Chongmin Wang Pacific Northwest National Laboratory
Rafal E. Dunin-Borkowski Technical University of Denmark
Niels de Jonge Vanderbilt University Medical School
V2: In-Situ Nanoscale Growth
Tuesday PM, April 06, 2010
Room 3003 (Moscone West)
2:30 PM - **V2.1
In-situ Gas Reaction Studies at Atomic Resolution Using an Advanced E-cell Capability.
Lawrence Allard 1 , Wilbur Bigelow 2 , David Nackashi 3 , John Damiano 3 , Steven Bradley 4 Show Abstract
1 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Materials Science & Engineering, University of Michigan, Ann Arbor, Michigan, United States, 3 , Protochips Inc., Raleigh, North Carolina, United States, 4 , UOP LLC., Des Plaines, Illinois, United States
Catalyst characterization via in-situ microscopy under gaseous environments at elevated temperatures is a significant challenge for ultra-high-resolution imaging in modern aberration-corrected electron microscopes. Aberration-corrected dedicated environmental TEMs with standard furnace-type heating stages are plagued by problems associated with temperature ramp up and down rates, limits on the types of source gases and their pressure, and specimen drift due to thermal influences caused by the bulk heating systems. A new heating technology employing MEMS-based heating elements (Protochips Inc., Raleigh, NC) has been shown to be highly stable at elevated temperatures, with drift rates limited only by the inherent drift in the microscope stage, and to offer remarkable heating and cooling rates of 106°C/sec. This technology has recently been incorporated into a novel environmental cell (E-cell) specimen holder, which has a specimen tip thickness of only 1.35mm and thus fits comfortably into the 2mm gap of a JEOL 2200FS aberration-corrected STEM/TEM objective lens pole piece. The closed cell semiconductor window design permits simultaneous viewing and temperature/gas control to allow direct observation of gas-solid reactions in real time. Catalyst specimens can be heated up to 1200°C and can handle internal pressures up to 1 atmosphere during reaction experiments, although imaging is best at significantly lower pressures. The combination of high temperature ramping rates and flexibility of gas sources and pressures allows several reaction schemes to be employed for in-situ studies, that are not possible with standard heating stages. Examples will be given showing of reduction reactions with atomic columns and single heavy atoms on oxide supports resolved, by high-angle annular dark-field techniques in our probe-corrected (CEOS GmbH, Heidelberg, Ger) JEOL instrument. This research at the Oak Ridge National Laboratory's High Temperature Materials Laboratory was sponsored by the U. S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Vehicle Technologies Program.
3:00 PM - V2.2
Fe Catalysts for Carbon Nanotube Growth Fabricated from Ferrocene Using Electron Beam Induced Decomposition.
See Wee Chee 1 , Renu Sharma 2 Show Abstract
1 LeRoy Eyring Center for Solid State Science, Arizona State University, Tempe, Arizona, United States, 2 , National Institute of Standards and Technology, Gaithersburg, Maryland, United States
Carbon nanotubes (CNT) are currently being developed for several important applications; in particular, for making electron field emission sources but one of the key challenges has been the synthesis of arrays of nanotubes with controlled size and placement. While the transmission electron microscope (TEM) has been an important characterization tool in studying carbon nanotubes, with the development of the environmental scanning TEM (E(S)TEM) it has become possible to conduct in situ experiments to study the growth of the nanotubes at atomic resolution. By using the ESTEM column as a CVD reactor, we can observe the entire growth process under constant temperature and pressure. Recently, we have reported the fabrication the Fe catalyst particles using diiron nonacarbonyl by electron beam induced deposition (EBID) in a Tecnai F20E(S)TEM. Using this technique, the particles can be placed on specific sites through the positioning of the focused electron beam and the particle size can be controlled with deposition time. While these particles are catalytically active for CNT growth, diiron nonacarbonyl has a relatively low decomposition temperature of about 100°C. Here, we report the EBID of the Fe catalysts using ferrocene as the organometallic precursor. Ferrocene has a decomposition temperature of about 500°C and has been commonly used for the fabrication of the Fe catalysts via pyrolysis. For our experiments, perforated SiO2 membranes are used as substrates. The substrate temperature is varied from room temperature to 450°C and the precursor pressure from 0.5 mTorr to 10 mTorr. We have found that ferrocene adsorbs to a certain extent on the substrate and so it is possible to deposit particles at low temperatures when the precursor flow is switched off after saturating the substrate surface. For carbon nanotube growth, the Fe containing particles were then heated in 100 mTorr of hydrogen up to 650°C before introducing acetylene. One of the key issues in EBID is the presence of carbon contaminants in the deposits and so electron energy loss spectroscopy (EELS) data are also collected from the deposited particles before and after heating in hydrogen. By comparing the various deposited catalysts, we seek to deduce the relationship between EBID growth parameters and the CNT growth. We will present how the catalyst particle size and composition changes with the deposition conditions and the subsequent change in CNT growth and morphology from these particles.
3:15 PM - V2.3
Direct Observation of Nucleation Events and Growth of III-V Semiconductor Nanowires.
Rosa Diaz 1 , Renu Sharma 1 , Subhash Mahajan 1 Show Abstract
1 School of Material, Arizona State University, Tempe, Arizona, United States
The group III nitride semiconductors have attracted special interest for applications in a number of optoelectronics devices, such as light emitting diodes (LEDs), solid state lasers, and ultraviolet (UV) detectors, owing to their special characteristics such as a direct and wide band gap that spans from ultraviolet to the infrared wavelengths, as well as shorter bond lengths relative to the other compound semiconductors, which make them more stable.Multi-layer epitaxial structures required for various devices are generally grown on sapphire substrates. The growth approaches that tend to obviate lattice mismatches between the group III nitride films and the substrates result in a high density of dislocations, which in turn reduce the efficiency of the device. One possible solution for this problem is to substitute single crystal semiconductor nanowires for epitaxial films, given that this type of one-dimensional structures often has stress-free surfaces and similar or even better electrical and optical properties.Vapor-liquid-solid catalytic growth is one of the most common methods used to synthesize nanowires. However, there is a lack of understanding of the process—specifically of the phase of the catalyst before and after nucleation, of the effect of the catalyst size on nucleation, of the nucleation limiting step, and of the behavior of the catalyst nanowires interface during growth.This work reports direct observations of nucleation events and growth of GaN nanowires (GaN-NWs) using an environmental scanning/transmission electron microscope [E(S)TEM]. These nanowires were formed at 800C by direct reaction of ammonia (NH3) with Au – Ga alloy particles as catalyst. Initially, Au was sputtered on porous polycrystalline Si film TEM grids. Later these grids were introduced into the E(S)TEM column and heated in two steps using a heating holder. For the first step the sample was heated up to 480C followed by the introduction of trimethylgallium (TMG) into the column. Next, the sample area and delivery lines were evacuated by closing the inlet of the TMG. Subsequently, in the second step the sample temperature was increased to 800C and NH3 was introduced into the E(S)TEM column. Low and high magnification images and digital videos were recorded. JEOL 2010F TEM was used for ex-situ imaging and EDX chemical analysis.The catalyst particles were observed to remain in liquid phase during both nucleation and growth. Therefore, the nucleation and growth of GaN-NWs followed the VLS mechanism. The catalyst particles presented irregular shapes, with thin film tails connected to the particles. It is within these tails that nucleation of GaN nanowires took place. During early stages of growth, the catalyst-nanowire interface presented more than one facet, and after increasing the NH3 pressure, the catalyst-nanowire interface became single-faceted. Finally, growth of GaN nanowires was observed to follow a zig-zag step growth.
3:30 PM - V2.4
Layer-by-layer Growth of Nanowires via Catalyst Droplet Oscillation.
Jeung Hun Park 1 , Cheng-Yen Wen 2 , Jerry Tersoff 3 , Eric Stach 2 , Suneel Kodambaka 1 , Frances Ross 3 Show Abstract
1 Department of Materials Science and Engineering, University of California - Los Angeles, Los Angeles, California, United States, 2 School of Materials Engineering and Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana, United States, 3 IBM Research Division, T. J. Watson Research Center, Yorktown Heights, New York, United States
Using in situ ultra-high vacuum transmission electron microscopy (TEM), we follow the Au-catalyzed vapor-liquid-solid growth of Si nanowires using disilane (2.0×10-6 – 5.6×10-6 Torr) at temperatures between 450 and 650 °C. During growth, we observe repetitive oscillations of the AuSi droplet occurring consistently at the edge of the droplet-wire interface, i.e. the vapor-liquid-solid triple phase line. From the TEM images of droplet/wire interface acquired at video-rate (30 frames/s), we measure the oscillations as a function of deposition time. We find that the droplet oscillations are periodic with a frequency that increases with both disilane pressure and substrate temperature. By comparing the wire growth rate with the oscillation frequency, we show that each oscillation corresponds to nucleation and growth of a new Si layer. We expect that these observations, which provide new insights into the dynamics of nanowire growth, are general and applicable to other materials systems.
3:45 PM - V2.5
Nucleation and Step-flow Kinetics of Sub-eutectic Ge Nanowire Growth.
Andrew Gamalski 1 , Renu Sharma 2 , See-Wee Chee 2 , Caterina Ducati 3 , Stephan Hofmann 1 Show Abstract
1 Engineering, University of Cambridge, Cambridge United Kingdom, 2 LeRoy Eyring Center for Solid State Science, Arizona State University, Tempe, Arizona, United States, 3 Dep. of Materials Science and Metallurgy, University of Cambridge, Cambridge United Kingdom
The integration of bottom-up assembled semiconductor nanowires in future nano/opto-electronic devices requires a detailed understanding of their growth mechanisms. We present a video-rate, environmental transmission electron microscopy study of Au catalysed Ge nanowire nucleation and growth under digermane exposure in the temperature range of 240-340°C . We construct a thermodynamic model to describe the observed Ge nanowire growth kinetics. This model provides physical insight into the observed solid-liquid catalyst particle phase changes during the initial nucleation stage and into the step nucleation and ledge-flow at the catalyst-nanowire interface . A. Gamalski et al, submitted (2009) S Hofmann et al, Nature Materials 7, 372 (2008)
4:30 PM - V2.6
Relationship Between the Shape and Morphological Evolution of Catalysts in Different Ambients and Their Effects on Carbon Nanotube Growth.
Seung Min Kim 1 2 , Dmitri Zakharov 2 , Avetik Hartyunyan 3 , Eric Stach 1 2 Show Abstract
1 School of Materials Engineering, Purdue University, West Lafayette, Indiana, United States, 2 Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana, United States, 3 , Honda Research Institute USA, Inc., Columbus, Ohio, United States
Recently, we have shown (Harutyunyan et al. ) that single-wall carbon nanotubes (SWNT) with metallic conductivity can be preferentially grown (with 91% population density) by varying the nobel gas environment (He and Ar) during thermal annealing of the Fe catalysts used to mediate nanotube growth, and in combination with residual pressures of H2 and H2O. Real time transmission electron microscopy observations of Fe nanoparticles in equivalent environments show that the catalysts are strongly facetted in the presence of He ambient, but rounded in Ar ambients. Additionally, the presence of different ambients and different thermal annealing durations prior to nanotube nucleation leads to markedly different populations of semiconducting and metallic nanotubes. These observations indicate that both the shape and the size distribution of the catalysts at the moment of nanotube nucleation strongly affect the resulting nanotube chirality. It is well known that the shape of the particles also affects the coarsening behavior: thus, it is crucial to fully understand how the affect of different ambients modifies coarsening behavior.Coarsening behavior among (catalyst) particles is a classic topic, and is often described in the framework of “Ostwald ripening”. Lifshitz, Slyozov, and Wagner (LSW) have obtained an analytical solution to describe this coarsening behavior, and their solutions have been proven valid for many experimental systems. However, they assumed that particles grow without any energy barrier for atomic attachment (i.e that they are spherical particles), and as a result their solutions cannot explain the coarsening behavior of particles with facetted shapes. Our observations show that in the presence of He ambients, the catalyst particles have strongly facetted shapes and exhibit a narrow size distribution.To more completely understand the effects of different ambient on the shapes of catalyst particles and resultant coarsening behavior, we will described quantitative in-situ annealing experiments conducted in an environmental-cell transmission electron microscope (E-TEM). These observations will be compared with recent coarsening models [4, 5] that describe how coarsening proceeds differently in particles with different equilibrium shapes. Finally, we will provide some speculations concerning the origins of the strong shape changes observed in different noble gas ambients, and highlight interrelationships between our observations and chirality development.A.R. Harutyunyan, et al.. Science 2009;326:116.I.M. Lifshitz and V.V. Slyozov, J. Phys. Chem. Solids 1961;19:35.C. Wagner, Z. Electrochem. 1961;65:581.Y.J. Park, et al., Metall. Trans. A 1996;27A:2809.Y.K. Cho, et al., J. Am. Ceram. Soc. 2004;87:443.
4:45 PM - V2.7
Metal Zn Nanocrystal Fabrication on ZnO Films by Thermally Assisted Electromigration in Transmission Electron Microscopy.
Jongmin Yuk 1 2 , Kwanpyo Kim 2 3 , Zonghoon Lee 2 , Masashi Watanabe 2 4 , A. Zettl 2 3 , Tae Whan Kim 5 , Young Soo No 5 , Won Kook Choi 6 , Jeong Yong Lee 1 Show Abstract
1 , KAIST, Daejeon Korea (the Republic of), 2 , Lawrence Berkeley National Laboratory, Berkeley, California, United States, 3 , University of California at Berkeley, Berkeley, California, United States, 4 , Lehigh University, Bethlehem, Pennsylvania, United States, 5 , Hanyang University, Seoul Korea (the Republic of), 6 , Korea Institute of Science and Technology, Seoul Korea (the Republic of)
The fabrication of zero (0-D) or one (1-D) dimensional nanocrystals with designing their size, shape and location on semiconductor substrates can lead to single-electron devices such as memories, transistors and sensors . As a potential engineering tool for direct fabrication of position-controlled nanocrystals, scanning probe techniques such as scanning tunneling microscopy (STM) and atomic force microscopy (AFM) has been intensively employed for their capabilities of single atom manipulation. However, these techniques have a limit to control of size and shape because governing mechanisms of nanocrystal formation still remain uncertain. Real-time direct observations required for elucidation of nanocrystal formation mechanisms at atomic scales is hardly achievable in current scanning probe instruments. Furthermore, in even the most recent study, these techniques have a principle drawback of repetitive manipulation of individual atoms to fabricate nanocrystals, which is extremely time-consuming (for example, 120 atoms / 9 hours) .In this study, 0-D and 1-D metal nanocrystals were successfully fabricated with accurate control in size, shape and position on semiconductor surfaces by using a novel in-situ fabrication method of nanocrystal with a biasing tungsten-tip in transmission electron microscopy. The dominant mechanisms of nanocrystal formation were identified mainly as electromigration assisted with the local Joule heating through the direct observation of formation and growth processes of nanocrystal. This method was applied to extracting metal atoms with an exceedingly faster growth rate (~105 atoms / second) from metal-oxide thin film with any desired size and position. By real-time observation of the microstructure and simultaneous measurement of the electric response from the biasing tip, it was found that the nanostructure formation can be completely controlled into various shapes such as 0-D nanodots and 1-D nanowires/nanorods. 1. V. Ray, R. Subramanian, P. Bhadrachalam, L. C. Ma, C. U. Kim, S. J. Koh, Nature Nanotech. 2008, 3, 603.2. Y. Sugimoto, M. Abe, S. Hirayama, N. Oyabu, Ó. Custance, S. Morita, Nature Mater. 2005, 4, 156.
5:00 PM - V2.8
Crystallographic Reorientation and Nanoparticle Coalescence.
Ralf Theissmann 1 2 , Martin Fendrich 3 , Ruslan Zinetllin 3 , Gerrit Guenther 4 , Gabi Schierning 1 2 , Dietrich Wolf 3 Show Abstract
1 CeNIDE, University of Duisburg-Essen, Duisburg Germany, 2 Faculty of Engineering, University of Duisburg-Essen, Duisburg Germany, 3 Department of Physics, University of Duisburg-Essen, Duisburg Germany, 4 Material Science and Engineering, Darmstadt University of Technology, Darmstadt Germany
Complementary experimental and theoretical results on the coalescence of nanoparticles demonstrate the importance of the crystallographic orientation on the coalescence process. In situ hot-stage transmission electron microscopy studies on self-supporting films consisting of indium tin oxide nanoparticles clearly show rotations of neighboring particles preceding their coalescence. Both rotation and coalescence are observed well below half the melting temperature. The coalescence of two adjacent nanoparticles is simulated by means of a combination of the kinetic Monte Carlo method for atomic diffusion with an integration of the equations of motion for the rigid body degrees of freedom of the two particles. This allows analyzing the reorientation of the two crystal lattices prior to the merging process. Thus, nanoparticle coalescence has theoretically as well as experimentally been shown to be a two-step process: first a reorientation of adjacent nanoparticles, and second their complete or incomplete coalescence depending on the matching of the crystallographic orientations.
5:15 PM - V2.9
Thermal Collapse of Nanopores in Palladium Alloys and Their Hydrides.
Benjamin Jacobs 1 , David Robinson 1 , Markus Ong 1 , Mary Langham 1 , Steven Fares 1 Show Abstract
1 , Sandia National Labs, Livermore , California, United States
Using in situ heating in a TEM, the pore collapse of nanoporous palladium and palladium alloys was viewed in real time. The nanoporous palladium and palladium alloy powers, with diameters on the micrometer-scale and perforated by 3 nm pores, were synthesized in a scalable fashion by reduction of palladium salts in a concentrated aqueous surfactant. In this investigation we show that pores in pure palladium are unstable at 150° C, but when alloyed with rhodium they are stable up to 400° C. In situ and ex situ heating and hydrogen exposure helped us to understand the mechanism of pore stability improvement, which is related to pore density, particle microstructure, and surface purity. EDS and EELS element mapping showed that the alloy particles have a graded core-shell structure with palladium making up the majority of the core and the majority of the second element making up the shell. The core-shell structure remained intact after heating to 400° C. The increased pore stability is obtained with minimal sacrifice of hydrogen storage properties.
5:30 PM - V2.10
The 3-D Pore Structure of Pd Nanoparticles as a Function of Temperature.
Matthew Klein 1 , Benjamin Jacobs 2 , Markus Ong 2 , Stephen Fares 2 , David Robinson 2 , Ilke Arslan 1 Show Abstract
1 Chemical Engineering and Materials Science, University of California, Davis, Davis, California, United States, 2 , Sandia National Laboratories, Livermore, California, United States
With the increasing interest and usage of alternative energy sources, the need for reliable and efficient energy storage methods is likewise increasing. Porous nanoparticles, and in particular Pd, are being investigated for their potential use in catalysis, hydrogen storage, and electrochemistry. For all of these applications, a very high surface area is desirable, with every point in the material ideally being within a few atoms of an interface. This would facilitate attributes such as high double-layer capacitance, higher reaction rates in kinetically limited interfacial reactions, and rapid charging with hydrogen. However, in order to ensure the reliable performance of these materials for such applications, the pore connectivity, diffusion, migration, and collapse must be understood for a variety of thermal treatments. As 2-D images only provide a projection of the structure of the nanoparticles, 3-D imaging is necessary to completely describe the complex pore structure and its age-dependent evolution. Here we investigate porous nanoparticles of Pd using a combination of STEM tomography and in-situ heating experiments. The particles in this study are heated to various temperatures and then cooled, thus “freezing in” the pore structure. This pore structure is then studied with STEM tomography and reconstructed in 3-D. Three sets of samples have been studied at particular temperatures where significant changes are seen: room temperature, 200° C and 600° C. The 3-D tomograms from the room temperature study show that the porosity is very complex, with pores connecting throughout the particles as well as going to the surfaces with a diameter of ~3nm. As the particles are heated to 200° C the pores begin to coalesce into 3-5 nm bubbles, and as temperatures of 400° C and greater are reached they merge to form larger 5-10 nm bubbles. After some time at elevated temperatures, these bubbles finally migrate to the surfaces leaving behind a solid particle of Pd with no porosity.
5:45 PM - V2.11
Exploring Templated Growth and Assembly Through in situ Fluid Cell TEM.
Michael Nielsen 1 , Jonathan R.I. Lee 2 , Yong Han 2 , James De Yoreo 1 Show Abstract
1 , Lawrence Berkeley National Lab, Berkeley, California, United States, 2 , Lawrence Livermore National Lab, Livermore, California, United States
One of the challenges in understanding templated growth and assembly of nanomaterials is probing the early events that determine the nucleation pathway and final mineral structure. Herein we report the development of an in situ transmission electron microscopy (TEM) technique suitable for imaging dynamic processes in liquid environments at high temporal resolution. The capability for in situ measurements is enabled by the combination of a custom designed TEM stage and cell. Significantly, the design of the cell and holder ensures temperature and electrochemical control over the reaction environment, which can be used to initiate processes of interest, such as the onset of crystal nucleation and nanoparticle growth. Moreover, because the working electrode sits in the path of the electron beam, the system allows for direct investigation of templated nucleation. Time-resolved imaging permits the observation of changes in the structural morphology of growing crystals. In conjunction with the solution parameters, these observations allow for determination of kinetic and thermodynamic factors that drive crystal nucleation and growth. Furthermore, dynamic diffraction allows for direct investigations into the pathways of crystal growth, enabling the determination of the underlying mechanisms that take a species from its solvated state to final crystalline form. Herein we report the use of in situ TEM to observe electrochemically driven calcium carbonate nucleation on self-assembled monolayers and surfactant-directed, oriented growth of gold nanoparticles. We present data on the dependence of nucleation rates on driving force, and on the morphological and structural evolution of the incipient nuclei and growing nanoparticles.
Chongmin Wang Pacific Northwest National Laboratory
Rafal E. Dunin-Borkowski Technical University of Denmark
Niels de Jonge Vanderbilt University Medical School
V3: TEM Imaging in Liquid Environment
Wednesday AM, April 07, 2010
Room 3003 (Moscone West)
9:30 AM - **V3.1
Real Time Observations of Electrochemical Processes Using Liquid Cell Transmission Electron Microscopy.
Frances Ross 1 Show Abstract
1 , IBM TJ Watson Research Center, Yorktown Heights, New York, United States
Electrochemical deposition is of key importance in fields as diverse as energy storage, microelectronics and photovoltaics. The nucleation and growth kinetics of the deposited material are particularly critical in determining its eventual morphology. However, electrochemical nucleation and growth are difficult to study using conventional techniques: for example, scanning probe microscopy has good spatial resolution but poor temporal resolution, while analysis of current-time transients provides no spatial information. Here we show that liquid cell TEM, with its unique ability to provide simultaneous temporally and spatially resolved information, can yield insights into the physics of electrochemical crystal growth. We start by discussing a TEM liquid cell design that allows electrochemical processes to be carried out while under observation with the electron beam, simultaneously controlling and recording current and voltage. We have recorded videos and current-time transients during the electrodeposition of copper clusters onto an Au electrode from acidified copper sulphate solution. We find that the process does not follow textbook models of nucleation and diffusion-limited growth, and instead it is necessary to include the effects of surface adsorption and diffusion. The inclusion of additives in the electrolyte modifies the cluster morphology and growth kinetics. We can directly resolve these changes using liquid cell TEM. However, electron beam effects can be important especially for organic additives. Finally, we show the formation and dissolution of dendrites. Their reaction kinetics are relevant to the charging and discharging of secondary batteries, suggesting further exciting opportunities for the use of liquid cell TEM for the quantitative study of electrochemical processes.
10:00 AM - V3.2
Observation of Single Nanocrystal Growth Trajectories in Solution Using Liquid Cell TEM.
Haimei Zheng 1 2 3 , Jungwon Park 3 , Ulrich Dahmen 1 2 , Paul Alivisatos 2 3 Show Abstract
1 National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 2 Materials Sciences Division, Lawrence Berkeley National Lab, Berkeley, California, United States, 3 Department of Chemistry, University of California, Berkeley, Berkeley, California, United States
Understanding of colloidal nanocrystal growth mechanisms is essential for predictable synthesis of nanocrystals with desired physical properties. Although there has been significant progress in nanocrystal synthesis, models of nanocrystal growth are mostly based on studies on the dried particles from post reactions. In situ observation of their dynamic growth process is expected to advance our understanding of nanocrystal growth mechanisms significantly. We have recently developed a self-contained liquid cell operating in a transmission electron microscope (TEM), which allows imaging through a liquid that is confined between two silicon nitride membranes. Sub-nanometer resolution has been achieved. We have applied the liquid cell TEM to real time observation of platinum nanocrystal growth trajectories in solution. Such observations provide insights on the formation of monodisperse colloidal nanocrystals. Here, we show that using the same set up we have observed Bi2O3 hollow nanoparticle formation through nanoscale Kirkendall effect. The dynamic changes of bismuth morphologies and the formation of hollow particles through faster outward diffusion of bismuth than inward diffusion of oxygen have been observed in real time. It is surprising that diffusion of bismuth shows fluid characteristics. The mechanisms of such hollow nanoparticle formation are discussed based on our observations and existing theories.
10:15 AM - V3.3
The Nanoaquarium: A Nanofluidic Platform for in situ Transmission and Scanning Transmission Electron Microscopy.
Joseph Grogan 1 , Haim Bau 1 Show Abstract
1 Mechanical Engineering and Applied Mechanics, University of Pennsylvania, Philadelphia, Pennsylvania, United States
We have developed a nanofluidic platform, “the nanoaquarium,” for in situ transmission electron microscopy of liquid samples. The nanoaquarium consists of a hermetically sealed 100 nm tall liquid-filled chamber sandwiched between two freestanding 50 nm thick silicon nitride membranes. Embedded electrodes are integrated into the device for sensing and actuation. Dynamic processes in the liquid-filled chamber are imaged, in real time, by transmission (TEM) or scanning transmission (STEM) electron microscopy. The fabrication approach applied herein affords a thinner cross-section than in previously reported devices, a distinction that provides for improved resolution. We describe the fabrication method, which is based on direct wafer bonding and allows for high-yield mass production of devices. Silicon wafers were coated with thin layers of silicon nitride and silicon oxide. Gold electrodes were deposited on the silicon nitride layer, beneath the silicon oxide. Conduits and chambers were patterned in the silicon oxide layer. Several physical specifications related to bow/warp, TTV (total thickness variation), surface roughness, and cleanliness of the wafers were satisfied to enable spontaneous room temperature bonding with low temperature, low force, and no electric field. Plasma treating the wafer surfaces allowed bond annealing to be performed at 250°C. Low processing temperatures and use of a dielectric spacer material allowed for direct integration of electrodes onto the chip. The technique can produce liquid chambers as thin as a few nanometers. Preliminary tests of the device consisted of imaging the aggregation of 5 nm gold particles, 50 nm gold particles, and 50 nm fluorescent polystyrene particles suspended in aqueous solutions. Images and videos of the particles were taken with a FEI Quanta 600 FEG Mark II scanning electron microscope with STEM detector. Sealed devices remained filled with solution for several days with no significant loss of volume, indicating excellent hermeticity. The deformation of the membrane window was monitored by filling the device, illuminating the window with monochromatic light, and interpreting the location and quantity of interference rings. Potential applications of the device in nanoscience include, among other things, the study of colloidal crystal formation, aggregation, nanowire growth, electrochemical deposition, and biological processes.This work was supported, in part, by the NSF-NIRT (CBET 0609062) and the Nanotechnology Institute, Ben Franklin Technology Partners of Southeastern Pennsylvania.
10:30 AM - V3.4
Developing in-situ TEM Capabilities for Li-ion Battery Research.
Raymond Unocic 1 , Karren More 1 , Nancy Dudney 1 Show Abstract
1 Materials Science and Technology, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
In order to advance Li-ion battery technology a science based understanding of how interfaces control the physical and chemical transport of Li+ ions during rapid electrochemical charge/discharge cycling is essential. The interface that is most often studied is the so-called solid electrolyte interphase (SEI), which develops at the electrode/electrolyte interface as a result of electrochemical reduction reactions. With respect to electrical energy storage performance and efficiency, the SEI serves two major functions: 1) the SEI regulates the degree of Li+ ion intercalation into the electrodes during electrochemical charge/discharge cycling and 2) the SEI acts to protect the anode and cathode materials from degradation. Due to the dynamically-evolving nature of this nm-scaled interface, it has proven difficult to design experiments that will reveal details regarding the fundamental mechanisms governing SEI nucleation and growth as a function of electrochemical cycling. Therefore, the scientific driving force for this research initiative is to develop and implement a unique method for conducting in-situ electrochemical experiments in a high-resolution transmission electron microscope (TEM) such that SEI formation can be directly observed (imaged) to understand the structural and chemical changes at high temporal and spatial resolution, elucidate Li+ ion intercalation mechanisms, and to monitor electrode degradation mechanisms. The emphasis of this talk will be on the development and application of a unique in-situ TEM electrochemical cell interfaced with a DC potentiostat for charge-discharge cycling, to correlate the electrochemical response and SEI formation simultaneously with the in-situ microscopy imaging and analysis capabilities. Research supported by (1) the Office of Vehicle Technologies, Office of Energy Efficiency and Renewable Energy and (2) ORNL’s SHaRE User Facility, which is sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences.
10:45 AM - V3.5
Direct Observation of Solid Electrolyte Interface Layer Formation in Lithium Ion Battery Using in-situ TEM.
Chongmin Wang 1 , Wu Xu 1 , Lax Saraf 1 , B. Arey 1 , Jun Liu 1 , Daiwon Choi 1 , Z. Gary Yang 1 , Jiguang Zhang 1 , S. Thevuthasan 1 , Donald R. Baer 1 , N. Salmon 2 Show Abstract
1 , Pacific Northwest National Laboratory, Richland, Washington, United States, 2 , Hummingbird Scientific , Lacey, Washington, United States
The gradual capacity fading accompanying each cyclic charge and discharge of a battery is one of the greatest challenges facing Li-ion battery development. Capacity fading is generally perceived to be a direct consequence of the irreversible microstructural evolutions of the active materials in a battery. Formation of solid electrolyte interface (SEI) layer and its thickening on the active electrode materials has been believed to be a key process for irreversible microstructural evolution. Despite extensive research, an understanding of the mechanisms associated with the formation of the SEI layer and its response to charging and discharging processes remain elusive. This is mostly due to the complexity of the battery materials system and the difficulties associated with directly observing the structural evolution of the active materials during battery operation. Here we report the direct observation of the formation of an SEI layer on a single nanowire anode using in situ transmission electron microscopy. This was made possible by the development of a miniature prototype Li-ion battery using a single SnO2 nanowire as the anode, an air stable salt: lithium bis(trifluoromethansulfonyl) imide (LiTFSI) in a hydrophobic ionic liquid: 1-butyl-1-methylpyrrolidium TFSI (P14TFSI) as the electrolyte, and LiCoO2 as the cathode. This micro-battery was integrated on a biasing holder on a transmission electron microscope (TEM). Due to the low vapor pressure of the ionic liquid, the battery could be directly loaded into the high vacuum column of the TEM for in situ observation during battery charging and discharging. During initial charging, the electrolyte was found to decompose and subsequently be electrodeposited on the anode, leading to the formation of a coating layer on the anode. This coating layer was enriched with Li and it apparently retarded the Li intercalation of SnO2. This in situ TEM observation provided direct evidence that accounts for the observed low capacity and fast fading of the Li battery when LiTFSI-P14TFSI is used as the electrolyte.
V4: In-Situ Nanoscale Transport
Wednesday PM, April 07, 2010
Room 3003 (Moscone West)
11:30 AM - **V4.1
In-situ TEM Electrical Characterization for Nano Devices.
S. Park 1 , Dongkyu Cha 1 , J. Kim 1 , S. Ahn 2 , Oleg Lourie 3 , Moon Kim 1 Show Abstract
1 Department of Materials Science and Engineering, University of Texas at Dallas, Dallas, Texas, United States, 2 , Samsung Electronics Co., Hwasung City Korea (the Republic of), 3 , Nanofactory Instruments AB, Goteborg Sweden
The scaling down of solid-state devices over the past 40 years has continuously driven improvement in productivity, performance, and power efficiency. Structural analysis of the nano size device can be performed routinely by various microscopy techniques. However, properties of nano devices have been measured at the package level and not at the level of individual components. Although several tools and techniques have been recently developed to measure the intrinsic properties of nano structures, the measurements mainly focused on one dimensional nano structures such as nanotubes, nanorods, and nanoparticles. Precisely controlled probing capability in transmission electron microscopy (TEM) allows for the characterization of electrical properties at specific positions in devices. Here we demonstrate how the microstructure of phase change memory with 90 nm technology evolves under the influence of electrical programming pulses. Dopants mapping in a single working transistor with a gate length of 200 nm is also determined by in-situ TEM electrical measurement.To observe phase evolution in phase change memory, a test device with N-doped Ge2Sb2Te5 and a 50 nm diameter thermal heater were fabricated. The TEM samples were prepared using the lift out technique in focused ion beam (FIB) in order to preserve the whole device structure as the memory material, a bottom contact as a heater, and top/bottom metal line. The samples were placed on the TEM-STM holder (Nanofactory Instrument AB) inside a JEOL 2100F TEM. STM probe was driven in to an individual memory cell. The memory-switching behavior between crystallization and amorphous states was successfully observed to mimic the behaviors of the macroscopic electrical signals. Crystallization kinetics, dependant on quenching speed, has been clearly resolved, implying that this method can be used to comprehend the fundamentals of phase-changing phenomena in order to solve the scaling and reliability issues of the future.A single-cell Si transistor sample was prepared by the FIB for in-situ STM-TEM analysis. Contact between STM probe tip and sample was constantly confirmed and maintained using the bright field image of the bend contour, indicating the level of specimen bending due to a pressing force. Multiple sets of current-voltage (I-V) curves were measured using a dc power supply in the range of ±15V. The doping type and area could be identified by the measured electrical behavior of each point on the sample. Mapping results revealed a presence of a dopant spreading at the junction interface.
12:00 PM - V4.2
Fast FIB-milled Electron-transparent Microchips for in situ TEM Investigations.
Anders Lei 1 , Dirch Petersen 1 , Christian Kallesoe 1 , A. Nicole MacDonald 2 , Oezlem Sardan Sukas 1 , Timothy Booth 1 , Peter Boggild 1 , Yvonne Gyrsting 3 Show Abstract
1 DTU Nanotech - Micro and Nanotechnology, Technical University of Denmark, Kgs. Lyngby Denmark, 2 DTU CEN - Center for Electron Nanoscopy, Technical University of Denmark, Kgs. Lyngby Denmark, 3 DTU Danchip, Technical University of Denmark, Kgs. Lyngby Denmark
In this work we present a fast approach to 50 nm resolution structures defined in a generic TEM-chip template in few minutes. While creating complex electrical and NEMS circuits for a specific insitu TEM experiment can be a cumbersome process, microchips with 100 nm thin flakes of single crystalline silicon and silicon nitride membrane templates suspended from the edge, can be patterned in less than 15 minutes using focused ion beam milling. This approach allows a FIB-SEM user to create free-form NEMS structures for nanoresonators, actuators, heaters, resistors or other structures for insitu TEM devices or materials research using the same template. We demonstrate insitu environmental TEM analysis of Au film migration on silicon during resistive heating of a microbridge, and show how the conductance of focused ion beam milled single crystalline silicon nanowires can be adjusted insitu over two decades using a high current to recrystallise the structure.
12:15 PM - V4.3
TEM Observations of Microstructural Modifications in Pt/TiO2/Pt Nano-Structures During (in-situ) and After Electroforming and Resistance Switching.
Ramanathaswamy Pandian 1 , Herbert Schroeder 1 Show Abstract
1 IFF, Forschungszentrum Juelich GmbH, Juelich Germany
Transition metal oxide (TMO) thin films stacked between electrodes show unipolar or bipolar resistance switching. Therefore, such stacks have been extensively investigated for the last few decades due to their potential for future non-volatile memory (NVM) devices. Titaniumdioxide, TiO2, is one of the most promising candidates for this purpose with a large resistance contrast between the high and low resistance states and low power consumption. Despite the clear observation of the resistance hysteresis and promising technical qualities for the device applications, the factors originating the resistance switching under the electric field (voltage or current) remain elusive. The microscopic nature of resistance switching and charge transport in such devices is still under debate. The hysteretic behavior of the resistance is expected to have connections with some microstructural changes or re-arrangements that modulates the electronic current. Since transmission electron microscopy (TEM) is one of the tools able to detect the interrelations between changes of the microstructure and resistance switching, we developed a TEM holder for electrically biasing an metal/insulator/metal (MIM) thin film stack and performed both in-situ and ex-situ TEM studies on the electroforming and resistance switching process. We produced appropriate MIM capacitor-like structures with sputtered (30nm) TiO2 films sandwiched between (20-60 nm thick) platinum electrodes with different geometries including the so-called nano-cross-bars which are essential for the future ultra-large scale-integrated memory chips because of its simplicity. Selected area electron diffractions patterns (SAED) and the related TEM bright-field and dark-field images of the observed microstructural variations during and after the electroforming and resistance switching processes will be reported. The SAED patterns indicate that there are variations in the degree of crystallinity (i.e. orientation changes and appearance of new nano-crystalline phases) upon the forming and consecutive switching cycles. Since the effect of the electron beam on the specimen is kept minimum, these microstructural changes are attributed to the forming and switching processes.
12:30 PM - V4.4
In-situ Observations of Dynamical Nanoparticle Behavior on a Monolayer Graphene Substrate Observed in a Cs-corrected TEM.
Jinho An 1 , Edgar Voelkl 2 , Xuesong Li 1 , Jiwon Suk 1 , Rodney Ruoff 1 Show Abstract
1 Department of Mechanical Engineering and the Texas Materials Institute, The University of Texas at Austin, Austin, Texas, United States, 2 , FEI, Hillsboro, Oregon, United States
Graphene, a single atomic layer of graphite has drawn significant attention for its possible energy and electronic applications, among other reasons. As of recently, graphene has also drawn attention to its possible application as a TEM substrate: Graphene provides a low background signal, and is mechanically robust and non-reactive. In this study, dynamical in-situ movements of nanoparticles on graphene were observed at 80keV on a FEI Titan 60-300kV electron microscope with a high brightness field emitter, monochromator and Cs corrector with the electron beam as the only external stimulus. The observed particles underwent rapid dissociation, diffusion and new particle formation during TEM observations. Significant spontaneous strain during transformations was observed as well. In all cases the particulates dissociated when on pristine graphene areas and then reformed on contaminated areas under the electron beam. This might be due to the lack of a significant interaction between the nanoparticle and graphene which allows the nanoparticles to dissociate, and migrate towards the ‘contaminated’ areas (areas with adsorbates), and bond with the adsorbates thus ultimately disallowing further migration behavior. The graphene substrate provides excellent imaging quality for such events. In general, particles tend to form bulk shapes over flat areas to minimize their surface energy. In this case, however, square holes readily formed in the middle of the particles during the dynamic process and this is not yet understood. An additional benefit of using a graphene substrate is its use as a calibration tool. When studying nanoparticles in the TEM, concurrent calibration is generally difficult unless a point of reference is included in the image. Graphene, with its relatively small C-C bond length of 0.142nm provides an excellent reference and allows accurate determination of the interplanar spacings of nanoparticles. Even at 200keV (and in a non-Cs corrected TEM), hexagonal spots can be detected in the FFT, even though the structure provides very little contrast and may not be readily identifiable in the actual image. To our surprise, we found graphene to be relatively stable at 200keV, where only occasional nanosized hole formation was observed over prolonged observations. After extended periods of observation, holes do occasionally form during observations, though not very frequently. These results show us that graphene can serve as a low background signal substrate in a TEM, and the physical properties of graphene as a support might also foster unique physical characteristics of nanoparticles that can be observed and probed, in-situ, in a TEM.
12:45 PM - V4.5
Restructuring of Pt Catalysts Driven by High Coverage Reactant Molecules.
Feng Tao 1 2 , Miquel Salmeron 2 , Gabor Somorjai 1 2 Show Abstract
1 Department of Chemistry, University of California at Berkeley, Berkeley, California, United States, 2 Materials Science Division, Lawrence Berkeley National Lab, Berkeley, California, United States
We have found that stepped Pt catalysts exhibit a pressure-dependent restructuring on surface and form nanoclusters at a pressure around 0.1 Torr or higher pressure of CO. By using high pressure STM, we clearly identified the structural evolution at different reaction conditions. Ambient pressure XPS provides evolution of electronic structure of surface Pt atoms and the adsorbed CO molecules, consistent with the evolution of geometric structures. The measured pressure-dependent coverage of reactant molecules rationalizes the formation of nanoclusters at high pressure. The experimental observation of restructuring of the stepped Pt catalysts was supported by DFT energy calculations.
V5: Poster Session: In-Situ TEM
Thursday AM, April 08, 2010
Salon Level (Marriott)
9:00 PM - V5.1
Direct Observations of Relaxation of Si/SiGe/Si on Insulator.
Tongda Ma 1 , Hailing Tu 1 Show Abstract
1 , General Research Institute for Nonferrous Metals, Beijing China
The past several years have witnessed rapid growth in the study of strained silicon on insulator due to its potential ability to improve the performance of very large scale integrated circuits. To my knowledge, in situ observations have not been performed on relaxation of Si/SiGe/Si on insulator using transmission electron microscope (TEM). In this work, both thin Si capping layer and SiGe layer are deposited on bonded and back etched silicon on insulator (SOI) by ultra high vacuum chemical vapor deposition (UHVCVD). Then, the epitaxial wafer is in-situ thermally treated in the growth chamber at 750 oC for 30 minutes. TEM, triple-axis x-ray diffractometer (TAD), and secondary ion mass spectrometer (SIMS) are employed to investigate defects, strain, and interdiffusion within Si/SiGe/Si on insulator. The results show that stacking faults and misfit dislocation dipoles exist in the strained silicon heterostructure. Strain in the Si capping layer differs from that in the SOI top Si layer. And interdiffusion proves to be one of the major ways to release strain. In order to further clarify the relaxation mechanism, the cross-sectional specimen of Si/SiGe/Si on insulator is heated from room temperature (R.T.) up to 840 oC in high voltage transmission electron microscope (HVEM). Higher than the temperature of 760 oC, some of the misfit dislocations at the lower interface of the SiGe layer begin to extend downwards. As heating is continuing, some other misfit dislocations move upwards slowly. Meanwhile, the lower interface of the SiGe layer takes the lead in roughening in comparison with the upper interface. The misfit dislocations are also introduced into the upper interface once it turns rough enough. The strain relaxation is obviously related to strain transfer, dislocation motion and interdiffusion according to comprehensive analyses.
9:00 PM - V5.10
Membrane-based Nano-discovery Platform for Nano-materials and Nano-devices.
Chi Won Ahn 1 Show Abstract
1 , NNFC, Daejon Korea (the Republic of)
The platform technology for the discovery of nano-scale phenomenon is developed on silicon based microchips by micro-electro-mechanical system (MEMS) technique. The platform is consisted of ultrathin transparent membrane that is a thin film of amorphous silicon nitride. The membrane has suitable mechanical, thermal, electrical, and optical properties for direct integration and observation of nano-scale materials and nano-devices in a nano-scale. Various applications of the nano-discovery platform on the nano-materials and nano-devices have been applied on percolation of metallic nano-clusters , fabrication and investigation of nano-sized pores, in-situ observation of grain boundaries migration of ZnO thin film, Si1-xGex nanowire field effect transistor(FET) , nano-structure of metal cluster in light emitting devices, and nano-wire FET biosensor.
9:00 PM - V5.2
In situ Molecular Spectroscopy and Molecular Dynamics Simulations for the Study of Boundary Lubricating Films.
Takakazu Suzuki 1 Show Abstract
1 , AIST, Tsukuba Japan
In situ techniques that enable observation of contacting surfaces are ideal, and have the potential to confirm or refute commonly accepted lubrication models, as well as to allow close comparison with molecular simulations of lubrication processes. Thin films on solid surfaces can be observed if a transparent solid is used in high-sensitivity reflection infrared spectroscopy. The absorption bands measured in the present study were the strongest characteristic symmetric and asymmetric stretching vibrations of the methylene group, which appear in the range of 2800–3000 cm-1. The pressure was calibrated with a force sensor and ranged from 0.2 to 2 MPa. The transparent solids were composed of KBr and LiF, and the incident angle of radiation was 60°. The substrate was iron, copper, stainless steel, or gold. The temperature of the substrates, which ranged from room temperature to 400 K, was observed with an Alumel-Chromel thermocouple that was attached to a metal plate or glass. The thickness of the films ranged from 20 to 100 nm, as determined from the absorption intensity of the films in the isotropic liquid phase.The absorption intensity increased rapidly with temperature when the polarization of the beam was parallel to the plane of incidence, but decreased gradually when the polarization was normal to the plane. The change in direction of the dipole moment of the asymmetric stretching vibration of the methylene group was estimated to be nearly parallel to the surface. Therefore, the methylene groups of n-octadecane were oriented nearly parallel to the metal surface. The absorption intensity decreased with temperature when the polarization of the beam was parallel and increased with temperature when the polarization of the beam was perpendicular. These results signify the restoration of molecular orientation in the film. At room temperature, the addition of C18 fatty acid increased the intensity of the methylene group stretching bands when the polarization of the beam was perpendicular and decreased the intensity of the methylene group stretching bands when the polarization of the beam was parallel. These results show that the addition of C18 fatty acid increases the anisotropic molecular orientation of straight-chain hydrocarbons. Chain-length matching in the hydrocarbon lubricant film that contained C18 fatty acid resulted in higher molecular orientation than chain-length mismatching in hydrocarbon lubricant films that contained fatty acids with straight-chain lengths ranging from C10 to C16. In the case of the gold plate, no effect on the orientation of the hydrocarbon molecules was observed. The addition of bulky isostearic acid resulted in a nearly isotropic orientation, regardless of temperature.Molecular dynamics simulations were conducted to verify the reproducibility of the above-mentioned molecular behavior, in addition to the behavior under more severe conditions.
9:00 PM - V5.3
Silicon Doping Effects on the Optical Properties of InAlSb Epilayers Grown on GaAs Substrates.
Hee Yeon Kim 1 , Mee-Yi Ryu 1 , J. Lim 2 , S. Shin 2 , S. Kim 2 , J. Song 2 Show Abstract
1 Department of Physics, Kangwon National University, Kangwon-do Korea (the Republic of), 2 Nano-Science Research Division, Korea Institute of Science and Technology, Seoul Korea (the Republic of)
InSb-based materials have attracted much attention for application to high speed, low power electronic devices because of their high electron mobility and low effective mass. In recent years, considerable progress has been made in high electron mobility transistors (HEMTs), resonant tunneling diodes (RTDs), and heterojunction bipolar transistors (HBTs) in the antimonide-arsenide materials system. Most of the recent advances in Sb-based HEMTs have involved heterostructures grown by molecular beam epitaxy (MBE). InSb has a room-temperature electron mobility of 78,000 cm2/V s and its saturation velocity is reported to be greater than 5x107 cm/s. HEMT quantum wells can be formed with InSb wells and InAlSb barriers. Higher electron mobility and sheet carrier density are typically desirable for HEMT applications. Silicon is the most common n-type dopant in III-V materials. However, it is amphoteric in the III-V’s, producing n-type GaAs, InAs, AlAs, and InSb, but p-type GaSb and AlSb. In this study, we investigated the optical properties of Si-doped InAlSb epilayers grown on GaAs substrates by using photoluminescence (PL) and time-resolved PL measurements. The 3.7-μm-thick In0.64Al0.36Sb layers were grown on GaAs substrates by MBE. The In0.64Al0.36Sb layers were doped with Si concentrations of 5x1016, 1x1017, 5x1017, 1x1018, and 5x1018 cm3 in GaAs. However, the measured Si concentrations in In0.64Al0.36Sb were 1x1015 (p-type), 4x1014 (p-type), 8x1015 (n-type), 4x1016 (n-type) and 4.5x1016 cm3 (n-type), respectively. The PL intensity is increased with increasing Si doping. The PL emission peak is strongly dependent on the Si doping concentrations. As the Si doping increases from 5x1016 to 5x1017 cm3, the PL peak of the In0.64Al0.36Sb shifts to high energy side from 1314 to 1232 nm. For the higher Si doping of 1x1018 and 5x1018 cm3 the PL peaks are located at 1272 and 1288 nm, respectively. The PL decay time is also dependent on the Si doping. The decay times for the p-type In0.64Al0.36Sb samples are faster than those for the n-type samples. The decay times measured as a function of the emission wavelength also shows different behavior with Si doing concentrations. These results indicate that the luminescence properties and carrier dynamics of the In0.64Al0.36Sb are strongly dependent on the Si doping.
9:00 PM - V5.4
Microscopic and Spectroscopic Changes in Soot Produced from Cellulose Burns: Implications for EC/OC Thermo-optical Measurements.
Shruti Prakash 1 , Ryan Moffet 1 , Mary Gilles 1 , Tom Kirchstetter 1 Show Abstract
1 , Lawrence Berkeley National Laboratory, Berkeley, California, United States
The use of biomass fuels for energy has achieved a wide range of interest due to two reasons: 1) they are renewable source of energy and 2) they are carbon neutral (i.e. the amount of CO2¬ generated during their combustion is equal to the amount consumed during their growth). However, it is necessary to understand the complete environmental impact of biomass burning/combustion to predict their effect on climate.Biomass crop development presents a high priority challenge, e.g. to make harvesting sugarcane easier, prior to harvest a pre-burn removes dead leaf litter. Smoke emitted from these pre-burns leads to increased hospital visits for local residents [Cancado 2006]. Furthermore, the effect on climate of the soot and other particulate matter emitted is extremely uncertain [IPCC 2007]. While soot warms the earth by directly absorbing solar radiation, recent studies indicate emission of other types of particulates such as salts, organic carbon, and mixed particulates during biomass burns In this study we have investigated the effect of charring on particulates from burning cellulose and have characterized them by a range of microscopic and spectroscopic techniques. The illustrated poster will present the results from ex-situ experiments. Furthermore,analyses of the particle samples using several analytical techniques will be presented: (1) STXM/NEXAFS( for speciation of the carbonaceous content, C/O ratios, and images of particle morphology), (2) CCSEM/EDX (for imaging of individual particles and elemental measurements) and (3) FTIR analysis( for further confirmation of chemical bonding changes in the samples). STXM/NEXAFS analyses of the samples were conducted at the Advanced Light Source (ALS) synchrotron facility located at the Lawrence Berkeley National Laboratory. Cancado, J. E. D., P. H. N. Saldiva, L. A. A. Pereira, L. B. Lara, P. Artaxo, L. A. Martinelli, M. A.Arbex, A. Zanobetti, A. L. Barga, Environmental Health Perspectives, 51, 1141 (2006)
9:00 PM - V5.5
Three-dimensional Structure of Twinned and Zigzagged One-dimensional Nanostructures Using Electron Tomography.
Han Sung Kim 1 2 , Yoon Myung 1 , Dong Myung Jang 1 , Kyung Hwan Ji 1 , Chan Soo Jung 1 , Jeunghee Park 1 , Jae-pyoung Ahn 2 Show Abstract
1 , Korea University Sejong Campus, Chungcheongnam-do Korea (the Republic of), 2 , Korea Institute of Science and Technology, Seoul Korea (the Republic of)
Electron tomography, which is a method to reconstruct 3-dimensional (3D) morphologies from a series of 2D images or projections, has been successfully applied to analyze the morphology of various nanostructures. Herein, electron tomography and high-resolution transmission electron microscopy were used to characterize the unique 3-dimensional structures of twinned Zn3P2, InAs nanowires, TiO2 nanobelts, and zigzagged CdO nanowires, synthesized by vapor transport method. Zn3P2 belongs to a unique tetragonal system, where its lattice constant c/a ratio (1.414) leads to have a pseudo cubic symmetry. The Zn3P2 nanowires adopt consequently a unique superlattice structure that consists of twinned octahedral segments having alternating orientation, along the axial  direction of pseudo cubic unit cell. Each octahedral segment has apices, indexed as six equivalent <112> directions. In each 60 degrees turn, the straight and zigzagged morphology appears repeatedly, with a zone axis of  and , respectively. The superlattice structure of the InAs nanowires has virtually the same as that of the twinned Zn3P2 nanowires. The rutile TiO2 nanobelts exhibit a remarkable superlattice structure that consist of twinned octahedral slices whose apices are indexed by the <011>/<001> directions with the axial  direction of tetragonal unit cell. In each 90 degrees turn, the straight morphology appears repeatedly, with a zone axis of  or , following the twisted forms at the  zone axis. In addition, we analyzed the 3D structure of the zigzagged CdO nanowires, showing the rhombohedral segments, whose six apices are matched to the <110> direction, linked along the  axial direction.
9:00 PM - V5.6
Investigation of the Structure of a New Phase in the Al-Cu-Re System Using Electron Crystallography Methods.
Louisa Meshi 1 , Vladimir Ezersky 1 , Benjamin Grushko 2 Show Abstract
1 Department of Materials Engineering, Ben-Gurion University of the Negev, Beer Sheva Israel, 2 Institut für Festkörperforschung, Forschungszentrum, Jülich Germany
Since 1959, following Feynman historic talk "Plenty of Room at the Bottom", nanoscience is developing rapidly. Particles of interest are getting smaller and standard methods for structure determination, such as X-ray diffraction technique, cannot be used for solving the atomic structure. Electron crystallography is emerging as a powerful (and sometimes the only) tool for addressing this problem. The first step of crystal structure determination by electron crystallography consists of analysis of electron diffraction patterns (conventional selected area and convergent beam patterns including high order Laue zones) for deducing the unit cell parameters of the unknown structure and describing its symmetry by a proper space group . The next step regards developing and verification of the structural model. One of the factors, that limit the use of electron crystallography for structure determination, is the dynamical nature of electron diffraction intensities. Newly developed method of Precession Electron Diffraction (PED)[2,3,4] can be considered as promising technique for reducing these dynamical effects. Although in precession experiments the multi-beam effect still remains, the diffraction intensities are averaged due to integration through all directions within Bragg reflection width and, as a result, have more kinematical character. This and other original features of PED technique greatly facilitate electron crystallography as method for structure determination.The present study was undertaken with the purpose to characterize the structure of the unknown phase found in the Al-Cu-Re system and to determine its unit cell and symmetry. Structure determination was performed using electron crystallography methods, in particular, Precession Electron Diffraction (PED) and Convergent Beam Electron Diffraction (CBED) techniques. The structure was described by hexagonal crystal lattice with the unit cell parameters: a=11.029(6) Å and c=12.746(1) Å. For the determination of the space group, describing the symmetry of this phase, analysis of powder X-ray diffraction pattern and micro-beam electron diffraction patterns were performed. However, the only technique that provided conclusive answer was CBED technique. The symmetry of the structure of the new Al65Cu25Re10 compound was described by the P63 (173) (non-centrosymmetric) space group. References:1. J.P. Morniroli, J.W. Steeds, Ultramicroscopy 45:219, 1992. 2. R. Vincent, P.A. Midgley, Ultramicroscopy 53:271, 1994. 3. P. Oleynikov, S. Hovmoller, X.D. Zou Ultramicroscopy 107:523, 2007.4. A.P. Dudka, A.S. Avilov, S. Nicolopoulos, Ultramicroscopy 107:474, 2007.
9:00 PM - V5.7
Study of Residual Stress Relief by Cryogenic Treatment in the Al 6061.
Kijung Park 1 , Bin Hwang 1 , Na-Hyun Kwon 1 , Young-Rae Cho 1 Show Abstract
1 School of Materials Science and Engineering, Pusan National University, College of Engineering, Pusan, Geumjeong-Gu, Korea (the Republic of)
Al alloys have long been of interest to the military community due to their modest specific strength, ease of manufacture, and low cost. Processes such as heat treatment, deformation processes, machining, and shape transformation may induce residual stresses in Al alloys. This residual stresses in Al alloys may generate distortion which causes some serious problems. The cryogenic process, a thermal process in which an object is cooled to -196°C with liquid nitrogen (LN2), has been touted as a method to relieve residual stresses in Al alloys. In this study, cryogenic treatment was applied to relieve the residual stresses, tensile strength, hardness, and precipitates of the Al 6061. The tested samples have the dimension of 10×10×10 mm, which contained 97.42 Al, 0.23 Cu, 1.08 Mg, 0.74 Si, 0.17 Fe, 0.08 Mn and 0.04 Zn (wt. %). In an argon atmosphere, the samples were heated at 529°C for a period of 30 minutes and quenched immediately in LN2. Then, the samples were put at room temperature for a period of 24 hours and heated at 157, 167, 177°C for a period of 7, 8, 9 hours, respectively. The heat treated samples were sectioned and prepared for metallographic examination. The samples were etched in Kellers or NaOH. Residual stresses were measured by XRD analysis and the precipitates were observed by in situ TEM analysis. The results showed that the cryogenic treatment significantly reduced the residual stresses by 45% and enhanced the hardness by 9% in the Al 6061. This study concludes that the cryogenic treatment could relieve the shape distortion in the Al 6061, which has found many applications in military weapons.
9:00 PM - V5.9
In-situ Nanoindentation Study of Ceramic Nanocomposites.
Joon Hwan Lee 1 , Ickchan Kim 1 , Dustin M. Hulbert 2 , Dongtao Jiang 2 , Amiya K. Mukherjee 2 , Xinghang Zhang 3 , Haiyan Wang 1 Show Abstract
1 Materials Science and Engineering Program, Electrical and Computer Engineering, Texas A&M University, College station, Texas, United States, 2 Chemical Engineering and Materials Science, University of California, Davis, California, United States, 3 Mechanical Engineering, Texas A&M University, College station, Texas, United States
At room temperature, in situ nanoindentation experiments in a transmission electron microscope were performed on fully dense ZrO2 : Al2O3 : MgAl2O4 nanocrystalline ceramic composites (AZM) processed by spark plasma sintering (SPS). Detailed TEM and EDX mapping reveal a bi-model grain size distribution, where the large transparent ones are Al2O3 and MgAl2O4 grains (~500nm-1μm) and the small black ones are the ZrO2 grains (~100-300nm). The deformation behavior of the AZM nanocomposites was studied in detail and compared with conventional nanoindentation. The AZM nanocomposites undergo the deformation mainly through the grain rotation and grain boundary sliding of small grains. Our study suggests that a certain amount of plastic and elastic deformation can occur in ceramic nanocomposites at room temperature.