Symposium Organizers
Suneel Kodambaka University of California-Los Angeles
Guus Rijnders University of Twente
Amanda Petford-Long Argonne National Laboratory
Andrew Minor Lawrence Berkeley National Laboratory
Stig Helveg Haldor Topsoe A/S
Alexander Ziegler Max-Planck Institute for Biochemistry
NN1/EE1: Joint Session: In-situ Nanomechanics
Session Chairs
Monday PM, December 01, 2008
Room 200 (Hynes)
9:00 AM - NN1.1/EE1.1
SEM In situ Compression of Silicon Nanowires.
William Mook 1 , Rudy Ghisleni 1 , Karolina Rzepiejewska-Malyska 1 , Samuel Hoffmann 1 , Laetitia Philippe 1 , Johann Michler 1
1 , Swiss Federal Laboratories for Materials Testing and Research (EMPA), Thun Switzerland
Show AbstractSilicon nanowires have created a great deal of interest for over a decade due to their enhanced electrical properties when compared to bulk values. These structures also show size-dependent mechanical properties and since they can determine the reliability of many nanodevices and nanosystems, it necessary to quantify their elastic and plastic mechanical response to externally applied loads. This, however, is experimentally challenging due to the length scales involved. Therefore uniaxial compression experiments have been performed in situ with a high resolution scanning electron microscope (SEM) on single crystal silicon nanowires with diameters ranging from 100 nm to 1 μm. A flat-punch indenter can be positioned above the structure of interest with nanometer precision without modifying it due to deformation from mechanical scanning. Compressions are then run under displacement-control at 1 nm/s. By observing the deformation and contact area throughout the experiment engineering stress-strain curves can be extracted from the load-displacement data. Nanowire compressive strength is compared to silicon micropillar compression experiments and to silicon wires in bending.
9:15 AM - NN1.2/EE1.2
SEM In situ Micropillar Compression - Room Temperature Ductile to Brittle Transition of Si, GaAs, InP Semiconductors.
Johann Michler 1 , Fredrik Oestlund 1 , Karolina Rzepiejewska-Malyska 1 , William Mook 1 , Klaus Leifer 2 , Rudy Ghisleni 1
1 , Swiss Federal Laboratories for Materials Testing and Research (EMPA), Thun Switzerland, 2 Electron Microscopy and Nanoengineering, Department of Engineering Science, Uppsala University, Uppsala Sweden
Show AbstractCurrent fabrication technology is capable of producing micro- to nano-meter scale structures. The mechanical response of such structures has been shown to depend upon length scales such as pillar diameter. These findings contradict the classical laws of mechanics which assume that mechanical properties are independent of sample size. This contradiction has fostered an increasing number of investigations into mechanical size effects in order to accurately design and fabricate devices at these scales. In an effort to characterize and understand the mechanical behaviour dependence on the size, an investigation on single crystal semiconductor micropillars is presented. Single crystal silicon, gallium arsenide, and indium phosphide micropillars were fabricated by a focused ion beam (FIB) technique. The diameter of the pillars ranged from 200 nm to 10 μm with a length to diameter aspect ratio of three. The micropillars’ mechanical response was investigated by uniaxial compression tests performed with a diamond flat punch using an in situ SEM nanoindenter instrument.Engineering stress-strain curves as a function of pillar diameter are presented. The results show that all the investigated semiconductor materials exhibited a brittle to ductile transition with a decrease in pillar diameter. The deformation mechanism that is responsible for the plasticity is shown to be the formation of Shockley partial dislocations. The decrease of the projected pillar diameter on the crystal slip plane below the equilibrium distance (proportional to the stacking fault energy) between the leading and trailing partial dislocation controls the transition from a brittle to ductile behavior.
9:30 AM - NN1.3/EE1.3
In-situ Investigation of Nano-scale Plasticity in Cubic and Tetragonal Crystals via Homogeneous Deformation of Nano-Pillars.
Julia Greer 1 , Ju-Young Kim 1 , Steffen Brinckmann 1
1 Materials Science, California Institute of Technology, Pasadena, California, United States
Show AbstractStrength of crystalline materials at reduced dimensions is important for fabrication and reliability of devices at nanometer scales such as MEMS and NEMS, bio-cell sensors, and fuel cells. Plastic flow stress of crystals, a size-independent property for bulk, is found to strongly depend on sample size as it is reduced to nano-scale. To investigate plasticity under homogeneous deformation, we have developed an in-situ micro-deformation methodology, where nano-pillars are mechanically deformed in a one-of-a-kind instrument, SEMentor, which merges the strengths of SEM and Nanoindenter, and offers the advantage of measuring mechanical response of nano-scale materials while capturing video frames throughout the deformation process. We present for the first time results of compression and tension tests performed in-situ inside SEMentor, where load-displacement data is correlated with real-time slip step formation on the surface of the deforming specimens. We perform a new robust technique for stress-strain calculation based on load-displacement data. We also report mechanical strengths of uniaxially-deformed single crystalline nano-pillars with different crystallographic structures (Au, Al, In, Mo) and compare them with one another. Our experiments demonstrate pronounced differences in the behavior of individual structures, and possibly plasticity mechanisms are discussed. We find that although all crystals show an increase in flow stress with decreasing diameter in a power-law fashion, the slopes of these size effects vary with the material, and the ratio between the observed maximum flow stress and the theoretical strength vary significantly.
9:45 AM - NN1.4/EE1.4
Quantitative In Situ Tensile Testing of 1D Nanostructures.
Daniel Gianola 1 , Reiner Moenig 1 , Oliver Kraft 1 2 , Cynthia Volkert 3
1 Institute for Materials Research II, Forschungszentrum Karlsruhe, Karlsruhe Germany, 2 , University of Karlsruhe, Karlsruhe Germany, 3 Institut für Materialphysik, Universität Göttingen, Göttingen Germany
Show AbstractPlasticity in extremely small volumes is fundamentally different than in large materials; the law of averages gives way to discrete processes that dominate the response. Probing the mechanical response and uncovering the underlying deformation mechanisms of diminishingly small structures at the micro- and nanoscale requires new strategies and approaches that circumvent difficulties associated with handling, gripping, loading, and measuring small specimens. The need for in situ experiments that give a one-to-one correlation between mechanical response and deformation morphology is exacerbated by the fact that electron optics are needed to image and manipulate nanostructures. Tensile experiments are the preferred modality at larger scales since they apply a homogeneous stress state and are less sensitive to boundary conditions, easing interpretation. Meanwhile, results obtained using the popularly employed techniques at the nanoscale (e.g. nanoindentation, micro-compression testing) are clouded by these unresolved issues. Here we describe quantitative in situ tensile experiments on 1D nanostructures in a dual-beam scanning electron microscope (SEM) and focused ion beam (FIB). Specimen manipulation, transfer, and alignment are performed using an in situ manipulator, independently-controlled positioners, and the FIB. Gripping of specimens is achieved using electron-beam assisted Pt deposition. Local strain measurements are obtained using digital image correlation of SEM images taken during testing. Examples showing results for single-crystalline metallic nanowires and nanowhiskers, having diameters between 30 and 300 nm, will be presented in the context of size effects on mechanical behavior, the theoretical strength of crystals, and the influence of defects on the accommodation of plasticity in small volumes.
10:00 AM - **NN1.5/EE1.5
Observation of Size-Dependent Plasticity by In Situ SEM and TEM.
Gerhard Dehm 1 2
1 Erich Schmid Institute of Materials Science, Austrian Academy of Sciences, Leoben Austria, 2 Materials Physics, University of Leoben, Leoben Austria
Show AbstractThe continuing trend of miniaturizing materials in many modern technological applications has led to a strong demand for understanding the complex mechanical properties of materials at small length scales. This talk focuses on the recent understanding of the size-dependent plasticity in face-centered cubic metals with dimensions of several microns down to some tens of nanometers. At that length scale sophisticated measurement approaches are required with the advantage of in situ microscopy techniques providing both, control of the deformation experiment and insight in the underlying deformation mechanisms. Size effects of the flow stresses are compared for “wires” and thin films on compliant or stiff substrates. The interpretation of the results is based on recent insights on dislocation nucleation, glide band formation, and dislocation mobility stemming from in-situ SEM and TEM studies of single-crystalline and polycrystalline samples. The results are discussed with the attempt to explain the size effects in straining experiments at small length scales.Acknowledgement: Significant contributions from D. Kiener, R. Pippan, S.H. Oh (Leoben), M. Legros (Toulouse), and P. Gruber (Stuttgart) are acknowledged.
11:00 AM - NN1.6/EE1.6
In Situ Examination of Nanoscale Deformation of Thin Film Bridges within a Scanning Electron Microscope.
Erik Herbert 1 , Arnold Lumsdaine 1 , R. Brian Peters 1 , Warren Oliver 1
1 , Agilent Technologies, Oak Ridge, Tennessee, United States
Show AbstractUsing a high precision nanoindentation head, a new technique has recently been developed to determine the elastic modulus and residual stress of a free-standing doubly-clamped thin film bridge [1]. A desire to examine the impact of certain anomalies in the experimental results (possibly occurring due to misalignment of the tip of the nanoindentation head with the surface of the bridge or due to adhesion of the tip with the surface of the bridge) motivates an examination of the experiment within a scanning electron microscope (SEM). A linear feedthrough mechanism has been developed to position the indentation head within the SEM chamber for precise targeting of the thin film bridge sample (placed on the SEM sample stage). This configuration also allows for the examination of the multi-dimensional deformation state of the bridge when the indentation head contact occurs offset from the center of the bridge.[1]E.G. Herbert, W.C. Oliver, M. P. de Boer, and G.M. Pharr, “Measuring the Elastic Modulus and Residual Stress of Free-Standing Thin Film Bridges by Nanoindentation,” 2007 MRS Spring Meeting, 2007.
11:15 AM - **NN1.7/EE1.7
A New Perspective on Nano-Mechanics: Quantitative Deformation Test in the TEM
Zhiwei Shan 1 , A. Minor 2 3 , J. Nowak 1 , S. Syed Asif 1 , O. Warren 1
1 , Hysitron Inc., Eden Prairie, Minnesota, United States, 2 , Lawrence Berkeley National Laboratory, Berkeley, California, United States, 3 , University of California , Berkeley, California, United States
Show AbstractIt is often a challenge to measure accurately the mechanical properties of nanostructures and nanomaterials on account of their extremely small physical dimensions. Recently, we have developed an in situ TEM nanomechanical testing apparatus. This device enables one to acquire quantitative mechanical data while simultaneously recording the microstructural evolution of the materials during deformation, developing a one-to-one relationship between an imposed stress and an individual deformation event. In this talk, we report on the current progress in the application of this in situ TEM device for measuring the mechanical behavior of individual single crystal nickel and metallic glass (MG) pillars. Prior to the deformation tests, the Focused Ion Beam (FIB) fabricated nickel pillars were observed to contain a high density of defects. However, quite unexpectedly, the defects density was observed to decrease dramatically during the deformation process and, in some cases, even resulted in a dislocation-free crystal. The phenomena which we termed as “mechanical annealing” is the first direct observation of the dislocation starvation mechanism and sheds new light on the unusual mechanical properties associated with submicron- and nano- scale structures (Shan et al, Nature Materials, 2008). The compression tests on Cu-Zr-Al MG pillars revealed the intrinsic ability of fully glassy MGs to sustain large plastic strains, which would otherwise be preempted by catastrophic instability in macroscopic samples and conventional tests (Shan et al, PRB, 2008).
11:45 AM - NN1.8/EE1.8
In- Situ Observation of Deformation Characteristics in Nanotwinned Copper Pillars.
Vinay Sriram 1 , Jia Ye 2 3 , Andrew Minor 2 3 , Jenn-Ming Yang 1
1 Department of Materials Science and Engineering, University of California Los Angeles, Los Angeles, California, United States, 2 National Centre for Electron Microscopy, Lawrence Berkeley National Lab, Berkeley, California, United States, 3 Department of Materials Science and Engineering, University of California Berkeley, Berkeley, California, United States
Show AbstractThe semiconductor industry is currently moving towards integration of “air gap” technology beyond the 32nm node. A major concern in the introduction of air gap technology is the mechanical integrity, reliability and stability of the vias and interconnects line structures. A new method based on In-situ Transmission Electron Microscopy nanocompression testing of copper pillars which are of the same size scale of vias, interconnects will be presented. Copper pillars having nanotwined boundaries and nanocrystalline grains were tested by this technique. We show direct evidence that twin boundaries can withstand extensive plastic deformation and still retain their structure when compared to regular grain boundaries. The deformation mechanisms of twin boundaries predicted by Molecular Dynamic (MD) simulations has been verified by real-time TEM analysis. Quantitative in-situ stress measurements for deformation twinning are in close agreement with those reported by first principle based calculations.
12:00 PM - NN1.9/EE1.9
In Situ TEM Nanocompression Testing of Gum Metal.
Elizabeth Withey 1 , Andrew Minor 2 , Jia Ye 2 , Shigeru Kuramoto 3 , Daryl Chrzan 1 , John Morris 1
1 Materials Science and Engineering, University of California, Berkeley, Berkeley, California, United States, 2 , National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 3 , Toyota Central R&D Laboratories, Inc., Nagakute Japan
Show Abstract“Gum Metal” is a newly developed β-Ti alloy that, in the cold-worked condition, has exceptional elastic elongation and high strength. The available evidence suggests that Gum Metal does not yield until the applied stress approaches the ideal strength, and then deforms by mechanisms that do not involve conventional dislocation plasticity. To study its behavior, submicron-sized pillars of solution-treated and cold-worked Gum Metal were compressed in situ in a quantitative compression stage in a transmission electron microscope. Quantitative load vs. displacement data was correlated to real-time images to determine a pattern of deformation that agrees with previous results from ex situ nanoindentation.
12:15 PM - NN1.10/EE1.10
Thermal Behavior of Gold Nanoparticles on Pyrite and Arsenopyrite Surfaces.
Niravun Pavenayotin 1 , Qiangmin Wei 2 , Yanbin Chen 1 , Lumin Wang 1 2
1 Nuclear Engineering and Radiological Sciences, University of Michigan, Ann Arbor, Michigan, United States, 2 Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States
Show AbstractDiffusion of gold nanoparticle on pyrite (FeS2) and arsenopyrite (FeAsS) surfaces was studied under in-situ TEM. The gold nanoparticles were deposited onto the surfaces by sputtering of gold TEM grids by ion milling. The gold nanoparticles have a uniform size of approximately 2 nm in diameter. The samples were heated up using a hot stage in the TEM to 100, 200, 300, 400, 500 and 550°C. The movement and characteristics of the nanoparticles were monitored by in situ TEM. The gold nanoparticles coalesce and grow by Oswald’s ripening as the temperature rises. At 500°C, pyrite starts to decompose into amorphous Fe and S. Gold particles on the decomposed surface are driven together and form particles as large as 30 nm in diameter while at the same temperature the gold particles in arsenopyrite are less than 20nm in diameter. Some of the solid gold nanoparticles on pyrite surface also melt and form a film-like morphology. Arsenopyrite does not decompose until 550°C. The gold particles that reside on top of the amorphous decomposed region are immobile. The particles on the crystalline surface grow at a fast rate and visibly mobile on the surface. The differences in the diffusion behavior of gold nanoparticles on two different pyrites will be explained.
12:30 PM - **NN1.11/EE1.11
Revealing the Deformation Processes Responsible for Controlling Mechanical Properties.
Ian Robertson 1
1 Materials Science and Engineering, University of Illinois, Urbana, Illinois, United States
Show AbstractTransmission electron microscopes have played a critical role in building our knowledge base regarding dislocations, dislocation-obstacle interactions and microstructural evolution as a function of deformation history. Past usage yielded primarily snapshots of the microstructure, leaving the pathways by which it was attained to be deduced. Development of straining stages for use in electron microscopes, cameras for capturing the reaction dynamics and computer technology and software for image processing have enabled observation of dislocation processes in real time and at the spatial resolution of the instrument. Provided the impact of the thin film geometry and the stress state are appreciated, this technique can and has been used to provide visual and quantitative information about dislocation reactions and processes. The results of these studies are now being incorporated into physically-based models for predicting the mechanical properties. Recent developments in stage design provide the capability to measure the macroscopic response and to simultaneously observe the deformation behavior, thus, providing the opportunity to correlate microscopic processes with a macroscopic property. In this talk, examples of applications of standard and new straining stages will be used to illustrate how these tools have advanced our understanding of dislocation reactions and processes and how this insight has been used to yield new models.
NN2: In-situ Growth and Characterization of Nanotubes
Session Chairs
Monday PM, December 01, 2008
Room 102 (Hynes)
2:30 PM - **NN2.1
In-Situ Electrical, Mechanical, and Thermal Properties of Carbon Nanotubes and Nanowires by using a TEM-SPM Platform.
Jianyu Huang 1
1 Center for Integrated Nanotechnologies (CINT), Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractIn this talk, I will review our recent progress in using a transmission electron microscopy – scanning probe microscopy (TEM-SPM) platform to probe in-situ the electrical, mechanical and thermal properties of carbon nanotubes [1] and nanowires. First, buckyballs are formed inside the hollow of multiwall carbon nanotubes, and the buckyballs shrink continuously until they disintegrate, proving the “shrink-wrap” buckyball formation mechanism. Second, using carbon nanotubes as heaters and carbon onions as high-pressure cells, a temperature higher than 2000 °C and a pressure higher than 40 GPa are created in the core of the carbon onions. At such a high pressure and a high temperature, the diamond formed in the carbon onion core exhibits a quasimelting state. Third, plastic deformation, such as superplasticity, kink motion, dislocation climb, and vacancy migration, is discovered in nanotubes. Fourth, nanowires are elongated to a record length without any dislocation activity. Finally, in-situ thermal measurement will be highlighted. [1]J.Y. Huang et al., Nature 439, 281 (2006); J.Y. Huang et al., Phys. Rev. Lett. 94, 236802 (2005); 97, 075501 (2006); 98, 185501 (2007); 99, 175593 (2007); 100, 035503 (2008).
3:00 PM - **NN2.2
Frontiers of In-situ TEM: Thermal Imaging of Nanotubes and Lorentz Imaging of Nanomagnetic Lattices.
John Cumings 1 , Todd Brintlinger 1 , Yi Qi 1 , Kamal Baloch 1 2
1 Department of Materials Science and Engineering, University of Maryland, College Park, Maryland, United States, 2 Institute for Physical Science and Technology, University of Maryland, College Park, Maryland, United States
Show AbstractIn-situ transmission electron microscopy is a rapidly-growing field with many frontiers of research. Most commonly, in-situ techniques are used to study the processing or growth of novel materials. In a different and expanding area of research, in-situ techniques are used instead for uncovering the properties of operational devices and dynamic systems. One example of this is carbon nanotubes under thermal transport conditions. To study this, we have developed a novel thermal imaging technique, electron thermal microscopy [1], and I will present results applying this technique to the thermal transport of carbon nanotubes. Another growing area of research is the study of interactions of magnetic elements structured at the nanoscale. In one groundbreaking avenue [2], interacting magnetic elements are patterned on periodic lattices that prevent long-range order. Such systems are frustrated and have the potential for revealing fundamental microscopic properties in materials as diverse as rare-earth oxides and ice. Furthermore, they are highly relevant to technologies which desire to pack magnetic information into increasingly smaller areas, such as MRAM and magnetic hard disk drives. I will present results on in-situ TEM studies of these novel artificially frustrated magnetic systems, and will discuss some of the implications for emerging technologies. This work was supported in part by the NSF-MRSEC at the University of Maryland and utilized its shared equipment facilities, under contract DMR 0520471[1] T. Brintlinger et al., Nano Letters, 8, 582 (2008). [2] R. F. Wang et al., Nature, 439, 303 (2006).
3:30 PM - NN2.3
Local Electrical Transport Measurements at LaAlO3/SrTiO3 Interfaces Using STM in TEM.
Johan Borjesson 1 , Alexey Kalabukhov 2 , Robert Gunnarsson 2 , Tord Claeson 2 , Dag Winkler 2 , Krister Svensson 3 , Eva Olsson 1
1 Microscopy&Microanalysis, Chalmers University of Technology, Gothenburg Sweden, 2 Microtechnology and Nanosience, Chalmers University of Technology, Gothenburg Sweden, 3 Physics and Electrical Engineering, Karlstad University, Karlstad Sweden
Show AbstractLaAlO3 (LAO) and SrTiO3 (STO) are insulators but when an epitaxial LAO thin film is deposited on a STO substrate the interface can show electrical conduction. The conductivity is believed to be due to an induced two-dimensional electron gas at the interface and/or oxygen vacancy doping of the STO in the vicinity of the film/substrate interface. The properties of the interface depend on the oxygen pressure during the LAO thin film growth and on the film thickness. In this work the atomic structure of different interfaces has been determined by high resolution analytical transmission electron microscopy (TEM) using a Titan 80-300 with a probe Cs corrector and a monochromator. The local electrical transport properties have been studied using an in-situ scanning tunneling (STM)-TEM holder. This holder allows simultaneous contacting/electrical characterization and imaging by TEM and scanning TEM (STEM). A direct correlation between atomic structure and electrical transport properties is thereby obtained. Information about oxygen vacancies at and in the vicinity of the film/substrate interface is obtained by electron energy loss spectroscopy.
3:45 PM - NN2.4
In-situ and Ex-situ TEM Microscopy and Spectroscopy Studies of Interfaces in Li-ion Battery Materials.
Chongmin Wang 1 , Gary Yang 2 , S. Thevuthasan 1 , J. Liu 3 , D. Baer 1 , L. Saraf 1 , Wu Xu 2 , J. Zhang 2 , D. Wang 3 , N. Salmon 4
1 Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, Washington, United States, 2 Energy and Environmental Directorate, Pacific Northwest National Laboratory, Richland, Washington, United States, 3 Fundamental and Computational Science Directorate, Pacific Northwest National Laboratory, Richland, Washington, United States, 4 , Hummingbird Scientific, Lacey, Washington, United States
Show AbstractElectrochemical energy storage devices (EES), such as Li-ion batteries, are complex multi-component systems that incorporate widely dissimilar materials and materials phases in physical and electrical contact. The operation of an EES relies critically on electronic and ionic transference across solid–solid and solid–liquid interfaces and within each of the constituent phases. These interfaces may include a reaction front moving through a particle in a two phase reaction; or an interface between the conducting electrode and the electrolyte. The largest and most critical challenge facing an EES is the basic understanding of the structural evolution within the constituent materials and that across the interface/interphase during the cyclic operation of a cell and the consequence of such structural evolution on the properties and lifetime of the cell. In general, mechanisms associated with the intercalation and deintercalation of Li ions in a Li-ion battery system is not fully understood. The structure of the interface between Li intercalated region and the Li free one and the propagation of this interface during charge and discharge of the battery are not well known. Overall, this imposes a fundamental scientific question as how the microstructures within the constituent materials and across the interface/interphase confined by the constituents evolve and impact the properties of the lithium ion battery. Ex-situ methods based on electron beam imaging and spectroscopy has been widely used for probing the structural features of an EES system. However, due to the dynamic structural nature of the process and the sensitivity of some of the materials to air, the ex-situ method cannot answer some of the questions that are related to the dynamical operation of the EES. In-situ capabilities that enable the observation of the structural and chemical changes during the dynamic operation of a battery are most appropriate for addressing this scientific and technological challenge. We have been developing a Transmission electron microscopy (TEM) holder that allows direct observation of the chemical and structural evolution at the interface between the electrolyte and the electrode as well as within the electrodes under the dynamic operation conditions of the Li ion battery system. We have investigated the structural evolution at the interface between TiO2 nanowire anode and the Li based electrolyte using TEM imaging, electron diffraction, and electron energy-loss spectroscopy (EELS) under the operating conditions a battery.
4:30 PM - **NN2.5
Investigating Catalyst Behavior Prior to and During the Growth of Carbon Nanotubes with Real Time TEM.
Eric Stach 1 , Sueng Min Kim 1 , Dmitri Zakharov 2 , Placidus Amama 4 , Cary Pint 3 , Robert Hauge 3 , Benji Maruyama 5
1 School of Materials Engineering and Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana, United States, 2 Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana, United States, 4 , Universal Technology Corporation, Dayton, Ohio, United States, 3 Department of Chemistry, Rice University, Houston, Texas, United States, 5 Materials and Manufacturing Direcorate, Wright Patterson Air Force Research Laboratory, Dayton, Ohio, United States
Show Abstract5:00 PM - NN2.6
In-situ Electrical Probing of Silicon During Nanoindentation.
Simon Ruffell 1 , Jim Williams 1 , Jodie Bradby 1 , Naoki Fujisawa 1 , Ryan Major 2 , Oden Warren 2
1 Electronic Materials Engineering, Australian National University, Canberra, Australian Capital Territory, Australia, 2 , Hysitron Inc., Minneapolis, Minnesota, United States
Show AbstractThe Hysitron nanoECR system allows in-situ electrical measurements to be performed during nanoindentation testing. With examples from our work on nanoindentation-induced phase transformations in silicon, we illustrate that the electrical measurements are extremely powerful in aiding understanding of the phase transformation behaviour. They have high sensitivity and can be directly correlated with the mechanical load/unload data.We have shown that under both constant voltage and I-V sweep modes we can track the formation of high pressure crystalline phases (Si-III and Si-XII) during unloading. Careful analysis of through-tip current during constant voltage experiments reveals that the nucleation of these crystalline phases, from the Si-II phase formed during loading, can also be monitored. In addition, the system can be operated as a point probe which has high sensitivity to the local microstructure of phase transformed zones. In particular the I-V characteristics of the tip/sample contact are extremely sensitive to the local material allowing spatial mapping of conductivity within a residual indent. This high sensitivity has allowed detection of seed volumes of these crystalline phases in amorphous Si, that are below detection limits of ex-situ techniques such as Raman micro-spectroscopy. Subtle changes in the final microstructure, which can be modified by changing the starting matrix (i.e. amorphous or crystalline silicon) can also be detected by through-tip conductivity measurements. Finally, we discuss some technical issues related to the capability of making quantitative measurements and show ex-situ electrical measurements which allow correlation of in-situ electrical measurements with electrical properties of the nanoindentation-induced silicon.
5:15 PM - NN2.7
Atomic Scale In-situ Environmental TEM of the Nanoparticle Catalysts for the Nucleation and Growth of Carbon Nanotubes in CVD Condition.
Hideto Yoshida 1 , Tetsuya Uchiyama 1 , Yuusuke Tanemoto 1 , Kazuto Ofuji 1 , Seiji Takeda 1 , Yoshikazu Homma 2
1 , Osaka Univ., Osaka Japan, 2 , Tokyo University of Science, Tokyo Japan
Show Abstract5:30 PM - NN2.8
In-situ XPS Study of Supported Transition Metal Catalysts during Carbon Nanotube Growth.
Stephan Hofmann 1 , Raoul Blume 2 , Tobias Wirth 1 , Cecilia Mattevi 3 , Cinzia Cepek 3 , Andrea Goldoni 4 , Axel Knop-Gericke 2 , Robert Schloegl 2 , John Robertson 1
1 Dep. of Engineering, Cambridge University, Cambridge United Kingdom, 2 , Frtiz-Haber Institute, Berlin Germany, 3 , TASC-CNR-INFM, Trieste Italy, 4 , Sincrotrone Trieste SCpA, Trieste Italy
Show Abstract5:45 PM - NN2.9
Hydrothermal Synthesis of Nano-BaTiO3 Particles using Titanate Nanotubes Precursors – A Kinetic Study.
Paula Vilarinho 1 , Florentina Maxim 1 , Paula Ferreira 1 , Ian Reaney 2
1 Department of Ceramics and Glass Engineering, University of Aveiro, Aveiro Portugal, 2 Department of Engineering Materials, Univeristy of Sheffield, Sheffield United Kingdom
Show AbstractNN3: Poster Session
Session Chairs
Tuesday AM, December 02, 2008
Exhibition Hall D (Hynes)
9:00 PM - NN3.1
In Situ Plasticity Measurements in Metallic Nanostructures.
Douglas Stauffer 1 , Ryan Major 2 , William Gerberich 1
1 Chemical Engineering & Materials Science, University of Minnesota, Minneapolis, Minnesota, United States, 2 , Hysitron, Inc., Minneapolis, Minnesota, United States
Show AbstractA conductive probe is used to probe incipient plasticity in metallic nanostructures by means of in situ conductivity experiments. In situ conductance measurements during nanoindentation have shown that conductance drops are observed at the instant of displacement excursions upon loading. This behavior is described by Matthiessen’s rule as having an inverse relationship between conductivity and dislocation density. Metallic nanostructures are then deformed in order to increase the local dislocation density. Regions of highly deformed material are scanned with the conductive probe to examine the extent of deformation. The local dislocation density can then be calculated from the conductivity measurement.
9:00 PM - NN3.10
Pulsed Electrical Stressing of Amorphous/Nano-Crystalline Silicon Wires.
Adam Cywar 1 , Gokhan Bakan 1 , Cicek Boztug 1 , Mustafa Akbulut 1 , Nathan Henry 1 , Helena Silva 1 , Ali Gokirmak 1
1 Electrical and Computer Engineering, University of Connecticut, Storrs, Connecticut, United States
Show Abstract9:00 PM - NN3.12
Negative Thermal Expansion and Other Anomalies in Supported Metal Nanoparticles.
Sergio Sanchez 4 , Laurent Menard 5 , Ariella Bram 1 , Joshua Kas 3 , Qi Wang 1 , Joo Kang 2 , Fernando Vila 3 , John Rehr 3 , Ralph Nuzzo 4 , Anatoly Frenkel 1
4 Chemistry , University of Illinois, Urbana-Champaign, Illinois, United States, 5 Chemistry, University of North Carolina, Chapel Hill, North Carolina, United States, 1 Physics, Yeshiva University, New York, New York, United States, 3 Physics, University of Washington, Seattle, Washington, United States, 2 , The Dow Chemical Company, Midland, Michigan, United States
Show AbstractNegative thermal expansion (NTE), a peculiar effect reported in 1996 in zirconium tungstate and other framework solids and not expected in fcc metals, was recently observed in alumina-supported Pt nanoparticles. In the smallest particles studied (0.9nm in diameter) the Pt-Pt distance decreased gradually by 0.04 Å over a controlled temperature range spaning ~400 K. These effects were also present in larger particles, albeit less extreme than in the 0.9 nm samples, and were attributed to the charge transfer between the cluster and support. Recently, more experimental information on structure and dynamics of Pt clusters was obtained for different sizes, support materials and gas atmospheres. Experimental results combined with the first principles, real-time calculations uncovered dynamic structure of supported metal clusters that exhibit large dynamic fluctuations. This dynamic behavior, previously unaccounted for by ground state DFT calculations, is characterized by strongly non-vibrational electronic and structural real-time effects in these supported clusters that explain their observed anomalies.
9:00 PM - NN3.4
Evanescent-wave Cavity Ring-down Spectroscopy for in Situ Kinetic Study on the Defect Evolution During the Interaction of Atomic Hydrogen and Amorphous Silicon Thin Films.
Mauritius van de Sanden 1 , Floran Peeters 1 , Jie Zheng 1 , Erwin Kessels 1
1 Applied Physics, Eindhoven University, Eindhoven Netherlands
Show Abstract9:00 PM - NN3.5
Minute-Long Measurement of Year-Long Creep Properties of Concrete by Nanoindentation.
Matthieu Vandamme 1 2 , Franz-Josef Ulm 2
1 , Université Paris-Est, Champs-sur-Marne France, 2 Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractWith an annual consumption of one cubic meter per person, concrete is the most manufactured material on Earth. But concrete subject to sustained load creeps, at a rate that deteriorates the durability and lifespan of concrete infrastructure. Creep experiments on concrete usually are performed on meter-sized specimens and last up to several years, which is both impractical and expensive.While it is generally agreed that concrete creep originates from the complex viscous behavior of its nanometer-sized building blocks (the calcium-silicate-hydrates C-S-H), the creep properties of C-S-H have never been measured directly since C-S-H cannot be recapitulated ex situ in bulk form. Here we develop a comprehensive nano-investigation approach to the creep properties of the fundamental building block C-S-H. This is achieved by extending the realm of classical indentation analysis of homogeneous solids to highly heterogeneous, linear-viscoelastic, cohesive-frictional materials. A formula is derived that enables the assessment of the contact creep compliance from sharp indentation testing, independent of the instantaneous plasticity exhibited during loading.Nine cement pastes with varying water-to-cement mass ratios (w/c), heat treatments (HT), additions of silica fumes (SF) and additions of calcareous filler (CF) are considered. On each sample, several hundreds of 3-minute-long indentation creep tests were performed. It is found that at the nanoscale all C-S-H phases exhibit a logarithmic creep, whose amplitude is inversely proportional to a contact creep modulus C. The contact creep modulus C governing the C-S-H creep rate (~1/t) scales linearly with the indentation hardness H, independent on mix proportions, processing conditions, or additions. Finally, we show that the logarithmic creep measured by indentation testing in some minutes at the nanoscale is as exact as macroscopic creep tests carried out on meter-sized concrete samples over years. This “length-time equivalence” (large time scales can be accessed by looking at small length scales) may turn out to be invaluable for the implementation of sustainable concrete materials.
9:00 PM - NN3.6
Using Localized Surface Plasmon Resonances to Probe the Nanoscopic Origins of Macroscopic Ordering Transitions in Liquid Crystals.
Gary Koenig 1 , Nicholas Abbott 1
1 Chemical and Biological Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States
Show AbstractSurface-induced ordering of micrometer-thick films of liquid crystals (LCs) has been reported to occur on the surfaces of a wide range of organic and inorganic materials. Although such studies reveal the ordering of the LC films to be highly sensitive to details of the structure and chemical functionality of these surfaces, the connection between the ordering of the LCs on the micrometer-scale (as probed, for example, by transmission of polarized light) and the near-surface (<20 nm) ordering of the LCs is complex and not well-understood. Non-linear optical measurements, such as optical second harmonic generation, have yielded important insights, including observations of near-surface order above the bulk nematic-to-isotropic clearing temperatures (TNI). Such measurements, however, are complicated to perform and are not generally possible in the presence of bulk LC due to quadrupolar contributions to the second harmonic signal. In this presentation, we will describe the use of localized surface plasmon resonances (LSPRs) of gold nanodots to characterize the nanoscale ordering of LCs. When combined with in situ polarized light microscopy, we demonstrate that this simple approach permits simultaneous measurement of changes in local (nanoscopic) and far-field (macroscopic) structure during ordering transitions in LCs. Changes in ordering of LCs due to thermal effects as well as specific binding of molecules at surfaces will be described. These results also suggest principles for new classes of plasmonic sensors.
9:00 PM - NN3.7
In-Situ High Resolution TEM Nanoindentation of Silver Nanoparticles.
Christopher Carlton 1 , Oleg Lourie 2 , Paulo Ferreira 1
1 Mechanical Engineering, University of Texas, Austin, Texas, United States, 2 , Nanofactory Instruments, Gothenburg Sweden
Show AbstractWhile there are still many questions unanswered in the field of nanomaterials, it is clear that downsizing the characteristic length of materials to the nanoscale has a significant impact on materials behavior and properties. Of particular interest to this work is the effect of the nanoscale on the mechanical behavior of nanoparticles, as well as how the nanoscale environment influences the nucleation and motion of crystalline defects, in particular dislocations. To address this issue, in-situ phase contrast transmission electron microscopy (TEM) nanocompression experiments have been performed on 20nm silver nanoparticles. High-resolution TEM images show the appearance of dislocations within the nanoparticle during deformation. Interestingly, the particle appears to be dislocation free both before and after deformation. An explanation for this behavior is presented, as well as the implications of this experiment to the greater field of nanoindentation in discussed.
9:00 PM - NN3.8
Nanomanipulation and Accurate Electrical Testing of Individual Gold Nanowires Studied by Nanomanipulators In-situ SEM.
Yong Peng 1 2 , Guenter Moebus 1 , Tony Cullis 2 , Beverley Inkson 1
1 Engineering Materials, University of Sheffield, Sheffield United Kingdom, 2 Department of Electronic and Electrical Engineering, University of Sheffield, Sheffield United Kingdom
Show Abstract
Symposium Organizers
Suneel Kodambaka University of California-Los Angeles
Guus Rijnders University of Twente
Amanda Petford-Long Argonne National Laboratory
Andrew Minor Lawrence Berkeley National Laboratory
Stig Helveg Haldor Topsoe A/S
Alexander Ziegler Max-Planck Institute for Biochemistry
NN4: Nucleation, Growth and Coarsening Kinetics of Nanostructures
Session Chairs
Stig Helveg
Suneel Kodambaka
Tuesday AM, December 02, 2008
Room 102 (Hynes)
9:15 AM - NN4.2
Thermal Stability of TiO2 Nanoparticles with Controlled Size and Shape:in-situ Studies by XRD and TEM.
Celine Perego 1 , Renaud Revel 1 , Olivier Durupthy 2 3 , Sophie Cassaignon 2 3 , Jean-Pierre Jolivet 2 3
1 , IFP-Lyon, 69360, Solaize France, 2 , UPMC Univ Paris 06, UMR 7574, Laboratoire de Chimie de la Matière Condensée de Paris, 75005, Paris France, 3 , CNRS, UMR 7574, Laboratoire de Chimie de la Matière Condensée de Paris, 75005, Paris France
Show AbstractTransition alumina are largely used as catalyst supports in refining and petrochemicals. However, titanium dioxide TiO2, was shown to display higher catalytic activity as a support of MoS2 in desulphurization process [1]. The low surface area generally obtained for these materials and the relatively poor thermal stability observed restrain their use. Therefore, the synthesis of smaller particles (10-100 nm) and the preservation of their size during thermal treatment should enhance catalytic performances. Indeed, these properties strongly depend on the surface properties of the support, which are closely related to the structure, the size and the shape of particles [2].We present in-situ studies of thermal stability of TiO2 nanoparticles. Those particles are pure phases of TiO2 (anatase, brookite and rutile) with controlled size and morphology [3-5]. For each pure polymorph, several morphologies in nanometric scale have been considered. The thermal stability of these particles, depending of their structure, size and shape, and specific adsorption of ions was studied. We show by in-situ XRD, that the evolution of nanoparticles size and the temperature of phase transition depend not only on the initial structure6, but also on the morphology and the nature of adsorbed species. Another promising result show the impact of the gas atmosphere during sintering on the particles size. The use of a nitrogen atmosphere during anatase sintering leads to much bigger rutile particles after phase transition. Crystal growth mechanisms were investigated through in-situ TEM, and also TDA/TGA, XRD, and HRTEM.[1] Ramirez, J.; Fuentes, S.; Diaz, G.; Vrinat, M.; Breysse, M.; Lacroix, M. Appl. Catal. 1989, 52 (1), 211-224.[2] Dzwigaj, S.; Arrouvel, C.; Breysse, M.; Geantet, C.; Inoue, S.; Toulhoat, H.; Raybaud, P. J. Catal. 2005, 236 (2), 245-250.[3] Cassaignon, S.; Koelsch, M.; Jolivet, J. P. J. Phys. Chem. Solids 2007, 68 (5-6), 695-700.[4] Durupthy, O.; Bill, J.; Aldinger, F. Crystal Growth & Design 2007, 7 (12), 2696-2704.[5] Pottier, A.; Chaneac, C.; Tronc, E.; Mazerolles, L.; Jolivet, J. P. J. Mater. Chem. 2001, 11 (4), 1116-1121.[6] Zhang, H. Z.; Banfield, J. F. J. Phys. Chem. B 2000, 104 (15), 3481-3487.
9:30 AM - NN4.3
In-situ TEM Sintering of FCC Nanoparticles.
Michael Asoro 1 , Desiderio Kovar 1 , Paulo Ferreira 1
1 Materials Science and Engineering, University of Texas at Austin, Austin, Texas, United States
Show AbstractNanoparticles are currently of great scientific interest due to their large number of possible applications - such as catalysts in fuel cells and as delivery vehicles for medicine. However, because nanoparticles have a high surface curvature when compared with larger particles, there is a much larger driving force for diffusion. As a consequence, sintering can take place over shorter time scales, even at room temperature. In this context, the objective of this work is to investigate the mechanisms of sintering in nanoparticles at temperatures slightly above ambient. In-situ transmission electron microscopy (TEM) heating experiments on silver nanoparticles are performed at 100°C so that the sintering process could be observed in real time. We observe a large increase in neck radius and a small reduction in inter-particle distance, suggesting that surface diffusion is the dominant sintering mechanism in FCC metals. The surface diffusion kinetics are calculated from the observed changes in nanoparticles morphology.
9:45 AM - NN4.4
Atomic Scale Real Time Observation of Iridium Cluster Formation on MgO Surface from Mononuclear Ir(C2H4)2 Complexes by Transmission Electron Microscopy.
Volkan Ortalan 1 , Alper Uzun 1 , Bruce C. Gates 1 , Nigel D. Browning 1 2
1 Chemical Engineering and Materials Science, University of California-Davis, Davis, California, United States, 2 Chemistry, Materials and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, California, United States
Show Abstract10:00 AM - NN4.5
Reduction of Oxide Islands on Metal Surfaces Investigated by In-situ UHV TEM.
Guangwen Zhou 1 2 , Weiying Dai 3 , Judith Yang 4
1 Mechanical Engineering, State University of New York at Binghamton, Binghamton, New York, United States, 2 & Multidisciplinary Program in Materials Science and Engineering, State University of New York at Binghamton, Binghamton, New York, United States, 3 MR Physics Center, Department of Radiology, Harvard University , Boston, Massachusetts, United States, 4 Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
Show AbstractThe reduction of metal oxides plays critical roles in many fields including materials science, microelectronics, and chemical applications. While the reaction equation is simple, many aspects of the reaction still remain poorly understood. Traditionally, the reduction process has been described using phenomenological kinetic models (e.g., “nucleation and growth model” and “interface model”) where the reduced oxide nucleates and grows on the surface of the parent oxide. Although these models have been found useful in the description of the reduction processes of bulk oxides, here we show using in situ UHV-TEM that they do not apply to the reduction of oxide nanoislands on metal surfaces. Our in situ TEM observations reveal that the reduction of Cu2O islands on Cu(100) follows a linear shrinkage behavior and the reduced phase (e.g., Cu) nucleates and grows on the substrate surface surrounding the reducing Cu2O islands, rather than on the parent oxide; this is fundamentally different from the assumption by the traditional phenomenological models. The reduction of these oxide islands leads to the formation of surface craters. Our Monte Carlo simulations reveal that the growth of the crater rim is controlled by the homoepitaxial growth of Cu adatoms decomposed along the perimeter of reducing Cu2O islands.[1] G.W. Zhou, W. Dai, J.C. Yang, Phys. Rev. B. 77, 245427 (2008) [2] G.W. Zhou, J.C. Yang, Phys. Rev. Lett. 93, 226101 (2004)
10:15 AM - NN4.6
In Situ Transmission Electron Microscopy Studies of the Kinetics of Carbothermal Synthesis of Titanium Carbide.
Marta Pozuelo 1 , Xiaofeng Zhang 2 , Jeung Park 1 , Rasit Koc 3 , Suneel Kodambaka 1
1 Materials Science and Engineering, University of California Los Angeles, Los Angeles, California, United States, 2 , Hitachi High Technologies America, Inc., Pleasanton, California, United States, 3 Mechanical Engineering, Southern Illinois University , Carbondale, Illinois, United States
Show AbstractTitanium carbide (TiC) has a wide variety of applications in the areas of catalysis, structural reinforcements, and hard wear- and oxidation-resistant coatings due to its extremely good properties such as high melting temperature, high hardness, excellent oxidation resistance, low thermal expansion coefficient, high wear resistance and light weight. One of the most commonly used methods for TiC production is carbothermal reduction of TiO2 at elevated temperatures (>1200 °C). This reduction reaction is suggested to occur via successive formation of lower oxides of titanium along with the emission of CO and CO2 gases. However, the exact details of the reaction kinetics, which control the final particle size, shape, and crystal structure are largely unknown. In situ lattice-resolution transmission electron microscopy (TEM) allows direct observation of the changes in particle shapes and sizes, their crystallinity, and chemical composition. Here, we present in situ TEM studies of the chemical reaction pathways and mass transport mechanisms underlying the carbothermal reduction synthesis of TiC. First, C-coated titania particles are prepared by pyrolysis of propylene (C3H6) gas in an oxygen-free environment at ~ 600 °C in a tube furnace filled with titania powders (average size ~ 20 nm). This process resulted in a uniform coating of pyrolytic carbon shell (thickness ~2-5 nm) around individual oxide particles. In situ TEM experiments are carried out at the Hitachi EM Lab in Pleasanton, California using an atomic resolution Hitachi H-9500 300 kV TEM (base pressure ~ 10-6 Torr) which allows in-situ heating in vacuum or in a gas environment. The oxide-core/C-shell nanoparticles are deposited directly onto a heating filament of the gas injection-heating TEM sample holder. Lattice-resolution TEM images are acquired at video rate (15 frames/s) while heating the particles in vacuum up to 1000 °C for times up to 5 h. Energy dispersive X-ray spectra (EDX) are obtained at room temperature from the samples before and after the annealing experiments. We find several interesting phenomena: 1) crystallization of carbon to form graphene layers preferentially on the lowest-energy planes of TiO2; 2) shrinking and eventual disappearance of the oxide cores while being encapsulated by carbon, resulting in the formation of hollow-core graphene shell structures; 3) reduction of TiO2 to lower oxides. These studies provide kinetic information and atomic-scale insights into the early stage carbothermal reduction process leading to the synthesis of TiC particles.
10:45 AM - **NN4.7
Gas-Induced Transformations in the Synthesis and Evolution of Catalytic Nanomaterials.
Peter Crozier 1
1 School of Materials, Arizona State University, Tempe, Arizona, United States
Show AbstractCatalytically active nanomaterials play a critically important role in modern technology significantly impacting areas such as energy production as well as pharmaceuticals, chemicals, and materials synthesis. Heterogeneous catalysis relies on the unique ability of highly dispersed forms of material to direct chemical transformations. However, the “active form” of the material may exist only inside a reactor where gas induced changes in the nanostructure of the catalyst such as phase transformation, shape changes and surface reconstructions may take place. Nanoscale characterizing of the composition, bonding and structure of the active form of the material is necessary to develop a deep understanding of the structure-property relations for heterogeneous catalysts. We are using in situ environmental transmission electron microscopy (ETEM) to study fundamental questions associated with the synthesis and evolution of catalytic nanomaterials under reactive gas conditions. The ability to perform atomic resolution imaging and nanospectroscopy in a reactive gas environment allows us to explore dynamic variations in the nanostructure and chemistry high surface area catalytic materials. This presentation will focus on the application of ETEM to supported metal and oxide catalysts. The nucleation and growth processes taking place during the synthesis of bimetallic nanoparticles on high surface-area oxide supports will be discussed (RuCo/Al2O3, NiCu/TiO2) [1-3]. Recent work on cerium-based oxide (CeO2 and ZrxCe1-xO2) demonstrates that the activity of individual nanoparticles can be measured and compared [4-6]. References[1] P. Li et al, J. Chem. Phys. B, 109, (2005), 13883.[2] P. Li et al, Surf. Sci., 600 (2006), 693.[3] P. Li, et al, Appl. Catal. A, 307(2006) 212.[4] R. Sharma et al, Phil. Mag. 84, (2004), 2731.[5] R. Wang et al, J. Phys. Chem B, 110 (2006) 18278.[6] R. Wang et al, Nanoletters, 8(3), (2008) 962.
11:15 AM - NN4.8
Environmental Electron Microscopy of the Nucleation and Growth of Si and Ge Nanowires.
Stephan Hofmann 1 , Renu Sharma 2 , Tobias Wirth 1 , Caterina Ducati 3 , Takeshi Kasama 3 , Rafal Dunin-Borkowski 4 , Peter Bennett 5 , Jeff Drucker 5 , John Robertson 1
1 Dep. of Engineering, University of Cambridge, Cambridge United Kingdom, 2 LeRoy Eyring Center for Solid State Science, Arizona State University, Tempe, Arizona, United States, 3 Dep. of Materials Science and Metallurgy, University of Cambridge, Cambridge United Kingdom, 4 Center for Electron Nanoscopy, TU Denmark, Lyngby Denmark, 5 Department of Physics, Arizona State University, Tempe, Arizona, United States
Show AbstractSilicon and germanium nanowires could be important constituents of future nano-electronic devices. These applications require greater control of the growth process and if possible the use of catalysts other than gold. We present a video-rate environmental transmission electron microscopy study of Si nanowire nucleation from Pd [1] and Ni under disilane exposure. The Pd and Ni catalyst films form silicide particles, which remain solid during nanowire nucleation and growth. A Si crystal nucleus forms by phase separation, as observed for the liquid Au–Si system, which we use as a comparative benchmark. The dominant coherent Pd silicide/Si growth interface subsequently advances by lateral propagation of ledges, driven by catalytic dissociation of disilane and coupled Pd and Si diffusion. We compare these catalyst interface dynamics to Ge nanowire growth from digermane.[1] S Hofmann et al, Nature Materials 7, 372 (2008)
11:30 AM - **NN4.9
Materials Interactions During the Growth of Heterostructure Nanowires.
Frances Ross 1
1 TJ Watson Research Center, IBM Research Division, Yorktown Heights, New York, United States
Show AbstractSemiconductor nanowires formed via the vapour-liquid-solid mechanism have a wide variety of technological applications, but many of the most exciting electronic device possibilities require the growth of heterostructures, where for example the wire composition changes along its length. Creating such heterostructures permits an extensive variety of interactions between the different materials in the wire and the catalyst itself. In this talk we focus on the use of in situ microscopy to unravel some of these interactions. We will discuss two cases of particular technological interest: the growth of “hybrid” nanowires, which contain segments of group IV and group III-V materials, and the formation of III-V nanowires on Si substrates. We show that certain materials pairs, such as GaP and Si, can be grown in the same nanowire using the same Au catalyst, and we present real-time observations, made using UHV-TEM, of the changes in composition and structure of catalysts on III-V wires as the second material, Si or Ge, is introduced. In situ observations allow us to characterize surface and interface reactions and measure parameters such as the critical supersaturation for nucleation of the second material. By visualizing the morphology of the second material as it grows, in situ observations also allow us to understand the overall morphology of the resulting wire, in particular whether it is straight or kinked, leading to the exciting possibility of growing interleaved segments of group IV and III-V semiconductors for electronic and optoelectronic applications. For III-V nanowires grown on Si substrates, we show that interactions between components of the wire, such as In, and the Au catalyst, can strongly influence the catalyst stability and hence the overall wire morphology in terms of tapering and growth rate. The mechanism of this effect is a change in the surface diffusion of Au on Si due to alloying, suggesting ways to control nanowire structure. These examples barely scratch the surface of the rich variety of materials interactions in play during nanowire growth, and it is clear that in situ observations are essential to understanding and controlling the formation of complex nanowire structures for applications.
12:00 PM - **NN4.10
Kinetics of Nano Silicide Formation in Nano Si Wires.
King-Ning Tu 1 , Kuo-Chang Lu 1 , Yi-Chia Chou 1
1 , University of California at Los Angeles, Los Angeles, California, United States
Show AbstractWhen two nanowires cross each other, they form a point contact. Point contact reaction between a nano metal wire and a nano Si wire has been studied by using ultra-high vacuum and high resolution transmission electron microscopy. Axel epitaxial growth of nano-silicdes of NiSi and CoSi2 in nanowires of Si has been observed. Due to the potential application of axel hetero-structure of silicide/Si/silicide as biosensor, we have been able to control the length of the nanogap of Si between the two silicide electrodes down to 2 nm. The nucleation stage and stepwise growth stage of the reactive epitaxial growth of nano silicide on nano Si have been measured. A repeating event of nucleation has been observed, which may enable us to estimate the number of atoms in a critical nucleus and the Zeldovich factor. A supply-controlled growth mode of point contact reactions in nanowires is assumed, which is different from the well-known diffusion-controlled and interfacial-reaction-controlled mode of growth in thin film and bulk reactions.
12:30 PM - NN4.11
In-situ TEM Observation of Repeating Events of Nucleation in Epitaxial Growth of Nano CoSi2 in Nanowires of Si.
Yi-Chia Chou 1 , King-Ning Tu 1 , Wen-Wei Wu 2 , Lih-Juann Chen 2
1 Materials Science and Engineering, University of California, Los Angeles, Los Angeles, California, United States, 2 Materials Science and Engineering, National Tsing Hua University, Hsinchu Taiwan
Show AbstractThe formation of CoSi and CoSi2 in Si nanowires at 700 °C and 800 °C, respectively, by point contact reactions between Co and Si nanowires have been investigated in situ in a ultrahigh vacuum high-resolution transmission electron microscope. The CoSi2 has undergone an axial epitaxial growth in the Si nanowire and a stepwise growth mode was found. We observed that the stepwise growth occurs repeatedly in the form of an atomic step sweeping across the CoSi2/Si interface. It appears that the growth of a new step or a new silicide layer requires an independent event of nucleation. We are able to resolve the nucleation stage and the growth stage of each layer of the epitaxial growth in video images. In the nucleation stage, the incubation period is measured, which is much longer than the period needed to grow the layer across the silicide/Si interface. So the epitaxial growth consists of a repeating nucleation and a rapid stepwise growth across the epitaxial interface. This is a general behavior of epitaxial growth in nanowires and it is also observed in NiSi formation in a Si nanowire. A discussion of the kinetics of supply-limited and source-limited reaction in nanowire case by point contact reaction is given. The axial heterostructure of CoSi2/Si/CoSi2 with sharp epitaxial interfaces has been obtained, which is promising as high performance transistors based on intrinsic Si nanowires.
12:45 PM - NN4.12
In situ Transmission Electron Microscope Study of the Nucleation and Growth of Platinum Nanocrystals in Solution.
Haimei Zheng 1 2 3 , Rachel Smith 3 , Young-wook Jun 2 3 , Chrisian Kisielowski 1 2 , Paul Alivisatos 2 3 , Ulrich Dahmen 1 2
1 National Center for Electron Microscopy, Lawrence Berkeley National Lab, Berkeley, California, United States, 2 Chemistry, University of California, Berkeley, California, United States, 3 Materials Sciences Division, Lawrence Berkeley National lab, Berkeley, California, United States
Show AbstractNN5: Ultra-Fast Microscopy and Diffraction
Session Chairs
Tuesday PM, December 02, 2008
Room 102 (Hynes)
2:30 PM - **NN5.1
Dynamic Transmission Electron Microscope: Studying Nanoscale Material Processes with Nanosecond Time Resolution and Beyond.
Thomas LaGrange 1 , Geoffery Campbell 1 , Nigel Browning 1 2 , Bryan Reed 1 , Judy Kim 1 , James Evans 1 , Mitra Taheri 1 3 , Wayne King 1
1 Chemistry Materaials and Life Sciences, Lawrence Livermore National Laboratory, Livermore, California, United States, 2 Department of Chemical Engineering and Materials Science, University of California-Davis, Davis, California, United States, 3 Department of Materials Science and Engineering, Drexel University , Philadephia, Pennsylvania, United States
Show AbstractThere have been many efforts in the past decades to improve the spatial resolution of transmission electron microscopes but little in way of improving the temporal resolution of in situ transmission electron microscopy. Most materials dynamics occur at rates much faster than can be captured with standard video rate acquisition methods. Thus, there is a need to increase temporal resolution in order to capture and understand salient features of these rapid materials processes. To meet the need for studying fast dynamics in material processes, we have constructed a nanosecond dynamic transmission electron microscope (DTEM) at Lawrence Livermore National Laboratory to improve the temporal resolution of in-situ TEM observations. The DTEM consists of a modified JEOL 2000FX transmission electron microscope that provides access for two pulsed laser beams. One laser drives the photocathode (which replaces the standard thermionic cathode) to produce the brief electron pulse. The other strikes the sample, initiating the process to be studied. A series of pump-probe experiments with varying time delays enable, for example, the reconstruction of the typical sequence of events occurring during the martensitic phase transformation. This presentation will discuss the core aspects of the DTEM instrument and how the DTEM has been used to study rapid solid-state phase transformations and chemical reactions.. Work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory and supported by the Office of Science, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, of the U.S. Department of Energy under contract No. DE-AC52-07NA27344.
3:00 PM - **NN5.2
Lights, Action, Camera: Making Movies of Molecules (and Materials) with Ultrafast Electron Diffraction.
Bradley Siwick 1
1 Departments of Physics and Chemistry, McGill University, Montreal, Quebec, Canada
Show AbstractIs it possible to obtain a real-time view of chemical reactions by fully resolving the elementary atomic motions that accompany the breaking and making of chemical bonds in the transition state region between reactant and product states? Or to make direct observations of the collective atomic motions that lead to structural phase transitions in material systems as they take place? The development of time-resolved diffraction techniques – both x-ray and electron – with ultrafast temporal resolution (< 10 ns) has recently made such experiments a reality. My talk will focus on ultrafast electron diffraction. I will describe its goals and methods as well as the technical challenges associated with the development of femtosecond electron sources. Despite these difficulties it is possible to design relatively simple pulsed electron sources that are effectively equivalent in flux to 3rd generation synchrotron sources of x-ray pulses, but 2-3 orders of magnitude better in temporal resolution. Experiments performed using such an electron source to study laser-induced solid-to-liquid phase transitions in metals will be discussed. Detailed pictures of the atomic configuration during the melting transition have been obtained in these studies – a molecular movie of sorts. I will conclude by describing one very promising way to significantly advance the current state-of-the-art that makes use of radio-frequency cavity technology; a common element in particle accelerator beamlines.
3:30 PM - NN5.3
Nanosecond Imaging in the Dynamic TEM Reveals Transient Phase Separation.
Judy Kim 1 2 , Thomas LaGrange 1 , Bryan Reed 1 , Nigel Browning 1 2 , Geoffrey Campbell 1
1 CMS, LLNL, Livermore, California, United States, 2 Chemical Engineering and Materials Science, University of California, Davis, California, United States
Show AbstractUntil recently, materials science characterization techniques have lacked the means for direct observation of sub-micron, dynamic materials processes that occur faster than the millisecond scale. Due to electron current density limitations and slow CCD readout times, Transmission Electron Microscopy (TEM) techniques that reveal nanoscale phase and morphology with real-space imaging and structure from diffraction have been limited to video-rate (~10-3 s) time-resolution.The Dynamic TEM (DTEM) has been developed [1] to address this gap in characterization capability by using a photoemitted electron pulse to probe dynamic events with “snap-shot” diffraction and imaging at 10 ns resolution. Using this capability, the moving reaction front (~10 m/s) of reactive nanolaminates is directly observed in situ. DTEM images show a transient cellular morphology in a dynamically mixing, self-propagating reaction front, revealing brief phase separation, and thus provide fundamental insights into the mechanisms driving the self-propagating high-temperature synthesis. Reactive Multilayer Foils (RMLF), also called nanostructured metastable intermolecular composites, are layers of polycrystalline reactant materials that go through exothermic, self-propagating reactions when mixing is driven by an external stimulus. Since RMLFs produce immense heat over a small surface area, they are used in application as localized heat sources for material bonding or biological neutralization. In addition, the periodic nano-construction makes RMLFs relevant for examination of in situ progression of interface-controlled diffusion.In this study, the foils undergo an exothermic self-propagating reaction as the bilayers mix to form intermetallics. This reaction front travels at a velocity of ~10 m/s and is observed directly in the DTEM for the complete progression of the material transition. By studying the transient states of these dynamic materials to identify the mechanisms that govern the rate of heat generation and transport, we can understand more about atomic diffusion between thin films and phase boundary motion for optimized engineering applications. A comparative study of varied stoichiometry in NiV/Al foils will be presented. The data reveals the variations in phase formation/separation morphology as well as highlight the relationship between foil stoichiometry and reaction front velocity. This experiment continues with foils of varied geometry and composition [2].References[1] M. R. Armstrong, et al., Ultramicroscopy 107 356-367 (2007).[2] This work performed under the auspices of the U.S. Department of Energy, Office of Basic Energy Sciences by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
3:45 PM - NN5.4
Femtosecond and Nanosecond Pulsed Laser Ignition Thresholds of Al/Pt Multilayer Foils.
Joel McDonald 1 , Eric Jones 1 , Kathryn Chinn 1 , Yoosuf Picard 3 , Steven Yalisove 2 , David Adams 1
1 Thin Films, Vacuum, and Packaging, Sandia National Labs, Albuquerque, New Mexico, United States, 3 , Naval Research Lab, Washinton, District of Columbia, United States, 2 Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States
Show Abstract4:30 PM - NN5.5
In-situ Analysis and Characterization of Morphology Evolution During Reaction of Energetic Co/Al Multilayer Foils.
Joel McDonald 1 , Eric Jones 1 , Kathryn Chinn 1 , Michael Hobbs 1 , David Adams 1
1 , Sandia National Labs, Albuquerque, New Mexico, United States
Show Abstract4:45 PM - NN5.6
In Situ X-ray Icrodiffraction with Microsecond Temporal Resolution of Phase Transformations in Rapidly Propogating Exothermic Reactions in Nanoscale Multilayers.
Jonathan Trenkle 1 , Lucas Koerner 3 , Mark Tate 3 , Sol Gruner 3 4 , Timothy Weihs 2 , Todd Hufnagel 2
1 Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 Physics, Cornell University, Ithaca, New York, United States, 4 Cornell High Energy Synchrotron Source, Cornell University, Ithaca, New York, United States, 2 Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland, United States
Show AbstractReactive multilayer foils are comprised of alternating nanoscale layers of materials that can sustain a self-propagating exothermic reaction. Depending on the foil architecture, the reaction can reach temperatures in excess of 1500 K in microseconds, making reactive foils attractive for use in several applications including ignition sources and joining heat-sensitive materials. From a scientific perspective, these materials provide an opportunity to study phase transformations in the presence of high heating rates and steep concentration gradients. In situ characterization of processes in the reaction zone however is challenging, requiring both temporal resolution better than ∼100 μs (the time required for the reaction front to pass a fixed location) and spatial resolution of <100 μm (the approximate width of the reaction zone).We have successfully used synchrotron x-ray radiation and a pixel array detector at the Cornell High Energy Synchrotron Source to study phase evolution in situ during self-propagating reactions in Al/Ni and Zr/Ni reactive multilayers. The temporal resolution (∼50 μs) and spatial resolution (∼60 μm) of the measurements was sufficient to allow us to observe the phase transformation sequence in detail, identifying key transformations in the development of the final structure. For example, in Al/Ni foils with overall composition Al3Ni2 and a heating rate ~106 K s-1, all of the Al and Ni is consumed within the first 200 μs of the reaction to form an Al-rich amorphous phase, which we predict is liquid, and cubic AlNi. The only other reaction occurs some 38 ms later during cooling when the equilibrium Al3Ni2 phase forms in a peritectic reaction. Similar results are observed for Al/Ni foils with overall composition AlNi.These results differ significantly from those observed in these foils at slower heating rates (~1 K s-1) where intermediate, metastable crystalline phases (Al9Ni2 and Al3Ni) form prior to final equilibrium phase formation. The in situ results for the Al/Ni systems thus provide a more accurate picture of the phase progression in self-propagating reactions in Al/Ni. In the case of Zr/Ni reactive foils, however, the first phase to form in a self-propagating reaction (with a heating rate of ~105 K s-1) and during annealing at slower heating rates (~1 K s-1) is a solid amorphous phase.
5:00 PM - NN5.7
Solving the Structure of Reaction Intermediates by Time-Resolved X-ray Absorption Spectroscopy.
Qi Wang 1 , Anatoly Frenkel 1 , Jonathan Hanson 2
1 Department of Physics, Yeshiva University, New York, New York, United States, 2 Chemistry Department, Brookhaven National Laboratory, Upton, New York, United States
Show AbstractA robust data analysis method of time-resolved x-ray absorption spectroscopy (TR-XAS) experiments suitable for chemical speciation and structure determination of reaction intermediates is presented. In this method, principal component analysis (PCA) is performed on the in-situ time-resolved x-ray absorption near-edge structure (TR-XANES) data of the reaction to achieve chemical specification and thus isolate the reaction intermediate. Then theoretical modeling by using FEFF6 is applied to the corresponding extended x-ray absorption fine-structure (EXAFS) data of the selected intermediate to determine its local structure. The method will be illustrated by using the reduction and re-oxidation reactions of Cu-doped Ceria catalysts where we detected reaction intermediates and measured fine details of the reaction kinetics. The approach can be directly adapted to many in-situ, real-time, x-ray spectroscopy experiments where new rapid throughput data collection and analysis methods are needed.AIF and QW acknowledge the U.S. Department of Energy (DOE-BES Catalysis Science) grant No. DE-FG02-03ER15476) for financial support of this work. The research carried out at BNL was financed through contract DE-AC02-98CH10886 with the US Dept. of Energy (Division of Chemical Sciences).
5:15 PM - NN5.8
In Situ Electron Transfer Studies of Rigid, Ruthenium Complexes Inducing Aggregation of Spherical Nanoparticles.
Natalie Herring 1 , Jordan Poler 1
1 Chemistry, University of North Carolina Charlotte, Charlotte , North Carolina, United States
Show AbstractUnderstanding nanoparticle aggregation is important for achieving long-range control over aggregating nanoparticles; this may provide the ability to direct self-assembly of nanoparticles for use in devices. In solution, coordination complexes act as coagulating agent and induce nanoparticle aggregation. Current studies focus on inducing flocculation of gold colloids using large, rigid, dendritic ruthenium coordination complexes. Dynamic light scattering (DLS) and absorption spectroscopy are being implemented to gain an understanding of in situ interactions of spherical nanoparticles in the presence of coordination complexes. DLS follows the effective hydrodynamic diameter of aggregating colloids and provides size distribution of aqueous solutions. DLS and absorption spectroscopy monitor in situ aggregation rates as a function of coagulant concentration; these methods describe aggregation kinetics and are used to determine the critical coagulation concentration. Conversely, absorption spectroscopy monitors the change in gold colloids’ optical properties, mainly, the surface plasmon absorption band, which is size dependent. Preliminary results yield novel spectra that are inconsistent with electrolyte induced aggregation, indicating charge transfer. Furthermore, scanning electron microscopy (SEM) and atomic force microscopy (AFM) are being utilized to examine the aggregate structure and morphology. Combining these methods provides information on the evolution of nanometer-sized particles into micrometer-sized aggregates for time scales that vary from microseconds to thousands of seconds. Characterization results demonstrate potential for controlling nanoparticles and will likely provide new opportunities for direct 3D manufacturing of nanoscale devices.
5:30 PM - NN5.9
In situ Time-Resolved X-ray Diffraction and X-ray Absorption Spectroscopy Studies of an Industrial Cu,Cr-Fe2O3 Catalyst for the Water-Gas Shift Reaction.
Daniela Zanchet 1 , Daniela Oliveira 1 , Cristiane Rodella 1 , Marco Logli 3 , Valeria Vicentini 3 , Wen Wen 2 , Jonathan Hanson 2 , José Rodriguez 2
1 Scientific Department, LNLS -Brazilian Synchrotron Light Laboratory, Campinas, São Paulo, Brazil, 3 , Oxiteno S.A. Ind. & Com., Mauá, São Paulo, Brazil, 2 Chemistry Department, Brookhaven National Laboratory, Upton, New York, United States
Show AbstractThe water gas shift (WGS) reaction, where CO and steam are converted to CO2 and H2, is an important step in several industrial processes since it removes the residual CO that acts as poison for fuel cells and maximizes the production of H2. In industrial operations, the WGS is carried out in two stages, known as HTS (High Temperature Shift) reaction (350-450°C) and LTS (Low Temperature Shift) reaction (200-250°C). The most common industrial HTS catalyst is commercialized as hematite (alfa-Fe2O3), promoted with chromium and copper. It is converted in-situ to magnetite (Fe3O4) during the activation process, the active phase in the HTS reaction. A careful control of the reducing conditions and temperature during activation and operation of the catalyst is required, to avoid the formation of metallic iron and maximize its performance. In this work, we address the activation and performance in isothermal operation of an industrial HTS (Cu,Cr-Fe2O3) catalyst by in situ time-resolved X-ray diffraction (TR-XRD) and X-ray Absorption Spectroscopy (TR-XAFS). In these experiments, the evolution of the crystalline structure and electronic state of the catalyst under WGS reaction conditions were followed, at the same time that its catalytic activity was measured. Complementary ex-situ data were obtained by X Ray Photoelectron Spectroscopy (XPS) and transmission electron microscopy (TEM). For comparison, samples of pure hematite (Fe2O3) and hematite promoted only with Cr (Cr-Fe2O3) were also studied. We show that the catalytic activities in the case of Fe2O3 and Cr-Fe2O3 catalysts are related to the Fe2O3 -> Fe3O4 transformation and that the presence of Cr delays this phase transition. In the case of the industrial Cu,Cr-Fe2O3 catalyst, however, the presence of Cu has a major effect, and strongly increases the catalytic activity, even before the full transformation to Fe3O4. The smaller Fe3O4 crystalline domains, detected by TR-XRD in the case of the HTS industrial catalyst, should also contribute to make it the most active catalyst. In-situ TR-XAFS gave complementary information about the changes of Fe, Cr and Cu environments during the activation process. While changes in Cr and Fe environments were detected at similar temperatures, above 300°C, Cu suffers major modification at much lower temperatures, segregating as metallic nanoparticles below 300°C. The formation of this metallic Cu matches the increase of the activity at low temperatures and contributes to the highest catalytic activity of Cu,Cr-Fe2O3 catalyst, compared to Fe2O3 and Cr-Fe2O3 ones. This is an important information revealed by in-situ time-resolved experiments since most of the works about industrial HTS catalysts target the iron oxide phase. It is clear that the Cu plays an important role and optimization of the activation process and performance requires a better understanding about the factors that affects the segregation of the metallic Cu phase.
5:45 PM - NN5.10
Carrier Behavior in a Quantum-confined Material Under High Applied Pressures: Fundamental Insights.
Jeffrey Pietryga 1 , Kirill Zhuravlev 2 , Victor Klimov 1 , Richard Schaller 1
1 Chemistry Division, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 2 Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, United States
Show AbstractSemiconductor nanocrystal quantum dots (NQDs) are the subject of intensive research because of their unique optical and electronic properties. These properties can differ markedly from those of the corresponding bulk material, but often arise from a combination of both bulk and size-dependent contributions. In fact, many key, fundamental aspects of even the most well-studied NQD systems remain largely theoretical, as strong assertions regarding this interplay between material and confinement effects lack definitive experimental verification even after 15 years of research. This disconnect ultimately limits the rational design of next-generation NQD-based devices, particularly those that strive to take advantage of phenomena unique to NQDs such as carrier multiplication.In this presentation, we describe the use of applied hydrostatic pressure as a powerful tool for studying and decoupling these co-emergent properties in infrared-emitting lead selenide NQDs. In an unprecedented set of correlated experiments, we combine diamond anvil cell techniques, synchrotron x-ray diffraction, and both static and ultra-fast spectroscopy to arrive at new and exciting conclusions about the behavior of excited carriers in this highly relevant material.
NN6: Poster Session
Session Chairs
Wednesday AM, December 03, 2008
Exhibition Hall D (Hynes)
9:00 PM - NN6.1
The Initial Oxidation Behavior of CuNi Alloys Observed by in Situ UHV-TEM.
Zhuoqun Li 1 , Judith Yang 1
1 Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
Show Abstract9:00 PM - NN6.10
Scanning X-ray Diffraction with 200 nm Spatial Resolution.
Michael Hanke 1 , Martin Dubslaff 1 , Martin Schmidbauer 2 , Torsten Boeck 2 , Sebastian Schoeder 3 , Manfred Burghammer 3 , Christian Riekel 3 , Jens Patommel 4 , Christian Schroer 4
1 Institute of Physics, Martin-Luther-University Halle-Wittenberg, Halle /Saale Germany, 2 , Institute of Crystal Growth, Berlin Germany, 3 , European Synchrotron Radiation Facility, Grenoble France, 4 , Technical University Dresden, Dresden Germany
Show Abstract9:00 PM - NN6.12
Three-Dimensional X-ray Imaging of Neurons in Brain
Jin Kyoung Kim 1 , So Eun Chang 1 , Im Joo Rhyu 2 , Kyoung Tai Kim 1 , Jung Ho Je 1
1 , POSTECH, PoHang Korea (the Republic of), 2 , Korea University, Seoul Korea (the Republic of)
Show AbstractThree-dimensional (3D) visualization of soft complex structures is a longstanding challenge of broad scientific interest (1). Recent technological advances need a better collaboration between material scientists and biologists to make a significant breakthrough for imaging of brain (neuron imaging) (2). Neurons are characterized by distinct dendritic morphologies that underlie specific functional properties of the cell. Many neuroscientists are interested in observing neuronal structure in detail. Most of neuronal imaging techniques which are currently applicable, despite well established, are still placed in limitations. For instance, computed tomography (CT) or magnetic resonance imaging (MRI) is unable to detect fine micron-structure in spite of providing better quality of images than conventional radiology. Meanwhile light or electron microscopy mostly provides not only narrow field of view but also 2D information of neurons that are present in thin-section of brain slice.To overcome the limitations, we develop a novel technique of X-ray microscopy (3) using coherent synchrotron X-rays that enables to observe neuronal structure from whole cerebellar structure to high–order dendrites of neurons with submicron resolution in mouse brain (4, 5). Just by combining the new technique of synchrotron X-ray microscopy and the well-established technique of Golgi-staining method, we are able to resolve effectively down to high-order dendrites structure. Based on 3D microtomographs of neurons, we quantitatively analyze their morphologies using segmentation, skeletonization, and 3D Sholl analysis (6). In particular we focus on Purkinje and Golgi cells that are two of representative neurons in the cerebellum. These quantitative results might provide a criterion for a quantitative study of neuronal microstructure in the cerebellum.References: (1) F. Lopez-Munoz, et al. Brain Res. Bull. 70, 391 (2006).(2) R. Wingat, et al. Nature Rev. Neurosci. 7, 745 (2006).(3) Y. Hwu, et al. J. Phys. D 35, R105 (2002).(4) R. V. Sillitoe, et al. Annu. Rev. Cell Dev. Biol. 23, 549 (2007).(5) Roy V. Sillitoe, et al. J. Neurosci. 28, 2820 (2008).(6) D. A. Sholl, et al. J. Anatomy 87, Part 4 (1953).
9:00 PM - NN6.13
In-Situ Synchrotron and First-Principles Studies of Oxygen-Induced Surface Structures on Cu (001).
Dillon Fong 1 , H. Iddir 1 , G. Zhou 1 , P. Fuoss 1 , P. Baldo 1 , P. Zapol 1 , J. Eastman 1
1 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractThe key to determining the role of oxygen in processes like oxidation, corrosion, and heterogeneous catalysis is in understanding the dynamic interaction between oxygen and metal surfaces. This insight can facilitate the development of greatly enhanced catalysts for reactions like the water gas shift; here improved copper-based catalysts could significantly lower the reaction temperature necessary for hydrogen production. In this study, we investigate the interaction between oxygen and Cu (001) surfaces through a combination of in-situ synchrotron x-ray scattering and density functional theory (DFT) calculations. We find that oxygen adsorption at temperatures above 473 K creates a c(2×2) oxygen layer atop a ¾-filled Cu plane that displays significant outward relaxation. At temperatures below 473 K, the vacancies within the topmost Cu plane undergo a two-dimensional order-disorder transition, forming a (2√2×√2)R45° reconstruction [1]. We will also describe surface stress-induced lattice constant variations in the c(2×2)-O adsorbate islands, the lattice mismatch scaling inversely with island size. These structural results will be compared with measurements of the adsorbate-induced surface stress by the crystal curvature technique and DFT calculations of the surface structure and surface stress, thereby allowing direct insight into the elastic properties of metal surfaces. This work is supported by the U.S. Department of Energy under Contract No. DE-AC02-06CH11357.[1] H. Iddir et al., Phys. Rev. B 76, 241404(R) (2007).
9:00 PM - NN6.14
Investigation of the Morphology of Nanoporous Silicon by Time-resolved Measurement of Changes to the Porosity during Dissolution.
Bernhard Goller 1 , Gazi Aliev 1 , Dmitry Kovalev 1 , Paul Snow 1
1 Physics, University of Bath, Bath, Somerset, United Kingdom
Show AbstractInformation about the morphology of the nanostructured pores in porous silicon can be obtained by a time-resolved measurement of the change in volume fraction of silicon during dissolution in hydrogen fluoride solution. The change of volume fraction (porosity) of the porous layers has been measured in-situ by monitoring the change in the optical density of a porous layer over a 30 hour period. Optical density has been found via the evaluation of interference fringes in the reflectivity spectrum. The porosity is related to effective refractive index using an effective medium approximation for dielectric constant. The porous silicon has been modelled by assuming that the microstructure can be represented as a regular foam either in the form of a regular 2D honeycomb structure of pores penetrating a solid silicon host or as open-faced cells constructed of “girders” of silicon. For the modelled time evolution during dissolution, it is assumed that the thickness of the foam walls decreases at a constant rate. In the literature, recent studies of the elastic properties of porous silicon layers prepared from heavily boron-doped crystalline silicon wafers have suggested that the dependence of the Young’s modulus on porosity is close to that shown by open-faced cellular foam whilst models for the properties of porous silicon are often based on assuming a honeycomb structure. We will present our dissolution results that are consistent with an open-faced cell model for the nanostructure.
9:00 PM - NN6.15
In-Situ Study of Material Response to Single Ion Events,
Yanwen Zhang 1 , William Weber 1
1 , Pacific Northwest National Laboratory, Richland, Washington, United States
Show AbstractKnowledge of ion-solid interactions and energy deposition during the slowing-down processes in nanomaterials is of fundamental and practical importance. When an ion penetrates a target, it experiences a number of collisions. Energetic charged particles interact with both electrons and atoms in materials. Kinetic energy transfers to atoms can result in displacement of atoms from their original sites; thereby forming atomic-scale defects in the structure. Energy transfers to the target electrons (either bound or free) produces electron-hole (e-h) pairs. Materials respond uniquely to ion energy deposition in picosecond time frame, such as production of atomic-level defects and electron-hole pairs, and associated secondary processes in nanosecond time frame, such as light emission from excitation-induced luminescence. A unique time-of-flight system has been utilized to study material response to single ion irradiation. Electronic energy loss and straggling in nanometer films is measured, which provides the capacity of a projectile to deposit energy in certain depth scale. Material response to the deposited energy is studied over a wide energy range. For semiconductors, the collected charge pulse response to single ions is measured. For scintillators, the photo emission of crystalline or polycrystalline films to single ion events is investigated, and the corresponding light yield, nonlinearity and energy resolution are used to evaluate materials performance for potential optical applications. Furthermore, ion-solid interaction leads to significant production of electron-hole pairs in the vicinity of the defects, local luminescence from the relaxation of the electron-hole pairs at defects may provide a self-excitation probe of defect production. In situ optical techniques to characterize defects and defect accumulation will be presented.
9:00 PM - NN6.16
Combined Spectroscopic Reflectometry and Spectroscopic Ellipsometry (SRSE) of Zinc Oxide (ZnO) and Strontium Titanate (STO) Thin Films.
Dionne Miller 1 , Glen Kowach 1
1 Chemistry, The City College of New York, New York, New York, United States
Show AbstractThe intense focus on the development of practical optoelectronic and photonic devices demands accurate characterization of the optical properties of the materials of interest. Some of these materials include zinc oxide (ZnO) and strontium titanate (STO). Spectroscopic reflectometry (SR) and spectroscopic ellipsometry (SE) are uniquely powerful tools for accurately characterizing the optical properties, structure and thicknesses of thin films. Combining both techniques in one measurement offers many advantages, not the least of which is reduced systematic errors from the simultaneous analysis of multiple data sets. We report for the first time, the use of SR and SE concurrently (SRSE), to successfully develop optical models, and determine the variation in refractive index, n and extinction coefficient, k above and below the band edge of ZnO, for thin films deposited on silicon and platinum substrates at various deposition temperatures to probe the morphological evolution as a function of substrate temperature during deposition. For the first time, a graded layer model is used to model the surface roughness layers to give extremely accurate fits to the data on Pt substrates.We also report the development of an optical model based on reflectometry (SR) data, for STO films deposited on silicon and platinum at various substrate temperatures. The analysis reveals an index gradient in the bulk of the STO deposited on silicon and no interface layer as reported in other publications. These models provide a more accurate description of the morphology of the film surface and the overall thickness useful for in situ measurements.
9:00 PM - NN6.17
In Situ X-ray Diffraction during Molecular-beam Epitaxy of Ge Islands on Si(001).
Takashi Hanada 1 , Osami Sakata 1 , Hiroo Tajiri 1 , Takafumi Yao 1
1 Institute for Materials Research, Tohoku University, Sendai Japan
Show Abstract9:00 PM - NN6.18
Thermal Transport Across the Gold Nanorod-Solvent Interface, an Investigation of Ligand Effects by a Pump-Probe Laser Technique.
Joshua Alper 1 , Aaron Schmidt 1 , Andy Wijaya 3 , Matteo Chiesa 1 , Gang Chen 1 , Kimberly Hamad-Schifferli 1 2
1 Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Biological Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractGold nanorods (Au NRs) are a promising material for a variety of applications due to their unique optical properties. The dependence of the optical properties on their easily tunable size and shape, along with the versatile nature of gold surface chemistry, leads to the use of Au NRs in, for example, tumor hyperthermia, drug delivery, and surface enhanced Raman spectroscopy substrates. For many of these applications heat transfer from the Au NR to the surroundings is critical. To analyze these situations, we need the thermal properties of the interface between the Au NR and the solvent. In this study, we characterize the effect of Au NR’s ligand on the nanoscale thermal transport. We determine the thermal interface conductance of a variety of ligand layers. These include hexadecyltrimethylammonium bromide (CTAB) both around and far from the critical micelle concentration, various lengths polyethylene glycol (PEG) chains, various length mercapto-carboxylic acid and, and various length mercapto-alcohols. Using a pump probe technique, we observe the small changes in the absorption of Au NRs excited by a femtosecond pulsed laser. From this, we deduce the lattice temperature as a function of time after a pump pulse. We fit a numerical model to the collected data and extract the interface characteristics of the Au NR-ligand-solvent system. We find that the ligands have a strong effect on the thermal transport, particularly in the diffusion regime (time > 300 picoseconds after the pump). The observations we make, and the conclusions we draw on the nature of ligand layers are useful in characterizing not only the thermal transport across the Au NR-solvent interface, but also in analyzing any thermal application of nanoparticles.
9:00 PM - NN6.2
In Situ Changes in Cerium Oxide Nanoparticles during Electron Irradiation.
Jonathan Winterstein 1 , Joysurya Basu 1 , C. Barry Carter 1
1 Chemical, Materials and Biomolecular Engineering, University of Connecticut, Storrs, Connecticut, United States
Show AbstractCerium oxide is important for a number of applications related to alternative methods of generating energy such as catalysis and as a fuel-cell electrolyte. Fluorite-structured oxides and other related oxides also display a high resistance to radiation damage and therefore have potential applications in technologies for producing nuclear energy. The usefulness of cerium oxide for these applications is essentially a result of how charged point defects behave in the material. In situ transmission electron microscopy (TEM) on pure and doped nanoparticles of cerium oxide with dimensions on the order of 10 nm has revealed different chemical and microstructural changes occurring during electron irradiation. Electron energy loss spectroscopy (EELS) reveals that the cerium ions can be reduced by irradiation with the beam. The kinetics of reduction vary significantly with dopant chemistry. The particles also sinter during irradiation and the sintering kinetics can be monitored directly. In addition, motion of surface atoms can be observed using high-resolution TEM. The relationship between behavior during irradiation and behavior under a more conventional driving force will be discussed.
9:00 PM - NN6.20
TEM Cross Section Research on the Interface of γ-Al2O3/NiAl Support.
Zhongfan Zhang 1 , Long Li 1 , Sergio Sanchez 2 , Qi Wang 4 , Lin-lin Wang 2 , Duane Johnson 3 , Anatoly Frenkel 4 , Ralph Nuzzo 2 , Judith Yang 1
1 Mechanical Engineering and Materials Science Department, University of Pittsburgh, Pittsburgh, Pennsylvania, United States, 2 Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 4 Department of Physics, Yeshiva University, New York, New York, United States, 3 Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Show Abstract9:00 PM - NN6.21
Uncovering the capabilities of Freeze-Fracture Electron Microscopy for Surface Science in the 21st Century.
Alex Wu 1 , Robert Lamb 2 3 , Grainne Moran 1 , Nick Roberts 1
1 School of Chemistry, University of New South Wales, Sydney, New South Wales, Australia, 2 School of Chemistry, University of Melbourne, Melbourne, Victoria, Australia, 3 , Australian Synchrotron Company Ltd, Clayton, Victoria, Australia
Show AbstractNew Presentation Date/Paper NumberTuesday, 12/2NN3.11 to NN6.21Uncovering the capabilities of Freeze-Fracture Electron Microscopy for Surface Science in the 21st Century. Alex Wu
9:00 PM - NN6.3
Nanostructure Evolution of Deposits Grown by Electron Beam Induced Deposition.
Juntao Li 1 , Milos Toth 2 , Vasiliki Tileli 1 , Kathleen Dunn 1 , Charlene Lobo 2 , Bradley Thiel 1
1 College of Nanoscale Science and Engineering, University at Albany, Albany, New York, United States, 2 , FEI Company, Hillsboro, Oregon, United States
Show AbstractEnvironmental scanning electron microscopy (ESEM) was used to fabricate tungsten-containing nanostructures by electron beam induced deposition (EBID), using WF6 precursor. High-resolution transmission electron microscopy (TEM), electron-energy-loss spectroscopy, and energy dispersive x-ray spectroscopy were used to characterize deposit nanostructure and composition. The deposits were found to consist of tungsten trioxide (WO3) nanocrystals embedded in an amorphous matrix. An extract of a mass spectrum of the precursor, were obtained during EBID using a differentially pumped mass spectrometer. The spectrum shows the presence H2O, O2, C2H5 and C2H6, which account for the formation of WO3 and the presence of C in the deposits. Under conditions of fixed electron flux, the degree of deposit crystallinity and WO3 grain size were found to increase with deposition time. These changes in nanostructure are ascribed to electron beam induced modification of the deposits occurring during EBID. Monte Carlo simulations of electron energy deposition into WO3-Si multilayers were performed to understand the changes in nanostructure with deposition. The total electron energy deposition profiles calculated as a function of depth for bulk Si, and for multilayers consisting of a WO3 overlayer on bulk Si, were simulated for WO3 thicknesses in the range of 100 to 800 nm. The energy deposition profiles during EBID of the deposits show that the energy deposited per electron per unit depth increases with the thickness of the WO3 overlayer at every point (z) inside the overlayer. Hence, the rate of electron beam induced material modification occurring during EBID is expected to increase with deposition time, consistent with the nanostructure evolution. Possible mechanisms behind the changes in nanostructure, and implications for EBID of functional materials will be discussed.
9:00 PM - NN6.4
Imaging Individual Nanowire Nucleation Events.
Bong Joong Kim 1 , J. Tersoff 2 , K. Dick 4 , C. Wen 1 , S. Kodambaka 3 , E. Stach 1 , F. Ross 2
1 Materials Science and Engineering, Purdue University, West Lafayette, Indiana, United States, 2 , IBM T. J. Watson Research Center, Yorktown Heights, New York, United States, 4 Solid State Physics, Lund University, Lund Sweden, 3 Materials Science and Engineering, University of California Los Angeles, Los Angeles, California, United States
Show AbstractWhen considering nanowires as candidates for electronic and optoelectronic elements, a high level of control over their growth is necessary to achieve a successful manufacturing process. In particular, the reliability of nucleation is a critical roadblock that limits nanowire integration. We have therefore examined nucleation in the model systems Si-Au, and here we present a quantitative analysis of both the initial transformation from solid Au to liquid eutectic and the formation of the nanowire nucleus. To model wire growth on amorphous substrates, Au is deposited onto an electron transparent SiN membrane, heated and exposed to disilane in an environmental transmission electron microscope while recording images. Video analysis shows a striking non-linearity in the growth rate of the nuclei which initially increase rapidly then slow down. We present a theoretical framework that balances the roles of supersaturation, pressure and interface energies during nucleation. Using this model we can determine the supersaturation of Si at which nucleation occurs; we show that it is surprisingly high, around 10% in a typical case. We also quantify the distribution of nucleation times in nominally identical Au particles and examine how nucleation times depend on the initial Au geometry, discussing how both effects relate to wire uniformity. The results of these studies show that it is possible to observe and analyse individual nucleation events in nanoscale systems, with results that may be relevant to the formation of nanostructures for real-world applications.
9:00 PM - NN6.5
A SWNT Synthesis Apparatus for Multivariable Analysis of Nucleation and Growth Factors.
David Liptak 1 2 , Roberto Acosta 1 3 , Benji Maruyama 1
1 Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson AFB, Ohio, United States, 2 , UES, Inc., Dayton, Ohio, United States, 3 Department of Physics, Wright State University, Dayton, Ohio, United States
Show Abstract9:00 PM - NN6.6
In Situ EELS in the Study of Dehydration of Mg(OH)2 by Electron Beam.
Nan Jiang 1 , Dong Su 1 , John Spence 1
1 Physics, Arizona State University, Tempe, Arizona, United States
Show AbstractNanocrystalline magnesium oxide MgO has attracted substantial interest for its voracious adsorbent properties due to enhanced surface areas and high surface reactivity [1, 2]. Instead of the complicated chemical synthesis or thin film deposition, nanocrystalline MgO can be obtained easily using a thermally activated dehydration process from Brucite Mg(OH)2 at about 450C [3]. During the dehydration reaction, the external shape and dimensions of Mg(OH)2 crystals was retained, while the volume of the MgO unit cell was reduced from the unit cell of Mg(OH)2, which makes MgO a porous material, with nanoscale pores. The decomposition of Mg(OH)2 also occurs in the transmission electron microscope (TEM), induced by electron irradiation [3 – 6]. Interestingly, the dehydration products of MgO in TEM have very similar morphology to that obtained by thermal methods. Their crystallographic relationship with the parent Mg(OH)2 are also similar [ref]. Therefore, it was believed that the dehydration of Mg(OH)2 in TEM was induced by the temperature rise caused by the electron beam, and the mechanisms were considered to be the same [3 – 6].Here, we report experimental observations of dehydration processes in Mg(OH)2 caused by an electron beam, using in situ electron energy-loss spectroscopy (EELS). One of the advantages of EELS over imaging and diffraction techniques is that EELS is more sensitive to the changes in local structure and chemistry. The new evidence shows that the dehydration in Mg(OH)2 using an electron beam is in fact different from that due to thermal annealing. During dehydration in Mg(OH)2, both low energy-loss spectra and the Mg L23 edge show the existence of partially oxidized Mg or O-deficient MgO in the dehydrated products, which is not seen in the thermally dehydrated MgO. Possible mechanisms of dehydration by electron beam may involve hydrogen sputtering by high-energy electrons, followed by release of O, which results in the collapse of layered Mg(OH)2 structure into MgO, accompanied by formation of partially oxidized or O-deficient MgO clusters or layers.This work is funded by the NSF DMR-0603993. The use of the facility within the Center for Solid State Science of ASU is also acknowledged.[1] R. Richards, W. F. Li, S. Decker, C. Davidson, O. Koper, V. Zaikovski, A. Volodin, T. Rieker, K. J. Klabunde, J. Am. Chem. Soc. 122, (2000) 4921. [2] A. Khaleel, P. N. Kapoor, K. J. Klabunde, Nanostruct. Mater., 12, (1999) 463. [3] R. R. Balmbra, J. S. Clunie, and J. F. Goodman, Nature (London) 209, (1966) 1083.[4] U. Dehmen, M. G. Kim, and A. W. Searcy, Ultramicroscopy 23, (1987) 365. [5] P. A. Van Aken, and F. Langenhorst, Eur. J. Mineral. 13, (2001) 329.[6] J. F. Goodman, Proc. Roy. Soc. (London) A 247, (1958) 346.
9:00 PM - NN6.8
X-Ray Microdiffraction in Conjunction with Discrete Dislocation Dynamics to Reveal Grain Boundary-dislocation Interaction Mechanisms.
Ralph Nyilas 1 , Miroslav Kobas 2 , Ralph Spolenak 1
1 Department of Materials, ETH , Zürich Switzerland, 2 , Swiss Light Source, Villingen Switzerland
Show AbstractUnderstanding the deformation mechanism of polycrystalline thin metal films on the mesoscale (0.1-10 micron) is crucial for the design and fabrication of microelectronic components. To date, the mechanical response of polycrystalline materials on the mesoscale cannot be understood adequately by continuum mechanics as it is largely determined by the discrete underlying microstructure and grain-to-grain interactions. Local submicron in situ strain and orientation measurements by X-Ray microdiffraction are the key to provide insight into the mechanism of deformation heterogeneities in polycrystalline ensembles. We conducted white beam X-Ray synchrotron microdiffraction experiments at the Swiss Light Source on thin gold films to locally map orientations and strain tensors over a polycrystalline ensemble. The gold films were in situ thermally strained over the complete strain hysterises cycle. We implemented second generation photon counting detector technology obtaining Laue microdiffraction patterns superior in the signal-to-noise ratio compared to conventional CCD detector systems. The local strain tensor and orientation maps in conjunction with a detailed peak profile analysis allowed us to reconstruct the deformation mechanism of several grains within the polycrystalline ensemble. We demonstrate a correlation between the directions of the maximum resolved shear stresses within the grain and an increase/decrease in the misorientation angle of the grain boundaries. The latter observation is interpreted as the transport of polar dislocation density between the grain boundaries. The elastic stress tensor maps show the development of a gradient in the normal and shear stress components around an individual grain prior to a shear and rotational deformation. We implement a discrete disclocation dynamics model simulating the annihilation reaction between edge dislocations emitted from the boundaries. The results suggest a supply of polar dislocation density from the surrounding grains and grain interior via the triple junction entry points to be necessary to generate the experimentally observed magnitude of rotation.
9:00 PM - NN6.9
Kinetic Studies of Initiated Chemical Vapor Deposition of Polymer Nanocoatings.
Gozde Ozaydin-Ince 1 , Karen Gleason 1
1 Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractPolymer films formed by the initiated chemical vapor deposition of vinyl monomers have applications ranging from conformal coatings of multiwall carbon nanotubes and microspheres to superhydrophobic fabrics. Copolymer film formation by including divinyl crosslinkers in the deposition process enhances mechanical properties and increases the resistance against solvents which is crucial for fabrication of air-gap structures. In this work, systematic in-situ kinetic studies of the initiated chemical vapor deposition of vinyl monomers and divinyl crosslinkers are performed and the effects of process parameters on deposition are investigated. The reactions are monitored with a gas phase FTIR (Induct 3100 Process Analyzer from MKS). Real-time quartz-crystal microbalance measurements are performed to correlate the surface adsorption to deposition rates. Tert-butyl peroxide is used as the initiator for all depositions.In-situ gas phase FTIR measurements are performed to obtain the concentrations of each chemical during the reaction. Concentrations are calculated by calibrating the carbonyl peaks of the monomers with known concentration values in ppm. Detection limit for the vinyl monomers is approximately .1 ppm.Residence time studies are performed at different reactor pressures and an optimal operating pressure of approximately 200 mTorr for a plug flow is determined. Deposition rates obtained at this operating pressure ranges from 5 nm/min to 70 nm/min for different process parameters.Studies performed at different filament temperatures, ranging from 180oC to 360oC, clearly show the kinetic and mass transfer limited regimes from which the apparent activation energies are extracted. The transition to a mass transfer limited regime is typically observed in the range of 230oC to 270oC. The separate studies of deposition rate dependence on the initiator and the monomer concentrations enable us to determine the reaction rate constant and the order of reaction. The effect of monomer flow on the deposition rate is studied for different flowrates. The overall deposition rate is then correlated to the monomer concentration on the surface by the utilization of the gas phase FTIR and the results are compared to QCM measurements which show a constant deposition rate throughout the experiments. In the final set of experiments, the effects of substrate temperature variations on the deposition rate are studied. The substrate temperature range studied is from 15oC to 45oC. The adsorption kinetics are discussed by using the relation between the substrate temperature variations and the variations in Pm/Psat values for the same flowrates.
Symposium Organizers
Suneel Kodambaka University of California-Los Angeles
Guus Rijnders University of Twente
Amanda Petford-Long Argonne National Laboratory
Andrew Minor Lawrence Berkeley National Laboratory
Stig Helveg Haldor Topsoe A/S
Alexander Ziegler Max-Planck Institute for Biochemistry
NN7: Kinetics of Phase Transformations in Nanomaterials
Session Chairs
John Cumings
Jianyu Huang
Wednesday AM, December 03, 2008
Room 102 (Hynes)
9:15 AM - NN7.1
Low-loss EFTEM Imaging of Surface Plasmon Resonances in Triangular Silver Nanoparticles.
Peter van Aken 1 , Jaysen Nelayah 1 , Lin Gu 1 , Wilfried Sigle 1 , Christoph Koch 1 , Vesna Srot 1 , Isabel Pastoriza-Santos 2 , Luis Liz-Marzan 2
1 Stuttgart Center for Electron Microscopy, Max Planck Institute for Metals Research, Stuttgart, Baden-Württemberg, Germany, 2 Departemento de Quimica Fisica, Universidade de Vigo, Vigo Spain
Show Abstract9:30 AM - NN7.2
In-situ TEM Study of Martensite Nucleation on Dislocations in Shape Memory Alloys.
Maria No 2 , Daniel Caillard 3 , Jose San Juan 1
2 Fisica Aplicada II, Universidad del Pais Vasco, Bilbao Spain, 3 CEMES, CNRS, Toulouse France, 1 Fisica Materia Condensada, Universidad del Pais Vasco, Bilbao Spain
Show Abstract9:45 AM - NN7.3
In-situ TEM Study of the Alloying Process of the Au/Ni/AuGe Ohmic Contact to n-type GaAs.
Sung-Dae Kim 1 , Dong-Su Ko 1 , Tae-Young Ahn 1 , Jung-Hun Oh 2 , Sam-Dong Kim 2 , Young-Woon Kim 1
1 Materials Science and Engineering, Seoul National University, Seoul Korea (the Republic of), 2 Millimeter-wave INnovation Technology Research Center, Dongguk University, Seoul Korea (the Republic of)
Show AbstractIn-situ hot stage transmission electron microscopy (TEM), which makes it possible to observe the microstructure changes and reactions with high spatial resolution in real time, can provide a key to understand the alloying mechanism. In this research, we developed an In-situ hot stage TEM holder which was specially designed to be fitted in the narrow gap of objective pole pieces of JEOL 2010F. To reduce the thickness of the stage tip, the insulating part of the stage tip was fabricated by a high density alumina plate. And the heating element which was made by a tungsten thin foil was inserted to the alumina plate. The heating element, insulator, and supporting mechanism were contained in the thickness of 1.0 mm. A K-type thermocouple was directly attached on a sample grid to measure the sample temperature and the TEM images were recorded in real-time streaming video using ES500 CCD camera. The cross-sectional TEM samples were prepared by the conventional sample preparation method involving grinding and polishing followed by Ar+ ion milling.Using the home-made in-situ hot stage TEM holder, we observed the microstructure change and the chemical trace of metallization element of the interlayer metal Ohmic contact to n-type GaAs system. The Au/Ni/AuGe system for Ohmic contacts to n-type GaAs has been investigated more than two decades. The detailed alloying mechanism of the system, however, is still not well understood because of the complexity of the diffusion paths and redistribution of alloying elements during alloying process. We will present the alloying process of the Au/Ni/AuGe Ohmic contact to n-type GaAs with a home-made in-situ hot-stage TEM holder, combined with chemical analysis using the X-ray energy dispersive spectroscopy (EDS).
10:00 AM - **NN7.4
Determining the Nanoscale Chemistry and Properties of Phases and Interfaces in Al-Si(-Cu-Mg) Nanoparticles Using In-situ TEM.
James Howe 1 , Santhana Eswaramoorthy 1 , Govindarajan Muralidharan 2
1 Department of MS&E, University of Virginia, Charlottesville, Virginia, United States, 2 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractThis presentation describes in-situ hot-stage transmission electron microscope (TEM) experiments performed on hypereutectic Al-Si(-Cu-Mg) nanoparticles to investigate the chemistry and properties of the three main phases: solid Si, solid Al and liquid Al-Si, as a function of temperature. Bright-field TEM imaging shows that solid Al is completely wet by the liquid and cannot nucleate heterogeneously on Si or the nanoparticle oxide, while Si nucleates heterogeneously on the oxide. The growth and dissolution behavior of the phases, particularly solid Si, was studied using the electron beam to heat and cool the nanoparticles. The faceted shape and interface kinetics observed during growth of Si are distinctly different from those found during dissolution. Because large undercoolings are required to homogeneously nucleate solid Al, it was possible to directly determine the metastable liquidus and solidus phase boundaries in the undercooled liquid Al-Si using energy-dispersive X-ray spectroscopy, in addition to the compositions across the solid Si-liquid interface. Valence-loss electron energy-loss spectroscopy was also used to study the collective behavior of the atoms in the liquid Al-Si phase as a function of temperature, also in undercooled conditions, and compared with the same behavior in pure liquid Al. These results reveal significant differences in the dependences of the volume plasmon energy and relaxation time in the Al-Si liquid compared to pure Al, providing insight into the role of Si on the behavior of the electron density and atomic volume of the liquid phase as a function of temperature. This research was supported by the National Science Foundation under Grant DMR-0554792. The ORNL part of this work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of FreedomCAR and Vehicle Technologies, Automotive Propulsion Materials Program, U.S. Department of Energy, under contract DE-AC05-00OR22725 with UT-Battelle, LLC.
11:00 AM - **NN7.5
Imaging Magnetization Dynamics.
Christian Back 1 , Korbinian Perzlmaier 1 , Ingo Neudecker 1 , Wolfgang Scheibenzuber 1 , Georg Woltersdorf 1
1 , University Regensburg, Regensburg Germany
Show Abstract11:30 AM - NN7.6
Scanning Probe Tomography Developed for Visualizing Buried Magnetic Structures.
Kenjiro Kimura 1 , Takumi Hiasa 1 , Hiroshi Onishi 1
1 Chemistry, Kobe University, Kobe Japan
Show Abstract Testing nanometer-scale magnetic structures is essential for the development of highly integrated magnetic recording devices. An excellent spatial resolution better than 5 nm has been achieved with spin-polarized scanning tunneling microscopes. This tunnel-based method is applicable only to flat, ferromagnetic surfaces. Magnetic force microscopes (MFM) are alternative testing tools for practical recording devices and actually utilized by device developers. The magnetic tip of MFM is lifted from the surface and traversed with a constant tip-surface distance. The tip-surface gap is essential to detecting the long-range magnetic force between the tip and surface. A possible cross talk with the short-range force, which reflects the surface topography, should be avoided. On the other hand, larger spacing degrades the imaging quality of MFM because magnetic potential field broaden far away from surface. Here we propose a novel method, scanning probe tomography (SPT), which is capable for remote sensing magnetic structures. The tip as potential sensor is scanned on planes over a remote magnetic object. The field strength is detected by the tip. The lateral distribution of the magnetic potential on a plane separated by a desired distance from the scanned planes is mathematically reconstructed without model-and-fit cycles. The first demonstration was done on a hard disk drive. With a scanning tip lifted by 330 nm faraway from surface passivation layer, the lateral distribution of the magnetic domains at the surface was successfully visualized. We believe that magnetic structures buried in thick passivation layers are observable by this method.
11:45 AM - NN7.7
Size-dependent Optically-induced Magnetization Dynamics in Colloidal Iron Oxide Nanocrystals.
Dong Hee Son 1
1 Chemistry, Texas A&M University, College Station, Texas, United States
Show AbstractSize dependence of the ultrafast optically-induce demagnetization and its recovery in superparamagnetic colloidal iron oxide (Fe3O4) nanocrystals were investigated via time-resolved Faraday rotation measurements. A flowing jet of colloidal solutions of spherical nanocrystals of 5-10 nm in diameter was used for the measurements. Optical excitation of metal-metal charge transfer transition at 780 nm resulted in sub-picosecond demagnetization, which recovered on multiple time scales. The time scale and magnitude of recovery were strongly dependent on the size of nanocrystals, while the static and transient absorption did not show any significant size dependence. The recovery of magnetization occurred more slowly with smaller amplitude as the size of nanocrystal increased. This observation could be explained phenomenologically in terms of size-dependent cooperativeness of spins. Since the size-dependence of the magnetization recovery could potentially be due to hot lattice with size-dependent cooling rate, we also measured the transient lattice temperature. Information on the lattice temperature of the photoexcited nanocrystals was obtained from the period of coherent acoustic phonon, which depends on the size of nanocrystal and temperature-dependent sound velocity. From the excitation fluence-dependent measurement of the coherent phonon period, initial temperature rise due to the photoexcitation was estimated. From the two-pump/probe transient absorption measurement, where the first pump heated the lattice and the time-delayed second pump generated coherent phonon, time dependence of the lattice temperature was also measured. At the excitation intensity, where size-dependent magnetization recovery was studied, the lattice temperature rise was too low to account for the observed size-dependent magnetization recovery dynamics. This indicates that the observed size-effect in magnetization recovery is directly on spin degrees of freedom.
12:00 PM - **NN7.8
Imaging Spin Dynamics of Nanomagnetic Materials with Magnetic Soft X-ray Microscopy.
Peter Fischer 1
1 Center for X ray Optics, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractModern magnetic microscopies are facing the challenge to provide both spatial resolution in the nanometer regime, a time resolution on a ps to fs scale and elemental specificity to be able to study novel multicomponent and multifunctional magnetic nanostructures and their ultrafast spin dynamics which is of both fundamental and technological interest.Magnetic soft X-ray microscopy is a very promising analytical tool since it combines X-ray magnetic circular dichroism (X-MCD) as element specific magnetic contrast mechanism with high spatial and temporal resolution. Fresnel zone plates used as X-ray optical elements provide a spatial resolution down to currently <15nm [1] thus approaching fundamental magnetic length scales such as the grain size [2] and magnetic exchange lengths. Images can be recorded in external magnetic fields giving access to study magnetization reversal phenomena on the nanoscale. Utilizing the inherent time structure of current synchrotron sources fast magnetization dynamics with 70ps time resolution, limited by the lengths of the electron bunches, can be performed with a stroboscopic pump-probe scheme [3]. In this talk examples of current research with magnetic soft X-ray microscopy will be presented with focus on current induced phenomena [4,5] and vortex dynamics in ferromagnetic elements [6,7]. Current developments of X-ray optics will soon provide less than 10nm spatial resolution and x-ray microscopy at upcoming high brilliant fsec X-ray sources makes snapshot images of fsec spin dynamics feasible.Many thanks to M.-Y.Im, B. Mesler, W.L. Chao, T. Hauet, O. Hellwig, S. Mangin, S, Kasai, A. Thiaville, G. Meier, L. Bocklage, M. Bolte. G. Portmann,.The help of the staff of CXRO and ALS is highly appreciated. This work was supported by the Director, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division, of the U.S. Department of Energy.References[1] W. Chao, et al., Nature 435, 1210, (2005); D.-H. Kim, et al., J. Appl. Phys. 99, 08H303, (2006)[2] M.-Y. Im et al, Advanced Materials 20 (2008) 1750[3] P. Fischer, et al., JMMM 310(2) pt 3 (2007) 2689[4] G. Meier et al, Phys. Rev. Lett. 98, 187202 (2007)[5] S. Kasai et al. (2008) submitted[6] B.L. Mesler et al, J. Vac Sci Techn 25(6) (2007) 2598[7] S. Kasai, A. Thiaville, M.-Y. Im, P. Fischer (2008) in preparation
12:30 PM - **NN7.9
Exploring Magnetic Nanostructures by Spin Polarized Low Energy Electron Microscopy.
Andreas Schmid 1
1 National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley , California, United States
Show AbstractMagnetic properties of materials can change in interesting ways when one prepares structures with very small sizes. Spin-polarized low- energy electron microscopy permits in-situ observation during sample growth, to reveal details of magnetic and electronic properties as a function of nanoscale sample structure. We use a spin-polarized beam of electrons to illuminate sample surfaces, and monitor spin- dependent electron reflection to form images. To show how SPLEEM can be used to study magnetic phenomena in low-dimensional systems, several examples including self-assembled magnetic nanodots and epitaxial multilayer structures will be discussed.
NN8: Low-Energy Electron and X-ray Microscopies
Session Chairs
Wednesday PM, December 03, 2008
Room 102 (Hynes)
2:30 PM - **NN8.1
In Situ Studies of Thin Film Atomic and Electronic Structure using LEEM/PEEM.
Rudolf Tromp 1
1 , IBM T.J Watson Research Center, Yorktown Heights, New York, United States
Show Abstract3:00 PM - **NN8.2
Surface and Step Evolution Driven by a Beam of Self-Ions and Observed by LEEM*R
Colin Flynn 1
1 Physics, University of Illinois, Urbana, Illinois, United States
Show AbstractWe have installed a SNICS II source of negative ions in a low energy electron microscope in order to examine the evolution of surface step structure during actual ion bombardment. Self-ions were employed in UHV in order to eliminate the effects of foreign chemical species. Here we report results for Pt- on Pt(111) for ion energies of 0-3 keV. Results are interpreted using a theory of the exact linear response to treat adatom and advacancy transport processes in the driven steady state. Four advances ar e described here:1. Perfect terraces ~ 5um in diameter are created as pans and mesas on Pt(111), by Pt- ion beam processing, each surrounded by a peripheral step bunch, to serve as experimental arenas on which transport is decoupled from surrounding surf ace features;2. The driven growth of adatom and advacancy islands nucleated near the centers of pans and mesas is examined and found to have a universal form that agrees with the prediction from theory of a non-analytical time dependance near t = 0.3. T he chemical potentials required to nucleate adatom and advacancy islands are determined, and compared to first-principles theory, by gradually increasing the irradiation flux until nucleation is seen to occur on pans or mesas; and4. The rates of ad-defec t creation deduced from island growth rates using self-ion beams are compared, as functions of ion energy, with values predicted from detailed molecular dynamics simulations for Pt- on Pt(111) of Averback et al. Theory and experiment agree within an unce rtainty ~ 10%.* With M Ondrejcek and W Sweich. Supported in part by DOE.Ç~
3:30 PM - NN8.3
In-situ Surface and Interface Characterization of Nanostructures in Materials Exposed to Particle Radiation Fields.
Jean Allain 1 , D. Rokusek 1 , Chase Taylor 1 , Martin Nieto-Perez 2 , Christopher Wagener 1
1 Nuclear Engineering, Purdue University, West Lafayette, Indiana, United States, 2 CICATA, IPN, Queretaro, Queretaro, Mexico
Show Abstract3:45 PM - NN8.4
Controlling the Kinetics of Molecular Crystal Growth by Tuning the Energy of Incident Molecules.
Aram Amassian 1 , Tushar Desai 2 , Sukwon Hong 2 , Arthur Woll 3 , Stefan Kowarik 4 , Vladimir Pozdin 1 , Detlef Smilgies 3 , Joe Goose 2 , Paulette Clancy 2 , Frank Schreiber 4 , George Malliaras 1 , James Engstrom 2
1 Materials Science and Engineering, Cornell University, Ithaca, New York, United States, 2 School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York, United States, 3 Cornell High Energy Synchrotron Source, Cornell University, Ithaca, New York, United States, 4 Institut für Angewandte Physik, Universität Tübingen, Tübingen Germany
Show AbstractThe performance of organic electronic devices is closely tied to the packing structure, morphology and interfaces in organic semiconductor thin films, which in turn are intricately linked to molecular processes operant during their assembly. Typically, vacuum sublimation/evaporation is used to fabricate ordered molecular films (e.g., pentacene). While the simplicity of thermal deposition processes makes them attractive, they provide few knobs in way of process control. Supersonic molecular beams have emerged as a way to tailor the growth of thin films from complex molecular building blocks by manipulating the state of incident molecules (e.g., kinetic energy, vibro-rotational states). Using a powerful combination of in situ real-time synchrotron X-ray scattering (time-resolved X-ray reflectivity and 2D grazing incidence X-ray diffraction), scanning probe microscopy, rate equation modeling and molecular dynamics simulations, we investigate molecular-scale processes of adsorption, soft-landing, as well as nucleation and growth of molecular crystallites during supersonic molecular beam deposition of small-molecule thin films of pentacene and diindenoperylene. Our research shows that tunable supersonic molecular beams can tailor the kinetics and growth of thin films from complex molecular building blocks, resulting in unprecedented control of the morphology of molecular thin films. These changes influence the electronic properties of organic semiconductors and offer a pathway to controlling the performance of organic electronic materials and devices.
4:30 PM - **NN8.5
3D X-ray Diffraction Microscopy and its Applications to Materials and Nano-Science.
Jianwei (John) Miao 1
1 , UCLA, Los Angeles, California, United States
Show Abstract5:00 PM - NN8.6
X-ray Imaging in Dynamic Studies on Soft Matter.
Byung Mook Weon 1 , Seung Kwon Seol 1 , Jung Ho Je 1 , Jae Mok Yi 2 , Yong Song Chu 2 , Yeukuang Hwu 3 , Giorgio Margaritondo 4
1 X-ray Imaging Center, Department of Materials Science and Engineering, Pohang University of Science and Technology, Pohang, GyungBuk, Korea (the Republic of), 2 Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois, United States, 3 Institute of Physics, Academia Sinica, Taipei Taiwan, 4 School of Basic Sciences, Ecole Polytechnique Fadarale de Lausanne, Lausanne Switzerland
Show AbstractWe apply X-ray imaging to real-time dynamic studies on a variety of soft materials. First we present three-dimensional (3D) growth of conducting polymer microstructures with high aspect ratios (HAR), based on using real-time synchrotron X-ray microradiography (1). Such structures are particularly important in a broad range of device applications in microelectronics, biomedical devices, and micro-systems such as actuators and sensors. We show several successful fabrication tests of freestanding polypyrrole (PPy) high-aspect-ratio microstructures with different shapes: straight, zigzag, and a complex geometry using real-time monitoring of localized electropolymerization of 3D PPy growth.We in turn present stable freestanding thin films of pure water by X-ray bombardment of small liquid volumes in capillary tubes (2). In spite of the strong fundamental and applied interest in water microstructure, so far, no technique was able to produce stable freestanding pure-water thin films, mostly due to rapid rupture caused by the very low viscosity and high surface tension of pure water. As a second example of soft matter, we demonstrate the first successful fabrication of stable free standing water film with a lifetime of 1h after 54 min irradiation, as illustrated by real-time microradiologies of pure water (2). The cause of the film evolved is explained by the surface tension reduction of water by X-ray irradiation (3).Finally phase contrast X-ray imaging of subcellular structures in nanometer-resolution (< 30 nm) will be demonstrated using hard X-ray microscopy with Fresnel zone plates (4). The important repercussions on materials science, nanotechnology, and life sciences will be discussed.References:(1) S. K. Seol, et al. Macromolecules 41, 3071 (2008).(2) B. M. Weon, et al. Appl. Phys. Lett. 92, 104101 (2008).(3) B. M. Weon, et al. Phys. Rev. Lett. 100, 217403 (2008).(4) Y. S. Chu, el al. Appl. Phys. Lett. 92, 103119 (2008).
5:15 PM - NN8.7
High-Temperature Synchrotron X-ray Diffraction Characterization of Three-Dimensional Strain/Stress Fields in Nanocrystalline Coatings on Steel.
Klaus Martinschitz 1 , Christoph Kirchlechner 1 , Mathias Bartosik 1 , Rostislav Daniel 2 3 , Christian Mitterer 2 3 , Keckes Jozef 1
1 Department of Materials Physics, Univeristy of Leoben, Leoben Austria, 2 Department of Physical Metallurgy and Materials Testing, University of Leoben, Leoben Austria, 3 Christian-Doppler Laboratory for Advanced Coatings, University of Leoben, Leoben Austria
Show AbstractHigh-temperature characterization of residual strains/stresses reveals thermo-mechanical phenomena contributing to the thermal fatigue of coated working tools. Since the thermal fatigue is usually a local effect, it is necessary to develop experimental approaches which can be used to characterize fatigue-induced degradation phenomena with a good spatial resolution. In this contribution, residual stresses in thermally cycled CrN nanocrystalline coatings (used as a model system) deposited on high-speed steel are characterized using high-temperature position-resolved synchrotron X-ray diffraction. In order to simulate the thermal fatigue, the CrN/steel samples were at first locally thermally cycled using a laser beam with a diameter of 1 mm in the temperature range of 50-850 °C applying up to 105 cycles. After the treatment, numerous cracks, coating rupture and surface waviness were observed.The structures were analysed at the EDDI beamline of BESSY (Berlin, Germany) and G3 beamline of Hasylab (Hamburg, Germany). In both cases, the samples were characterized in-situ in a temperature range of 25-700 °C using a heating chamber DHS1100 (Anton Paar GmbH, Graz, Austria). The measurements at the EDDI beamline using high-energy photons (20-100 keV) were used to evaluate residual stress depth gradients in the spot irradiated by the laser as a function of the penetration depth down to 80µm. In the case of the measurements at the G3 beamline, a lateral distribution of residual stresses in and around the irradiated spot was determined in 106 spots applying dedicated pollycapillary X-ray optics. Using the combined approach, it was possible to determine a three dimensional distribution of residual stresses in the irradiated spot as a function of the temperature. The room temperature measurements indicated that the laser treatment caused a relaxation of compressive stresses in the coating and a formation of high tensile stresses in the underlying substrate. Those effects were depended on the number of applied laser cycles and on the maximal heating temperature. The cracks were observed only in the samples with plastically deformed substrate. One could observe very strong gradients of residual stresses across the irradiated spot. The sample heating during the X-ray diffraction experiment resulted in a relaxation of the gradients in the coating and in the substrate. The presented approach allows a complex characterization of thermo-mechanical processes in coating-substrate composites and opens the possibility to understand phenomena related to the thermal fatigue of coated tools.This work was supported by Austrian NANO Initiative within the project "StressDesign - Development of Fundamentals for Residual Stress Design in Coated Surfaces”.
5:30 PM - NN8.8
Development of Novel In-situ High-Temperature X-ray Microprobe Techniques and Their Application to Crystalline Silicon Solar Cell Materials.
Steve Hudelson 1 3 , Sarah Bernardis 2 3 , Matthew Marcus 4 , Sirine Fakra 4 , Barry Lai 5 , Stefan Vogt 5 , Tonio Buonassisi 1 3
1 Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 Laboratory for Manufacturing and Productivity, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Materials Science, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 4 Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 5 Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractMany energy systems experience extreme conditions during processing and operation. Examples include solid oxide fuel cells, which operate in the range of 600-1000°C; nuclear and fossil fuel-fired power generation plants; and the production of crystalline silicon solar cells, which occurs at temperatures exceeding 1400°C. A limited amount of information can be obtained by studying such systems far from their operating temperature and environments. Much more helpful is the ability to characterize the systems in conditions approximating those under which they are operated. In order to improve the performance of these systems, enabling the development of abundant, sustainable energy sources for the future, we need to develop a fundamental understanding of the high temperature kinetics, in-situ, on a sub-micron scale.In this vein, we present the results of the development of a novel in-situ high temperature synchrotron-based x-ray microprobe setup. With this setup, we create the ability to heat samples to 1500°C, in a controlled ambient. This allows us to use x-ray fluorescence microscopy (μ-XRF) and x-ray absorption microspectroscopy (μ-XAS) to probe with sub-micron resolution the spatial distribution and chemical state of metal impurities in silicon during realistic processing conditions.Previous synchrotron-based μ-XRF work has shown the prominence and detrimental impact of metal impurities which form along grain boundaries in as-grown material [1]. The nano-scale structure of these precipitates has been studied, and a model for their formation via a liquid-route process has been proposed [2]. Preliminary results seem to validate this model, showing the formation of phase-segregated silicide precipitates at lower temperatures from a homogeneous phase at higher temperatures.References: [1] T. Buonassisi, A. A. Istratov, et al. Prog. Photovolt: Res. Appl. 14 (2006) 513–531.[2] T. Buonassisi, M. Heuer, et al. Acta Materialia 55 (2007) 6119–6126.
5:45 PM - NN8.9
In-situ Studies of Morphology Evolution in Polymer/clay Nanocomposites During Bi-axial Deformation.
Bilge Hatiboglu 1 , David Bucknall 1 , Yonathan Thio 1
1 Polymer, Textile and Fiber Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractThe mechanical performance of polymers is not only affected by their thermal history but is also affected by processing and deformation parameters such as the strain, strain rate and temperature. Small angle and wide angle X-ray scattering techniques (SAXS and WAXS) provide a useful insight for understanding crystallite formation and orientation of polymers as a result of deformation. We report an in-situ X-ray scattering study of the bi-axial deformation of polyolefin films. For these experiments, an in-situ multi-axial deformation device with a heating chamber has been designed and built, which allows us to mimic the deformation experienced during processing. Initial quasi-in-situ biaxial deformation tests have been performed on polyethylene films at room temperature at two different strain rates (10mm/sec and 100mm/sec). Differences in the monoclinic and orthorhombic peak intensities have been observed with increasing deformation amount. Using high flux synchrotron X-ray sources we have undertaken in-situ biaxial deformation studies of polyolefin/clay nanocomposites. In this presentation we present results on the effect of clay content, strain rate and deformation temperature on the structural evolution observed during deformation.
NN9: Poster Session
Session Chairs
Thursday AM, December 04, 2008
Exhibition Hall D (Hynes)
9:00 PM - NN9.1
Atomic Force Controlled Nanolithography with Gas Phase Reagents.
Shalom Weinberger 2 , Aaron Lewis 1 , Chaim Sukenik 2
2 Department of Chemistry, Bar-Ilan University, Ramat Gan Israel, 1 , The Hebrew University, Jerusalem Israel
Show Abstract9:00 PM - NN9.10
Extended Probe Tip Lifetime Considerations in True Non-Contact Mode AFM.
Yueming Hua 1 , Nicole Munoz 1 , Cynthia Coggins 1 , Doru Florescu 1 , Sung Park 1 , Sang-il Park 1
1 , Park Systems, Inc, Santa Clara, California, United States
Show AbstractNon-Contact mode AFM (NC-AFM) was the first dynamic mode AFM. However, because of the lack of high resonance frequency Z piezoelectric scanners and high performance controller electronics, the probe tip could not be well controlled to stay in the attractive force region, and the true non-contact scanning mode was hard to achieve. A few years later, intermittent contact mode (usually known as tapping mode) was introduced as an alternative to NC-AFM. However, since large oscillation amplitudes and stiff cantilevers have to be used in tapping mode, the striking force usually is high and the tip wears out quickly when the sample surface is hard. When imaging soft materials, the pattern can be affected by the tip and permanent defects can be introduced to the sample surface. By using high quality electronics, and re-designing the Z piezoelectric scanner architecture, we developed the true NC-AFM scanning mode. This true non-contact mode can be operated very stably in air, and works seamlessly with both hard and soft surface samples.In this paper, we report on probe tip wearing experiments conducted by utilizing the true non-contact mode. Hard and rough samples, with sharp features, were used as both the imaging sample and test sample for tip wearing evaluation. When the AFM was operated in true non-contact mode, the tip was found to preserve its sharpness after taking images over 100 times on a 1um square area of the sample. But when the AFM was operated in intermittent contact mode, we noticed severe tip damage after only 10 images on the same sample even with minimal amplitude set point. This report not only experimentally proves that true NC-AFM can be operated very well in air, but also shows that the same probe tip can be used for multiple scans without degradation, and its lifetime is much longer than when used in tapping mode. This issue is of significant importance for many nano-metrology applications.
9:00 PM - NN9.13
Local Thermomechanical Characterization of Phase Transitions in Polymers using Band Excitation Atomic Force Microscopy with Heated Probe.
Maxim Nikiforov 1 , Stephen Jesse 1 , Lou Germinario 2 , Sergei Kalinin 1
1 Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 , Eastman Chemical Company, Kingsport, Tennessee, United States
Show AbstractLocal thermomechanical properties of mixed-phase polymeric materials and composites have attracted much attention in the recent decade. Local thermal analysis (LTA) has emerged as a Scanning Probe Microscopy based method that allows melting and glass transition temperatures to be probed on a 100 nanometer length scale. To date, LTA utilizes one the displacement of the tip due to penetration into the sample or the change in thermal impedance as detection mechanisms. However, these detection mechanisms are generally insensitive to changes in the dissipative properties in the material (e.g. changes in the loss modulus), precluding a high-accuracy determination of the glass transition temperature.In this presentation, we discuss two experimental approaches for local thermomechanical probing that reproducibly tracks changes in mechanical properties of polymeric materials. The first approach is based on the combination of atomic force acoustic microscopy (AFAM) and band excitation detection that allows the unambiguous detection of changes in resonance frequency and tip-surface dissipation using a heated tip probe. The second approach is based on the heating the tip in a contact with the surface with specially designed electrical signal and measuring the frequency and amplitude of the oscillations caused by thermal expansion of the material. Furthermore, we develop an experimental protocol that maintains a constant tip/surface pressure and reproducible contact area during a temperature sweep, effectively extending the Oliver – Pharr method for nanoindentation to LTA. This heating mode, when combined with cantilever defection feedback-on operation, is expected to provide control of both the contact area and maintenance of a constant force during the variable temperature cycle, as necessary preconditions for quantitative SPM data analysis (similar to Oliver-Pharr method in nanoindentation).The observed decrease in quality factor and resonance amplitude of the tip – surface junction is indicative of polymer softening and subsequent melting. When the polymer melts, the coupling between the tip and surface decreases significantly, as evidenced by the observed decrease in amplitude. Simultaneously, Q factor for mechanical resonance decreases due to viscous damping in the molten polymer. A simplified model of a spring in a series with mass and Kelvin – Voight element describes the dynamics of the cantilever in contact with the surface and allows extraction of polymer’ mechanical properties. We believe that this approach provides a valuable tool for micro and nanoscale local thermomechanical property evaluation of polymers and thin films.The development of BE-AFAM was sponsored by the Center for Nanoscale Materials Sciences at the Oak Ridge National Laboratory, Office of Basic Energy Sciences, U.S. Department of Energy. The research was supported by CNMS User proposal [CNMS2008-120]. The VT BE AFAM is available as a part of user program at the CNMS.
9:00 PM - NN9.14
Molecular-scale Hydration Structures Investigatedby Frequency Modulation Atomic Force Microscopy.
Kenjiro Kimura 1 2 , Shinichiro Ido 2 , Noriaki Oyabu 1 2 , Kei Kobayashi 1 3 , Takashi Imai 4 , Hirofumi Yamada 1 2
1 , Japan Science and Technology Agency, Advanced Measurement and Analysis, Saitama Japan, 2 Electronic Science and Engineering, Kyoto University, Kyoto Japan, 3 Innovative Collaboration Center, Kyoto University, Kyoto Japan, 4 , RIKEN, Hyogo Japan
Show AbstractMolecular-scale investigations of hydration structures at a solid-liquid interface are essentially important for understanding the mechanisms of various biochemical processes. However, theoretical calculations such as molecular dynamics simulations and liquid statistical theory have been so far the only ways to study hydration structures at a molecular level. We recently found that oscillations with the period close to the liquid molecular size appeared in the force-distance curves measured by FM-AFM and that the oscillatory structures reflected local hydration structures [1]. In this study molecular-scale hydration structures at an interface between a muscovite mica surface and an aqueous solution containing salt were investigated both experimentally and theoretically using an FM-AFM force mapping method and a three-dimensional reference interaction site model (3D-RISM) calculation. We conducted a two-dimensional (surface direction and vertical direction toward the surface) frequency shift mapping (reflecting interaction forces), which was taken above a mica surface in a 1.0 M KCl aqueous solution. In the experimental result, 0.52 nm periodicity of mica corresponding to the honeycomb core structure of the mica surface is clearly resolved. Additionally, three layered structure at water/mica interface is also observed. Among three layers, first layer is strongly modulated depending on the surface crystal structure. Second and third layer have small correlation with surface crystal site, and this result implies smaller interaction forces between mica surface and water-molecules at upper layers. This crystal site-dependent force is probably due to the water-molecules regularly adsorbed onto the mica surface, which is also supported by the 3D-RISM calculation. In the future, we have a plan to measure hydration structure above various solid materials such as bio-molecules and photocatalyst materials.1) K. Kimura et al, The 10th International Conference on Non-Contact Atomic Force Microscopy, September 2007, Antalya, Turkey, Abstract booklet, p83.
9:00 PM - NN9.16
Material Identification and Characterization using AFM Based sub-100nm Nanoscale Thermal Analysis and Imaging.
Kevin Kjoller 1 , Craig Prater 1 , Roshan Shetty 1 , Bill King 2
1 , Anasys Instruments, Santa Barbara, California, United States, 2 Dept of Mechanical Engg, University of Illinois, Urbana, Illinois, United States
Show Abstract9:00 PM - NN9.17
In Situ Nanometer Scale Study of the Thermal Degradation Process of Ultrathin HfSixOy/Si by UHV-STM.
Kun Xue 1 , Ho Po Ho 1 , Jian Bin Xu 1
1 Electronic Engineering Department, The Chinese University of Hong Kong, Hong Kong China
Show AbstractThe thermal decomposition process of ultrathin HfSixOy(~1-3nm) on Si(111) by ultrahigh vacuum (UHV) thermal annealing at 200-800 oC is in situ investigated on nanometer scale by high temperature scanning tunneling microscopy (STM). The reaction process is scrutinized via time-lapse STM movie. It shows that the degradation behavior is strongly dependent on the film thickness. With a thickness less than 1nm, the process is initiated by the creation of circular voids which expose to the underlying silicon substrate, similar to ultrathin SiO2 thermal decomposition. However, when the thickness is greater than 2nm, there are no observable changes of the surface morphology until 570oC. Then conformal self-organized Hf silicide nanodots formed instantly. In situ STM investigation shows that two distinct sets of nanodots formed with average diameters of about 60 or 5nm and average heights of 20 or 2nm, respectively. The areal density is about 10^10/cm2. The formation mechanism for two sets of nanodots is believed to be the interaction between HfSixOy thermal decomposition and Si substrate terrace pinning. Based on the above observation, it shows that the thickness of the film determines the dominant reaction occurs whether in the HfSixOy film or near the interface between HfSixOy and Si substrate.
9:00 PM - NN9.2
Monitoring Organic Thin Film Growth in Aqueous Solution In-situ with a Combined Quartz Crystal Microbalance and Ellipsometry.
Amitabha Sarkar 1 , Tapani Viitala 3 , Thomas Tiwald 2 , Tino Hofmann 1 , Ann Kjerstad 1 , Bahar Laderian 1 , John Woollam 2 , Mathias Schubert 1
1 , University of Nebraska, Lincoln, Lincoln, Nebraska, United States, 3 , KSV Instruments Ltd., Helsinki Finland, 2 , John A. Woollam Co., Lincoln, Nebraska, United States
Show AbstractMeasuring thin films in aqueous environments pose a challenge because they may have an affinity for water (e.g. hydrogels) while adsorbed on a substrate. Typically, either the optical ellipsometry technique or the electromechanical Quartz Crystal Microbalance technique are used to study thin films in-situ in aqueous environments. An ellipsometer measures the change in elliptically polarized light whereas the Quartz Crystal Microbalance utilizes the piezoelectric properties of an AT cut quartz crystal to measure properties of thin films. However, each technique has its limitations. The ellipsometer has the inherent limitation of coupling thickness of films of the order of a few nm with the index. Commonly, the refractive index of the material is derived from ex-situ measurements performed on the bulk material. The Quartz Crystal Microbalance has the limitation that the density and the thickness of a film are coupled. Thus a reasonable assumption for the density must be made in order to determine the thickness. The ellipsometer can determine the actual amount of polymer present in a film. When measuring in-situ, an ellipsometer does not distinguish between water molecules attached to polymers comprising the film and the water in the ambient. However, the Quartz Crystal Microbalance measures the total mass attached to a substrate, i.e. both the polymer and the water molecules attached to it. Thus by combining the two instruments and correlating the thickness determined by each instrument, one can find the surface coverage. We introduce a new parameter called the “coverage factor (f )” to characterize surfaces in aqueous environments. Our findings on formation of synperonic film on hydrophobic gold surface in aqueous environment are presented and discussed.
9:00 PM - NN9.20
Studying Surface Forces and Thin Film Patterns Induced by Electric Fields using a New SFA Technique.
Hongbo Zeng 1 2 , Yu Tian 1 2 , Travers Anderson 1 2 , Matthew Tirrell 1 2 , Jacob Israelachvili 1 2
1 Chemical Engineering, University of California Santa Barbara, Santa Barbara, California, United States, 2 Materials Research Laboratory, University of California Santa Barbara, Santa Barbara, California, United States
Show AbstractOne of the most interesting current problems in surface and colloid science is understanding the effects of external electric fields on surface and interparticle interactions. In the presence of an electric field, the flow properties of some fluids can becontrolled and greatly changed (so-called electrorheology), and patterned structures such as chains of particles can form in colloidal suspensions. Patterns can be induced in thin polymer films by an electric field. The formation of desired patterns has the potential to eliminate complex steps in conventional imprinting techniques, such as the photoresist and exposure stages, in the fabrication of microelectromechanical systems (MEMS). Electric field gradients also show great promise in the design of DNA separation devices.In this study, we describe a new method to measure normal and/or lateral forces between two surfaces in a surface forces apparatus (SFA) while an electric field is applied between the surfaces. The new method involves depositing thin conductive layers on the exposed substrate (usually mica) sheets or using the optically reflecting silver layers on the back surfaces of the sheets as the electrodes. Two types of experiments were performed using the new technique: (1) measuring the effects of an electric field on the rheology of an ~40-um-thick film of zeolite particles suspended in silicone oil and (2) a dynamic study of electric field-induced pattern formation of a thin polymer film. In the first study, under an electric field of strength ~1,000,000 V/m the shear force or effective viscosity of the colloid suspension was found to be two orders of magnitude higher than in the absence of the field, when the expected bulk value was measured. In the dynamic study, the initially uniform film transformed into a 2-D honeycombed network of depressed cells bounded by elevated ridges that grew slowly with time in a way consistent with previously derived theories. The new technique should be applicable to studies of other systems and interactions, such as double-layer forces, micro- and nanoelectrorheology, electric field-induced ordering of particles, and the effects of electric fields on adhesion, friction, and lubrication.
9:00 PM - NN9.3
Scanning Probe Study of TiO2 Surfaces Placed in Reactive Environments.
Takumi Hiasa 1 2 , Suzumi Kataoka 1 2 , Kenjiro Kimura 1 2 , Hiroshi Onishi 1 2
1 Chemistry, Kobe University, Kobe Japan, 2 , Japan Science and Technology Agency, Advanced Measurement and Analysis, Kawaguchi Japan
Show AbstractTiO2 expresses familiar applications such as photocatalysts, super-hydrophilic coatings, and dye-sensitized solar cells. The atomically flat (110) surface of rutile polymorph has been thoroughly studied in a vacuum. The vacuum-annealed surface contains oxygen vacancies and interstitial titanium atoms to be colored in blue. On the other hand, most applications are utilized on fully oxidized, transparent TiO2 surrounded by vapor and liquid environments. It is hence important to know how the physical and electrostatic topography of this surface is affected by oxidation in air and also by exposing to reactant environments. This has been done in this study using an advanced frequency-modulation atomic force microscope (FM-AFM) and electric force microscope (EFM).In FM-AFM the tip-surface force causes the resonance-frequency shift of the cantilever vibration. The highly sensitive detection of the force is enabled in the vacuum where the Q factor of the resonance vibration exceeds 104. The Q factor reduces to 100 in air and less than 10 in liquids due to the viscous resistance. The atomistic resolution was achieved in an atmospheric pressure of N2 gas [1] and also in water [2] by the latest technical developments.When a (110)-oriented TiO2 wafer was calcined in air at 1300 K, the wafer was fully oxidized to be transparent. Terraces and single-height steps were present in the FM-AFM topography, thought an atomic resolution has not been achieved. On the other hand, periodic arrays of surface atoms have been observed on the TiO2(110) surface annealed in a vacuum. Topographic and electrostatic imaging is systematically undertaken in the vacuum, reactive or inert vapor, polar or non-polar solvent. Response to UV-light irradiation in vapor and liquid surroundings is also monitored to reveal photochemical reactions at the surface.[1] A. Sasahara, S. Kitamura, H. Uetsuka, H. Onishi, J. Phys. Chem. B 108, 15735 (2004).[2] T. Fukuma, K. Kobayashi, K. Matsushige, H.Yamada, Appl. Phys. Lett. 86, 193108 (2005).
9:00 PM - NN9.5
Ferroelectric Domain Stability Characterized by Piezo Force Microscopy and Scanning Surface Potential Microscopy.
James Bosse 1 , Nicholas Polomoff 1 , Ramamoorthy Ramesh 2 , Bryan Huey 1
1 Institute of Materials Science, University of Connecticut, Storrs, Connecticut, United States, 2 Materials Science and Engineering, University of California, Berkeley, Berkeley, California, United States
Show Abstract9:00 PM - NN9.6
Improving Scanning Probe Microscopy Resolution by Combining Trace and Retrace Results.
Atif Rakin 1 , Nicholas Polomoff 1 , Bryan Huey 1
1 Institute of Materials Science, University of Connecticut, Storrs, Connecticut, United States
Show Abstract9:00 PM - NN9.7
Dissociation of Tin Hydride on a Surface of Polycrystalline Ruthenium Film.
Nadir Faradzhev 1 2 , Vadim Sidorkin 3
1 Department of Physics, Rutgers, The State University of New Jersey, Piscataway, New Jersey, United States, 2 , National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 3 Faculty of Applied Sciences, TU Delft, Delft Netherlands
Show AbstractIn this report we discuss the interaction of atomic hydrogen with tin and thin ruthenium film at room temperature. The study is done using a combination of photoelectron and low energy ion scattering spectroscopies as well as secondary electron microscopy. The adsorption of hydrogen on a Sn surface leads to the formation of stannane (SnH4) which dissociatively adsorbs on the surface of polycrystalline ruthenium film. In the range of effective Sn coverages studied (up to 1ML) the resulting overlayer consists of randomly distributed 3D islands with average size below 50 nm occupying up to several percent of the surface area. Nucleation of tin is observed presumably at defect sites (e.g. grain boundaries). Ion scattering data is found consistent with Volmer-Weber growth mode: no initial transition wetting layer formation is detected. The results can be explained in terms of the availability of adsorption sites and of the hindering effect of the hydrogen atoms on a ruthenium surface. Oxidation of Sn islands on a ruthenium surface at room temperature results in the formation of SnO; neither metallic nor oxidation states of tin higher than Sn2+ are observed by photoelectron spectroscopy.
9:00 PM - NN9.8
In Situ XPS Investigation About the Growth of the First Atomic Layer of Ta(N) Films Deposited by ALD.
Steffen Strehle 1 , Daniela Schmidt 1 , Martin Knaut 1 , Matthias Albert 1 , Johann Bartha 1
1 Semiconductor and Microsystems Technology Laboratory (IHM), Technische Universität Dresden, Dresden Germany
Show AbstractTa(N) films are used as copper diffusion barriers and considered as a candidate for electrodes of memory devices, capacitors and CMOS transistors. To meet the requirements of suitable step coverage and conformal film thickness with respect to miniaturization and high aspect ratios of trench or stack structures, conventional deposition techniques like CVD and PVD can be hardly applied. However, atomic layer deposition (ALD) allows the deposition of ultra thin films (film thickness of a few nanometers) with excellent step coverage and precisely determined film thickness by sequential self-limiting reactions between substrate or film surface and a gas phase, respectively. As precursor molecule TBTDET (tert-butylimidotris(diethylamido)tantalum) in combination with ammonia was applied at a working pressure of about 190 Pa at 270°C. The sequential TBTDET and ammonia inlet steps where separated by Ar purging. After deposition samples were transferred in an UHV XPS chamber without vacuum break, which prevents oxidation of the tantalum by ambient oxygen. XPS was done with non-monochromatic MgKα radiation at an electron pass energy of 30 eV. The chemical reaction between the precursor molecule and the substrate surface at the first ALD cycles is intimately connected to the chemical surface condition (substrate material, impurities, functional groups). For our investigations c-Si wafers in two simple modifications were used: after HF cleaning and covered by a native oxide. In case of a silicon substrate covered by native oxide the amount of hydrocarbon contamination and the amount of Si-OH binding sites is significantly higher as expected and examined by XPS. Starting from the first single TBTDET pulse the XPS investigations show that the number of chemisorbed precursor molecules is significantly lower on HF etched substrates in comparison to a native oxide surface. Additionally, Ta should exist in two binding states indicated by a Ta4f7/2 peak position at 27.4 eV and 26.3 eV, which can be referred to a stable Ta(V) and a Ta(IV) oxidation state. After storing the sample at ambient air the Ta(IV) state disappears. The amount of Ta deposited and the binding states were investigated furthermore for a complete first cycle, at three and at ten cycles. The investigations show that there is an interesting rapid shift in the binding states of about 1 eV between the third and the tenth cycle which can be measured for both substrate modifications. From the XPS data a first growth model describing the chemisorption of the TBTDET precursor molecules at the substrate surface during the first ALD cycles has been deduced leading to an understanding about the growth of the first atomic layer.
9:00 PM - NN9.9
Determination of Hierarchical Strains in Intercalated clay-Polypropylene Nano-Composites.
Guenther Maier 1 2 , Michael Feuchter 4 2 , Milan Kracalik 3 , Gerald Pinter 4
1 , Materials Center Leoben Forschung , Leoben Austria, 2 , Erich Schmid Institut, Leoben Austria, 4 , Institute of Materials Science and Testing of Plastics, University of Leoben, Leoben Austria, 3 , Institut für Kunststoffverarbeitung, Montanuniversität Leoben, Leoben Austria
Show AbstractWhen external loads are applied on a polymer-nano-composite (PNC) the internal strains are distributed in the matrix and the filler. In exafolated (large distance between filler particles) polymer nano-composites load transfer occurs between filler particle and polymer. Intercalated PNC’s (filler particles separated by a thin layer of polymer) have an additional possibility to react on applied stresses: load transfer over the thin polymer layer from one filler particle to the next. In principle, the same is true for semi-crystalline polymers itself: The thin crystallites are separated by a thin layer of amorphous polymer and therefore consist of a stiff (polymer crystallites) and soft (amorphous) layers. Therefore, in a composite of semi-crystalline polymer and intercalated clay has many different ways to react on external loads: Polymer itself: -lamellae separation; -strain in polymer crystal; -strain in amorphous polymer; -nearly all kinds of plastic deformation modesClay itself: -strain in clay crystal; -strain in interlayer between clay plateletsComposite: -all previous mentioned; -deboning For determination and separation of all of these effects in an intercalated poly-propylene (PP) clay nano-composite system as a function of filler concentration we performed in-situ 2D synchrotron SAXS and WAXD measurements during tensile loading. This allowed for determination of strains in crystals (polymer and clay) (<0.5nm) and in stacks of intercalated clay and polymer (>3nm). With these experiments we were able to determine the effective stress transport from polymer matrix to clay filler and the influence of filler on the deformation mechanisms of the polymer. As an addition, we were able to appreciate the binding strength between polymer and filler and link this to mechanical properties of material at higher strains.
Symposium Organizers
Suneel Kodambaka University of California-Los Angeles
Guus Rijnders University of Twente
Amanda Petford-Long Argonne National Laboratory
Andrew Minor Lawrence Berkeley National Laboratory
Stig Helveg Haldor Topsoe A/S
Alexander Ziegler Max-Planck Institute for Biochemistry
NN10: In-situ Studies of Thin Film Growth
Session Chairs
Thursday AM, December 04, 2008
Room 102 (Hynes)
9:00 AM - NN10.1
X-Ray Diffraction Study of Nanoporous Gold.
Steven Van Petegem 1 , Stefan Brandstetter 1 , Andrea Hodge 2 3 , Juergen Biener 2 , Helena Van Swygenhoven 1
1 ASQ/NUM – Materials Science & Simulation, Paul Scherrer Institut, Villigen PSI Switzerland, 2 , Lawrence Livermore National Laboratory, Livermore, California, United States, 3 Aerospace and Mechanical Engineering Department, University of Southern California, Los Angeles, California, United States
Show AbstractRecently nanoporous metals synthesized by selective dealloying of binary alloys have attracted considerable attention because to their possible application as sensors or actuators. These materials exhibit a sponge-like structure with a pore size distribution on the nanometer length scale. Special attention has been given to the Ag-Au model system because it can be synthesized with a wide range of ligament sizes and densities. Furthermore interesting mechanical properties have been reported such as a size dependent Young’s modulus and strength.Although large progress is made in understanding the dealloying process and corresponding formation of pores, little is known about the evolving microstructure of the Ag-Au alloy and the final Au matrix. In this work we present a comprehensive x-ray diffraction study of nanoporous gold, including in-situ x-ray diffraction during synthesis and ex-situ Laue micro-diffraction. We find that during synthesis the ligament sizes continuously increase with time, even when the dissolving process has finished. Post dealloying microdiffraction experiments indicate that the crystal structure of the grains is very well preserved. No indication for the formation of additional boundaries could be found.
9:15 AM - NN10.2
Mapping Hillocks in Gold Thin Films with X-ray Microdiffraction: Mesoscopic Mapping and In-Situ Growth Studies.
Karen Magid 1 , Ralph Nyilas 1 , Julie Nucci 2 , Martin Kunz 3 , Nobumichi Tamura 3 , Ralph Spolenak 1
1 Laboratory for Nanometallurgy, ETH-Zurich, Zurich Switzerland, 2 Center for Nanoscale Systems, Cornell University, Owego, New York, United States, 3 Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractUnderstanding thin film plasticity in metals is essential to ensure the performance, reliability, and lifetime of thin film devices, since internal stresses arising during manufacturing can lead to device failure. High temperature fabrication processes induce stresses during temperature cycling as a result of the difference in thermal expansion coefficients between the metal films and the silicon substrate. One observed result from the heating of metal thin films is the formation of large-grained hillocks from fine-grained thin films. Theses hillocks are of importance as they can be a source of reliability issues in devices. However, details of the formation and growth of these hillocks remain unexplained. Hillock growth was studied in sputter-deposited thin gold films via in-situ Laue microdiffraction at the Advanced Light Source (ALS). Laue microdiffraction was employed to better understand hillock growth as a high-temperature compressive stress relaxation mechanism in thin Au films. Pre-marked hillocks from films with a variety of morphologies were thermally cycled in-situ to study the strain state, defect distribution, and microstructure that evolve as they grow. The large hillock grain size in comparison to the film grain size makes them suitable for microdiffraction studies, and the sub-micron spatial resolution of the x-ray beam allows the measurement of local strain states as well as orientation gradients within the hillocks. The latter are indicative of organized substructures of geometrically-necessary dislocations. These pre-identified hillocks were mapped over the course of a heating cycle to track hillock growth. The goal is to elucidate aspects of the growth mechanism of the hillocks by correlating stress state and defect structure. Since Au does not oxidize, it is a model system for investigations into this type of high-temperature deformation behavior. In addition, monochromatic diffraction measurements were taken so that the full strain tensor can be calculated. The combination of these measurements enables the direct observation of stress relaxation and the local orientation of the hillocks and surrounding areas. With this non-destructive probing technique, we have the ability to locally measure the stresses around the hillocks, and thereby examine several of the diffusion theories proposed to drive hillock growth. By examining columnar and non-columnar morphologies, we are able develop a picture of the structure and morphology within and around the hillocks to determine the dominant mechanism.
9:30 AM - NN10.3
X-Ray Photoemission Diffraction: A Technique to Resolve the Structure of Ultra-thin Films.
Gertjan Koster 1 , Wolter Siemons 1 2 , Jeroen Blok 1 , Guus Rijnders 1 , Malcolm Beasley 2 , Dave Blank 1
1 TNW, University of Twente, Enschede Netherlands, 2 GLAM, Stanford University, Stanford, California, United States
Show AbstractX-ray photoemission is a very surface sensitive technique because of the electron escape depth which is on the order of 20 Å. By tilting the sample with respect to the detector, the amount of signal that comes from nearer the surface is enhanced due to the greater distance the electron has to travel through the material. For amorphous materials this technique works ideally. However, when some order exists in the studied sample, because it is crystalline for example, the intensity has an angular distribution that is related to the ordering in the sample. The technique that exploits this is called x-ray photoemission diffraction (XPD) and was first observed in 1970 by Siegbahn et al.[1]. They found that diffraction of the photoelectrons of the crystal lattice caused the angular distribution and when atoms line up along a certain direction the intensity was greatly enhanced.In XPD the primary electron wave coming from an atom interferes with the secondary electron wave from a nearby atom, which results in an angular dependence of the electrons escaping from the sample. These diffraction peaks are dependent on the wavelength of the electron waves, as opposed to the diffraction peaks along the direction of some lattice points, which are subject to what is most commonly called “forward focusing”. The strongest diffraction peaks are therefore to be expected when most atoms line up. The great advantage of this technique is that you can measure element specifically by looking at the angular distribution of electrons with a characteristic kinetic energy, which means that a substrate (containing different elements) is not interfering with the measurement of a thin film even when it is grown epitaxially. The niche for this technique lies in the regime where the layer thickness is of the order of a few nm or highly epitaxial thin films with almost identical lattice parameters as the substrate material. At that point it becomes hard for x-ray diffraction (XRD) to resolve the unit cell, whereas photoemission only probes the top few nm.The analysis of the spectra is not very straightforward and requires simulation. Simulating the data is the only way to reproduce the more intricate diffraction features which can help to resolve the structure. To obtain most reliable measurements, the XPD experiment should take place in situ, to maintain a freshly grown film surface, without the complications of exposure to air.In the field of oxide electronics ultra-thin films and interfaces are widely studied and XPD could be a useful technique in special cases. We will demonstrate the applicability of this technique by focusing on some oxide materials systems in which either in-situ measurements are required and/or the films are too thin to be analyzed with XRD.[1] K. Siegbahn, U. Gelius, H. Siegbahn, and E. Olson, Physics Letters A 32, 221 (1970).
9:45 AM - NN10.4
In-situ X-ray Measurements of Coarsening During Pulsed Laser Deposition.
John Ferguson 1 4 , Gökhan Arikan 2 4 , Hui-Qiong Wang 2 4 , Arthur Woll 3 , Joel Brock 2 4
1 Materials Science and Engineering, Cornell University, Ithaca, New York, United States, 4 Cornell Center for Materials Research, Cornell University, Ithaca, New York, United States, 2 Applied and Engineering Physics, Cornell University, Ithaca, New York, United States, 3 Cornell High Energy Synchrotron Source, Cornell University, Ithaca, New York, United States
Show AbstractTime resolved in-situ diffuse x-ray scattering measurements were performed on homoepitaxial SrTiO3 (001) thin-films grown via pulsed laser deposition using a CCD camera operating in streak camera mode. At early times, the lobes of diffuse scattering around the specular peak give the average distance between islands and, since the coverage is known, a measure of the average island size. The average distance between islands increases between laser pulses, especially at low (<0.4 monolayers) coverage, and is associated with island coarsening. We observe that at temperatures as low as 600oC, ripening occurs on a timescale of 300 milliseconds or less. Thus, coarsening needs to be included in accurate models of the PLD process. The scaling behavior of the island coarsening process in PLD does not follow either simple attachment limited or diffusion limited models. Additionally, decreasing the time between laser pulses from 20 seconds (0.05 Hz) to 0.33 seconds (3.0 Hz) at 850oC and 2x10-4 Torr of O2 produces more persistent layer-by-layer growth oscillations. The decrease in the rate of roughening at higher laser repetition rates is correlated with the decrease in the coarsening between laser pulses – which implies a smaller average island size.
10:00 AM - **NN10.5
In-Situ Synchrotron X-Ray Studies of Synthesis of Oxide and Nitride Epitaxial Structures.
Stephen Streiffer 1 , Marie-Ingrid Richard 2 , Matthew Highland 2 , Tim Fister 2 , Dillon Fong 2 , Paul Fuoss 2 , Jeff Eastman 2 , Carol Thompson 3 , Anneli Munkholm 4 , Ken Elder 5 , G. Stephenson 2 1
1 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States, 2 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 3 Dept. of Physics, Northern Illinois University, DeKalb, Illinois, United States, 4 , Philips Lumileds Lighting Co., San Jose, California, United States, 5 Dept. of Physics, Oakland University, Rochester, Michigan, United States
Show AbstractUnderstanding the synthesis-structure-property relationships of multicomponent epitaxial heterostructures is a grand challenge in materials science. Using the two examples of metalorganic chemical vapor deposition (MOCVD) of epitaxial Pb(Zr,Ti)O3 and of (In,Ga)N, this talk will illustrate how in-situ synchrotron x-ray scattering and fluorescence can be utilized to address this challenge. In particular, fundamental issues in the growth of compositionally complex systems such as these will be discussed. As a first example, strain-coupled composition modulation has been previously observed in semiconductor alloy thin film systems, and in this presentation we will demonstrate its impact on alloy growth for both oxides and nitrides. A second critical aspect in synthesis of these systems is phase stability and constituent volatility. Specifically, growth of InN and high-In-content nitride alloys requires relatively low temperatures and high nitrogen activities because InN is less stable than other group III nitrides. This talk will show how the complex behavior of the MOCVD process results in a new type of oscillatory chemical system with time-dependent changes in InN stability. A cyclic process occurs: epitaxial islands of crystalline InN nucleate and grow; the InN islands collectively decompose into liquid In droplets; the liquid In evaporates; and then another cycle of InN growth begins. These examples demonstrate the strength of synchrotron x-ray scattering for observing such phenomena in real time under actual growth conditions, thus enabling a clear description of the underlying synthesis processes.This work was supported by the U.S. Dept. of Energy, Office of Science Basic Energy Sciences, under contract DE-AC02-06CH11357.
11:00 AM - **NN10.6
In-situ Control of the SrTiO3 Surface.
Fabio Miletto Granozio 1 , Umberto Scotti di Uccio 2 , Marco Salluzzo 1 , Milan Radovic 3 , Paolo Perna 1 2 , Gabriella De Luca 1 , Roberto Di Capua 3 , Alessia Sambri 3 , Nathascia Lampis 3
1 , CNR-INFM, Napoli Italy, 2 DiMSAT, Università di Cassino, Cassino (FR) Italy, 3 Physics Department, Università Federico II, Napol Italy
Show AbstractThe surface properties of SrTiO3 are extremely relevant to the optimization of functional oxide epitaxial films for electronics. The interface of SrTiO3 with oxide epilayers, is not only crucial in determining the structural quality of the film, but it is presently under the scientific attention of a wide community because of the possible charge transfer process induced by specific polar materials.Viable routes for the in situ control of surface termination and oxygen stoichiometry are shown, by resorting to a complex multichamber UHV system allowing to perform RHEED assisted PLD, X-ray and UV photoemission spectroscopy, low energy electron diffraction and scanning probe microscopy/spectroscopy. The laser ablation process during growth is monitored by resorting to fast (ns scale) photography. The earliest stages of growth of polar oxide materials of the SrTiO3 surface, yielding the formation of conducting interfaces, are also analysed.
11:30 AM - NN10.7
In Situ Studies of the Atomic Layer Deposition of ZrO2 and ZnO using X-Ray Synchrotron Radiation.
Paul Fuoss 1 , Dillon Fong 1 , Timothy Fister 1 , Matthew Highland 1 , Marie-Ingrid Richard 1 , Peter Baldo 1 , Jeffrey Eastman 1
1 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractAtomic layer deposition (ALD) has a demonstrated ability to grow select oxide materials one atomic layer at a time on both flat and complex surfaces. This capability originates from atomic level control of chemistry where surfaces are saturated with precursor molecules that are then reacted with a second species to form a single monolayer of the desired material. Extending this capability to a broad range of materials, however, presents challenges and the consistent growth of fully dense, high-quality, single-crystal heterostructures with precise control of composition requires improved understanding of the relations between deposition conditions, chemical state of the adsorbed precursor and film morphology. Probing the details of these processes is a challenge since ALD typically occurs under higher pressures (greater than one Torr) where traditional surface sensitive probes cannot reliably operate. Using x-ray synchrotron radiation, x-ray reflectivity, grazing incidence diffraction and total reflection x-ray fluorescence can provide in situ, real-time structural and chemical information under the conditions employed for ALD. We have constructed a small chamber that mounts onto a six-circle diffractometer at the Advanced Photon Source and studied changes in film thickness, roughness, layer density and composition in real-time during ALD of both ZrO2 and ZnO. ZrO2 films are grown on (001) oriented single-crystal yttria-stabilized zirconia substrates at 200°C by alternately exposing the substrate to zirconium tert-butoxide and water vapor. We find that under these deposition conditions ALD of ZrO2 never reaches a self-limiting growth condition (i.e., the film thickness depends on precursor exposure time). ZnO films have been grown onto either Al2O3 (0001) or Si (001) substrates at 125° using diethylzinc and water precursors. Interestingly, we find that the growth behavior of ZnO depends strongly on the choice of substrate. Growth on Si substrates is found to be self-limiting, but the change in film thickness per cycle increases during the first several precursor exposures before reaching a steady-state condition. In contrast, ALD growth of ZnO on Al2O3 (0001) substrates resulted in nanoparticles rather than smooth, continuous films despite having a small lattice mismatch. The capabilities discussed in this talk should be generally applicable to growth of a wide range of materials by ALD and provide valuable insight into the mechanisms of this important growth technology.This work is supported by the U.S. Department of Energy under Contract No. DE-AC02-06CH11357.
11:45 AM - NN10.8
In-situ X-Ray Investigaton of SiGe/Si(001) NanoscaleIslands Grown by Liquid Phase Epitaxy (LPE).
Steffi Deiter 1 , Michael Hanke 1 , Christian Eisenschmidt 1 , Torsten Boeck 2 , Thomas Teubner 2 , Uwe Jendritzki 2
1 , Martin-Luther-Universität Halle-Wittenberg, Halle (Saale) Germany, 2 , Institut für Kristallzüchtung, Berlin Germany
Show AbstractSelf organized low dimensional structures as quantum dots have attracted an increasing interest. Liquid phase epitaxy is a convenient method to investigate self ordering phenomena. To understand the crystal growth it is important to get information not only about the final structure but also about the evolution of the interface during the growth.Therefore we apply ex-situ and in-situ methods. For this purpose the material system Silicon-Germanium serves as an advantageously model system. For the in-situ experiments we combine liquid phase epitaxy with x-ray diffractionmethods. Because of technical reasons we can’t use a conventional LPE setup for x-ray diffraction experiments. Therefore we constructed a growth chamber combined with special pre-processed samples which allows the crystal growth under N2-atmosphere at a synchrotron beamline. For the in-situ measurements we recorded the intensity distribution as a function of the growth temperature thusthe evolution status of the structure. With our setup we applied first in-situ experiments which give some insights into the evolution of the SiGe-islands.
12:00 PM - NN10.9
RHEED for Real Time Extraction of Quantum Dot Size.
Chandani Rajapaksha 1 2 , Alex Freundlich 1 2
1 Department of Physics, University of Houston, Houston, Texas, United States, 2 , Center for Advanced Materials, University of Houston, Houston, Texas, United States
Show AbstractTo achieve a better performance of many of the advanced semiconductor devices the ability to control and reproduce structural properties during the growth of semiconductor nanostructures, especially self-assembled Stranski Krastanov quantum dots is critical. To this end it has been shown that the quantum dot (QD) coverage density and the average facet orientation could be extracted real time from the evolution of reflection high energy electron diffraction (RHEED) patterns. However, extracting the average dot size necessary to fully characterize self assembled quantum dots arrays has been limited to post growth microscopic and x-ray diffraction analysis. Recently Feltrin and Freundlich predicted the presence of intensity fringes along RHEED chevron tails and the possibility of extracting the size of the QD from the periodicity of these fringes. In this work we present our theoretical investigations combined with experimental evidence of the intensity fringes along the RHEED chevron tails and demonstrate the real time monitoring of dot size during the growth of self assembled Stranski Krastanov quantum dots (SKQDs).Self assembled InAs SKQDs were grown on GaAs(001) substrates at 480-500 0C by chemical beam epitaxy in a growth chamber equipped with a 15keV Staib™ RHEED gun. RHEED patterns were recorded during growth along <1-30>, [110] and [1-10] crystallographic directions using KSA 400™ RHEED data acquisition setup. The evolution of RHEED patterns was also recorded during samples cool down under As stabilized conditions. The dot size and distribution of the samples were extracted independently using atomic force microscope (AFM) observations following the growth process. The obtained AFM data were used to simulate RHEED patterns using previously developed modeling tool [1] based on the kinematical electron diffraction theory that accounts for the atomistic distribution of strain in dots and the refraction of electrons at the quantum dot/vacuum interface and the thermal diffuse scattering of electrons.The observed angle between chevrons in the experimental RHEED images was found to be consistent with calculated images for InAs SKQD having shapes similar to those proposed by Xu and coworkers , indicating that dots were bounded by {137} family of facets. A careful inspection of RHEED intensity profiles along chevron tails revealed the presence of periodic fringes whose spacing decreased with increasing InAs growth duration. The experimentally measured periodicity of these intensity fringes was found to be in good agreement with calculated intensity profiles and was inversely proportional to the dot height.In summary we demonstrate the applicability of RHEED as a readily available in-situ analysis tool in assessing quantum dots average size and structural properties’ time evolution during the growth of self assembled Stranski- Krastanov InAs/GaAs quantum dots.1. A. Feltrin, A. Freundlich, J. Cryst. Growth 301-302, 38-41(2006)
12:15 PM - NN10.10
RHEED Surface Pole Figure -- A New In-situ Technique to Study Surface Texture Evolution of Polycrystallines and Nanostructures.
Gwo Ching Wang 1 , Fu Tang 1 , Toh-Ming Lu 1
1 Physics, Rensselaer Polytechnic Institute, Troy, New York, United States
Show AbstractThe supply of thin films and nanostructures is driven by the demand of high technology industries for many diverse applications such as electronics, energy, magnetism, catalysts, and optics. The reduced dimensions in thin films and nanostructures contain rich fundamental sciences. In reality most thin films and nanostructures are not single crystalline but polycrystalline with grains and grain boundaries. Often there exists preferred orientation(s) or texture in polycrystalline thin films and nanostructures. To date the basic understanding of atomistic mechanisms on the texture evolution remains a challenging task due to the lack of experimental techniques that allow one to measure quantitatively the surface texture evolution. Conventional x-ray pole figure analysis with a few micron penetration depth probes an average texture of the entire thin film and nanostructures, and hence the information on the surface texture evolution is lost. In this work we will introduce a new surface pole figure technique using reflection high energy electron diffraction (RHEED) [1,2]. The electron used in RHEED has a sub-angstrom wavelength and a few nanometer penetration depth and thus can probe the atomic structure and the texture evolution of the growth front from the initial stage (nm thick) to the later stage (μm thick). We shall explain the principle, measurement, and construction of RHEED surface pole figures. An example of the measurements of surface texture evolution during the growth of unusual Mg nanoblades on an amorphous substrate using in-situ RHEED surface pole figure will be presented. These nanoblades were grown by thermal evaporation under shadowing effect using oblique angle deposition. From the surface pole figure measurements, we observed the time evolution of a (10-10)[0001] biaxial texture in the Mg film during the growth. The impact of this new method on material research will be discussed.Work partially supported by the NSF.Refs.1. F. Tang, G.-C. Wang, and T.-M. Lu, "In situ RHEED surface pole figure study of biaxial texture evolution in anisotropic Mg nanoblades during shadowing growth”, J. Appl. Phys. 102, 014306 (2007).2. F. Tang, T. Parker, G.-C. Wang, and T.-M. Lu, “Surface texture evolution of polycrystalline and nanostructured films: RHEED surface pole figure analysis”, J. Phys. D: Appl. Phys. 40, R427 (2007).
12:30 PM - NN10.11
Monitoring Oxide Thin Film Growth with In-situ Atomic Force Microscopy.
Joska Broekmaat 1 , Guus Rijnders 1 , Dave H.A. Blank 1
1 MESA+ Institute for Nanotechnology, University of Twente, Enschede Netherlands
Show AbstractComplex oxides exhibit various physical properties such as ferromagnetism, ferroelectrics, and superconductivity. The nature of these physical properties is determined by very small characteristic length scales. Devices based on heteroepitaxial oxides have great potential for applications provided that the growth can be controlled on an atomic level.Currently, in-situ growth morphology characterization is mostly performed by diffraction techniques such as Reflection High Energy Electron Diffraction (RHEED). We have now realized a system, in which Atomic Force Microscopy (AFM) can be performed during Pulsed Laser Deposition (PLD). Deposition and force microscopy are performed in one vacuum chamber and via a fast transfer (in the order of seconds) the surface of a sample can be scanned. In our system we take advantage of the pulsed deposition process, because microscopy measurements can be carried out between the pulses. This provides real-time morphology information on the microscopic scale during growth. The transfer mechanism allows switching between microscopy and deposition with a re-position accuracy of ±500 nm which gives new opportunities to study growth processes. This system is especially useful to study crystal growth, phase transitions, diffusion processes and nanoparticle formation. Furthermore, it can provide information if RHEED is not possible, for example during amorphous and polycrystalline growth. In this contribution, we will present our in-situ AFM as well as the latest equipment developments. To scan at elevated temperatures, small heaters have been developed. These small thermal mass heaters are designed to obtain stable monitoring settings at temperatures >700C in a high pressure environment. We will furthermore show in-situ growth studies of perovskite oxides, such as SrRuO3 and PbTiO3 on SrTiO3 substrates. These studies indicate that high temperature microscopy, growth characterization at typical deposition conditions of complex oxides becomes feasible.
12:45 PM - NN10.12
In-situ Scanning Tunneling Microscopy Studies of Sb Incorporation into GaAs Surfaces.
Jessica Bickel 1 , Chris Pearson 2 , Joanna Mireki Millunchick 1
1 Materials Science Department, University of Michigan, Ann Arbor, Michigan, United States, 2 Computer Science, Engineering Science and Physics, University of Michigan-Flint, Flint, Michigan, United States
Show AbstractUnderstanding the surface structure and morphological evolution of thin semiconductor films is critical to the design of smaller and faster devices and may in the future provide a pathway for self-assembly of structures. While the surface structure of the binary III-V semiconductor compounds are relatively well understood and characterized, those of the III-V alloy systems are less well known. Binary films typically exhibit a single reconstruction over the film surface. Ternary alloys often exhibit a coexistence of reconstructions which may be influenced by typical growth parameters as well as phenomena such as surface segregation, anion exchange, atomic size mismatch strain, and global misfit strain. These mixed surface reconstructions have interesting implications and understanding the reason for coexistence lends insight to the surface and possible properties which might be exploited in device design.Thin films of Sb and GaSb on GaAs(001)-(2x4) exhibit a mixed surface reconstruction of α2(2x4) and α(4x3). Initially, Sb reacts with Ga on the surface to form 2D islands of GaSb with an α(4x3) surface reconstruction. The 2D islands grow to a critical size of 30nm2, beyond which the atomic surface structure of the 2D island transforms to a α2(2x4) reconstruction. This transformation is limited by the availability of Ga, which is necessary in higher quantities for the α2(2x4) reconstruction than for the α(4x3). The transformation results in a mixed α2(2x4)-α(4x3) surface where the surface reconstruction is coupled to the surface morphology. Slight variations in the growth parameters result in a mottled (1x3) or a (2x8) reconstruction. With this we are able to analyze the saturation of Sb on the GaAs surface. All of these observations lead to a model of incorporation of Sb into the α2(2x4)-α(4x3) surface.Density Functional Theory studies suggest that this coexistence of reconstructions occurs in order to reduce the strain induced surface energy and the ability of the α2(2x4) to more effectively relieve compressive strain. There is a 1.3Å height difference between the α2(2x4) and α(4x3) surface reconstructions. Thus, the surface reconstruction is coupled to the surface morphology and is a result of the strain on the surface, thus effectively mapping the compressive strain on the Sb/GaAs surface by showing where the α2(2x4) and α(4x3) reconstructions appear respectively. Material also will incorporate into the α2(2x4) and the α(4x3) reconstructions different both due to inherent structural differences but also due to the strain field differences between the two reconstructions. These results point to the role of the surface structure in film growth, and suggest how nanostructures with variable composition may be tailored.
NN11: In-situ Scanning Probe Microscopy Studies of Surface Structures and Properties
Session Chairs
Thursday PM, December 04, 2008
Room 102 (Hynes)
2:30 PM - **NN11.1
Surface Dynamics and Instabilities at Electrode Surfaces.
Margret Giesen 1
1 IBN 4, Juelich Research Centre, Juelich Germany
Show AbstractIn vacuum studies, vicinal surfaces frequently serve as ideal substrates for nanostructuring, nucleation and growth because of their regular arrays of parallel steps stabilized by an elastic step-step repulsion. Whereas stepped surfaces are generally stable in vacuum, an interaction with adsorbates may cause step-doubling or step-bunching, hence it is a priori not clear whether vicinal surfaces are stable also in electrolyte. In the first part of this work it is shown that vicinal Ag(111) surfaces prepared by chemical polishing and subsequent annealing initially display rather regular arrays of steps in scanning tunneling microscopy (STM) images when immersed into an electrolyte under potential control, just as surfaces in vacuum. However, as time progresses, steps begin to merge into bunches of two and more steps. A complete merging into a new (111) facet was not observed. Since the interaction of surface atoms with the electrolyte is comparatively weak the local strain fields around steps should not significantly be affected, and the elastic repulsive force between steps should thus remain as on surfaces in vacuum. It therefore seems that the repulsive interactions are surpassed by an attractive force of unknown nature. While the nature of a possible pair-wise attractive interaction would have to be explored via a microscopic theory of the energetics of electrode surfaces it is relatively straight forward to show that surfaces in an electrolyte are unstable with respect to a phase separation into large areas with step bunches and flat terraces. This instability is a natural consequence of the lower potential of zero charge on stepped surfaces which in turn is due to the dipole moment associated with step atoms. The energy gain in the phase separation is large enough to overcome the repulsive step–step interaction on the vicinal surfaces of Ag(111), Au(111) and Pt(111). The energy gain becomes larger with increasing difference to the potential of zero charge (pzc) on either side of the pzc.
3:30 PM - **NN11.3
In-situ, Real-time Observation of Thin Film Deposition:Roughening, Zeno, Grain Boundary Crossing Barrier, and Steering.
Marcel Rost 1
1 Kamerlingh Onnes Laboratory, Leiden University, Leiden Netherlands
Show AbstractThin polycrystalline metal films are becoming increasingly important, as is reflected in the multitude of applications in nanotechnology, nanooptics, microelectronics, vacuum coating, catalysis, medical science, sensor elements, wear protection layers, decorative coatings, and the synthesis of new materials.
As thin film properties are intrinsically linked to the precise film structure, one would like to control the overall film morphology down to the nanometer scale.This clearly demands fundamental research that links well-known atomic processes, such as diffusion and nucleation, with the mesoscopic film evolution during film growth.
Applying video-rate Scanning Tunneling Microscopy (STM) [1], we succeeded in visualizing film growth with atomic-scale resolution in real-time [2]. We evaporated several tens of monolayers of gold on top of a well-annealed polycrystalline gold film, while continuously observing the evolving surface with the microscope. These measurements directly visualize atomic processes that take place during film growth.
Analyzing the evolving film structure, we observe a significant increase in the film roughness, which we explain by considering both “well-known”, single crystalline growth modes in combination with additional polycrystalline effects [2, 3]. The grain boundaries play a crucial role in the evolution, as they initiate mound formation, thereby significantly increasing the total film roughness. A possible additional roughness contribution comes from atom steering, which also can delay the film closure in the early stages during film growth.
[1] M.J. Rost et al.; Rev. Sci. Instr. 76, 053710-1 (2005)
[2] M.J. Rost; Phys. Rev. Lett. 99, 266101 (2007)
[3] M.J. Rost et al.; Phys. Rev. Lett. 91, 026101 (2003)
4:30 PM - **NN11.4
Probing Local Electrical, Chemical and Optical Interactions with Scanning Probe Microscopy.
Dawn Bonnell 1
1 Department of Materials Science, University of Pennsylvania, Philadelphia, Pennsylvania, United States
Show AbstractScanning Probe Microscopy accesses local properties in a manner that is inherently amenable to in situ studies. After an overview of the wide range of possibilities for in situ observations, three explicit examples will be described. The first involves electronic transport across grain boundaries in polycrystalline and bicrystals of semiconducting oxides. By varying applied bias across the sample and temperature while measuring localized potential, impedance, conductance, etc., the effect of interface charge on properties adjacent to the interface are quantified. Dielectric constant suppression, disorder in defect distribution, and dipole alignment are determined with nm scale precision. Second, chemical reaction variations due to ferroelectric domain orientation are quantified. Molecular adsorption on BaTiO3 and PZT are probed via influence on surface potential (work function) to determine local variations in sticking coefficients and adsorption energies. These properties vary dramatically on domains with different orientations. The atomistic mechanism of the molecular interactions are determined for water, CO2, pyridine, and alcohol. The atomic mechanisms of the local electric field effect differ from case to case, but the influence of local fields at surface is ubiquitous. Finally the effect of optical excitation on molecular monolayers is characterized with scanning tunneling microscopy and torsionally stabilized conducting atomic force microscopy. This approach is applied classes of organic molecules and molecular nanostructures designed to have opto electronic properties. Here single porphyrin molecules isolated in alkane monolayers and designed peptide/lipid monolayers will be illustrated.
5:00 PM - NN11.5
In situ Optical and Electrical Characterization at Nanoscale by a Transparent Probe of a Scanning Tunneling Microscope.
Ilya Sychugov 1 , Hiroo Omi 1 , Tooru Murashita 2 , Yoshihiro Kobayashi 1
1 NTT Basic Research Labs, NTT Corporation, Atsugi, Kanagawa, Japan, 2 NTT Photonics Labs, NTT Corporation, Atsugi, Kanagawa, Japan
Show AbstractA new type of a scanning probe microscope, combining features of a scanning tunneling microscope (STM), a scanning tunneling luminescence microscope (STML) and an aperture scanning near-field microscope (SNOM) is described. The proof-of-the-concept experiments carried out under ultra high vacuum conditions and varying temperature on GaAs/AlAs heterostructures and PbS quantum dots are discussed. Switching between different microscopy regimes is realized by in situ tip exchange preserving the vacuum. Previously the STML operation regime was demonstrated in addition to STM mode. It was achieved with a conductive and transparent tip, featuring ~ 40 nm full width at half maximum (FWHM) spatial resolution. In order to complement the existing STML instrument with the possibility of all-optical measurements new tips were prepared by metal deposition and focused ion beam milling. The optimum tip geometry was numerically evaluated using the finite-element method. The tip apex was milled into a pyramidal shaped to make it transparent for the light for the SNOM mode and sharp enough for the STM mode of operation. The signal from the tip apex can be collected in a spectroscopy mode or in a photon mapping regime. Optically excited (by the green line of the second-harmonic Nd:YAG laser, 532 nm) luminescence from GaAs was detected in the spectroscopy regime both at room temperature and at 80 K. PbS quantum dots dispersed on ITO-covered glass substrates were characterized in the photon mapping regime to evaluate instrument spatial resolution.This approach may find its niche not only where all-optical measurements with subwavelength resolution are required in addition to STM and STML characterization, but also where electrical modification with subsequent in situ optical probing is desirable.
5:15 PM - NN11.6
Extended Conduction Mechanisms in Nano-Structures.
Victor Gehman 1 , Karen Long 1 , Francisco Santiago 1 , Kevin Boulais 1 , Alfredo Rayms-Keller 1
1 Code Q23, Naval Surface Warfare Center, Dahlgren Division, Dahlgren, Virginia, United States
Show AbstractMany technologies require the understanding of conduction and electrical transport mechanisms through nanostructures. Previous research has revealed unusual and enhanced conduction properties in pores whose width is significantly less than 1μm over a range of +10V to -10V. Characterization of the enhanced conduction will include experimental measurements and theoretical models looking to explain the effects of nanopore size, bulk ionic concentration, solute ionic charge, solvent, semiconductor versus metallic contacts and voltage upon conduction current. An initial model adapted the concepts of the ionic atmosphere, dielectric effects at interfaces, ionic density and mobility to the unique environment within the nanopore. This paper will report on new experimental results from AFM-derived conduction measurements as well as refinements to the computer model that extend the double-layer concept and attempt to better explain the experimental data.By exploiting the enhanced current, there exists the potential for order-of-magnitude improvements in sensors, computation and communications. Conduction and attachment mechanisms are the cornerstone to the successful integration of nano-devices into Naval systems using conventional semiconductors.
5:30 PM - NN11.7
A New Scanning Probe Microscope to Measure Coupled Transport Coefficient.
Alexandre Cuenat 1 , Andres Muniz-Piniella 1
1 , National Physical Laboratory, Teddington United Kingdom
Show Abstract5:45 PM - NN11.8
High Speed Surface Property Mapping: Nanoscale Properties Monitored at >1kHz Line-Rates.
Nicholas Polomoff 1 , Ramesh Nath 1 , James Bosse 1 , Atif Rakin 1 , Bryan Huey 1
1 Institute of Materials Science, University of Connecticut, Storrs, Connecticut, United States
Show Abstract