Stephen Jesse Oak Ridge National Laboratory
Brian Rodriguez University College Dublin
Takeshi Fukuma Kanazawa University
Ricardo Garcia Instituto de Microelectronica de Madrid
QQ1: Probing near Surface Fields, Electrostatic and Magnetic Nanoscale Properties
Monday AM, November 28, 2011
Room 305 (Hynes)
9:30 AM - QQ1.1
Low Magnetic Signals Measured by a Combination of MFM and KPFM.
Miriam Jaafar 1 3 , David Martinez - Martin 1 , Ruben Perez 2 , Julio Gomez - Herrero 1 , Oscar Iglesias Freire 3 , Luis Enrique Serrano 3 , Ricardo Ibarra 4 5 , Jose Maria de Teresa 4 , Agustina Asenjo 1 Show Abstract
1 Física de la Materia Condensada, Universidad Autónoma de Madrid, Madrid Spain, 3 , Instituto de Ciencia de Materiales de Madrid, CSIC, Madrid, Madrid, Spain, 2 Dpto. Física Teórica de la Materia Condensada, Universidad Autónoma de Madrid, Madrid, Madrid, Spain, 4 , Instituto de Ciencia de Materiales de Aragón, CSIC, Zaragoza, Aragón, Spain, 5 , Instituto de Nanociencia de Aragón, CSIC, Zaragoza, Aragón, Spain
The most outstanding feature of the Scanning Force Microscopy (SFM) is the capability to detect different short and long range interactions. In particular, Magnetic Force Microscopy (MFM) is used to characterize the domain configuration in ferromagnetic materials like thin films grown by physical techniques or ferromagnetic nanostructures. The MFM is nowadays proposed as valuable technique to characterize more complex system as organic nanomagnets, magnetic oxide nanoislands and carbon based materials . In those cases, the magnetic nanoelements and its substrate present quite different electronic behavior i.e. they exhibit large surface potential differences which causes heterogeneous electrostatic interaction between tip and sample  that could be interpreted as magnetic interaction. To distinguish clearly the origin of the tip-sample forces we propose two different methods: (i) by applying in situ magnetic field during the MFM operation to detect the variation in the magnetic state of the sample , (ii) by performing a combination of Kelvin Probe Force Microscopy (KPFM) and MFM to compensate the electrostatic contribution in the frequency shift signal The useful of the KPFM-MFM combination is proved by studying Co nanostripes grown by Focused Electron Beam . Moreover, with this technique we investigate possible ferromagnetic order on the graphite surface . By combining KPFM and MFM, we are able to separate the electrostatic and magnetic interactions obtaining an upper bound for the magnetic force gradient in graphite of 16 µN/m. Our experiments suggest the absence of ferromagnetic signal in graphite at room temperature. J.Cervenka, et al., Nature Physics, 5(2009) 840  R. Schmidt et al., Nanotechnology, 20 (2009) 264007  M. Jaafar et al., Ultramicroscopy, 109 (2009) 693 M. Jaafar et al. submitted BJ Nano D. Martínez et al., Phys. Rev. Lett., 105 (2010)257203
9:45 AM - **QQ1.2
Pushing the Time Resolution of SPM into the Nanosecond Regime.
Andreas Heinrich 1 Show Abstract
1 , IBM Research, San Jose, California, United States
ABSTRACT BODY: The scanning tunneling microscope has been an extremely successful experimental tool because of its atomic scale spatial resolution. In recent years this has been combined with the use of low temperatures, culminating in microvolt energy resolution. However the time resolution of typical STM experiments is limited to about one millisecond for spectroscopy on a single atom. In this talk we will discuss the use of inelastic tunneling spectroscopy with low-temperature STM for the study of spins, a technique coined spin-excitation spectroscopy. With this approach it is possible to measure the energy eigenstates of the quantum spin Hamiltonian that describes spins on surfaces with very high precision. We will briefly discuss its application to the measurement of the Zeeman energy and to magneto-crystalline anisotropy. We will then focus on a new way of achieving fast time resolution based on an all-electrical pump probe spectroscopy. In this approach, a strong voltage pulse applied between tip and sample drives a spin out of thermal equilibrium (the pump pulse) [Nature Physics 6, 340 (2010)]. A short time later (typically a few nanoseconds) a smaller voltage pulse (the probe pulse) is applied which probes the state of the system. I will demonstrate this technique for the measurement of the spin relaxation time of individual magnetic atoms [Science 329, 1628 (2010)] and chains of atoms on a surface.
10:15 AM - QQ1.3
Magnetic Force Microscopy without Lifting - Using Intermodulation Spectroscopy.
Daniel Forchheimer 1 , Daniel Platz 1 , David Haviland 1 Show Abstract
1 Nanostructure Physics, Royal Institute of Technology, Stockholm Sweden
Atomic Force Microscopy is commonly used to probe long range magnetic forces with the help of a magnetized tip. Close to the surface the forces on the tip are dominated by repulsion and van-der-Waals attraction. A few nano meters away from the surface the magnetic interactions dominate. To image these magnetic interaction we must separate short and long-range components of the tip-surface force. The most common method to achieve this separation is to use lift-mode, in which one line is first scanned close to the surface to determine topography, then scanned again, while lifting the tip to a constant distance above the known topography to measure the magnetic forces. Presently methods are emerging which separate the force components by other means . We present a novel method to image magnetic and surface forces simultaneously in one scan, using a new multi-frequency AFM mode called Intermodulation AFM [2,3].Intermodulation AFM excites the cantilever with two closely spaced frequencies creating a beat-like motion. Due to the non-linearity of the tip-surface force, the cantilever responds not only at the drive frequencies, but also at mixing frequencies called intermodulation products. We measure the amplitude and phase of 32 intermodulation products while scanning using a specially designed multi-frequency intermodulation lock-in analyzer [4,5]. For a given measurement bandwidth, the intermodulation technique generates much more information about the tip-surface force than other dynamic AFM modes.At each of these 32 frequencies we can make an amplitude and phase image showing rich and varied contrast. However to interpret this contrast requires combining the information contained in all images to extract the tip-surface interaction at every pixel of the image. We have developed a method to determine parameters of an arbitrary tip-surface force model by fitting the model to the measured intermodulation spectrum. Using this method we show how a model which parameterizes short and long-range components of the force can be used to generate an image of the magnetic interaction. Furthermore, in comparison with other magnetic force microscopy techniques which images the amplitude or phase of only one frequency, our multi-frequency method allows for a more quantitatively accurate determination of the long range interactions. C. Dietz et al. Nanotechnology 22 125708 (2011) D. Platz, et al.. Appl. Phys. Lett. 92, 153106 (2008) D. Platz, et al.. Ultramicroscopy 110, 6, 573-577 (2010) E. A. Tholen, et al.. Rev. Sci. Instr. 82, 026109 (2011)  http://www.intermodulation-products.com
10:30 AM - QQ1.4
Measurements of Nanoscale Potential Distribution in Liquid by Dual Frequency Open-Loop Electric Potential Microscopy.
Naritaka Kobayashi 1 , Hitoshi Asakawa 2 , Takeshi Fukuma 1 2 Show Abstract
1 Frontier Science Organization, Kanazawa University, Kanazawa, Ishikawa, Japan, 2 Bio-AFM Frontier Research Center, Kanazawa University, Kanazawa, Ishikawa, Japan
Local potential distribution at a solid/liquid interface plays important roles in various processes in biology, chemistry, and industrial devices. To understand the mechanism of these processes, it is important to directly measure local potential distribution in liquid. Kelvin probe force microscopy (KFM) has been used for local potential distribution measurements in air and vacuum. However, KFM cannot be used in liquid due to electrochemical reactions and redistribution of ions and water caused by the application of ac and dc bias voltages between a tip and a sample. These phenomena generate uncontrollable spurious forces, which disturb the stable operation of KFM.To overcome these problems, we have developed a method to measure local potential distribution in liquid, which is referred to as open-loop electric potential microscopy (OL-EPM). In this method, only an ac bias voltage with a relatively high modulation frequency (fm) is applied between a tip and a sample. Owing to the slow time response of electrochemical reactions and redistribution of ions and water, the application of an ac bias voltage with a high modulation frequency does not cause the problems. Potential values are calculated from the amplitudes of the first and second harmonic cantilever oscillations (A1 and A2, respectively) induced by the ac bias voltage. Thus, combined with atomic force microscopy, surface structure and local potential distribution at a solid/liquid interface can be imaged simultaneously.To date, we have demonstrated that OL-EPM can measure local potential distribution in liquid by measuring the potential distribution of a dodecylamine thin film in 1 mM NaCl solution. We have also measured the potential value of the positively and negatively charged nanoparticles in 1 mM NaCl solution. The potential difference approximately agrees with their zeta potential difference. These results demonstrate that OL-EPM has a capability of quantitative measurements of potential values.The practical issue in OL-EPM is the difficulty in the operation in a high concentration solution. The time response of electrochemical reactions and redistribution of ions and water becomes much faster with increasing the concentration of the electrolytic solution. Thus, a higher modulation frequency is required for operating OL-EPM without inducing these unwanted events. However, the detection of A2 signal at 2fm becomes more difficult with increasing fm. This is because the sensitivity of the cantilever deflection to an electrostatic force is severely reduced when its frequency exceeds the resonance frequency of the cantilever. In this study, we also present a method to overcome this problem by applying the sum of the ac bias voltages with different frequencies. The proposed method enables to apply OL-EPM measurements in a high concentration solution such as buffer solution used in biological applications and electrolytic solution used in the studies on electrochemical reactions.
11:15 AM - QQ1.5
Quantitative Characterization of Electrostatic Properties Using a Dual-Harmonic Scanning Probe Microscopy Approach.
Liam Collins 1 , Jason Kilpatrick 1 , Suzanne Jarvis 1 , Brian Rodriguez 1 Show Abstract
1 Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Dublin, Dublin 4, Ireland
Surface potentials and electrostatic interactions play a key role in many biological processes. In nature, electrostatic fields propagating from the surface of biomolecules work in concert to mediate structure, function, and signalling in biosystems. For example, transport across cellular membranes is largely governed by changes in the surface potential of the membrane, and provides a crucial pathway for cells to interact with their environment. Electrostatic interactions also play a fundamental role in the central process of protein folding and protein interactions and it is likely they play an equally significant role in misfolding events, which can be related to diseases such as Alzheimer’s. Although the importance of electrostatics in nature is quite clear, few techniques allow for electrostatic characterization of single biomolecules. Kelvin Probe Force Microscopy (KPFM) is a promising technique towards this goal, combining the high sensitivty and resolution of Atomic Force Microscopy (AFM) with the capability of simultaneously mapping topography and surface potential at the nanoscale. Here, we demonstrate high-resolution surface potential mapping of biomolecules and model systems using several variants of KPFM, and quantify differences between the measurement techniques. Specifically, we investigate a multi-frequency approach for quantitative surface potential mapping refered to here as Dual Harmonic-KPFM (DH-KPFM) (Takeuchi et al., 2007; Kobayashi et al., 2010). We directly compare conventional KPFM and DH-KPFM in terms of frequency and phase dependence, and apply them both to model systems in order to relate the measured contact potential difference (CPD). Unlike standard KPFM, DH-KPFM does not require the application of a DC bias offset and is therefore a promising technique for the investigation of voltage sensitive materials such as ferroelectrics, photovoltaics, and biomolecules. Moreover, the elimination of the DC bias overcomes a significant barrier towards extending Kelvin measurements to liquid enviroments, and therefore could provide an opportunity to unravel the relationship between structure and electronic function of biosystems in physiologically relevant conditions.
11:30 AM - **QQ1.6
Atomic-Scale Functional Imaging by Combined Scanning Tunneling and Atomic Force Microscopy.
Mehmet Baykara 1 , Harry Moenig 1 , Todd Schwendemann 1 2 , Milica Todorovic 3 , Ruben Perez 3 , Eric Altman 1 , Udo Schwarz 1 Show Abstract
1 , Yale University, New Haven, Connecticut, United States, 2 , Southern Connecticut State University, New Haven, Connecticut, United States, 3 , Universidad Autónoma de Madrid, Madrid Spain
On surfaces, forces extending into the vacuum direct the behavior of many scientifically and technologically important phenomena such as corrosion, adhesion, thin film growth, nanotribology, and surface catalysis. To advance our knowledge of the fundamentals governing these subjects, it would be desirable to simultaneously determine a surface’s structure, map electron densities, quantify force interactions, and identify chemical species. For example, in the case of a catalytically active surface, this would allow study of the role and effectiveness of surface defects such as vacancies, steps, kinks, impurities, and domain boundaries as active sites. In this talk, we will show with the example of an oxygen/copper(100) surface phase that much of this information can be derived from combining the new method of three-dimensional atomic force microscopy (3D-AFM) [1,2], a variant of noncontact atomic force microscopy, with simultaneous scanning tunneling microscopy. The surface oxide layer of Cu(100) features domain boundaries and a distinct structure of the Cu and O sublattices that is ideally suited for such model investigations. By combining experimental results with theoretical simulations, we will show how 3D data sets enable the site-specific quantification of force interactions and tunneling currents, how different chemical species can be imaged using different tips, different tunneling conditions, and different interaction mechanisms, and how structure-induced stress fields and their influence on the local chemical activity and topographical deformation can be studied.  B. J. Albers et al., Nature Nanotechnology 4 (2009) 307. M. Z. Baykara et al., Advanced Materials 22 (2010) 2838.
12:00 PM - QQ1.7
DFT Analysis of Combined 3D NC-AFM and STM Imaging of Cu(100)-O Oxide Surface.
Milica Todorovic 1 , Mehmet Baykara 2 3 , Harry Moenig 2 3 , Todd Schwendemann 2 3 4 , Eric Altman 3 5 , Udo Schwarz 2 3 5 , Ruben Perez 1 Show Abstract
1 Depto. de Fisica Teorica de la Materia Condensada, Universidad Autonoma de Madrid, Madrid Spain, 2 Dept. of Mechanical Engineering and Materials Science, Yale University, New Haven, Connecticut, United States, 3 Center for Research on Interface Structures and Phenomena (CRISP), Yale University, New Haven, Connecticut, United States, 4 Physics Department, Southern Connecticut State University, New Haven, Connecticut, United States, 5 Dept. of Chemical and Environmental Engineering, Yale University, New Haven, Connecticut, United States
Investigation of novel catalytically active surfaces requires a comprehensive experimental method for the identification and rapid characterization of prospective catalytically active sites. The powerful method of three-dimensional atomic force microscopy (3D-AFM) in non-contact mode  has been combined with scanning tunneling microscopy (STM) to study the oxygen-terminated copper (100) surface. Complex 3D data sets, obtained by simultaneously recording the tunneling current and the AFM frequency shift, allow for site specific quantification of forces and tunneling currents. The wealth of information obtained is promising for future applications, but the interpretation of the wide range of contrast modes requires a thorough characterization of the sources of contrast in AFM and STM imaging.We combine DFT total-energy calculations with Non-equilibrium Green's Function (NEGF) methods for electronic transport to determine the tip-surface interaction and tunnelling current [2,3,4] for a large set of tip models in order to clarify the different contrast modes obtained in the experiments. At the outset, we obtained a stable Cu(100)(2√2x√2)R45°-O surface reconstruction model. Surface features were found to be in good agreement with experimental data, and the analysis of surface electronic properties enabled us to identify prospective reactive sites. The effect of tip changes on contrast modes was explored by considering tips of different reactivity. Our simulations, in comparison with AFM experimental images, identified a contaminated tip with a Cu-terminated experimental configuration. Charge density and current calculations further helped to investigate the STM imaging mode and explain the lateral shift between surface features identified separately in AFM and STM images. Consideration of different atom defect species and geometries helped us to understand detailed STM image features. The combination of conductance calculations with total energy methods provides insight into (1) the fundamentals of contrast formation in this novel experimental technique and (2) into the correlation between tip-sample forces and local chemical reactivity, factors that are essential for the further development and application of this approach to characterise catalytic activity. B. J. Albers, T. C. Schwendemann, et al., Nature Nanotechnology, 4, (307), (2009)  Y. Sugimoto, P. Pou, M. Abe, et al., Nature, 446, (64), (2007) P. Jelinek, M. Švec, P. Pou, et al., Phys. Rev. Lett., 101, (176101), (2008) J. M. Blanco, F. Flores and R. Pérez, Prog. Surf. Sci., 81, (403), (2006)
12:15 PM - QQ1.8
High-Resolution Surface Potential Imaging of Single-Walled Carbon Nanotubes Using Frequency-Modulation High-Frequency Electrostatic Force Microscopy.
Masanao Ito 1 , Kei Kobayashi 2 , Yuji Miyato 3 , Kazumi Matsushige 1 , Hirofumi Yamada 1 Show Abstract
1 Department of Electronic Science and Engineering, Kyoto University, Kyoto Japan, 2 Office of Society-Academia Collaboration for Innovation, Kyoto University, Kyoto Japan, 3 Graduate School of Engineering Science, Osaka University, Osaka Japan
Carbon nanotube field effect transistors (CN-FETs) are one of the most promising candidates for future nanoelectronic devices because of the superior transport properties of carbon nanotubes (CNTs). Kelvin-probe force microscopy (KFM) is a powerful tool to investigate surface potential (SP) distribution on the gate channel of the CN-FET. However, since the width of the CNT, especially the single-walled CNT (SWNT), is usually smaller than the tip radius, the electrostatic force between the tip and the SWNT is overwhelmed by that between the tip and the peripheral area of the SWNT, which hinders quantitative SP measurement on the SWNT. In particular, the trapped charges on the insulating surface around the CNT significantly affect the SP measurement. Here we propose a novel method, frequency-modulation high-frequency electrostatic force microscopy (FM-HF-EFM), that is capable of measuring the SP distribution on the CNT less affected by the background electrostatic force, by combining FM-KFM and HF-EFM.
We fabricated a pair of palladium electrodes whose gap width was 500 nm on a silicon dioxide layer thermally-grown on a silicon substrate. Then, an SWNT was aligned between these two electrodes by dielectrophoresis. This sample was investigated by FM-KFM and FM-HF-EFM. We applied a dc bias voltage to the drain electrode during FM-KFM measurement. In the SP image acquired by FM-KFM, a high SP contrast was observed around the SWNT and the drain electrode. This contrast was mainly due to the background electrostatic force between the tip and the charges trapped on the silicon dioxide surface, and it degraded the SP image resolution. For FM-HF-EFM, we applied two high-frequency modulation voltages with slightly different frequencies (f1, f2) to the drain electrode, and the magnitude of the frequency modulation of the cantilever resonance frequency at a beat frequency (fb = f2−f1) was recorded. The contrast of the FM-HF-EFM image corresponds to the magnitude of the HF voltages along the conductive regions. Since the distribution of the background charges was not modulated by the high-frequency voltages, a sharp voltage drop at an SWNT defect was clearly observed.
 M. Ito et al., e-J. Surf. Sci. Nanotech. 9, 210 (2011).
 S. Kitamura et al., Appl. Phys. Lett. 72, 3154 (1998).
 A. Hou et al., Electron. Lett. 28, 2302 (1992).
12:30 PM - QQ1.9
Three Dimensional Kelvin Probe Microscopy for Spatial Potential Mapping and Nanowire Characterization.
Dylan Bayerl 1 , Matthew Starr 1 , Xudong Wang 1 Show Abstract
1 , University of Wisconsin - Madison, Madison, Wisconsin, United States
Piezoelectric nanowires (NWs) are recently the focus of much interest for the development of nanogenerators for harvesting ambient mechanical energy. To maximize efficiency of such devices, it is essential to both theoretically predict and experimentally quantify the piezoelectric potential output of individual NWs. There exists an absence of well-defined experimental methods for quantifying the piezoelectric potential generated by individual NWs. We present a scanning probe microscopy technique for quantification of true piezoelectric potential in individual NWs. This technique enables full 3-dimensional mapping of electrical potential distribution, completely free of the measurement errors due to ambiguous probe-sample separation distance and absolute reference potential to which the widely used Scanning Kelvin Probe Microscopy (SKPM) is subject. Our novel technique is consequently named 3DKPM. The ability of the 3DKPM technique to map a spatial potential distribution was verified on a standard Au electrode sample to which a DC bias was applied. Supported by finite element simulations, we demonstrated that 3DKPM can accurately map the electric potential in a 3D space with an electric potential gradient resolution of at least 5mV per 50 nm. A linear relationship was also determined between measured surface potential and actual surface potential, indicating a high precision measurement of voltage difference magnitude by 3DKPM. With the capability for high-resolution surface potential quantification established, 3DKPM was applied to the characterization of potential generated by strained piezoelectric ZnO NWs. Abrupt topological change along the edges of NW showed negligible effect to the acquired potential distribution map, thus allowing a reliable quantification of piezoelectric potential differences across the ZnO NW. The 3DKPM technique offers a new approach for characterizing the true topology-related surface properties with minimized artifacts from surface feature variations, which is essential for studying the strain-size-potential and piezotronic relationships in piezoelectric NWs.
QQ2: Probing Ionic and Electronic Properties on the Nanoscale
Monday PM, November 28, 2011
Room 305 (Hynes)
2:30 PM - **QQ2.1
Multifrequency Ultrasound Holography for High Resolution Imaging of Buried Nano Structures and Sub-Cellular Nano-Mechanics.
Gajendra Shekhawat 1 , Vinayak Dravid 1 Show Abstract
1 Department of Material Science and Engineering and NUANCE Center, Northwestern University, Evanston, Illinois, United States
Imaging high resolution sub-surface defects non-destructively in advanced Interconnect structures, interfaces and devices is a challenge and no known metrology tools are available to identify such defects in a non-destructive way at nanometer level. Monitoring these defects necessitate the understanding of their growth mechanism of these interconnects as well as defect formation. We will talk about new development “Multifrequecy Scanning Near Field Ultrasound Holography” (MSNFUH) as a powerful and high resolution metrology toolset for imaging buried nanostructures. The interference of object and reference ultrasonic waves would nominally form a surface acoustic standing wave, which is analogous to, for example, x-ray standing waves that result from interference of scattered and reference x-ray waves. The perturbations to the phase and amplitude of the surface acoustic standing wave are locally monitored by the SPM acoustic antenna via multi-lock-in approach and a dedicated electronic module. As the specimen acoustic wave is perturbed by buried features, the resultant alteration in the surface acoustic standing wave, especially its phase, is effectively monitored by the SPM cantilever. Thus, within the near-field regime (which enjoys superb spatial resolution), the acoustic wave (which is nondestructive and sensitive to mechanical and/or elastic variation along its path) is fully analyzed, point-by-point, by the SPM acoustic antenna in terms of its phase and amplitude. The efficacy of MSNFUH is demonstrated with examples on imaging buried defects in copper interconnects, low-K dielectric materials and point defects in multilayer extreme ultraviolet lithography mask test structures. Successful identification of these buried defects in these architectures in a non-destructive way will open up new paradigm shift in using this technique to detect sub-surface defects and material imperfections. This new methodology is further extended to study the nanomechanics of sub-cellular structures and is demonstrated with imaging buried nanoparticles in silica core-shell structures and effect of stimulating agents on the cell mechanics. This will open wide range of in-vitro biological imaging capabilities to monitor the behavior of numerous taggants, tracking the spatial-temporal behavior of such taggant and to fathom the intricate signal transduction, cellular transfection pathway. The new development reported here holds significant potential as a strategy for biomedical imaging of living cells and have significant potential to improve biological discovery and drug development processes.
3:00 PM - QQ2.2
Visualization of Electrons Localized in Metal-SiO2-SiN-SiO2 - Semiconductor Flash Memory Thin Gate Films by Detecting the Higher-Order Nonlinear Dielectric Constant Using Scanning Nonlinear Dielectric Microscopy.
Koichiro Honda 1 2 , Yasuo Cho 1 Show Abstract
1 , Tohoku University, Sendai Japan, 2 , Fujitsu Laboratories Ltd., Atsugi Japan
Charge accumulation in semiconductor devices was studied by using Scanning nonlinear dielectric microscopy (SNDM) detecting ε3333 higher-order nonlinear permittivity with much higher resolution than that of the conventional SNDM that measures the lowest-order nonlinear permittivity (ε333). It enables us to visualize highly resolved charge patterns stored in SiO2-SiN-SiO2 (ONO) films of downscaled metal-ONO -semiconductor (MONOS) flash memory in high contrast.Special features of the MONOS flash memory devices include high integration density and low manufacturing cost because they do not need floating gates. MONOS memory devices store charges in the SiN layer of the ONO gate film of the cell transistor. The charges are localized in two places of the SiN film adjacent to the source and drain edges. In downscaled MONOS memory devices, charges are confined in a further narrow area of the cell transistor. Therefore, a high-resolution evaluation method is necessary to detect such localized charges. We compared the ε333 and ε3333 images of flash memory with 0.08 μm channel length. In the ε333 image, the bright image of electron stored area extends to both the diffusion area and the hole-injected area. This suggests that in downsized devices, it is difficult to determine the electron stored area precisely by using the ε333 image. In contrast, in the ε3333 image, a clear dark-bright patch pattern can be seen in the same area where electrons and holes were present. A dark contrast appears in the electron stored area, and a bright contrast appears in the region where holes were slightly injected for Vth control. This dark contrast extends neither to the diffusion area nor the hole-injected area. From this comparison, it can be said that there are two advantages of detecting the ε3333 together with the ε333 for visualizing the charges stored in ONO films, namely: achieving a high resolution and obtaining an electron SNDM signal with high contrast, since the signal is inverted from the channel area. (In the case of the ε333, both the SNDM signals were found to be positive.) As mentioned above, SNDM can be recommended as a powerful method for visualizing the spatial charge distribution in dielectric thin films because of its high sensitivity in detecting the associated capacitance variation.
3:15 PM - **QQ2.3
Probing Local Bias-Induced Transitions: The Case for 6D SPM.
Sergei Kalinin 1 Show Abstract
1 , ORNL, Oak Ridge, Tennessee, United States
The Holy Grail of scanning probe microscopy is probing materials functionality on a level of a single structural element. Molecular unfolding spectroscopy has emerged as powerful and universal tool for analysis of kinetics and thermodynamics of chemical reactions on a single molecule level and decoupling the role of individual molecular elements on these processes. Similarly, defects in solids control kinetics and thermodynamics of phase transformations and electrochemical reactions by serving as nucleation and pinning centers. The field confinement at the junction between a biased scanning probe microscopy (SPM) tip and solid surface allows local probing of bias-induced transformations including polarization switching, ionic motion, or electrochemical reactions in solids. The nanoscale size of the biased region which is smaller or comparable to the spacing between extended defects such as grain boundaries and dislocations potentially allows the kinetics and thermodynamics of these processes to be studied on the level of single defect. These studies then allow linking structure and functionality of material in a deterministic fashion and deciphering associated mesoscopic and atomistic mechanisms, contrasting classical statistically averaged approaches. However, the critical element of these studies is detection of the local changes in materials structure. In this presentation, I systematically analyze the requirements for the SPM method for probing reversible local bias-induced transformations in terms of the contact mechanics, microscope operation, and dimensionality of collected data. The systematic studies of hysteretic and time dependent phenomena in the presence of topographic cross-talk is possible if (a) signal is weakly dependent on tip-surface contact area or the latter can be readily calibrated, and (b) the 6D data set is acquired. The current progress in multidimensional SOM techniques based on band-excitation time and voltage spectroscopies is illustrated, including data acquisition, dimensionality reduction, and visualization. The technique development is illustrated for ferroelectric and ionic materials including Li-ion batteries and solid oxide fuel cells. The extensions of these methods for high resolution mapping of irreversible electrochemical phenomena are discussed.This material is based partially (Li-ion) upon work supported as part of the Fluid Interface Reactions, Structures and Transport (FIRST) Center, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number ERKCC61. Part of worked is performed as a user proposal in the Center for Nanophase Materials Sciences (CNMS) at ORNL. The oxygen conductor work is supported by the CNMS.
4:15 PM - QQ2.4
Spatially Resolved Mapping of Electronic and Ionic Motions in NiO Thin Films.
Yunseok Kim 1 , Amit Kumar 1 , Stephen Jesse 1 , In Rok Hwang 2 , Taekjib Choi 3 , Bae Ho Park 2 , Sergei Kalinin 1 Show Abstract
1 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 School of Physics, Konkuk University, Seoul Korea (the Republic of), 3 Department of Nano Science and Technology, Sejong University, Seoul Korea (the Republic of)
Resistive switching (RS) behavior in transition metal oxides has started to draw interest for the next generation non-volatile memory devices. The switching occurs via formation and rupture of conducting filaments which are randomly distributed over the films. Among various transition metal oxides, NiO has been particularly considered as a promising candidate. For the NiO films, both metallic nickel defects and nickel vacancies influence the formation and the rupture of the conducting filaments. Hence, both electronic and ionic motions are relevant to the RS behavior of the NiO films. However, so far, nanoscale RS behavior has been only investigated using conductive atomic force microscopy (CAFM). The current measurement itself cannot provide information of electronic and ionic contributions, thus the ionic motions and their contributions to the RS mechanism are still lack of information. Recently, we proposed electrochemical strain microscopy (ESM) method enabling to study local electrochemical activity of ionic motion. This ESM method allows us to explore local electrochemical activity of nickel vacancies in NiO films. In this presentation, we present spatially resolved mapping of ionic motions in NiO films using ESM methods. We further develop CAFM to observe spatially resolved mapping of the RS behavior such as electroforming voltages. The present approach combined with ESM and CAFM is able to find out electronic and ionic contributions to the RS behavior. Moreover, it allows studying the fundamental origin of the RS behavior since NiO thin films can have both uni- and bi-polar RS behaviors. Finally, this present study will open pathways to explore fundamental RS mechanism.Acknowledgment: This research was conducted at the Center for Nanophase Materials Sciences, which is sponsored at Oak Ridge National Laboratory by the Office of Basic Energy Sciences, U.S. Department of Energy.
4:30 PM - **QQ2.5
Nano-Mechanical and Functional Properties of Energy Storage Materials.
Roger Proksch 1 Show Abstract
1 Roger Proksch, Asylum Research, Santa Barbara, California, United States
Progress in development and optimization of energy storage and conversion materials necessitates understanding their ionic and electrochemical functionality on the nanometer scale level of single grain cluster, grain, or extended defect. In electrochemical strain microscopy (ESM), the biased scanning probe microscopy tip acts as a moving electrocatalytically active probe exploring local electrochemical activity. The probe concentrates an electric field in a nanometer-scale volume of material, and bias-induced, picometer-level surface displacements provide information on local electrochemical processes. In the context of ESM measurements, we will focus on a technique that simultaneously quantifies the electromechanical response amplitude, phase, contact stiffness and dissipation of an AFM cantilever imaging a surface. The method is based on measuring the contact resonance frequency using Dual AC Resonance Tracking (DART), where the contact resonance is tracked while the amplitude and phase of the cantilever response are monitored at two frequencies on either side of the contact resonance. By modeling the tip-sample contact as a driven damped harmonic oscillator, the four measured quantities (two amplitudes and two phases) allow the four model parameters, viz., drive amplitude, drive phase, resonance frequency and quality factor, to be calculated. These mechanical parameters can in turn be used to make quantitative statements about localized sample properties. This method has been used to study the electromechanical coupling coefficients in ferroelectric materials and the storage and loss moduli in viscoelastic materials and more recently, battery electrode materials. This technique can be combined with simultaneous current transport measurements. Simultaneous DART and electronic current images of a LiCoO2 cathode underscores the lack of correlation between the ionic and electronic current flow in the sample, and hence the complementary nature of ESM and cAFM contrast.
5:00 PM - QQ2.6
Conductive AFM of Photovoltaic Materials: Mitigation of Contact Area Uncertainty Using PeakForce™ Assisted Current Measurements.
Maxim Nikiforov 1 , Seth Darling 1 Show Abstract
1 Center for Nanoscale Materials, Argonne National Laboratory, CHICAGO, Illinois, United States
Solar cells are anticipated to become one of the primary electricity generating devices of the future. Among all types of cells, organic bulk heterojunction photovoltaic technology is one of only a few that utilize low-cost materials and are suitable for inexpensive large scale manufacturing (printing, roll-to-roll etc.). However, performance degradation of these cell types under load is a main hurdle for this technology. Active layer degradation plays a major role in overall performance degradation of bulk heterojunction photovoltaic cells. Insights into changes within the active layer under electrical stress are crucial for understanding—and hence minimizing—degradation processes.In order to study processes causing degradation, we have developed a new technique for electrical measurements. This technique utilizes PeakForce™ mode (Bruker Nano), but in addition to high-throughput measurements of force–distance curves, current–distance curves are also collected. Combination of force–distance and current–distance data enables unprecedented accounting for contact area dependence of current at each point, thus, decreasing contribution of topographical cross-talk to current measurements. Performance of this technique is demonstrated on ITO-coated glass, ITO/PEDOT:PSS, and ITO/PEDOT:PSS/P3HT:PCBM systems. Evolution of electrical properties and material diffusion are measured on ITO/PEDOT:PSS/P3HT:PCBM.MPN is grateful to the Director’s Fellowship Program for financial support. Use of the Center for Nanoscale Materials was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under contract No. DE-AC02-06CH11357.
5:15 PM - QQ2.7
Dynamic Conductive Atomic Force Microscopy and Spectroscopy.
Klara Maturova 1 , Manuel Romero 1 , Nikos Kopidakis 1 , Jao van de Lagemaat 1 Show Abstract
1 , National Renewable Energy Laboratory, Golden, Colorado, United States
Soft matter semiconductors are of great interest for applied science. Polymer-polymer blends, polymer-quantum dots blends, carbon nanowires and weakly-bound quantum dots have interesting properties for solar energy harvesting. Proper understanding of exciton dissociation and charge transport in these systems is crucial for device optimization.Scanning probe microscopes such as scanning tunneling microscopy (STM) and conductive atomic force microscopy (c-AFM) enable us to look at the charge collection or injection of different materials on nm-scale. However, both sharp metallic STM and c-AFM tips can damage soft polymer layers or sweep weakly-bound nanowires and quantum dots away.Here we present our results from c-AFM in dynamic contact mode. The metallic tip mounted at the end of the tuning fork is driven at its resonant frequency and briefly touches the surface. Next to the fact that this technique is less invasive compare to STM and contact mode c-AFM, time-resolved spectroscopy can be performed due to short contact of the tip with the sample. For example, simultaneous current measurement and light detection can show us how fast charge carriers moves across the sample. So far, we have succeeded to resolve single CdSe quantum dots on Au(111). We have found the “on” periods with high current injection and the “off” periods of no current. During the “on” state electrons or holes are injected into the quantum dot depending on the polarity of the applied bias. On the other hand, during the “off” state, trapped charges prevent current injection by a Coulomb blockade effect. Next to the quantum dots, we have also measured a matrix of interconnected metallic and semiconducting carbon nanotubes and photocurrent in polymer:polymer organic solar cells. Duration of one single tap (<5% of tip’s duty cycle) is dependent on the oscillation frequency of the fork. The resonant frequency of the tip and high speed data acquisition enables us to see single current injection events as ~ 1 us wide peaks. Next to the current measurements, we also correlate our results with I-V spectroscopy.
5:30 PM - QQ2.8
Exploration of Ferroelectric Domains and Conductivity in BiFeO3 Thin Films Using a Hybrid Near-Field Microwave Microscope and Scanning Tunneling Microscope.
Christian Long 1 , Anbu Varatharajan 1 , Jonghee Lee 1 , Ichiro Takeuchi 1 Show Abstract
1 Materials Science and Engineering, University of Maryland, College Park, Maryland, United States
We explore the ferroelectric domain structure and conductivity of BiFeO3 thin films using a hybrid scanning probe microscope that combines Near-Field Microwave Microscopy (NFMM) with Scanning Tunneling Microscopy (STM). The NFMM is based on a two-port resonant microwave cavity. The cavity is resonant at 2.5 GHz and has a quality factor of ~500. Coupling the resonator to a probe tip produces GHz frequency electric and magnetic fields confined to the region around the probe tip. The interaction of these fields with the sample produces a shift in the resonant frequency and quality factor of the resonant cavity, enabling measurement of local material properties. In this case, NFMM is used to map the complex permittivity and dielectric non-linearity at 2.5 GHz, while STM is used simultaneously to characterize the DC conductivity. We have chosen to study BiFeO3 due to the recent discovery of tunable conductivity near ferroelectric domain walls in BiFeO3 thin films. This memristive behavior can potentially be utilized for high density information storage or construction of neuromorphic circuits.This work was supported by the NSF-MRSEC at the University of Maryland, DMR 0520471.
5:45 PM - QQ2.9
Limitations of Frequency and Voltage Dependent Electrical Characterization at the Nanoscale.
Rosario Gerhardt 1 Show Abstract
1 Materials Science and Engineering, Georgia Institute of Technology, Atlanta , Georgia, United States
Interest in using frequency dependent and voltage dependent measurements to characterize the electrical properties of materials and devices at the nanoscale has substantially increased in recent years. This is because it has been found that at certain frequencies or voltages, it is possible to detect the presence of regions that display a different electrical response which can sometimes be associated with a topographical feature, the presence of electroactive interfaces, the onset of signal induced tunneling or the onset of surface phenomena. While such measurements have been widely available to characterize materials in bulk and thin film form for nearly 50 years, its application to the nanoscale is rather new. While using frequency and voltage dependent measurements in a scanning probe microscope provides the added benefit of acquiring simultaneous electrical and topographical information, the acquisition of those high resolution images comes at a price. It will be shown that one must be extremely careful in choosing probe tip types, sizes, shapes and imaging mode before one can conclude whether a given response is truly representative of a nanoscale feature or not. In this talk, a roadmap for properly identifying features and their corresponding electrical response will be presented and discussed.
Stephen Jesse Oak Ridge National Laboratory
Brian Rodriguez University College Dublin
Takeshi Fukuma Kanazawa University
Ricardo Garcia Instituto de Microelectronica de Madrid
QQ3: Nanomechanical Properties through Advanced Scanning Probe Microscopy I
Tuesday AM, November 29, 2011
Room 305 (Hynes)
9:15 AM - **QQ3.1
Surface and Subsurface Physical and Chemical Characterization of Materials at the Nanoscale.
Laurene Tetard 1 , Ali Passian 1 , Rubye Farahi 1 , Brian Davison 1 , Thomas Thundat 1 Show Abstract
1 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
The discontinuity in the atomic fabric of materials that defines the transition into a new medium gives rise to intriguing properties. Examples include the electronic tunneling behavior in scanning tunneling microscope or gigantic enhancement in the Raman emission from molecules near the surfaces of noble metals. In modern microscopy, spatial and spectral resolutions are of great importance in tackling questions related to material properties. The emergence of the atomic force microscopy (AFM), which surpasses what can be achieved optically due to the inherent diffraction limit, has opened numerous opportunities for investigating surfaces. However, a contemporary challenge in nanoscience is the non-destructive characterization of materials. The ability to non-invasively explore subsurface domains for presence of inhomogeneities is of tremendous importance. In addition, techniques providing both physical and chemical information are needed to reach a comprehensive understanding of the composition and behavior of complex systems. In order to tackle the subsurface and spectral imaging, here we propose to make use of the nonlinear interaction forces between the atoms of an AFM probe tip and those of a given sample surface. Such forces are known to contain a short range repulsive component and a long range van der Waals attractive contribution. This interfacial force can give rise to a multiple-order nanomechanical coupling between the probe and the sample, offering tremendous potential for obtaining a host of material characteristics. By applying a multi-harmonic mechanical forcing to the probe and another multi-harmonic forcing to the sample, we obtain, via frequency mixing a series of new operational modes. By varying the nature of the excitations, using elastic or photonic coupling, it is possible to obtain physical and chemical signature of a heterogeneous medium with nanoscale resolution. The technique, termed mode synthesizing atomic force microscopy (MSAFM) is therefore described as a generalized multifrequency AFM. We highlight the versatility of MSAFM and its potential to contribute to important problems in material sciences, toxicology and energy research, by presenting three specific studies: 1- imaging buried nanofabricated structures; 2- investigating the presence and distribution of embedded nanoparticles in a cell; and 3- characterizing the complex structures of plant cells.
9:45 AM - QQ3.2
Enabling Accurate Modulus Measurements on Stiff Ultrathin Films with High Eigenmode Contact Resonance Force Microscopy.
Jason Killgore 1 , Donna Hurley 1 Show Abstract
1 , NIST, Boulder, Colorado, United States
Contact resonance force microscopy (CR-FM) is a scanning probe technique that enables sensitive measurement of a material’s local elastic properties. Typically, accurate measurements of stiff materials (>30 GPa) have relied on very stiff, tapping-mode cantilevers and large (>500 nN) applied forces to achieve sufficient sensitivity. For applications such as thin films or fragile materials, use of much lower forces is vital. Here, we show how use of a cantilever’s higher-order contact eigenmodes enables accurate nanomechanical measurements on stiff, thin materials at sub-100 nN forces, even when the contact stiffness is much greater than the cantilever stiffness. We first validated our approach with measurements on a thick niobium (Nb) film with the fourth contact eigenmode of a very compliant (lever stiffness ~0.1 N/m), ultrananocrystalline diamond cantilever. Modulus values obtained with this approach were in excellent agreement with those obtained by conventional CR-FM methods as well as literature values for bulk Nb (modulus ~125 GPa). We also investigated silica (SiO2) films as thin as 10 nm on silicon substrates. For most methods involving contact techniques, the substrate properties strongly affect the measured modulus of such thin films. With the fourth eigenmode of a compliant cantilever and an applied force of ~7 nN, the modulus was only 4 % and 2 % higher than bulk values for 20 nm and 50 nm films, respectively. In contrast, conventional CR-FM measurements with the first eigenmode of a stiff cantilever at ~300 nN applied force overpredicted the film modulus by 45 % and 22 % for films 20 nm and 50 nm thick, respectively. Overall, the ability of low-force, high-eigenmode CR-FM to reduce substrate influence while maintaining high stiffness sensitivity can lessen dependence on empirical corrections when characterizing thin, stiff films.
10:00 AM - **QQ3.3
Atomic Force Microscopy in Higher Eigenmodes: Elasticity, Friction and Nanomanipulation.
Robert Stark 1 2 Show Abstract
1 Center of Smart Interfaces, Technische Universität Darmstadt, Darmstadt Germany, 2 Materials Sciences, Technische Universität Darmstadt, Darmstadt Germany
Dynamic atomic force microscopy essentially employs variations of the cantilever vibration to create topographic and compositional maps of the surface. Various oscillation modes can be used for imaging such as flexural, torsional or bending vibrations. The non-linear interaction between tip and sample introduces non-linear phenomena, such as the generation of higher harmonics, co-existing states of oscillation or even chaos. The combination of both, multiple system resonances and non-linearity implies a complex system behaviour. Various mathematical models of the cantilever dynamics have been derived so far. The analysis of the full transfer function allows us to investigate very significant dynamic aspects, which simple first mode approximations cannot capture. In-plane surface properties can be measured by torsional oscillations. In a standard AFM, such a shear force imaging can be realized by taking advantage of the torsional eigenmodes of atomic force microscope (AFM) cantilevers that are highly sensitive toward in-plane material properties. Sample viscosity and lateral contact stiffness lead to variations in resonance frequency, oscillation amplitude, or phase response. In both modes, amplitude (AM) and frequency modulation (FM) feedback, a compositional contrast can be achieved on hard surfaces. A separation of conservative and dissipative forces, however, can only be achieved by constant amplitude mode of torsional FM-AFM. On soft surfaces, such as polymers, the tip indents into the specimen. The imaging contrast is then more complex because the indentation depth varies in the case of a constant frequency shift measurement. Approach – retract curves reveal further details on the contact mechanics. The tip oscillations can be minimized by passive torsional measurements, i.e. by analyzing the thermomechanical noise of the force sensor. At minimum vibration amplitudes it is possible to obtain insights into the details of static friction (sticktion).Concluding, torsional shear force AFM provides a powerfull toolbox to investigate nanoscale friction phenoma at surfaces and interfaces.
10:30 AM - QQ3.4
How Localised Are Energy Dissipation Processes in Nanoscale Interactions?
Sergio Santos 1 , Tewfik Souier 1 , Karim Gadelrab 1 , Li Guang 1 , Amro Alkhatib 1 , Matteo Chiesa 1 Show Abstract
1 Material Science and Engineering, Masdar Institute, Abu Dhabi United Arab Emirates
The mechanisms through which energy is dissipated in the nanoscale might involve tens or hundreds of atoms. In this contribution we discuss two aspects of fundamental energy dissipation processes in dynamic nanoscale interactions, namely, the degree of localisation in the interaction and the disentanglement of each dissipative mechanism. We focus the discussion on short and long range viscosity and hysteresis .First, we develop a method to calculate the areal density of the energy dissipated in the dynamic mode and also the effective area of interaction for each of the four dissipative processes. Then we define M as the ratio between these two parameters. We further show that neither the phase lag, nor the magnitude of the energy dissipated alone provide information about energy localization in the nanoscale, but M has to be considered instead. Secondly, we develop a method to analyse and distinctively distinguish between each of the four dissipative mechanisms by looking at the phase difference between the conservative and the dissipative phase and the product of this and the energy dissipated per cycle. In a significant contribution, Garcia et al.[2-4] showed how to differentiate between dissipative short range viscosity and hysteresis processes by calculating the derivative of the energy dissipation with decreasing oscillation amplitude. In the long range the calculation of derivatives also allowed them finding a distinctive pattern for long range hysteresis. In our approach the calculation of derivatives is not required and long range viscosity and hysteresis processes are also distinguishable by the presence or absence of maxima in phase difference at intermediate values of oscillation amplitude. While our approach is general, we direct our experimental study to disentangle the mechanisms of energy dissipation between a silicon atomic force microscope tip, a carbon nanotube and a quartz surface. By stabilizing the tip in situ  we find quantitative information in a reproducible manner where robust quantification of nanoscale interactions is obtained. Santos S, Barcons V, Verdaguer A, Font J, Thomson N H and Chiesa M 2011 How localised are energy dissipation processes in the nanoscale? . In: Nanotechnology,Garcia R, Gómez C J, Martinez N F, Patil S, Dietz C and Magerle R 2006 Physical Review Letters 97 016103-4Garcia R, Magerele R and Perez R 2007 Nature Materials 6 405-11J.Gomez C and Garcia R 2010 Ultramicroscopy 110 626–33Santos S and Thomson N H 2011 Applied Physics Letters 98 013101-3
11:15 AM - **QQ3.5
Intermodulation Atomic Force Microscopy.
David Haviland 1 , Daniel Platz 1 , Daniel Forchheimer 1 , Erik Tholen 2 Show Abstract
1 Applied Physics, Royal Institute of Technology (KTH), Stockholm Sweden, 2 , Intermodulation Products AB, Solna Sweden
The analytical power of the Atomic Force Microscopy (AFM) lies in its ability to make a quantitatively accurate measurement of the minute forces between a very sharp tip and a surface. For dynamic modes of AFM, these forces must be determined from analysis of the cantilevers motion. Our approach to this problem is to consider motion in a relatively narrow frequency band around one resonance of the cantilever, where a simple harmonic oscillator model is valid and where simple, direct calibration methods exist to determine the cantilever stiffness. Working at resonance also allows us to exploit the enhanced sensitivity associated with high Q factor. In order to increase the information content available in this limited frequency band, we measure intermodulation, or the frequency mixing of two pure tones that are driving the cantilever . Using a specially designed intermodulation lockin , we simultaneously acquire the amplitude and phase of the response at 32 intermodulation product frequencies, allowing us to make 32 amplitude and phase images in one scan.In comparison to phase imaging of traditional dynamic AFM, the intermodulation method provides vastly more information for the same measurement bandwidth (measurement time). This information is encoded in the amplitude and phase data at the different intermodulation frequencies. We have developed a variety of analysis algorithms which decode this data and reveal the tip surface interaction at each pixel of the image . The intermodulation data is actually a highly compressed representation of the cantilever motion, or more accurately, that motion which is possible to detect, given the limited mechanical bandwidth of the force transducer and the significant detector noise. One can consider the intermodulation method as a highly efficient way of recording the motion, compressing the data so that it can be easily stored for later analysis. Intermodulation AFM works with standard, inexpensive cantilevers, and can easily be implemented on nearly any AFM. A commercial spin-off  was recently established which sells the intermodulation lockin and a software package for calibration, data acquisition, image display and data analysis. This talk will begin with a general introduction describing the basic idea behind the intermodulation measurement and analysis technique. The application of these methods to mechanical force transducers and Atomic Force Microscopy will be emphasized. References : D. Platz, E. A. Tholen, D. Pesen and D. B. Haviland. Appl. Phys. Lett. 92, 153106 (2008). E. A. Tholen, D. Platz, D. Forchheimer, V. Schuler, M. O. Tholen, C. Hutter and D. B. Haviland. Rev. Sci. Instr. to be published (2011), arXiv:1008.2722 C. Hutter, D. Platz, E. A. Tholen, T. H. Hansson and D. B. Haviland, Phys. Rev. Lett. 104, 050801 (2010).  http://www.intermodulation-products.com
11:45 AM - QQ3.6
Multi-Frequency Imaging in the Intermittent Contact Mode of Atomic Force Microscopy: Beyond Phase Imaging.
Senli Guo 1 , Santiago Solares 2 , Neitzel Ioannis 3 , Vadym Mochalin 3 , Yury Gogotsi 3 , Sergei Kalinin 1 , Stephen Jesse 1 Show Abstract
1 CNMS, Oak Ridge National Lab, Oak Ridge, Tennessee, United States, 2 Department of Mechanical Engineering, University of Maryland, College Park, Maryland, United States, 3 Department of Materials Science and Engineering, Drexel University, Philadelphia, Pennsylvania, United States
Force-based scanning probe microscopies have emerged as a mainstay for probing structural and mechanical properties of materials on the nanometer and molecular levels. Despite tremendous progress, the cantilever dynamics in single frequency SPMs is not fully defined due to having only two output variables. A new multiple frequency SPM imaging mode developed by combining the broad band excitation and detection technique (BE) with the traditional tapping imaging mode allows richer information on tip-surface interactions in intermittent contact SPM to be acquired. Specifically, the cantilever is simultaneously excited at two of its eigenmodes; the amplitude signal at one eigenmode is used for the surface topographic feedback and the signal in a broad frequency band around the other eigenmode is collected to extract information on sample properties. As model systems, we have characterized detonation diamond called nanodiamond (ND). ND has a narrow size distribution with an average diameter of ~5 nm where both non-functionalized nanodiamond (ND) and octadecylamine functionalized nanodiamond (ND-ODA) have been used. The difference in surface chemistry of ND and ND-ODA has been used to demonstrate the resolution and detection limit of the new technique.A portion of this research was conducted at the Center for Nanophase Materials Sciences, which is sponsored at Oak Ridge National Laboratory by the Office of Basic Energy Sciences, U.S. Department of Energy.
12:00 PM - **QQ3.7
Challenges and Perspectives in Multi-Frequency Atomic Force Microscopy Combining Amplitude- and Frequency-Modulation.
Santiago Solares 1 , Gaurav Chawla 1 Show Abstract
1 Mechanical Engineering, University of Maryland, College Park, Maryland, United States
Significant progress has been achieved in atomic force microscopy (AFM) since its invention in the 1980s. A variety of imaging modes (contact, intermittent-contact, noncontact, etc.) equipped with different types of probes (conventional pyramidal or conical tips, nanotubes, nanowires, etc.) have enabled the acquisition of high-resolution topography and material property images of a wide range of nanoscale samples in liquids, air and vacuum environments. More recently dynamic AFM has been enhanced by incorporating multi-frequency characterization, whereby more than one eigenmode of the microcantilever is excited and controlled simultaneously, such that new characterization channels become available in addition to the fundamental eigenmode response. Since the response variables acquired through these channels (e.g., oscillation frequency, amplitude, and phase) are sensitive to different material properties, multi-frequency operation can effectively increase the amount of information that can be acquired during each scan of the sample. This talk will describe recently proposed techniques that combine amplitude and frequency modulation in bimodal and trimodal AFM operation, and will also present typical computational and experimental results obtained for polymer samples. The methods will be discussed in terms of their capability, advantages and disadvantages, as well as opportunities for future enhancements that could enable the development of standard characterization procedures.
12:30 PM - QQ3.8
Modeling Active Time Resolved Interaction Force Imaging for Simultaneous Topography and Material Property Imaging.
H. Oral 1 , F. Degertekin 1 Show Abstract
1 G. W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Simultaneous topography and material property mapping in micro and nano scale has been an interesting and challenging problem in atomic force microscopy (AFM). For example, in the pulsed-force mode (PFM), a cantilever is actuated far below its resonance frequency while maintaining feedback control of the peak force to follow the topography. As opposed to the resonant behavior of the cantilever in tapping mode, this slower modulation enables measurement of nonlinear interaction forces on the cantilever as a function of time. Although relatively high bandwidth cantilevers can resolve the interaction forces in time, lack of sufficient damping might be problematic for controlling the true peak repulsive force. The amplitude of transient ringing might be larger than the controlled repulsive force, creating undesirable taps on surface. This is the case when a calibrated cantilever with a stiffness of 65 N/m, resonance frequency of 282 kHz, and a Q factor of 522 is modulated at 2 kHz under peak force control. For a peak force value of approximately 400 nN, the ringing is shown to exceed 600 nN. Force integrated readout and active tip (FIRAT) probe is a broadband, damped and active AFM probe. Damped nature of FIRAT eliminates ringing during time resolved interaction force measurement while the repulsive force is limited to a user specified value throughout the tap by directly actuating the tip electrostatically. A detailed nonlinear model of the FIRAT probe performing imaging on a sample with topography and elasticity variations has been implemented in Simulink. The active tip force can be set to as low as 20 nN with a 25 N/m, 85.3 kHz band FIRAT according to simulations. Numerical simulations also show that active tip control (ATC) results in a more accurate topography measurement than that of stand-alone peak force control. For a sample surface with effective elastic modulus difference of 100 GPa, ATC and peak force control yield topography errors of 5.96 nm and 16.3 nm, respectively. By means of ATC, the repulsive force can be limited to a value further below the specified peak force. This imposes less indentation on the sample surface, reducing the error in topography measurements especially on softer regions of the sample. In addition to earlier experimental verification of this hypothesis, a direct tip-sample interaction force measurement technique for ATC is introduced in order to develop a method for topography correction during simultaneous topography and material property imaging.
12:45 PM - QQ3.9
Morphology Study of Multi-Component Polymer Blends by Dual AC AFM.
Liang Fang 1 , Sean Stabler 1 Show Abstract
1 , Arkema Inc., King of Prussia, Pennsylvania, United States
The conventional tapping-mode AFM technique is a powerful tool for studying phase separation in multi-component polymer blends and composites. However, when the hardnesses of the individual components are too similar, the phase contrast of the standard technique may not be sufficient to visualize all components in a complicated blend. To overcome this limitation we applied the Dual AC AFM technique to study polymer blend morphology. Enhancement in the contrast in both amplitude and phase images allowed visualization of all components in a four-component and a five-component blend. Additionally, the higher frequency phase image was found to be a useful tool to fingerprint each of the components in a blend based on the individual hardness/ modulus properties. The technique also allows us to establish structure-property relationship in these complex blends. The physical meaning of the amplitude image remains under investigation.
QQ4: Nanomechanical Properties through Advanced Scanning Probe Microscopy II
Tuesday PM, November 29, 2011
Room 305 (Hynes)
2:30 PM - **QQ4.1
High-Resolution Bimodal Dynamic Force Microscopy and Spectroscopy of Atomic-Scale Interactions.
Shigeki Kawai 1 Show Abstract
1 Department of Physics, University of Basel, Basel Switzerland
Bimodal dynamic force microscopy (bi-DFM) using a large amplitude (A1st~10 nm) of the first flexural mode and an unltrasmall amplitude (A2nd<100 pm) of the second flexural mode can overcome potential tip instabilities in single-mode measurements with a small amplitude, especially at room temperature on surfaces of soft materials like KBr. Since the frequency shift of the second flexural mode is proportional to the force gradient time-averaged over A1st, the distance dependence of df2nd is higher than that of df1st in conventional DFM with a large amplitudes (time-averaged force). This high-sensitive detection was demonstrated with bi-DFM imaging and bimodal dynamic force spectroscopy (bi-DFS), measuring on KBr. A further improvement of the detection sensitivity to the short-range interaction was achieved with simultaneous excitation and FM detection of the flexural and torsional modes. Since a site-independent tip-sample interaction causes no lateral force variations , an unprecedented sensitivity to a short-range forces and site-dependent long-range force is achieved. This enhanced sensitivity is dramatically illustrated on the nominally flat and inert Graphite(0001) via bi-DFM and bi-DFS, in agreement with model calculations based on an extension of the theory derived in ref. The lateral force gradient is extracted from the measured torsional shift, and a lateral force variation of at most 20 pN is obtained by integrating this gradient parallel to the surface. A further integration reveals an ultrasmall potential energy variation in the attractive force range of only 3 meV. S. Kawai, Th. Glatzel, S. Koch, B. Such, A. Baratoff, and E. Meyer, Phys. Rev. Lett. 103 220801 (2009). S. Kawai, Th. Glatzel, S. Koch, B. Such, A. Baratoff, and E. Meyer, Phys. Rev. B 81 085420 (2010). S. Kawai, N. Sasaki, and H. Kawakatsu, Phys Rev. B 79 195412 (2009).
3:00 PM - QQ4.2
An Investigation Regarding the True Phenomena behind Water Interactions in Dynamic Nanoscale Processes.
Amro Alkhatib 1 , Sergio Santos 1 , Tewfik Souier 1 , Karim Gadelrab 1 , Li Guang 1 , Matteo Chiesa 1 Show Abstract
1 Material Science and Engineering, Masdar Institute, Abu Dhabi United Arab Emirates
The behaviour of water in the nanoscale can be investigated with high spatial resolution with the use of an atomic force microscope. Nevertheless, an understanding of the temporal behaviour of water molecules in nanometric volumes and their dynamic interactions with their surroundings is still emerging [1-4]. In particular, several theoretical studies conducted in the dynamic mode of atomic force microscopy have been carried out where different approaches towards the modelling of the capillary neck have been used [1, 5-7]. Here, we conduct a study where the different models for the capillary contribution are systematically investigated and compared with experimental data. Each parameter in the models is analysed separately to arrive to an understanding of its role in the dynamic response of the cantilever. Our approach shows that some of the typical parameters currently used to model the capillary interaction have to be excluded due to these predictingphenomena which are not corroborated experimentally. Then, we discuss the parameters that have a direct implication in capillary nucleation. Once the physical parameters that account for capillary interactions are found, we show that these can be used to provide temporal resolution regarding the nucleation of water columns in the nanoscale. We show this via both the multi-frequency approach and the standard phase, deflection and amplitude response. Our findings have implications in the study of water nucleation processes in the nanoscale, and, in general, in the fields of tribology and surface chemistry whenever surface hydration is present. Sahagun E, Garcia-Mochales P, Sacha G M and Saenz J J 2007 Physical Review Letters 98 176106Bocquet L, Charlaix E, Ciliberto S and Crassous J 1998 Nature 396 735-7Verdaguer A, Sacha G M, Bluhm H and Salmeron M 2006 Chemical Reviews 106 1478-510Raviv U, Laurat P and Klein J 2001 Nature 413 51-4Köber M, Sahagún E, García-Mochales P, Briones F, Luna M and Sáenz J J 2010 Small 6 2725–30Zitzler L, Herminghaus S and Mugele F 2002 Physical Review B 66 155436-8Choe H, Hong M-H, Seo Y, Lee K, Kim G, Cho Y, Ihm J and Jhe W 2005 Physical Review Letters 95 187801-4
3:15 PM - **QQ4.3
Mapping Local Mechanical Properties of Biological Samples in Liquids Using Multi-Harmonic Dynamic Atomic Force Microscopy.
Arvind Raman 1 Show Abstract
1 , Purdue University, West Lafayette, Indiana, United States
There is growing interest in the measurement of mechanical properties of biological samples -live cells, membranes, viruses, sub-cellular structures under quasi physiological conditions due to their role in mechanotransduction, cell morphogenesis, and drug-cell interactions. The dAFM community has been focusing recently on the use of anharmonics of cantilever vibration to map such local properties at sub 10 nm resolution at ~100 piconewton forces. In this presentation we will review recent work and lay out a method that allows the harmonics to map qualitatively the local material properties at resolution and speed far larger than what would be possible using the force-volume method.
3:45 PM - QQ4.4
Quantitative Force Modulation Microscopy in Liquid for Viscoelasticity Measurements of Monolayers.
Zehra Parlak 1 2 , Jianming Zhang 2 , Terrence Oas 1 , Stefan Zauscher 2 Show Abstract
1 Biochemistry, Duke University, Durham, North Carolina, United States, 2 Mechanical Engineering and Material Science, Duke University, Durham, North Carolina, United States
Characterizing the dynamic mechanical properties of monolayers can give insight into the molecular dynamics of biomolecules and the designs of artificial nanostructures. Acoustic AFM methods are promising tools for this aim, since they enable sensitive mechanical properties mapping of the sample by introducing high frequency modulation while imaging the topography.In this study, we employed force modulation microscopy (FMM) in a frequency spectroscopy mode to measure the viscoelastic properties of monolayers quantitatively in liquid. In FMM the cantilever tip-surface contact is modulated by a small amplitude high frequency signal. The high frequency component in the deflection of the cantilever is monitored by a lock-in amplifier. A wide range of frequencies can be used in FMM, which means that the characterization frequency is not limited to cantilever resonances. One can measure the phase and amplitude at different frequencies on a sample surface and determine the frequency dependent behavior of the sample.For many biomolecules and stimuli responsive monolayers, it is important to quantify the viscoelastic properties in physiological environment. In this research, we showed that it is possible to utilize FMM in liquid and to obtain high contrast amplitude and phase images of the monolayers while ensuring viability of the biomolecules. The initial samples are constructed by patterning and backfilling the gold surface with different mutants of protein A (surface protein of staphylococcus aureus bacteria) as a monolayer. The applied mutations are known to change the folding-unfolding dynamics of protein A. Contrast between two different protein variants are observed in the preliminary FMM testing, while the control samples (patterned and backfilled with the same protein) did not show any contrast. These results demonstrate that FMM can detect slight differences in dynamic properties of samples. Even though FMM can provide high contrast images of mechanical differences on the surface, obtaining quantitative viscoelasticity data is challenging due to the complex cantilever dynamics. In this research, we introduce a calibration method to convert amplitude and phase data into stiffness and viscosity at different frequencies. This calibration technique maps the amplitude and phase versus contact stiffness by varying the force on gold. The created calibration curve helps the user to differentiate the changes caused by the surface properties and cantilever dynamics while analyzing the FMM data. As a result, not only the stiffness is measured, but also the frequencies that cause high loss are identified. Initial FMM measurements demonstrate no significant frequency dependent behavior on EG3 thiols, whereas 25.5 kHz and 45 kHz are detected as the frequencies where two protein variants have highest loss.
4:30 PM - **QQ4.5
Dynamic Study of Nanomaterials Using Scanning Probe Microscopy.
Chanmin Su 1 Show Abstract
1 Bruker-Nano, AFM Unit, Bruker, Santa Barbara, California, United States
Recent developments in improving scanning speed and material property mapping capacity of atomic force microscope (AFM) lead to progress in capturing dynamic processes of nanoscale components. Through improving speed by 10 to 100 times, many dynamic processes in the time scale of seconds can be studied with temporal resolution to observe nanometer scale morphology or structure evolutions directly. Tip scanning mechanism further enhances in-situ environmental control capacity for samples up to wafer-scale data-storage media or semiconductor devices. As demonstrations, we have studied morphology evolution of both nano-composites and thermal plastic crystallizations. The photoresist development process on Si wafers was also investigated with high temporal and spatial resolution. As a result, we have established the correlation of surface adhesion energy and photoresist etching process. Applications of the high speed imaging and property mapping further extend to biomaterials with sub-nanometer resolution. The high-speed AFM not only improved the efficiency of time-to-data but also presents exceptional opportunities to study dynamic processes in materials at the single-molecular scale.
5:00 PM - QQ4.6
AFM-Based Mapping of Nanomechnical Properties of Polyelectrolyte Brush Covered Nanoparticles.
Gunnar Duner 1 , Esben Thormann 1 , Andra Dedinaite 1 2 , Per Claesson 1 2 , Krzysztof Matyjaszewski 3 , Robert Tilton 4 5 Show Abstract
1 Department of Chemistry, Royal Institute of technology, Stockholm Sweden, 2 , YKI, Institute for Surface Chemistry, Stockholm Sweden, 3 Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States, 4 Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States, 5 Department of Biomedical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
In present years colloids consisting of polyelectrolyte brush covered nanoparticles have been of interest due to their ability to disperse insoluble core particles, controlled adhesive properties and to introduce stimuli responsiveness. When adsorbed to oppositely charged surfaces these particles also provide a unique interface where the brush normal direction has an angular distribution compared to the substrate’s normal direction. This provides an opportunity to study how the brush polyelectrolytes respond to an external force applied at different angles with respect to the brush normal direction. However, since the poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) covered SiO2 nanoparticles, used in the present study, only have a diameter of approximately 50 nm the challenge is to probe the local force response of the different regions of the particle. Here we have applied a novel AFM technique, PeakForce QNM, to map nanomechanical properties of a single isolated particle under controlled salt and pH with a nanometer scaled lateral resolution. With this technique we are continuously sampling force-distance curves at a sampling rate of 2 kHz while scanning over the sample. The maximum force (the peak force) in each approach-retraction cycle is used as a constant feedback parameter to create a topographical image as in other AFM imaging modes. However, simultaneously the force vs. distance data provides maps of surface deformation and of the adhesion and energy dissipation from the tip-sample interaction, with nanometer scaled resolution. In the present case of a PDMAEMA covered SiO2 nanoparticles adsorbed to a silica substrate we find that the mechanical response is strongly position dependent and that the spatial distribution of the response further is strongly dependent on the applied force. At low applied force the edge of the particle is easily deformable while the center of the particle shows a more solid-like response. We interpret that as if the low force can bend the brush polyelectrolytes when the external force is applied almost orthogonal to the brush normal direction (on the particle edge) but not significantly compress the brush polyelectrolytes when the external force is applied parallel to the brush normal direction (at the particle center). At higher applied load the center of the particles becomes more deformable than the particle edge. Due to the boundary conditions given by the silica substrate the brush polyelectrolytes can only bend to a certain degree and the edge of the particle does thus not become more deformable as the external force is increased above a certain threshold. However, the center of the particle does not have the same threshold value and the center of the particle thus becomes more deformable as the feedback peak force is increased. Similar correlations can be made between the lateral position, the applied load and the additional achieved properties: adhesion and energy dissipation.
5:15 PM - QQ4.7
In Situ Atomic Force Microscopy: SEM Meets AFM.
Andrew Smith 1 , Stephan Kleindiek 1 , Klaus Schock 1 , Jochen Sterr 1 , Gregor Renka 1 Show Abstract
1 , Kleindiek Nanotechnik, Reutlingen Germany
Combining the advantages of SEM with the high resolution,three-dimensional information available from atomic force microscopyyields new possibilities in sample characterization. The SF-AFMconsists of a micromanipulator and a super flat piezo scanner mountedto a load-lockableplatform. The AFM cantilever is mounted to the micromanipulator -which has a resolution of less than 1 nm in X and Y directions and 2-3nm in Z direction. Once the cantilever has been positioned over thearea of interest, the piezo scanner is used during the AFMmeasurement. The three-axis piezo scanner has a scan range of 12 um,12 um, 3 um and can be used for AFM imaging as well as for recordingforce-distance curves. The entire system can be introduced into theSEM chamber via the load lock for quick and effortless sample and tipexchange with very short cycle times between experiments.
5:30 PM - QQ4.8
On-line Scanned Probe Microscopy Transparently Integrated with Twin SEM/FIB Systems.
Aaron Lewis 1 , Andrey Ignatov 2 , Anatoly Komissar 2 , Hesham Taha 2 , Eran Maayan 2 Show Abstract
1 Applied Physics, Hebrew University of Jerusalem , Jerusalem Israel, 2 , Nanonics Imaging Ltd., Jerusalem Israel
Scanning electron microscopy (SEM) is a moving force in the nanotechnological revolution. Focused ion beam microscopes (FIB) have also become potent in nanotechnology and their combination with SEM have shown the power of such on-line combinations. We describe in this paper the tansparent integration in SEM/FIB of another enabling imaging & sensing technology, scanning probe microscopy (SPM). This is accomplished without effecting any detectors, injectors, analyzers or obscuring the sample stage of such twin beam systems. The transparent combination is accopmplished so that the probe does not abscure the election/ion beam axis and also sits at the eucentric point. This permites the SPM to rotate into position when either the electron or ion beam is in place for standard normal operation relative to the sample surface. Such a Triple BeamTM combination is a disruptive technology affecting the potential of both electron, ion and scanned probe applications. It will be shown that it is now possible to rapidly place an SPM probe at a nanometric position within a large field of view to provide for ultrahigh resolution protocols unavailable in a SEM or FIB such as nanometric Z imaging or regions of charging in a sample. The combination effectively allows for a variety of 3D functional SPM imaging possibilities with on-line FIB material slicing. This is accomplished while allowing for deep trench profiling and side wall imaging enabled by unique SPM and probe design. Such new directions in functional understanding of materials will be discussed in this presentation while monitoring probe tip characteristics and often effectively repairing the probe tip on-line. The lack of these possibilities has limited SPM technology. A NanoTool KitTM of electron/ion beam friendly probes with a wide spectrum of functionality will be described based on singular glass probe technology. Examples will cover on-line measurements of elasticity, electrical, thermal and even super-resolution optical imaging of cathodoluminescence and biomaterial staining. The integration described in this talk portends new directions of application in fundamental and applied science not previously accessible.
Stephen Jesse Oak Ridge National Laboratory
Brian Rodriguez University College Dublin
Takeshi Fukuma Kanazawa University
Ricardo Garcia Instituto de Microelectronica de Madrid
QQ5: Probing Photonic, Thermal and Chemical Properties on the Nanoscale I
Wednesday AM, November 30, 2011
Room 305 (Hynes)
9:30 AM - QQ5.1
Probing Optical Field-Distributions Produced by Twisted Liquid Crystals Cells by Means of Metallic Nano-Probes.
Antonio Ambrosio 1 , Pasqualino Maddalena 1 Show Abstract
1 , CNR-SPIN and Dipartimento di Scienze Fisiche, Università degli Studi di Napoli Federico II, Napoli Italy
Due to their size, cobined with the easy in procuction by means of chemical synthesis and their optical properties, a plasmonic resonance in the visible spectral region, gold nano-probes has been largely used as probes in high resolution microscopy, expecially in the biological framework .Nematic twisted liquid crystals cells has been instead recently used in quantum opticis experiments in order to analyse the orbital anguular momentum of entangled laser beams . In particular, these cells, can turn a linearly polarized beam into a radially or azimutally polarized beam. In our experimental setup we use chemically synthetized gold nanoparticles as probes of the local distribution of focused laser beams both radially or azimutally polarized and linearly polarized. The optical maps that can be obtained are in perfect agreement with the thoretical simulations obtained by using numerical integration of the e.m. fields in the focal plane. The imaging resolution is set by the nanoparticle dimensions, usually about 30nm in diameter, and has been so good to recognize spatical features due to pi phase jump inside the twisted cells . As the employment of such liquid crystal devices in quantum optics will growth, we think that the resolution achieved in our experimental method, will provide an usefull tool for the investigation of the characteristics of the fields at the nanoscales. A. Verma, O. Uzun, Y. HU, Y. HU, H.-S. HAN, N. Watson, S. CHEN, D.J. Irvine, F. Stellacci, Nature Materials, Nature Materials 7, 588 - 595 (2008) E. Nagali, L. Sansoni, F. Sciarrino, F. De Martini, L. Marrucci, B. Piccirillo, E. Karimi, E. Santamato, Nature Photonics 3, 720 - 723 (2009) A. Ambrosio, P. Maddalena, Appl. Phys. Lett. 98, 091108 (2011)
9:45 AM - **QQ5.2
Probing Sub-Microsecond Dynamics in Nanostructured Solar Cells with Time Resolved Electrostatic Force Microscopy.
David Ginger 1 Show Abstract
1 , University of Washington, Seattle, Washington, United States
Measuring transient phenomena with high resolution in time and space is a long-sought goal in nanoscience. We demonstrate sub-cycle discrimination of transient phenomena faster than 1 microsecond using only commercially available cantilevers and minimal supplemental hardware. In addition to the technical details of the experimental method, we also describe how fast time-resolved electrostatic force microscopy can be applied to characterize performance in nanostructured solar cells including processes such as charge generation, trapping, and recombination in organic photovoltaics and solution processed inorganic photovoltaics.
10:15 AM - QQ5.3
A Model for Organic Solar Cells Based on Scanning Probe Measurements.
Martijn Kemerink 1 , Klara Maturova 1 , René Janssen 1 Show Abstract
1 Applied Physics, Eindhoven University of Technology, Eindhoven Netherlands
It is well known that the photovoltaic performance of organic bulk heterojunction solar cells (OBHJs) is strongly influenced by the morphology of the active layer. However, when trying to develop a quantitative model for OBHJ performance that accounts for the morphology one typically finds that conventional current-voltage (I-V) characterization gives insufficient information to obtain a unique solution: the problem is underdetermined.Here, we combine bulk characterization with scanning probe measurements to develop a ‘morphological device model’ that is able to reproduce, with a single set of parameters, bulk device characteristics as well as locally obtained surface potentials and local current-voltage characteristics. This assures that charge generation and charge transport on the nano scale are correctly accounted for in the model.We applied this methodology to various polymer:PCBM OBHJs that are characterized by morphologies that differ substantially in the degree of phase separation. Surface potential maps in the dark and under illumination are taken by scanning Kelvin probe microscopy. An STM is used for measuring local I-V curves in dark and light. These are taken on densely spaced grids to resolve feature sizes in the 10-100 nm range. All scanning probe measurements are taken in an N2 filled glovebox.The device model that we develop is based on the coupled drift-diffusion and Poisson equations that are numerically solved on a 2D grid onto which the actual 3D morphology consisting of donor and acceptor phases is mapped. The input parameters are taken from independent electrical characterization and TEM/AFM images. Apart from reproducing the experiments, the model allows us to make statements about the optimal morphology for the various material systems investigated.
10:30 AM - QQ5.4
Characterization of Heterogeneous Materials by True Surface Microscopy.
Detlef Sanchen 1 , Peter Spizig 1 , Wolfram Ibach 1 , Ute Schmidt 1 , Thomas Dieing 1 , Olaf Hollricher 1 Show Abstract
1 , WITec GmbH, Ulm Germany
Confocal Raman imaging opened the door for many applications in Raman spectroscopy and imaging that were previously unavailable for measurement with conventional (non-confocal) Raman methods. A high confocality ensures suppression of out-of-focus light that strongly enhances image contrast. However, high confocality results in high focus sensitivity and can be challenging when analyzing large or rough surfaces. In these cases, only those points that are in focus contribute to the image. WITec`s award winning True Surface Microscopy option (patent pending) allows confocal Raman imaging guided by surface topography. True Surface Microscopy follows the surface topography with high precision, so that even rough or inclined samples always stay in focus. To achieve this unique capability, the WITec alpha500 series can be equipped with a highly precise sensor for optical profilometry. The topographic coordinates from the profilometer measurement are used to perfectly follow the sample surface in confocal Raman imaging mode. The result is an image revealing chemical properties at the surface of the sample, even if this surface is rough or inclined, without compromising the confocality of the system.The aim of this paper is to illustrate the measuring principle with examples from various fields of application.
11:15 AM - **QQ5.5
Recent Advances in Scanning Probe Thermal Measurements.
William King 1 2 Show Abstract
1 Department of Mechanical Science and Engineering, University of Illinois Urbana-Champaign, Urbana, Illinois, United States, 2 Department of Materials Science and Engineering, University of Illinois Urbana-Champaign, Urbana, Illinois, United States
This talk describes recent advancements in both measurement techniques and cantilever technology for scanning thermal microscopy and hot tip atomic force microscopy (AFM). Microcantilevers with integrated solid-state heaters enable measurements of nanometer-scale heat flow and temperature distributions at point contacts and near semiconductor junctions. Such heated AFM tips can be used to investigate thermoelectric voltage and temperature-dependent piezoelectric response at nanometer-scale point contacts. The heated AFM tips can also be used to measure thermophysical and thermochemical transitions at the nanometer scale. The talk will describe how this work is enabled by advances in the design, fabrication, characterization, and use of atomic force microscope cantilevers with integrated heaters. In particular, we report recent advancements in thermal AFM cantilevers that can operate at high speed, have integrated mechanical actuation, and have electrodes integrated into the cantilever tips.
11:45 AM - QQ5.6
Temperature Dependent Switching Spectroscopy Piezoresponse Force Microscopy.
Bikram Bhatia 1 , Karthik Jambunathan 2 , Lane Martin 2 , William King 1 Show Abstract
1 Mechanical Science and Engineering, University of Illinois Urbana-Champaign, Urbana, Illinois, United States, 2 Materials Science and Engineering, University of Illinois Urbana-Champaign, Urbana, Illinois, United States
Temperature governs the switching characteristics of ferroelectric materials, however high temperature characterization is challenging in conventional atomic force microscopy (AFM). We present an AFM technique to study the nanometer-scale electronic properties of ferroelectric films using a microfabricated platform that is capable of achieving temperatures up to 1000 C. A microfabricated heater structure of width 10 um can be resistively heated and its temperature precisely controlled. A thin film of polycrystalline PbZr0.2Ti0.8O3 is grown on the silicon micro-heaters using pulsed laser deposition. Polarization switching at elevated temperatures is studied using switching spectroscopy piezoresponse force microscopy (SS-PFM). Theory predicts that piezoresistive coefficnet (d33) increases with temperature. However previous AFM based measurements did not observe this effect due to the dominance of electrostatic interactions over the ferroelectric electromechanical response . However, we have been able to minimize the electrostatic and non-local interactions between the conductive tip and the sample by virtue of our tip-sample orientation relative to our extremely small microfabricated heater. We observe a distinct increase in the electromechanical response up to 400oC. The piezoresponse disappears above 400oC, which we believe corresponds to the ferroelectric-paraelectric phase transition. Our measurements are compared to Ginzburg-Landau-Devonshire phenomenological models, which predict the divergence of d33 at the Curie temperature. S. Jesse, H.N. Lee, and S.V. Kalinin, Rev. Sci, Instrum. 77, 073702 (2006). S.V. Kalinin, and D.A. Bonnell, Appl. Phys. Lett. 78, 1116 (2001).
12:00 PM - **QQ5.7
Nanoscale Chemical Composition Mapping with AFM-Based Infrared Spectroscopy.
Craig Prater 1 , Michael Lo 1 , Curtis Marcott 2 , Isao Noda 4 , Alexandre Dazzi 3 , Ariane Deniset 3 , Bruce Chase 5 , Kevin Kjoller 1 Show Abstract
1 , Anasys Instruments, Santa Barbara, California, United States, 2 , Light Light Solutions, Athens, Georgia, United States, 4 , The Procter & Gamble Company, West Chester, Ohio, United States, 3 , Université Paris-Sud, Orsay France, 5 , University of Delaware, Newark, Delaware, United States
We have employed AFM-based infrared spectroscopy (AFM-IR) to map nanoscale chemical, structural and mechanical variations in polymers and other samples. The AFM-IR technique irradiates the sample with light from an infrared laser and measures the absorption of this light on a sub-wavelength scale using the tip of an AFM by detecting local thermal expansion of the sample. AFM-IR can be used both to obtain point spectra at arbitrary points and to spatially map IR absorption at selected wavelengths. Simultaneous measurement of the cantilever’s contact resonance frequency as excited by the IR absorption provides a complimentary measurement of relative mechanical properties. We have used these techniques to chemically identify individual chemical components in polymer nanocomposites and multilayer films. Using self-heating probes we have been able to locally modify the state of a semicrystalline polymer and observe the resulting change in absorption spectra on the nanoscale. We have also observed orientation effects in polymer fibers by varying the polarization of the IR source. Finally have also used the AFM-IR technique to perform label-free subcellular spectroscopy and chemical imaging on biological cells.
12:30 PM - QQ5.8
Electrical and Thermal Characterization of B1-xSrxTiO3 Ferroelectric Thin Film by a Conductive Atomic Force Microscopy Probe with an Integrated Heater.
Richard Jackson 1 , Yan Wu 1 , Patrick Fletcher 2 , William King 2 , Karthik Jambunathan 3 , Lane Martin 3 Show Abstract
1 Chemistry and Engineering Physics, University of Wisconsin-Platteville, Platteville, Wisconsin, United States, 2 Mechanical Science and Engineering, University of Illinois, Urbana, Illinois, United States, 3 Material Science and Engineering, University of Illinois, Urbana, Illinois, United States
Polarization switching of nanometer-scale domains in ferroelectric materials allows for extremely high-density data storage applications, fast access times, device longevity, and low energy expenditure. The development of piezoresponse force microscopy (PFM) has greatly facilitated the understanding of local polarization dynamics in ferroelectric materials due to the highly inhomogeneous electrical field under the tip. In the present study a unique AFM probe that implements both temperature and voltage control in a single device was applied in piezoresponse force microscopy. Independent thermal and electrical control is obtained by electrically isolating the heating circuit elements of the AFM micro-cantilever from the electrical probe tip by an NPN semiconductor back-to-back diode. The heater temperature can be raised up to more than 600°C while the tip can be independently biased to ±10 volts. Ba1-xSrxTiO3 (BST) thin films were deposited using Pulsed Laser Deposition (PLD). The Curie temperature of the thin film is estimated to be around 80°C. An AC excitation voltage with a frequency range from 50kHz to 750kHz is applied to the sample through the AFM tip and the piezoelectric response of the thin film is detected by the bending amplitude of the AFM cantilever at the excitation frequency. At the same time, the integrated heater on the cantilever serves as a localized heat source that affects a nanometer scale volume of the sample material that is directly under the tip. With the unique AFM probe, we study the localized temperature dependence of the piezoelectric response of the BST ferroelectric thin film around the phase transition temperature. The results reveal key differences between bulk and localized heating methods of investigating the temperature-dependence of ferroelectric properties using PFM. This provides insight to the polarization switching mechanism in near-surface or interface regions of ferroelectric materials, as well as the domain structure and local electromechanical properties of the BST thin film.
QQ6: Probing Photonic, Thermal and Chemical Properties on the Nanoscale II
Wednesday PM, November 30, 2011
Room 305 (Hynes)
2:30 PM - QQ6.1
SKPFM and Micro FT-IRRAS Study of Corrosion Inhibitor Mobility on Zinc Oxide Surfaces.
Ozlem Ozcan 1 , Agata Pomorska 1 , Guido Grundmeier 1 Show Abstract
1 Technical and Macromolecular Chemistry, University of Paderborn, Paderborn Germany
The surface chemistry of zinc oxide is governing the adhesive and corrosive properties of galvanized steel. Recently, a new concept of self-healing coatings has been developed as an alternative to conventional systems, where corrosion inhibitor loaded nanoparticles are incorporated into polymeric coatings. These inhibitors are released by various triggering mechanisms like change of pH or concentration of certain ions at the defect area. The success of these systems depends on the mobility of these inhibitor molecules on the steel surface and the stability of the formed thin layers in presence of corrosive electrolytes.
In this paper we will be presenting Scanning Kelvin Probe Microscopy (SKPFM) as a tool to study the stability and mobility of an organic corrosion inhibitor on zinc oxide surface exposed to high humidity and corrosive electrolytes. Micro-contact printing was used for patterned deposition of the inhibitor and polished zinc sheets and model ZnO single crystals with defined morphology were used as substrates. On both substrates the inhibitor layer was detected with high resolution by means of the phase and potential signals. In case of the single crystalline ZnO, the inhibitor layer was resolved in the topography image, where as for the polished Zn samples the as-prepared layers did not give topography contrast due to the high roughness of the substrate.
Exposure to high humidity resulted in swelling of the inhibitor layer detectable on both single crystalline ZnO and polished zinc, where in the case of the latter a topography contrast appeared. Mobility of the inhibitor was not observed at the initial stages of exposure, where as in the case of prolonged exposure the inhibitor was mobile after a certain degree of swelling was reached. When the sample was exposed ex-situ to corrosive electrolyte, the inhibitor has shown high mobility on the surface, which resulted in successful corrosion protection not only at patterned spots but on the whole stamped area and the potential contrast of the patterns decreased significantly. Supporting results were obtained by means of FTIR-microscopy (micro FT-IRRAS, 50 µm lateral resolution) on samples with larger patterns. The combination of SKPFM and FTIR-microscopy enabled the direct analysis of inhibitor mobility on zinc oxide surfaces. The results present a promising methodology for the selection of inhibitor molecules to be used in the design of self healing coatings.
2:45 PM - QQ6.2
Application of In Situ Raman Spectroscopy for the Study of Corrosion Processes on ZnO Nanorods on Metals.
Katharina Pohl 1 , Ozlem Ozcan 1 , Guido Grundmeier 1 Show Abstract
1 Technical and Macromolecular Chemistry, University of Paderborn, Paderborn Germany
Zinc oxide nanorod films are of high interest in the fields of catalysis and energy conversion due to their high photosensitivity, non-toxic nature, large band gap and chemical stability. Recently, the corrosion protection ability of these films has been reported on zinc surfaces. For the design of ZnO based corrosion protection coatings it is crucial to establish a fundamental understanding of the processes taking place at the ZnO-electrolyte interface. The aim of this paper is to investigate the corrosion resistance of zinc surfaces modified with zinc nanorods and to illustrate the local reactivity of the film as a function of the electrolyte composition and nanorod chemistry by means of Confocal Raman spectroscopy. Oxygen and hydrogen plasma treatments were applied on the ZnO nanorod films to modify their semiconducting properties by an effective incorporation of oxygen and hydrogen atoms into the crystalline structure of the nanorods, which leads to suppression of cathodic and anodic corrosion reactions, respectively. Raman measurements were performed with a custom designed flow cell which enables the simultaneous measurement of electrochemical data during the collection of Raman spectra and provides a precise control of the polarisation of the sample and composition of the corrosive electrolyte. Additionally, Scanning Kelvin Probe measurements were performed to analyse the electrochemical wetting behaviour of the films in presence of an actively corroding defect and the proceeding electrolyte front during the oxygen reduction process was visualised. The results have clearly shown that the ZnO nanorod films have a great potential to be utilised as corrosion protection treatments and plasma modifications can further enhance the protection effect.References:1. O. Ozcan, K.Pohl, G. Grundmeier: Effect of hydrogen and oxygen Plasma treatments on the electrical and electrochemical properties of zinc oxide nanorod films on zinc substrates, Electrochemistry Communications (2011), article in press
3:00 PM - **QQ6.3
NanoElasticity Measurements Using Tuning Fork Frequency Modulation Correlated with Online Raman and Scanning Electron Microscopy Imaging.
Aaron Lewis 1 , Andrey Ignatov 2 , Patricia Hamra 2 , Rimma Dekhter 2 Show Abstract
1 Applied Physics, Hebrew University of Jerusalem, Jerusalem Israel, 2 , Nanonics Imaging Ltd., Jerusalem Israel
Today Raman together with atomic force microscopy (AFM) is becoming a standard and synergistic measurement combination. Such a combination has many advantages over standard microRaman for providing functional insights into the material being studied. These advantages include for Raman online AFM auto focus for chemical characterization without topographic artifacts, online functional and chemical imaging including thermal and electrical characterization and the possibility for nanoscale Raman with tip enhanced Raman spectroscopy. For SEM it brings the same functional insights noted above together with optical characterization with near-field scanning optical microscopy. A preferred method of feedback for such AFM Raman combinations is to use non-optical feedback based on normal force tuning forks feedback with glass probes that have no Raman background and are non-obscuring in terms of the Raman signal or the electron beam. One important aspect of such tuning fork feedback is the ability to monitor elasticity with greater sensitivity and without artificial processing of the data which is required in beam bounce technology. Specifically, in standard beam bounce technology there are discontinuities in the operation of the AFM cantilever due to jump to contact and adhesion ringing. Both of these discontinuities in standard AFM feedback are overcome using the tuning fork. This presentation will focus on tuning fork based elasticity measurements as correlated with online Raman chemical characterization and scanning electron microscopy.
Stephen Jesse Oak Ridge National Laboratory
Brian Rodriguez University College Dublin
Takeshi Fukuma Kanazawa University
Ricardo Garcia Instituto de Microelectronica de Madrid
QQ7: Probing Nanoscale Bio-Functionality
Thursday AM, December 01, 2011
Room 305 (Hynes)
9:30 AM - **QQ7.1
Tip-Surface Interactions in Aqueous Environments.
Suzi Jarvis 1 , Jason Kilpatrick 1 Show Abstract
1 , University College Dublin, Dublin Ireland
Recent advances in atomic force microscopy including noise reduction techniques and the successful implementation of the sensitive frequency modulation dynamic mode in a liquid environment have made it possible to measure tip-surface interactions in aqueous environments with unprecedented sensitivity. Here we discuss the influence of water and ions in the near surface region on tip-surface interactions and explore the modification of tip and surface hydrophobicity in order to isolate surface features within the tip-surface interaction profile.
10:00 AM - QQ7.2
Study of Nano-Mechanics of Collagen I Triple-helices by Computerized Processing of AFM Images.
Arkady Bitler 1 , Emanuel Perugia 2 , Inna Solomonov 2 , Sidney Cohen 1 Show Abstract
1 Chemical Research Support, Weizmann Institute of Science, Rehovot Israel, 2 Structural Biology, Weizmann Institute of Science, Rehovot Israel
Collagen forms the main connective tissue in the body. The breakdown of collagen in various pathologies such as inflammatory arthritis and cancer is linked to disease progression and accompanied by profound changes in its structure and mechanical response. The mechanics of collagen on the length scales 10-100 nm should significantly influence these processes. However, most of the previous studies of collagen mechanics have focused on much larger scales corresponding to the collagen fibrils and bundles. The nanoscale dimensions of the single collagen triple-helix presents a challenge in studying the mechanics of these molecules. We used the atomic force microscope (AFM) to acquire high-resolution images of collagen I triple-helices under ambient conditions in tapping mode. Analysis using custom software was applied to track and measure the angles between fixed-length segments along each triple-helix. Statistics were collected for hundreds of molecules (thousands of angles). Changing the segment length allowed exploring the mechanics of the triple-helices at various scales. Corresponding angular distributions are compared and analyzed, and persistence length and elastic constant evaluated.
10:15 AM - QQ7.3
Optical Sizing of Immuolabel Clusters through Multispectral Plasmon Coupling Microscopy.
Hongyun Wang 1 2 , Guoxin Rong 1 2 , Bo Yan 1 2 , Linglu Yang 1 2 , Bjoern Reinhard 1 2 Show Abstract
1 Department of Chemistry, Boston University, Boston, Massachusetts, United States, 2 The Photonics Center, Boston University, Boston, Massachusetts, United States
Plasmons of individual noble metal nanoparticles can interact with each other over tens of nanometers and these near-field interaction can be detected in the far-field as a spectral shift of the resonance wavelength. The distance dependency of the plasmon coupling has been utilized in plasmon coupling microscopy for monitoring nanoparticle assemblies laterally diffusion on a cell surface with nanometer scale spatial resolution. In this work, we developed a multispectral plasmon couping microscopy for optical sizing the two-dimensional nanoparticle cluster without the need for monitoring their formation. The wavelength dependent scattering cross-sections of self-assembled silver nanoparticle clusters of known size were measured on five different wavelength channels between 427nm and 510nm through correlation of multispectral imaging and scanning electron microscopy. A multivariate statistical analysis of the spectral response of this training set provided a correlation between spectral response and cluster size and enabled a classification of new measurements into four distinct nanoparticle association levels(I1-I4) whose compositions were dominated by monomers (I1), dimers (I2), trimers and tetramers (I3), and larger clusters (I4), respectively. One potential application of the optical sizing approach is to map association levels of silver immunolabels on cellular surfaces. We demonstrated the feasibility of this approach using silver immunolabels targeted at the epidermal growth factor receptor on A431 cells in a proof of principle experiment. The ability to measure immunolabel association levels on subcellular length scales in an optical microscope provides new opportunities for experimentally assessing receptor density distributions on living cells in solution.
10:30 AM - QQ7.4
Development of a Novel Combined Scanning Electrochemical Microscope (SECM) and Scanning Ion-Conductance Microscope (SICM) Probe for Soft Sample Imaging.
Andrew Pollard 1 , Nilofar Faruqui 1 , Debdulal Roy 1 , Charles Clifford 1 , Yasufumi Takahashi 2 , Yuri Korchev 2 , Neil Ebejer 3 , Patrick Unwin 3 , Julie Macpherson 3