asylum Research MFP-3D AFM utilizing an internal digital lock-in amplifier, and an external ground wire was run from the ITO surface to the stage. Strong amplitude and phase responses were seen from the cell, perhaps because of enhanced contrast provided by the conductive ITO compared to uncoated glass, but there was no enhanced detail of the cell surface, again suggesting a predominant elastic contribution. To realize molecular resolution PFM of cells, shielded tips that will localize the metal coated tip’s bias, coupling of PFM with optical techniques, and PFM models of membranes and other cellular constituents need to be used.
B10: Thermal Phenomena on the Nanoscale
Session Chairs
Wednesday PM, November 28, 2007
Back Bay A (Sheraton)
4:30 PM - B10.1
Contact Potential Measurement using a Heated Atomic Force Microscope Tip.
Jessica Remmert 1 , Yan Wu 1 , Mark Shannon 1 , William King 1
1 Mechanical Science and Engineering, University of Illinois Urbana-Champaign, Urbana, Illinois, United States
Show AbstractScanning probe microscopy may be used to characterize the thermoelectric properties of a substrate with nanometer-scale resolution, with the requirements being variable temperature and potential measurement with the probe tip. A few recent papers have performed temperature-dependant potential measurements using scanning tunneling microscopy and sample-side heating. This paper describes potential measurements using a heated atomic force microscope (AFM) cantilever tip. The experiments were performed on substrates that were either gold or doped silicon. The substrate was unheated such that there was a steep temperature gradient in the substrate near the tip. Potential offsets to the substrate and cantilever legs were independently controlled to establish a wide combination of probe temperatures and electrostatic field strengths. The cantilever heater temperature was in the range 25 - 250 °C, and the offset voltages were in the range -10 - 10 V. As the tip was brought into contact with the surface at constant source voltage, continuous measure of the electrostatic force yielded a contact potential describing their net attraction. The contact potential shifted to increasingly negative offsets with temperature at fixed distance from contact. For the unbiased tip, a nearly linear dependence on temperature was observed. The heated cantilever could differentiate between the substrates according to the sign and relative magnitude of the characteristic Seebeck coefficients.
4:45 PM - B10.2
Mechanical Evaluation of Thermal Transitions in Polymer Nanofibres Using SPM.
Wei Wang 1 , Shuangwu Li 1 , Asa Barber 1
1 Materials Department, Queen Mary, University of London, London United Kingdom
Show AbstractPolymer nanofibres produced by electrospinning techniques have unique mechanical properties due to their large surface area to volume ratio and potentially high molecular orientation. The effects of temperature on mechanical properties is challenging to measure due to the small fibre diameters produced. In this paper, scanning probe microscopy (SPM) is successfully used to elucidate the mechanical performance of individual electrospun polymer nanofibres over a range of temperatures. As observed in the results, thermal transitions have a dramatic effect on the mechanical behaviour of the nanofibres and are highlighted using SPM techniques analogous to dynamic mechanical thermal analysis but at the nanoscale. Interestingly, polymer nanofibre thermal transitions are shown to be mediated by fibre diameter and the driving force of reducing the surface area of the nanofibre.
5:00 PM - B10.3
Overcoming Raman Spectroscopy Spatial Resolution Limits with Nanoscale Thermal Analysis for Complete Polymer Blend Characterization.
Jiping Ye 1 , Michael Reading 2 , Roshan Shetty 3 , Kevin Kjoller 3
1 Materials Characterization, Nissan Analytical Research, Yokohama Japan, 2 Dept of Chemcial Sciences and Pharmacy, Univ of East Anglia, Norwich United Kingdom, 3 , Anasys Instruments, Santa Barbara, California, United States
Show AbstractThe goal of this work was to characterize a PA6 and PET using a combination of Raman Spectroscopy and AFM techniques. The Raman Microscopy Image revealed the general structure of a PA6 and PET Blend but an D-3100 AFM phase image revealed complex sub-structures not seen in the Raman image due to its resolution limit of 500nm. Given that the AFM suffers from an inability to get chemical information, nanoscale thermal analysis was performed to identify the sub-structures from their phase transition temperatures. This retained the AFM's high lateral resolution while adding the ability to identify the components in the blend via their phase transition temperatures. Thus nanoscale thermal analyis permitted us to identify structure at 100nm resolution which was not visible in a Raman microscopy study due to its 500nm resolution limit. The end result revealed that the PA6-PET was a much more complex chemical blend than revealed by the Raman image but the complementary information provided by nanoscale thermal analysis enabled us characterize the complexity of the blend.
5:15 PM - B10.4
Heating Tip Microscopy for Quantitatively Probing Thermophysical Properties of Polymeric Films.
Jing Zhou 1 , Brian Berry 1 , Jack Douglas 1 , Chad Snyder 1 , Christopher Soles 1 , Alamgir Karim 1
1 Polymers Division, National Institute of Standards and Technology, Gaithersburg, Maryland, United States
Show AbstractScanning probe microscopy is increasingly being exploited to study material properties, such as electrical, mechanical, chemical and thermal, with nanoscale spatial resolution. For example, scanning thermal microscope has been used to map relative thermal conductivities of composite materials, and scanning Seebeck microscope is being used to characterize local thermoelectric response under a temperature gradient. These technologies are useful in rapidly probing material thermal properties. We explore the possibility of utilizing heating AFM tips for quantitative thermophysical probing properties of polymeric films to investigate nanoscale heat transfer and energy dissipation, and it is envisioned to be one of the future local thermal analysis methods. First, by increasing tip temperature, a “softening” transition occurs in a polymer thin film, which was found to be a characteristic quantity apparently associated with glass/melting transition, mechanical response as well as heat dissipation. All together, these effects render an informative means to investigate the interplay of thermal and mechanical responses of nanoscale materials. It is demonstrated in a model system, polystyrene and its nanocomposites, that the observed transition temperature can be used not only to identify the materials, but also to differentiate molecule size and local environment. Second, we explored the possibility of quantitatively measuring thermal conductivity of a polymer thin film. An analytic model involving the heat conduction from the AFM tip, to the film and substrate is constructed to capture the essences of heat transfer in a heating tip/thin film system, and the simple numerical simulation is conducted. According to this model, the absolute quantity of through-plane thermal conductivity can be extracted from the power-input difference when the heating tip contacts the polymer thin film. Experiments are being conducted to validate this technique that may develop into a standardized tool for simple, rapid, quantitative thermophysical probing at high spatial resolution.In brief, this study focuses on exploration of quantitative thermal analysis using heating tip microscopy. These newly developed techniques may find a variety of applications including rapid identification of extremely small amounts of materials, thermal analysis of nanoscale heat dissipation in microelectronics, and characterization of energy transfer processes in advanced energy conversion systems.
5:30 PM - B10.5
In situ Investigation of Ultrathin Si Oxide Thermal Decomposition by High Temperature Scanning Tunneling Microscopy.
Kun Xue 1 , Jin An 1 , Ho Po Ho 1 , Jian Bin Xu 1
1 Electronic Engineering Department, The Chinese University of Hong Kong, Hong Kong China
Show AbstractA quasi two dimensional surface chemical reaction the thermal decomposition of ultrathin silicon oxide (~1nm) by ultrahigh vacuum (UHV) thermal annealing at 600 to 800oC is in situ investigated on nanometer scale by high temperature scanning tunneling microscopy (STM). The reaction is initiated by the creation of circular voids which expose the underlying silicon substrate. Growth kinetics of the voids is scrutinized via time lapse STM movie. It shows that the minimal observable void diameter is less than 5nm and the void perimeters grow linearly with time before coalescence. Furthermore, the reaction happens peripherally at the void perimeter. We demonstrate that the decomposition rate varies concomitantly with the local environment near the reaction fronts. The observed low-high-low rate evolution is explained. Increased reaction activation energy is found in the final decomposition stage and the local morphological origin of this increase is discussed in detail.
5:45 PM - B10.6
Thermal Stability Investigations of Phosphonic Acid Self-Assembled Monolayers: Disorganization and Phase Separation.
Mariana Prado 1 , Bernardo Neves 1
1 Physics, UFMG, Belo Horizonte Brazil
Show AbstractSelf-assembly constitutes an important process of substrate modification/functionalization and has been subject of intense scientific studies in the past two decades. Phosphonic acid molecules with different chain lengths are known to form self-assembled monolayers (SAMs) and bilayers (SABs) on mica and other substrates [1, 2]. In a previous study, the thermal stability of octacylphosphonic acid (OPA; CH3(CH2)17PO(OH)2) SAMs has been investigated by ex situ annealing and AFM, indicating a disorganization of OPA SAMs for annealing temperatures above 100C [3]. Recently, a ToF-SIMS investigation of OPA SAMs suggested a structural transition from monolayers to bilayers when annealed in situ at ~ 80C, following the inverse mechanism of bilayer to monolayer transition proposed in reference 1 [4]. Therefore, in the present study, the thermal stability of OPA SAMs on mica was carefully investigated by AFM with in situ annealing capability in the temperature range from 20C to 120C. The AFM images acquired at temperatures above 80C unambiguously show monolayer disorganization with no evidence of bilayer formation, in disagreement with the suggestion of Francis and co-workers and corroborating early ex situ annealing studies [3]. At temperatures between 60C and 80C, AFM images show the initial stage of SAMs disorganization caused by the increased mobility of OPA molecules due to their thermal energy. At temperatures below 60C, OPA SAMs are shown to be stable.In a complementary study, OPA molecules were mixed in 1:1 molar ratio to octylphosphonic acid (OcPA; CH3(CH2)7PO(OH)2) molecules. The shorter alkyl chain of OcPA molecules result in smaller van der Waals (vdW) interactions among them, precluding the formation of pure OcPA SAMs [2]. Nevertheless, the present work shows that 1:1 OPA-OcPA solution also produces SAMs which are morphologically similar to OPA SAMs. The only difference is a smaller average thickness of the OcPA-OPA mixed SAMs due to weaker vdW interactions and occurrence of non all-trans configurations of OPA molecules. When submitted to in situ annealing at temperatures ~70C, the AFM images of mixed chain length SAMs explicitly identify a phase separation process, in which, OPA molecules are grouped together forming thicker SAMs (similar to pure OPA SAMs at such temperatures), separated from the thin OcPA-rich monolayer. The stronger vdW interaction among OPA molecules, due to their long alkyl chains, coupled with higher molecule mobility, due to their thermal energy, constitute the main driving forces behind such phase separation process.References:[1] – B.R.A. Neves et al., Langmuir 17 8193 (2001).[2] – G.N. Fontes et al. , Langmuir 21 11113 (2005).[3] – B.R.A. Neves et al., Langmuir 16 2409 (2000).[4] – J.T. Francis et al., Langmuir 22 9244 (2006).
B11: Poster Session II
Session Chairs
Thursday AM, November 29, 2007
Exhibition Hall D (Hynes)
9:00 PM - B11.1
Nanowire Thermal Conductivity Measurement using Bilayer AFM Cantilevers.
Shireen Goh 1 , Arvind Narayanaswamy 2 , Gang Chen 3
1 Materials Science & Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Mechanical Engineering, Columbia University, New York, New York, United States, 3 Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractNanowires are attractive for thermoelectrics for potential quantum size effects on electrons and classical size effects on phonons. The low thermal conductance of nanowires, however, makes their characterization experimentally challenging. The bilayer cantilever, primarily used to detect IR radiation and calorimetry, is an attractive candidate for measuring the thermal conductivity of nanowires because it can measure temperature variations down to 0.1mK and thermal conductance as low as 1nW/K. In this work, we explore the potential of using bilayer cantilevers to measure the thermal conductivity of nanowires. The nanowire is heated by a laser beam. By modulating the heating laser at different frequencies, the thermal diffusivity of the nanowire can be calculated by comparing the experimental and modeled result of the phase relationship between the response of the cantilever and the modulation of the heating laser. The experiment is performed under high vacuum to reduce heat loss by convection.
9:00 PM - B11.11
Investigation of Tobacco Mosaic Virus Based Nanowires Using Scanning Probe Microscopy.
Jie Liu 1 , Zhihua Cai 1 , Zhongwei Niu 2 , Goutam Koley 1 , Qian Wang 2
1 Electrical Engineering, University of South Carolina, Columbia, South Carolina, United States, 2 Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina, United States
Show AbstractThe electronic properties of tobacco mosaic virus (TMV) based nanowires have been studied using scanning spreading resistance microscopy (SSRM). The nanowires were deposited on silicon surface for SSRM analyses. The topography and current mapping images were taken simultaneously with tip bias of 10V. The diameter of nanowires was found to be around 20-30 nanometers and their length was longer than 2 micrometers. We observed the current of nanowires on the silicon surface was much smaller that of silicon. The stationary current (I) - voltage (V) measurement was performed where the cantilever tip was located exactly on the nanowires, which were deposited on gold surface. The stationary I-V characteristic relationship was found be almost linear, and the conductivity of the nanowires was calculated through modeling the spreading resistance.
9:00 PM - B11.12
Investigation of CdZnTe Crystal Defects Using Scanning Spreading Resistance Microscopy.
Jie Liu 1 , Zhihua Cai 1 , Goutam Koley 1 , Krishna Mandal 2
1 Electrical Engineering, University of South Carolina, Columbia, South Carolina, United States, 2 , ElC Laboratories, Norwood, Massachusetts, United States
Show AbstractThe surface electrical properties of CdZnTe (CZT) crystals have been studied using scanning spreading resistance microscopy (SSRM) and infrared transmittance maps. The topography and current mapping images were taken simultaneously on CZT samples, and the images show good correlation with Te precipitations determined by infrared images. The average probe current for the sample with higher Te precipitates was observed to be more than two orders of magnitude higher. The stationary probe current (I) - voltage (V) characteristic measurement was performed in different positions on the CZT surface. The relationship of the I-V characteristics was found to be exponential and was modeled based on thermionic emission theory. The sample with higher density of Te precipitate was found to have its barrier lowered significantly based on the model, which was confirmed independently by Kelvin probe measurements.
9:00 PM - B11.13
Phase Imaging for Loaded Diblock Copolymer Micelles by Tapping Mode Atomic Force Microscopy.
Cleva Ow-Yang 1 , Taner Aytun 1 , Osman el-Atwani 1 , Omer Faruk Mutaf 1
1 Materials Science & Engineering, Sabanci University, Istanbul Turkey
Show AbstractThe use of soft materials to synthesize inorganic nanoparticles has recently become a subject of intense research activity, and these systems are well-suited for characterization by atomic force microscopy. In particular, phase imaging in tapping mode could be leveraged toward investigating composite nanomaterials, precisely because of the inherent nanoscale differences in phase and corresponding mechanical properties. Diblock copolymer micelles nowadays are used as nanoscale reactor vessels for the synthesis of different metallic and semiconductor nanoparticles. Characterizing these nanoreactors at each step during the synthesis process helps in developing a controlled reaction inside the micelles. In the study we are presenting, phase imaging was used to characterize polystyrene-b-poly2vinlpyridine (PS-b-P2VP) reverse micelles loaded with zinc acetate in the micelle core. Assuming that the zinc cations had attached to the pyridine units at the core, the bright spots near the center of each micelle were observed at low drive amplitudes. The correlation between the phase and the topographic images helped in estimating the size of the micelle core, as well as in determining if the micelles were successfully loaded. Furthermore, the size of the micelles also was observed to increase upon loading with increasing amounts of zinc acetate. The increase was also observed using dynamic light scattering. Because the micelles were imaged by AFM outside of the solution, the micelle might actually be deformed. To analyze the degree of deformation in the collapsed micelle, dynamic light scattering was used to estimate the hydrodynamic diameter, and found not to differ much from the height profile obtained by tapping mode AFM.
9:00 PM - B11.14
A Cryogenic Quadraprobe Scanning Tunneling Microscope System with Fabrication Capability for Nano-transport Research.
Tae-Hwan Kim 1 , Zhouhang Wang 2 , John Wendelken 1 , Hanno Weitering 3 , Wenzhi Li 4 , An-Ping Li 1
1 Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 , RHK Technology, Inc., Troy, Michigan, United States, 3 Department of Physics and Astronomy, The University of Tennessee, Knoxville, Tennessee, United States, 4 Department of Physics, Florida International University, Miami, Florida, United States
Show AbstractMeasuring electron transport behaviors in nanostructured materials presents a significant challenge to experimental physicists. Conventional transport electrodes and probes are very invasive; namely, they change what we are trying to measure. For a large conductor, the probes only represent a minor perturbation. But for a small conductor, especially at the nanoscale, the probes can very well be the dominant source of scattering. Therefore, using weakly coupled scanning tunneling probes to detect transport phenomena around individual scatterers appears to be the best approach. The advantage of using the four-point method is that it separates the current supplying electrodes from the voltage-probing electrodes and thus can eliminate the parasitic resistance introduced by the probes. Furthermore, for observing quantum behavior of electrons, it is often necessary for transport measurements to be carried out in the nanometer scale at cryogenic temperatures so that electronic excitation processes can be controlled and studied in such nanosystems. We describe the development and the capabilities of a Quadraprobe system, consisting of a low temperature four-probe scanning tunneling microscope (STM) and a high resolution scanning electron microscope (SEM), coupled to a molecular-beam epitaxy sample preparation chamber. The four STM probes can be manipulated independently with sub-nanometer precision, enabling atomic resolution STM imaging and four-point electrical transport study of surface electronic systems and nanostructured materials at temperatures down to 10 K. Additionally, the four scanning probes with automated motion controls allow for atom assembly to perform “bottom-up” fabrication of nanostructures. Some testing results are presented. The desired physical information in such system includes: the electron transport process in reduced dimensionality, the quantized electron energy distributions arising from spatial or potential confinements, the shape of the confining potentials and the spatial extent of electronic wavefunctions, the emergent phenomena associated with electron-electron interactions and electron-phonon coupling in the presence of confining boundaries, and finally, the spin injection and transport in hybrid spin electronic systems. The Center for Nanophase Materials Sciences at Oak Ridge National Laboratory is a collaborative nanoscience user research facility for the synthesis, characterization, theoretical modeling, and design of nanoscale materials. It is the first of five Nanoscale Science Research Centers being established by the Office of Science, U.S. Department of Energy.
9:00 PM - B11.15
Development of Multi-Probe AFM with Optical Beam Deflection Method.
Eika Tsunemi 1 , Nobuo Satoh 1 , Kei Kobayashi 2 , Kazumi Matsushige 1 , Hirofumi Yamada 1
1 Dept. of Electronic Science and Engineering, Kyoto University, Kyoto Japan, 2 International Innovation Center, Kyoto University, Kyoto Japan
Show AbstractAtomic force microscopy (AFM) has been widely used for these two decades as a high-resolution imaging tool for the quantitative study of surface structures as well as a nanometer-scale characterization method for investigating various surface properties. However, simultaneous measurements of different surface properties are often limited because only a single probe tip is used in AFM. Thus, the implement of two or more probe tips can tremendously expand the capability of AFM. In fact, multi-probe STMs have been already developed and applied to four-point probe electrical measurements of various metallic nanowires[1].There are some difficulties in the development of a multi-probe AFM because AFM has a rather complicated optical deflection method for the measurement of a force-sensing cantilever. The use of self-sensing cantilevers such as piezoresistive cantilevers or PZT cantilevers with the integrated piezoelectric sensors drastically reduces its complexity. We actually developed a multi-probe AFM (MP-AFM) using these cantilevers. Nevertheless, the use of the complicated optical beam deflection method is remarkably useful because of its extremely high measurement sensitivity. In this presentation, a newly-developed multi-probe AFM with the method is described. Our MP-AFM system has two cantilevers independently controlled by piezostack actuators and a sample is scanned with a tube scanner. We succeeded in simultaneously taking frequency modulation AFM (FM-AFM) images of an address-patterned sample (test sample) by two independent probes. The address-patterned sample allows us to obtain the information of each probe position exactly. It has an array of two sets of binary patterns made of 5-nm-thick Pt layers on a SiO2/Si substrate. Because a set of binary patterns corresponds to the x and y coordinates on the sample surface, the absolute position of the tip was determined from the obtained AFM image. The obtained images indicated that the distance between the AFM tips of the cantilevers was less than 300 nm. [1] H. Okino, I. Matsuda, R. Hobara, Y. Hosomura and S. Hasegawa, Appl. Phys. Lett., 86, 233108 (2005)
9:00 PM - B11.16
Three Dimensional Nanofabrication with `Au' Ink Using Dip-Pen Nanolithography.
Abhishek Jain 1 , Theodorian Borca-Tasciuc 1
1 Department of Mechanical, Aerospace and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States
Show Abstract9:00 PM - B11.17
Electrostatic Force Microscopy in Liquids Using Active Atomic Force Microscope Cantilevers.
Jae Woo Yoo 1 , Jaewan Kim 2 , Youngjin Choi 1 2 , Yongsang Kim 1 3 , Chijung Kang 1 2
1 Nano science and engineering, Myongji University, Yongin Korea (the Republic of), 2 Physics, Myongji University, Yongin Korea (the Republic of), 3 Electrical Engineering, Myongji University, Yongin Korea (the Republic of)
Show Abstract9:00 PM - B11.18
Localized Ferromagnetic Resonance Force Microscopy of a Continuous Permalloy-cobalt Film.
Evgueni Nazaretski 1 , Denis Pelekhov 2 , Ivar Martin 1 , Kitty Cha 1 , Elshan Akhadov 1 , Peter Hammel 2 , Roman Movshovich 1
1 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 2 Department of Physics, Ohio State University, Columbus, Ohio, United States
Show AbstractMagnetic resonance force microscopy (MRFM), a novel type of scanning probe technique, attracted a lot of interest in the past decade due to its high force sensitivity and potential for excellent spatial resolution [1-2]. Recently, ferromagnetic resonance (FMR) has been detected by MRFM technique [3]. Contrary to electron spin and nuclear magnetic resonance experiments where the spatial image reconstruction has been successfully demonstrated [4-5], ferromagnetic resonance poses a challenge for spatially resolved FMR due to the presence of a strong exchange coupling between spins. Observed resonance spectra usually involve precession of the magnetization in the entire sample, and locally resolved FMR is not possible with conventional techniques. We report on the MRFM experiments preformed on a 50 nm thick permalloy [6] and a combined 20 nm thick permalloy – cobalt film. We studied the evolution of the MRFM spectra as a function of the probe-sample distance, and also scanned the cantilever across the permalloy/cobalt interface. We performed numerical simulations of the FMR modes excited in the presence of a non-uniform tip field of the cantilever and compared simulation results with experimental findings. With our experiments we demonstrate the capability of MRFM to perform local FMR spectroscopy of different materials in continuous ferromagnetic films. [1]. D. Rugar, O. Zuger, S. Hoen, C. S. Yannoni, H. M. Vieth, R. D. Kendrick, Science 264, 1560 (1994)[2]. D. Rugar, R. Budakian, H. J. Mamin, and W. Chui, Nature 430, 329 (2004)[3]. Z. Zhang, P. C. Hammel, and P. E. Wigen, Appl. Phys. Lett. 68, 2005 (1996)[4]. O. Zuger, and D. Rugar, Appl. Phys. Lett. 63, 2496 (1993)[5].H. J. Mamin, M. Poggio, C. L. Degen, D. Rugar, Xiv:cond-mat/0702664[6]. E. Nazaretski, D. V. Pelekhov, I. Martin, J. W. Baldwin, M. Zalalutdinov, T. Mewes, B. Houston, P. C. Hammel, and R. Movshovich, Appl. Phys. Lett. 90, 234105 (2007)
9:00 PM - B11.19
Imaging, Spectroscopy and Manipulation of Water on Au(111), and Au/Pd and Cu/Pd alloys: from Single Molecules to Nanoscale Ice Crystals.
Heather Tierney 1 , Ashleigh Baber 1 , E. Charles Sykes 1
1 chemistry, Tufts University, Medford, Massachusetts, United States
Show AbstractUnderstanding the properties of water is crucial in a vast variety of chemical, physical and biological systems. In particular, adsorption of water on surfaces is a key area of interest in the fields of biophysics, electrochemistry, semiconductors and catalysis. Low-temperature scanning tunneling microscopy (LT-STM) allows us to image the preferred adsorption sites of water on Au(111). Au(111) was chosen for preliminary experiments as an inert metal with a variety of nucleation sites. We report the structure of water at 7 Kelvin, from single molecules to small ice crystals. STM spectroscopy performed on both the bare Au surface and on ice crystals reveals how the metal’s electronic structure (dI/dV) changes as water is absorbed, and which vibrational excitations are present in the ice overlayer (d2I/dV2). We also report the manipulation of individual water molecules and intact ice clusters with the STM tip. Au/Pd and Cu/Pd alloys play key roles in hydrogenation and hydrogen purification processes respectively; therefore, the interaction of water with these systems is of great importance. The atomic-scale structure of these near-surface alloy systems will de discussed as well as their interaction with water at a variety of surface coverages and temperatures.
9:00 PM - B11.2
High-resolution Raman Imaging by Optically Tweezing Dielectric Microsphere.
Johnson Kasim 1 2 , Ting Yu 1 , Yumeng You 1 , Jinping Liu 2 , Alex Kai Hung See 2 , Zexiang Shen 1
1 Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore Singapore, 2 , Chartered Semiconductor Manufacturing Ltd., Singapore Singapore
Show AbstractRaman microscopy has been a versatile characterization technique in research and industry. The main stumbling block of employing Raman microscopy in the nanoscience and nanotechnology is the spatial resolution, which is limited by the diffraction of light. Several approaches have been employed to improve the spatial resolution to nanometer scale, among which laser delivered through metal-coated tapered optical fiber (aperture) [1] and tip-enhanced (apertureless) [2] near-field Raman techniques are the most frequently used. Raman intensity using the aperture technique is extremely weak, making imaging impractical. The latter has very low success rate and the signal is not purely near-field. We report a new near-field Raman imaging technique by trapping and scanning a dielectric microsphere over the sample surface.In this technique, a dielectric microsphere is being used to focus the excitation laser (532 nm) on the sample surface. The Raman signal is also being collected by the microsphere. Raman signal from the substrate can be enhanced, hence it has better signal to noise ratio (SNR) and imaging can be done in shorter time. There is no need to combine it with scanning probe system as in aperture and apertureless techniques. So the implementation is very straightforward and the reproducibility is also very good.Here we show the Raman imaging of 100 nm gold nanopattern fabricated on silicon substrate. 65 nm lines in a SiGe/Si device structure can also be easily resolved and strains derived show excellent reproducibility and correlation with the structure. This shows that this technique is versatile, easy to be implemented and reliable, making it extremely useful for nano-characterization.1. Hecht, B., Sick, B., Wild, U. P., Deckert, V., Zenobi, R., Martin, O. J. F. & Pohl, D. W. Scanning near-field optical microscopy with aperture probes: Fundamentals and applications. J. Chem. Phys. 112, 7761-7774 (2000).2. Sun, W. X. & Shen, Z. X. Near-field scanning Raman microscopy using apertureless probes. J. Raman Spectrosc. 34, 668-676 (2003).
9:00 PM - B11.20
Controlled Fabrication of Gold and Silver Tipped Nano Probes for Tip Enhanced Raman Spectroscopy (TERS).
Rimma Dechter 1 , Hesham Taha 1 , Galina Fish 1 , Galia Zinovev 1 , David Lewis 1 , Mila Palchan 2 , Aaron Lewis 2
1 , Nanonics Imaging Ltd., Jerusalem Israel, 2 Applied Physics, Hebrew University of Jerusalem, Jerusalem Israel
Show AbstractThe generation of probes for scanning probe microscopic apertureless enhancement of optical signals is an area of considerable interest in nanophotonics and in nanochemical characterization. In this paper, we will show that the controlled fabrication of gold or silver nanoparticles at the tip of a cantilevered glass atomic force nanosensor gives enhancements of optical Raman signals that are between 10(5) and 10(6).The sample used to measure this enhancement effect is a thin strained silicon layer on silicon. The scanning probe microscope that was used had the ability to independently move the probe or the sample and to investigate opaque samples in a standard back-scattering Raman geometry. It will be demonstrated that such probes with gold nanoparticles have unique enhancement properties relative to simple coating techniques for the development of such sensors. The results obtained portend interesting future applications in nanochemical characterization.
9:00 PM - B11.3
Enhanced Light Emission of Polymer Nanotubes with Attaching Au Nanoparticles.
Dong Hyuk Park 1 , Yong Baek Lee 1 , Hyun Seung Kim 1 , Won Jun Choi 1 , Q-Han Park 1 , Jinsoo Joo 1 , Dae Chul Kim 2 , Hyun Jun Kim 2 , Jeongyong Kim 2
1 Physics, Korea University, Seoul Korea (the Republic of), 2 Physics, Universuty of Incheon, Incheon Korea (the Republic of)
Show AbstractHybrid nanotubes of light emitting polythiophene (PTh) or poly (3-methylthiophene) (P3MT) with attaching gold (Au) nanoparticles were synthesized. The light emitting PTh or P3MT were prepared by using nanoporous anodic aluminum oxide (Al2O3) template through electrochemical polymerization method. The Au nanoparticle was synthesized through the reduction of the gold salt (HAuCl4 3H2O) with the diameter of 3~5 nm. The formation of hybrid nanotubes of light emitting PTh or P3MT with Au nanoparticles (PTh/Au NP or P3MT/Au NP) were confirmed by SEM, TEM, and elemental analysis. Structural properties of the hybrid nanotubes of light emitting PTh/Au NP or P3MT/Au NP were examined by using XRD and HR-TEM experiments. Using home made laser confocal microscope (LCM), the photoluminescence (PL) and Raman spectra of the PTh and P3MT single nanotube and their hybrid single nanotube were compared. From the LCM experiments of a single strand of hybrid nanotube, we observed the enhancement of PL in light emitting PTh/Au NP and P3MT/Au NP systems. This enhancement could be explained as the effect of surface plasmon resonance (SPR) effect. Through the UV-Vis absorbance spectra and the FDTD method of the hybrid nanotubes, we confirmed the effect of the SPR to the enhanced light emission of hybrid nanotube.
9:00 PM - B11.4
Method for Observing Crack Propagation in Thin Polymer Films.
Udo Lang 1 , Andrea Cambruzzi 1 , Jurg Dual 1
1 Zfm -IMES, ETH Zurich, Zurich Switzerland
Show AbstractPolymers are widely used in microelectronics and organic electronic devices based on intrinsically conductive materials. For reliability issues the knowledge of fracture toughness and crack growth properties for these materials is of great importance. Therefore setups have to be developed which allow for the determination of these properties.There have been various setups for observing mechanical properties of crystalline and polycrystalline materials at the nanoscale [1-3]. They have in common that a transmission electron microscope (TEM), a scanning electron microscope (SEM) or x-ray diffraction is used for observation. In case of TEM and x-ray observation this approach is not feasible for many polymeric materials due to their amorphous structure or possible beam damage. If a SEM is used, very often organic materials have to be sputtered with a conductive material, which can lead to wrong interpretations, as it could be unclear if one observes cracks in the substrate or in the sputtered layer. A tool commonly used for determining material properties at the micro- and nanometer scale is the atomic force microscope (AFM). This approach can especially be helpful for observations of amorphous and nonconductive materials.In this paper we present a method that incorporates the AFM into a micro tensile test setup similar to [4]. The microfabricated specimens consist of the polyimide PI 2723, have a length of about 1 mm and a thickness of 3 microns. They have dogbone shape but with a notch in the middle of them. As the tensile tests are conducted underneath the AFM the crack propagation in the notch can be monitored during pulling. At the same time the specimens are connected with two silicon double fixed beams, which allow for the measurement of the forces acting on the specimens by recording the double beam deflections as proposed in [1]. Therefore crack propagation on the micrometer scale and forces in the range of several millinewtons can be observed simultaneously. This allows the determination of fracture toughness and crack propagation in thin amorphous organic layers and can therefore be of great use in improving the mechanical reliability of polymeric devices.[1]Haque, M.A.; Saif, M.T.A., “In-situ Tensile Testing of Nano-scale Specimens in SEM and TEM”, Experimental Mechanics, Vol. 42, No. 1, March 2002, pp. 123-128.[2]Zhu Y, Espinosa HD, “An electromechanical material testing system for in situ electron microscopy and applications”, PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA 102 (41): 14503-14508 OCT 11 2005.[3]Bohm J. et al., “Tensile testing of ultrathin polycrystalline films: A synchrotron-based technique”, REVIEW OF SCIENTIFIC INSTRUMENTS 75 (4): 1110-1119 APR 2004.[4]Michel, B., “NanoDAC – a New Technique for Nanodeformation and Nanoreliability Analysis”, mstnews No. 4/06, August 2006, p 37.
9:00 PM - B11.5
Measuring the Mechanical Properties of Human Corneal Basement Membranes with Atomic Force Microscopy.
Julie Last 1 , Sara Liliensiek 1 , Shauheen Soofi 1 , Christopher Murphy 1
1 School of Veterinary Medicine, University of Wisconsin, Madison, Wisconsin, United States
Show AbstractDiseases of the ocular cornea have a devastating impact on vision. Knowledge about the biophysical and biochemical features of the various layers of the cornea aid in our understanding of the disease processes. The compliance of a substrate has been shown to influence a variety of cell behaviors. Therefore, determining the compliance of the basement membrane can lead to a greater understanding of cell-surface interactions. The ability to accurately determine the modulus of the corneal basement membrane is therefore of great importance. In addition, the ability to engineer therapeutic artificial corneas with properties resembling the native tissues requires detailed knowledge of the mechanical properties of each layer of the cornea. Atomic force microscopy (AFM) has been proven to be an invaluable technique for the topographical imaging and characterization of biological materials. In particular, AFM indentation can produce forces several orders of magnitude lower than those applied by traditional indentation techniques. These lower forces can be critical for local modulus determination on the surface of soft biological tissues. In this study, AFM indentation has been used to determine the local modulus of the corneal basement membranes. A spherical probe was used with a radius approximating that of a typical cell focal adhesion. Values obtained for the modulus of the anterior basement membrane range from 2 kPa to 15 kPa. This range was observed within each cornea tested. Preliminary experiments on Descemet’s membrane, the membrane on the inner part of the cornea, reveal values that are slightly higher than those observed for the anterior basement membrane. The topography of Descemet’s membrane has been shown to be similar to that of the anterior basement, but with smaller pore sizes resulting in a more tightly packed structure. This structural difference may account for the observed modulus differences.
9:00 PM - B11.6
Scanning Tunneling Microscopy and Spectroscopy with Microfabricated Tips.
James Lawton 1 , Christopher Jones 1 , Mi Yeon Song 1 , Adriano Pulisciano 1 , Peter Sloan 1 , Alex Robinson 1 , Richard Palmer 1
1 School of Physics and Astronomy, University of Birmingham, Birmingham United Kingdom
Show AbstractOne of the frontiers in scanning probe microscopy is the development of nanoscale spectroscopic and chemical analysis capabilities to complement nanoscale imaging. Here we report the fabrication and first applications of microfabricated silicon tips for use in STM, Scanning Probe Energy Loss Spectroscopy (SPELS) [1] and electron energy analysis. SPELS uses an STM tip in field-emission mode and analyses the energy of backscattered electrons [4], with the potential of providing spectroscopic information [2] on the sub-10 nm scale [3]. However, the electric field applied between tip and surface distorts the trajectories of the backscattered electrons and reduces signal levels. Thus a screened “co-axial” field emission tip would be highly desirableSilicon field emission tips were fabricated using reactive ion etching of a patterned, highly doped n-type silicon substrate. The tips sit on top of high (60 µm) mesas (posts) that are produced using ECR etching. The process reliably produces tips of radii ~10 nm. Furthermore, an insulating SiO2 layer can be thermally grown on the tip followed by deposition of gold. This produces co-axial tips that present a field free region for the scattered electrons. Further layers can be added to produce multi-layer tips for use as energy analysers.Fowler-Nordheim field emission plots show the performance of the microfabricated tips is comparable with chemically etched tungsten tips. The apex size inferred is smaller than typical etched tips. A tip with apex radius 14 nm produced a field emission current of 10 nA at 73 V and was stable for 30 mins. In-air STM using these tips shows atomic resolution on graphite, while first UHV STM images of gold with co-axial tips show performance comparable with standard tungsten tips.The electric field effects in SPELS are illustrated by local Secondary Electron Emission (SEE) measurements of an Au thin film using tungsten tips. In addition to the single peak observed in conventional SEE [5], additional features are observed in the SPELS instrument - a shoulder at 11.67 eV and a second peak at 16.30 eV (w.r.t. Evac). At large tip-sample distances (100 µm), the high-energy peak disappears. This behaviour may be attributable to surface diffraction of secondary electrons to enable escape from the tip-surface field.[1] B.J. Eves, F. Festy, K. Svensson, and R.E. Palmer, Applied Physics Letters, 77, 4223 (2000); F. Festy and R.E. Palmer, Applied Physics Letters, 85, 5034 (2004).[2] J. Yin, A. Pulisciano and R.E. Palmer, Small, 2, 744 (2006).[3] R.E. Palmer, B.J. Eves, F. Festy, K. Svensson, Surface Science, 502, 224 (2002).[4] M. Hirade, T. Arai and M. Tomitori. Jpn. J. Appl. Phys., 42:4837 (2003).[5] R. Bindi, H. Lanteri and P. Rostaing.J. Phys. D: Appl. Phys., 13:461 (1980).
9:00 PM - B11.7
Noise Analysis of Frequency Modulation Atomic Force Microscopy in Liquids.
Takashi Horiuchi 1 , Kenjiro Kimura 1 2 , Kei Kobayashi 2 3 , Kazumi Matsushige 1 , Yoshiki Hirata 4 , Hirofumi Yamada 1 2
1 Department of Electronic Science and Engineering, Kyoto University, Kyoto Japan, 2 Advanced Measurements and Analysis, Japan Science and Technology Agency, Kyoto Japan, 3 International Innovation Center, Kyoto University, Kyoto Japan, 4 , National Institute of Advanced Industrial Science and Technology, Tsukuba Japan
Show AbstractAlthough frequency modulation atomic force microscopy (FM-AFM) imaging in liquids is severely hindered by the extreme reduction of the Q-factor due to the hydrodynamic interaction between the cantilever and the liquid, we recently demonstrated that the difficulty was overcome by sufficient noise reduction in the cantilever deflection sensor and operation in small amplitude [1]. In fact, we have succeeded in obtaining high-resolution FM-AFM images of mica and biological molecules in liquids. However, the relationship between the deflection sensor noise in the self-oscillation loop and the frequency noise in FM-AFM working in low Q-factor environments such as in liquids has not been fully understood. We clarified the relationship between these noises quantitatively from both theoretical and experimental standpoints. While the phase fluctuation in the oscillation frequency can be ignored in FM-AFM working in UHV environment, it is a major factor causing the frequency noise in liquid environment because of the extremely low Q-factor (usually less than 10). Therefore the noise reduction in the self-oscillation loop is essentially important in liquid FM-AFM. There are various noise sources such as the thermal Brownian motion and the deflection sensor in the self-oscillation loop, each causing the phase fluctuation. When the oscillator noise is negligible as in the case of UHV-FM-AFM, the frequency noise spectrum measured by the FM-detector shows a linear increasing slope with the modulation frequency. In this case the magnitude of the slope is proportional to the sensor noise level. In contrast, when the Q-factor is extremely low, the floor level of the frequency noise spectrum is raised with an increase in the sensor noise. We also found that both spurious mechanical resonance of the liquid cell and band pass filter (BPF) in the self-oscillation loop had an effect to reduce the frequency noise.[1] T. Fukuma, M. Kimura, K. Kobayashi, K. Matsushige and H. Yamada, Rev. Sci. Instrum., (2005) 053704.
9:00 PM - B11.8
Structure and Physical Properties of Electrospun Semicrystalline Polymer Fibers.
Chunhua Li 1 , Anna Gromadzka 2 , Jun Jiang 1 , Tadanori Koga 1 , Miriam Rafailovich 1 , Jonathan Sokolov 1
1 Department of Materials Science and Engineering, State University of New York at Stony Brook, Stony Brook, New York, United States, 2 Department of Chemical and Molecular Engineering, State University of New York at Stony Brook, Stony Brook, New York, United States
Show AbstractElectrospinning is one of the most efficient methods to fabricate polymer nanofibers. In this study, Semicrystalline polymer Polyethylene Vinyl Acetate (PEVA) was dissolved in chloroform and electrospun onto solid substrate. Fiber diameter can be controlled by changing the solution concentration. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to characterize the fiber morphology. Shear modulation force microscopy (SMFM) was preformed to measure the nanomechanical properties and melting point of electrospun fibers as a function of the fiber diameter. Differential Scanning Calorimetry(DSC)and Small Angle X-ray Scattering (SAXS) were utilized to measure the crystallization behavior of these Electrospun Semicrystalline Polymer Fibers.
9:00 PM - B11.9
Direct Observation of Electric Field Induced Magnetization in Multiferroic BaTiO3-CoFe2O4 Nanocomposite Thin Films.
Feiming Bai 1 2 , Santosh Kurinec 1 , Surenda Kupta 2 , Jiefang Li 2 , Dwight Viehland 2
1 Microelectronic Engineering, Rochester Institute of Technology, Rochester, New York, United States, 2 Materials Science & Engineering, Virginia Tech, Blacksburg, Virginia, United States
Show AbstractB12: Poster Session III
Session Chairs
Thursday AM, November 29, 2007
Exhibition Hall D (Hynes)
9:00 PM - B12.10
Influence of Molecular Ordering on Surface Free Energy of Polymer Nanofibres using Scanning Probe Microscopy.
Shuangwu Li 1 , Wei Wang 1 , Asa Barber 1
1 Materials, Queen Mary College, University of London, London United Kingdom
Show AbstractFibrous materials are used in a variety of applications due to their relatively high surface area to volume as well as anisotropic behaviour. Electrospinning is a popular fabrication method which produces polymer nanofibres with a potentially high molecular alignment. In this work we examine the surface free energy of electrospun polyvinyl-alcohol nanofibres and its relation to molecular ordering using scanning probe microscopy adhesion measurements. Comparisons are made with polymer films to show that a high degree of molecular orientation is present at least at the surface of the polymer nanofibre. As a result, the surface free energy of electrospun polymer nanofibres is greater than that of an unaligned polymer film. This effect is independent of the nanofibre diameter, indicating that the electrospinning process is effective at polymer alignment over a variety of experimental parameters.
9:00 PM - B12.11
Biomedical Imaging with Raman Spectral Imaging - Molecular and Morphological Characterization.
Eunah Lee 1 , Sergey Mamedov 1 , Fran Adar 1 , Andrew Whitley 1
1 Molecular and Microanalysis Division, Horiba Jobin Yvon, Edison, New Jersey, United States
Show AbstractIn the recent years, the spectral imaging has gained the momentum as a material characterization tool for nano and bio systems. The goal is to achieve total characterization by taking advantage of both microscopy and spectroscopy technologies, While microscopy technique provides the location and morphology of target material at as high spatial resolution as nanometer, spectroscopy extracts the molecular or elemental composition of the target material with no ambiguity. Various microscopy techniques (e.g. standard optical microscopy, atomic force microscopy, scanning electron microscopy) are combined with one or more spectroscopy techniques (e.g Raman, IR, NIR, photoluminescence, cathodoluminescence, X-ray fluorescence), and applied to a wide range of materials from single cell bacteria and nanotubes to pharmaceutical products and integrated circuits.The engineering - hardware and software - and applications - measurements, processing and interpretation - have reached different levels of maturity. Combination of optical microscopy and vibrational spectroscopy has already arrived at a handful of mature designs and is now competing to be accepted as a routine analysis tools. AFM and SEM hybrid are still largely at the state of development and exploration of different designs.This paper will provide the brief background of theory and history on combining microscopy and spectroscopy into the field of spectral imaging. The benefits and unique information of spectral imaging for different combination techniques will be followed by the application examples on pharmaceutical, biological and nano-materals.
9:00 PM - B12.12
Investigating the Insulator-Metal Transition in CMR La0.7Ca0.3MnO3 Thin Films by Scanning Tunneling Spectroscopy.
Simon Kelly 1 , Federica Galli 1 , Ivan Komissarov 1 , Jan Aarts 1
1 Kamerlingh Onnes Laboratory, Leiden Institute of Physics, Leiden Netherlands
Show AbstractThe phenomenon of phase separation in CMR manganites such as La0.7Ca0.3MnO3 is by now well documented. It is also becoming clear from scanning tunneling spectroscopy that degree of inhomogeneities can vary considerably, and that their occurrence is influenced by crystal inhomogeneities such as can occur in strain relaxation [1,2]. In such studies, the inhomogeneities are usually observed well below the insulator-to-metal transition temperature TIM. Much less studied are the changes in local current (I) - voltage (V) characteristics when cooling the sample through the transition. It was shown by Mitra et al. [3] that the conductance (measured by the dI/dV) shows a deep dip on a small (200 mV) voltage scale around zero bias, which can be interpreted as a depletion of the density of states. We have performed similar experiments, both on strain-free and on strained films. Strain-free films of La0.7Ca0.3MnO3 were grown on NdGaO3, with TIM around 280 K, and measured in a cryostate in He atmosphere. We clearly observe a similar depletion in the density of states (DOS) over a small temperature range of about 25 K. Correlating this to the temperature dependence of the resistance R, we find that the depletion actually starts around the temperature TRmax where the maximum value of R is reached, and is largest well below TRmax. This indicates the presence of a pseudogap in the metallic state just below the temperature where it is forming. When applying a magnetic field of typically a few Tesla in the temperature range where the depletion occurs, the gap disappears. This could be expected since the field promotes the metallic state. Unlike what is seen in the resistance, however, we find that the DOS-variation show hysteretic behavior. When heating the system to (just) above TRmax and cooling down again, the DOS-depletion does not occur again even when the field is removed. Apparently, the first-order nature of the phase transition conserves the metallic state which has formed under influence of the field when making a small temperature sweep.[1] T. Becker et al, Phys. Rev. Lett. 89, 237203 (2002).[2] S. F. Chen et al., Appl. Phys. Lett. 82, 1242 (2003).[3] J. Mitra et al., Phys. Rev. B 71, 094426 (2005).
9:00 PM - B12.13
High Resolution Multiple Material Property Imaging Using AFM.
Vijayaraghava Nalladega 1 3 , Shamachary Sathish 1 , Paul Murray 1 , Kumar Jata 2 , Mark Blodgett 2 , Eunsung Shin 1 , Leanne Petry 1 4
1 , University of Dayton Research Institute, Dayton, Ohio, United States, 3 Department of Mechanical and Aerospace Engineering, University of Dayton, Dayton, Ohio, United States, 2 , Air Force Research Laboratory, WPAFB, Dayton, Ohio, United States, 4 Department of Materials Engineering, University of Dayton, Dayton, Ohio, United States
Show AbstractHigh resolution multiple physical property imaging techniques are extremely useful in material characterization especially when multiple phases are present. While traditional AFM produces high resolution surface topography images, modifications to AFM can be used to achieve this goal. In the present paper, we describe external modifications to conventional AFM setup that can lead to high resolution imaging of elasticity, magneto-elasticity, electrical conductivity and magnetic properties of materials. The modified AFM has been used to image nanoparticle coatings of Iron, Platinum, mixed nanoparticles coatings of Iron and Carbon synthesized by a recently developed Through Thin Film Ablation (TTFA) technique. In TTFA, a thin film target is ablated in vacuum to deposit a uniformly dispersed coating of nanoparticles on a substrate. These techniques were used to study the distribution, dispersion of the nanoparticles. Results of the multiple physical property imaging of the samples are presented and the differences in the contrast and the resolution are discussed.
9:00 PM - B12.14
Observation of Atomic Dipole Moment on GaAs(110) Cleavage Surface using Non-Contact Scanning Nonlinear Dielectric Microscopy.
Akio Saito 1 , Ryusuke Hirose 1 , Yasuo Cho 1
1 Research Institute of Electrical Communication, Tohoku University, Sendai , Miyagi Prefecture, Japan
Show AbstractScanning Nonlinear Dielectric Microscopy (SNDM) has been developed as the technique for observing the local dielectric properties of material surface. Especially, this technique is powerful tool for measuring the polarization of ferroelectrics. This microscopy can measure the higher order nonlinear dielectric signal as well as the lowest order nonlinear dielectric signal that contains the polarization information [1].Recently, we have developed Non-Contact Scanning Nonlinear Dielectric Microscopy (NC-SNDM) with a new height-control technique utilizing higher order nonlinear dielectric signal detection [2]. NC-SNDM can observe not only surface topography but also microscopic electric dipole moment distribution by measuring the lowest order nonlinear dielectric signal simultaneously. As a result, we have succeeded in simultaneous observation of the topography and electric dipole moment distribution on Si(111) 7x7 structure with atomic resolution [3]. Therefore we have found that NC-SNDM is microscopy technique with atomic resolution and can measure electric dipole moment distribution on semiconductor surfaces on an atomic scale. In this study, we measured nonlinear dielectric characteristics and electric dipole moment on GaAs(110) cleavage surface by using NC-SNDM. III-V compound semiconductor surface such as (110) surface is composed of two different kinds of atoms (anions and cations) and this surface is easily exposed by cleaving (100) wafer. It is expected that NC-SNDM will be able to distinguish these two kinds of atom, for example, Ga and As atom.All NC-SNDM measurements were carried out under ultra high vacuum condition (~1x10-10 Torr ) at room temperature. A commercially available n-type GaAs single crystal wafer was used as a sample. The samples were cleaved in UHV chamber immediately before NC-SNDM measurements. As a result, we have succeeded in simultaneous observation of both atomically resolved surface topography and electric dipole moment on GaAs(110) surface. The corrugation pattern of electric dipole moment distribution directly corresponds to the each surface atom positions. Hence it is considered that each electric dipole moment was detected at the Ga or As atom site. We expect that NC-SNDM will be able to distinguish the atomic dipole moment of Ga atom from that of As atom and to identify the atomic species of III-V compound semiconductor. [1] Y. Cho and K. Ohara, Appl. Phys. Lett., 79 (2001) 3842.[2] K. Ohara and Y. Cho, Nanotechnology, 16 (2005) S54.[3] R. Hirose and Y. Cho, Nanotechnology, 18 (2007) 084014.
9:00 PM - B12.15
Self-assembled Molecular Ordering of Conjugated Thiophene Molecules at the Liquid-solid Interface Through STM Investigations.
Peisi Keg 1 , Anup Lohani 1 , Moawia Omer Ahmed 1 , Yeng Ming Lam 1 , Subodh Mhaisalkar 1
1 School of Materials Science and Engineering, Nanyang Technological University, Singapore Singapore
Show AbstractConjugated oligothiophene molecules and their polythiophenes counterparts have been successfully shown by various research groups to function as potential materials for semiconductor electronic materials. As the conductance of these thin film devices typically resides in the first one or two monolayers, the structural organization of these molecules in the monolayers becomes an important issue. The molecular organization of these materials onto surfaces affects the charge mobility transport across the self-assembled thin films. In order for the thin films to show conducting characteristics, these molecules must possess conjugated backbone structures and achieve structure co-planarity on adsorption. Consisting of an interplay of interaction forces between the molecule-molecule and molecule-substrate, the molecular ordering of these self-assembled systems can be investigated in the nanoscale level through the use of scanning probe microscopy techniques. In this paper, a series of novel thiophene oligomers consisting of a fused pair of thiophene rings in the backbone would be investigated in the liquid-solid interface using the STM to determine the effect of molecular architecture on its packing order on two different substrates, the highly oriented pyrolytic graphite and reconstructed gold (111). Possessing different alkyl chain substituents on their main chain, these molecules are designed and synthesized to function as potential semiconducting organic materials. Anticipated to give rise to different molecular packing due to the alkyl chain induced ordering, the effect of molecular architecture on the packing order would be discussed, with reference to its electrical performance, through the use of STM studies.
9:00 PM - B12.16
Statistics of Electrical Breakdown in high-K Materials from Millimeter to Nanometer Length Scales: Macroscopic Testing vs. Conductive-AFM.
Cedric Sire 1 2 , Serge Blonkowski 1 , Michael J. Gordon 2 , Thierry Baron 2
1 , STMicroelectronics, Crolles France, 2 , CNRS-LTM, Grenoble France
Show AbstractDielectric materials with higher permittivity than SiO2 are being investigated as gate insulators in metal-oxide-semiconductor (MOS) devices and for metal-insulator-metal (MIM) capacitors used in DRAM and RF applications. Understanding the electrical breakdown mechanisms in these materials at the nanoscale is becoming ever more important as device dimensions decrease. In this work, we compare the statistical distributions of breakdown electric field (Ebd) for different dielectrics (SiO2, HfO2, ZrO2, and HfSiO) using macroscopic IV tests on standardized capacitors (areas ≥ 100 µm2, distributed over a 200 mm patterned wafer) with nanoscale measurements using conductive-AFM under UHV (contact area ~ 1-10 nm2). IV curves and Ebd were measured with both methods for all materials at different oxide thicknesses (1.2-6 nm) on P and N-type Si (MOS structures) as well as TiN/oxide/TiN stacks (MIM capacitors). Despite the vastly different length scales sampled in these two approaches (macro, 10-100 µm2 vs. AFM, 1-10 nm2), it is seen that breakdown field follows a single Weibull distribution based on testing area. This trend suggests that the defect density extrapolated from the statistical distribution is very high (~1E15 cm-2), and may indicate that breakdown in these new high-K materials is initiated by bond breaking rather than extrinsic defects such as vacancies or interstitials. Other electrical phenomenon linked to charge injection, trapping, stress and reversible breakdown will be discussed to highlight conduction and breakdown mechanisms in high-K materials. This work demonstrates that AFM-based statistical electrical probing is a viable, informative, and potentially easier alternative to macroscopic testing which requires more process line steps such as lithography, etching, electrode deposition, etc. Additionally, C-AFM can give important clues about electrical conduction mechanisms at the nanoscale which are not measurable via macro-level probing on device structures.
9:00 PM - B12.17
Quantitative Analysis of VideoAFM™ Images.
Jeremy Howard-Knight 1 , Jamie Hobbs 1 2 , Andy Humphris 2 , Tsvetelin Vasilev 1
1 Chemistry, Sheffield University , Sheffield, 0, United Kingdom, 2 , Infinitesima, Oxford United Kingdom
Show AbstractThe resonant scanning VideoAFM[1] allows surface images to be collected around a thousand times faster than conventional atomic force microscopes (AFM). The technique has not only allowed crystallisation and biological processes that occur in the sub-minute or second timescales to be resolved, but provides the flexibility to be able to image large areas with little or no drift between scan-lines. With tip velocities comparable to velocities inherent in the macro-world, nano and macro-tribology may also be compared directly for the first time with widespread potential applications.Conventional microscopes allow the cantilever to reach steady state at each of the data points, generally maintaining constant deformation and tip surface contact force, and intrinsically limiting the tip velocity. The VideoAFM removes this limitation on tip velocity by negating the requirement that steady state must be maintained in order for an image to be collected. However converting the beam-bounce deflection signal obtained into a quantitative picture of the surface has proved challenging as the cantilever is required to respond to surface features at frequencies well above its first oscillatory mode making it’s motion non-Hookian in nature. We have performed Finite Element Analysis (FEA) of the cantilever-probe system so as to better understand the deflection signal obtained and the mechanism by which energy is removed. These studies show that the VideoAFM image can be accurately reconstructed from the true, conventionally measured, surface topography, and a finite element model describing the cantilever geometry including corrected Rayleigh damping coefficients. This process is unfortunately difficult to reverse (to obtain the true surface topography from a VideoAFM image) due to the dependence of the signal obtained on the historic motion of the cantilever, but it is possible to side step this issue as will be discussed. This study puts the VideoAFM technique on a firm footing, and opens up the possibility of extracting complex material information, similar to that obtained with conventional AFM, but now at video rate.[1]A mechanical microscope: High-speed atomic force microscopy. A. D. L. Humphris, M. J. Miles, J. K. Hobbs; App. Phys. Lett. Jan 17 2005, 86
9:00 PM - B12.19
Electronic Properties of Quasi Ordered Systems of Nano-Scale Size Crystallites on the Surface of Plasma Treated Materials.
Nicolay Kulagin 1 , Jagos Puric 2 3 , Ivan Dojcinovic 3 , Jablan Dojcilovic 3 , Eugene Garkusha 4
1 Physics, KhNURE, Kharkov Ukraine, 2 , Center for Science and Technology Development , Belgrade Serbia, 3 Physics , University of Belgrade, Belgrade Serbia, 4 , Institute of Plasma Physics NTC “KhFTI” NANU, Kharkiv Ukraine
Show AbstractRelations of electronic and crystallographic structure, and properties of nano-scale size crystallites on the surface of non-stoichiometrical pure and doped oxide materials, such as SrTiO3, Y3Al5O12, α-Al2O3 etc., separate chloride and iodide materials before and after plasma treatment were investigated on the base of original approaches [1, 2]. The main attention was focused to study of electronic structure of the systems of crystallites with size near 1-5 nm raising on the surface of the materials after treatment in compression plasma flow (time of stable plasma impulse up 10E(-3) to 10E(-5) s, particles velocity inside plasma near 10E5 m/s and electrons density up to 10E18 cm-3). Results of study of the bulk and surface of the samples before and after plasma treatment by AFM, SEM, TEM techniques, X ray structural analysis and high resolution X ray spectroscopy methods and theoretical calculations have been presented this communication. Nature, electronic and crystallographic structure of nano-scale samples were explained in the frame work of self-consistent theory of electronic structure of clusters [2].1.N.A. Kulagin. D.T. Sviridov. Electronic Structure Calculation for Free and Impurity Ions. Nauka, Moscow. 1986.2. Physics of Laser Crystals. Eds. J.-C. Krupa, N. A. Kulagin. Kluwer Academic Publisher. Brussels. 2003
9:00 PM - B12.2
Investigating Charge Injection in Semiconductor and Metallic Single-Wall Carbon Nanotubes.
Ana Barboza 1 , Ana Gomes 1 , Debora Pinto 1 , Paulo Araujo 1 , Ado Jorio 1 , Andre Ferlauto 1 , Rodrigo Lacerda 1 , Mario Mazzoni 1 , Bernardo Neves 1
1 Physics, UFMG, Belo Horizonte Brazil
Show AbstractThe understanding of the electronic behavior of charged carbon nanotubes (CNT) is of crucial importance in electronic applications such as field-effect transistors or CNT-based nanoelectromechanical devices. Therefore, in this work, electric properties of conducting and semiconducting single-wall CNT have been investigated by charge injection, electric force microscopy (EFM), Raman spectroscopy and ab initio calculations. Charge injection is achieved by pressing a given nanotube with the EFM tip biased with respect to the sample substrate. The resulting charge transfer along the nanotube is then characterized by EFM, mapping the spatial distribution of electric field and charges at the nanometer scale. The concomitant use of Resonant Raman spectroscopy techniques enabled the assessment of the conducting character (metallic or semiconductor) of each individual CNT prior to the charging experiment. Thus, the influence of several parameters on CNT charging was investigated: tip-CNT contact time, tip type, ambient humidity, tip bias and, finally, tip-CNT force during injection. As expected, CNT charging is found to be more effective for longer contact times, more conducting tips, drier environments and higher biases. The most striking effect is observed during force experiments. While charge injection in metallic CNT shows a small dependence on the applied tip force, semiconducting CNT present a different behavior: below a certain force threshold, there is no charge injection; then, above it, charge injection grows rapidly with applied force and finally achieves the same charge density of a metallic CNT above a given tip force. Such experimental result agrees quantitatively with ab initio calculations which show that charge injection in semiconducting CNT, for low tip bias, depends on the force-induced deformation of the CNT. The maximum charge injection is achieved when the applied force induces a local semiconductor-metallic transition due to its deformation. Finally, Raman investigation of each CNT before and after charge injection enables a detailed study of defect creation associated to this process.
9:00 PM - B12.3
Piezoelectric Poly(3-hydroxybutyrate)-Poly(lactic acid) Three Dimensional Scaffolds for Bone Tissue Engineering.
Juana Mendenhall 1 , Juan Hinestroza 2 , Margaret Frey 2 , Omotunde Babalola 3 , Lawrence Bonassar 3 , Carl Batt 1
1 Food Science, Cornell University, Ithaca, New York, United States, 2 Fiber Science & Apparel Design, Cornell University, Ithaca, New York, United States, 3 Biomedical Engineering , Cornell University, Ithaca, New York, United States
Show Abstract9:00 PM - B12.4
Micro Four-probe Measurement of the Resistance for a Highly Phosphorous Diffused Surface Layer on Si(100) in Ultra-high-vacuum (UHV).
Xiaojing Zhou 1 , Warrick Clarke 1 , Michelle Simmons 1
1 Physics, University of New South Wales, Sydney, New South Wales, Australia
Show Abstract9:00 PM - B12.5
Quantitative Measurement of Dopant Concentration Profiling by Scanning Nonlinear Dielectric Microscopy.
Kenya Ishikawa 1 , Koichiro Honda 2 , Yasuo Cho 1
1 , RIEC, Tohoku Univ., Sendai Japan, 2 , Fujitsu Laboratories Ltd., Atsugi Japan
Show AbstractBy using a scanning nonlinear dielectric microscopy (SNDM), we have succeeded in the high-resolution visualizing of a dopant profile in the n-channel MOSFET with 40 nm gate channel and have demonstrated that the SNDM has much higher performance and resolution than conventional scanning capacitance microscopy (SCM) [2] for observing the dopant concentration profiling, because the sensitivity to capacitance variation of SNDM is 10-22F which is much higher than that of SCM with typical sensitivity of 10-18F.This time, as the next step of successive SNDM based dopant concentration profiling study for quantitative measurement on semiconductor devices, we observed standard Si samples, which have known one-dimensional dopant concentration values calibrated by using conventional secondary ion mass spectroscopy (SIMS), and then correlation between dopant density values and SNDM signals was evaluated.As standard samples, two epitaxcially grown staircase structures covering the doping ranges 1015-1018 cm-3 p type and 1015-1019 cm-3 n type were produced for this study. Phosphate was doped in the n-type Si sample and boron was doped in p-type Si sample.Using both SIMS and SNDM, we evaluated dopant concentrations on several terraces with a thickness of 4-5 μm. As the result, good quantitative agreement between SNDM signals and dopant density values by SIMS was obtained.On the other hand, in the conventional SCM based dopant profiling study, it has been reported and widely accepted among the SCM researchers that contrast reversal effect in the response function typically occurs at a doping level of around 1017 cm-3 in n-doped sample and around 1018 cm-3 in p-doped sample, respectively. This means the SCM signal level is not single-valued function against the dopant density. Thus, to avoid this effect and to express the relationship between SCM signal and dopant density as a single-valued function, dc bias application method has been proposed. [2] This is the reason why it has been widely believed that the SCM based dopant profiling data does not have a quantitative accuracy.However, our results indicated that without dc bias application, single valued-function relationship with good correlation between dopant density and SNDM signals was obtainable. Thus, it is expected that SNDM will be an effective method for observing the quantitative measurement of two-dimensional dopant profiling on semiconductor devices.[1] K. Ishikawa, K. Honda and Y. Cho, Nanotechnology, 18 (2007) 084015.[2] R. Stephenson, A. Verhulst, P. D. Wolf, M. Caymax and W. Vandervorst, Appl. Phys. Lett., 73 (1998) 2597.
9:00 PM - B12.6
Probing and Imaging the Electrical Domains in CaCu3Ti4O12 Ceramics.
Patrick Fiorenza 1 , Raffaella Lo Nigro Lo Nigro 1 , Vito Raineri 1 , Derek Sinclair 2
1 , CNR-IMM, Catania, Catania, Italy, 2 , University of Sheffield, Sheffield United Kingdom
Show AbstractOne of the main tasks in portable electronics is the integration of passive components in one chip. Actually condenser cover 95% of the devices area for example in smart phones or pocket PC. To date, innovative passive components are mainly based on the use of ferroelectric materials. However recently, studies on the calcium copper titanate, CaCu3Ti4O12 (CCTO) have demonstrated that this material possesses an impressive giant dielectric constant value of 105 times the vacuum permittivity ε0 at 1MHz, which remains constant in the 100-600 K temperature range and depends slightly on the frequency in the 102-105 Hz range. In addition, CCTO does not show ferroelectric transition. These interesting properties render the CCTO a real attractive alternative material to the currently used ferroelectrics which in turn possess lower dielectric constant values having stronger temperature dependence. The full understanding of those phenomena needs to go beyond the usual electrical characterization, requiring characterization methods with high lateral resolution able to image the material properties at nanoscale. In fact, the presence of micro-domains within single grains and/or of the contribution of interfacial effects (i.e. internal-barrier-layer (IBLC)) could justify the raising of such dielectric response.This paper reports on the electrical characterization of CCTO ceramics with scanning probe (SPM) based techniques. Previous works highlighted the importance of SPM to investigate the conduction and insulating behaviours. In particular, we report on the electrical characterization of CCTO ceramics at nanometre scale with scanning probe methods. The width (about 130 nm) of the depleted regions at the grain boundaries and their dependence by the applied voltage and the grain dimension have been obtained. Then, a “theoretical” permittivity value of about 150, in good agreement with the simulation, has been found. The presence of domains with different electrical characteristic represent one of the most important and possible explanation for the extrinsic origin of the CCTO colossal dielectric response and SPM based techniques, in particular conductive atomic force microscopy (C-AFM) and scanning impedance microscopy (SIM) have demonstrated their presence, shape and size in CCTO ceramics with different grain dimensions. The electrical characteristics of single grains and of single domains have been evaluated through those techniques and the semi-conductive grain resistance has been found to be two orders of magnitude lower than the resistance of the domain regions. Furthermore, similar resistance value for the domains and for the grain boundaries have been obtained. In particular, conductive part of the CCTO single grain surrounded by insulating blocking domains have been discovered. Thus, a novel model including the domain contributions to provide a possible explanation also for the colossal permittivity response of the CCTO single crystal is presented.
9:00 PM - B12.7
Study of Hydrophobic and Hydrophilic Materials Using Attenuation and Adhesion Force Measurement with Atomic Force Microscopy.
Sahar Maghsoudy-Louyeh 1
1 Eng. Science and Mechanics, Pennsylvania State University, University Park, Pennsylvania, United States
Show AbstractThe deposition of films and coatings is sometime influenced by the presence of small amounts of moisture, which can affect the nucleation and growth processes. It is important to understand the behavior of coating materials -especially in semiconductors - in terms of hydrophilicity/hydrophobicity along with adhesion forces. Our technical approach centers on the use of the Atomic force microscope (AFM) which was found to be a reliable tool for studying the surface characteristics of materials. In addition to obtaining topographic information, the AFM can also probe attractive or repulsive forces between the tip and the sample surfaces.In this research, a systematic study of the influence of humidity on the adhesion forces between different AFM tips (silicon and silicon nitride) and both hydrophilic and hydrophobic materials (quartz, calcite, mica, graphite) has been conducted using Atomic Force Microscopy. Several force-distance curves measured by the M5 AFM have been gathered at a series of different humidity levels and different locations on the samples. In this research work, measurements of the adhesion force for hydrophobic and hydrophilic materials versus humidity are presented. The results show that the adhesion force in graphite which has hydrophobic character is independent of humidity variation. Results also show that the adhesion force for fused quartz, mica, and calcite which are hydrophilic materials, change dramatically with increasing humidity due to capillary forces. This is in good agreement with theoretical calculations. In addition, Map plot software was used with the ultrasonic atomic force microscope (U-AFM), to see the different behavior of hydrophilic and hydrophobic surfaces due to humidity changes. The attenuation ( ) varied differently for hydrophilic fused quartz and hydrophobic graphite at different humidity levels.
9:00 PM - B12.8
Theoretical Study of Benzene-1,4-dithiolate Molecular Bridge Between Au Electrodes in Water Solution.
Arihiro Tawara 1 2 , Tomofumi Tada 1 2 , Satoshi Watanabe 1 2
1 Department of Materials Engineering, The University of Tokyo, Tokyo Japan, 2 , CREST, Japan Science and Technology Agency, Tokyo Japan
Show AbstractRecently, much experimental and theoretical research has been devoted to clarifying the characteristics of single molecules bridging two electrodes in order to explore the possibility of single molecular devices. However, clear discrepancy is seen between experimental and theoretical results even in the case of the most studied system, benzene-1,4-dithiolate (BDT) between Au electrodes: the observed conductance ranges from 10-3 to 10-2 G0 [1,2], where G0 is the unit of conductance (2e2/h), while the conductance computed using the density functional theory (DFT) and nonequilibrium Green’s function (NEGF) method ranges from 10-2 to 10-1 G0 [3,4]. Considering the fact that the effects of clear differences in conditions between the experimental and theoretical works, the environment (solution/vacuum) and temperature, have seldom been reported so far, we have examined the solution and temperature effects on conductance using ab initio NEGF-DFT [5,6] and Car-Parrinello molecular dynamics (CPMD) calculations. We considered Au(100)/BDT/Au(100) with 1g/cm3 water solution surrounding the BDT molecule. To generate reasonable configurations of water molecules, we performed CPMD simulations of 1.2 ps at 300K using Perdew, Burke, and Enzerhof (PBE) functional in Generalized-gradient approximation. Using the water configurations from the CPMD simulation, we calculated the zero-bias conductance of Au(100)/BDT+water/Au(100) using the NEGF-DFT (ATK code) at the level of PBE/SZP, and obtained a time-averaged conductance and histogram. The time-averaged conductance of BDT in water is 0.312 G0 and the most probable conductance obtained from the histogram is 0.315 G0. Since the conductance of BDT without water is calculated to be 0.341 G0 using PBE/SZP, water molecules clearly affect the transport properties of the single molecule, though the difference is small to explain the discrepancy between the experimental and theoretical works. In the presentation, we will also discuss the electrostatic influence of water on electronic states of BDT on the basis of the calculated effective potential map. [1] X. Xiao et al., Nano Lett. 4, 267 (2004). [2] M. Kiguchi et al., Appl. Phys. Lett. 89, 213104 (2006). [3] P. S. Damle et al., Phys. Rev. B 64, 201403 (2001). [4] K. Stokbro et al., Comp. Mater. Sci. 27, 151 (2003). [5] M. Brandbyge et al., Phys. Rev. B 65, 165401 (2002). [6] http://www.atomistix.com/
9:00 PM - B12.9
Atomic Force Microscopy Investigations of the Interconversion of Crystalline and Amorphous Raffinose.
Catherine Gardner 1 , William Jones 1 , Barry Aldous 2 , Anthony Auffret 2
1 Chemistry Department, University of Cambridge, Cambridge United Kingdom, 2 Pfizer Global R&D, Pfizer Ltd, Sandwich United Kingdom
Show AbstractRaffinose is a trisaccharide which exists as a crystalline pentahydrate. Previously published work1 has shown that after removal of two water molecules from the structure, the crystalline nature of raffinose persists. Upon removal of further water molecules, however, the crystalline structure collapses and an amorphous phase is formed. SEM images have shown that, even in the amorphous phase, the overall shape of the crystals is retained.In this work, atomic force microscopy (AFM) has been used to study, at the nanoscopic scale, the surface structural changes associated with the dehydration and amorphisation of raffinose crystals. In complementary experiments, the ‘reverse’ process has been studied with AFM data being used to characterise the gradual process of recrystallisation/ rehydration in raffinose glasses, both in terms of changes in the sample topography and material properties such as adhesion and surface free energy. 1. Kajiwara, K.; Franks, F.; Echlin, P.; Greer, A. L. Pharm.Res. 1999, 9, 1441.
Symposium Organizers
Dawn Bonnell University of Pennsylvania
Sergei V. Kalinin Oak Ridge National Laboratory
Sidney R. Cohen Weizmann Institute of Science
Richard E. Palmer University of Birmingham
B13: Transport on the Nanoscale
Session Chairs
Yossi Rosenwaks
Mark Topinka
Thursday AM, November 29, 2007
Back Bay A (Sheraton)
9:30 AM - **B13.1
Torsional Electromechanics of Carbon Nanotubes.
Ernesto Joselevich 1 , Tzahi Cohen-Karni 1 , Kavoori Sethumadavan Nagapriya 1 , Lior Segev 1 , Onit Srur-Lavi 1
1 Materials and Interfaces, Weizmann Institute of Science, Rehovot Israel
Show AbstractCarbon nanotubes are known to be distinctly metallic or semiconducting depending on their diameter and chirality. Here we show that continuously varying the chirality by mechanical torsion can induce conductance oscillations, which can be attributed to metal-semiconductor periodic transitions. The phenomenon is observed in multi-walled carbon nanotubes, where both the torque and the current are shown to be carried predominantly by the outermost wall. The oscillation period with torsion is consistent with the theoretical shifting of the corners of the first Brillouin zone of graphene across different subbands allowed in the nanotube. Beyond a critical torsion, the conductance irreversibly drops due to torsional failure, allowing us to determine the torsional strength of carbon nanotubes. Our experiments indicate that carbon nanotubes could be used as self-sensing torsional springs for nanoelectromechanical systems (NEMS).[1]E. Joselevich, Twisting nanotubes: From torsion to chirality, ChemPhysChem 2006, 7, 1405.[2]T. Cohen-Karni, L. Segev, O. Srur-Lavi, S. R. Cohen, E. Joselevich, Torsional electromechanical quantum oscillations in carbon nanotubes, Nature Nanotechnology, 2006, 1, 36.
10:00 AM - B13.2
Understanding Electron Flow Through Very High Mobility Two-Dimensional Electron Gases.
Mark Topinka 1 , Mike Jura 1 , David Goldhaber-Gordon 1 , Lukas Urban 2 , Ali Yazdani 2 , Hadas Shtrikman 4 , Loren Pfeiffer 3 , Ken West 3
1 , Stanford University, Stanford, California, United States, 2 , Princeton University, Princeton, New Jersey, United States, 4 , Weizmann Institute of Science, Rehovot Israel, 3 , Bell Labs Alcatel-Lucent, Murray Hill, New Jersey, United States
Show AbstractWe present here our work on understanding the nature of disorder and the effect it has on electron mobility and flow in very high (>1x10^6cm^2/V*s) mobililty GaAs/AlGaAs two-dimensional electron gases (2DEGs). High mobility 2DEGs are used commonly in microwave frequency HEMT transistors and other high frequency applications. We introduce in this talk a new means of probing the small amount of disorder which remains in the cleanest of these samples, and of imaging the effect this disorder has on electron flow through nanostructure devices made with this material. We present direct spatial images of electron flow in a variety of two dimensional electron gas samples using a home-built scanning gate microscope. These samples have been chosen to represent a wide range in mobility, going from moderate (140000 cm^2/V*s) to very high (4.4x10^6 cm^2/V*s). It is commonly difficult to characterize the details of the disorder that remain in the high mobility samples, and we present a new technique using scanned gate microscopy to both directly image the flow of electrons through these high mobility samples and to probe the details of the underlying disorder. We find that in electron flow in the highest mobility samples is completely dominated by small angle scattering from the smooth disorder potential present from the silicon donors located above the 2DEG layer, and that highest mobility samples seem to have reached the point of no longer being limited by sharp, large angle scattering from impurities and defects.[1] Topinka, M. A., Westervelt, R. M. & Heller, E. J. Physics Today 56, 47 – 52 (2003).
10:15 AM - B13.3
Electrostatic Force Microscopy of Carbon Nanotubes, Nanofibers, and Graphene: Quantitative Analysis Using Simulation and Experiment.
Sujit Datta 1 , Cristian Staii 1 2 , Nicholas Pinto 3 , Douglas Strachan 1 4 , Alan Johnson 1
1 Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania, United States, 2 Department of Physics, University of Wisconsin, Madison, Wisconsin, United States, 3 Department of Physics and Electronics, University of Puerto Rico, Humacao, Puerto Rico, United States, 4 Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States
Show AbstractElectrostatic force microscopy (EFM) is a widely used scanning-probe technique for the characterization of electronic properties of nanoscale samples without the use of electrical contacts. Here we present a three-dimensional finite element analysis of EFM of extended nanostructures as a means of simulating position-dependent phase data. We use this generalized technique to quantify the influence of sample geometry on the measured EFM signal, extending approximate theoretical models and previous analyses. We support our calculations with experimental data of EFM of carbon nanotubes and conducting or insulating electrospun polyaniline-based nanofibers. Furthermore, we show how EFM can be used as a powerful tool to better understand electronic structure at the nanoscale, presenting measurements of few-layer graphene samples and scanning-probe approaches to non-invasively probing the local density of electronic states of single-walled and multi-walled carbon nanotubes.
11:00 AM - **B13.4
Using Cross-Sectional STM/S As A Diagnostic Tool On Working Semiconductor Devices.
Steve Wilks 1 , R. Cobley 1 , K. Teng 1 , M. Brown 1
1 Multidisciplinary Nanotechnology Centre, University of Wales Swansea, Swansea United Kingdom
Show Abstract11:30 AM - B13.5
Nanoscale Analysis of Defects in Semiconductors by Means of Capacitance- and Charge-transient Spectroscopy/microscopy.
Stefan Lanyi 1 , Vojtech Nadazdy 1 , Miloslav Hruskovic 2 , Jan Hribik 2
1 , Institute of Physics, SAS, Bratislava Slovakia, 2 Dept. of Electrical Engineering and Information Technology, Slovak University of Technology, Bratislava Slovakia
Show AbstractWe shall report on the possibilities of analysis of electrically active defects in semiconductors and dielectrics by means of the Isothermal Capacitance-Transient Spectroscopy and the Isothermal Charge-Transient Spectroscopy, modifications of Deep Level Transient Spectroscopy, applied on sub-micrometre level. While the first of them utilizes the relaxation of the depletion layer, caused by emission of trapped charges, and requires sufficient conductivity, the second directly integrates the transient current and can be applied also to low-conductivity materials like dielectrics. The capacitance microscopes achieved a resolution sufficient to resolve the charge of a single electron. However, the standard interpretation of DLTS results is statistical, therefore many defects should be within the reach of the probe, to be applicable. At low concentration few-event relaxation can be analyzed using time-domain statistics. At slow relaxation (on the order of ms and more) this can become extremely time-consuming, requiring negligible thermal drift.Our charge-transient spectrometer achieved the resolution of hundreds of electrons but it can be further improved approximately by one order of magnitude. In materials with relatively high defect concentration, using optimal shape of the probe a resolution on the order of tens of nanometers can be achieved. At low concentrations, e.g. in device quality silicon, a resolution on the hundred nm level is expected.We shall present some results obtained on pentacene thin films, nanocrystallized silicon and crystalline islands in amorphous silicon.
11:45 AM - B13.6
Schottky Barrier of Nanoscale CoSi2 Islands on Si.
Lifeng Hao 1 , Peter Bennett 1 2
1 school of materials, Arizona State Univ., Tempe, Arizona, United States, 2 Physics, Arizona State Univ., Tempe, Arizona, United States
Show AbstractWe report in situ measurements of the Schottky barrier for nanoscale epitaxial CoSi2 islands on Si(111) using a UHV-STM. Defect-free islands of CoSi2 of various sizes (400 to 8000 nm2) are grown by depositing Co onto a heated substrate. Island size can be controlled by varying the deposition temperature. Controlled approach allows repeated electrical contact without damaging the STM tip. I-V curves are fit to a thermionic diode model with parallel conductance. We find that the ideality factor decreases with island size (n=2.1 for 7000nm2 and n = 2.6 for 400nm2)but is insensitive to temperature in the range -80C to +100C. It varies strongly with island shape, being n ~ 5 for small hexagon islands. The departure from ideal values (n ~ 1, phi ~ 0.6eV) is believed to result from enhanced tunneling due to the small island size and shape, which creates a strong electric field at the interface. The tunneling contribution may be decoupled from thermionic current via its temperature dependence.
12:00 PM - B13.7
High Resolution Characterization of Defects in Thin Oxide Films with Multiple Modulation SPM.
Maxim Nikiforov 1 , Matthew Brukman 1 , Dawn Bonnell 1
1 Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States
Show AbstractAs electronic devices become ever smaller, the roles of surfaces and defects become more prominent and characterization of defects in the context of local structure is critical to understanding the behaviors and failures of nanostructures and devices. Here, multiple modulation scanning probe techniques are used with ideal thin oxide films to quantify the limits of spatial resolution, electrical properties, electronic structure and breakdown of defects. Conductance (DC), I/V characteristics (low frequency modulation), impedance spectroscopy (frequency dependent modulation), and dielectric function (2nd harmonic of potential modulation) of individual defects on high quality HfO2 films on Si (100) are compared, allowing quantitative consideration of measurement limits. The electronic defects exhibit asymmetry in I/V properties which is used to distinguish various types of defects. Defects much smaller than the apparent tip radius are detected, yielding spatial resolution < 5nm. The basis of this high spatial resolution will be discussed in terms of simple models and ultimate limits speculated.
12:15 PM - B13.8
One by One Single-Electron Transport in Nanomechanical Coulomb Blockade Shuttle.
Yutaka Majima 1 , Yasuo Azmua 1 , Teruyoshi Hatanaka 1 , Masayuki Kanehara 2 , Toshiharu Teranishi 2 , Simon Chorley 3 , Jonathan Prance 3 , Charles Smith 3
1 Department of Physical Electronics, Tokyo Institute of Technology, Tokyo Japan, 2 , University of Tsukuba, Tsukuba Japan, 3 , University of Cambridge, Cambridge United Kingdom
Show AbstractNanomechanical Coulomb blockade shuttle devices have attracted considerable attention due to the interesting phenomena that they exhibit and are expected to become emerging devices in the field of nanoelectronics[1,2]. In nanometer-sized double-barrier tunneling structures, electron tunneling is restrained and the number of electrons on Coulomb islands, n, is quantized due to a Coulomb blockade (CB). It notes that the polarity of electrons on a Coulomb island strongly depends on the ratio of the tunneling resistance between the Coulomb island and two reservoirs. Gorelik et al. have proposed a novel theory for electron transport, i.e., the shuttle mechanism[1]. This was attributed to the charging and discharging process on the Coulomb island that occurred under the application of a dc voltage when the Coulomb island was movable and the ratio of the tunneling resistance between the Coulomb island and the two reservoirs was periodically inverted. When the Coulomb island shuttles, the probe tunneling current due to the electron shuttle is described by I=gnef, where gn is the average number of electrons transported in each cycle and f is the oscillation frequency of the Coulomb island. In the ideal condition of n=1, an electron and a hole is transported one by one per cycle of the oscillation of the Coulomb island, i.e., gn=2 and I=2ef[1]. We have demonstrated the single electron on a nanodot by noncontact atomic-force spectroscopy (AFS)[3]. The oscillation frequency f is a key parameter in nanomechanical Coulomb blockade shuttle devices since the probe tunneling current due to the electron shuttle is proportional to f[1]. Here we demonstrate transport of electrons through an Au nanodot under a nanomechanical vibration of an Au nanodot on cantilever that consists of scanning tunneling microscopy probe/vacuum/Au nanodot/cantilever. We have fabricated a Au-Ti-coated SiO2 cantilever with an high eigenfrequency of f= 86 MHz on a Si substrate[4]. We discuss the probe tunneling current-distance characteristics in relation to one by one single-electron transport per cycle of operation in nanomechanical Coulomb blockade shuttle. In the probe tunneling current-distance characteristics, a constant probe current of 2ef has been observed as a plateau region where f is an eigenfrequency of the cantilever of 86 MHz. We discuss this quantized tunneling current in relation to one by one single-electron transport per cycle of operation in nanomechanical Coulomb blockade shuttle.[1] L. Y. Gorelik, A. Isacsson, M. V. Voinova, B. Kasemo, R. I. Shekhter and M. Jonson, Phys. Rev. Lett. 80, 4526 (1998).[2] H. Park, J. Park, A. K. L. Lim, E. H. Anderson, A. P. Alivisatos and P. L. McEuen, Nature 407, 57 (2000).[3] Y. Azuma, M. Kanehara, T. Teranishi, Y. Majima, Phys. Rev. Lett. 96, 016108 (2006).[4] Y. Azuma, S. Chorley, J. Prance, C. G. Smith and Y. Majima, Jpn. J. Appl. Phys. 46, 3152 (2007).
12:30 PM - B13.9
Probing Electron Transport in Nanostructured Materials with A Cryogenic Quadraprobe Scanning Tunneling Microscope system
Tae-Hwan Kim 1 , John Wendelken 1 , Hanno Weitering 2 , Wenzhi Li 3 , An-Ping Li 1
1 Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Department of Physics and Astronomy, The University of Tennessee, Knoxville, Tennessee, United States, 3 Department of Physics, Florida International University, Miami, Florida, United States
Show AbstractMiniaturization of electronic devices down to nanoscale continues challenging our understanding of the quantum transport phenomena in nanostructured materials. At the nanoscale, different laws of physics come into play (quantum physics), the broken symmetry effect at surfaces starts to dominate transport behavior, and new modes of physical behavior open up. Specifically, when a conductor of size L is smaller than the electron phase coherence length ξ, the classical Drude conduction mechanism no longer holds, and the system enters a mesoscopic regime of quantum transport, where universal conductance fluctuations become important. When the system size is even smaller and L becomes smaller than the elastic mean free path l, the system enters the ballistic regime where electrons traverse the conductor ballistically without, on average, suffering impurity scattering. In this situation, the factor which limits the current is the scattering at the boundaries (i.e., contacts) of the conductor, and the conductance is described by the Landauer theory. Besides the size effect, the electron-electron interactions, hot-electrons, and microscopic doping gain importance in a low-dimensional system, and the reduced dimensionality can lead to qualitatively different transport than bulk materials. As an example, a material that is conducting in 3-dimensions can become insulating in 2-dimensions via the Anderson localization process. Probing electron transport behaviors and the correlations with size, dimensionality, and multiple interactions in nanostructured materials presents a significant challenge to experimental physicists. In this work, we utilize a quadraprobe scanning tunneling microscope (STM) system, in which the four STM probes can be manipulated independently with atomic precision, to study electrical transport of surface electronic systems and nanostructured materials at temperatures down to 10 K. In contrast to conventional transport electrodes which are very invasive, quadraprobe STM utilizes weakly coupled scanning tunneling probes to detect transport phenomena around individual scatterers, providing non-destructive probing of electron transport. Furthermore, the uniform cryogenic environment both for sample and probes enables controlling and studying electronic excitation processes in such nanosystems. Here, we present results on the electron transport properties in nanowire structures. Examples include multiple electronic phases in rear earth silicide nanowires grown in situ with the ultra high vacuum chamber, and the rectifying conductance in branched carbon nanotubes that were synthesized with chemical vapor deposition method. The Center for Nanophase Materials Sciences at Oak Ridge National Laboratory is a collaborative nanoscience user research facility for the synthesis, characterization, theoretical modeling, and design of nanoscale materials.
12:45 PM - B13.10
SPM-based Electrical Characterization of Aged Waspaloy Microstructures.
Siva Kumar V. Kelekanjeri G. 1 , Rosario Gerhardt 1
1 Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractWaspaloy is an age-hardenable nickel-base superalloy that is used in turbine engine applications that demand superior strength retention properties at high temperatures. The excellent mechanical properties of Waspaloy are attributed to the presence of nanometer sized γ' precipitates, which exist coherently with the nickel-rich matrix (γ) phase. With continued thermal exposure during service, the microstructure of the initial alloy evolves with time, which in turn affects the mechanical properties of the alloy. Previous research in our group has focused on the detection of microstructural variations in Waspaloy microstructures that vary in a controlled fashion using electrically-based techniques such as DC four-point probe resistivity. However, the effective resistivity obtained from the four-point probe technique is a macro property, which is dependent on the average sub-grain microstructure of the alloy. The electrical attributes of the microstructural constituents, viz. γ' precipitates, grain boundaries etc. can only be investigated by using localized Scanning Probe Microscopy (SPM) techniques, at least qualitatively. Herein, we report preliminary results of SPM-based electrical investigations on Waspaloy microstructures using Electrostatic Force Microscopy (EFM), Scanning Kelvin Probe Microscopy (SKPM) and Current-Atomic Force Microscopy (I-AFM).Waspaloy specimens were imaged in three different surface conditions- preferential γ' etch, preferential γ etch and in an unetched condition. Localized electrical characterization was conducted on a PSIA XE 100 SPM with additional attachments of SR830 DSP lock-in amplifier and DLCPA-200 variable gain low noise current amplifier.γ-γ' electrical contrast was clearly observed via all the electrical modes investigated and in all three surface conditions. In both EFM and SKPM modes, preferential removal of γ or γ' phase introduced non-homogeneous surface topography, which resulted in a complex non-linear SPM tip-surface interaction. A clear reversal of EFM amplitude contrast was noted in the EFM mode upon inversion of topographic etch. SKPM imaging of the unetched specimen showed a higher surface potential near γ' precipitates relative to the surrounding γ regions, which could be indicative of the differences in the work functions between these phases. I-AFM experiments on etched Waspaloy specimens were influenced by geometric effects introduced by non-homogeneous surface topography. However, I-AFM imaging of an unetched specimen revealed localized regions of low current in the current image, which corresponded to γ' precipitate regions in the topographic image. This qualitative observation confirmed that γ' precipitates had a lower resistivity than the surrounding γ phase in the present heat-treated Waspaloy microstructures.
B14: Single Molecule Studies by SPM
Session Chairs
Thursday PM, November 29, 2007
Back Bay A (Sheraton)
2:30 PM - B14.1
Design and Realization of Multilevel Switches by Atomic Engineering Inside a Molecule to Break the Moor’s Law.
Anirban Bandyopadhyay 1
1 International Center of Young Scientists, National Institute of Material Science, Tsukuba, IBARAKI, Japan
Show Abstract2:45 PM - B14.2
Electrical Transport of Lutetium Endohedral Metallofullerene on Alkanethiol Self Assembled Monolayer.
Yuhsuke Yasutake 1 , Keijiro Kono 1 , Norihiro Kobayashi 1 , Hisashi Umemoto 2 , Yasuhiro Ito 2 , Haruya Okimoto 2 , Hisanori Shinohara 2 3 , Yutaka Majima 1
1 Dept. of Physical Electronics, Tokyo Institute of Technology, Tokyo Japan, 2 Dept. of Chemistry, Nagoya University, Nagoya Japan, 3 Institute for Advanced Research, Nagoya University, Nagoya Japan
Show AbstractThe formation of a functional structure of a desired texture on the sub-nanometer-scale is a primary concern while designing the molecular nanodevices. Endohedral metallofullerenes are one of the candidate materials for creating single molecular orientation switching devices owing to their electric dipole moment due to the exchange of electrons between the encapsulated metal atom and a fullerene cage. To realize single molecular orientation switching, the interaction control between endohedral metallofullerene and metal substrate is important.[1] Self-assembled monolayer (SAM) is expected to be a suitable interlayer to control the interaction between endohedral metallofullerene and metal substrate.[2] Here, we demonstrate the interaction control between an endohedral metallofullerenes Lu@C82 and an Au(111) substrate by using alkanethiol SAM with different chain length. We compare the scanning tunneling microscopy (STM) images and spectroscopy (STS) of Lu@C82 on alkanethiol SAMs with different chain length (hexanethiol, octanethiol) at 65 K. From STM images of Lu@C82 on hexanethiol, we have observed the internal structure of Lu@C82 which suggests that the thermal rotational states of Lu@C82 on hexanethiol SAM should terminate at 65 K. On the other hand, we have not observed the internal structure of Lu@C82 on octanethiol SAM since Lu@C82 on octanethiol still rotates at 65 K. From STS of Lu@C82 on hexanethiol and octanethiol, we observe that alkanethiol chain length dependence of the Coulomb gap. We discuss these alkanethiol chain length dependence by considering the effective applied voltage in double barrier tunnel junction, molecular charge states, and thermal rotational states of Lu@C82. [1]Y. Yasutake, Z. Shi, T. Okazaki, H. Shinohara, and Y. Majima, Nano Lett., 5, 1057 (2005).[2]Y. Yasutake, Z. Shi, T. Okazaki, H. Shinohara, and Y. Majima, J. Nanosci and Nanotechnol., 6, 3460 (2006).
3:00 PM - B14.3
Attaching Biological Entities to AFM Cantilevers for Molecular Recognition Studies.
Travis Johnson 1
1 Nanotechnology Measurements Division, Agilent Technologies, Chandler, Arizona, United States
Show AbstractAtomic force microscopy (AFM) is an important tool for high resolution studies in biophysics and mechanical studies directed at biological materials. A strong suit of AFM is its ability to measure hardness/elasticity, nonspecific adhesion, or ligand-receptor interactions at the picoN scale. Molecular interactions are critical factors in a variety of biological phenomenon; such as initiation, modulation, and termination of DNA replication, transcription, enzyme activity, infection, immune responses, tissue generation, wound healing, cell differentiation, apotopsis, and physiological responses from drugs, hormones, or toxic agents. Using AFM scientists can probe and quantify these interactions in their native, liquid environments at physiological pH or perform dynamic experiments in situ by removing or adding ions, solutes, and reagents to the sample environment. Bioconjugation chemistry and surface chemistry are crucial because a selective ligand must be immobilized on the tip of a cantilever so that the AFM can resolve the mechanical force that is required to separate the ligand and its target. The resulting data can be used to calculate forces of unbinding, derive rate constants, and infer structural information about the binding pocket. Biomolecular recognition experiments with AFM can be greatly enhanced through the use of relatively short (~8-10 nm), heterobifunctional, elastic, polyethylene glycol (PEG) linkers to immobilize ligands. Heterobifunctional linkers are used in order to permit their sequential immobilization and bioconjugation, while minimizing undesirable polymerizations or self-conjugation. The linkers have an N-hydroxysuccinimide ester at one end to permit their attachment to aminated silicon or silicon nitride AFM cantilevers. Other specifically reactive functional groups, such as a biotin, maleimide, disulfide, aldehyde, or a photoreactive group, reside at the opposite end of the linker to permit the direct or indirect attachment of intact antibodies, Fab fragments, peptides, nucleic acids, or other biological entities. The PEG linkers are flexible, so an attached ligand has freedom to diffuse within a defined volume of space and approach the binding site in a thermodynamically favorable manner. PicoTREC, an accessory for the Agilent AFM, uses ligand-PEG modified cantilevers to generate a topography image and a recognition image of biomolecular interactions. As the modified cantilever gently oscillates at defined amplitude, it is scanned across a sample, and PicoTREC converts the information derived from ligand-receptor interactions into a high resolution, nanometer-scale map. Consequently, the locations of discrete molecular interactions can be easily determined and compared with a topography image of the sample.
3:15 PM - B14.4
Single Molecule Surface Chemistry with Feedback Control.
Nathan Yoder 1 , Mark Hersam 1 , James Fakonas 1
1 Materials Science, Northwestern University, Evanston, Illinois, United States
Show AbstractIn the past 25 years, the scanning tunneling microscope (STM) has enabled the detailed study of the chemistry and physics of single molecules on surfaces. These advances have greatly contributed toward the realization of precise control of chemical processes at the single molecule level. Electron-driven processes (including desorption and dissociation) are especially advantageous because they offer the possibility of rapidly exciting a molecule far from equilibrium with exceptional spatial localization of the excitation [1]. Attaining precise control over the electron dose requires a method for both detecting the desired events and rapidly terminating the flow of electrons to prevent overdosing. A significant advance in this area was Feedback Controlled Lithography (FCL) [2], which demonstrated the creation of atomic-scale reactive sites on H:Si(100) through the controlled desorption of single hydrogen atoms. In the context of electron-driven single molecule reactions at surfaces, the byproducts of such reactions are frequently susceptible to overdosing with electrons. Consequently, the ability to both detect a molecular conformational change and immediately terminate the flow of electrons is fundamentally relevant to the study of single-molecule chemistry at surfaces. In this study [3], we demonstrate this capability and apply it to the investigation of the byproducts of cyclopentene desorption [4] from clean Si(100). Experiments were performed using a cryogenic ultra-high vacuum (UHV) STM [5] operating at 8 K and 80 K. At low temperatures, cyclopentene molecules are controllably desorbed, and a feedback loop is utilized to detect the desorption events and halt electron flow. At the desorption conditions of –4 V and 2 nA, the desorption reaction alternately results in three distinct surface features: a clean silicon dimer (55 %), a half-dimer dark feature (30 %), and fully darkened silicon dimer (15 %). Additionally, the radial and angular distributions of the byproduct binding sites were measured. Interestingly, the desorption products were often observed at significant distances from the initial desorption site, with some features as far as 3 dimer rows (~23 Å) away. The dark desorption products are attributed to hydrogen-passivated silicon atoms resulting from the dissociation of a cyclopentene C-H bond and the subsequent bonding of the ejected hydrogen with the reactive silicon surface. Finally, tunneling electrons from the STM tip were used to induce hopping and desorption of hydrogen from the partially passivated silicon dimers.[1] A. J. Mayne et al., Chemical Reviews 106, 4355 (2006). [2] M. C. Hersam et al., Nanotechnology 11, 70 (2000).[3] N. L. Yoder, J. S. Fakonas, and M. C. Hersam, Manuscript in Preparation.[4] N. L. Yoder et al., Physical Review Letters 97, 187601 (2006).[5] E. T. Foley, N. L. Yoder, et al., Review of Scientific Instruments 75, 5280 (2004).
3:30 PM - B14.5
An STM Investigation into the Initial Stages of Copper Phthalocyanine Growth on Passivated Silicon Surfaces.
Jules Gardener 1 2 , J. Owen 2 , K. Miki 2 , S. Heutz 3
1 London Centre for Nanotechnology, University College London, London United Kingdom, 2 International Centre for Young Scientists and Nanomaterials Laboratory, National Institute for Materials Science, Tsukuba Japan, 3 Department of Materials, Imperial College, London United Kingdom
Show AbstractCopper phthalocyanine (CuPc) is an archetypal molecular semiconductor forming the basis of some of the most successful organic optoelectronic devices to date. Studies on technologically important substrates such as silicon yield a wide range of film properties depending on the silicon crystal orientation, surface termination and film thickness [1]. Thin layers of CuPc on passivated Si(001) therefore provide a good model system for studying the initial stages of film formation on a molecular level using scanning tunneling microscopy (STM).We have compared two different types of passivation: Si surfaces terminated with ammonia (Si(001):NH3) and hydrogen (Si(001):H) [2]. In-situ STM studies show that at the onset of the growth, defects in the passivated layer are saturated with strongly-pinned flat-lying CuPc molecules (seen as four-lobed features). Subsequently, islands are formed that are of a uniform height corresponding to the known diameter of CuPc. The Si termination species influences the shape and coverage of the molecular layer before the onset of multilayer formation: on NH3, large elongated islands are formed, whereas H passivation leads to smaller islands with a higher coverage, a phenomenon that can be attributed to a molecular mobility lower than on the more repulsive NH3 surface. High-resolution STM at sub-monolayer coverage shows that the islands possess a striped texture and that only two directions exist, both of which are aligned at an angle of ±64°C with respect to the underlying [110] substrate directions. More detailed images demonstrate that the stripes are made of columns of CuPc where the molecules are stacked perpendicular to the substrate surface. Upon further deposition, multilayers form and these are templated by the underlying molecular layer. We have found that the molecular orientation we observe is very similar to the bulk alpha-phase CuPc [2], and can rationalize the reduced crystallite size characteristic of thicker phthalocyanine films.[1] M. Gorgoi, W. Michaelis, T. U. Kampen, D. Schlettwein, D. R. T. Zahn, Appl. Phys. Lett., 244 (2004) 138.[2] J. Gardener, J. H. G. Owen, K. Miki, S. Heutz submitted to Langmuir[3] S. M. Bayliss, S. Heutz, G. Rumbles, T. S. Jones, Phys. Chem. Chem. Phys., 1 (1999) 3673
3:45 PM - B14.6
Hydrogen and Water on Palladium/Gold and Palladium/Copper Alloys; Imaging, Spectroscopy, and Dynamics.
Charles Sykes 1 , Ashleigh Baber 1 , Heather Tierney 1
1 Chemistry, Tufts University, Medford, Massachusetts, United States
Show AbstractB15: Semiconductors
Session Chairs
Thursday PM, November 29, 2007
Back Bay A (Sheraton)
4:30 PM - B15.1
Dopant Location in Synthesized Silicon and Germanium Semiconductor Nanowires.
Ping Xie 1 , Yongjie Hu 1 , Ying Fang 1 , Jinlin Huang 1 , Charles Lieber 1 2
1 Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts, United States, 2 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States
Show AbstractUnderstanding the location of dopants in nanoscale structures is central to the rational development of electronic and photonic devices based on these materials. Here we report studies defining the location of electrically–active dopants in silicon and germanium nanowires prepared by nanocluster catalyzed vapor-liquid-solid growth. The nanowires were characterized by AFM, STM and electrical transport measurements before and after selective etching of the surface in a highly controlled manner. Notably, these measurements demonstrate a transition from bulk-like to surface doping as the diameter is decreased below ~25 nm for both n- and p-type silicon nanowires. Similar diameter-dependent results were observed for n-type germanium nanowires, and suggest that the diameter-dependent bulk to surface doping transition may be general for synthesized nanowires. The implications of these results to enhanced transport properties of synthesized versus fabricated nanowires will be discussed.
4:45 PM - B15.2
Nanoscale Potential Fluctuations on Semiconductor Surfaces: Single Dopants and Quantum Dots.
Alexander Schwarzman 1 , Sergey Shusterman 2 1 , Eli Lepkifker 1 , Arie Raizman 2 , Ariel Sher 2 , Amir Boag 1 , Yossi Paltiel 2 , Yossi Rosenwaks 1
1 Dept. of Physical Electronics, Faculty of Engineering, Tel-Aviv University, Tel-Aviv Israel, 2 Solid State Physics, Electro-Optics Division, Soreq NRC, Yavne Israel
Show AbstractUltra-high vacuum Kelvin probe force microscopy (UHV KPFM) was used for characterization of strain and composition within individual quantum dots (QDs), and nanoscale potential distribution around single dopants in in-situ cleaved III-V semiconductors. The QDs were grown on highly Te-doped GaAs, InSb, and GaSb (100) oriented substrates by the droplet heteroepitaxy (DHE) method. The KPFM measurements conducted on the InSb/GaAs dots showed a 'bagel-shaped' surface potential in the circumference of each dot. In general, the dots work function may be affected by their composition, by mismatch strain in both the substrate and the QD, doping variation, strain dependent piezoelectric band shifts, surface states, quantum effects, and 2D electron gas formation. Considering all these factors and measuring the strain using high resolution cross-sectional TEM, we show that the surface potential fluctuations are mainly due to strain, which changes the dots band gap, and gradual internal composition changes from InAs to InSb. Fitting the measured surface potential profiles of several dots has allowed us to accurately extract the strain and composition within and around each dot. In the case of in-situ cleaved III-V (110) surfaces, we find that even a perfectly cleaved surface of a homogenously doped semiconductor shows a strikingly rough potential landscape characterized both by small potential peaks (~10 nm in diameter, 50 mV in magnitude) and larger cluster-like higher potential (~100 mV) regions. Using a novel deconvolution algorithm[1] has enabled us to restore the actual surface potential image from the KPFM measurements and obtain the potential distribution around single dopants and/or surface states. Comparison of the experimental results with theoretical calculations and extension of the method towards location of the dopants 2 or 3 atomic layers below the surface are also demonstrated and discussed. [1] Strassburg, et al, Rev. Sci. Inst., 76, 83705 (2005)
5:00 PM - **B15.3
Surface Electron Spectroscopy using Scanning Probe Microscopy from Field-emission to Force Interaction under a Tip-sample Bias Voltage.
Masahiko Tomitori 1 , Toyoko Arai 2 3 , Masato Hirade 1
1 School of Materials Science, Japan Advanced Institute of Science and Technology, Ishikawa Japan, 2 Natural Science & Technology, Kanazawa University, Kanazawa Japan, 3 SORST, Japan Science and Technology Agency, Saitama Japan
Show AbstractIn nanoscale material science and technology, scanning probe microscopy (SPM) is one of the most powerful tools to depict surface atomic structures. In addition, the spectroscopic features of SPM have attracted much interest for analyzing and characterizing sample surfaces on a nanoscale. A typical way to obtain spectroscopic information is applying and changing a bias voltage between an SPM tip and a sample, and measuring a response, e.g., current. The response concerning surface electronic states is chiefly governed by a tunneling barrier between the tip and the sample; the barrier changes with a tip-sample separation as well as the bias voltage. Understanding and utilizing the features of the barrier changing with the separation and the voltage, one can develop fascinating SPM methods towards nanoscale surface electron spectroscopy. In this study we present two types of scanning probe spectroscopy based on the SPM. When a negative voltage applied to the tip exceeds the work functions of a tip and a sample, electrons are field-emitted through the tunneling barrier. The electrons accelerated under a high bias voltage between them can excite the electrons, resulting in backscattering from the sample. By analyzing the energy of backscattered electrons one can perform surface electron spectroscopy using an SPM setup. This is an application of the field-emission scanning tunneling microscopy (STM). By combining an energy analyzer and optimizing a setup we obtained energy spectra of electrons backscattered from Si and metal-coated Si surfaces; Auger peaks and plasmon energy loss peaks are found even at a tip-sample separation of ~1 µm. To improve spatial resolution, the electron beam should be confined. A key technology lies in preparation of an SPM tip with capability of a single confined electron beam from the tip apex: we carried out this with a [111]-oriented single crystal W tip sharpened by a thermal field treatment. On one hand, the bias voltage changes the force interaction between a tip and a sample. Noncontact atomic force microscopy (nc-AFM) gives atom-resolved images by detecting the force; the shift of a resonance frequency of an AFM cantilever due to the force is a measure. On the base of nc-AFM we developed noncontact atomic force spectroscopy (nc-AFS) with capability of changing bias voltage to examine the force change. Prominent peaks were found in force-bias voltage curves over a Si adatom on a Si(111)-7x7 surface, corresponding to the enhancement of chemical covalent bonding between a tip and a sample at specified bias voltages. This indicates that the chemical covalent bonding, i.e., the quantum mechanical electron resonance, can be tuned through shifting the energies of surface electronic states by changing bias voltage. Here, the tip preparation is also an important key; we grew a Si nanopillar using the SPM setup, which will be also presented.
5:30 PM - B15.4
A Combined Scanning Kelvin Probe Microscopy and Conductive Atomic Force Microscopy Study of Charge-Induced Band Bending on GaN Films.
J. Moore 1 , M. Reshchikov 2 , J. Xie 3 , H. Morkoc 3 , A. Baski 2
1 Department of Chemistry and Physics, Longwood University, Farmville, Virginia, United States, 2 Department of Physics, Virginia Commonwealth University, Richmond, Virginia, United States, 3 Department of Electrical and Computer Engineering, Virginia Commonwealth University, Richmond, Virginia, United States
Show AbstractLocalized charge-induced band bending on MBE-grown GaN films was investigated using a new combination of conducting atomic force microscopy (CAFM) and scanning Kelvin probe microscopy (SKPM). CAFM was first used to locally inject charge at the surface oxide/semiconductor interface, and then SKPM was performed to monitor the evolution of the resulting surface potential. In a dark environment, the additionally charged interface states due to CAFM charge injection resulted in an induced additional band bending that persisted for hours. The induced band bending is nominal (<0.5 eV) for CAFM voltages less than 8 V, and reaches a saturation value of ~3 eV for voltages greater than 10 V. The saturation band bending corresponds to a total density of charged interface states (2×1012 cm-2) that is double the value observed for the intrinsic surface. Induced band bending greater than 0.5 eV could still be observed up to 4 h after charge injection, indicating that charge trapping is relatively stable in a dark environment. Charged interface states could be rapidly neutralized, however, by illumination with UV light. A phenomenological model was used to successfully describe the CAFM charge injection via a tunneling mechanism, where electrons travel from the tip through an oxide barrier and become trapped at oxide/GaN interface states. Saturation occurs due to the existence of a finite density of chargeable states at the interface. After charge injection, the decrease in induced band bending with time was found to be consistent with a thermionic model of charge transfer from the interface to the bulk. Calculated values from our model for the intrinsic band bending (0.6 - 1.0 eV) were in good agreement with previous studies using other methods.Funding provided by NSF and AFOSR.
5:45 PM - B15.5
Kelvin Force Microscopy - Frequency Response Optimization and Application to Semiconductor Nanowire or Nanotube Devices under Polarization.
Heinrich Diesinger 1 , Djamila Hourlier 1 , David Brunel 1 , Dominique Deresmes 1 , Jean-Jhilippe Nys 1 , Thierry Melin 1
1 ISEN, Institut d'Electronique, Microélectronique et Nanotechnologie, Villeneuve d'Ascq France
Show AbstractB16: Poster Session IV
Session Chairs
Friday AM, November 30, 2007
Exhibition Hall D (Hynes)
9:00 PM - B16.1
Ultrananocrystalline Diamond as a New Material for Atomic Force Microscope Probes: Fabrication and Nanoscale Wear Performance.
Jingjing Liu 1 , Shuang Li 1 , John Carlisle 3 , Nicolaie Moldovan 3 , Kevin Turner 1 , Robert Carpick 2
1 Materials Science Program, Mechanical Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States, 3 , Advance Diamond Technologies, Inc., Romeoville, Illinois, United States, 2 Mechanical Engineering and Applied Mechanics, University of Pennsylvania, Philadelphia, Pennsylvania, United States
Show AbstractNanoscale tip wear is a key limitation of conventional silicon and silicon nitride atomic force microscope (AFM) probes used in many basic research scanning modes, industrial metrology and probe-based manufacturing processes. Tip degradation induced by tip-sample interaction forces results in decreased resolution and uncertainty in almost all AFM measurements. Diamond is well respected as the ultimate probe material due to the many superior surface and bulk materials properties of diamond, including its ultra-high stiffness and hardness, extremely low friction coefficient, and chemical inertness. To date, however, efforts to manufacture diamond probes that consistently exhibit tip radii less than 30 nm without resorting to expensive post-processing (i.e. FIB) have not been successful.We report the wafer-level batch fabrication of Ultrananocrystalline diamond (UNCD®) probes with high aspect ratio tips that were manufactured using traditional lithographic-based micromachining, molding, oxidation-sharpening, and wafer bonding. Transmission electron microscopy (TEM) of the as-fabricated UNCD probes shows a smooth tip surface and tip radii of 8 to 15 nm. High-resolution contact mode topography images were successfully obtained using the UNCD probes.The performance of UNCD and commercial silicon nitride probes were compared under conventional imaging conditions for multiple probes by conducting systematic wear tests consisting of 100 contact-mode scans over a 1 x 1 μm2 area on a UNCD film. Over the course of the tests, changes in the tip’s behavior were monitored using TEM, pull-off force measurements, and tip radius measurements obtained through a blind reconstruction process. The experimental results show virtually no wear or change in adhesion of the UNCD probe after 100 scans, while significant blunting of the silicon nitride tip occurs after only 10 scans. This study shows great potential in both industrial fabrication of a new generation AFM probes as well as improving the understanding of fundamental nanoscale wear mechanics and tip-sample interactions.
9:00 PM - B16.10
Characterization of Chemical Heterogeneity with Atomic Force Microscopy.
Xiaohong Gu 1 , Lijiang Chen 1 , Xu Chang 2 , Michael Fasolka 2 , Tinh Nguyen 1
1 Materials and Construction Research Division, NIST, Gaithersburg, Maryland, United States, 2 Polymer Division, NIST, Gaithersburg, Maryland, United States
Show AbstractNanoscale spatial chemical information is essential for developing a molecular-level understanding of many surface phenomena; therefore, the ability to probe and image surface chemical heterogeneity with nanometer scale spatial resolution is needed. In this study, a well-controlled humidity system is used to enhance the AFM sensitivity in characterizing surface chemical heterogeneity of patterned self-assembled monolayers (SAMs) and polymer brushes. A chemically-gradient SAMs patterned with alternating regions of hydrophilic and hydrophobic materials and a heterogeneous surface patterned with alternating regions of different polymer brushes are prepared for this study. Dependence of the AFM image contrasts (phase and friction) on the surface free energy differences between the hydrophilic regions and hydrophobic regions of the chemically heterogeneous samples has been investigated as a function of relative humidity (RH). Effects of RH and the surface chemistry on the tip-sample adhesion are also investigated using functionalized tips. It has been found that both AFM image contrast and tip-sample adhesion differences between the hydrophilic and hydrophobic regions are enhanced by the elevated RH. The adhesion force increases exponentially with surface free energy at RH >25%, but essentially unaffected by the surface chemistry under dry condition. The results clearly demonstrate that, by using proper RH at the tip-sample environment, chemically heterogeneous regions can be distinguished with the AFM.
9:00 PM - B16.11
Effect of Humidity and Tip Shape on Resolution in Electrostatic Force Microscopy of Low k Dielectrics.
Todd Gross 2 , Igor Tsukrov 2 , Sylvain Saleur 2
2 Mechanical Engineering, University of New Hampshire, Durham, New Hampshire, United States
Show AbstractWe used electrostatic force microscopy to detect process induced damage to low k dielectrics. We quantified the effect of humidity on the force of attraction and the lateral resolution for materials with differing hydrophobicity. We used an axisymmetric finite element model to estimate the force as a function of height and then used that height dependence to estimate the effect of the non-linearity of the force on the frequency shift. We also used a three-dimensional finite element model to compare our with our experimental measurements of lateral spatial resolution.
9:00 PM - B16.13
Optimal Roughness for Minimal Adhesion.
Deli Liu 1 , Jack Martin 2 , Nancy Burnham 1
1 Physics Department, Worcester Polytechnic Institute, Worcester, Massachusetts, United States, 2 Micromachined Products Division, Analog Devices Incorporated, Cambridge, Massachusetts, United States
Show AbstractDiffering views on the effect of surface roughness on adhesion have appeared in the literature recently. Molecular dynamics has been used to simulate the contact of two surfaces and found that atomic-scale roughness can have a large influence on adhesion, causing the breakdown of continuum mechanics models [1]. An experimental study showed that roughness can determine the adhesion in nanometer contacts and indicated that continuum mechanics still works down to nanometer length scales [2]. In this work, we use a single-asperity model to describe a smooth tip in contact with a rough surface and predict that there is an optimal size of asperity that will yield a minimum of adhesion. Experimentally, adhesive forces on silicon wafers with varying roughness from 0.2 nm to 39 nm were measured using AFM (atomic force microscope) cantilevers with varying tip radii from 75 nm to 9.08 um. It is found that for all tip radii, the adhesion falls significantly for roughness greater than 1-2 nm and drops at higher roughness for larger tips. Minimum adhesion was observed as expected in the 1-10 nm range and the optimal roughness for minimum adhesion increases as the tip radius increases, which is consistent with the predictions. The work presented here should help minimize stiction for future MEMS devices and progress the understanding of adhesion between the atomic- and macro-scale. [1] B. Luan and M.O. Robbins, Nature 435, 929-932 (2005).[2] E.J.Thoreson, J. Martin, N.A. Burnham, J. Colloid Interface Sci. 298, 94-101 (2006).
9:00 PM - B16.14
Bending Tests of Tungsten Disulfide Nanotubes.
Ifat Kaplan-Ashiri 1 , Sidney Cohen 2 , Nathan Apter 2 , Yuekui Wang 3 , Gotthard Seifert 3 , Hanoch Wagner 1 , Reshef Tenne 1
1 Materials and Interfaces, Weizmann Institute of Science, Rehovot Israel, 2 Surface Analysis Unit, Weizmann Institute of Science, Rehovot Israel, 3 Institut für Physikalische Chemie, Technische Universität, Dresden Germany
Show AbstractThe mechanical properties of WS2 Nanotubes are of great interest from both scientific and applicative point of view. The cylindrical geometry of the nanotubes dictates a strong anisotropy of their physical properties. In practice, the difficulty in extracting individual components of the elastic tensor has limited the available information to only very partial and indirect experimental data. In former studies we have shown that these nanotubes have Young's modulus of 150GPa, tensile strength of 16GPa, elongation of 14% and completely elastic behavior under axial tension and compression. Lately, the interlayer shear (sliding) modulus (C44) of single multiwalled WS2 nanotubes was studied by atomic force microscopy bending tests. The nanotubes were suspended on trenches and then force was applied to a suspended nanotube by means of lateral deflection of the cantilever. Analysis of the bending by using Timoshenko's equation takes into account tension, compression and shear of the nanotube. Since the shear stress is believed to facilitate sliding of the layers, the shear modulus which was measured is probably the elastic constant C44. The observed value of 2 GPa agrees well with the value of 4 GPa obtained for density functional tight binding calculations for 2H-MoS2.
9:00 PM - B16.16
Characterization of Local Electrical Property of Coincidence Site Lattice Boundary in Location-controlled Silicon Islands by Scanning Probe Microscope.
Nobuyuki Matsuki 1 , Ryoichi Ishihara 1 , Alessandro Baiano 1 , Yasushi Hiroshima 2 , Satoshi Inoue 2 , Kees Beenakker 1
1 DIMES-ECTM, Delft University of Technology, Delft Netherlands, 2 Frontier Device Research Center, SEIKO-EPSON Corp., Fujimi-machi, Nagano, Japan
Show AbstractLocal electrical property of coincidence site lattice boundaries (CSLBs) in location-controlled silicon islands, which are fabricated using μ-Czochralski process (grain filter) [ref], was characterized by scanning capacitance microscopy (SCM) and scanning spreading resistance microscopy (SSRM). Prior to the measurements, density of states (DOS) of the CSLBs was calculated using ab-initio calculation. The result shows that, for {221}Σ9 CSLB, no states are observed in the gap, while tail states at valence band edge is higher than that of the bulk Si due to structural distortion at the interface. The same DOS data was input to a device simulator to estimate a current change at {221}Σ9 CSLB in the SSRM. The simulation result showed a possibility for SSRM to detect change of current there.Location-controlled silicon islands having 4 μm of the average diameter was prepared as follows: First, grain filters having 100 nm by diameter of the hole were formed on an n-type silicon (100) wafer by wet oxidation and low pressure chemical vapor deposition (CVD). Then, 250 nm-thick of an amorphous silicon film was deposited by plasma enhanced CVD. Finally, Boron implantation followed by crystallization using XeCl excimer laser was performed. SCM and SSRM were performed with a commercial scanning probe system similar to a typical atomic force microscope, however, with which capacitancemeter, electrometer and voltage source were equipped in additional. Silicon cantilevers with a gold or platinum coated tip were used to SCM or SSRM, respectively. Bias voltage ranging from -10 to +10V was applied to the Si layer during SCM and SSRM. Some CSLBs found in a silicon island are analyzed as Σ3 and Σ9 by electron back scattering diffraction pattern. These CSLBs are determined as {111}Σ3 and {221}Σ9 by referring to previous observation results made by transmission electron microscopy. {111}Σ3 CSLBs shows no activity for SCM or SSRM; this is consistent with previous prediction that {111}Σ3 CSLB is not electrical active. SCM and SSRM exhibited increase of local capacitance and resistance, respectively, at {221}Σ9 CSLBs. This result implies that {221}Σ9 CSLB has electrical activity, which is less significant than that of the random grain boundaries leading to segregation of dopants or metals. We verified a capability of SCM and SSRM for characterizing local electrical property of coincidence site lattice boundary in silicon.[ref] R. Ishihara, M. He, V. Rana, Y. Hiroshima, S. Inoue, T. Shimoda, J. W. Metselaar, C. I. M. Beenakker: Thin Solid Films 487 (2005) 97.
9:00 PM - B16.17
Molecular Resolution Imaging of Polymer Crystals using Force Modulation Microscopy.
Kuniko Kimura 1 2 , Kei Kobayashi 3 , Hirofumi Yamada 1 , Kazumi Matsushige 1
1 Electronic Science and Engineering, Kyoto University, Kyoto Japan, 2 Innovation Cluster Creation Project, Kyoto University, Kyoto Japan, 3 International Innovation Center, Kyoto University, Kyoto Japan
Show AbstractAtomic force microscopy (AFM) has been used for molecular resolution topographic imaging of highly stretched crystalline polymer films [1]. However, high resolution imaging becomes very difficult for the case when the crystal surface is covered with amorphous layers. Generally, thin amorphous layers spread on the surface of multi-crystalline polymer thin films when they are obtained by wet coating and subsequent annealing treatment. The amorphous layers hinder topographic imaging in molecular resolution.Force modulation microscopy (FMM) is a prominent technique to obtain viscoelastic information on polymer film surface using AFM. It has been often applied to investigate phase separation of polymer blends or that of block copolymers [2]. This technique provides viscoelastic information about the subsurface structure, which brought us an idea of the application for molecular imaging of crystals under the amorphous layer.We have recently succeeded in molecular resolution imaging on polymer crystals using FMM technique [3]. We used a commercially available cantilever (Nanosensors CONT) whose nominal spring constant was 0.2 N/m, and an AFM instrument (JEOL JSPM-4200) with some modifications of optics and electronics for reducing noises in deflection sensing. FMM imaging was performed at room temperature under ambient conditions. After contacting the cantilever tip to the sample surface, the tip force was decreased as low as possible for realizing a small contact area. Under this condition, the sample was oscillated perpendicular to the sample surface by driving the tube scanner located beneath the sample.We obtained molecular resolution FMM images of a poly(vinylidenefluoride-trifluoroethylene) (P(VDF-TrFE)) edge-on lamella whose surface was covered with thin amorphous layer. In the FMM image, we clearly recognized aligned molecular chains on the edge-on lamellar surface, and the domain boundary, where the direction of molecular chains changed, was observed. As another sample for molecular resolution FMM imaging, we obtained viscoelastic molecular images on cleaved b-c plane of a poly(2,4-hexadiyne-1,6bis(p-toluene-sulphonate) (poly-PTS) single crystal. In this case, we visualized detailed structures of polymer main chains and side groups in submolecular resolution. Especially, the FMM phase image brought the clear contrast which is related to the relaxation of mechanical deformation induced by the modulation force. FMM is a powerful tool to visualize viscoelastic information of polymer crystals in molecular resolution. It brings molecular images even on crystal surfaces covered with thin amorphous layers. In case of clean surfaces of single crystal, it enables us direct visualization of the molecular dynamics.[1] For example; K. D. Jandt et al., Macromolecules, 26, 6552 (1993).[2] For example; H. N. Lin et al., Appl. Phys. Lett., 74, 2785 (1999).[3] K. Kimura et al., Nanotehcnology, in press.
9:00 PM - B16.2
Electro-oxidative Lithography – Tool to Manipulate Material on the Nanometer Scale in 2 and 3 Dimensions.
Stephanie Hoeppener 1 , Claudia Haensch 1 , Ulrich Schubert 1 2
1 Laboratory of Macromolecular Chemistry and Nanoscience, Eindhoven University of Technology, Eindhoven Netherlands, 2 Laboratory of Organic and Macromolecular Chemistry, Friedrich-Schiller-University , Jena Germany
Show Abstract9:00 PM - B16.3
Directed-Assembly of Robust Single Nanoparticle-attached AFM Tip for Contact Force Measurement and Stable Imaging.
Taekyeong Kim 1 , Sung Myung 1 , Seunghun Hong 1
1 School of Physics and Astronomy, Seoul National University, Seoul Korea (the Republic of)
Show AbstractIn previous works, single nanoparticle (NP) attached Atomic Force Microscope (AFM) tips have been utilized for optical imaging and non-contact mode surface force research. However, the NP tip was not strong enough to survive during the AFM imaging and contact force curve study. Herein, we present a directed-assembly method to mass-produce robust single Au nanoparticle attached AFM tip which enables stable tapping mode imaging of carbon nanotubes (CNTs) and contact force curve measurements under ambient conditions.In this method, the end of the AFM tip was functionalized with amine-terminated molecular layers, while other regions passivated by methyl-terminated layer. Then, the assembly of a negatively-charged single Au NP was directed to the end of the AFM tip via electrostatic interaction in solution. We successfully achieved repeated tapping mode imaging of CNTs using the Au NP tip, and verified that the Au NP was still firmly attached at the end of the tip after the imaging process. The tapping mode AFM image of CNTs showed the expected tip convolution effect from the flattened Au NP. As far as we know, this is the first report on stable AFM imaging using a single NP tip. Furthermore, we performed contact force curve measurement on the flat surface using our robust Au NP tip and measured about the contact deformation of the tip-end with the Au NP. It confirmed that our Au NP tip is also strong enough for contact force curve measurement. Since we can precisely control the shape and chemical groups of our NP tips, these tips could be utilized for various nanoscale researches such as surface force study, nano-SERS imaging, and etc.
9:00 PM - B16.4
Single Asperity Wear and Stress-Assisted Dissolution of Copper.
Bin Chua 1 , Abhijit Chandra 1 , Pranav Shrotriya 1
1 Mechanical Engineering, Iowa State University, Ames, Iowa, United States
Show AbstractCopper is becoming a commonly used material in integrated circuit devices because of its high electric and heat conduction. Copper based devices are manufactured using additive patterning and subsequently undergo chemical mechanical planarization (CMP) to ensure reliable interconnection. During CMP, material removal is accomplished through synergistic combination of chemical effects and mechanical abrasion. The focus of this paper is to investigate the influence of stress-assisted dissolution on material removal during mechanical stimulation of copper surface under different chemical environments. A unique setup was used to generate well characterized stress states on a polished copper specimen. Stressed surface of copper specimen is stimulated using tip of the atomic force microscope (AFM) as a well characterized asperity. Material removal rates are measured for different contact loads and in plane stress states under different chemical environment in order to characterize stress-assisted dissolution of copper specimens. Measured material removal rates display a complex dependence on contact pressures, in-plane stress state and chemical environment. A surface material removal mechanism based on a single asperity wear and stress-assisted dissolution is proposed to explain the experimental observations.
9:00 PM - B16.5
Characterization using Ballistic Electron Emission Microscopy of 2D-patterned GaNxAs 1-x Quantum Dots Fabricated using Ion Implantation and Pulsed Laser Melting.
Taeseok Kim 1 , Michael Aziz 1 , Venkatesh Narayanamurti 1
1 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States
Show AbstractWe will present Ballistic Electron Emission Microscopy (BEEM) measurements on 2D patterned GaNxAs 1-x nanostructures fabricated in a GaAs matrix using nitrogen ion implantation followed by pulsed laser melting and rapid thermal annealing (RTA). As a three terminal scanning tunneling microscopy technique, BEEM can image both the surface topography and the local hot electron transport. Using ion implantation through a lithographically patterned mask and varying subsequent processing conditions, we have made locally confined GaNxAs1-x dots with different activated nitrogen concentrations. By analyzing BEEM images of the quantum dots, we study giant bandgap bowing effects on the Schottky barrier height. We will also discuss the effects of different implanted nitrogen concentrations, laser fluences and RTA conditions on the conduction band structures of these quantum dots.
9:00 PM - B16.6
Measurement of Ferromagnetic Resonance Using a Scanning Evanescent Microwave Microscope to Map Local Magnetic Properties of Magnetic Thin Films.
Christian Long 1 , Ichiro Takeuchi 1 , Haitao Yang 2 , Xiao-Dong Xiang 2
1 Physics, University of Maryland, College Park, Maryland, United States, 2 , Intematix Corporation, Fremont, California, United States
Show AbstractWe present our recent efforts in the development of a scanning evanescent microwave microscope (SEMM) for the measurement of ferromagnetic resonance (FMR) in thin films. The use of evanescent fields allows for nondestructive characterization of samples with a spatial resolution on the order of the size of the probe tip, in our case ~100 microns. A fixed frequency (2.4 GHz) resonator is used to measure FMR field and line width for a variety magnetic thin film samples. The probe tip is scanned over the surface of a sample with continuously varying composition and the magnetic field is swept for each point, allowing for measurement of the variation in FMR parameters as a function of composition.
9:00 PM - B16.7
Kelvin Force Microscopy on GaN Wide Gap Materials.
Sophie Barbet 1 , Raphael Aubry 1 3 , Dominique Deresmes 1 , Marie-Antoinette Di Forte-Poisson 3 , Heinrich Diesinger 1 , Thierry Melin 1 , Didier Theron 2
1 Physics ISEN, Institut d'Electronique, de Microélectronique et de Nanotechnologie (IEMN), Villeneuve d'Ascq France, 3 , Thales III-V Lab, Marcoussis France, 2 DHS, Institut d'Electronique, de Microélectronique et de Nanotechnologie (IEMN), Villeneuve d'Ascq France
Show AbstractKelvin Force Microscopy (KFM) [1] enables to probe the contact potential difference between two materials, which is related to physical quantities such as work function differences and/or surface states. We address in this contribution the issue of quantitative measurements of such physical quantities using KFM in the case of GaN wide-gap materials. We will first focus on the z-spectroscopy of KFM measurements performed by nullifying the oscillation amplitude of the cantilever when the tip-surface capacitance is submitted to an electrostatic excitation at the cantilever resonance frequency. Even on metallic layers, an unexpected asymmetry of the V(z) curves (surface potential versus tip-substrate distance) can be observed experimentally, depending whether the electrostatic excitation is applied to the tip or to the substrate. This effect is demonstrated to originate in instrumental capacitive cross talks between the electrostatic excitation and the microscope photodiode signals. When suppressing these cross-talks, artefact free V(z) curves can be measured. Their monotonous variation at the scale of a few hundred of nanometers is interpreted in terms of contaminants forming a surface dipolar layer at the sample and tip.The scheme has been applied in a second step to n and p-type GaN layers grown by MOCVD on a (0001) sapphire substrate [2]. The n-type GaN (respectively p-type GaN) is doped by Si (Mg) with an effective doping level of 1.6e19 cm−3 (1e16 cm−3). To get a potential reference for KFM measurements, ohmic contacts on n-type GaN (resp. p-type GaN) were achieved using Ti/Al (resp. Ni/Au) metallization layers with thickness 20/200 nm (resp. 50/100 nm), followed by a Au thickening. Experiments show that the contact potential difference between n- and p-type GaN is ~0.8V. The lower value compared to GaN band-gap (3.4 eV) is attributed to surface-state induced band-bending at the oxidized GaN surface. This interpretation will be compared with transport experiments using conducting atomic force microscopy in the 150K-500K range.Finally, KFM experiments will be shown on AlGaN/GaN high-electron mobility transistor devices [4]. Surface potential maps here strongly depend on parasitic capacitive couplings between the cantilever and the device, which occur at the scale of a few tens of µm. In order to get quantitative measurements of surface potentials (and thus of charge distributions between source and drain contacts), the purpose is here to measure the transfer function of the tip-cantilever probe and use it as a deconvolution of experimental KFM images.[1] M. Nonnenmacher et al, Appl.Phy.Lett., 58,25,2921-2923 (1991).[2] M.A.di Forte-Poisson et al., Phys.Stat.Sol. (a), 203, 1, 185-193 (2006).[3] H.O.Jacobs et al., J. Appl.Phys., 84, 3, 1168-1173 (1998).[4] G.Koley et al., IEEE Transactions on Electron Devices, 50, 4, 886–893 (2003).
9:00 PM - B16.8
Ferroelectric Nanolithography on Organic Substrates.
Christopher Rankin 1 , C. Chou 1 , David Conklin 1 , Dawn Bonnell 1
1 , University of Pennsylvania, Philadelphia, Pennsylvania, United States
Show Abstract9:00 PM - B16.9
Growth of Nanodots on a Strained GaAs Epilayer Using Scanning Tunneling Microscope.
Haeyeon Yang 1 , Dong Jun Kim 1 , Edward Everett 1 , Joseph Abel 1
1 Physics, Utah State University, Logan, Utah, United States
Show AbstractWe report growth of nanodots on strained GaAs surfaces using a scanning tunneling microscope (STM) at room temperature. To create a tensile strained epilayer, a 5nm-thick GaAs layer was epitaxially deposited over InGaAs quantum dot chains by molecular beam epitaxy (MBE) at 460°C. Reflection high energy electron diffraction (RHEED) patterns showed that the top GaAs layer had a 2x4 surface reconstruction, which was confirmed by STM. The MBE grown samples were then transferred to an STM chamber through an attached ultra-high vacuum transfer port for in-situ surface images. The STM images were obtained at low negative sample bias of 3V for filled state images at feedback set current of 0.1nA. The images of the as-grown GaAs surface showed that the surface has hills of ~100nm wide separated by shallow trenches of a few nanometers deep. Nanodots of various shapes were fabricated using the STM on the strained surface when high positive sample biases of 7 to 9 volts at various feedback currents of 6 to 10 nA were pulsed on a single spot for few hundred milliseconds ranging from 100 to 1000 ms at room temperature. The in-situ STM images of the nanodots showed that their average width, length, and height increased as the bias voltage increased. The dots were elongated along the [11-0] direction and the top surface had reconstruction with dimer rows. The width, length, and height grow exponentially over the bias application period. However, the growth exponent for the length was found larger than those of the width and height. The analysis suggested that the localized diffusion on the strained GaAs surface is anisotropic at room temperature, faster along the dimer row direction.