Liane G. Benning, University of Leeds
Arda Genc, FEI Company
Dongsheng Li, Pacific Northwest National Laboratory
Jeffrey D. Rimer, University of Houston
Symposium Support Agilent Technologies, Inc.
OO2: In Situ Characterization of Nucleation, Growth and Transformation II
Monday PM, December 01, 2014
Hynes, Level 1, Room 101
2:30 AM - *OO2.01
Solution-Mediated Transformations between Uric Acid Phases
Jennifer Swift 1 Janeth Presores 1
1Georgetown University Washington USAShow Abstract
Uric aicd, a natural product of purine metabolism, can precipitate under physiologic conditions in a variety of anhydrous, hydrated and salt pforms leading to symptoms associated with kidney stones and gout. The evolution of these physiologic deposits is a multi-step process that operates on several different length scales. This talk will describe our efforts to address some of the key steps in the solution-mediated phase transformation of metastable uric acid dihydrate to anhydrous uric acid using a combination of X-ray diffraction, thermal analysis and optical microscopy techniques. The kinetics suggest that the interconversions between uric acid forms is very sensitive to the initial method under which the metastable phase was prepared as well as the composition of the solution in which it transforms.
3:00 AM - OO2.02
ZnO@SiO2 Core-Shell to Hollow Zn2SiO4: An In-Situ TEM Study of Hollow 1-D Nanostructure Formation
Shalini Tripathi 1 Ravishankar N 1
1IISc Bangalore IndiaShow Abstract
Zinc silicate (Zn2SiO4) has gained significant interest as a multifunctional material with several applications. In this study, we demonstrate a method to synthesize Zn2SiO4 nanotubes by exploiting Kirkendall effect at nanoscale. The reaction proceeds through interdiffusion of Zn2+ from ZnO nanorods into the chemically-synthesized Stöber-SiO2shy; shell. Using in-situ heating in the TEM, we have monitored the nucleation and coalescence of the Kirkendall voids in the ongoing process. While heating the samples ex-situ in air leads to microstructural evolution that is similar to the in-situ experiments, there is a significant difference in the samples heated under reducing conditions. Heating the ZnO@SiO2 nanostructures in a reducing atmosphere (95% Ar + 5% H2) leads to the formation of amorphous silica nanotubes owing to etching of ZnO in H2 atmosphere. Moreover, eletron-beam was also found to affect the course of the reaction, by sintering the tubes at higher temperature, thereby damaging the desired tubular morphology. Thus, this ambience-dependent thorough understanding of the relevant diffusion processes for the ZnO-SiO2 diffusion couple at nanoscale presents a general conceptual platform to fabricate different multifunctional one-dimensional hollow nanostructures. These two materials, namely the Zn2SiO4 and SiO2 nanotubes can respectively be used as cathode and anode materials for Li-ion battery.
3:15 AM - OO2.03
High Speed Atomic Force Microscopy Growth Monitoring during Pulsed Laser Deposition
Werner Wessels 1 Tjeerd Bollmann 1 Alexei Ofitserov 2 Gertjan van Baarle 2 Gertjan Koster 1 Guus Rijnders 1
1Mesa+ Institute for nanotechnology University of Twente Enschede Netherlands2Leiden Probe Microscopy Leiden NetherlandsShow Abstract
Pulsed Laser Deposition (PLD) is a physical vapor deposition technique to fabricate a wide range of high quality thin film materials for the next generation devices such as solar-cells, MEMS and OLED&’s. This research is focused on in situ growth front monitoring between subsequent deposition pulses using an high speed Atomic Force Microscope (AFM). A scientific instrument is under development, in which a fast AFM (<10s /frame, 512*512 pixels) is combined with a PLD system, with special attention to a fast and accurate transfer and approach (<1s) mechanism1. Using this instrument, we intend to repeatedly monitor the developing surface during growth (repositioning repeatability +/-60nm) with AFM at typical deposition conditions for complex oxides, nitrides and metals. In the case of PLD, the deposition and growth are separated in time, and therefore the above instrument aims to monitor the decay in adatom density after each laser pulse.
The described technique is an improvement of an earlier instrument, which demonstrated that it is feasible to combine in situ AFM with PLD in above manner2.
This scientific instrument will help to improve the fundamental understanding of the kinetic growth during PLD. In addition, the approach to monitor the same surface area using AFM shortly after a chemical, biological or physical modification on a separated position has the potential to become widely accepted. Here, we present the design and test results of the current setup and our future plans to improve the scan rate and resolution further. This work is supported by NanoNext NL and in strong collaboration with Leiden Probe Microscopy (LPM)
1 W.A. Wessels, J.J. Broekmaat, R.J.L. Beerends, G. Koster & G. Rijnders, Fast and gentle side approach for atomic force microscopy. Rev. Sci. Instru. 84, 123704 (2013)
2 J.J. Broekmaat, In-situ growth monitoring with Scanning Force Microscopy during Pulsed Laser Deposition, PhD Thesis ISBN 978-90-365-2655-5, University of Twente, 2008
3:30 AM - OO2.04
In Situ TEM Studies on Transformations from and to Quasicrystals in Mg-Zn-Y Alloys
Zhiqing Yang 1 Jianfang Liu 1 Hengqiang Ye 1
1Institute of Metal Research, Chinese Academy of Science Shenyang ChinaShow Abstract
Since the discovery of quasicrystals in an Al-Mn alloy, quasiperiodic ordering states have been found in hundreds of intermetallic alloys, soft materials, oxide film, and even dense stacking of hard tetrahedra. Extensive studies have provided explicit knowledge for understanding and modeling the atomic arrangements in intermetallic quasicrystals. Mackay, Bergman or Cd-Yb icosahedral clusters were believed to be building blocks of three-dimensional (3D) icosahedral quasicrystals (IQC). Computer simulations showed that a dodecagonal quasicrystal seed nucleus grew through assimilation of icosahedral clusters in a supercooled liquid. However, the fundamental questions concerning why quasicrystals form, and how they nucleate and grow, are still unclear experimentally on the atomic scale, especially for 3D intermetallic IQCs.
Intermetallic quasicrystals are usually formed in undercooled liquids or frozen supercooled liquids (i.e. metallic glasses) both containing icosahedral atomic clusters that formed in liquids at higher temperature. A hexagonal phase without large icosahedral clusters in a Zn65Mg25Y10 alloy transformed into IQC upon heating at 873 K which is around the melting point of the alloy, consistent with the law of entropy-optimized arrangement of atoms benefiting the stability of quasicrystals at high temperatures. However, it remains a challenge to realize solid-state crystal-to-quasicrystal transformation at relatively low temperatures when entropy doesn&’t predominate the free energy.
We found that Zn6Mg3Y icosahedral quasicrystals started to nucleate and grow epitaxially on Zn3MgY crystals in Mg matrix of a Mg-Zn-Y alloy at about 573 K during in situ heating on a transmission electron microscope (TEM). Interdiffusion resulted in segregation of Y and Zn in Mg at the Mg/Zn3MgY interfaces, which then triggered tetrahedral atomic rearrangement in Mg to form icosahedron pairs with surface distorted icosahedra of Zn3MgY. The icosahedron pairs are tiny embryos of icosahedral quasicrystals. The interfacial icosahedron pairs inherited the same interconnectivity of those in the interior of Zn3MgY, minimizing the nucleation barrier for icosahedral quasicrystal nanoparticles, lattice mismatch and distortion, and interfacial energy. The solid-state icosahedral ordering at lower temperatures sheds new light on understanding the nucleation and growth of quasicrystals.
In addition, In situ TEM observations showed the dynamical processes of eutectic IQC to W and H transformations at 688 K during heating, and the H to W transformation at 623 K on cooling. Quantitative analysis of the in situ transformation process reveals that both of the growth of H and W are diffusion-controlled growths, which agree with Avrami&’s model. These results provide useful information for microstructural optimization in order to improve the mechanical properties of Mg-Zn-Y alloys.
3:45 AM - OO2.05
Surface Step Induced Oscillatory Oxide Growth
Liang Li 1 Langli Luo 1 Jim Ciston 2 3 Wissam A Saidi 4 Eric A Stach 2 Judith C Yang 4 Guangwen Zhou 1
1State University of New York at Binghamton Binghamton USA2Brookhaven National Laboratory Upton USA3Lawrence Berkeley National Laboratory Berkeley USA4University of Pittsburgh Pittsburgh USAShow Abstract
Fundamental understanding of metal oxidation has received extensive interest due to its significant importance in many fields including high temperature corrosion, catalytic reactions, and thin film processing. However, many fundamental questions still remain unresolved concerning the early stages of oxidation, which is inaccessible by the traditional surface science and ‘‘bulk&’&’ materials science techniques. A detailed understanding of the early-stage oxidation is often complicated by surface inhomogeneities caused by the presence of surface defects such as steps. In this work, through the use of in-situ transmission electron microscopy (TEM) we observe that the presence of surface steps leads to the decomposition of the oxide overlayer at the growth front, thereby resulting in oscillatory oxide film growth. Using density-functional theory (DFT) total energy calculations and ab initio molecular dynamics (AIMD) simulations, we show that oxygen adsorption on the lower terrace destabilizes the oxide film formed on the upper terrace that leads to oxide decomposition. Our results reveal the unique role of surface defects in oxide film growth and may have broader implications for understanding the fundamental process governing gas-surface reaction kinetics as modulated by atomic defects on a solid surface.
4:30 AM - *OO2.06
In Situ Study of Uranium(VI) Oxide Colloid Formation and Their Relevance to Geodisposal Relevant Conditions
Sam Shaw 1 Pieter Bots 1 Gareth T.W. Law 2 Katherine Morris 1
1University of Manchester Manchester United Kingdom2University of Manchester Manchester United KingdomShow Abstract
In many countries a significant legacy of radioactive wastes exists. The strategy for radioactive waste management includes, for intermediate level wastes, containment in a Geological Disposal Facility (GDF) in the deep sub-surface which typically will contain cementitious materials. Interaction of groundwater with the cement and wastes will form a plume of hyperalkaline leachate (pH 13 - 10) . Under these conditions, thermodynamic modelling predicts that U(VI) solubility will be limited (ppb or lower) and controlled by equilibrium with alkali and alkaline-earth uranates . In addition to transport in the dissolved phase, colloidal transport of radionuclides may be significant . However, the potential formation of hexavalent uranium (U(VI)) colloids has received little interest despite the observation that U(VI) will be stabilised at elevated pH conditions relative to U(IV) . Here, we focused on the formation and characterisation of such colloidal phases.
Charactersiaterion of colloidal particles using conventional extraction and separation techniques (e.g. filtration) can be challenging for suspended nanoparticles (i.e. <10nm). In this study we have utilised in situ time resolved Small Angle X-ray Scattering (SAXS) to characterise the formation of U(VI) oxide nanoparticles from a synthetic cement leachate (pH asymp; 13) with 10-60 ppm U(VI), and their aging over 2.5 years. Experiments were performed on beam line I22 of the Diamond Light Source. The results show the colloids consisted of 1.5 - 1.8 nm nanoparticles with a proportion of 20 - 60 nm aggregates which form within a few hours. In addition, the colloid remained stable for at least 2.5 years, and in the presence of several mineral phases (e.g. calcite). X-ray absorption spectroscopy in combination with TEM showed that the nanoparticles had a clarkeite (Na/K/Ca-uranate) type structure.
The presented results have clear and hitherto unrecognised implications for the mobility of U(VI) in cementitious environments, in particular those associated with the geological disposal of nuclear waste.
 Small and Thompson (2009) Scientific Basis for Nuclear Waste Management 1124, 327-332  Gorman-Lewis et al (2008) J. Chem. Thermodyn. 40, 980-990  Silva and Nitsche (1995) Radiochim. Acta. 70-1, 377-396  Gaona et al (2012) Appl. Geochem. 27, 81-95
5:00 AM - OO2.07
Surface Reconstruction Mechanism of Carbon Nanotube Growth on Bulk Stainless Steel
Sebastian William Pattinson 1 Viswanath Balakrishnan 1 Dmitri Zakharov 2 Eric A Stach 2 Anastasios John Hart 1
1Massachusetts Institute of Technology Cambridge USA2Brookhaven National Laboratory Upton USAShow Abstract
The direct growth of carbon nanotubes (CNTs) from bulk stainless steel enables the economical production of corrosion-resistant hierarchical materials with exceptional surface area as well as high thermal and electrical conductivity. Such direct growth has been achieved previously on stainless steel, typically through air annealing or acid treatment prior to synthesis, but often suffers from relatively poor yield, alignment, and lack of control over CNT morphology, preventing the realization of diverse applications ranging from heat exchangers to filtration membranes and capacitors. Previous work has suggested the importance of nanoscale roughness on the stainless steel surface as well as the removal of the steel&’s native chromium oxide outer layer. However, these findings result primarily from ex-situ studies and the exact role that they play, if any, in CNT growth remains unclear. Furthermore, how stainless steel geometry affects CNT growth has not been studied. We present the first direct observations of CNT growth from stainless steel using lattice fringe imaging and electron energy loss spectroscopy in an environmental transmission electron microscope. We will show how the sequential oxidation and reduction of the surface, and associated mechanical forces, lead to the formation of loosely bound, discrete nanoparticles that nucleate and grow CNTs. Among other findings, our in-situ study demonstrates that CNT growth can proceed from Fe-Cr and Fe-Ni alloy particles, and that CNT growth does not require the removal of the chromium surface oxide. We subsequently use the understanding gained from these detailed observations to improve CNT yield and morphological control on diverse stainless steel geometries through sequences of pre-treatments in oxidizing, reducing, and inert atmospheres. In addition to enabling the manufacture of CNT/stainless steel hybrids, these mechanisms are applicable to the general direct growth of CNTs from bulk metal substrates and will help to realize this new class of hierarchical materials.
5:15 AM - OO2.08
In Situ Imaging of Zeolite Surface Growth by Atomic Force Microscopy
Jeffrey Daniel Rimer 1 Manjesh Kumar 1
1University of Houston Houston USAShow Abstract
The exceptional thermal stability, tunable porosity, unique shape-selectivity, and high acidity of zeolites contribute to their frequent use as catalysts and adsorbents. The inability to a priori control crystal growth, however, often yields materials with undesirable physicochemical properties. Approaches capable of selectively tailoring zeolite size, morphology, and/or crystal structure can lead to dramatic improvements in their performance. Given the application of zeolites in areas of biofuels, methane conversion, and CO2 sequestration, there exists a need to expand the fundamental understanding of zeolite growth as well as design synthetic routes to optimize their properties. In this talk, we will discuss a new advancement in atomic force microscopy (AFM) that has enabled us to image zeolite surface growth in situ under realistic synthesis conditions (i.e., high temperature and long duration). AFM offers unparalleled insight of dynamic processes governing zeolite growth at near-molecular resolution . We used in situ AFM to characterize zeolite surface growth over the course of 10 - 30 hours of continuous scanning. A systematic study of silicalite-1 revealed that growth occurs by two concurrent mechanisms: a classical route (i.e., molecule addition) and a non-classical pathway defined by the addition and subsequent rearrangement of amorphous precursor particles. These studies have been expanded to other zeolite crystal structures. We will discuss these findings and place their significance within the broader context of other zeolite crystal structures that are believed to grow by a variety of different pathways.
 A.I. Lupulescu and J.D. Rimer, In Situ Imaging of Silicalite-1 Surface Growth Reveals the Mechanism of Crystallization, Science 344 (2014) 729-732
5:30 AM - OO2.09
Real-Time X-Ray Study of Structural Evolution during Layer-by-Layer Growth of SrTiO3
I-Cheng Tung 1 2 G. Luo 3 Z. L. Luo 4 5 J. H. Lee 2 S. H. Chang 4 D. Morgan 3 H. Hong 2 M. J. Bedzyk 1 J. W. Freeland 2 D. D. Fong 4
1Northwestern University Evanston USA2Argonne National Laboratory Argonne USA3University of Wisconsin-Madison Madison USA4Argonne National Laboratory Argonne USA5University of Science and Technology of China Hefei ChinaShow Abstract
Functional materials based on complex oxides in thin film form offer new and exciting strategies for meeting many of our outstanding energy challenges through systematic control of layer sequencing, strain, etc. However, synthesis of such oxide films can be a major challenge even when utilizing reactive molecular-beam epitaxy (MBE), a powerful deposition technique that is often regarded to allow the construction of materials atomic plane by atomic plane. To understand the fundamental physics of oxide growth by reactive MBE, we present in situ surface x-ray scattering results of the homoepitaxial growth of SrTiO3 thin films on (001)-oriented SrTiO3 substrates. By comparing sequential deposition (alternating Sr and Ti monolayer doses) with that of co-deposition of Sr and Ti, both in a background of oxygen pressure, we find drastically different growth pathways. While the co-deposition is marked by the usual roughening-smoothing transition associated with the completion of each layer, sequential deposition demonstrates strong islanding of the SrO monolayer followed by a smoothing transition during the TiO2 layer deposition. Using in situ x-ray specular reflectivity and surface diffuse x-ray scattering during growth, an area detector simultaneously recorded both the specular x-ray scattering connected to out-of-plane atomic positions and the diffuse x-ray scattering associated with in-plane correlations. During growth of SrTiO3 by co-deposition, where the fluxes of Sr and Ti are roughly equal, the specular intensity at the half-order position is at a minimum while the diffuse intensity is at a maximum. This is consistent with a 2D island growth mode with unit-cell-high SrTiO3 islands that nucleate/grow on the terraces and coalesce before the next layer starts. For the case of sequential deposition, the scattering indicates that the SrO grows as islands and then restructures into SrTiO3 unit cells during the growth of the TiO2 to form an atomically flat layer. Theoretical calculations indicate that the growth of a single monolayer of SrO layer is thermodynamically preferable, so kinetic processes cause the formation of SrO islands. However, smoothing of SrO bilayer islands during the deposition of TiO2 to form perovskite SrTiO3 is energetically favorable. A detail comparison of sequential deposition and co-deposition will be presented, demonstrating the power of quantitative x-ray probes for understanding the process of thin film synthesis.
Work at Argonne, including the Advanced Photon Source, is supported by the U.S. Department of Energy, Office of Science, and Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
5:45 AM - OO2.10
In-Situ Observations during Graphene and Hexagonal Boron Nitride Growth by Scalable Chemical Vapour Deposition Processes
Piran Ravichandran Kidambi 1 Bernhard C Bayer 2 Raoul Blume 3 Carsten Baehtz 4 Robert S Weatherup 1 Philipp Braeuninger 1 Andrea Cabrero 1 Sabina Caneva 1 Tomasz Cebo 1 Robert Schloegl 3 Stephan Hofmann 1
1University of Cambridge Cambridge United Kingdom2University of Vienna Vienna Austria3Fritz Haber Institute Berlin Germany4Forschungszentrum Dresden-Rossendorf Dresden GermanyShow Abstract
Scalable synthesis of 2D materials such as graphene and hexagonal boron nitride h-BN by chemical vapour deposition (CVD) has generated considerable research interest. However, the growth mechanisms of graphene and h-BN during CVD remain poorly understood. Simplistic models of elemental solubility of the constituent elements (eg: C, B etc.) in metallic catalysts eg: Ni (high solubility - precipitation from bulk) and Cu (low solubility - surface reaction) have so far been speculatively proposed based on ex-situ experiments while critical in-situ experimental evidence remains elusive. [1,2]
Here, using a combination of high-pressure process, time and depth resolved in-situ X-ray photoelectron spectroscopy (XPS) at the BESSY II synchrotron in Berlin [1,2] and in-situ X-ray diffraction (XRD) at the ESRF synchrotron in Grenoble, [1,2] we study the behaviour of polycrystalline transition metal catalyst films and foils during CVD at industrially relevant CVD conditions, i.e. pressure (~0.001 - 0.5 mbar) and extreme temperatures (800-1000oC).
These complementary in-situ XPS and XRD experiments allow us to identify the chemical state/phase of the catalyst and the elemental species at any point of time during CVD. This allows us to observe elemental incorporation into the 2D material structure on the catalyst surface as it happens. The growth mechanisms of these 2D nanostructures is found to be predominantly isothermal along with some precipitation on cooling for both Ni and Cu, i.e. we observe the detailed dynamics of the catalytic behaviour during growth as a complex interplay of isothermal and precipitation based growth mechanisms with kinetic effects playing an important role.
We highlight the use of our in-situ approach as a generic framework to study the growth other 2D and 1D nanostructures during CVD.
1. Kidambi et al. Nano Letters (submitted)
2. Kidambi et al. Nano Letters 13 (10), 4769-4778 (2013).
3. Kidambi et al. J. Phys.Chem. C. 116, 42, 22492-22501 (2012).
4. Kidambi et al. PSS RRL. 5, 9, 341-343 (2011).
OO1: In Situ Characterization of Nucleation, Growth and Transformation I
Monday AM, December 01, 2014
Hynes, Level 1, Room 101
10:00 AM - *OO1.01
An In Situ View of Nucleation
Jim J De Yoreo 1 2
1PNNL Richland USA2University of Washington Seattle USAShow Abstract
Nucleation is the seminal process in the formation of ordered structures ranging from simple inorganic crystals to self-assembled macromolecular matrices. Yet due to its inherent dynamics much of what we know about nucleation comes from observations of the products rather than the processes. Consequently, in situ techniques of imaging and spectroscopy are critical to developing a foundational framework to describe this key step in materials synthesis. Molecular scale observations of structural and morphological evolution provide direct knowledge of nucleation pathways, while measurements of nucleation rates vs. temperature and supersaturation enable one to determine the kinetic and free energy barriers that define these pathways. Optical and force spectroscopic probes then establish the connection between this energy landscape and the underlying molecular interactions. Here we illustrate this approach to understanding nucleation by using in situ methods including AFM, TEM, and optical microscopy combined with FTIR and dynamic force spectroscopy (DFS) to investigate nucleation of ordered states in protein and mineral systems. TEM observations of calcium carbonate reveal the multiple complex pathways available to the system, due to the high driving force required to overcome the large free energy barrier to homogeneous nucleation of the stable phase. AFM and optical measurements of nucleation rates vs. supersaturation demonstrate that organic matrices can direct nucleation of a fixed phase by dramatically reducing these barriers. DFS measurements demonstrate that the underlying source of this control is the matrix-crystal binding energy. AFM studies of self-assembly in both the S-layer protein and collagen systems reveal the key role played by conformational transformations in controlling the pathways and kinetics of matrix assembly. The results demonstrate that the pathway to the final ordered state often passes through transient, less-ordered conformational states. Thus the concept of a folding funnel with kinetic traps used to describe protein folding is also applicable to nucleation of ordered protein matrices. Finally, both AFM and TEM studies of matrix mineralization illustrate the strong control that ion-matrix binding has in defining the location of mineral nucleation. Taken together, these results provide new insights into the mechanisms and pathways controlling nucleation of ordered states in biomolecular and biomineral systems.
10:30 AM - OO1.02
In-Situ Characterization of the Nucleation, Phase Formation, and Chemistry during the Molecular Beam Epitaxy of Oxides
Oliver Bierwagen 1 James S. Speck 2 Patrick Vogt 1 Michael Hanke 1 Andre Proessdorf 1 Vladimir M. Kaganer 1
1Paul-Drude-Institut (PDI) Berlin Germany2University of California Santa Barbara USAShow Abstract
Molecular beam epitaxy (MBE) is a thin film growth method that allows to synthesize high-quality, single-crystalline layers with defined thickness and stoichiometry. During MBE the elements to form the layer are provided as elemental vapor with defined flux in an ultra-high vacuum environment. This setup enables a simple chemistry that is free from incorporation of impurities and free from unwanted reactions and their products.
The MBE growth of oxides is realized by subliming the oxidic source material or evaporating the source metal and providing an oxidizing flux (molecular oxygen or an oxygen plasma).
This contribution demonstrates the in-situ investigation of the MBE of La2O3, In2O3, and Ga2O3 during growth.
In particular, the nucleation and phase formation was analyzed by in-situ reflection-high-energy electron diffraction (RHEED) and x-ray diffraction (XRD) of La2O3 oxide growth. The nucleation of the cubic polymorph on Si(111) substrate was followed by the formation of the bulk-stabile hexagonal phase as determined by XRD, wheras the growth rate could be measured using RHEED oscillations.
In-situ RHEED was also used to investigate the nucleation of In2O3 on ZrO2:Y(001) substrates as function of growth temperature and O/In flux ratio. A regime of fast nucleation was able to realize continuous films whereas the opposite regime of suppressed nucleation could be used to grow isolated islands.
The growth of Ga2O3 on Al2O3 was investigated by in-situ laser reflectometry to determine the growth rate and by line-of-sight quadrupole mass spectrometry to identify the desorbing species. Measuring the (positive or negative) growth rate as function of Ga and oxygen flux and the identification of the desorbing species helped identifying the chemical reactions at play. These are: 2Ga+3O->Ga2O3 and 4Ga+Ga2O3 ->3Ga2O.
Being not limited to oxides, these examples demonstrate the suitability of molecular beam epitaxy for many different types of in-situ measurement.
10:45 AM - OO1.03
Nucleation Kinetics of Carbon Nanotube Populations
Mostafa Bedewy 2 1 Viswanath Balakrishnan 2 Sebastian W Pattinson 2 Eric A Stach 3 Dmitri Zakharov 3 Eric R Meshot 4 Erik Polsen 1 Fabrice Laye 1 A. John Hart 2
1University of Michigan Ann Arbor USA2Massachusetts Institute of Technology Cambridge USA3Brookhaven National Laboratory Upton USA4Lawrence Livermore National Laboratory Livermore USAShow Abstract
Understanding the spatiotemporal evolution of populations of carbon nanotubes (CNTs) during the growth of vertically aligned "forests" by chemical vapor deposition (CVD) is key to engineering their morphology and properties. Hence, in situ characterization of the successive stages of the growth process is sought after. Previously, it was shown that Synchrotron X-ray scattering and absorption can provide valuable quantitative information about the morphological evolution and population dynamics of CNTs within a forest. However, the initial stages of nanoparticle formation and CNT nucleation are more elusive and cannot be inferred directly from transmission X-ray measurements. Grazing incidence X-ray scattering was also used to study the dynamics of catalyst film dewetting, but decoupling the scattering signal from catalyst nanoparticles and CNTs becomes challenging upon CNT nucleation. To further elucidate the early nucleation behavior of CNTs, we carry out in situ and operando experimental studies of CNT growth in an environmental transmission electron microscope (TEM). Real-time imaging of particle formation and CNT nucleation shows a characteristic S-shaped kinetics that span a few second, highlighting the non-instantaneous nature of nucleation. Although further studies are needed to identify the differences between active nanoparticles and inactive nanoparticles, results show that inactive nanoparticles that do not bear CNTs are generally encapsulated inside a graphitic coating. In situ TEM images also show the mechanical interactions between neighboring CNTs during the crowding stage that leads to the build-up of alignment in the forest morphology. Moreover, electron energy loss spectroscopy (EELS) is used to infer the kinetics of carbon deposition upon the introduction of the hydrocarbon gas (acetylene) to the reactor. Our findings indicate that tuning the catalyst annealing and growth conditions can modulate the "popping" kinetics of nanoparticles to enable instantaneous nucleation of CNTs and therefore the growth of uniform functional CNT forests.
11:30 AM -
11:45 AM - *OO1.05
In Situ, Environmental Transmission Electron Microscopy of Material-Gas Reactions
Robert Sinclair 1 Sang Chul Lee 1 Chia-Jung Chung 1 Ai Leen Koh 2
1Stanford University Stanford USA2Stanford University Stanford USAShow Abstract
Our work on in situ studies of the atomic mechanisms of material reactions by high resolution transmission electron microscopy has now been extended to environmental (ETEM) investigations (e.g. ). This technique will be reviewed and recent applications discussed. Our research has focused on simple reactions with a single pure gas and some recent results will be presented.
The oxidation of matter is a basic process with broad implications. Here we demonstrate in situ observations of the oxidation of carbon nanotubes being developed as field emission sources for X-ray medical imaging purposes. The oxidation mechanism is quite different than had been previously proposed but is easily demonstrated by the ETEM .
Likewise, hydrogen storage is promising for possible future energy applications, and so the reaction of hydrogen gas with candidate materials has fundamental importance. Following prior work on hydrogenation of magnesium/palladium thin films , we have extended this investigation to the hydrogenation of magnesium films with palladium nanoparticles. The formation of magnesium hydride in the ETEM is demonstrated, as is the utility of a new vacuum transfer specimen holder.
It is clear from both these studies that the imaging electron beam can influence the observations. Accordingly, protocols have been established whereby any possible influence of the electron beam is avoided, and these procedures will be discussed.
 Sinclair, R., In Situ High-Resolution Transmission Electron Microscopy of Material Reactions, Mats. Res. Bull., 38, 1065-1071, 2013
 Koh, A.L., Gidcumb E., Zhou, O., Sinclair, R, Observations of Carbon Nanotube Oxidation in an Aberration-Corrected Environmental Transmission Electron Microscope, ACS Nano, 7 (3), 2566-2572, 2013
 Chung, C.J., Lee, S.C., Groves, J.R., Brower, E.N., Sinclair, R., Clemens, B.M., Interfacial Alloy Hydride Destabilization in Mg/Pd Thin Films, Phys. Rev. Lett, 108, 106102 1-4, 2012
12:15 PM - OO1.06
In Situ Observation of Graphene Formation on Polycrystalline Cu Substrate
Huafeng Wang 1 Chisato Yamada 1 Shohei Chiashi 2 Shigeo Maruyama 2 Yoshikazu Homma 1
1Tokyo University of Science Tokyo Japan2The University of Tokyo Tokyo JapanShow Abstract
As a stable 2-dimensional material, graphene has been extensively studied. Currently, most of explanations on growth mechanisms are based on the experimental results after graphene formation, and the direct observation on the whole growth process is still lacking. To produce single-crystal graphene as large as possible and finally control its growth, the deep understanding on the growth mechanisms is indispensable. By in situ technique, it is possible to observe the whole process including the morphology change of the substrate surface, formation of graphene crystal and so on during growth. In situ scanning tunneling microscopy (STM) analyses have showed this process at atomic scale . Complementary to in situ STM, in situ scanning electron microscopy (SEM) observation provides a larger field of view, which may help us to better understand the growth mechanisms .
In this study, the whole graphene growth process on polycrystalline Cu substrate is observed by in situ SEM. The morphology changes of Cu surface and graphene structures formed under various conditions are carefully investigated. The influences of experimental parameters including temperature and growth time on the layer number of graphene as well as its quality are also discussed. According to our experimental observations, graphene is not created directly on the surface of Cu substrate but on an adsorbed gas layer over the surface, which is formed during graphene growth. The removal of this gas layer leads to the disappearance of graphene from SEM observation. Therefore, to finally obtain high quality graphene, the adsorbed gas layer on the surface of substrate has to be carefully considered. This result may suggest a possible direction for future research on graphene formation.
 Niu, T.; Zhou, M.; Zhang, J.; Feng, Y.; Chen, W. J. Am. Chem. Soc.135, 8409 (2013).
 Kidambi, P. R. et al. Nano Lett.13, 4769 (2013).
Corresponding Author: Huafeng Wang
Tel: +81-3-5228-8244, Fax: +81-3-5261-1023
12:30 PM - OO1.07
Nanoscale Phase Transformation of Pt-Alloys - Probing Thermally Induced Composition Segregation and Atomic-Ordering via In Situ Single-Nanoparticle Annealing
Sagar Prabhudev 1 Matthieu Bugnet 1 2 Guo-Zhen Zhu 3 Christina Bock 4 Gianluigi A Botton 1 2
1McMaster University Hamilton Canada2McMaster University Hamilton Canada3Shanghai Jiao Tong University Shanghai China4National Research Council Ottawa CanadaShow Abstract
Platinum-alloy nanoparticles are a system of great interest for fuel cell electrocatalysis and magnetic applications. Fine-tuning their structure to enhance catalytic activity and durability is crucial to commercialize fuel cell systems. In an ongoing attempt to reduce the mass loading of platinum (Pt) in proton exchange membrane fuel cells, there has been a tremendous research till date; constantly suggesting that a nanoscale alloying of Pt with 3d transition metals is a more viable option. Pt-Fe nanoalloys, in particular, have gathered much attention in recent years not just as a better catalyst to Pt/C, but also because of its magnetic properties that are deployable in ultra-high density information storage . However, a nanoscale phase transformation of an ensemble of alloy nanoparticles, polydispersed in both their size and composition, results in an assortment of materials with miscellaneous properties . Controlling their collective evolution and probing the interplay between compositional segregation and atomic-ordering is therefore imperative, and demands, full-fledged understanding at the atomic scale. Traditionally, a bulk approach has been followed in this respect, by deriving inference from ex-situ thermal treatments, before and after. Given the inherent dynamicity associated with nanoscale processes, an atomic-perspective is hence so far not been possible. Looking beyond, here we demonstrate an in-situ atomic-resolution imaging and spectroscopy — on single Pt-Fe alloy nanoparticles — over the course of thermal treatment .
Same particle was tracked all through and a combination of atomic-resolution STEM-HAADF imaging and STEM-EEL spectroscopy was performed. While our STEM-HAADF results clearly demonstrate evolution of particle shape, size, ordering and sintering kinetics (ripening and coalescence) over the course of heat treatment, the EELS maps reveal new insights into the segregation process. Additionally, we have stumbled across a new phenomenon that comes to play as a consequence of interaction of nanoparticles with their chemical environment and our results bear witness to its unique role in creating unusual structures (unicore-multishells, as an instance) at the nanoscale. We illustrate through a model as to how these dynamic processes can collectively lead to the formation of various nanoalloy configurations. We believe that a dedicated attempt to understand the nanoscale phase transformation as this, is central to fine-tune the catalytic properties of alloyed-Pt nanoparticles in general, and hence could redefine a new methodology to synthesize next generation fuel cell nanocatalysts.
 Prabhudev, S.; Bugnet, M.; Bock, C.; Botton, G. ACS Nano 7 6103-6110 (2013)
 Prabhudev, S.; Bugnet, M.; Zhu, G-Z.; Bock, C.; Botton, G. (submitted)
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Interrelationship of Growth Stress Evolution and Phase Transformations in Metallic Thin Film Multilayers
Li Wan 1 Xiao-xiang Yu 1 Gregory B. Thompson 1
1University of Alabama Tuscaloosa USAShow Abstract
As materials are reduced to the nanometer length scale, pseudomorphic phases can be stabilized. Thin films provide ideal systems to understand this phase stability because of their near atomic level control of thickness coupled to a high surface area; this creates tailored materials with high surface area-to-volume ratios. Thin films are also susceptible to significant epitaxial strains during growth which can contribute to the effects of interfacial energy reduction for the stabilized these pseudomorphic phases. Using an in situ laser reflectometry technique, the stress evolution of growing thin films was captured in real-time to understand how intrinsic growth stresses relate to phase stability. These associated growth stresses provide insights into adatom mobility during deposition. In the present work, this in situ technique has been utilized to elucidate the pseudomorphic bcc to ‘bulk&’ hcp stability of Ti in either a Ti/Nb or Ti/W multilayer. For Ti/Nb, the bcc phas