Program - Symposium CCC: Local Probing Techniques and In-Situ Measurements in Materials Science

2012 MRS Spring Meeting logo

2012 MRS Spring Meeting & Exhibit

April 9-13, 2012San Francisco, California
Download Session Locator (.pdf)2012-04-10  

Symposium CCC

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Symposium Organizers

  • Nina Balke, Oak Ridge National Laboratory
  • Howard Wang, State University of New York, Binghamton Institute for Materials Research
  • Job Rijssenbeek, GE Global Research
  • Thilo Glatzel, University of Basel

Support

  • Asylum Research
    Zurich Instruments Ltd

    CCC1: Spectroscopic Techniques for the Investigation of Energy Storage Materials

    • Chair: Nina Balke
    • Tuesday AM, April 10, 2012
    • Marriott, Golden Gate, Salon A
     

    8:15 AM - *CCC1.1

    Industrial Applications of In-situ Phase and Strain Mapping by High-energy Synchrotron X-Ray Diffraction

    Yan  Gao1.

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    A particular challenge in industrial materials research is to study materials or systems under the conditions as they are used or operated, which is often difficult to be accomplished by using conventional characterization techniques. At GE Global Research, we have used high-energy synchrotron x-rays in many areas of materials research, which have the advantages of being in-situ, non-destructive, and spatially resolved. Two examples will be given in this presentation. The first deals with cathodes of sodium metal chloride batteries, for which the phase distribution inside actual battery cells were mapped in-situ during charge and discharge cycles. The second involves Ni-based superalloys, which are widely used in gas turbines for aviation and energy generation. High-energy x-ray diffraction was used to map the strain distribution around the site of crack initiation, to understand fatigue failure mechanisms and improve the reliability of component lifing predictions. The importance of using non-destructive and in-situ techniques to solving industrial problems will be discussed.

    8:45 AM - *CCC1.2

    Development of ``Insitu'' X-Ray Raman Scattering Technique and its Application to Redox Reactions in Battery Materials

    Mahalingam  Balasubramanian1, Swati  Pol1, Kenneth  Nagle2, John  Vinson2, Gerald  Seidler2.

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    Energy storage devices with high energy and power density are needed for a variety of existing and emerging technologies. Knowledge of the redox chemistry and changes in the structure during electrochemical cycling is of paramount importance in designing new battery materials with superior properties. In situ x-ray diffraction (XRD) and x-ray absorption (XAS) studies have played a vital role in elucidating the structural and electronic changes that accompany electrochemical cycling. The advent of third generation synchrotron sources coupled with dedicated and specialized instruments for specific-type of x-ray scattering studies has opened a new window to systematically investigate the structure property relationship of advanced materials under operating conditions. Using a combination of XAS, x-ray Raman scattering (XRS) and x-ray emission based spectroscopic methods we seek to provide definitive characterization of the redox chemistry of operating batteries, a topic of continuing fundamental and applied interest. XRS, which involves inelastic scattering of x-rays from core electrons, is becoming an important method to study the electronic structure of condensed matter systems. In the limit of small momentum transfer, XRS is equivalent to soft XAS or electron energy loss spectroscopy (EELS). However, unlike EELS and soft XAS, XRS uses strongly penetrating x-ray radiation, making it easier to design an x-ray compatible electrochemical cell. Furthermore, at sufficiently high momentum transfers XRS is sensitive to dipole-forbidden transitions, providing additional information on low-energy (< 1.9 keV) electronic transitions . We have earlier utilized XRS to study lithium and carbon K-edges of lithiated graphite and have expanded the studies to working half cells with canonical transition metal containing electrodes (lithium cobalt oxide, titanium disulphide and lithium titanate) and Li-oxygen systems. The rich excitation spectra obtained using XRS helps unravel fundamental information on the electronic changes that accompany electrochemical cycling. Details of the XRS technique and its application to understand charge compensation mechanisms will be presented.

    9:15 AM - CCC1.3

    Real-time Interfacial Changes at the Interface of Thin Film Lithium Ion Batteries Measured by X-Ray Reflectivity

    Tim  T  Fister1, Brandon  R  Long2, Andrew  A  Gewirth2, Bing  Shi3, Sang Soo  Lee1, Paul  Fenter1.

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    Capacity losses in lithium ion batteries are often attributed to reactions at the electrode/electrolyte interface. While post-mortem studies using electron microscopy and models based on electrochemical data have shed some light on these processes, there is a palpable lack of in situ probes with the interfacial resolution to resolve changes at the charged battery interface. Here, we apply synchrotron-based x-ray reflectivity to measure structural changes in silicon-based thin films with sub-nanometer resolution at controlled electrochemical potential. For instance, silicon thin films are found to expand vertically 360% during their first discharge, in agreement with near-theoretical capacities measured by simultaneously voltammetry. We also see evidence for a Li+ concentration gradient near the film’s top surface at intermediate potentials that eventually forms a reversible 1-2 nm-thick layer of Li+ near 0 V vs Li/Li+. With a chromium current collector, silicon intermixes and ultimately stratifies into stable chromium silicide phases. In this case, the film preferentially lithiates at each interface forming grain-boundary lithium silicides that only partially delithiate. We will also discuss extensions to x-ray reflectivity toward: (i) understanding chemical changes by working near an element’s resonant energy and (ii) measuring lateral heterogeneity by coupling diffraction with full-field imaging. This work is part of the Center for Electrical Energy Storage, an Energy Frontier Research Center funded through DOE-BES.

    9:30 AM - CCC1.4

    Imaging of Chemical Transformations in Single Particles of Li-ion Battery Materials

    Ulrike  Boesenberg1, Yijin  Liu2, Florian  Meirer2 3, Apurva  Mehta2, Joy  C  Andrews2, Piero  Pianetta2, Thomas  J  Richardson1, Robert  Kostecki1, Jordi  Cabana1.

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    Understanding ongoing phase transformation and morphology changes can be regarded as a key to understand and improve materials for energy storage. This paper will focus on in- and ex-situ XANES microscopy of materials for electrodes in Li-ion batteries, where application in high demand fields such as transportation and grid storage require ever increasing energy density. One approach is to find new electrode materials with higher storage capacity. Conversion reactions have received a lot of attention in this respect, because they display a transfer of multiple electrodes per mole of Li by complete reduction of a transition metal (M) compound, e.g. MaXb (X=N, O, F, P, S, H) to metal nanoparticles and LinX, thus promising extremely high capacities [1]. However, major obstacles must be addressed to make this concept practical, namely (1) the high voltage hysteresis between charge and discharge, (2) very large first cycle inefficiency, (3) reduced capacity with extended cycling and (4) disintegration of the electrodes due to the formation of nanoparticles. But also phase transformations and reactions in commercially available materials such as LiFePO4 are not fully understood, despite extensive experimental investigations and calculations [2, 3]. Hard X-ray XANES imaging can provide insight into the ongoing phase transformation and morphological changes within a single particle/crystal and thus help clarify the fundamental processes. XANES microscopy combines the high resolution and large field of view (FOV) of full-field transmission X-ray microscopy (TXM) with X-ray absorption near edge structure (XANES) to produce 2D and 3D chemical speciation maps [4]. Using the TXM on beamline 6-2 at SSRL, which is capable of imaging from 4.5 to 14 keV at down to 30 nm resolution, the XANES microscopic technique has been applied to study the conversion reaction of NiO with Li as a model system. The experiments were performed at the Ni-K edge to map the distribution of Ni and NiO at different stages of the reaction and in situ. Ni was found to form on the outside of particles where exposure to the electrolyte is extensive, as well as through cracks. The volume expansion and release of energy is enormous during conversion of NiO+Li→Ni+LiO, resulting in a fine nanostructure. The results were used to build a comprehensive picture of ongoing phase transformations in battery materials for conversion reactions. Also using the same technique, special attention is drawn to phase transformations and phase distributions in single crystals of LiFePO4 upon delithiation and relithiation. 1. Zhou, J.G., et al., J Mater Chem, 2009. 19(37) 2. Chen, G., et al., ESL, 2006. 9(6): p. A295-A298. 3. Malik, R., et al., Nat Mater, 2011. 10(8): p. 587-590. 4. Meirer, F., et al., JSR, 2011. 18(5): p. 773-781.

    9:45 AM -

    BREAK

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    CCC2: In-situ Electron Microscopy Studies of Battery Materials

    • Chair: Tsukasa Hirayama
    • Tuesday AM, April 10, 2012
    • Marriott, Golden Gate, Salon A
     

    10:15 AM - *CCC2.1

    Piercing into Some Fundamental Microstructural Designing Concepts for High Capacity and Long Cycle Life of Anode Materials in Lithium Ion Battery

    Chongmin  Wang1, Xiaolin  Li1, Wu  Xu1, Jun  Liu1, Ji-Guang  Zhang1, Jane  Howe2, David  J  Burton3, Zhongyi  Liu4, Xingcheng  Xiao4, Suntharampillai  Thevuthasan1, Donald  R  Bare1.

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    For lithium ion battery, a range of materials has a high theoretical capacity, while in reality, this type of materials cannot be used directly due to a fast capacity fading. It is believed that the capacity fading and short cycle life of the battery using this type of materials are directly related to the overall large volume expansion and anisotropic accommodation of the volume change. Silicon is a typical example with a theoretical gravimetric capacity of ~ 4200 mAh g-1 and a volumetric capacity of ~ 8500 mAh cm-3. However, it is known that upon lithiation, Si will expand 400% with dramatic anisotropic change of dimensions, showing obvious elongation along the [110] direction. It is a far more common practice in materials science and engineering that for addressing these two aspects of problems is to fabricate material with a desired microstructure. For this reason, a range of materials designing concepts has emerged intending to address the failure of the battery associated with large volume expansion, typically such as using Si nanowires, nanotubes, and nanoparticles. Carbon is a commonly used conductor additive in the lithium electrode materials and it has a range of tailorable structures, ranging from nanofiber, graphene, and particles. Therefore, it is a natural approach to rationally design a composite materials based on Si and carbon. Due to their nanoscale dimensions, the lithiation induced volume expansion and shape change can be accommodated, therefore, reducing the chance of the failure of the battery. In this presentation, we review some of the fundamental designing concepts and associated challenges for tailoring composite materials based on Si and carbon as anode materials with high capacity and long cycle life. In a specific example, amorphous Si was coated on both exterior and interior of the hollow carbon nanofibers. The electrochemical properties of this composite material were investigated with an emphasis being placed on in-situ TEM investigation of the structural evolution and the phase transformation of the material during the cyclic charging and discharging. Reversible expansion and contraction of the coated Si layer can be seen during the cyclic charging and discharging processes. The thin Si layer sticks to the carbon nanofiber and showing no spallation or cracking during the early stage of cyclic charging/discharging. However, with progressive cycling, damage was gradually accumulated on the Si layer, which may eventually lead to the catastrophic failure of the battery.

    10:45 AM - *CCC2.2

    In-situ TEM Structure Evolution and Electrochemical Property Correlation of Lithium Ion Batteries

    Jianyu  Huang1, Xiaohua  Liu1, Yang  Liu1, John  Sullivan1, Kevin  Zavadil1, Li  Zhong2, Liqiang  Zhang2, Jiangwei  Wang2, Akihiro  Kushima3, Wen Tao  Liang4, Ting  Zhu5, S.  T  Picraux6, Ju  Li3, Scott  Mao2, Sulin  Zhang4.

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    Recently, we created the first Li-ion electrochemical cell (a nano battery) inside a transmission electron microscope (TEM) and observed, in real time with atomic scale resolution, the battery charging and discharging processes. This experiment opened the door for a suite of experimental studies involving in-situ TEM characterization of Li-ion battery materials. In this presentation, I’ll first review our latest progress of using the nano-battery setup inside the TEM to reveal the intrinsic electrochemistry of several high energy density anode materials such as SnO2, ZnO, Si, Ge, Al nanowires, Si nanoparticles, carbon nanotubes, and graphene. Several electrochemical mechanisms were observed and characterized in real-time, including lithiation induced stress, volume changes, phase transformations, pulverization, cracking, embrittlement, and mechanical failure in anode materials. These results indicate the strong material, size and crystallographic orientation dependent electrochemical behavior and degradation mechanisms that occur in Li-ion battery anodes. In the future, we will need further advancements in in-situ characterization for understanding important processes in Li-ion batteries. For example, liquid cells are required in order to examine the electrochemical reactions between battery materials and the standard battery electrolytes, which are ethylene carbonate-based. Furthermore, in-situ microstructure evolution is correlated with electrochemical properties of individual nanowires, revealing new nanoscale electrochemical phenomena. I will present a comparison between our in-situ results and electrochemical studies on conventional battery electrodes and highlight how in-situ studies can have important impact on the design of Li-ion batteries. Finally I will discuss outstanding challenging issues and opportunities in the field of Li-ion battery research. References: Science 330, 1515 (2010); 330, 1485 (2010); Nano Lett. Doi: 10.1021/nl200412p, 10.1021/nl2024118, 10.1021/nl201684d, 10.1021/nl202088h, ACS Nano, doi: 10.1021/nn200770p, 10.1021/nn202071y; PRL 106, 248302 (2011); Eng. Env. Sci. doi: 10.1039/c1ee01918j

    11:15 AM - *CCC2.3

    Probing Local Behaviour and Microstructural Evolution of Li-ion Battery Cathode Materials

    Dean  Miller1, Daniel  Abraham2, Jianguo  Wen1, Yuxin  Wang3.

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    Microstructural changes that take place during electrochemical cycling of Li-ion batteries can influence long-term behavior. A challenge in correlating those microstructural changes with battery performance is the fact that working batteries and test cells consist of ensembles of many elements. Thus, the knowledge gained from characterization on a microscopic level may be difficult to correlate with macroscopic behavior. One approach to this challenge is to carry out electrochemical measurements and microstructural characterization on isolated, individual elements such as a single cathode oxide powder. In the present work we focused on characterization of single powders of Li(Ni,Co,Al)O2 and Li(Ni,Co,Mn)O2 cathode materials. In situ electron microscopy studies of single cathode powders during cycling revealed dramatic changes in secondary particle microstructure even during the very first charge cycle that can influence how electrolyte penetrates the powders. Comparing these observations with baseline data from full cells that were subjected to long-term cycling and studied by post-test, ex situ characterization using FIB-SEM provides some explanation for the large changes in impedance associated with the positive electrode on full coin cells. Correlative characterization and microscopy using photons and electrons can provide additional information over different length scales. The results and insight gained from these experiments will be discussed during our presentation. *Research sponsored by the U.S. DOE, Office of Science and by the EERE – Vehicle Technologies Program, under contract DE-AC02-06CH11357. The Electron Microscopy Center at Argonne and the Advanced Photon Source are supported by the Office of Science.

    11:45 AM - CCC2.4

    In situ TEM Charaterization of Functional Liquid Systems

    Shen  J  Dillon1, Kyong Wook  Noh1.

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    The transmission electron microscope is an ideal platform for in-situ investigations of nanoscale processes, due to its high spatial and temporal resolution. For example, features as small as 1 nm are easily resolved in aqueous solution with temporal resolution greater than 5 frames per second. Complex materials systems may be fabricated in environmental cells for TEM investigation. This talk highlights our recent work related to in-situ TEM characterization of the behavior of nanoscale systems in complex environmental conditions. For example, strain effects in lithium ion battery electrodes have been observed in systems such as tin and tin oxide. Gas evolution due to titania photocatalysis has also been observed in-situ recently. The talk will discuss the scientific importance of these recent results and will address challenges and opportunities associated the technique.

    CCC3: Microscopic Investigation of Energy Storage Materials

    • Chair: Steve Buratto
    • Tuesday PM, April 10, 2012
    • Marriott, Golden Gate, Salon A
     

    1:30 PM - *CCC3.1

    Local Probe Studies of Interfacial Phenomena in Li-ion Batteries

    Robert  Milosz  Kostecki1, Nicolas  Norberg1, Ivan  Lucas1.

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    Li-ion batteries are complex multicomponent electrochemical systems that incorporate widely dissimilar phases in physical and electrical contact. Electron and ionic transfer across solid-solid, solid-liquid interfaces and within each of constituent phases determine the behavior of the composite electrodes and the electrochemical performance of the entire battery system. The continuous charge-discharge and/or prolonged storage of Li-ion batteries invariably leads to performance degradation caused by irreversible changes in the structure, morphology, topology, and composition of the materials, the nature and mechanism of which has not yet been fully identified. Adequate surface sensitive techniques must be used to detect, monitor and analyze surface layers on composite electrodes[1,2,3,4]. Interfacial phenomena and structural changes in composite electrodes in Li-ion battery systems occur and often manifest themselves at nano- or micro-scales. These effects can be detected and characterized only by techniques of suitable sensitivity, selectivity and resolution. The development and application of in situ non-destructive photon- and particle based spectroscopic, microscopic, and scattering techniques capable of the highest sensitivity, structural and elemental specificity, and temporal resolution is crucial to gaining a fundamental understanding of the mechanism of chemical and electrochemical processes, which are responsible for the Li-ion battery electrochemical performance [5]. This work presents an overview of the selected studies that illustrate an effective use of advanced in situ characterization techniques to sense and monitor physico-chemical properties of the electrode/electrolyte interface and within the active material phase, and provide unique insight into the mechanism of chemical and electrochemical processes, which contribute to the complex Li-ion system chemistry. ACKNOWLEDGEMENT This work was supported by the Assistant Secretary of Energy Efficiency and Renewable Energy, Office of Freedom CAR and Vehicle Technologies of the U.S. Department of Energy under Contract No. DE-AC03-76SF00098. REFERENCES 1. Y. Wang, X. Guo, S. Greenbaum, J. Liu, and K. Amine. Electrochem. Solid-State Lett., 2001, 4, A68 2. M. Balasubramanian, H. S. Lee, X. Sun, X.Q. Yang, A. R. Moodenbaugh, J. McBreen, D. A. Fischer and Z. Fu, Electrochem. Solid-State Lett., 2002, 5, A22. 3. D. Aurbach, K. Gamolsky, B. Markovsky, G. Salitra, Y. Gofer, U. Heider, R. Oesten, and M. Schmide, J. Electrochem. Soc., 2000, 147, 1322. 4. Jinglei Lei, Frank McLarnon, Robert Kostecki, J. Phys. Chem. B. 2005, 109, 952. 5. “Basic Research Needs for Electrical Energy Storage“, report of the Basic Energy Science Workshop on Electrical Energy Storage, Washington DC, April 2-4, 2007, http://www.sc.doe.gov/bes/reports/files/EES_rpt_print.pdf

    2:00 PM - CCC3.2

    Local Electrode Atom Probe Tomography of LiFePO4 Single Crystals

    Dhamodaran  Santhanagopalan1, Thomas  McGilvray1, Yuri  Janssen2, Peter  Khalifah2, Rich  Martens3, Shirley  Meng1.

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    Local electrode atom probe (LEAP) tomography of oxide materials is feasible now due to laser assisted controlled field evaporation. In this work, we discuss its use in Lithium ion battery cathode materials research by investigating LiFePO4 (LFP). LFP is a potential cathode material with high energy density, increased safety and equally cost effective. One dimensional Lithium diffusion channels along the b-axis makes it highly sensitive to defects. In the recent years it has been demonstrated that the Fe-Li anti site defects are very important in LFP which can block selective channels and possibly alter the lithium diffusion paths. To understand such anti-site defects in single crystal LFP, orientation specific samples prepared using focused ion beams (FIB) have been subjected to LEAP measurements. A 3D tomography and subsequent bulk and surface compositional variations have been investigated. Defect analysis in LFP and its relevance to lattice site correlation of elements in LFP will be described. Finally, we also discuss the advantages and disadvantages of LEAP and possible ways to overcome the disadvantages.

    2:15 PM - CCC3.3

    In-situ Study on Cyclic Changes of Topography, Phase and Volume of TiO2 Anode in All-solid-state Thin Film Li-ion Microbattery by Biased Scanning Probe Microscopy

    Jing  Zhu1, Li  Lu1, Kaiyang  Zeng1.

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    All-solid-state thin film Li-ion microbatteries have extensive applications in precise electronic devices, such as micro-electromechanical-systems (MEMS), implanted medical devices, smart cards, integrated circuits and semiconductor chips. Since all electrochemical reactions and Li ion diffusion are confined in an internal multilayer structure, they are also suitable and significant tools to investigate the electrochemical mechanisms of the solid electrode/electrolyte without binders. Although numerous studies have been focused on electrochemical mechanisms, the microscopic mechanisms, such as local phase transformation, ionic/electronic transportation, charge/vacancy trapping and many others, are still not very clear. Recently, scanning probe microscopy (SPM), a powerful technique to characterize multiple properties of functional materials with high spatial resolution, have been applied to the field of energy storage system to investigate micro- and nano-scale electrochemical functionalities. However, previous SPM studies were mainly conducted using special electrochemical atomic force microscopy (EC-AFM), or combining with external electrochemical attachments such as potentioastat. In this study, we propose a new in-situ method using biased SPM without any external attachment, to induce Li+ diffusion within a real all-solid-state thin film Li-ion battery (TiO2/LiPON/LiNi1/3Co1/3Mn1/3O2), while monitoring the local cyclic changes of topography, phase and volume of TiO2 anode at nanoscale with the same SPM tip. Results clear show that the reversible topographical change as the volume expansion/contraction is related to the cyclic Li+ insertion/extraction induced by local bias-induced electrical field. This phenomenon is analogues to charge/discharge behavior observed in traditional EC-AFM, indicating that the local cyclic bias can be used for modeling the charge/discharge processes in Li-ion battery. In addition, combining simultaneous measurements of phase and amplitude images, high spatially resolved mapping of “nano-spots” which are related to Li-ion distribution and trapping can be obtained, providing a new insight into the mechanism of ionic transport and the distribution of diffusion preferred paths in a real all-solid-state Li-ion battery. Furthermore, this new in-situ SPM method is also very promising for in-situ characterization of other electrical properties of Li-ion batteries.

    2:30 PM - CCC3.4

    Nansocale Probing of Anisotropic Ionic Transport

    Nina  Balke1, Stephen  Jesse1, Sergiy  Kalnaus1, Claus  Daniel1, Nancy  Dudney1.

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    The growing use of renewable energy sources is strongly tied to the need for advanced energy storage technologies. The functionality of energy storage systems, such as Li-ion batteries, is based on and ultimately limited by the rate and localization of ion flows through the device on different length scales ranging from atoms over grains to interfaces. The fundamental gap in understanding ionic transport processes on these relevant length scales strongly hinders the improvement of existing and development of future battery technologies. The development of Electrochemical Strain Microscopy (ESM) offers a pathway to close this gap. ESM is a Scanning Probe Microscopy based technique which allows studies of the local Li-ion flow in electrode materials and across interfaces on length scales down to 100 - 10 nm. It can be used to extract information about the ionic transport kinetics and investigate the correlation between functionality and structure. Here, we present how ESM can be used to measure the three dimensional ionic transport properties in cathodes for Li-ion batteries. The ionic transport is highly anisotropic in commonly used cathode materials, such as layered LiCoO2. By investigating the vertical and lateral component of the material volume change as the local ionic concentration changes, conclusions on texture and its role in ionic transport can be made. Theoretical calculations are shown to support the experimental data and to give insight into the signal generating mechanism. Research was sponsored as part of the Fluid Interface Reactions, Structures and Transport (FIRST) Center, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences. Research was conducted at the Center for Nanophase Materials Sciences at Oak Ridge National Laboratory, which is sponsored by the Office of Basic Energy Sciences, U.S. Department of Energy. Part of this research was sponsored by the Vehicle Technologies Program for the Office of Energy Efficiency and Renewable Energy.

    2:45 PM - CCC3.5

    Effect of Local Mechanical Damage on Li-ion Mobility

    Sergiy  Kalnaus1, Thomas  Arruda1, Nina  Balke1, Hongbin  Bei1, Nancy  Dudney1, Sergei  Kalinin1 2, Claus  Daniel1 2.

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    Local Li-ion mobility in LiCoO2 thin films was investigated by means of the Electrochemical Strain Microscopy (ESM), a recently developed method for detecting strains associated with motion of ions in the material host structure [Balke et al. ACS Nano 4(12) 2010, 7349-7357]. The method is based on application of local periodic bias which changes concentration of ions under the AFM tip, and allows for investigation of Li-ion kinetics at the nano-meter scale. This technique was used to probe pristine LiCoO2 thin films, deposited by RF magnetron sputtering, and mechanically damaged films. The damage was applied locally by using nano-indentation technique. Indenter with a spherical tip was used and the degree of damage was controlled by the depth of indentation. ESM response was then collected and quantified as a function of the indentation depth. Experiments were conducted at different values of state of charge of the material. ESM signal reduction or enhancement due to mechanical compression was investigated with the prospect of optimizing such damage for better electrode performance. In this way, concepts for Li ion mobility improvement can be examined without a change in chemistry of the active material. In addition, the work may help in understanding the degree of influence of damage introduced during commercial electrode manufacturing (for instance calendering) on electrochemical performance. This research at Oak Ridge National Laboratory, managed by UT Battelle, LLC, for the U.S. Department of Energy under contract DE-AC05-00OR22725, was sponsored by the Vehicle Technologies Program for the Office of Energy Efficiency and Renewable Energy. Nina Balke acknowledges support from the Early Career Award program of the U.S. Department of Energy. Part of this research was conducted at the Center for Nanophase Materials Sciences at Oak Ridge National Laboratory, which is sponsored by the Office of Basic Energy Sciences, U.S. Department of Energy.

    3:00 PM -

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    CCC4: Examination of Electrochemical Reactions

    • Chair: Job Rijssenbeek
    • Tuesday PM, April 10, 2012
    • Marriott, Golden Gate, Salon A
     

    3:30 PM - *CCC4.1

    Neutron Metrology Methods for In-Situ Diagnostics of Electrochemical Systems

    Jon  P  Owejan1.

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    Metrology methods based on a variety of neutron beam techniques are well-suited to diagnostic applications in a variety of practical electrochemical energy systems. Given the large neutron cross-section of hydrogen and lithium, liquid water in fuel cells and charge distributions in lithium-ion batteries can be imaged with high spatial resolution (13 µm). For diagnostics of interfacial interactions, neutron reflectivity has suitable resolution (0.1 nm) for probing the thin interphase layers inherent to fuel cell and battery electrodes. Electrode diagnostics that probe intermediate length-scales (0.1 µm) include neutron depth profiling, which measures lithium transients through the depth of intercalation electrodes, and small angle neutron scattering for monitoring bulk and interfacial changes in electrode materials. All of these methods are non-destructive and can be applied in-situ with minimal modifications to the key components of electrochemical test fixtures. A summary of these methods with focus on the practical aspects of in-situ application is provided. This talk will also highlight recent results from each of these measurements and demonstrate how these methods are enabling the optimization of materials and control strategies for fuel cells and lithium batteries.

    4:00 PM - *CCC4.2

    Direct Correlations of Electrolyte Dynamics with Ion Mobility for Energy Storage Technologies

    Christopher  Soles1, Huagen  Peng1, Madhusuhan  Tyagi2, Youmi  Jeong3, Jim  Runt3.

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    It is well understood that the ions move much slower than the electrons in the conventional Li-ion battery. In this respect, the low mobility of the Li-ions through the electrolyte medium imposes a bottleneck on battery performance. Liquid electrolytes, such as propylene or ethylene carbonates, that can readily solvate Li are typically preferred over solid polymer electrolytes such as polyethylene oxide because they enable ion conductivities that are approximately an order of magnitude greater. However, liquid electrolytes are also problematic because they are difficult to handle/seal and offer no mechanical resistance against Li metal dendrite formation, a phenomenon that can lead to catastrophic failure and ignition of the battery stack. There is considerable interest in realizing solid polymer electrolytes with improved ion mobility that will also mechanically inhibit dendrite formation and improve battery safety. In solid polymer electrolytes it is recognized that ions move via a Grotthus hopping mechanism where they hop between adjacent association sites on the polymer chain. This catch and release hopping mechanism requires collective motions of the polymer chain. It is not a vehicular transport mechanism where the ion remains bound to the same polymer chain as it moves. It is straight forward to quantify the ion mobility in these systems through dielectric spectroscopy. The signal is dominated by the strong dipoles of the ions. It is, however, more difficult to quantify the dynamics of the polymer that were responsible for enabling these catch and release events. To better understand how the polymer enables ion transport we introduce inelastic neutron scattering measurements that are only sensitive to the dynamics of the hydrogenous polymer chains, not the inorganic ions. We perform in-situ measurements of the vibrational and relaxational properties that occur on the pico- to nanosecond type scale using both back scattering and time of flight quasielastic neutron scattering techniques. These measurements are done on single ion conductor systems where we can also directly quantify the ion mobility. Systematic perturbations to the ion mobility of these single ion conductor polymers are introduce with either small molecule diluents to enhance mobility or strong states of confinement in a porous support media to inhibit mobility. Under this broad range of conditions, we demonstrate a quantitative correlation between the macroscopically measured ion mobility and the intrinsic fast dynamics (pico to nanosecond) of the electrolyte. We discuss how this understanding provides insight into developing new high mobility solid polymer electrolytes.

    4:30 PM - CCC4.3

    In-Situ Analytical Transmission Electron Microscopy for Probing Nanoscale Electrochemistry

    Thomas  McGilvray1, Feng  Wang2, Dhamodaran  Santhanagopalan1, Dongli  Zeng2, Ming-Che  Yang3, Nancy  Dudney4, Jason  Graetz2, Shirley  Meng1.

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    To understand energy storage materials during dynamic electrochemical operation, for instance in a lithium ion battery, few techniques can yield more critical information than high resolution analytical transmission electron microscopy coupled with electron energy loss spectroscopy (EELS). EELS is ideal for Li-containing materials because of its ability to detect Li with high spatial resolution. Functional thin film battery stacks are prepared through a combination of sputtering and pulsed laser deposition (PLD) techniques. Nanoscale functional batteries are fabricated using focused ion beam (FIB), then mounted on custom designed TEM grids capable of applying an electrical bias. Since electrochemically functional cross sections of nanoscale batteries have been extremely difficult to prepare, we have developed a new protocol to eliminate sources of shorting during the FIB preparation process. We will discuss the structural and electrochemical properties of the nano scale batteries characterized both ex situ and in situ.

    4:45 PM - CCC4.4

    Study of In situ Corrosion Mechanisms of Metallic Materials by Scanning Probe Microscopy

    Christophe  Harder1, Lilian  Berlu1, Benoît  Reneaume1.

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    This work consists in the in situ study of corrosion mechanisms of several metallic materials. Those phenomena take place at the extreme surface of materials before spreading in the bulk. In this way, in situ surface characterization techniques as scanning probe microscopy (Scanning Tunneling Microscopy (STM) and Atomic Force Microscopy (AFM)) allow the observations of the very initial reaction steps. The main goal of this study is to display the surface’s modifications of metallic materials due to heat treatments and during corrosion reactions under different atmospheres for pressure levels up to 20 bars. To achieve that goal, the CEA Valduc has build an environmental fence that is able to integrate either an atomic force microscope (AFM) or a scanning tunneling microscope (STM). This fence can resist to internal pressures from primary vacuum (i.e. ~10-4mbar) to overpressures up to 20 bars. It’s also fitted out with two thermocouples that allow the measurement of two different temperature points inside (inside medium and sample), a visualization window and a lateral displacement system made by a combination of two micrometric screws that allows the study of the whole sample’s surface without opening the fence. A gaseous transfer line, has been drawn and build to achieve the introduction of a huge variety of more or less reactive atmospheres in the fence. In this way, heterogeneous “solid – gas” reactions that only occur with pressures above several atmospheres, will be studied, especially by the following of the topographical evolution of the surface’s samples put in contact with different reactive gas. The identification of the surface defects at the origin of corrosive attacks as well as proposition of reaction mechanisms are the main objectives of this work. The first in situ measurements are shown here to validate this new and unique experimental High Pressure Atomic Force Microscope, so called “HP-AFM”. Special care are made concerning the study of the atmosphere composition’s impact into the environmental fence as well as the pressure values on the topographic measurements recorded by both AFM and STM systems. In this way, samples with well known properties and calibration standards are used in order to highlight a working drift of the AFM or STM systems (scanner head displacements, optical detection …) that could lead to eventual distortions of pictures recorded.

    CCC5: Poster Session: Nanoscale Probing of Material Properties Using Electron Microscopy and Scanning Probe Techniques

    • Tuesday PM, April 10, 2012
    • Moscone West, Level 1, Exhibit Hall
     

    5:00 PM - CCC5.1

    Investigation of Growth Behavior of ZnS Nanocrystal by HR-TEM and STEM-Tomography

    Masato  Uehara1.

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    Nanocrystals (NCs) have received much attention because of their attractive properties. These properties are governed by the morphology. We must control them for the development of NCs material. In particular, the characterization of surface structure is very important, because this structure is key information for the control of particle growth. We are able to obtain the atomic structure information of individual NCs by HR-TEM. However, these images lack the 3D figure information. The image contrast of HAADF is made of atomic mass and specimen thickness, and consequently this technique provides the information of 3D figuration in nano-scale. By combination of HR-TEM and HAADF-Tomography, we can crystallographically and 3-dimensionally discuss the surface structure of NCs. I successfully synthesized high quality ZnS nanorods which exhibited the band-edge fluorescence in UV region. ZnS is one of the attractive materials because of the optical and electric properties. Although many papers describe the fluorescence of ZnS NCs, the papers describing the excitonic emission are few. Consequently, production of ZnS NC exhibiting excitonic emission without tailing would be worthwhile mission. In this paper, I investigated the structural evolution of these ZnS NCs by HR-TEM and HAADF-Tomography. The NCs were synthesized from zinc-amine complex in organic solvent by gradual heating. I confirmed the small particles at 125 °C. The particles one-dimensionally grew along to <001> in hexagonal phase below 175 °C. At 200 °C, the hexagonal phase transformed to cubic phase. The nanorods diameter was about 4 nm and the length was about 10 nm. The nanorods exhibited band-edge emission around 320 nm in fluorescence spectra. By the furthermore heating, I observed the coalescence of nanorods at the each lateral face, leading to the nanoplate formation 225 °C. Furthermore, the nanorods coalesced three-dimensionally at 250 °C, resulting in the formation of the large particle with 10nm diameter. These coalesced particles had no grain boundary. The particle would grow by the Oriented Attachment Process as reported by some papers. In HR-TEM observation for 250°C sample, the particles had a triangle head. According to images from <1-10> direction, the triangle head visually consisted of {110} and {114} facets. This is strange because the surface energy of {110} plane is very low but that of {114} plane is high. Using HAADF-Tomography, I found that the 3D-shape of triangle head was not pyramid but rather corn. In other words, the triangle head had a curved surface rather than truncations of low energy plane. The surface consisted of not only {110} low energy planar segments but high energy planar segments like as {114}. These high energy segments would come in by {110} faces. This appearance of high energy segments would be noteworthy for NCs developments, because these high energy planes have high reactivity as catalytic and doping sites.

    5:00 PM - CCC5.2

    Probing Irreversible Electrochemical Reactions in (LaxSr1-x)CoO3-δ Cathode Materials

    Amit  Kumar1, Donovan  Leonard1, Francesco  Ciucci2, Stephen  Jesse1, Mike  Biegalski1, Hans  Christen1, Eva  Mutoro3, Ethan  Crumlin3, Yang  Shao-Horn3, Albina  Borisevich1, Sergei  Kalinin1.

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    The energy conversion in electrochemical energy conversion systems is underpinned by a series of complex mechanisms like ion and vacancy diffusion, electronic transport and solid-gas and solid-liquid reactions at surfaces and triple phase junctions.Spatial variability of reversible and irreversible electrochemical processes on a (La0.5Sr0.5)2CoO4±δ-modified (LaxSr1-x)CoO3-δ surface is studied using first-order reversal curve method in electrochemical strain microscopy. The reversible oxygen reduction/evolution process is activated at voltages as low as 3-4 V and the degree of transformation increases linearly with applied bias. The irreversible processes associated with static surface deformation become apparent above 10-12 V. The critical voltages for the onset of reversible and irreversible electrochemical transformations on the LSCO214/113 surface are different, and hence these phenomena can be studied separately under appropriate bias conditions. Ex-situ focused-ion milling combined with atomic resolution scanning transmission electron microscopy and electron energy loss spectroscopy is used to establish the mechanisms of irreversible transformations. These studies both establish the framework for probing irreversible electrochemical processes in solids and illustrate rich spectrum of electrochemical transformations underpinning catalytic activity in cobaltites. The work was supported (AK, DL, AB) by the Materials Science and Engineering Division of the U.S. DOE. This research was conducted in part (AK, SVK, MB) at the Center for Nanophase Materials Sciences, which is sponsored at Oak Ridge National Laboratory by the Scientific User Facilities Division, U.S. Department of Energy. MIT group (YSH, EC, EM) acknowledges US DOE (SISGR DESC0002633).

    5:00 PM - CCC5.3

    Supercooling of Nanoscale Ga Drops with Controlled Impurity Levels

    Eli  Sutter1, Peter  Sutter1, Emanuele  Uccelli2, Anna  Fontcuberta i Morral2.

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    Melting and crystallization are fundamental processes by which most substances change between a disordered liquid and an ordered solid state. Nanoparticles can melt and freeze at temperatures different from the bulk, undergo significantly higher supercooling, crystallize along different pathways [1], and in structures different from the bulk [2]. Ga is a particular metal that can be supercooled to half of its melting temperature, and thus Ga droplets have become a model system for studying deep supercooled liquids. The extent of achievable supercooling can presumably vary with droplet size, purity, interactions with supports, etc. The understanding of the ultimate limits of supercooling of liquids and their intrinsic crystallization pathways, long-standing fundamental issues in the physics of fluids, requires eliminating heterogeneous crystallization, e.g., due to contact with confining matrices and foreign materials (from supports and uncontrolled impuritites). Here we investigate the melting and crystallization of Ga drops at the tips of GaAs nanowires (NWs). This particular geometry avoids any matrix effects, and limits the interactions between liquid Ga nanodroplets and the support surface to a well-defined solid-liquid interface. We use in-situ, variable temperature transmission electron microscopy (TEM) to follow the phase behavior of individual Ga droplets, among a large ensemble of similar drops confirming the generality of the observations on single drops. This unprecedented level of control allows us to perform identical experiments on pure Ga nanodroplets and on liquids containing different impurities levels [3] and show that the crystallization temperature, and hence the ultimate achievable supercooling, strongly depends on the concentration of impurities. All drops show predominant β- and γ-Ga correlations in the liquid phase and ultimately crystallize to solid β- and γ-Ga, which provides support for a scenario, in which impurities limit the achievable supercooling without significantly templating the crystalline phase. 1. P. Sutter and E. Sutter, Nature Mater. 6, 363 (2007). 2. E. Sutter, P. Sutter, Nanotechnology, 22, 295605 (2011). 3. B. Ketterer, E. Mikheev, E. Uccelli, A. F. I. Morral, Appl. Phys. Lett. 97, 223103 (2010).

    5:00 PM - CCC5.4

    Micromechanics of Fracture in Polycrystaline Materials

    Luis  Armando  Flores1, Pedro  A  Tamayo1, Viacheslav  Yermishkin2.

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    Recently, elementary results in the study of the mechanisms of fracture in polycrystal specimens were obtained from macroscopic mechanical tests, analysis of the structure by TEM and fractographic analysis of surfaces by SEM. As the grain size of polycrystalline materials is significantly greater than the thickness of the thin film, it can be analyzed by in situ methods in the HVTEM. It is a serious limitation for the widespread use of these methods in studying the micromechanics of fracture in these materials. However, for the study of the fundamental mechanisms of incubation and growth of cracks in polycrystalline microspecimens at the stage of the interaction of the defects in the crystalline structure, there are no many alternatives than the use of High Voltage Transmission Electron Microscopy. Moreover, the conclusions obtained from fracture studies in specimens tested in situ in the HVTEM column must be carefully interpreted especially when they are compared with studies obtained from single crystal specimens, and it is desirable to complement them with some other similar SEM experiments performed in situ or mechanical standard essays. Considering that, we will try to give an answer of how the results obtained by HVTEM are characteristic for monocrystalline and polycrystalline specimens also; how is it the behavior of grain boundaries during crack propagation; what is the role of the elements of the original structure such as the inclusions and second phase segregations in the processes of incubation and growth of cracks.

    5:00 PM - CCC5.6

    In-Situ Mechanical Characterization of Pristine and Hydrogen-Exposed Palladium Nanowires

    Jennifer  Carpena-Nunez1, Dachi  Yang1, Jae-Woo  Kim2, Luis  F  Fonseca1.

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    Palladium nanowires (Pd NWs) are of great interest for gas sensing and activated switches due to their low power consumption and short response time. Changes in a NWs crystal lattice upon hydrogen exposure by absorption and interstitial introduction of H atoms within the Pd matrix can induce swelling of the structure and generate dislocations through the solid that may alter the overall mechanical performance of the material. It has been well known that embrittlement can take place for some metal matrices, which in turn can shorten the lifetime of a sensing cell or even interrupt the electrical circuitry and lower the sensing proficiency of the device. Thus, understanding the mechanical endurance of Pd NWs pre- and post- absorption of hydrogen can provide information regarding the material’s durability, as prototype manipulation can potentially threaten the sensing device. We hereby present in-situ transmission electron microscope – atomic force microscope (TEM-AFM) mechanical characterization for as-prepared and hydrogen-exposed Pd NWs. Quantitative analysis and real-time observation of the Pd NWs in the TEM-AFM allow understanding the mechanical behavior and performance upon applied loads before and after hydrogen exposure of these sensing NWs. A series of compression and tension experiments have been conducted and values for the Young’s modulus, tensile strength and strain will be presented.

    5:00 PM - CCC5.7

    Microstructural Changes in CdSe-Coated ZnO Nanowires Evaluated by in situ Annealing in Transmission Electron Microscopy and X-Ray Diffraction

    Hasti  Majidi1, Christopher  R  Winkler2, Mitra  L  Taheri2, Jason  B  Baxter1.

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    We report on microstructural and morphological transformations in thin CdSe coatings on ZnO nanowires upon annealing. Evolution of the microstructure was monitored in situ using transmission electron microscopy (TEM) and X-ray diffraction (XRD), providing new insight into the rates and mechanisms of crystallite growth and the phase transition from zinc blende to wurtzite. These studies illustrate the power of in situ microscopy and diffraction while also providing insight into the design of nanostructures useful for extremely thin absorber (ETA) solar cells. CdSe, a II-VI compound semiconductor with band gap of 1.7 eV, has been used as the absorber in ETA solar cells. In a typical ETA cell, an absorber is sandwiched between nanostructured, interpenetrating n-type and p-type semiconductors. The large interfacial area, provided here by an array of ZnO nanowires, allows much thinner absorber compared to a planar photovoltaic. This structure reduces bulk recombination and enhances charge separation at the interface. Absorber thickness should be comparable to charge collection length. Collection length is determined by mobility and lifetime of the photoexcited carriers, which are directly related to the microstructure of the coating. Ideally, a single crystallite will extend through the entire absorber thickness. Specifically, we will describe thermally-induced crystallite growth and phase change of CdSe coatings electrodeposited on ZnO nanowires. Both in situ TEM and XRD reveal that crystallite size increases from ~3 nm to ~10 nm upon annealing at 350 C for one hour. Another one hour annealing at 400 C increases the nanocrystal size to over 30 nm. Annealing also induces a structural phase change from zinc blende to wurtzite. Real-time observations show that crystallite growth is much faster at 400 C than 350 C, indicating two different growth regimes. Ostwald ripening dominates at 350 C while other mechanisms of matter transport also become important at 400 C. Increased CdSe crystallite size, comparable to the film thickness, will improve charge separation in ETA solar cells.

    5:00 PM - CCC5.8

    In-situ Electrical Measurements in Transmission Electron Microscope

    Maria  Rudneva1, Henny  W  Zandbergen1.

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    Ongoing miniaturization of electrical devices places new demands on more precise and reliable methods for sample investigation. Combination of observation and measurement techniques can give deeper insights into the micro- and nano- scale processes occurring in the samples and give better understanding of the influence of external factors such as electrical current on nanostructural changes in such devices. In the present contribution, we discuss real-time electrical measurements on nano-samples combined with simultaneous examination by transmission electron microscope (TEM). Application of electrical current may lead to nanostructural changes in the sample and thus the possibility to correlate such changes with the corresponding I-V measurements. Real-time video recordings using a fast scan camera (up to 25 images per second) allows us to correlate features appearing on current-voltage (I-V) characteristic or changes in resistance of the sample with changes of its nanostructure. A special sample holder built in-house has 8 feedthroughs for carrying out the electrical measurements. It allows to connect chip-like samples with the measurement setup and to perform experiments in different temperature ranges. Using the aforementioned system, several investigations were carried out, which yielded very interesting results. Firstly, the phenomenon of electromigration (EM) was investigated in Pt nano-bridges (14 nm thick, 200 nm wide and 300 nm long). The evolution of grain size in nanocrystalline Pt bridges was correlated to the change in the electrical resistance by in-situ transmission electron microscopy. The EM experiments were performed in 2 different modes: with and without feedback control. Using the feedback control mode, symmetric electrodes were obtained with the formation of a gap at the center of the Pt nanobridge while the absence of feedback control resulted in asymmetric electrodes with the formation of gap at a random position along the bridge. A high-angle annular dark-field scanning TEM technique allows the determination of the 3D profile of electrodes near the gap. Exact knowledge of the geometry of this junction makes it possible to validate various tunneling models and to use obtained electrodes for electrical measurements on nano-sized objects. With the described method it is possible to carry out the in-situ electrical measurements in TEM on a wide range of materials such as metallic and semi-conductor nanowires, nanobridges, nanopatricles and novel materials such as graphene. We gratefully acknowledge NIMIC for support

    5:00 PM - CCC5.9

    Size Dependent Fracture Modes Transition in Copper Nanowires

    Cheng  Peng1, Yongjie  Zhan1, Jun  Lou1.

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    In situ uni-axial tensile tests of single crystalline copper nanowires were performed using a micro mechanical device inside a scanning electron microscope (SEM) chamber. The single crystalline copper nanowires were synthesized by solvothermal processes, and the growth direction along the wire axis is <110> orientation as confirmed by transmission electron microscope (TEM) selected area diffraction (SAD) analysis. The facture strengths of copper nanowires were found to be much higher than that of bulk copper. More interestingly, both ductile and brittle-like fracture modes were found in the same batch of fabricated nanowires and the fracture modes appeared to be dependent on diameters of tested nanowires. From the analysis of fracture surfaces, sample morphologies and corresponding stress-strain curves, the competition between deformation and fracture mechanisms controlled by initial defects density and by the probability of dislocation interactions was attributed to this intriguing size dependent fracture modes transition.

    5:00 PM - CCC5.10

    Direct Observation of Surface and Internal Structure of Nanoporous Materials with Low Acceleration Voltage FE-SEM

    Akira  Endo1, Akiko  Kawai1, Mitsuhiko  Yamada1.

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    Recent progress on scanning electron microscope (SEM) technology has enabled us to observe the porous structure of nanoporous materials in a nanometer scale. The most commonly used method for the direct structural observation of nanoporous materials employs a high-resolution transmission electron microscopy (TEM). However, the TEM images correspond to the projected structures of the specimen because the electrons are accelerated at a high voltage of generally more than 100 kV. In addition, certain pre-treatment processes that may damage the structure of the specimen, such as the use of a focused ion beam (FIB), or ion thinning with Ar ions, are necessary prior to the TEM observation. In contrast, an SEM has advantages over a TEM in terms of ease of sample preparation and the observation of top-surface images with a lower electron acceleration voltage. We can also expect to use high-resolution FE-SEM to investigate internal porous structures with a cross-section fabrication technique. Very recently, we proposed an HR-SEM observation technique of internal mesostructure in combination with a broad ion beam (BIB) method. We reports recent results for the direct imaging of the surface and internal structure of nanoporous materials using a low acceleration voltage FE-SEM and recently developed techniques.

    5:00 PM - CCC5.12

    In situ TEM Study of Dielectric Breakdown of SiO2-Based Dielectric Layers

    Cecile  Bonifacio1, Klaus  van Benthem1.

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    The dielectric layer is a critical component of the metal-oxide-semiconductor devices and the reduction of its thickness is a challenging aspect of scaling. As the dielectric layer thickness decreases, electron tunneling may lead to device failure due to the inability of the insulating oxide layer to keep its capacitance. Defect formation over time under electrical stress provides information about the nanoscopic mechanisms of dielectric breakdown. The time dependent dielectric breakdown of ultrathin SiO2 dielectric layer in Co-silicide/poly-Si/SiO2/Si field-effect transistor devices was studied using in situ transmission electron microscopy (TEM). A comprehensive structural and chemical characterization of the SiO2 dielectric layer and its interfaces was carried out before and after dielectric breakdown was imposed. An STM tip mounted on the TEM specimen holder was used to apply an electrical bias to the gate electrode of a cross-sectionally prepared TEM sample of the device structure. TEM imaging allowed the observation of structural changes due to the applied electrical field. Constant bias and ramped bias stress experiments resulted to soft breakdown (SBD) and hard breakdown (HBD) of the device structure, respectively. SBD events revealed relative leakage current increases below 100% due to roughening of the interfaces with the silicon substrate and the gate electrode. HBD, however, showed relative leakage current increases as high as 200 to 400% combined with Co atom migration into the SiO2 layer and partial crystallization of the previously amorphous SiO2. In addition, a reduction-oxidation reaction at the Si/SiO2 interface was observed that was triggered by the applied electrical field. Oxygen subsequently diffused into the silicon substrate. The experimental results demonstrate that it is feasible to directly measure defect structure evolution during dielectric breakdown using a combined STM-TEM setup.

    5:00 PM - CCC5.13

    FIB/SEM/TEM Imaging of Multilayer PC/PVDF-HFP Films for High Energy Density Capacitors

    Mason  Atom  Wolak1, Alan  Wan3, Vaibhav  Jain1, James  S  Shirk1, Matt  Mackey2, Eric  Baer2.

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    Multilayer polymer films show great promise for use as the dielectric material in high energy density capacitors. The multilayer structure enhances both the dielectric strength (EB) and energy density (Ud) of the composite relative to single-layer films of the component polymers. Films comprising alternating layers of polycarbonate (PC) and polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) demonstrate EB > 750 kV/mm and Ud > 13 J/cm3. To elucidate the role of the layer structure during electrical breakdown, we have developed a tandem focused ion beam (FIB) / scanning electron microscope (SEM) imaging technique. The FIB is used to mill site-specific trenches into a film and the resulting cross-sections are imaged via SEM. The layer structure can be resolved due to the differences in electron density between PC and PVDF-HFP. The technique has been used to obtain images on both ‘as fabricated’ control films, and those subjected to high electric fields. Individual layers as thin as 50 nm have been successfully resolved. For films subjected to electrical breakdown under divergent field conditions, the location and propagation of damage is tracked with sequential FIB milling and SEM imaging cycles. The spatially resolved FIB/SEM imaging allows preparation of quasi-3D maps that display the evolution of internal voids in areas adjacent to the breakdown location (typically a pinhole with d = 30-80 μm). A majority of the voids are localized at the interfaces between layers and may propagate as far as 30-50 μm from the pinhole. The data suggest that the enhancement in dielectric properties arises from a barrier effect, whereby the propagation of an electrical breakdown in the direction of the applied field is impeded by the layer interfaces. Because the layer interfaces apparently play a prominent role in influencing the breakdown mechanism, detailed structural, elemental, and chemical analysis of the interfacial region is required. High resolution imaging of the interfaces has been achieved via TEM on very thin (< 100 nm) cross-sections prepared using the FIB ‘Liftout’ technique. For films where the individual PC and PVDF-HFP layers are ~ 370 nm thick, initial measurements indicate that the interfacial region is approximately 7 ± 2 nm in width. Energy-dispersive X-ray spectroscopy (EDX) has also been used to map the PVDF-HFP concentration gradient across the interface.

    5:00 PM - CCC5.14

    In-situ Probing of Polarization Dynamics in Ferroelectric Materials: From Mesoscopic to Atomic Levels

    Hye Jung  Chang2 1, Young-Min  Kim1, Seung-Yeul  Yang3, Pu  Yu3, Ramamoorthy  Ramesh3, Sergei  V  Kalinin1, Albina  Borisevich1.

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    Ferroelectric materials in the capacitor, gate dielectric, or tunneling barrier geometry are actively explored for non-volatile memory applications. Implementation of these devices necessitates understanding of local switching mechanisms as affected by device geometry, structural defects, and strain relaxation mechanisms. Particularly of interest are these phenomena in multiaxial ferroelectric materials that allow for ferroelastic switching and polarization rotations. Here, we explore polarization switching in BiFeO3 films using combined scanning probe microscopy – scanning transmission electron microscopy. In our setup, the biased SPM probe is used to focus electric field in the small volume of material, whereas STEM provides the information on the evolution of resultant domain structures. Using in situ STEM, we study the domain switching dynamics in films with SrRuO3 bottom electrodes, and observe surface and interface domain nucleation, domain wall pinning on defects, and changes in the domain wall angles as a function of the bias sign. We correlate these studies to the high resolution STEM imaging and structure mapping to identify the polarization distribution around domain wall and the structure of domain-wall pinning dislocations. Progress towards in situ observation of cation displacements will also be discussed. These studies provide pathway for probing atomistic switching mechanisms in ferroelectrics. This research is sponsored by the Materials Sciences and Engineering Division (HJC, YMK, SVK, AYB) and Office of BES of the U.S. DOE, and by appointments (HJC, YMK) to the ORNL Postoctoral Research Program administered jointly by ORNL and ORISE. Instrument access via SHaRE User Facility, which is supported at ORNL by Office of BES of the U.S. DOE, is gratefully acknowledged.

    5:00 PM - CCC5.16

    Sliding on a Nanotube: Interplay of Friction, Deformations and Defects

    Hsiang-Chih  Chiu1, Suenne  Kim1, Erio  Tosatti2 3, Christian  Klinke4, Elisa  Riedo1.

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    Because of their exceptional physical properties, Carbon nanotubes (CNT) have found applications as reinforcements in composite materials and essential components in micro and nano-electro-mechanical devices, such as actuators and sensors. However, CNTs often have structural defects inevitably present throughout the nanotubes and defects are known to change the mechanical properties of CNTs. For most applications, CNT are in contact with their supporting surfaces. Therefore it is imperative to understand their frictional properties as well as the role of structural defects. In our work, we show how structural defects can influence the frictional properties of supported CNTs grown by Arc Discharge (AD) and Chemical Vapor Deposition (CVD) methods, the latter having more structural defects than the former, as measured by Raman Spectroscopy. A nanosize AFM tip is used to slide along (longitudinal sliding) and across (transverse sliding) the CNT axis. As a general trend observed for all CNTs, a larger friction coefficient is found during the transverse sliding than the longitudinal sliding. This is explained by a lateral deformation (also called hindered rolling) of CNT during transverse sliding, which produces an additional friction dissipation channel that is absent during longitudinal sliding [1]. Furthermore, the defects and CNT chirality couple the transverse and longitudinal sliding motions, resulting in more energy dissipation during longitudinal sliding and hence higher longitudinal friction forces. The friction anisotropy, defined as the ratio of the shear strength measured during transverse and longitudinal sliding, can be as high as 13.7 for AD CNTs while for CVD CNTs, this friction anisotropy is always below 6. This is attributed to different structural defects present in CNTs. A simple analytical model has been developed to compute the amount of coupling between the transverse and longitudinal sliding, the “intrinsic” hard contact sliding shear strength, and the soft “hindered rolling” shear strength. This model captures very well the observed experimental behavior. The defects clearly increase the transverse-longitudinal coupling, the transverse deformation of CNT, and the intrinsic friction force between the tip and the carbon sheets. Our finding provides a better understanding of the tribological properties of individual carbon nanotube and might assist manipulations of nano objects at the nanoscale. [1] M. Lucas et al., Nature Mater. 8, 876 (2009)

    5:00 PM - CCC5.17

    Encased Cantilevers and Alternative Scan Algorithms for Ultra-gentle High Speed Atomic Force Microscopy

    Dominik  Ziegler1, Alex  Chen2, Sindy  Frank4 1, Andreas  Frank4 1, Rodrigo  Farnham3, Nen  Huynh3, Travis  Meyer2, Jen-Mei  Chang3, Ivo  Rangelow4, Andrea  Bertozzi2, Paul  Ashby1.

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    Live cells and many biological samples readily deform under the minimum force required to perform an AFM measurement precluding imaging at high temporal and spatial resolution. We reduced the force noise of the measurement by building a protective encasement around the cantilever. This keeps the cantilever is dry reducing the fluid viscosity and damping but allows the tip to probe the sample in solution. Encased cantilevers have exceptionally high resonance frequency, Q factor, and detection sensitivity and low force noise enabling gentle high speed imaging. Present raster scan techniques are poorly matched to the instrument limitations of Atomic Force Microscopy making data collection slow. We have used advanced image processing tools such as inpainting to recover high-resolution images from sparse quickly collected images to improve temporal resolution without applying more force or increasing bandwidth. We are also using spiral scanning to increase temporal resolution by allowing higher tip velocities without distortion. Inpainting or interpolation is used to quickly create images from the nongrided data.

    5:00 PM - CCC5.18

    Relationship of Resistance and Contact Force Using Flexible Au Nanowire SPM Probe

    Jong-Hyun  Seo1 3, Kon Bae  Lee2, Tae-Yeon  Seong3, In-Suk  Choi4, Bongsoo  Kim5, Jae-Pyoung  Ahn1.

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    SPM has become a mainstream technique of nanoscience by providing easy to use methodology for noninvasive imaging and manipulation on atomic scales. Beyond topographic imaging, SPM techniques have found an extremely broad range of applications in probing electrical, magnetic, optical and mechanical properties. Among the applications, the direct measurement on the electrical properties at nano-scale is challenging because the SPM probe has main problems such as low aspect ratio, easy deformation and poor measurement reliability. In these aspects, flexible and strong nanowires will be an ideal SPM probe because those intrinsically have high aspect ratio and high flexibility. In addition to the requirement of SPM probes, the dynamic relationship of contact force and contact area between SPM probe and sample surface has to be investigated for measurements of the precise and reliable electrical properties. In this study, we fabricated SPM probes using Au nanowires, which have superior mechanical and electrical properties such as high aspect ratio, high elasticity, high strength and excellent conductivity, and measured the in-situ electrical resistance of the Au nanowire SPM probe during compressive loading. In compressive test, the Au nanowire SPM probes show buckling phenomena when the Au nanowire comes to the high elastic strain of 1.14% and a critical stress of 8.87 MPa. The Young’s modulus of Au nanowires under compressive stress was calculated by 77.77 GPa similar to theoretical Young’s modulus of bulk Au (78 GPa). The resistance variation of SPM nanoprobe is exactly corresponding to the change of the mechanical property of Au nanowires in elastic region and buckling region. Until buckling onset, the contact resistance decreases as a function of the increase of compressive stress, which induces the increase of contact area. The deformation of nanoprobe tip deciding the contact area agrees with elastic deformation theory. As soon as the buckling occurs, the compressive stress becomes constant and thereby there is no change in the contact area anymore. Furthermore, the constant stress allows the Au nanowire SPM probe to have a constant resistance. In conclusion, the stabilization of contact area by the buckling provides not only stable contact between SPM probe and sample surface, but also high electrical reliability without noise.

    5:00 PM - CCC5.19

    Atomic Scale Dynamics of Frictional Processes

    Filippo  Federici Canova1 2, Shigeki  Kawai3, Thilo  Glatzel3, Adam  S  Foster1 2, Ernst  Meyer3.

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    Friction has generated a lot of scientific interest in recent years due to its recurrence in almost every aspect of our life. It is one of the most fundamental processes in nature, and remains a key design concept in machines and devices. Friction and wear are the main source of failure in every kind of machinery, macro- and microscopic, as well as biological applications, from prosthetics to drug design/delivery; efforts to reduce and control their effects forms a wide research area. As this field of research has developed alongside modern experimental techniques, it has become evident that friction originates at the nanoscale thus atomic force microscopy became the tool of choice for creating a controllable nanocontact with a surface, where the friction and wear properties and can be studied in detail. Torsional resonance (TR) AFM offers the opportunity to map lateral forces on a sample at extremely high resolution, without damaging the surface as it relies on the same principles of non-contact AFM. The TR frequency shift is related to the lateral force while the excitation signal (or damping) is related to the energy lost to atomic scale frictional processes. While the former is well understood, interpretation of the latter, remains challenging, and an area of intense research, and as yet there are no theoretical or experimental studies of lateral dissipation in TR-AFM. Studying frictional processes at the atomic scale can provide understanding of how materials degrade due to wear, aiding design to improve durability. Our studies focus on NaCl (001) surface, which is an important benchmark system for theoretical models and is easily prepared in the laboratory. Experimental data showed that the vertical interaction with the tip was too weak to give a distinct topography of the surface, whereas lateral interaction, detected via the lateral frequency shift provided surface images with atomic resolution. Although the lateral frequency shift map showed the checkerboard pattern typical of ionic crystals, the damping image looked different. Along a scanline along the atomic rows, the damping signal gives two peaks around one site. In order to understand this, we performed classical molecular dynamics (MD) simulations of the torsional oscillation cycles. We create the model tip via MD, following a procedure similar to the experimental one, and we process it so that vertical dissipative processes are inhibited, as we know from the experiments that no dissipation was detected in the vertical mode. We simulate several cycles, and we repeat the whole calculation placing the tip in several positions on the scanline. Preliminary results show that, while the frequency shift contrast reveals intuitively the surface pattern, the dissipated energy gives a double feature close to one of the two atomic species.

    5:00 PM - CCC5.20

    Extreme Sensitivity in Potential Characterization of an Insulating Step Edge

    Filippo  Federici Canova1 3, Shigeki  Kawai2, Thilo  Glatzel2, Adam  S  Foster1 3, Ernst  Meyer2.

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    Understanding potential variations near step edges of surfaces is of cardinal importance to control surface processes such as adsorption, growth, catalysis and friction. Ionic crystal surfaces attract the scientific attention due to their high band gap, and in particular, there is a large interest in studying step edges, for their key role in the adsorption chemistry. In our dynamic force spectroscopy (DFS) experiments, we study the potential variations near a LiF (001) step edge using the flexural and torsional resonance of the cantilever. The flexural oscillation is used to regulate the tip-sample distance, while the torsional one detects the site-dependent interaction. The lateral oscillation is not affected by long range site-independent interactions and thus has a very high sensitivity to the lateral potential gradient. Our measurements show how the vertical interaction is quite weak across the step edge and it does not show a strong dependence on the applied bias voltage. However, the torsional frequency shift, shows a remarkable contrast, and far away from the step, it has a linear dependence on the bias voltage. In order to better understand this effect we performed atomistic calculations with the shell model, using a model LiF (001) surface with a step edge, a planar electrode below the surface and a spherical electrode representing the tip. Because the electrodes in the simulation are applied few atomic layers below the surface, while the real ones have few millimetres of insulating material on top, the effective bias to be used in the atomistic model was evaluated from a finite elements calculation considering the whole cantilever, the macroscopic LiF sample and the grounded vacuum chamber. Such details were found to be quite important since the effective potential calculated in a simpler setup can be 10% larger. After relaxing the surface at different bias voltages and tip positions, we evaluated the gradient of the Coulomb interaction between the resulting surface and a dipole fixed on the tip, and from this, the torsional frequency shift. We found the same linear trend seen in the experiment. The potential change can then be related to the different reconstruction at the step edge, when the ions are more free to move and affect the surface dipole.

    5:00 PM - CCC5.21

    Time Dependent Mechanical Properties of Materials at Nanometer Length Scale

    Syed Amanulla  Syed Asif1, Oden  L  Warren1, Jeremiah  S  Vieregge1, Todd  E  Stanley1, Richard  Nay1.

    Show Abstract

    Depth sensing nanoindentation enables examination of surface mechanical properties of ultrathin films and compliant materials with far greater resolution and accuracy than ever before. At Hysitron, we have recently implemented improved nanoscale dynamic mechanical analyses of materials (nanoDMA III) which combine depth-sensing nanoindentation with force modulation and in-situ imaging capabilities. This combination allows surface sensitive, quantitative mechanical properties measurements of materials at a single point as well as while scanning. We illustrate these expanded capabilities with several examples: (a) dynamic nanoscale indentation test with new dual frequency referencing and frequency sweep (b) dynamic nanoscale creep test, and (c) mechanical property mapping. The dynamic nanoindentation test is used for measuring dynamic properties (loss and storage moduli) as a function of depth, load, frequency and temperature. The dynamic nanoscale creep test allows the study of mechanical property as a function of time and temperature for a long period without having much influence of thermal drift in the measurement. Mechanical property mapping provides a means of directly imaging mechanical response and properties with sub-micron spatial resolution. We will discuss how these enhanced capabilities can be used to measure surface mechanical properties and test the models and limits of continuum mechanics.

    5:00 PM - CCC5.22

    Nanoscale Observation of the Distribution Polarization in Lithium Niobate Thin Films

    Dmitry  A  Kiselev1, Roman  N  Zhukov1, Alexandr  S  Bykov1, Mikhail  D  Malinkovich1, Yuriy  N  Parkhomenko1.

    Show Abstract

    Lithium niobate (LiNbO3) is known as a transparent material which has superior piezoelectric and electro-optic properties. The resultant integrated optical devices of LiNbO3 crystal have been widely applied in optical signal systems, optical computing systems and optical sensing systems. The parameter of LiNbO3 thin film such as the refractive index, relative dielectric constant and lattice constants are very similar to LiNbO3 single crystal. Furthermore, although the electromechanical coupling coefficient of LiNbO3 thin film is smaller than that of LiNbO3 single crystal, but the surface acoustic wave (SAW) velocity of LiNbO3 thin film is much faster than LiNbO3 single crystal. Therefore, many investigations of LiNbO3 have been focused on the thin film technology and integration of LiNbO3 thin film in compatible with Si technology. In this work, an Atomic Force Microscope (AFM) in the so-called piezoresponse mode (PFM) is used to image the grains and ferroelectric domains in lithium niobate thin films. Films of LiNbO3 with a 100 nm thickness were sputtered (radio-frequency (RF) sputtering) at 550 °C for 1 h onto commercial (100) Si substrates with SiO2 layer. After deposition of the ferroelectric layer, the whole stack has been annealed in air at 850 °C for 1 h to improve the crystallization state of the active ferroelectric material. Such as-deposited films exhibit a granular morphology, without any predominant crystallographic orientation. A typical X-ray diffraction pattern is illustrated that reveals that LiNbO3 films deposited through a continuous one-step process are polycrystalline. The surface of the sample shows small grains which diameter ranges from 70 nm to 150 nm. From the statistical analysis of the topography thin lithium niobate films found that its roughness is less than 13 nm. Piezoresponse images on polycrystalline LiNbO3/SiO2/Si heterostructures not showed contrast from grains (that reflects the arrangement of domains in such non-oriented ferroelectric films), because in the case of LiNbO3/SiO2/Si composite structures, due to the electric insulating nature of the substrate and the lack of conductive interface, charge storage occurs at the interface during piezoresponse measurements. However, after the local polarization of the film surface under positive and negative DC voltage it is possible observe remanent piezoresponse signal (poling area). Charge entrapment at the existing domain boundaries in the bulk of the films, as well as charge accumulation on both the top and the bottom surfaces can significantly contribute to the decrease, and even suppression, of the switchable polarization. These results suggest that it may be possible to fabricate novel structures combining the ferroelectric and optical capabilities of LiNbO3 with the electronic processing advantages of SiO2.

    5:00 PM - CCC5.23

    Leakage Mechanism of Self-assemble BiFeO3-CoFe2O4 Nanostructure

    Ying-Hui  Heish1, Chen-Wei  Liang1, Ya-Ping  Chiu2, Yi-Chun  Chen3, Qing  He4, Qian  Zhan5, Ying-Hao  Chu1.

    Show Abstract

    Multiferroic materials with strongly coupled ferroelectricity and anti/ferromagnetism have been widely studied in recent years because of their potential applications for next-generation electronic devices. However, using single-phase materials under ambient environment meets certain limitations for their lack of composition variety and low coupling effect. An alternative approach using self-assembled nanostructured ferroelectric and magnetic composites has been adapted. One of the model systems is the combination of immiscible perovskite BiFeO3 (BFO) and spinel CoFe2O4 (CFO) by virtue of the strong piezoelectricity and high ferroelectric Curie temperature of BFO and the remarkable magnetostriction of CFO. However, large leakage current is often observed in these nano-composite thin films and hence limits their applicability. In this study, we focus on the mechanisms of the electrical leakage in high quality nano-composite thin films. Transport characterizations have been carried out using capacitor structures to study the vertical conduction through BFO-CFO nano-composite thin films with controlled mis-orientations. Local conduction has been investigated at micro scale by conducting atomic force microscope (C-AFM) as well as scanning tunneling microscope (STM). An interface limit model is found to be the dominant leakage mechanism and the nature of the interfacial band structure is also resolved. Knowledge extracted from our results could serve as a guide for future works on integration of nano-composites into functional microelectronic devices.

    5:00 PM - CCC5.26

    In-situ and Real Time Micro-Phase Separation Kinetic Analysis of Nanocomposite Polymer Thin Films Using Atomic Force Microsopy

    Skylar  N  White1, Brian  H.  Augustine1, Christopher  Hughes2.

    Show Abstract

    Poly(propylmethacrylisobutyl POSS co-methylmethacrylate) (POSS-MA) is a nanocomposite co-polymer that contains polyhedral oligomeric silsesquioxane (POSS) cages co-polymerized with a poly(methyl methacrylate) (PMMA) backbone. The properties of thin films of POSS-MA can be varied significantly by varying the composition of the weight percentage of POSS in the co-polymer. For this study, 2 mg/mL solutions of 20 – 70 wt% POSS-MA were dissolved in chloroform and deposited onto samples of oxidized Si wafers via spin-casting. Immediately after spin-casting, these samples were analyzed using in-situ and real-time atomic force microscopy (AFM) while being heated over a range of 25-90° C. We have observed micro-phase separation and crystallization with typical dendritic features from 1 – 10 µm through in-situ AFM. Typical 30 – 70 wt% POSS-MA thin films exhibit varying rates of micro-phase separation. Once this micro-phase separation is complete, the pixel areas of the dendritic structures were measured using the AFM software on the complete time-series of AFM scans. The measured area was normalized and then fit to an Avrami plot by graphing ln(-ln(1-f)) vs. ln (time) with “f” being the normalized area and the time being time after spin-casting. From this analysis, the dimensionality of growth constant rate constant (lnk) can be determined. Data shows the dimensionality of growth constant to vary from 1.72 to 2.15 and the ln(k) to vary from -9.02 to -14.14 when the scan is conducted at 35°C for 30 wt% POSS-MA thin films. This data is consistent with the literature values of two dimensional micro-phase separation in polymer thin films. Current work involves characterization of the silicon composition of the dendritic structures present on the POSS-MA thin films, and the effect of the nanoaggregation state of the polymer solution on the resulting thin films.

    5:00 PM - CCC5.29

    Kelvin-probe Measurements of MoS2 on Insulating Substrates

    Benedict  Kleine Bussmann1, Oliver  Ochedowski1, Kolyo  Marinov1, Marika  Schleberger1.

    Show Abstract

    Single layers of graphite are discussed as a substitute of silicon in future transistors. But graphene lacks an intrinsic bandgap which is required to obtain large current on/off ratios. In contrast, single layers of MoS2 are semiconducting and have therefore attracted much attention recently. In any insulator gated field effect device the charge exchange between the insulator and the semiconductor plays a crucial role. To investigate this effect in MoS2 we have measured the surface potential of thin MoS2 sheets, prepared by mechanical exfoliation on SiO2 as well as on SrTiO3. Monolayer regions were identified by μ-Photoluminescence before Kelvin-Probe-Force Microscopy was performed. For the system MoS2/SiO2 we find 1,85 eV for the band-gap, in good agreement with earlier results [1]. Our Kelvin probe data shows that the SrTiO3 substrate leads to an effective doping of the MoS2 monolayer with electrons. This shows, that also in MoS2 the carrier type as well as concentration is influenced by the choice of the substate as has been recently demonstrated for graphene [2,3]. [1] A. Splendiani, L. Sung, Y. Zhang, T. Li, J.Kim, C.-J. Chim, G. Galli, F. Wang, Nano Lett. 2010, 10, 12711275 [2] B. Kleine Bussmann, O. Ochedowksi and M. Schleberger Nanotechnology 22, 265703 (2011) [3] H. Bukowska, F. Meinerzhagen, S. Akcöltekin, O. Ochedowski, M. Neubert, V. Buck and M. Schleberger New J. Phys. 13, 063018 (2011)

    5:00 PM - CCC5.30

    Stress and Structure Evolution during Cu / Au(111) - √3x22 Heteroepitaxy: An In-situ UHV STM Study

    Jungwoo  Nah1, Cody  Friesen1.

    Show Abstract

    This presentation focuses on the stress and structure evolution observed in-situ during the earliest stages of thin film growth in the Cu / Au(111) √3x22 system. This work was enabled through the development of an ultra high vacuum-scanning tunneling microscopy (UHV-STM) system that was modified to have the additional capabilities of in-situ deposition and in-situ stress evolution monitoring. The deposition source enabled imaging during the deposition of Cu thin films, while also being columnar enough to avoid negatively impacting the function of the microscope. The substrate was in a cantilevered beam configuration, which allowed for the measurement of the stress-change-induced deflection by monitoring the extension of the tip via the z-piezo voltage. It was found that the stress-induced changes in piezo voltage were on a substantially longer time scale and larger piezo scale than that used for imaging, allowing for the deconvolution of the two sources of piezo voltage change. The intrinsic stress evolution observed at the onset of Cu growth was tensile in character and reached a maximum of 0.18 N/m at approximately 0.8ML, with an average tensile slope of 1.02GPa. As the film thickness increased beyond 0.8 ML, the stress became less tensile as the observation of disordered stripe and trigon patterns of misfit dislocations began to appear. The transport of atoms, from the surface of enlarged Cu islands into the strained layer, played an important role in this stage, because they effectively reduce the activation barrier for the formation of the observed surface structures. A rich array of structures were observed in the work presented here including stripe, disordered stripe and trigon patterns co-existing in a single Cu layer.

    5:00 PM - CCC5.31

    STM and STS Studies on Iridium Modified Si(111)and Si(001) Surfaces

    Nuri  Oncel1, Dylan  Nicholls1.

    Show Abstract

    Iridium silicides have the lowest (highest) Schottky barrier for holes (electrons). This makes them perfect for metal oxide semiconductor devices (MOSFET’s) even more attractive than platinum silicide based contacts for the integration of PMOS transistors. [ i,ii ] The morphology of the metal-semiconductor interface significantly influences the Schottky barrier heights therefore it is vital to know how metal-semiconductor interface grows right from the beginning. The study presented here focuses on uncharted territories of iridium (Ir) modified silicon (Si) (111) and (100) surfaces. To the best of our knowledge, there is no prior Scanning Tunneling Microscopy/Spectroscopy (STM/STS) study on initial stages of Ir growth on Si surfaces. Ir growth is monitored and controlled with an Auger/LEED system. In order to study the temperature effect on the surface morphology, the samples were annealed at various temperatures ranging from 600 °C to 1250 °C. The STM images measured on Ir modified Si(111)surface show that there are ‘1×1’ domains that coexist with 7×7 domains of Si(111). In addition to this, we observed the formation of quantum dots on ‘1×1’ domains. We think that these clusters contain both Ir and Si. The local density of states measurements performed on these ‘1×1’ domains show that the electronic properties of these domains are significantly different than the electronic properties of 7×7 domains of Si(111). On the other hand, Ir modified Si(001) surface exhibits missing dimer defects running along dimer bonds. Annealing Ir modified Si(001) at 1250 °C causes these defects to disappear suggesting that Ir atoms either sink in further in to the substrate or evaporated back to the vacuum. i E. Dubois, G. Larrieu, Solid State Electronics 46, 997 (2002). ii G. Larrieu, E. Dubois, X. Wallart, X. Baie, J. Katchi, J. Appl. Phys. 94, 7801 (2003).

    5:00 PM - CCC5.32

    Quantum Tunneling in Carbon-nanotube-based Scanning Tunneling Microscopy

    Meng-Mu  Shih1.

    Show Abstract

    The principle and mechanism of scanning tunneling microscopy (STM) have applications such as in nano fabrication, in situ measurements and manipulators. Due to the unique combination of properties, carbon nanotubes (CNTs) can serve as the probe tips in order to economically enhance the resolution, adaptation, durability, and speed of STM. This work modifies the quantum tunneling model to explain the working principle of such CNT-based STM by considering CNT-related parameters. Numerical results show how the tunneling probability, applied voltage, and CNT type affect the sample-to-tip separation distance, and vice versa. Results with physical interpretations will be discussed in order to potentially improve the design and performance of STM applications.

    5:00 PM - CCC5.34

    Enabling In situ Sub-micron Scale Chemical Imaging with Soft X-Ray Spectromicroscopy

    Stephen  T  Kelly1, Gregory  T  Carroll1, Tobias  Roedel1, Pascal  Nigge1, Shruti  Prakash1, Alexander  Laskin2, Mary  K  Gilles1.

    Show Abstract

    In the rapidly developing fields of energy generation and storage, novel devices often include a mix of organic and inorganic materials (both of which may be structured on sub-micron length scales) and utilize increasingly complex chemical reactions. The ability to observe these reactions in situ with detailed chemical information can provide valuable insight into the inner workings of these reactions. Soft x-ray spectromicroscopy such as scanning transmission x-ray microscopy (STXM) is ideally situated to probe the chemical environment of a wide range of elements (using K-, L-, and M-edge x-ray absorption spectroscopy) with spatial resolution below 0.1 μm. While traditional in situ measurements using STXM have been made using a variety of methods, most were tailored specifically for a particular measurement. Widespread implementation of capable reactor chambers which enable a variety measurements quickly and easily will open up a host of new capabilities, leading to valuable new scientific insight. We have developed two gas-phase reactors which can accommodate a wide variety of STXM experiments. Both reactors are based on a simple transmission chamber with single gas inlet and outlet ports, with a depth along the optical axis below 2 mm. Process gas is supplied from outside the microscope chamber through small diameter gas lines which mate to a dedicated feedthrough flange. The first reactor, designed specifically for measurements under a water vapor atmosphere, contains an integrated sensor to actively measure the relative humidity and temperature inside the reactor enclosure. The second reactor design allows measurements under a wide variety of process gasses, with the eventual inclusion of a small MEMS heater chip to enable control of local sample temperature. As examples, we present here our recent results using these reactors to probe several diverse material systems such as the deliquescence of submicron sized salt particles and carbon dioxide sorption in metal-organic-framework materials.

    Download Session Locator (.pdf)2012-04-11  

    Symposium CCC

    Show All Abstracts

    Symposium Organizers

    • Nina Balke, Oak Ridge National Laboratory
    • Howard Wang, State University of New York, Binghamton Institute for Materials Research
    • Job Rijssenbeek, GE Global Research
    • Thilo Glatzel, University of Basel

    Support

    • Asylum Research
      Zurich Instruments Ltd

      CCC6: Novel Techniques for Material Characterization

      • Chair: Sergei Kalinin
      • Chair: Dean Miller
      • Wednesday AM, April 11, 2012
      • Marriott, Golden Gate, Salon A
       

      8:30 AM - *CCC6.1

      Lithium Ion Distribution Profiles in an All-solid-state Lithium Ion Battery by In situ Electron Holography

      Tsukasa  Hirayama1, Kazuo  Yamamoto1, Yasutoshi  Iriyama2, Zempachi  Ogumi3.

      Show Abstract

      Rechargeable batteries are an essential technology of the 21st century because they serve as storage devices for renewable energy. Of the several battery technologies available, Li-ion is the most promising because it can provide the largest energy storage densities. However, the distribution and diffusion of Li ions which control the performance of the batteries are not yet fully understood. The ability to visualize Li-ion distributions would be very useful for analyzing the chemical reactions taking place during cycling, and such knowledge can help contribute to the development of safer, cheaper and more efficient batteries. In the field of transmission electron microscopy (TEM), Li is generally assumed to be invisible because its scattering factor in response to the electron beam is very small. Despite this, we recently realized that it should be possible, using electron holography, to map the electric potential distributions formed by Li ions within the device during operation [2]. To demonstrate this, we prepared a TEM sample from a working all-solid-state Li-ion microbattery. The sample was loaded into the microscope with a holder equipped with two electrodes for applying voltage. Using this specially-constructed apparatus, the potential distributions formed by Li ions could be clearly observed during charging and discharging cycles. Further details about the preparation and observation techniques will be given in the talk, and the insights gained by measuring the Li-ion distribution profiles near both the cathode/electrolyte and electrolyte/anode interfaces under different charged states will be presented. This work was done as part of the Research & Development Initiative for Scientific Innovation of New Generation Batteries (RISING) project of the New Energy and Industrial Technology Development Organization (NEDO), Japan. Thanks are given to Drs. H. Moriwake, A. Kuwabara and C. Fisher at JFCC for helpful discussions. References [1] M. Armand and J.-M. Tarascon, Nature 451, 652-657 (2008). [2] K. Yamamoto, et al., Angew. Chem. Int. Ed. 49, 4414-4417 (2010).

      9:00 AM - CCC6.2

      A Combined Scanning Tunneling Microscope - Atomic Layer Deposition Tool

      Philip  Van Stockum1, James  Mack1, Hitoshi  Iwadate2, Fritz  Prinz1.

      Show Abstract

      We have built a combined scanning tunneling microscope - atomic layer deposition (STM-ALD) tool that performs in situ imaging of deposition. It operates from room temperature up to 200 degrees C, and at pressures from 1e-6 Torr to 1e-2 Torr. The STM-ALD system has a complete passive vibration isolation system that counteracts both seismic and acoustic excitations. The instrument can be used as an observation tool to monitor the initial growth phases of ALD in situ, as well as a nanofabrication tool by applying an electric field with the tip to laterally pattern deposition. In this presentation we describe the design of the tool and demonstrate its capability for atomic resolution STM imaging, atomic layer deposition, and the combination of the two techniques for in situ characterization of deposition.

      9:15 AM - CCC6.3

      Nanoscale Imaging of Density and Strain with Coherent X-Ray Diffraction

      Stephan  O.  Hruszkewycz1, Chad  Folkman1, Ash  Tripathi4, Matt  Highland1, Martin  Holt3, Jorg  Maser2 3, Paul  Fuoss1.

      Show Abstract

      Recent advances in x-ray optics and coherent x-ray flux at state of the art synchrotron light sources have enabled the development of lensless coherent x-ray diffraction imaging (CXDI). As a nanomaterials imaging probe, CXDI exploits both the nondestructive in-situ penetrating power of x-rays and sensitivity to nanoscale structure and morphology with nanometer resolution. We will present data collection and computational approaches for Focused Beam Bragg Ptychography (FBBP) – a new CXDI technique that can extend the resolution of x-ray nanoprobes and target individual nanostructures for study [1]. FBBP uses hard x-rays focused to <100 nm to measure diffraction peaks from a set of spatially overlapping beam footprints with curved phase illumination. The resulting diffraction data can be computationally phased and real space density and strain fields can be determined with nanometer resolution. In addition to discussing the computational and experimental challenges that this technique presents, we will highlight the potential of FBBP by presenting results of a non-destructive comparison of domain characteristics in ferroelectrically poled epitaxial BiFeO3 multiferroic films [2]. Using FBBP, it was determined that high energy (010)-type twin walls present in the as-grown structure were maintained using a perpendicular electric field orientation. This study demonstrated that polarization depinning processes can be controlled to favor specific, dynamically stable, twin wall formations, having potential impacts on utilization of these nanostructures in functional devices. The combination of maturing CXDI methodology and emerging nano-focused coherent hard x-ray instrumentation provides an opportunity to advance the current state of the art in coherent diffractive imaging towards three dimensional reconstructions of targeted nanostructures, pushing coherent imaging to new realms of nanoscience. This work, including use of the Advanced Photon Source and the Center for Nanoscale Materials, was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. [1] S. O. Hruszkewycz, et al., Optics Letters, 36, 2227(2011). [2] S. O. Hruszkewycz, et al., Applied Physics Letters, To Be Published, (2011).

      9:30 AM - CCC6.4

      Revisiting In-situ Thermopower Measurements of Cation Distributions in Spinels: A Co3O4 Case Study

      Taylor  Sparks1, Aleksander  Gurlo2, David  Clarke1.

      Show Abstract

      Magnetic, optical and electrical properties in spinels depend critically on the distribution of cations over A and B sites. Nevertheless, precise determination of the cation distribution, particularly at high temperatures, is notoriously difficult. For 30 years in-situ thermopower measurements have been used as a unique approach to determine site occupancy. The original model proposed by Wu and Mason relies on the Heikes formula to relate thermopower to carrier concentration in small-polaron conductors. Several authors observe that this model doesn’t fit experimental results unless the electron degeneracy term is not calculated, but rather, used as an arbitrary fitting parameter. In recent years Koshibae et al have put forward a modified Heikes formula that takes into account the ratio of electron degeneracy between conducting ions. This modified formula famously described with success the anomalously large thermopower in NaCo2O4 and is now widely applied in the area of oxide thermoelectrics. Even so, no reports have examined how this new model compares to Wu’s original model for using thermopower to determine cation distribution in spinels. Furthermore, both these models ignore any possible contribution to thermopower from tetrahedral site hopping which may not be a valid assumption at high temperatures. In order to examine thermopower measurement of cation distribution based on Heikes original formula vs Koshibae’s modified Heikes formula as well as the role that tetrahedral site hopping may play we undertook a case study on the compound Co3O4. This compound, a normal spinel at low temperatures, is an ideal candidate for the study because authors have suggested that high temperature inversion simultaneously hole dopes the octahedral sites and electron dopes the tetrahedral sites. In addition, due to unexplained heat capacity, lattice parameter and other measurements a great controversy exists regarding the high temperature structure just before decomposition to CoO. Many authors attribute the phenomenon to spin unpairing of octahedral Co3+ ions, but the high temperature cation distribution is still debated. We examine and compare different models to ascertain the role of inversion, spin state transition or both on the thermopower in Co3O4. Furthermore, other high temperature characterization is employed such as in-situ heating Raman microscopy, in-situ XRD and TGA/DTA. The thermopower measurement of cation distribution is compared against Chen et al’s thermodynamic cation distribution prediction for Co3O4 as well as calculation based on changing octahedral and tetrahedral bond lengths performed in this study.

      9:45 AM -

      BREAK

      Show Abstract

      10:15 AM - CCC6.5

      Three-dimensional Coherent Diffraction Microscopy and Its Applications in Biomaterials

      Huaidong  Jiang1, Jiadong  Fan1, Jian  Zhang1.

      Show Abstract

      X-rays have been widely used for microstructural characterization of materials due to their significant penetration ability and non-destructive sample preparation procedures. Coherent X-ray diffraction microscopy, as a promising technique currently under rapid development, is extending the methodology of X-ray crystallography to allow the 2D and 3D structural determination of crystalline and noncrystalline specimens. Herein, we illustrate a few applications of X-ray diffraction microscopy to imaging micro/nanometer sized particles and biological materials, such as biominerals, cells and viruses. By using coherent X-rays from 3rd generation synchrotron radiation sources, X-ray diffraction microcopy has been developed to imaging noncrystalline specimens at the nanometer scale resolution, in which X-ray diffraction patterns are directly inverted to high-resolution images by the oversampling iterative method. This technique provides a new tool for nondestructive and quantitative 3D characterization of a wide range of crystalline and noncrystalline materials at the nanometer scale resolution. REFERENCES 1. J. Miao, P. Charalambous, J. Kirz and D. Sayre, Nature 400, 342-344 (1999). 2. H. Jiang, D. Ramunno-Johnson, C. Song, et al., Phys. Rev. Lett. 100, 038103 (2008). 3. H. Jiang, C. Song, C.-C. Chen,et al., Proc. Natl. Acad. Sci. USA 107, 11234 (2010).

      10:30 AM - CCC6.6

      Probing Local Strain Gradients in Two-Phase Composites with 3D X-Ray Microscopy

      Rozaliya  Barabash1, J.  D  Budai1, J.  Z  Tischler1, W.  J  Liu2.

      Show Abstract

      To understand the small-scale mechanical behavior of composite materials, it is critical to develop techniques to characterize their defect distributions at appropriate length scales. Recently x-ray beams have become available with beam sizes down to ~100 nm. These small penetrating beams can be used to probe very small volumes of materials to determine local strain gradients and defect states. We show how 3D spatially-resolved polychromatic microscopy can be used to nondestructively obtain depth-dependent elastic strain gradients in the constituent phases of a directionally solidified NiAl–Cr(Mo) eutectic composite consisting of ~500-800 nm Cr(Mo) lamellae/fibers in a NiAl matrix after local deformation by indentation. The Cr(Mo) lamellae/fibers were analyzed both in their embedded state and after the matrix was etched back to expose them. Large strain gradients are observed in the indentation-affected area. Research supported by the Division of Materials Sciences and Engineering, Basic Energy Sciences, U.S. Department of Energy. Data collection was carried out on beamline ID-34-E at the Advanced Photon.

      10:45 AM - CCC6.7

      Structure and Dynamics of Materials by Surface Enhanced NMR Spectroscopy

      Lyndon  Emsley1.

      Show Abstract

      The precise understanding of the structure of surfaces is a key element for controlling complex materials and improving their design in a rational way. NMR would be a method of choice for characterising materials, but its poor sensitivity has traditionally made sophisticated NMR approaches difficult if not impossible for many materials. We show that materials NMR spectra can be greatly enhanced by Dynamic Nuclear Polarization, where polarization is transferred from unpaired electrons to the rare nuclei (at natural isotopic abundance) at the surface, yielding at up to a hundred-fold signal enhancement for surface species in silica frameworks. As examples of this new approach, we demonstrate the fast characterization of the distribution of surface bonding modes and interactions in a series of functionalized materials using this technique. Surface enhanced carbon-13, silicon-29, nitrogen-15 and aluminum-27 DNP NMR spectra were obtained by using incipient wetness impregnation of samples with solutions containing a polarizing radical. Furthermore, the remarkable gain in time provided by surface enhanced DNP NMR spectroscopy (typically on the order of a factor 400) allows the facile acquisition of two-dimensional correlation spectra, allowing access to conformational features of the surface groups. The presentation will include details of the method, and the latest results obtained using this approach. Lesage et al., J. Am. Chem. Soc. 132, 15459 (2010). Lelli et al., J. Am. Chem. Soc. 133, 2104 (2011). Rossini et al., Chem. Sci., in press (2011), DOI: 10.1039/C1SC00550B. Zagdoun et al., Chem. Commun., in press (2012), DOI: 10.1039/C1CC15242D. Rossini et al., Angew. Chem., in press.

      11:00 AM - CCC6.8

      State of the Art Full Field X-Ray Transmission Microscopy of Catalytic Solids at Work

      Florian  Meirer1, Ines  Gonzalez-Jiminez2, Korneel  Cats2, Matthijs  Ruitenbeek3, Yijin  Liu4, Johanna  Nelson4, Joy  C  Andrews4, Piero  Pianetta4, Frank  M  de Groot2, Bert  M  Weckhuysen2.

      Show Abstract

      The full-field transmission x-ray microscope (TXM) at the 54-pole wiggler end station on beam line 6-2 of the Stanford Synchrotron Radiation Lightsource (SSRL) is being used for chemical speciation at high spatial resolution (down to <30 nm). Recent developments in hard- and software enable the combination of TXM with x-ray absorption spectroscopy (XAS) to perform 2D and even 3D chemical speciation of relatively large areas (up to mm^2) or volumes (up to 30x30x30 microns^3), while maintaining the high spatial resolution of the microscope[1]. Here we present the expansion of full-field TXM-XAS to in-situ measurements, paving the way for future 4D measurements investigating dynamic changes in morphology, porosity and chemical composition of samples with time. TXM was combined with a specially designed in-situ reactor, analyzing a single catalyst particle at 10-30 bar and up to 600 deg C in a reactant stream. High quality single-pixel X-ray Absorption Near-Edge Structure (XANES) have been recorded during reaction, and 3D tomography with tens of nanometer spatial resolution was performed, which allows for location of specific components within an individual catalyst particle and interrogation of their catalytic chemistry. We believe that 2D and 3D in-situ TXM, which combines the capability of chemical speciation at unprecedented spatial resolution and the possibility to analyze large sample volumes, will open new ways for the characterization of solid porous materials under realistic reaction conditions. [1] Meirer, F. et al. Three-dimensional imaging of chemical phase transformations at the nanoscale with full-field transmission X-ray microscopy. J. Synchrotron Radiat. 18, 773-781 (2011).

      11:15 AM - CCC6.9

      Real-Time Probing of Nanophase Evolution in Solutions

      Yugang  Sun1.

      Show Abstract

      Colloidal nanoparticle synthesis and transformation in solution phase represents a cost-effective and scalable strategy for mass production of functional materials. Availability of nanomaterials with tailored properties is the critical foundation for implanting nanoscale science and engineering in a variety of areas, such as catalysis, energy conversion/storage, biological imaging, medical therapy, etc. However, the current scenario is that the developed recipes are not robust for synthesizing high-quality nanoparticles due to the poor understanding of the complex nucleation and growth processes involved in nanoparticle synthesis. In this presentation, a couple of in-situ synchrotron x-ray techniques including time-resolved high-energy x-ray diffractions (TRHEXRDs) and transmission x-ray microscopy (TXM) will be introduced to show their capability in real-time probing of the chemical and physical processes associated with the nanophase evolution in solution-phase reactions. By taking the advantages of strong penetration of hard x-rays in liquid media and weak interaction with reactants, TRHEXRDs and TXM have been successfully used to study the synthesis of colloidal silver nanocubes and chemical transformation of silver nanowires into nanotubes, respectively. The real-time observations reveal the kinetic processes that are difficult to obtain with conventional techniques. The new understanding on the nanophase evolution may help us to design and establish more robust recipes for the synthesis of colloidal nanoparticles with more precisely tailored properties. Use of the Center for Nanoscale Materials was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.

      11:30 AM - CCC6.10

      Using In-situ TEM to Explore the Kinetics of Wear at the Nanoscale

      Tevis  Jacobs1, Robert  W  Carpick2.

      Show Abstract

      Many novel devices in energy conversion and storage either contain nanoscale sliding contacts (e.g. nanoelectronic mechanical systems (NEMS)) or rely on nanomanufacturing techniques that require nanoscale sliding contacts (e.g. probe-based nanolithography). These contacts suffer excess energy consumption and premature failure due to wear. Therefore, the effective development and efficient operation of these technologies requires understanding, predicting, and controlling nanoscale wear. However, relatively little is known about the fundamental physics of wear at any length scale due to the difficulty of analyzing buried, evolving surfaces.

      In the present study, wear tests were conducted inside of a transmission electron microscope (TEM) using a modified in-situ nanoindentation apparatus. This permitted real-time visualization of contact between a sharp nanoscale tip and a flat surface. Video and periodic high-resolution still images (with atomic lattice resolution) allowed for characterization of the contact geometry, measurement of the shape evolution of the wearing asperity, and quantification of the volume lost due to wear, all with nanometer-scale resolution or better. This technique is shown to resolve volume changes as small as 25 nm3 (or roughly 1250 atoms).

      This approach was used to study the wear of single crystal silicon asperities under adhesive loads, a system relevant to nanoscale devices. The majority of the wear in this regime was shown to occur via gradual surface modification, consistent with bond formation across the interface followed by atomic removal. The direct imaging allows us to rule out fracture or plastic deformation as mechanisms of wear. Further, the rate of volume lost was demonstrated to be inconsistent with the classic Archard wear law. Instead, the rate [/s] of atom loss due to wear was shown to obey an exponential dependence on stress in the contact, as predicted by a recent model of atomic-scale wear based on stress-assisted chemical kinetics. This analysis allows us to extract an activation volume of 5.8 Ã…3 and an activation energy of 0.9 eV. Thus, these results demonstrate the appropriate law for prediction of the wear of silicon in this regime.

      CCC7: Structure and Properties of Organic and Inorganic Photovoltaics

      • Chair: David Ginger
      • Chair: Sascha Sadewasser
      • Wednesday PM, April 11, 2012
      • Marriott, Golden Gate, Salon A
       

      1:30 PM - *CCC7.1

      Electronic and Structural Grain Boundary Properties of Chalcopyrite Solar Cell Materials

      Sascha  Sadewasser1 2, Robert  Baier2, Michael  Hafemeister2, Harry  Moenig2, Daniel  Abou-Ras2, Martha  C  Lux-Steiner2.

      Show Abstract

      Polycrystalline p-type Cu(In,Ga)Se2 semiconductors represent the absorber material in thin film solar cells currently reaching the highest power conversion efficiency. Efficiencies above 20% are surprising considering the high density of grain boundaries in these thin films. Their electronic structure as well as their role in the solar cell are largely investigated and discussed. To improve understanding of the grain boundary properties detailed studies are required providing information on materials characteristics on the nanometer scale. We have applied Kelvin probe force microscopy (KPFM), scanning tunneling microscopy (STM) and electron backscatter diffraction (EBSD) to investigate the electronic grain boundary properties and relate them to their structural properties. We present KPFM and STM studies on individual grain boundaries in polycrystalline solar cell grade Cu(In,Ga)Se2 materials. STM reveals a reduced density of states in the band gap directly at the grain boundary [1]. For a series of samples with different Ga-contents between 0% and 100% we studied the work function variation across grain boundaries using KPFM [2]. Evaluation of many grain boundaries shows the presence of upward, downward and no band bending, which we attribute to negative, positive or no charges present at the grain boundary, respectively. To enhance the understanding, model samples were prepared consisting of large bicrystals that allow, in addition to KPFM characterization, also the application of macroscopic electrical characterization techniques. Structural information about the symmetry of the grain boundary was obtained by EBSD. In the case of a Σ3 grain boundary a charge neutral barrier (ΔΦ~30meV) to majority carrier transport could be identified, while a higher disorder Σ9 grain boundary showed the presence of charges and a significantly higher transport barrier [3]. We present a model for the electronic grain boundary structure, which requires an electronic barrier of 1-2nm in width and several 100meV in depth to fully describe electrical transport. For a polycrystalline CuInSe2 thin film, we succeeded in combining EBSD and KPFM on the same position [4]. We find that the probability of Σ3 grain boundaries to be charge neutral is very high, while non-Σ3 grain boundaries exhibit predominantly positive or negative band bending. Combining our results, we conclude that the abundantly present Σ3 grain boundaries are predominantly charge neutral and therefore most likely harmless to the solar cell device. Higher disorder grain boundaries exhibit a very thin and high barrier to charge transport, through which tunneling dominates. [1] H. Mönig et al., Phys. Rev. Lett. 105, 116802 (2010). [2] R. Baier et al., under review (2011) [3] M. Hafemeister et al., Phys. Rev. Lett. 104, 196602 (2010). [4] R. Baier et al., Appl. Phys. Lett. 99, 172102 (2011).

      2:00 PM - CCC7.2

      Competitive Role of Impurities on the Electrical Activity of as-grown sigma=13, sigma=25 and Deformed sigma=9 Grain Boundaries in p-type Silicon Bicrystals

      Sofia  Gaiaschi1, Amin  Kouadri-Boudjelthia2 1, Gabrielle  Regula1, Nelly  Burle1, Abdelmadjid  Mesli1, Thomas  Neisius3, Maurizio  Acciarri4, Virginie  Mong The Yen1, Olivier  Palais1, Esidor  Ntsoenzok2, Bernard  Pichaud1.

      Show Abstract

      Though new technologies are conceived and developed involving organic or non-organic materials to reduce as much as possible photovoltaic solar cell manufacturing costs, 90% of the industrial production is still made out of silicon. In 2010 a multi-crystalline silicon (mc-Si) module has reached 17 percent of energy conversion efficiency. What drastically limits the latter is the electrical activity at room temperature of grain boundaries (GBs). Though it is a long time running topic, few techniques are nowadays more sensitive and new ones were developed. Coupling different techniques for cross checking results, this work consists of studying the role of gold contamination on the electrical properties of three kinds of Czochralski bicrystals having the same doping level but different oxygen content: as grown (sigma=13, sigma=25) and deformed (sigma=9) ones. The bicrystal orientation was checked by the Laue method and the samples were characterized by Fourier transform infrared spectroscopy measurements (FTIR), 4 point probe technique, X-ray topography, microwave phase shift (µW-PS), electron beam induced current (EBIC) before and after gold diffusion at 685°C for 6 hours. Though the full width at half maximum (FWHM) of GBs taken on µW-PS mapping are found identical for as grown sigma=13 an sigma=25, the double value measured on gold diffused sigma=13 is ascribed to a geometrical effect. Since it has the higher disorientation angle, a higher open space of its structural units is expected and hence it has a bigger sink to eliminate self interstitial generated during the diffusion step. From the EBIC maps the contrast C at grain boundaries was calculated as C=(Ib-Igb)/Ib, where Ib and Igb are the current collected in the bulk and at the GB respectively. The oxygen content has an impact on the GB contrast C: when it is low, the contrast is low. This effect can however be hindered by segregation of gold atoms keeping C steady to about 38%. Eventually, at room temperature, EBIC measurements showed that extrinsic dislocations are not able to activate sigma=9, though a gold diffusion can do it partially. The contrast of the dislocations in sigma=9 bicrystal is about the same as the one of the GB. Gold diffused GBs are planned to be imaged in high resolution mode by high angle angular dark field (HAADF) in a geometrical aberration corrected microscope and local gold levels to be determined by deep level transient spectroscopy (DLTS).

      2:15 PM - CCC7.3

      Beneficial Roles of Grain Boundaries in Sulfide Thin Film Solar Cells Revealed through Scanning Probe Measurements

      Joel  B  Li1, Vardaan  Chawla2, Bruce  M  Clemens2.

      Show Abstract

      Semiconductor materials for optoelectronic or transistor applications typically perform worse in their polycrystalline form because of carrier recombination at the grain boundaries (GBs). However, for polycrystalline Cu2InGaS4 (CIGS) and CdTe solar cells, this is not the case. GBs in these materials are found to be electrically benign and do not act as strong recombination sites. In addition, these GBs attract minority carriers (electrons) and provide a current pathway for them to reach the n-type CdS and ZnO layers for carrier collection. Here we use scanning kelvin probe microscopy (SKPM) and conductive-AFM (C-AFM) measurements to show that grain boundaries in Cu2ZnSnS4 (CZTS) and Cu2ZnSnS4-xSex(CZTSSe) have similar electrical properties to those in CIGS, leading to the hope that these beneficial GBs will lead to CZTS solar cells with similar high efficiencies. SKPM measurements performed on CZTS and CZTSSe films with solar cell efficiencies of 3.4% and 7.8% respectively demonstrate higher positive potential at the GBs. This indicates negative band bending in the energy band diagram, which aids the flow of minority carriers (electrons) into the GBs. C-AFM measurements show higher photocurrent flow in the vicinity of the GBs, suggesting that minority carriers do not recombine significantly at these GBs. In addition, we have shown for the first time that current mainly flows adjacent to the GBs rather than at the GB core. This phenomenon can be explained by the lower electron mobility in the GB core compared to the surrounding regions. Because of the low recombination rate at the GBs, minority carriers that are attracted into the GBs can be guided towards the contact for collection. These two measurement results are similar to those obtained for CIGS and CdTe and together they demonstrate the enhanced minority carrier collection taking place at the GBs of CZTS and CZTSSe. Since GBs are the key to achieving high efficiencies in polycrystalline CIGS and CdTe solar cells and the same beneficial GB electronic properties has been observed in CZTS and CZTSSe solar cells, we theorize that similar high efficiencies can be achieved for these solar cells. The goal of achieving low cost, high efficiency solar cells composed of earth abundant, non-toxic elements could be made possible through CZTS and CZTSSe thin film solar cells.

      2:30 PM - CCC7.4

      Using Scanning Probe Microscopy to Study the Photo-induced Degradation of Organic Solar Cell Materials

      Esha  Sengupta1, Anna  L  Domanski1, Stefan  Weber1, Maria  Untch1, Hans-Juergen  Butt1, Tobias  Sauermann2, Hans Joachim  Egelhaaf2, Ruediger  Berger1.

      Show Abstract

      Intense research is being done in the field of photovoltaics in order to identify organic molecules which are more stable against degradation under illumination in the presence of oxygen [1]. In particular, the role of photo-induced degradation on the nano-scale morphology and electrical performance is desirable in order to understand degradation pathways. Thus, Scanning Probe Microscopy (SPM) is a unique method for the characterization of surface potential changes and conductivity changes under operating conditions. In order to quantify the degradation in these photovoltaics, we investigated the photo-induced changes in the surface potential and conductivity for locally degraded active layers of organic solar cell materials using electrical modes of scanning probe microscopy. Typical blends used for organic solar cell, i.e. P3HT and PCPDTBT along with PCBM were degraded under different partial pressures of oxygen and humidity in the presence of light (1 sun) and investigated by Kelvin Probe Force Microscopy (KPFM) and conductive Scanning Probe Microscopy (cSPM) [2]. However, tip changes can occur while scanning which can lead to changes observed in the potential or current values. Thus, a proper measurement of the surface potential or photocurrent requires an internal reference, ideally within the same image. In order to obtain non-degraded reference areas in our samples, we used a shadow mask while degradation. Using this mask, the sample was partly illuminated and thus partly photo-oxidized. This analysis allowed us to quantify the extent of degradation and compensate the contribution of the probe tip. These relative measurements also allowed us to see changes in topography between the degraded and the non-degraded parts. In the early stages of degradation, an increase in the topography was observed. The increase was attributed to the incorporation of oxygen in the active layer. In the later stages of degradation, the breaking of the polymer chains and evaporation of the active layer dominated over the photo-oxidation. This was seen as a decrease in the layer thickness compared to the non-degraded part. Both the phenomena were supported by NMR studies. These experiments show the possibility to record electrical parameters at a nanometer scale in addition to topography making the SPM method unique for studying nanoscale morphology, their interfaces and the related degradation effects. [1] Jorgensen, M. et al, Sol. Energy Mater. Sol. Cells 2008, 92, 686. [2] Sengupta, E. et al, J. Phys. Chem. C 2011, 115, 19994

      2:45 PM - CCC7.5

      Microscopic Surface Photovoltage Spectroscopy on Dye-Sensitized TiO2 Photoelectrodes

      Alex  Henning1 2, Gino  Guenzburger1, Res  Joehr1, Yossi  Rosenwaks2, Ernst  Meyer1, Thilo  Glatzel1.

      Show Abstract

      Dye-sensitized solar cells (DSSC) provide an alternative concept in photovoltaics based on the spectral sensitization of a wide bandgap semiconductor. Nanostructured TiO2 is a low-cost material well suitable as a substrate in DSSCs. Due to a lack of locally resolved investigations of the DSSC properties, its mechanisms are not fully enlightened so far. Investigation of nanoscaled photovoltaic devices require nanometre scale measuring methods including time-resolved measurements of the carrier dynamics[1]. Surface photovoltage (SPV) spectroscopy is a non destructive and valuable tool for optoeletronic device characterisation limited by its poor lateral resolution[2]. By combining a tunable illumination system with Kelvin probe force microscopy the SPV can be measured with the nanometre scale precision of an atomic force microscope. Here we present a setup for microscopic SPV spectroscopy operated under a nitrogen atmosphere (< 5 ppm H2O) with a lateral resolution less than 30 nm. SPV Spectra can be obtained as a function of the wavelength or the intensity of a solar light simulator and on any desired position on the sample. Investigation of surface potential variations and characterization of surface states in dye-sensitized TiO2 at the nanoscale may help to get further insights into the mechanisms behind it. [1] P. Nicholson and F. Castro, “Organic photovoltaics: principles and techniques for nanometre scale characterization,” Nanotechnology, vol. 21, no. 492001, pp. 1–26, 2010. [2] L. Kronik and Y. Shapira, “Surface photovoltage spectroscopy of semiconductor structures: at the crossroads of physics, chemistry and electrical engineering,” Surface and Interface analysis, vol. 31, no. 10, pp. 954–965, 2001.

      3:00 PM -

      BREAK

      Show Abstract

      3:30 PM - *CCC7.6

      Scanning Probe Microscopy of Thin Film Photovoltaics

      David  S  Ginger1.

      Show Abstract

      Many low cost photovoltaic technologies currently under development make use of nanostructured materials. These new technologies range from nanostructured organic bulk heterojunctions, to inorganic thin films processed from colloidal nanocrystal inks. Quite often, the resulting materials exhibit spatial heterogeneity in their performance. While many techniques can provide high resolution structural information, scanning probe methods are unique in their ability to make high resolution maps of local performance including photocurrent, charge transport, and recombination. This talk will review our scanning probe imaging work using techniques such as photoconductive atomic force microscopy (pcAFM) and time-resolved electrostatic force microscopy (trEFM) on both organic and inorganic materials for use in next generation solar cells with an emphasis on identifying performance bottlenecks and improving materials processing.

      4:00 PM - CCC7.7

      Manipulating the Morphology of P3HT-PCBM Bulk Heterojunction Blends with Solvent Vapor Annealing

      Eric  Verploegen1 2, Michael  F  Toney2, Chad  E  Miller2, Zhenan  Bao1.

      Show Abstract

      Using grazing incidence X-ray scattering we observe the effects of solvent vapors upon the morphology of poly(3-hexylthiophene)-phenyl-C61-butyric acid methyl ester (P3HT-PCBM) bulk heterojunction thin film blends in real time; allowing us to observe morphological rearrangements that occur during this process as a function of solvent. We detail the swelling of the P3HT crystallites upon the introduction of solvent, and the resulting changes in the P3HT crystallite morphology. We also demonstrate the ability for tetrahydrofuran vapor to induce crystallinity in PCBM domains. Additionally, we measure the nanoscale phase segregated domain size as a function of solvent vapor annealing and correlate this to the changes observed in the crystallite morphology of each component. Finally, we discuss the implications of the morphological changes induced by solvent vapor annealing on the device properties of BHJ solar cells.

      4:15 PM - CCC7.8

      Dynamic Nanostructure Development of P3HT:PCBM Photovoltaic Blend during Solvent Casting Using Spectroscopic Ellipsometry and Grazing Incidence X-Ray Scattering

      Tao  Wang1, Alan  D  Dunbar2, Andrew  J  Pearson1, Richard  A  Jones1, David  G  Lidzey1.

      Show Abstract

      Organic photovoltaics (OPVs) are promising solar energy conversion devices owing to the advantages of low cost, light-weight, solution-processability and mechanical-flexibility. Photovoltaic blends based on poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) can be used to create devices with power conversion efficiency of 4 to 5%. This work concerns the real-time monitor of the evolution of P3HT crystallization in P3HT:PCBM photovoltaic blends during their drying process after solvent casting using in-situ spectroscopic ellipsometry and GI X-ray scattering. We identify three stages in film drying: (I) rapid solvent-evaporation and slow-crystallization, (II) slowed solvent-evaporation and rapid crystallization, and (III) slow-solvent evaporation and slow crystallization. The P3HT assembles into ordered crystalline lamellae through heterogeneous nucleation once the solvent volume-fraction in the wet film falls below 50% as a result of evaporation. The rate of P3HT crystallization is initially rapid, but slows when the solvent volume fraction falls below 20%. We found that the degree of P3HT crystallinity in a P3HT:PCBM blend is dependent on a number of parameters including the solvent evaporation rate and the casting temperature. The crystallization of P3HT is a heterogeneous nucleation process, and we observed a self-annealing (i.e. a reduction in kinks, twists, distortions etc) of crystal defects during the P3HT crystallization process, with the characteristic lamella spacing in the P3HT crystallites decreases while crystal domains grow. This study provides a direct insight and fundamental understanding into the dynamic nanoscale morphology evolution in such photovoltaic blend films in its initial formation stage; an advance that we believe offers the prospect of guiding the formation and optimization of thin film-structure for high performance OPV devices.

      4:30 PM - CCC7.9

      Sub-Microsecond Time Resolution Atomic Force Microscopy for Probing Nanoscale Dynamics: Applications to Organic Solar Cells

      Rajiv  Giridharagopal1, Glennis  E  Rayermann1, Guozheng  Shao1, David  T  Moore1, Obadiah  G  Reid1, Andreas  F  Tillack1, David  J  Masiello1, David  S  Ginger1.

      Show Abstract

      Measuring transient phenomena with nanoscale spatial resolution is a long-sought goal across many areas of science. We introduce a new mechanical detection method to analyze atomic force microscopy (AFM) cantilever motion that enables discrimination of transient events with ~100 ns temporal resolution and ~80 nm spatial resolution without the need for custom AFM probes, specialized instrumentation, or expensive add-on hardware. The method, fast free time-resolved electrostatic force microscopy (FF-trEFM), enables the study of dynamic local phenomena with an unprecedented combination of resolution and user-accessibility by extracting transient information from the freely oscillating cantilever in response to an excitation. The experimental data agree well with finite element simulations, and we show that a simple model including both transient force and force gradient terms captures the key parameters of the cantilever motion. As an example application, we use FF-trEFM to screen the performance of organic photovoltaic devices over a technologically-relevant performance window under realistic testing conditions. The nanoscale charging dynamics measured by FF-trEFM on each device correlate well with their external quantum efficiency, thereby linking local behavior with overall solar cell performance. We anticipate that these methods will find application in scanning probe experiments of fast local changes, including carrier dynamics, biological processes, and magnetic resonance measurements.

      CCC8: Poster Session: Scattering Techniques and Probing/Sensing on the Macroscale

      • Wednesday PM, April 11, 2012
      • Marriott, Yerba Buena, Salons 8-9
       

      8:00 PM - CCC8.3

      Non-Destructive, High-Resolution Characterization of Heterogeneous Materials: Solutions for the Nano- and Millimeter Range

      Ute  Schmidt1, Jianyang  Yang3, Wei  Liu3, Thomas  Dieing1, Matthias  Eberhardt2, Olaf  Hollricher1.

      Show Abstract

      Knowledge about the morphology and chemical composition of heterogeneous materials on a sub-micrometer scale is crucial for the development of new material properties for highly specified applications. Such materials can have mono-atomic flat surfaces or a roughness of several hundred micrometers or millimeter. In the past two decades, AFM (atomic force microscopy) was one of the main techniques used to characterize the morphology of nano-materials spread on nanometer-flat substrates. From AFM images it is possible to gain information about the physical dimensions of the material on the nanometer scale, without additional information about their chemical composition, crystallinity or stress state. Raman spectroscopy on the other hand is known to be used to unequivocally determine the chemical composition of a material. By combining the chemically sensitive Raman spectroscopy with high resolution confocal optical microscopy, the analyzed material volume can be reduced below 0.02 µm3, thus leading to the ability to acquire Raman images with diffraction limited resolution. The combination of confocal Raman microscopy with Atomic Force Microscopy (AFM) was a breakthrough in microscopy. Using such a combination, the high spatial and topographical resolution obtained with an AFM can be directly linked to the chemical information provided by confocal Raman spectroscopy. High confocality in Raman imaging always results in high focus sensitivity and this can make measurements difficult with rough inclined samples. Especially when performing scans on a larger scale (scan size larger than 1 mm), this often necessitated careful alignment and sample preparation. True Surface Microscopy, a new imaging technique developed for measurements on rough surfaces over large areas, allows confocal Raman imaging guided by the surface topography obtained by an integrated non-contact optical profilometer. Large-area topographic coordinates from the chromatic confocal profilometer measurements can be precisely correlated with the large area confocal Raman imaging data. This allows true surface Raman imaging on heavily inclined or rough surfaces, with the true sample surface held in constant focus, while maintaining highest confocality. In summary, the combination of confocal Raman microscopy with AFM and true surface microscopy allows the characterization of materials at high, submicron resolution, as well as on mm-rough surfaces across large areas. Additionally production line solutions using Raman spectroscopy will be presented.

      8:00 PM - CCC8.6

      Accurate Current Integration for Heavy Ion Rutherford Backscattering at University of North Texas

      Naresh  Deoli1, Duncan  Weathers1.

      Show Abstract

      An experimental set up have been designed to suppress electron currents generated during energetic ion irradiation to obtain accurate current integration for heavy ion Rutherford backscattering technique used for measurement of heavy element concentrations and target depth profiling. A combination of an electron trap to suppress any electrons ejected from collimators and slits, and a biased aluminium mesh to suppress any secondary electron ejected from target was used. Several standard samples known to an accuracy of better than 2% have been used as targets to check the accuracy of the system for 1.5 MeV O+ projectile ions. Details of the experimental set up and data are presented.

      8:00 PM - CCC8.9

      Structural Order in Bulk Heterojunction Films Processed with Solvent Additives

      James  T  Rogers1 2 3, Kristin  Schmidt4, Michael  F  Toney4, Guillermo  C  Bazan1 3, Edward  J  Kramer1 2 3.

      Show Abstract

      Solution deposition by using high boiling point additives, such as octanedithiol (ODT), provides a simple and widely used fabrication option for improving the power conversion efficiencies of solar cells comprising narrow bandgap conjugated polymer donors and fullerene acceptors. Examination of the active layers by grazing incidence wide angle x-ray scattering (GIWAXS) provided important information regarding the effect of additives on the internal structure of the polymer domains within the bulk heterojunction morphology. In-situ GIWAXS as a function of time after spin-casting was used to explore the dynamics of the BHJ evolution. These studies have shown that the additives induce the formation of polymer crystals throughout the film drying process whereas no crystals develop in the absence of additives. A direct relationship between device performance and crystal correlation lengths and orientation of the crystallites was found.

      8:00 PM - CCC8.10

      A Dual Potentiostat for Amperometric Detection of Pesticides on a CE-AD Chip

      Kamrul  Islam1, Sandeep  k  Jha1, Rohit  Chand1, Dawoon  Han1, Yong-Sang  Kim1 2.

      Show Abstract

      A simple and rapid capillary electrophoresis (CE) separation followed by in-channel pulsed amperometric detection (PAD) of three common triazine herbicides: simazine, atrazine and ametryn have been studied. The CE-PAD microfluidic chip was fabricated using standard photolithography methods. Cyclic voltammetry was conducted on these herbicides that exhibited a characteristic cathodic peak at -0.70V for simazine or atrazine and -0.80V for ametryn, without any anodic peak at reverse scan, indicating that the cathodic peaks were irreversible electron transfer processes. For effective CE-PAD separation of triazine complex, the capillary was filled with 1.5 % agarose. The pulsed amperometric detection of these chemicals ensured better sensor response and low electrode fouling. The average electropherogram of simazine, atrazine and ametryn showed single peaks at 58, 66 and 74 seconds respectively at 20 V/cm separation potential. A mixture of all three herbicides showed similar separated peaks. HPLC was also conducted in a soil spiked with these pollutants to compare the method. The results hold the promise of detecting triazines within a very short time. The CE-PAD technique on a microfluidic chip as such may prove to be a useful qualitative and quantitative tool for similar environmental pollutants.

      8:00 PM - CCC8.11

      Highly Sensitive SERS Analysis Using Dielectrophoresis

      Adam  Francis  Chrimes1, Khashayar  Khoshmanesh2, Vipul  Bansal3, Kourosh  Kalantar-zadeh1.

      Show Abstract

      Using a microfluidics system, combinations of DEP and flow forces will be demonstrated for controlling the spacing of suspended silver nanoparticles with the aim of SERS detection. This system has been tested using Dipicolinic acid (DPA), technically known as 2,6-pyridinedicarboxylic acid, is a bio-marker used for the detection of Bacillus anthracis. The system can quickly and easily manipulate suspended silver particles to form dense silver aggregates at pre-determined locations. The dynamics of the system allows careful control of the silver nanoparticles’ spacing, which can effectively increase the SERS signal intensity, while avoiding irreversible aggregation of the particles. This method allows microfluidics to become a reliable and sensitive SERS platform. Detection of DPA is demonstrated at low concentrations using commercially available silver nanoparticles. This system could be used for the future analysis of other bio-molecules, as the system proved to be a very powerful tool for such processes. We believe that the system is a significant step forward in the field of portable SERS devices.

      8:00 PM - CCC8.12

      Development of Simple and Low-cost Modified Silica Gel for Colorimetric Detection and In-situ Determination of Hydrogen Sulfide Gas and Sulfide Ion

      Eric  Arifin1, Seung-Jin  Ryu2, Jin-Kyu  Lee1 2.

      Show Abstract

      Due to its toxicity, the detection of sulfide ion and hydrogen sulfide gas has gained much attention from biological and industrial point of view and the development of new methods for detecting sulfide has sparked great interest. Inhalation of high concentration of hydrogen sulfide gas causes blood poisoning, burst or blistering of lung’s alveoli and deadening of human sensing and smelling ability. A high concentration of sulfide ion in human blood (> 5 ppm) can be lethal and be a cause of death. There is an urgent need for the rapid, highly sensitive, reliable and portable system for detection and determination of toxic gases or liquids not only from security perspective but also for other applications in clinical, forensic and industrial area. A simply prepared, low cost yet highly sensitive colorimetric sulfide ion and hydrogen sulfide gas sensor was developed. The sensor consists of lead-modified or silver-modified silica gel sandwiched in between commercial silica gel placed in a glass tube whose color changed upon precipitation reaction in the presence of sulfide ion or hydrogen sulfide gas. The simple preparation method eliminates time-consuming sample preparation and pre-treatment, the need for special reaction condition, expensive and complicated laboratory apparatus. The sensor is not affected by environment condition such as temperature or humidity and offers straightforwardness, fast response time, high sensitivity and easy understanding result based on absolute yes/no selectivity

      8:00 PM - CCC8.13

      Nanoindentation Probing of High-aspect Ratio Pillar Structures on Optical Multilayer Dielectric Diffraction Gratings

      Karan  Mehrotra1 3, Heather  P  Howard2 3, Stephen  D  Jacobs2 3, John  C  Lambropoulos1 2 3.

      Show Abstract

      As work in inertial confinement fusion (ICF) and the fast ignition concept have expanded and evolved over the past few decades, so too have the laser systems that support ICF research. Ultra-short pulse, high power laser systems place stringent requirements on optical components in terms of both optical performance and resistance to laser damage. At the Laboratory for Laser Energetics (LLE), the peak power capability – and thus the overall performance – of the petawatt-class OMEGA EP laser system is limited by the laser damage resistance of diffraction gratings in the chirped-pulse amplification (CPA)1 pulse compressors for each beamline. Increasing the damage thresholds of these components is therefore an important objective at LLE. The multilayer dielectric (MLD) gratings used in OMEGA EP’s pulse compressors are surface relief gratings, composed of an MLD mirror with a periodically grooved top diffraction layer. The MLD high reflector is a modified quarter-wave stack2 of alternating low and high refractive index layers on a glass substrate, typically hafnia (HfO2) and silica (SiO2) coated onto BK7 glass. The grating is patterned by small-beam interference lithography (SBIL)3 and etched into the top silica MLD layer at Plymouth Grating Laboratory (PGL)4-5. During the final step, aggressive chemical cleaners such as acid piranha (mixture of H2O2 and H2SO4) are used to strip away residual photoresist, antireflective coating (ARC), and other debris from the grating surface. There is some concern that this cleaning step mechanically weakens the fragile grating pillars, possibly affecting the grating’s optical performance as well as its resistance to laser damage. The development of a methodology for monitoring a grating’s mechanical properties could enable a better understanding of the fabrication and cleaning process, and point to appropriate modifications that will preserve the grating’s integrity. This work, therefore, is aimed towards measuring the mechanical response of optical multilayer dielectric (MLD) diffraction gratings using nanoindentation. The results are explained using a stress-strain model, which reveals a yield stress of 5.2 GPa and predicts a similar dependence of yield stress on loads for both fully-elastic and fully-plastic solutions. It is shown that the indentation response of the high-aspect ratio “pillar” geometry (constrained in one transverse direction but free in the other) can be expressed in terms of yield stress rather than material hardness. References: 1D. Strickland, G. Mourou, Optics Comm. 56, 219 (1985) 2 J. B. Oliver, et al., Proc. of SPIE 5991, 5911 A (2005) 3 M.L. Schattenburg, et al., ISNM (2006) 4 D.J. Smith, et al. , ICUIL (2008) 5 B. Ashe, et al., LLE Review 112, 228 (2007)

      8:00 PM - CCC8.14

      Quantitative ``-situ'' Electromechanical Characterization of Materials Using Conductive Ceramic Probes

      David  John  Sprouster1, Simon  Ruffell1, Jodie  Bradby1, Douglas  Stauffer2, Ryan  Major2, Oden  Warren2, James  Williams1.

      Show Abstract

      In the present work, we discuss the electromechanical properties of metallic and semiconductor materials using hard, electrically conductive, PulsarTM tips fitted to a Hysitron Triboindenter. The shape and structural properties of the tips were characterised prior to and after extensive use, and both were found to be resistant to mechanical and electrical degradation. The tips display superior electrical properties when compared to their Boron-doped diamond counterparts. Sweeping the voltage and measuring current gives Ohmic behavior when indenting clean, smooth, metallic standards, and through-tip currents that are proportional to the surface area of the tip/sample contact. The tip/sample contact and subsurface electrical resistivity changes dominate the through-tip electrical measurements and provide a unique method for measuring the electrical properties of the material immediately below the indenter tip. These new tips also allow direct correlation between the electrical signatures associated with mechanically-driven effects including pile-up, sink-in, and phase-transformations. Furthermore, we demonstrate that quantitative electrical information can be successfully extracted from the through-tip measurements by carefully determining the tip surface area and including the effects of the resistive elements in the complete circuit.

      8:00 PM - CCC8.15

      Optical Determinations of a Gold Nanowire’s Thermal Conductivity

      Andrew  Green1, Hugh  Richardson1, Michael  Carlson1.

      Show Abstract

      A contact free experiment of a one dimensional nanostructure has yet to be established. We measure the thermal conductivity of lithographically prepared Au nanowires in-situ by using a 532 nm laser that heats the gold nanowire via plasmonic excitation as well as excites two thermalized virtual states of an AlGaN:Er3+ temperature sensing thin film on a silicon substrate. An scanning optical microscope is used to collect a spectral image from the thin films temperature dependent photo luminescence. The spectral image is then converted into a temperature image using a Boltzmann factor. The wire’s resulting thermal profile can be fit to the solution of a heat transfer model with an adjustable parameter m that is sensitive to the nanowire’s thermal conductivity. Nanostructure materials show promise in maximizing thermoelectric performance via an inherent reduction of thermal conductivity via low dimensionality. Our novel technique will allow for an in-situ experimental determination of a single wire’s thermal conductivity.

      8:00 PM - CCC8.16

      Simulation and Process Flow of Radiation Sensors Based on Chalcogenide Glass for In situ Measurement

      Mahesh  S  Ailavajhala1, Maria  Mitkova1, Darryl  P  Butt2.

      Show Abstract

      In this work, we present our data about simulation and fabrication of microelectronic devices based on a planar structure, electrode/nanophase chalcogenide glass/electrode in proximity to a source of silver (Ag) which changes the electrical resistivity of the nanophase chalalcogenide glass upon radiation with α,x-ray, γ, electron, ion or neutron radiation. The change in resistance is due to radiation induced structural effects in the chalcogenide glass layer that generate defect states and introduce internal electrical fields which can be the main driving force for silver ion diffusion from the silver source. The silver ions incorporate into the structure rather than being an interstitial entity therefore participating in the electrical conductivity. In in situ measurements, the main goal is to study the change in conduction as a direct result of radiation. For the measurements, one has to apply a bias, which depending on the field distribution can contribute to the silver ion diffusion. To reduce the effect of such non radiation based diffusion events, simulations have been used to enlighten a specific device structure to perform in situ measurements. These devices are oriented laterally over the chalcogenide glass film with the two inert electrodes, spaced at specified distance apart from each other used for measuring the conductivity of the film in between. Silver sources are also spaced at specific distance apart from these electrodes to reduce the effect of the electric fields generated from the inert electrodes. Spacing of the electrodes as well as their geometries were chosen after an in-depth investigation into the electric field and electric field energy displacement simulations with the aid of COMSOL multi-physics software. These two types of simulations are vital in making the eventual decision of device structure and performance for which many different geometries and structures were simulated. From preliminary device testing results, a few parameters such as bias voltage, inert electrode material and thickness of the films were used as standards for all different types of simulations while only varying the spacing and geometries to affect the electric fields. A 1V bias was experimentally confirmed as a good bias since it will provide reliable measurements above the noise floor while the bias is not large enough to directly affect ion diffusion. For these reasons, the simulations were conducted by placing this bias on the inert pads. Process flow was developed for fabrication of simulated devices which involved masks creation and photolithography applied in such manner that there is no photoresist development in contact with the chalcogenide glass. The main motivation of this research is to find an appropriate dimensions and geometry, which does not cause change in conduction as a direct result of the applied electric field, but rather effectively measures the radiation induced change in the devices conductivity.

      Download Session Locator (.pdf)2012-04-12  

      Symposium CCC

      Show All Abstracts

      Symposium Organizers

      • Nina Balke, Oak Ridge National Laboratory
      • Howard Wang, State University of New York, Binghamton Institute for Materials Research
      • Job Rijssenbeek, GE Global Research
      • Thilo Glatzel, University of Basel

      Support

      • Asylum Research
        Zurich Instruments Ltd

        CCC9: Nanoscale Investigations of Fuel Cells

        • Chair: Robert Kostecki
        • Thursday AM, April 12, 2012
        • Marriott, Golden Gate, Salon A
         

        8:30 AM - *CCC9.1

        AFM and Conductive AFM of Fuel Cell Materials

        Steve  Buratto1.

        Show Abstract

        A technique to map surface domains responsible for proton transport in PEM fuel cells has been developed. Specifically, this technique couples two operating modes of atomic force microscopy—dynamic and contact modes—to determine the distribution and relative electrochemical activity of proton transport domains. In dynamic mode, a cantilever is driven to oscillate near its resonance frequency either just above or making intermittent contact with the surface of a proton exchange membrane. Operating in this mode yields both topography and phase images, where contrast in latter arises from different probe-sample interactions. In membranes whose proton transport is governed by aqueous domains, phase contrast is caused by different forces exerted on the probe by aqueous and non-aqueous domains. In perfluorosulfonic acid type polymer membranes, aqueous domains are associated with sulfonic acid groups and non-aqueous domains with fluorocarbon groups. Through dynamic mode imaging we obtain a map of the aqueous domains with spatial resolution approaching 1 nm and in the limit of a single aqueous channel. Current derived from the reduction of oxygen is visualized in contact mode, in which the Pt coated AFM tip acts as a nanoscale cathode as it scans the surface of the membrane whose opposite side has been hot pressed with a gas diffusion electrode and is continuously exposed to hydrogen gas. These current images allow for direct visualization of the electrochemical activity at the surface of the membrane. We have been successful in imaging Nafion ® membranes with spatial resolution of a single channel, and have measured the conductance of a single channel. Furthermore, overlaying phase images taken in dynamic mode with current images taken in contact mode reveals that approximately half of the aqueous surface domains of a Nafion ® membrane are not electrochemically active (i.e. not all aqueous domains facilitate proton transport and contribute to fuel cell performance). Initial work has focused on Nafion ® membranes and commercially available electrode materials imaged under ambient conditions, while changes in electrode fabrication and membrane preparation have also been explored. Controlled variations in membrane water content and chemical structure may elucidate additional properties of the ion transport channels. We will report on the progress of these experiments.

        9:00 AM - *CCC9.2

        Nanometer-scale Probing of Voltage-induced Gas-solid Reactions: Towards Electrochemistry on Single-defect and Atomic Levels

        Sergei  Kalinin1, Stephen  Jesse1.

        Show Abstract

        Electrochemical reactions in solids underpin multiple applications ranging from electroresistive non-volatile memory and neuromorphic logic devices memories, to chemical sensors and electrochemical gas pumps, to energy storage and conversion systems including metal-air batteries and fuel cells. Understanding the functionality in these systems requires probing reversible (oxygen reduction/evolution reaction) and irreversible (cathode degradation and activation, formation of conductive filaments) electrochemical processes. Traditionally, these effects are studied only on the macroscopically averaged level. In this talk, I summarize recent advances in probing and controlling these transformations locally on nanometer level using scanning probe microscopy. The localized tip concentrates the electric field in the nanometer scale volume of material, inducing local transition. Measured simultaneously electromechanical response (piezoresponse) or current (conductive AFM) provides the information on the bias-induced changes in material. Here, I illustrate how these methods can be extended to study local electrochemical transformations, including vacancy dynamics in oxides such as titanates, LaxSr1-xCoO3, BiFeO3, and YxZr1-xO2. The formation of electromechanical hysteresis loops indistinguishable from those in ferroelectric materials illustrate the role ionic dynamics can play in piezoresponse force microscopy and similar measurements. In materials such as lanthanum-strontium cobaltite, mapping both reversible vacancy motion and vacancy ordering and static deformation is possible, and can be corroborated by post mortem STEM/EELS studies. The possible strategies for elucidation ionic motion at the electroactive interfaces in oxides using high-resolution electron microscopy and combined ex-situ and in-situ STEM-SPM studies are discussed. Finally, the future possibilities for probing electrochemical phenomena on in-situ grown surfaces with atomic resolution are discussed. Research supported (SVK) by the U.S. Department of Energy, Basic Energy Sciences, Materials Sciences and Engineering Division and partially performed at the Center for Nanophase Materials Sciences (SVK, SJ), a DOE-BES user facility.

        9:30 AM - CCC9.3

        Oxygen Reduction Activity of (La,Sr)CoO3/(La,Sr)2CoO4 Hetero-structures Studied by In situ Scanning Tunneling Microscopy and Spectroscopy

        Wen  Ma1, Yener  Kuru1 2, Yan  Chen1, Zhuhua  Cai1, Harry  L  Tuller2, Bilge  Yildiz1.

        Show Abstract

        Strontium-doped lanthanum cobaltite is one of the most promising cathode candidates for intermediate temperature solid oxide fuel cells. Recently, the hetero-interfaces between the perovskite (La,Sr)CoO3 (LSC113) and the Ruddlesden-Popper (La,Sr)2CoO4 (LSC214) phases have shown highly enhanced oxygen exchange kinetics.[1,2]The physical origin of this enhancement near the interface is still unknown. If well-understood, this observation offers the potential for a new class of cathode structure design, either via multilayering or by forming vertical heteroepitaxial nanocomposites,[3] which have high densities of these special interfaces. In this study, our aim is to form high quality hetero-structures at the nanoscale with well-defined interfaces, and to probe the local oxygen reduction activity on the basis of the local electronic structure of the interface. For this purpose, we perform in situ scanning tunneling microscopy and spectroscopy (STM/STS) at elevated temperatures (up to ~550 oC) and in controlled oxygen partial pressures. Two types of hetero-structures were prepared and examined: vertically aligned nanocomposite (VAN) films and multilayers, both made of LSC113 and LSC214. The VAN structures, with domain sizes of about 200 nm, are formed by pulsed laser deposition (PLD) on single crystal SrTiO3 (001) substrates. The structure and chemistry are confirmed by x-ray diffraction, and by spatial mapping of the cation concentrations using nano-probe Auger electron spectroscopy. The LSC113 domains in the VAN structures have, screw dislocations and the LSC214 domains exhibit a layered structure. As another model structure, high quality multilayers of LSC113 and LSC214 with 20 nm modulation length are also formed by PLD on single crystal SrTiO3 (001) substrates. The buried interfaces of multilayers are then exposed to the ambient by glancing angle focused ion-beam milling.[4] Interestingly, the local electronic structure of the LSC214 phase in both the VAN and the multilayer structures, probed by in situ STS, are found to be significantly modified with respect to the single-phase LSC214 film - above 200 oC, the tunneling spectra on the LSC214 component shows a metallic-like behavior without a band gap, in contrast to the presence of a band gap larger than 1eV on the singe-phase LSC214 thin film as reference. One possible reason for this is the electronic activation of LSC214 by its vicinity to the LSC113. This finding directly shows that the LSC214 domain has a higher electronic density of states near the Fermi level and a higher electronic conductivity, and thus, a higher activity to oxygen reduction at elevated temperatures in the VAN and multilayer structures compared to the single-phase reference. [1] Sase, M. et al., Solid State Ionics 2008, 178. [2] Crumlin, E.J. et al, J. Phys. Chem. Lett. 2010, 1. [3] MacManus-Driscoll, J. et al. Nature Materials, 2008, 7. [4] Kuru, Y., et al. Adv. Mater. 2011, 23

        9:45 AM - CCC9.4

        Microstructural Evolution of Gadolinium-doped Barium Cerate in Moisture at Elevated Temperatures

        Aravind  Suresh1, Maria  J  Arellano-Jimenez1, Barry  Carter1, Benjamin  A  Wilhite2.

        Show Abstract

        Doped barium cerates (BaCeO3) have been widely investigated as high-temperature protonic conductors, with potential applications as membranes for hydrogen purification and electrolytes for Solid-Oxide Fuel Cells (SOFCs). Proton incorporation in these materials has been reported to occur at elevated temperatures by the interaction of moisture in the atmosphere with oxygen-ion vacancies in the material; such vacancies compensate the charge when Ce4+ is replaced by trivalent dopants such as Y, Yb, Gd, etc. However, the stability of doped BaCeO3 against decomposition into Ba(OH)2 and CeO2 under such operating conditions has been a matter of debate, with conflicting reports in literature regarding the thermodynamic models to be used to study the decomposition, the effect of dopants and the mechanism of decomposition. As a step towards clarifying the debate, the present study uses advanced techniques in electron microscopy to investigate the chemical stability of sintered Gd-doped BaCeO3 in the presence of moisture at elevated temperatures. A significant feature of this new study is the ability to observe the exposed sintered material in reference to its surrounding microstructural environment, thereby enabling a clearer understanding of the underlying mechanism of the processes occurring during the exposure. Two compositions of Gd-doped BaCeO3, one with A:B~1 and one with A:B>1, were synthesized by solid-state reaction. The powders were analyzed using X-ray Diffraction (XRD) and pressed and sintered into pellets. The sintered pellets were then maintained at high temperatures for up to 24 h under a continuous flow of an inert gas with a fixed partial pressure of moisture. Sections from the exposed pellets were then studied using Transmission Electron Microscopy (TEM) to observe any changes in the material and to propose a mechanism for decomposition based on the observations. Sections from the as-sintered pellets were also studied to provide a frame of reference.

        10:00 AM -

        BREAK

        Show Abstract

        10:30 AM - *CCC9.5

        In situ Studies of Surface Chemistry of Perovskite Oxides at Elevated Temperatures

        Yang  Shao-Horn1.

        Show Abstract

        There is a large pressure and temperature gap between the ultra-high vacuum and room temperature conditions under which solid oxide fuel cell (SOFC) cathode materials are characterized typically, and SOFC operating conditions at high temperature (~500 – 1000 °C) and ambient pressure (~1 atm). Understanding how the physical and chemical properties of SOFC cathode materials change under operating conditions can provide insights into the mechanism of oxygen reduction reaction (ORR) and lead to material development strategies to improve cathode performance. Our recent work has shown that (001) epitaxial films of La0.8Sr0.2CoO3-δ (LSC)3 can exhibit enhanced surface oxygen exchange rates relative to LSC bulk up to 1 order of magnitude. In this work, we investigate the chemical and structural properties of bulk and (001) epitaxial films at near SOFC operating conditions to provide insights into the physical origin responsible for the observed enhancement. In situ XRD was conducted to show that epitaxial LSC films were stable from 30 – 550°C at p(O2) of 1 atm, from which the film structural parameters were compared with those of bulk LSC.6,7 Using near ambient X-ray photoelectron spectroscopy (APXPS) at Lawrence Berkley National Laboratories Advanced Light Source (ALS) synchrotron facility,4 the chemical states and relative atomic concentrations for La, Sr, Co, O from LSC bulk pellet and epitaxial film samples were examined. In this presentation, we will discuss how the cations and oxygen species change as a function of temperature (30 – 520 oC) and pressure (1*10-9 – 1*10-3 atm), from which a hypothesis is proposed for enhanced ORR activity on epitaxial LSC3 relative to bulk LSC. 1 van der Heide, P. A. W., Systematic x-ray photoelectron spectroscopic study of La1-xSrx-based perovskite-type oxides. Surface and Interface Analysis 33 (5), 414 (2002). 2 Imamura, et al., Catalytically active oxygen species in La1-xSrxCoO3-delta studied by XPS and XAFS spectroscopy. J. of Phys. Chem. B, 104 (31), 5 (2000). 3 la O', G.J., et al., Catalytic Activity Enhancement for Oxygen Reduction on Epitaxial Perovskite Thin Films for Solid-Oxide Fuel Cells. Angewandte Chemie International Edition 49 (31), 3 (2010). 4 Bluhm, H. et al., Methanol oxidation on a copper catalyst investigated using in situ X-ray photoelectron spectroscopy. J. of Phys. Chem. B 108 (38), 14340 (2004). 5 Powell, C.J., et al., NIST Electron Inelastic-Mean-Free-Path Database - Version 1.2. (National Institute of Standards and Technology, Gaithersburg, MD, 2010). 6 Mastin, J., et al., Structural and thermal properties of La1-xSrxCoO3-delta. Chem. of Mat. 18 (25), 6047 (2006). 7 Chen, X.Y., et al., Thermal and chemical expansion of Sr-doped lanthanum cobalt oxide (La-1-xSrxCoO3-delta). Chem. of Mat. 17 (17), 9 (2005).

        11:00 AM - CCC9.6

        Oxygen Valence Changes in Solid Oxide Fuel Cell Catalysts

        Robert  Ezra  Usiskin1, Tim  T  Fister2, Kee-Chul  Chang3, Sossina  M  Haile1.

        Show Abstract

        In oxides, the oxygen ions are often assumed to be fixed-valent. We tested this assumption for two representative solid oxide fuel cell (SOFC) catalyst materials using in situ non-resonant inelastic x-ray scattering (NIXS) at the Advanced Photon Source. The materials were bulk samples of a cobalt-based perovskite, SrCo0.9Nb0.1O3-d, and an iron-based perovskite, La0.6Sr0.4FeO3-d. Other methods for probing the partial density of states of oxygen use lower energy electrons or soft x-rays with low penetrating power, and this constraint drives the experiments towards low-pressure, low-temperature, out-of-equilibrium, surface-sensitive measurements that may not give accurate information about the bulk chemistry under fuel cell operating conditions. In contrast, by using NIXS with hard x-rays, we took variable-pressure, high-temperature, in-equilibrium, surface-insensitive measurements of oxygen K-edges and transition metal M-edges. Our results provide strong evidence that in such materials, the oxygen ions are not fixed-valent. Rather, the oxygen and transition metal ions exhibit substantial covalency, and both ions undergo reversible valence changes when the materials are oxidized or reduced. This finding has important implications for understanding why these materials are excellent oxygen reduction catalysts.

        11:15 AM - CCC9.7

        Atomic-Scale Imaging and Measurement of Oxygen Concentration in Vacancy Ordered Cobaltite Thin Films

        Young-Min  Kim1, Michael  D  Biegalski1, Jun  He1 2, Hans  M  Christen1, Sokrates  T  Pantelides2 1, Stephen  J  Pennycook1, Albina  Borisevich1.

        Show Abstract

        Functionality of ionic materials and devices exemplified by solid oxide fuel cells and memristors is underpinned by the dynamics of oxygen vacancies. Of interests for these applications is vacancy injection and annihilation at the gas-solid surfaces, vacancy transport in the bulk and across the internal interfaces, as well as vacancy ordering and associated changes in the connectivity of the host lattice. These processes are sensitively affected by the presence of structural defects, interfaces, and strain field that couple to the electrochemical potential of oxygen in the host lattice. Hence, to decipher the interplay between local ionic and physical phenomena and to elucidate contributions of defects and interfaces to the oxygen transport properties, local probing of oxygen distribution with atomic precision is required. Here, we explore a direct approach to mapping oxygen concentration in ionic oxides via unit-cell-by-unit-cell lattice parameter mapping by aberration-corrected scanning transmission electron microscopy (STEM) and explore the coupling between the ionic behavior and collective tilts in the network of oxygen octahedra. As a model system, we chose lanthanum/strontium cobaltite (La0.5Sr0.5CoO3-x, LSCO), a prototypical material for SOFC cathodes. In the pristine state, LSCO is characterized by the presence of the a-a-a- tilt system giving rise to the rhombohedral R-3c state. At the same time, vacancy ordering occurs in the (001) pseudocubic direction, forcing tetragonal symmetry. This symmetry mismatch suggests that tilts can affect the vacancy ordering. Here, LSCO films were grown by Pulsed Laser Deposition in identical conditions on two different substrates, La0.3Sr0.7Al0.65Ta0.35O3 (LSAT, cubic) and NdGaO3 (NGO, orthorhombic). These substrates have nearly identical lattice parameters, but different symmetry of the oxygen octahedral network. STEM imaging revealed oxygen vacancy ordering in both samples, as detected both by Electron Energy Loss Spectroscopy (EELS) and by lattice parameter mapping. Surprisingly, the film on NGO appears to be La0.5Sr0.5CoO2.5, while the film on LSAT is less oxygen deficient. Comparison of measured lattice parameters with the first-principles calculations allows us to reconstruct the local lattice spacing-oxygen concentrations trends. In La0.5Sr0.5CoO2.5/NGO films, EELS reveals different valence states of Co at the interface for different interface terminations. These studies suggest that (1) changes in octahedral tilts can induce changes in oxygen stoichiometry of the vacancy ordered structures and (2) local vacancy concentration can be quantitatively determined by STEM. * This research is sponsored by the Materials Sciences and Engineering Division (YMK, JH, SJP, AYB) and Scientific User Facilities Division (MDB, HMC), Office of BES of the U.S. DOE, and by appointment (YMK) to the ORNL Postoctoral Research Program administered jointly by ORNL and ORISE.

        11:30 AM - CCC9.8

        Studies of Dynamic Phenomena in Oxygen Conductors by In situ and Ex situ Scanning Transmission Electron Microscopy

        Donovan  N  Leonard1, Amit  Kumar1, Stephen  Jesse1, Sergei  V  Kalinin1, Yang  Shao-Horn2, Ethan  Crumlin2, Eva  Mutoro2, Michael  D  Biegalski1, Hans  M  Christen1, Kate  Klein3, Stephen  J  Pennycook1, Albina  Borisevich1.

        Show Abstract

        Functionality of ionic materials and devices is ultimately determined by the field-induced dynamics of oxygen vacancies and associated changes in connectivity and composition of the host lattice. Here, we report comparative studies of reversible and irreversible electrochemical processes in model lanthanum-strontium cobaltite (LSCO), a prototypical solid oxide fuel cell material, using combined scanning probe microscopy – scanning transmission electron microscopy(STEM) approach. The ex situ combination of SPM and STEM is ideally suited to explore the irreversible bias induced transformations. In these studies, SPM is used to apply bias stress to selected regions on LSCO surface, then the region of interest is extracted using focused ion beam (FIB) lift-out, and subsequently imaged with atomic resolution in STEM. In the in situ approach, the STM tip is used to induce electrochemical process locally, directly in the field of view of STEM. Finally, attaching FIB lift-out samples to patterned nanocontact grids is used to create nanodevices that can be uniformly biased directly in STEM environment. The synergy of these three approaches is used to develop the comprehensive picture of reversible and irreversible processes in LSCO. We observe very high propensity of material for the formation of ordered vacancy structures. The relatively high mobility of vacancies renders these systems ferroelastic in nature and allows for effective strain compensation. The irreversible reactivity associated with highly localized electrochemical processes leads to partial amorphization of material. Interestingly, this process strongly enhances the reversible oxygen reduction/evolution reactions. Within crystalline areas of the sample, bias cycling can sometimes induce formation of highly strained ferroic boundaries between domains of vacancy ordered phases. STEM imaging allows direct, atomically resolved, and quantitative mapping of resulting materials structure. Overall, the combination of in situ and ex situ electrochemical stimulation and STEM imaging opens the pathway for probing electrochemical reaction mechanisms in solids on atomic level. * This research is sponsored by the Materials Sciences and Engineering Division (DNL, SJP, AYB) and Scientific User Facilities Division (MDB, HMC) of the U.S. DOE Instrument access via SHaRE User Facility, which is supported at ORNL by Office of BES of the U.S. DOE, is gratefully acknowledged.

        11:45 AM - CCC9.9

        Spatially Resolved Mapping of Oxygen Reduction/Evolution Reaction on Solid-oxide Fuel Cell Cathodes with sub-10 nm Resolution

        Amit  Kumar1, Donovan  Leonard2, Mike  Biegalski1, Anna  Morozovska3, Francesco  Ciucci4, Stephen  Jesse1, Albina  Borisevich2, Sergei  V  Kalinin1.

        Show Abstract

        The energy conversion electrochemical energy conversion systems based on gas-solid interactions such as solid oxide fuel cells (SOFC) and Li-air batteries is underpinned by a series of complex mechanisms like ion and vacancy diffusion, electronic transport and solid-gas and solid-liquid reactions at surfaces and triple phase junctions. One of the critical steps in the SOFC and Li-air battery operation leading to large overpotentials and charge-discharge hysteresis was the kinetics of the oxygen oxidation reaction (ORR). While it is well-recognized that ORR efficiency can be greatly enhanced by catalytic particles or morphologies, the mechanisms behind this enhancement remain elusive, largely due to the lack of experimental techniques capable of probing ORR on the nanoscale. Spatial localization of the oxygen reduction/evolution reactions (ORR/OER) on lanthanum strontium cobaltite (LSCO) surfaces with perovskite and layered perovskite structures is studied on the sub-10 nanometer level. The electrical field-dependence of ionic mobility is explored to determine the critical bias required for the onset of electrochemical transformation, potentially allowing to deconvolute reaction and diffusion processes in the fuel cell system on a local scale. Comparison between Electrochemical Strain Microscopy (ESM) and structural imaging by scanning transmission electron microscopy (STEM) suggest that small-angle grain boundaries act as diffusion pathways for oxygen vacancies which may contribute to enhanced electrochemical activity. The ESM activity is compared across a family of LSCO samples, demonstrating excellent agreement with macroscopic behaviors. This study potentially paves the way for deciphering the mechanisms of electrochemical activity of solids on the level of single structural defect. The work was supported (AK, DL, AB) by the Materials Science and Engineering Division of the U.S. DOE. This research was conducted in part (AK, SVK, MB) at the Center for Nanophase Materials Sciences, which is sponsored at Oak Ridge National Laboratory by the Scientific User Facilities Division, U.S. Department of Energy.

        CCC10: Electrical and Mechanical Properties of Metals and Oxides

        • Chair: Thilo Glatzel
        • Thursday PM, April 12, 2012
        • Marriott, Golden Gate, Salon A
         

        1:30 PM - *CCC10.1

        Kelvin Probe Force Microscope Study of Modified TiO2 Surfaces

        Hiroshi  Onishi1.

        Show Abstract

        The charge transfer from a nanometer-sized transition metal particle to a catalyst support is thought to affect reactions over metal particles. We have proposed application of a Kelvin probe force microscope (KPFM) to observe the charge transfer particle-by-particle. Observed lateral distributions of the contact potential difference are interpreted to be the local work function affected by the electric dipole moments at the particle-support interface. Our recent results demonstrating successful applications with Na adatoms [1], Cl adatoms [2], Pt adatoms [3] and particles [4], and Ni particles evaporated on TiO2(110) are reviewed. Positive and negative shifts of the work function were observed on the adatoms and particles as expected. Organometallic compounds, N3 dye [5] and black dye [6], adsorbed on the TiO2 surface were also examined to simulate a photoelectrode of dye-sensitized solar cells. When the electrode was irradiated with visible light, some dye molecules presented a negative shift of the work function. Electron injection from the dye to the surface is proposed to cause the negative shift. These results offer applications of KPFM in catalyst and photoelectrode research. References [1] A. Sasahara, H. Uetsuka, H. Onishi, Japanese Journal of Applied Physics 43 (2004) 4647. [2] K. Hiehata, A. Sasahara, H. Onishi, Japanese Journal of Applied Physics 47 (2008) 6149. [3] A. Sasahara, C. Pang, H. Onishi, Journal of Physical Chemistry B 110 (2006) 13453. [4] A. Sasahara, C. Pang, H. Onishi, Journal of Physical Chemistry B 110 (2006) 17584. [5] M. Ikeda, N. Koide, L. Han, A. Sasahara, H. Onishi, Journal of Physical Chemistry C 112 (2008) 6961. [6] M. Ikeda, N. Koide, L. Han, A. Sasahara, H. Onishi, Langmuir 24 (2008) 8056.

        2:00 PM - CCC10.2

        In-Situ Transmission Electron Microscope Observation of Ferroelastic Domain Wall-defect Interactions in Bismuth Ferrite Thin Films

        Michael  Jablonski1, Christopher  R  Winkler1, Jianguo  G  Wen2, Dean  J  Miller2, Lane  W  Martin3, Mitra  L  Taheri1.

        Show Abstract

        BiFeO3 (BFO) is a multiferroic material that exhibits coupling between its antiferromagnetic and ferroelectric ordering. The magneto-electric coupling allows an applied electric field to control magnetism in devices based on this material. BFO films also have high Néel and Curie temperatures with an average ferroelectric polarization around 90 µC/cm2. Due to these unique properties, BFO shows promise for use in both ferroelectric and magnetoresistive memories and in magnetic sensor technologies. In order for BFO to be incorporated into device technology, the ferroelastic switching mechanisms must be understood. One of the major factors controlling domain wall kinetics is the presence of defects in the material; with one-dimensional, two-dimensional and three-dimensional defects having unique interactions with the domain boundaries. These interactions are not well known at this point and need to be documented in order to be understood. We use a biasing holder to apply DC voltage to the BFO thin films in the TEM. Alterations to the bias magnitude, polarity and electrode geometry allow for control of the internal electric field and thus the ferroelastic domains. We use in-situ TEM observation along with HRTEM to observe the location and motion of domain boundaries in correlation with the presence of dislocations and point defects. Quantitative domain kinetic data is determined from the in-situ TEM videos. This data indicates that the ferroelastic domain switching and motion is impeded by the presence of defects in BFO films. These observations allow for a more complete understanding of the effects of the local microstructure on domain boundary kinetics. The Electron Microscopy Center and the research at Argonne are supported by the U.S. DOE Office of Science under contract DE-AC02-06CH11357.

        2:15 PM - CCC10.3

        3D Atom Probe Investigation of Nanoscale Austenite Reversion at Interfaces in a Martensitic Stainless Steel

        Lei  Yuan1, Dirk  Ponge1, Dierk  Raabe1.

        Show Abstract

        Austenite reversion during tempering of a Fe-13.6Cr-0.44C (wt.%) martensite results in an ultra-high strength martensitic stainless steel with excellent ductility. The austenite reversion mechanism is coupled to the kinetic freezing of carbon during partitioning at the interfaces between martensite and retained austenite and to carbon segregation at martensite-martensite grain boundaries. The reverted austenite acts as a barrier to prevent cracks development during deformation. The austenite reversion process, nano-carbide precipitation, and carbon segregation have been characterized by atom probe tomography (APT) in order to develop the structure-property relationships that control the material's strength and ductility. A 3D reconstruction was established base on the APT results especially at the interfaces.

        2:30 PM - CCC10.4

        Three-Dimensional X-Ray Analysis of Tin Whisker Formation

        Jeff  Gelb1, Elizabeth  Hoffman2, Xiaodong  Li3, Yong  Sun3.

        Show Abstract

        Tin whisker formation continues to be a challenge for electronics manufacturers with the expanding use of Pb-free solders and platings. The metallic whisker formations have been attributed to electronic failures in numerous industries, including medical and aerospace. Physical sectioning tools have been utilized in the past to explore the microstructure under the whisker and at the interface between the tin thin film and substrate. However, physical sectioning has the inherent disadvantage in that it modifies the material, producing a free surface. Once physically sectioned, the material can no longer be reevaluated to study the effect of time. Three-dimensional X-ray microscopy not only capable of evaluating the subsurface, but it can also be used to view multiple planes in a particular area. The intrinsically non-destructive nature of x-rays further enables repeated imaging studies of the one sample’s 3D microstructure, making it particularly advantageous for microstructure evolution studies. Current state-of-the-art laboratory instrumentation is capable of producing spatial resolution down to 50 nm, opening up these evolutionary studies to a new range of fundamental phenomena. In the work presented here, x-ray microscopy was used to evaluate whisker growth in a tin thin film deposited onto a copper substrate. Initial results reveal that whiskers grow not only on the outer surface, but they also grow on closed pore surfaces within the tin and Cu6Sn5 intermetallic layer near the interface of the copper substrate. Initial results from three-dimensional X-ray imaging have provided new insight into the whisker growth phenomenon. It is expected that this non-destructive local probing tool will provide a critical understanding of the tin layer subsurface.

        2:45 PM - CCC10.5

        Measurements of Materials during In-situ Experiments Using X-Ray Tomography

        Brian  M  Patterson1, Kevin  Henderson1.

        Show Abstract

        X-ray tomography as been commercially available since the 1970's; only since the 1990's with a rapid growth in computer power and x-ray source development has it become commonplace in the laboratory. Unfortunately during most of this time, x-ray tomography has been limited to generating 'pretty', albeit useful pictures of materials. These 3D images give scientists a qualitative understanding of the sample morphology, distribution of voids or inclusions, or damage features. More recently, scientists have begun to take this data one step further and added the ability to quantify these features, void sizes, shapes and their distributions. Coupling this with an in-situ cell such as tension, compression, tearing, or heating, now it is possible to quantifiably measure how these features are changing as a result of response of the sample to this dynamic change. Now it becomes possible to measure these changes and to compare the performance of the material as a result of age, previous stress, or other environmentally induced effects. In this talk we will discuss our recent work with polymers and metals using a compression/tension load cell within a micro computed tomography instrument. We will demonstrate how five dimensional information can be collected. Three dimensions are the 3D image, a fourth dimension will be time or compressive load, with the fifth dimension corresponding to the change in statistics (for example voids colored by equivalent diameter). Using this information, we can compare lot-to-lot or experiment-to-experiment variations as a result of some previously applied stress such as age degradation, compression set or radiation damage.

        3:00 PM - CCC10.6

        Effect of Tip Shape and Atomic Structure in Nano-indentation

        Wen-Dung  Hsu1, I-Hsien  Chen1, Ping-Yu  Chuang1.

        Show Abstract

        Mechanical properties of metal thin films are always a challenging work to characterize especially in nano-scale. Nano-indentation which is a local and small destructive method is one of the promising techniques to measure nano-mechanical properties directly. Literatures have shown that many factors, such as shape of indent tip, material of the tip, indent speed …etc, influence the results a lot. The details of the effects of those factors are however still not clear. In this study, molecular dynamics simulations were performed to study the nano-indentation process. Three types of commonly used tips, conical-shape tip, Vickers tip and half spherical shape tip, were considered. The tips then indented on copper thin film with (100) surface or (111) surface. To study the effect of atomic structure of substrate, indentation on iron thin film with (100) surface or (110) surface were also simulated. The results demonstrate that shape of tip plays an important role on defect nucleation and growth during indentation and hence the load-depth curve. It is found that the load-depth curve closely related with contact area between indent tip and substrate. Therefore, the load-depth curve in the case of conical-shape tip and vickers tip is proportional to the square of indent depth and is linearly proportional to indent depth in the case of half spherical-shape tip. This result is consistent with macroscopic sense. After detailed curve fitting to quantify the deviation of load-depth curve from theoretical predictions by considering contact area only, it is found that besides contact area, the apex angle of the tips, the coherence of atomic structure between tip and substrate and the atomic structure of substrate all play important roles . The apex angle of the tips influences the indent depth to initiate defect nucleation and growth. The structure of substrate influences the motion of defect structure, such as motion of glide systems. The most important is the coherence of atomic structure between tip and substrate influences the generated defect structure. If the atomic structure of tip and substrate are coherence (atoms have identical arrangement), the ring-shape defect structure generated. It then emitted toward close-packed directions into the substrate. Thus the strength of stress field surrounding to tip decreases and hence decreases the measured load. Since the ring defects emitted out, there are fewer defects accumulated and making the indented site less damage. From snap shot of surface topology, it is found that less surface pile-up and less surface damage occur. This finding has grand help in surface probing techniques, since it implies that through design of atomic structure and shape of indent tip, one can obtain a less destructive indentation measurement.

        3:15 PM -

        BREAK

        Show Abstract

        CCC11: Functional Polymers and Molecules

        • Chair: Hiroshi Onishi
        • Thursday PM, April 12, 2012
        • Marriott, Golden Gate, Salon A
         

        3:30 PM - CCC11.1

        Dynamics of Pentacene Based Organic Field-Effect Transistors Examined with a Kelvin Probe Force Microscope

        Christopher  Siol1, Christian  Melzer1, Heinz  von Seggern1.

        Show Abstract

        In this contribution the results on the dynamic response of pentacene based organic field-effect transistors (OFETs) investigated with a Kelvin probe force microscope (KPFM) are presented. KPFM is one of the most essential tools allowing for the determination of the local potential within the channel of organic field-effect transistors and thus providing a closer look into the device physics. Here the manifold applicability of the Kelvin probe force microscope is demonstrated on basis of pentacene field-effect transistors. At first, the quasistatic potential distribution of pentacene based OFETs is investigated under device operation and the obtained potential distributions are compared to the theory of Vissenberg and Matters [1] in conjunction with the current-voltage characteristics. Good agreement between model and experiment is obtained requiring, however, the introduction of short-channel effects. It will be further shown that electrical defects in the pentacene layer can be traced with the KPFM, disturbing the uniformity of the surface potential distribution. Afterwards device instabilities and hysteresis effects will be discussed and it will be shown that the trapping of electrons in common p-type pentacene OFETs is of importance [2]. Finally, the bipolar switching behavior of pentacene based OFETs is presented and repeated charge reversal is used to estimate the charge-carrier transport properties of the carrier front entering the transistor channel from the contacts. [1] M.C.J.M. Vissenberg, M. Matters, Theory of the field-effect mobility in amorphous organic transistors, Phys. Rev. B, 57 (1998) 12964-12967. [2] C. Siol, C. Melzer, H. von Seggern, Electron trapping in pentacene based p- and n-type organic field-effect transistors, Appl. Phys. Lett., 93 (2008) 133303.

        3:45 PM - CCC11.2

        In situ Optical and X-Ray Diffraction Study of Organic Semiconductor Crystal Growth during Solution Shearing

        Gaurav  Giri1, Detlef  Smilgies2, Ruipeng  Li3, Aram  Amassian3, Zhenan  Bao1.

        Show Abstract

        Organic electronics have been considered a leading candidate to make transparent and flexible electronics at a low cost. The main building block of an organic circuit is the organic thin film transistor (OTFT), which is created by using organic semiconductors (OSCs). It has been shown from literature that the best performing OTFTs are created when the OSCs form thin film, aligned crystals. Solutions processing of these crystals are important in order to lower the price of fabricating organic electronics. Growing crystals from solution processing methods are usually performed by using kinetic crystallization, so that the time frame for thin film growth is more compatible with industrial fabrication time scales. We have previously shown that the solution shearing method (SSM) is a process that improves OTFT performance for a range of OSCs, and the method is compatible with roll to roll industrial processing. Because the crystallization process happens kinetically, it is difficult to study the morphological features that enable high OTFT performance. Not only does the thin film crystallize at a fast time scale, the evaporation front, where the crystal grows from the solution, is very small. The entire evaporation front is less than 200 microns, so the solution evolves into a thin film within seconds, and within an area less than 0.2 mm wide. We use an X-ray ‘microbeam’ at the Cornell High Energy Synchrotron Source, with a beam width of < 20 microns, in conjunction with a high speed CCD detector to resolve and follow crystallization on the evaporation front of the solution sheared material. We have collected up to 100 frames per second X-ray images, and are able to create grazing incidence x-ray diffraction movies to easily see how crystallization occurs in the solution shearing system in real time. We also have an optical microscope trained at the evaporation front, which we can use to collect optical videos of the evaporation front. Being able to simultaneously study kinetic crystallization using both optical and X-ray movies will help us understand how different processing conditions result in various crystal morphologies. We study the model OSC 6,13-bis(triisopropyl)-silylethynyl pentacene (TIPS-pentacene) and the polymer poly 3(hexyl-thiophene) (p3HT) in various organic solvents in order to see how solution-sheared based crystallization occurs. We are able to study drying times of the thin films, the evolution of the solvent evaporation front as well as polymorph formation of different OSCs in real time. Using CHESS, we aim to understand crystallization processes under a variety of conditions.

        4:00 PM - CCC11.3

        Nanomechanical Measurements of Transparent Poly(urethane urea) Elastomers: The Effect of Tunable Microstructure

        Kenneth  Strawhecker1, Alex  J  Hsieh1.

        Show Abstract

        Morphology of select model poly(urethane urea), PUU, elastomers is investigated by atomic force microscopy (AFM) and compared with modulus measurements from AFM, nanoindentation, and bulk techniques. The PUU microstructure changes as soft segment (SS) molecular weight (MW) of poly(tetramethylene oxide), PTMO, is varied; PUU with PTMO MW of 2000 (g/mol) exhibits a compliant SS-rich matrix with isolated spherulite-like hard domains of various sizes indicative of a typical microphase-separated elastomer, whereas at MW of 1000 (g/mol) there is a coexistence of an amorphous matrix consisting of predominantly phase-mixed hard and soft segments along with lamellar hard segment domains. As the PTMO MW further decreases to 650 (g/mol) the microstructure is almost dominant with phase-mixed hard and soft segments, thus appears featureless. AFM is used to measure these features qualitatively through AFM-phase imaging and quantitatively through AFM-modulus imaging. The two modes proved to be consistent with one another.

        4:15 PM - CCC11.4

        Force and Energy Involved in Mechanically-induced Single-porphyrin Manipulation

        Remy  Pawlak1, Sweetlana  Fremy1, Shigeki  Kawai1, Thilo  Glatzel1, Hongjuan  Fang2, Leslie-Anne  Fendt2, Francois  Diederich2, Ernst  Meyer1.

        Show Abstract

        Molecular diffusion plays a key role in biological systems and on-surface chemistry. In such processes, the intrinsic properties of molecules like elasticity or reactivity are essential but poorly know. Non contact atomic force microscopy (nc-AFM) is perfectly suitable for such atomic-scale investigation since it allows the detection of forces during manipulations (M. Ternes et al., Science, 319 1066, 2008), the imaging of chemical structures (L. Gross, Science, 325, 1110, 2009) as well as the determination of mechanical properties within molecular structures (R. Pawlak et al. ACS Nano, 5, 6349, 2011). In this contribution, we explore the directed diffusions of single porphyrins equipped with peripheral carbonitrile groups ( L.-A. Fendt et al., Eur. J. Org. Chem., 4659, 2007; ) and stabilized in a saddle-shaped conformation on a well-defined metal using nc-AFM (T. Yokoyama et al. J. Chem. Phys., 115, 3814, 2001). By spectroscopic measurements, these specific functional groups are identified as local reactive centers driving the adsorption. By covalently attaching the AFM tip to one of them, a mechanical stress is applied to one side group until a directed motion of the whole molecule is induced. In response of this pulling force, the molecular structure appears to be elastically deformed and slightly changes its conformation while moving. Dissipated energy during this manipulation, which is related to the adsorption energy of the molecule, is also quantitatively measured.

        4:30 PM - CCC11.5

        Acetylene on Cu(111): Evolution of Adsorption Phases and Substrates Stress with Coverage

        Yeming  Zhu1, Jon  Wyrick1, Connor  Holzke1, Daniel  Salib1, Kamelia  D  Cohen1, Zhihai  Cheng1, Dezheng  Sun1, Ludwig  Bartels1.

        Show Abstract

        Using variable temperature STM and DFT simulation, we identify the phases of acetylene adsorbed on the Cu(111) surface. Depending on the coverage, a number of different surface structures are found, which are characterized by different acetylene-substrate interactions and, as a consequence, impart different types and amounts of stress on the underlying surfaces. In this contribution, we correlate the compressive or tensile stress induced to the prevalence of different adsorption geometries at different coverages. The interaction of carbonaceous species such as acethylene with Cu(111) may be regarded as an intermediate step in the formation of graphene; the conceptualization of surface interactions in terms of induced stress on the substrate may have widespread applicability.

        Download Session Locator (.pdf)2012-04-13  

        Symposium CCC

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        Symposium Organizers

        • Nina Balke, Oak Ridge National Laboratory
        • Howard Wang, State University of New York, Binghamton Institute for Materials Research
        • Job Rijssenbeek, GE Global Research
        • Thilo Glatzel, University of Basel

        Support

        • Asylum Research
          Zurich Instruments Ltd

          CCC12: Materials Synthesis

          • Chair: Howard Wang
          • Friday AM, April 13, 2012
          • Marriott, Golden Gate, Salon A
           

          8:30 AM - CCC12.1

          In situ X-Ray Scattering Studies of Supercritical Nanoparticle Synthesis

          Christoffer  Tyrsted1 2, Bo  B  Iversen1.

          Show Abstract

          Nanoparticles form a cornerstone of nanoscience and nanotechnology having their effectiveness in a variety of applications governed by the specific nanoparticle characteristics. Control of nanoparticle structure, size, size distribution, crystallinity and morphology are therefore key points in the synthesis of nanoparticles. Supercritical synthesis offers a fast, one-step route for the production of nanomaterials utilising environmentally friendly reaction mediums such as water, ethanol or methanol. The procedure offers the possibility of synthesizing a large variety of inorganic nanoparticles with tuneable characteristics (size, morphology and crystal structure). The main body of work leading to the understanding of the chemical processes involved in nanoparticle formation and growth, is based on characterisations of the products obtained after varying synthesis parameters (pressure, temperature, concentrations, pH etc.), i.e. ex situ investigations. Even though these methods have provided invaluable knowledge, a complete understanding of the mechanisms involved during synthesis, however, remains elusive. So-called in situ studies are, therefore, required to probe the reactions as they occur. X-ray techniques are common characterization tools in the field of in situ studies, and may be used for a wide variety of in situ experiments including, small-angle scattering, powder diffraction, total scattering, and absorption experiments. We have developed a range of unique in situ reactors which makes it possible to probe the hydrothermal/solvothermal/supercritical reaction medium with X-rays allowing comprehensive characterisation of the nanoparticulate materials during synthesis. Here in situ studies on the supercritical synthesis of yttria stabilized zirconia (YxZr1-xO2-x/2) and gadolinium doped ceria (GdxCe1-xO2-x/2) are presented. The studies reveal the changes in material characteristics (particle size/shape/distributions, crystallinity, atomic structure and more) throughout the synthesis to give a comprehensive description which may be used to direct syntheses on a larger scale.

          8:45 AM - CCC12.2

          Disclosing Growth Kinetics of Metal Nanoparticles through Plasmonic Response: The Case of Ag/α-Al2O3(0001)

          Remi  Lazzari1, Jacques  Jupille1.

          Show Abstract

          The determination of size and shape of supported particles is an unavoidable step in the understanding of the chemical or physical properties appearing at the nanoscale. For metals, plasmonics offer a powerful and flexible tool to characterize at a glance the average morphology in situ during growth. Its outcomes compare favorably with Grazing Incidence Small Angle X-Ray scattering [1,2]. The strength and sensitivity of this approach will be illustrated through the study by Surface Differential Reflectivity Spectroscopy of the vapor deposition of silver on Al2O3(0001) at various temperatures (190-675K). Changes in size, shape and density were derived from the optical response modeled in the framework of surface susceptibilities by assuming that supported clusters were in the form of truncated spheres. The pivotal importance of temperature dependence of the dielectric constant and of plasmon absorption broadening was demonstrated. The methodology was validated through a critical comparison with the physics of crystalline growth. The sticking coefficient is found close to one up to 575K before dropping at T~675K. The growth proceeds through a growth step at a nearly constant particle density followed by particle coalescence. Sensitivity to nucleation is achieved in the low flux regime. Time dependence exponents of size are consistent with this growth scenario but discard static coalescence and may favor a process with mobile clusters above a critical size. The Arrhenius dependence of the saturation density highlights a nucleation on defects at low temperature (T < 300K) and enhanced detraping above. For particles bigger than 10 nm in size, values of contact angle and adhesion energy (θ=127.5 ± 1° and 0.48 ± 0.02 J.m-2) nicely agree with tabulated data and theoretical calculations. The fine evolution of the particle contact angle is assigned to a competition between surface stress, interface adhesion and strain induced by lattice-mismatch. Some perspectives of use of plasmonics in gas adsorption characterization will also be given. [1] R. Lazzari, G. Renaud, C. Revenant, J. Jupille, Y. Borensztein, Phys. Rev. B. 79, 125428 (2009) [2] G. Renaud, R. Lazzari, F. Leroy, Surf. Sci. Rep. 64, 255-380 (2009) [3] R. Lazzari and J. Jupille, Nanotechnology to appear [4] R. Lazzari and J. Jupille, Phys. Rev. B submitted

          9:00 AM - CCC12.3

          Growth of Mesoporous Silica Nanoparticles Monitored by In-situ Time-resolved Small-angle Neutron Scattering

          Martin  James  Hollamby1 2, Dimitriya  Borisova2, Paul  Brown3, Julian  Eastoe3, Isabelle  Grillo4, Dmitry  Shchukin2.

          Show Abstract

          Here, for the first time, we apply time-resolved small-angle neutron scattering (tr-SANS) to study the complete formation of mesoporous silica nanoparticles (MSNs) (Langmuir, accepted, 2011). With high colloidal stability and a large pore volume, MSNs are extensively studied for a variety of delivery applications (e.g. Adv. Mater 2011, 23, 1361; Small 2007, 3, 1341; JACS 2008, 130, 2382). However, because MSNs are typically prepared using surfactant concentrations much lower than those preferred in the bulk case, it is likely that their formation mechanism might differ from the bulk case (e.g. Aust. J. Chem. 2005, 58, 627). Previous mechanistic evidence has proposed several possible routes (e.g. ACIE 2002, 41, 2151; Chem. Mater. 2008, 20, 2779), but has typically been obtained by electron microscopy, the early-stage interpretation of which can suffer inherent difficulties of e.g. low resolution or further crystallization and reorganization upon drying. A distinct advantage of in-situ tr-SANS is the ability to detect contributions from the whole system, enabling the visualization not only of particle genesis and growth but also the concurrent changes to the coexistent micelle population without perturbing the system. Using contrast-matching tr-SANS, we were able to highlight the individual contributions from the silica and surfactant respectively. Analysis of the data agrees well with the ‘current bun’ model describing particle growth. We will present these mechanistic results, in addition to the influence of changing the reaction conditions (i.e. concentration of silica precursor, temperature). In doing this, we highlight the importance of in-situ techniques, in particular tr-SANS, for mechanism elucidation in materials science.

          9:15 AM - CCC12.4

          In-situ Spectroscopic Investigation of Nanoparticle Growth for Identifying and Optimizing Multiple Synthesis Parameters

          Michael  Krueger1 2, Simon  Einwaechter1 2, Frank  S  Riehle1.

          Show Abstract

          Nanoparticles usually have size dependent properties. Controlling the size, shape and surface composition of nanoparticles is of uppermost importance for dedicated applications. The question: “When is the synthesis over” is in the case of nanoparticles strongly correlated with the question: “For what do you want to use the nanoparticles”. In-situ photoluminescence UV-vis absorption spectroscopy during the synthesis of nanoparticles gives a fast feedback of the growth and performance of nanoparticles. This has impact for fundamental investigations of nanocrystal formation as well as for the realization of reproducible synthesis protocols for dedicated functional nanoparticles. We present a novel automated microwave-based synthesis reactor with integrated online spectroscopic detection and demonstrate the usability for dedicated optimization of nanoparticle synthesis. The individual reactions can be characterized and visualized by three-dimensional plots acting as fingerprints for the respective synthesis enabling the direct comparison of various reactions.

          9:30 AM - CCC12.5

          Real-Time Grazing Incidence Small Angle X-Ray Scattering Study of Amorphous Silicon Thin Film Growth

          Gozde  M  Erdem1, Alexander  DeMasi2, Priya  V  Chinta3, Randy  Headrick3, Karl  Ludwig2.

          Show Abstract

          Quantitatively understanding surface morphology evolution during thin film growth remains an important problem in materials science. In the past decade, in-situ Grazing Incidence Small Angle X-ray Scattering (GISAXS) has become a powerful non-destructive tool for examining surface structure and evolution [1] . Here, we report real-time GISAXS studies of amorphous silicon thin film growth at room temperature performed at the National Synchrotron Light Source of Brookhaven National Laboratory. The effects of different growth processes on surface morphology evolution were examined using two hyperthermal growth processes: RF off-axis and on-axis sputter deposition and a thermal process: deposition from a sublimation source. For the plasma-based sputter deposition processes, we also investigated the effect of deposition pressure on surface morphology evolution. Ex-situ Atomic Force Microscopy (AFM) topographs were used to measure the final surface morphology in real space for comparison with the GISAXS results. This work was supported by the Department of Energy, Basic Energy Sciences. [1] G. Renaud, et.al., “Probing surface and interface morphology with Grazing Incidence Small Angle X-Ray Scattering”, Surf. Sci. Rev. 64, 255-380 (2009).

          9:45 AM - CCC12.6

          In-situ X-Ray Synchrotron Studies of Epitaxial Multiferroic BiFeO3 (001) Thin Films on SrTiO3 Substrates

          Priya  V  Chinta1, Randy  Headrick1, Matthew  Dawber2, Sara  Callori2, Ashrafi  Almamun1.

          Show Abstract

          Real time X-ray specular reflectivity and surface diffuse X-ray scattering measurements allow one to investigate the initial nucleation stage giving insight into atomic–scale processes and mechanisms occurring during film deposition. Surface X-ray scattering techniques coupled with the availability of fast single photon counting two dimensional X-ray pixel detector makes it feasible to probe both specular and diffuse scattering simultaneously thus giving both height distribution of material (out of plane) and lateral ordering on surface (in-plane) information respectively. In this work we investigate in-situ growth of multiferroic BiFeO3 (001) thin films on SrTiO3 substrates using two growth techniques: a) pulsed laser deposition (PLD) and b) magnetron sputter deposition using X-ray specular and diffuse measurements. The results for PLD deposited BiFeO3 films show heteroepitaxial growth oscillations of specular intensity monitored at (00 ½) crystal truncation rod (CTR) indicating layer-by-layer growth mode during the first three monolayers beyond which the growth oscillations decay and disappear. The in-plane detail obtained from diffuse scattering has a characteristic V-shape and oscillates out of phase with specular indicating coarsening with time during each monolayer growth, which is characteristic of the layer-by-layer growth mode. A characteristic in-plane length scale obtained from the line shapes shows that the in-plane length scale is time dependent indicating coarsening of islands with deposition. We believe that coarsening process is caused both by ripening and coalescence of islands which could be identified as key fundamental processes in growth of BiFeO3 (001) films. A key result in PLD deposited films is the increase in diffuse intensity beyond three unit cells which suggests imperfect layer-by-layer growth where a later layer nucleates before the completion of a former layer. The surface features were corroborated with ex-situ Atomic Force Microscopy (AFM) measurements where surfaces have ordered step structure for three unit cell thick films and corrugated rougher surfaces for films with thickness greater than three unit cells. Results for sputter deposited films showing strong specular and diffuse oscillations will also be discussed.

          10:00 AM -

          BREAK

          Show Abstract

          CCC13: Characterization of Thin Film Surfaces

          • Chair: Howard Wang
          • Friday AM, April 13, 2012
          • Marriott, Golden Gate, Salon A
           

          10:30 AM - CCC13.2

          Characterization of Atomic Processes on Insulating Surfaces via Dissipated Energy

          Filippo  Federici Canova1, Shigeki  Kawai2, Thilo  Glatzel2, Adam  S  Foster1 3, Ernst  Meyer2.

          Show Abstract

          NC-AFM is an invaluable tool when probing surfaces, providing atomic resolution topography and detailed 3D force maps. This characterization technique is a key approach to revealing the microscopic properties of, for example, novel catalysts determining their performance and lifetime in clean energy production applications. As the tip scans the surface, the feedback gain signal associated to the energy dissipated in the oscillation cycles is also recorded, and this often differs from conventional topography images, showing different contrast patterns, periodicity and tip-surface distance dependence. Although many different surfaces have been studied with atomic resolution, a routine interpretation of these measurement has yet to be found, since the atomic processes at the surface responsible for energy dissipation are not well understood and the influence of the tip is not clear. Interpretation of dissipation images can lead to a better understanding of the physics behind surface processes, and can be a tool as powerful as standard topography imaging. In order to understand better the role of the tip in measured dissipation, we carried out extensive atomistic calculations using a wide variety of different tip materials and structures, and an ideal NaCl (100) surface. After studying simple processes with quasi-static calculations, testing several tip geometries and materials, we are now investigating the atomic-scale dissipative processes using GPU accelerated finite temperature molecular dynamics (MD) simulations, and comparing directly to static force spectroscopy (SFS) and dynamic force spectroscopy (DFS) experiments. Ideal NaCl tips are too stable and do not give dissipation although in presence of defects at the apex, the system shows reversible reconstructions involving the tip and the surface, giving an average dissipation up to 0.02 eV/cycle, smaller than experimentally seen. MgO tips are even more stable but the oxygen’s charge at the apex makes the surface unstable leading to formation of atomic chain and, consequently, irreversible surface alteration, which is again in contrast with the experiment, showing no decoration and stable operation. Finally we focused our efforts on simulating the experiment from the very beginning, where an oxidized tip indents the surface adsorbing a NaCl nanocluster at the apex. The average dissipation we calculate with this tip is in a quantitative agreement with DFS data and the distance dependence is also reproduced. We found that dissipation comes from stochastic formation of atomic chains of different lengths.

          10:45 AM - CCC13.3

          In situ Methods in Tribology and Contact Mechanics

          Brandon  Alexander  Krick1, W. Gregory  Sawyer1.

          Show Abstract

          Tribological phenomena occur at interfaces which are often difficult to access with many experimental techniques. This has led to the rapid development of in situ experimental techniques which can illuminate the physical, mechanical, chemical and biological interactions between two surfaces in intimate contact. We have developed many in situ tribometers to probe this buried interface. An in situ Surface Plasmon Resonance (SPR) tribometer is used to measure molecular transfer of solid lubricants during sliding. For some systems, such as PTFE, transfer is detected as early as the first cycle of sliding, while minimal transfer is observed in other systems such as UHMWPE. Transfer films generated during in situ SPR experiments are studied with Surface Enhanced Raman Spectroscopy (SERS) to confirm the chemical identity of the transferred material measured with SPR. An in situ XPS tribometer allows for us to monitor environmental dependencies of solid lubricants and explore tribochemical changes that occur in many solid lubricant systems. An optical in situ microtribometer allows us to probe the real area of contact between solids and map out the surface topography of the near contact region in contact and sliding experiments. These experiments have allowed us to verify contact mechanics models of elastomers, thin films, and adhesive-elastic materials and observe wear and transfer film generation. To complement the optical in situ microtribometer, we have developed an in situ thermal imaging tribometer to map out the surface temperature within the contact region of a solid during sliding to explore flash temperatures.

          11:00 AM - CCC13.4

          Nanoprobing Friction and Charge Transport Properties of Chemically Modified Graphene

          Sangku  Kwon1, Jae-Hyeon  Ko2, Ki-Joon  Jeon3, Yong-Hyun  Kim2, Jeong  Park1.

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          Atomically thin graphene is the ideal model system for studying nanoscale friction due to its intrinsic two-dimensional anisotropy. Furthermore, modulating its tribological properties could be an important milestone for graphene-based micro- and nano-mechanical devices. Here, report the correlation between electrical transport property and mechanical deformation of graphene layer grown on Cu substrate by chemical vapor deposition method was studied with conductive probe AFM / friction force microscopy in ultra-high vacuum. We studied the nanoscale friction and charge transport properties of pristine and chemically modified graphene. Current mapping reveals the domain and domain boundaries on the graphene surface. We found that the friction of graphene increased by a factor of 6 after fluorination, while the adhesion force is reduced by 25 percent. Results of density functional theory (DFT) calculations show that the out-of-plane stiffness of graphene is sensitive to fluorination, in contrast to the rather insensitive in-plane stiffness. The FFM experiment and DFT simulation suggest that nanoscale lateral friction of the two-dimensional atomic sheet is dominated by normal stiffness, and the frictional energy mainly dissipates through the softest transverse-acoustic (TA) phonons, which can be readily modified by chemical treatment of the surface.

          11:15 AM - CCC13.5

          Debonding and Environmental Degradation in Transparent Barrier Films and Protective Coatings

          Tissaphern  Mirfakhrai1, Fernando  Novoa1, Reinhold  Dauskardt1.

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          Transparent barrier film structures and protective coatings in photovoltaic and display technologies are exposed to operating conditions that include moisture, oxygen, and other chemically active species present in the environment, together with mechanical stresses and temperature cycling. They are also exposed to solar radiation where higher energy UV photons are known to cause photo-chemical and photo-oxidation damage. The coupling between such photo-degradation processes and the mechanical stresses and environmental species remains poorly understood and characterized. This is particularly important for the adhesion and debonding of the many internal interfaces in barrier films and protective coatings. Interfacial failure results in the loss of barrier integrity and the creation of fast diffusion paths for environmental species. This in turn will result in shortening the lifetime of the solar device. We describe quantitative in-situ characterization techniques to measure the synergistic effect of mechanical stresses, temperature, environmental species and the presence of in-situ simulated solar UV light on the debonding kinetics and cohesive failure of interfaces and layers in transparent barrier films and coatings. Measurements are reported for a number of film structures and coatings in the as-processed condition and following pre-exposure to aging (hot, wet and simulated solar) conditions. The in-situ UV characterization in the presence of other environmental factors allows us to quantify over a wide range of defect evolution rates the effects of these “stressing” parameters on the fundamental mechanisms of molecular bond rupture kinetics. Subsequent surface characterization of the debonded surfaces is used to investigate the detailed debond path and its location in the barrier structure, together with the surface chemistry. We show that a fundamental understanding of the adhesive and cohesive behavior of barrier films and coatings is important for longer term reliability and quantifying the kinetics of the molecular bond rupture kinetics provides the basis for long term reliability predictions.

          11:30 AM - CCC13.6

          Low Micrometer to Nanometer Scale Spatially Resolved Surface Sampling and Chemical Imaging Using Laser Ablation and Thermal Desorption/Ionization Coupled with Mass Spectrometry

          Olga  S  Ovchinnikova1, Gary  J  Van Berkel1.

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          The goal of atmospheric pressure chemical imaging at the nanometer scale with mass spectrometry has been until now been approached by our group using near field effect laser desorption and proximal probe thermal desorption for surface sampling followed by a secondary ionization process like electrospray. Each of these sampling approaches can be coupled with an AFM platform to give a multimoldal, physical and chemical, imaging platform. The thermal desorption approach allows for the easy scaling of the technique all the way from the millimeter to the nanometer regime. In the nanometer regime an AFM platform with silicon based heating AFM probes is used to locally desorb material from nanometer sized craters. The latest results from our group in these two areas will be presented. We also have been investigating a new approach to improve the effectiveness of laser ablation/ionization through a secondary ionization of the neutrals ablated by capturing the laser desorption plume into a liquid and then electrospaying the solution. The added benefit of being able to capture the desorption plume into a liquid is the ability to carry out post sampling processing of the captured analyte, such as high performance liquid chromatography. The ability to clean up a sample via HPLC eliminates matrix ion suppression and allows for the confident detection of isobaric compounds as well as trace level materials which otherwise would be obscured by chemical noise in complicated sample matrixes. The future of all these techniques and the potential of high resolution chemical imaging via mass spectrometry applied to the study of energy storage and conversion materials will be discussed. This work was supported by the Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences, United States Department of Energy. ORNL is managed by UT-Battelle, LLC for the U.S. Department of Energy under contract DE-AC05-00OR22725.

          11:45 AM - CCC13.7

          In Situ Light Scattering Determination of Film Formation of Immiscible Polymer Blends during Spin Casting

          Youmna  Mouhamad1, Nigel  Clarke1, Richard A.L.  Jones1, Mark  Geoghegan1.

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          Spin casting is a process broadly used to obtain a uniform film on a flat substrate. A homogeneous film results from the balance between centrifugal and viscous forces. Here we revisit the Meyerhofer model of the spin casting process by taking in account the centrifugal forces, a uniform time dependent evaporation rate, and account for the changes in viscosity using the Huggins intrinsic viscosity. Time resolved light reflectometry is used to monitor the thickness changes of a polystyrene-poly(methyl methacrylate) (which we denote as PS and PMMA) film initially dissolved in toluene and spin cast for ten seconds at 1000 rpm. The experimental data are in good agreement with the model. We also investigate how the volume fraction of PS and PMMA influences the thinning of the film during spin casting. A distinct change in the temporal evolution of thickness as a function of time delimits the first phase of the spin casting process where centrifugal forces are dominant from a second phase dominated by the solvent evaporation. This hypothesis is supported by in-situ off specular scattering data. The time at which this change from centrifugal to evaporation-dominated behaviour is delayed as the volume fraction of PMMA increases.

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