Symposium Organizers
Haimei Zheng, Lawrence Berkeley National Laboratory
Dongsheng Li, Pacific Northwest National Laboratory
Judith Yang, University of Pittsburgh
Henry Zandbergen, Delft University of Technology
Yimei Zhu, Brookhaven National Laboratory
Symposium Support
Direct Electron, LP
Henan University
Hitachi
CM4.1: In Situ Characterization of Electrochemical Processing and Energy Materials
Session Chairs
Reza Shahbazian-Yassar
Chaoming Wang
Monday PM, April 17, 2017
PCC North, 100 Level, Room 127 B
2:30 PM - *CM4.1.01
In Situ Transmission Electron Microscopy of Advanced Materials for Li-Ion and Na-Ion Batteries
Reza Shahbazian-Yassar 1
1 , University of Illinois at Chicago, Chicago, Illinois, United States
Show AbstractThis talk gives an overview of the PI’s research program on the opportunities and challenges of in-situ transmission electron microscopy (TEM) to study novel two-diemnsional materials and metal oxides for Li-ion and Na-ion battery applications. Various anode materials including SnO2, ZnSb, MnO2 , phosphorene were subjected to lithiation/sodiation process and the transport of Li ions was visualized within their atomic structure. For SnO2 nanowires, it was observed that the Li ion transport results in local strain development preferably along (200) or (020) plans and [001] crystallographic directions. Extremely fast ionic transport was also observed along [100] directions of phosphorene and in ZnSb crystalline materials indicating that atomic structure engineering of electrode materials can provide an efficient path for the movement of larger ions such as sodium ions overcoming their sluggish kinetics. In one-dimensional materials the structural engineering of tunnels and the tunnel stabilizers can be very effective in allowing the ions to be transported at fast rates. Overall a summary will be given on new science obtained from the in situ TEM studies and how this new information can help to further grow the opportnities in materials designed for electrochemistry.
3:00 PM - CM4.1.02
Electric-Field Induced Dynamics and In Situ Core-Shell Formation of BNT-ST Piezoelectric Nanoparticles
Leopoldo Molina-Luna 1 , Matias Acosta 1 , Yevheniy Pivak 2 , Alexander Zintler 1 , Qiang Xu 2 3 , Shuai Wang 1 , Bai-Xiang Xu 1 , Hans-Joachim Kleebe 1
1 , TU Darmstadt, Darmstadt Germany, 2 , DENSsolutions, Delft Netherlands, 3 Kavli Centre of NanoScience, National Centre for HREM, TU Delft, Delft Netherlands
Show AbstractFerroic materials play a key role in a wide range of technologically relevant devices. They all share the common feature that the microstructure and domains determine to a great extent their functionality. Among the promising piezoelectric materials for actuation applications is the solid solution Bi0.5Na0.5TiO3 (BNT)-SrTiO3 (ST). Recently it was found that this material is characterized by a core-shell microstructure that largely determines its electromechanical and dielectric properties. In this contribution, we reveal the core-shell and domain formation in nanoparticles during a calcination process by means of in-situ TEM experiments. The solid state chemical reactions occurring upon heating could be followed in real time and the temperature-dependent core-shell formation and structural evolution was investigated. Furthermore, combined in situ TEM electric-field (at elevated temperatures) and Finite Element Analysis (FEAP) based modelling revealed a strain dependant response in the BNT-ST nanoparticle that includes an interplay between the core and the shell regions and induces nanometer sized polar regions. When an electric-field of up to 20 kV/mm is applied a monodomain state forms in the core region and tends to align in the direction of the applied electric-field.
3:15 PM - CM4.1.03
Understanding the Effect of Additives in Li-Ion and Li-Sulfur Batteries by Operando ec- (S)TEM
B. Layla Mehdi 1 , Andrew Stevens 1 , Karl Muller 1 , Nigel Browning 1
1 , Pacific Northwest National Laboratory, Richland, Washington, United States
Show AbstractThe high demand for new energy storage materials has created the need for novel experimental techniques that can provide real-time information on the dynamic structural changes and processes that occur locally at the electrode/electrolyte interface during battery operation. The recent development of in-situ liquid electrochemical stages for (scanning) transmission electron microscopes ((S)TEM) enables fabrication of a “nano-battery” to study the details of electrochemical processes under operando conditions. However, high complexity of electrochemical process during the battery cycling requires careful calibration of the system prior to in-situ/operando observations to circumvent i.e. e--beam damage of the electrolyte and artifact affecting the electrochemical cycling. Therefore, affecting stability and introducing varies degradation mechanisms in battery electrolytes. Here, we describe the effect of the electron beam in the operando observations and determine the condition to minimize electrolyte damage. In particular, we demonstrate application of an in-situ liquid electrochemical (S)TEM cell paying attention to rechargeable Li-ion battery and alternative systems such as Li-sulfur and Li-O2. The full operation of these complex systems is yet not fully understood and typically involves multi-step electrochemical reduction/oxidation reactions, which often lead to lithium dendrite formation and require an increased fundamental understanding to bring beyond Li-ion technology to wide-spread commercialization similar to Li-ion batteries. There are many strategies to improve the interfacial stability of the Li anode and control/suppress Li dendrite growth, which is highly dependent on nature of electrolyte itself, such as mixture of different electrolyte solvents, salts and additives (e.g. HF, LiNO3 etc). Here we use an operando electrochemical cell (ec-cell) in the STEM to investigate the role of electrolyte additives on the initial stages of Li deposition/stripping and the SEI layer formation. As a test of the fundamental process, we compare two commercially used electrolytes, electrolyte used in Li-ion battery contacting controlled trace-amounts of water (10 ppm and 50 ppm) with electrolyte used in Li-sulfur battery in the presence of LiNO3 additive to understand the mechanism of Li dendrite nucleation, growth and suppression.
Acknowledgement
This work was primarily supported by JCESR, an Energy Innovation Hub funded by DOE-BES. The development of the operando stage was supported by the Chemical Imaging LDRD Initiative at PNNL. PNNL is a multi-program national laboratory operated by Battelle for the U.S. DOE under Contract DE-AC05-76RL01830. A portion of the research was performed at the EMSL user facility sponsored by DOE-BER and located at PNNL.
3:30 PM - CM4.1.04
Understanding the Origins of Activity through In Situ Annealing and Dealloying of Fuel Cell Catalysts
David Cullen 1 , Raymond Unocic 1 , Brian Sneed 1 , Karren More 1 , Jonah Erlebacher 2 , Amy Hester 3 , Sean Luopa 3 , Andrew Steinbach 3
1 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 , Johns Hopkins University, Baltimore, Maryland, United States, 3 , 3M Company, St. Paul, Minnesota, United States
Show AbstractPolymer electrolyte membrane fuel cells are under intense research and development for transportation applications. Highly active, lower cost oxygen reduction reaction catalyst can be made by replacing a portion of the costly Pt catalyst with a transition metal such as Co or Ni, and further gains can be achieved through annealing and dealloying to create highly active Pt-rich skins or shells. In this work, in situ scanning transmission electron microscopy was employed to study the impact of starting catalyst morphology and composition on the formation of highly-desired Pt-skin structures. The Protochips Atmosphere system was used to anneal PtNi ultra-thin film catalysts in the presence of a forming gas (4% H2 balance Ar) to observe changes in grain and surface morphology as the temperature was ramped to 400 oC at a rate of 5 oC/min. The effect of starting Ni content and grain size on the formation and thickness of Pt-rich skins was correlated with electrochemical measurements of similarly annealed specimens. The Protochips Poseidon electrochemical system was also used to study electrochemical dealloying behavior in nanoporous thin film catalysts. The removal of excess Ni by dealloying is an effective method for increasing both surface area and specific activity, and may also be used to stabilize the catalyst from further dealloying within the fuel cell. Bulk electrochemical dealloying protocols were replicated within the TEM to study the mechanisms for the formation and stability of nanoporosity within these catalysts. The distribution of Pt and Ni within the catalysts was imaged before and after annealing using energy dispersive X-ray spectroscopy. These combined efforts of in situ annealing and dealloying provide insight into important mechanisms for improving and stabilizing costly precious metal catalysts for fuel cell applications. This research is sponsored by the Fuel Cell Technologies Office, Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy and through a user project supported by ORNL’s Center for Nanophase Materials Sciences (CNMS), which is a DOE Office of Science User Facility.
3:45 PM - CM4.1.05
Base Growth vs Tip Growth Mechanism via In Situ Multimodal Study of Sodium/Lithium Metal Deposition Using Electrochemical Liquid Cell
Zhiyuan Zeng 1 , Haimei Zheng 1
1 , Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractWe report the observation of lithium metal/sodium metal deposition behavior in commercial battery electrolytes through in-situ Electrochemical liquid cell Transmission electron microscopy (TEM) and X-ray Absorption Spectroscopy (XAS) techniques, which showed huge differences for the deposition of Li and Na. Based on that, we proposed the tip growth vs base growth mechanism of Li and Na metal. In Li tip growth mode, the SEI on lithium metal is stable with fix thickness, so that Li+ ions can penetrate through SEI layer and achieve tip growing. However, in Na base growth mode, the SEI layer is not stable and getting thicker and thicker, then it blocked the existing Na islands to grow, instead, another Na island nucleated at the bottom and stopped again when grown to certain size. Just like this, a successive sodium islands emerged one after another and finally forming “volcano” style Na heap, which sheds lights on strategies of elucidating the electrode-electrolyte interface reactions for lithium/sodium ion batteries. The in situ study of Li/Na deposition can also provide insights on improving the battery design for the applications of lithium/sodium ion batteries in related energy devices.
4:30 PM - *CM4.1.06
In Situ TEM Probing of Structural and Chemical Evolution of Energy Materials—Rechargeable Batteries and Fuel Cells
Chongmin Wang 1 , Pengfei Yan 1
1 , Pacific Northwest National Laboratory, Richland, Washington, United States
Show AbstractThe fading and eventual failure of energy device is closely related to the structural, chemical, and electronic evolution of the active materials in the device. However, detailed characterization of these evolutions during the device operation has been a significant challenge, requiring innovative technique development and creative experiments. In-situ transmission electron microscopy and spectroscopy, coupled with other in-situ spectrometry, appears, no doubt, to be the essential approaches that enable the capturing of these evolutions with high spatial and fast temporal resolution. In this presentation, I will highlight recent progress on in-situ and operando S/TEM imaging and spectroscopy techniques and their application for probing the fading mechanism of rechargeable batteries and the deactivation of catalyst in proton exchange membrane (PEM) fuel cells. For rechargeable battery, in-situ high resolution imaging enables direct observation of structural evolution, phase transformation and their correlation with mass, charge and electron transport, providing insights as how active materials failure during the cyclic charging and discharging of a battery. For the PEM fuel cell, direct atomic level visualization lead to the isolation of the critical factors that contribute to the deactivation the catalyst involving H2, O2, and H2O. In perspective, challenges and possible new direction for future development will also be discussed. In essence, integration of different analytical tools was viewed as the key for capturing complementary information
5:00 PM - CM4.1.07
In-Liquid Observation of Electrodeposition Processes Using In Situ Transmission Electron Microscopy
Jie Yang 1 , Carmen Andrei 1 , Gianluigi Botton 1 , Leyla Soleymani 1
1 , McMaster University, Hamilton, Ontario, Canada
Show AbstractIn-situ liquid transmission electron microscopy enables the observation of nanoscale processes inside their native liquid environments and in real time. This method has the potential to advance scientific understanding in several areas involving nanomaterials synthesis, electrode processes, and biointerfaces. A major challenge in employing this technique towards improving fundamental understanding in various areas is related to the interference of the imaging electron beam probe with the process under study.
In this paper, we used an electrochemical liquid cell for the in-situ observation of electrodeposition processes. We further used this technique to study the structural differences between beam-induced and electrodeposited structures developed during the same in-situ experiment. We developed a strategy based on modifying the liquid thickness for reducing the amount of beam-induced structures to negligible values. Using the optimized electrochemical liquid cell, we observed the nucleation and growth of gold crystallites on carbon working electrodes during electrodeposition processes, and compared the quantity of deposited materials derived from imaging and current transient measurements. While the measured current transients demonstrated a behaviour similar to that observed in ex-situ experiments, there was a large discrepancy between the quantity of electrodeposited gold measured from imaging and current transient measurements. Post-situ electron microscopy demonstrated significant heterogeneity in electrodeposited structures in the imaged and non-imaged areas, which explains the observed discrepancy.
In sum, we demonstrated that it is possible to reduce beam-induced processes inside in-situ liquid transmission electron microscopy systems to negligible levels to observe nucleation and growth processes caused by electrode processes. However, the heterogeneity in deposition processes inside in-situ liquid cells could be significant causing discrepancies between data obtained from imaging and electrochemical techniques.
5:15 PM - CM4.1.08
Redox Mechanism Differences in Copper Systems Studied via In Situ TEM and Atomistic Simulations
Judith Yang 1 2 , Christopher Andolina 1 , Matthew Curnan 1 , Qing Zhu 1 , Wissam Saidi 3
1 Department of Chemical and Petroleum Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States, 2 Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, Pennsylvania, United States, 3 Department of Mechanical Engineering & Materials Science, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
Show AbstractPredicting the stability of engineered materials is critically important to assessing their properties in the unique environments necessitated by applications involving catalysis, corrosion prevention, and steam reformation. In contrast to the assumptions made by the classical Cabrera-Mott and Wagner oxidation theories that propose uniform oxide film growth on metal surfaces, modern in situ environmental transmission electron microscopy (ETEM) studies reveal that the initial stages of copper oxidation are controlled by surface oxygen diffusion followed by nucleation and growth of non-uniform oxide layers. Using a Hitachi H9500 ETEM, we have investigated the oxidation and reduction of several faceted low-index copper surfaces under various environmental conditions and temperatures to further elucidate the mechanism of copper oxidation. These studies have focused on the preferential nucleation and growth of copper oxide islands on particular features of these surfaces, as well as on the surface reconstructions preceding oxide nucleation. We are using a multimodal characterization by comparing these later stage oxidation experimental results with analogous early stage, comprehensive surface oxygen diffusion simulations. These simulations were performed using both first-principles density functional theory and molecular mechanics methods.
The correlation of these experimental and simulation resolved results reveals relationships between reaction mechanisms and structural feature stability over the various stages of copper oxidation. Preliminary experimental results have shown distinct surface reconstruction patterns and preferential nucleation and growth behaviors that are facet-specific and oxygen dependent. These findings are in agreement with preliminary simulation results, which indicate high O surface diffusion energy barrier anisotropy on Cu(100) surfaces, consistent preferential O diffusion along Cu(110) step edges, and consistent energy barrier anisotropy on Cu(111) surfaces. Development of these relationships is crucial for the predictive design of oxidation-resistant coating materials, possibly leading to paradigm shifts in the fundamental understanding of oxidation theory and the development of more robust catalysts for specific applications.
Symposium Organizers
Haimei Zheng, Lawrence Berkeley National Laboratory
Dongsheng Li, Pacific Northwest National Laboratory
Judith Yang, University of Pittsburgh
Henry Zandbergen, Delft University of Technology
Yimei Zhu, Brookhaven National Laboratory
Symposium Support
Direct Electron, LP
Henan University
Hitachi
CM4.2: Liquid and Gas Environmental TEM Methods, Advances and Applications
Session Chairs
Dongsheng Li
Haimei Zheng
Tuesday PM, April 18, 2017
PCC North, 100 Level, Room 127 B
2:30 PM - *CM4.2.01
Physical Chemistry of Nanocrystals with the Graphene Liquid Cell
A. Paul Alivisatos 1 , Matthew Jones 1
1 , Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractColloidal nanocrystals have emerged as a major building block for nanoscience and nanotechnology. Today it is possible to control the size, shape, and topology of nanocrystals and to harness the variations of their properties with size to create materials with proven applications in biological imaging and electronic displays, and many more applications under development in renewable energy. Despite these advances, there is much we still do not know about nanocrystals. The advent of in situ liquid cell electron microscopy and especially the graphene liquid cell, have opened the door to a series of new experiments that reveal key aspects of the physical chemistry of nanocrystals. This includes the first structural determination of the positions of all the atoms in a colloidal nanocrystal; methods for directly imaging and tracking individual nanocrystals as the grow or dissolve; and the ability to measure the inter-particle potentials by observing pairwise relative motions. These new tools are enabling a second revolution in the science of nanoscrystals, as they will permit to us to quantitatively control artificial colloidal nanoscale builidng blocks with atomic precision.
3:00 PM - CM4.2.02
Single-Particle Mapping of Non-Equilibrium Nanocrystal Transformations Using In Situ Liquid Cell TEM Imaging
Xingchen Ye 1 , Matthew Jones 1 , Layne Frechette 1 , Qian Chen 1 , Alexander Powers 1 , Peter Ercius 2 , Gabe Dunn 1 , Grant Rotskoff 1 , Son Nguyen 1 , Vivekananda Adiga 1 , Alex Zettl 1 , Eran Rabani 1 , Phillip Geissler 1 , A. Paul Alivisatos 1
1 , University of California, Berkeley, Berkeley, California, United States, 2 , Lawrence Berkeley National Lab, Berkeley, California, United States
Show AbstractChemists have developed mechanistic insight into numerous chemical reactions by thoroughly characterizing non-equilibrium species. While methods to probe these processes are well-established for molecules, analogous techniques for understanding intermediate structures in nanomaterials have been lacking. We monitor the shape evolution of individual anisotropic gold nanostructures as they are oxidatively etched in a graphene liquid cell with a controlled redox environment. Short-lived, non-equilibrium nanocrystals are observed, structurally analyzed, and rationalized through Monte Carlo simulations. Understanding these reaction trajectories provides important fundamental insight connecting high energy nanocrystal morphologies to the development of kinetically-stabilized surface features and demonstrates the importance of developing tools capable of probing short-lived nanoscale species at the single particle level.
3:15 PM - CM4.2.03
Probing Dynamics of the Solid-Liquid Interface with In Situ Scanning Transmission Electron Microscopy
Ryan Hufschmid 1 , Kannan Krishnan 1 , Nigel Browning 1 2
1 Materials Science and Engineering, University of Washington, Seattle, Washington, United States, 2 Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, Washington, United States
Show AbstractDynamic processes at interfaces are fundamental to many environmental, biological, and engineered systems. Iron oxides are ubiquitous in nature and serve as a platform for many engineered applications. Interactions between minerals, organic molecules, and ions in aqueous environments are fundamental for both engineered nanoparticles that interface with complex biological media, and for naturally occurring particles in delicate environmental systems. In this work we directly observe and quantify dynamic phase changes of iron oxide (Fe3O4 and α-FeOOH) nanoparticles in solution. We alter surface chemistry with organic molecules to systematically study colloidal stability at the nanoscale.
Recent advances in in-situ transmission electron microscopy (TEM) techniques and instrumentation enable direct nanoscale imaging and spectroscopy in relevant environments. For example, specialized holders encapsulate liquid samples, enabling direct observation of dynamic liquid phenomena under controlled electron dose conditions. At high scattering angles contrast in scanning (S)TEM is proportional to atomic number. Growth or dissolution of the high-contrast mineral phase can thus be quantified.
Here we use in-situ STEM techniques to directly observe the behavior of iron oxide nanoparticles with different surface chemistries in organic and aqueous solutions. By quantifying the kinetics of mineral phase transformations we are able to determine the influence of different organic species. In many cases, aqueous iron oxide nanoparticles dissolve even under relatively low dose conditions of <1 e-/Å2s. However certain surface functionalizations, for example poly-cationic peptide promotes growth at the Fe3O4 surface. Under some conditions the growth and dissolution reactions are reversible. Similar phase transformations also occur in aqueous suspensions of α-FeOOH, where addition of organic molecules alters particle surface energies and template recrystallization. Colloidal stability depends strongly on surface chemistry and local solution conditions, while bulk indicators of stability such as zeta potential may not predict all behavior of individual nanoparticles. For systems that depend on dynamic nanoscale phenomena, in-situ TEM characterization is therefore an important complement to conventional analyses. With increasingly widespread application, in-situ methods will enable direct visualization at unprecedented length and time scales in materials science and beyond.
This work was supported by the Chemical Imaging Initiative, a LDRD program at PNNL. PNNL is operated by Battelle for DOE under Contract DE-AC05-76RL01830. A portion of the research was performed using EMSL, a US DOE national scientific user facility sponsored by the DOE’s Office of Biological and Environmental Research and located at PNNL. The nanoparticle synthesis and functionalization was also supported NIH 1R01EB013689-01/NIBIB, 1R41EB013520-01, 1R42EB013520-01.
3:30 PM - CM4.2.04
Understanding Interaction of Anode Materials in Lithium Ion Batteries through In Situ Transmission Electron Microscopy
Hyun-Wook Lee 1 , Yi Cui 2
1 , Ulsan National Institute of Science and Technology, Ulsan Korea (the Republic of), 2 , Stanford University, Stanford, California, United States
Show AbstractExtensive research for new energy storage materials has created a high demand for experimental techniques that can provide real-time, single-particle-level information on the dynamic electrochemical processes taking place at the electrode materials during battery charge/discharge cycles. In situ transmission electron microscopy (TEM) on lithium ion batteries has been offered exceptional opportunities for monitoring the dynamic processes of electrode materials during electrochemical reaction at both spatial and temporal resolution.
In this talk, I will introduce in situ TEM studies on Si anodes which suffers the anomalous volumetric changes and fracture during lithiation process. Previously, the lithiation behavior of a single Si particle has been explained in detail by simulation data and experimental observation. However, in real batteries, since lithiation occurs simultaneously in clusters of Si in a confined medium, understanding how the individual Si structures interact during lithiation in a closed space is necessary. In this regard, I demonstrated physical and mechanical interactions of swelling Si structures during lithiation using well-defined Si nanopillar pairs. Ex situ SEM and in situ TEM studies reveal that compressive stresses change the reaction kinetics so that preferential lithiation occurs on free surfaces when the pillars are mechanically clamped. Such mechanical interactions enhance the fracture resistance of lithiated Si by lessening the tensile stress concentrations in Si structures. This experiment reveals the surprising effects of nanostructure shape, size, and void space for lithiation and the results will contribute to improved design of Si structures at the electrode level for high-performance Li-ion batteries.
3:45 PM - CM4.2.05
Imaging Gas Bubble Evolution During Water Heating and Electrolysis with High-Speed Transmission Electron Microscopy
John Vance 1 , Shen Dillon 1
1 Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Show AbstractGas bubbles are of significance in a great range of physicochemical processes occurring in liquid systems. Mesoscale bubbles extant at solid-liquid interfaces mediate phenomena as diverse as boiling, capillary bridging, and electrolytic gas evolution. By reducing active area, adsorbed gas bubbles limit heat flux during boiling and induce polarization losses in electrolytic reactions. Understanding such behavior is key to designing interfaces and systems for desired performance. Previous work on nanobubbles has generally employed techniques unsuitable for probing dynamic behavior at relevant length and time scales. Here we apply high frame rate (400-1600 frames/sec) direct electron detection to liquid cell transmission electron microscopy to probe gas bubble evolution and stability in situ. Two prototype systems, water heating and electrolytic generation of hydrogen gas in aqueous electrolyte were investigated. In the former, gas-vapor bubbles were produced with a metal wire heater, and hydrogen gas was generated on a Pt film electrode in the latter. Bubble nucleation, growth, interfacial detachment, migration, and ripening were observed and characterized. Thermodynamic and kinetic data are extracted by modeling bubble systems in mechanical quasi-equilibrium. Effects of chemical potential gradients, momentum transfer, and interfacial energies (vapor-liquid and solid-liquid) on bubble evolution are considered. The results provide new insight into the nature of capillary (Marangoni) effects at interfaces, which drive gas bubble migration at the mesoscale.
4:15 PM - *CM4.2.06
Visualizing Solution Based Nanofabrication Processes
Utkur Mirsaidov 1
1 , National University of Singapore, Singapore Singapore
Show AbstractUnderstanding how nanoscale materials and structures are formed via solution based processes requires that we capture their formation pathways as these processes take place.
Using dynamic in situ TEM imaging [1-4] in liquids, we will show how nanoparticles form in solution and how these nanoparticles interact with each other. First, I will discuss how phase separation of a solution containing Au ions into solute-rich and solute-poor phases leads to formation of Au nanocrystal through a pathway that does not follow classical nucleation theory (CNT) [5]. Namely, I will show that there are multiple steps that lead to formation of nuclei from which nanocrystal grow. These steps are: 1) phase separation of liquid solution into solute-poor and solute-rich phases, from which 2) an amorphous nanoparticles which serve as a precursor for nuclei, emerge. This is followed by 3) crystallization of amorphous nanoparticles into a crystalline nuclei.
Next, I will show multiple routes for self-assembly of nanoparticles into nanostructures [6-8]. We will describe the types of chemical and physical interactions and their effect on assembly dynamics. Specifically, I will describe the role of hydration, vdW, hydrogen bonding and capillary forces on guiding the self-assembly of nanoparticles.
Finally, I will describe our work where we track the nanoscale dynamics of wet-etch processes to shape nanomaterials.
Our findings highlight the importance of understanding the intermediate stages in physical and chemical processes used in bottom-up and top-down fabrication processes.
References:
[1] M. J. Williamson, R. M. Tromp, P. M. Vereecken, R. Hull, F. M. Ross, Nature Materials 2 (2003), p. 532.
[2] H. Zheng, R. Smith, Y. Jun, C. Kisielowski, U. Dahmen, A. P. Alavisatos, Science 324 (2009), p. 1309.
[3] N. de Jonge, D. B. Peckys, G. J. Kremers and D. W. Piston, Proc. Natl. Acad. Sci. U.S.A., 106 (2009), p.2159
[4] U. Mirsaidov, H. Zheng, D. Bhattacharya, Y. Casana, P. Matsudaira, Proc. Natl. Acad. Sci. U.S.A. 109 (2012), p. 7187.
[5] N. D. Loh, S. Sen, M. Bosman, S. F. Tan, J. Zhong, C. Nijhuis, P. Kral, P. Matsudaira, and U. Mirsaidov, "Multi-step Nucleation of Nanocrystals." Nature Chemistry (2016) doi:10.1038/nchem.2618
[6] U. Anand, J. Lu, N. D Loh, Z. Aabdin, U. Mirsaidov, Nano Lett. 16 (2016), p. 786.
[7] G. Lin, S. W. Chee , S. Raj, P. Kral, and U. Mirsaidov, "Linker-mediated Self-assembly Dynamics of Charged Nanoparticles." ACS Nano 10(8) (2016), p. 7443.
[8] G. Lin, X Zhu, U. Anand, Q. Liu, J. Lu, Z. Aabdin, H. Su, U. Mirsaidov, Nano Lett. 16 (2016), p. 1092.
[9] This work was supported by the Singapore National Research Foundation’s Competitive research program funding (NRF-CRP16-2015-05), and NUS Young Investigator Award.
4:45 PM - CM4.2.07
Exploring Metal Oxide Nanostructure Synthesis Mechanisms Using In Situ TEM
Lei Yu 1 , Ruixin Han 1 , Honore Djieutedjeu 1 , Amita Patel 1 , Beth Guiton 1
1 , University of Kentucky, Lexington, Kentucky, United States
Show AbstractMetal oxides are of interest for their applications as electrocatalysts, gas sensors, diodes, solar cells and LIBs. Nano-sized metal oxides are especially desirable since they have larger surface-to-volume ratios advantageous for catalytic properties, and can display size- and shape-dependent properties such as magnetism. Researchers have been investigating the synthesis of various complex metal oxides with different nanostructured morphologies, such as nanoparticles, nanowires, nanotubes and core-shell structures, for use as functional materials. Controlling size and shape still poses a technological challenge, however, for ternary and more complex metal oxides. In order to understand the formation mechanisms of nano-sized metal oxides and their resulting functionalities, we used in situ TEM to observe the reaction directly as it progresses in real time, in combination with ex situ application measurements such as magnetic and electrochemical property testing. We will present our studies of the structural transformation mechanisms of two reaction types: a conversion reaction and a decomposition reaction. In the conversion reaction, we observed the reaction of an individual binary oxide nanowire with a secondary metal source to form a single-crystalline ternary metal oxide nanowire, in which the anisotropic morphology is maintained during conversion from a pyrolusite to spinel crystal structure. In the decomposition reaction, single-crystalline FeOOH nanorods and nanowires form hollow Fe2O3 structures in which the outer morphology is again maintained.
5:00 PM - CM4.2.08
Experimental Design for In Situ Measurements in a Liquid Electrochemical TEM Holder Cell
Stephen Maldonado 1 , Eli Fahrenkrug 1 , Daan Hein Alsem 2 , Norman Salmon 2
1 , University of Michigan, Ann Arbor, Michigan, United States, 2 , Hummingbird Scientific, Lacey, Washington, United States
Show AbstractBesides beam-liquid interactions, potential electrical measurement artifacts in hybrid electrochemical-TEM experiments can arise from three distinct sources. (1) Electrochemical TEM experiments involve measurements with coupled instrumentation, each with (possibly) different definitions of ground, introducing the possibility of ground loops. (2) The actual area of the electrodes exposed to solution can be very different from the area probed by the e- beam. (3) Absorption of the e- beam of the TEM by an electrode could change the average density of transferrable electrons in the material and thereby alter its measured potential.
This presentation highlights data that describe the extent that these three aspects have on the accuracy and precision of current and potential measurements performed in liquid cell electrochemical TEM experiments. First, the specific design features of potentiostats most relevant to in-situ TEM measurements and the various methods of grounding are detailed. Second, the influence that absorption of the electron beam by different parts of the cell has on the measured potential is described. Third, the dependence that the area of the electrode wetted by the electrolyte is discussed. The cumulative findings identify technical considerations relevant to electrochemical measurements inside a TEM and general design criteria that mitigate spurious potential measurements inside a TEM. These results also serve as the basis for studies aimed at directly studying crystal growth phenomenon in electrodeposition experiments. Preliminary data on the direct electrodeposition of crystalline Ge nanowires in a TEM are presented.
5:15 PM - CM4.2.09
Comment on In Situ (Scanning) Transmission Electron Microscopy Study of Liquid Samples
Nan Jiang 1
1 , Arizona State University, Tempe, Arizona, United States
Show AbstractCurrently, the electron transparent window in a liquid cell for (S)TEM consists of two ultrathin SiNx membranes, which confines a layer of liquid between them [1]. Amorphous SiNx is a good insulator, while the liquids in between usually contain charged ions, which are mobile in solution. This specimen configuration resembles a solid TEM specimen, which is insulating to electrons but conducting to ions. In the solid specimen, beam damage is not only caused by the knock-on or radiolytic processes. Rather, the electron beam can induce electric fields in the specimen, which can be strong enough to displace atoms (or ions), driven by electrostatic forces [2, 3]. Although it is also a key factor in liquid (S)TEM experiments, the current interpretations of beam effects are all based on radiolytic processes in solution; specifically damage initiated by radicals and aqueous electrons. Here, we discuss the possible effects of this induced electric field in liquid cell specimens.
The electric field is induced by the emission of electrons, which cannot be neutralized immediately due to the low electric conductivity of the membranes [2, 3]. For broad-beam TEM illumination, the positive charges distribute in the SiNx windows. For focused-beam STEM illumination, the positive charges mainly concentrate within the probed region [2]. The effects of the induced electric field in liquid cells have two aspects. One is to change the Gibbs free energy of nucleation [4] and the other is to affect the random Brownian atomic diffusion. For a uniform external electric field E, the Gibbs free energy of a small spherical precipitate (containing N atoms) can be simplified as [4]
ΔG=ΔG0+Nc|E|2
△G0 is Gibbs free energy without electric field and c=3εmf(λ)vc/8π is a constant, in which f(λ)=(1-λ)/(2+λ) and λ=εc/εm. Here vc is the average volume of atom, εc and εm are the permittivity of a nucleus and the solution, respectively. It is seen that the △G of nucleation may be reduced if εc > εm, or increased if εc < εm by the electric field. Under the electric field, the conducting ions may drift along the direction of the electric field, which violates the conditions for Brownian motion. Therefore, the observed crystal growth process in a liquid cell specimen may not be the same process of nucleation and growth seen without an electron beam. In conclusion, observations from in situ liquid (S)TEM studies should not be used to support or oppose conventional nucleation and crystal growth theories. Instead, the results should be only interpreted within their own domain of relevance.
[1] N. Jonge and F. M. Ross, Nature Nanotechnology 6 (2011) 695-704.
[2] N. Jiang, J. Phys D: Appl. Phys. 46 (2013) 305502.
[3] N. Jiang, Report on Progress in Physics 79 (2016) 016501.
[4] J. O. Isard, Phil. Mag. 35 (1977) 817-819.
5:30 PM - CM4.2.10
Fabrication of Integrated Liquid Specimen for Transmission Electron Microscopy
Wei Huan Tsai 1 , Jui-Yuan Chen 1 , Chih-Yang Huang 1 , Chia-Fu Chang 1 , Wen-Wei Wu 1
1 , National Chiao Tung University, Hsinchu Taiwan
Show AbstractNowadays, The new development of liquid specimen became an important technique in biomedical engineering, chemical synthesis, and interfacial science, which enables the object to be observed in liquid phase.
However, the present liquid specimen are fabricated by sealing top and bottom chips with epoxy after assembly. The total thickness is large and the large sealed area may result in the leakage.
In this work, we developed a new type of liquid TEM specimen, Integrated liquid specimen, which could overcome the above disadvantages. The integrated liquid specimen was fabricated by one chip without the bonding/sealing process, which declined the leakage issue in the TEM vacuum environment, and it was suitable for all the model of JEOL TEM. Besides, we adopt solution to this specimen to observe the motion and growth mechanism of Au nanoparticles, demonstrating the practicability of Integrated liquid specimen.
This study offers a useful technique for liquid phase observation via TEM and provides the information for understanding the behaviors of nanomaterials.
5:45 PM - CM4.2.11
Formation of Hollow Structures during Galvanic Replacement of Ag Nanocubes by Au Studied with Liquid Cell TEM
See Wee Chee 1 , Shu Fen Tan 1 , Zhaslan Baraissov 1 , Michel Bosman 2 , Utkur Mirsaidov 1
1 , National University of Singapore, Singapore Singapore, 2 , Institute of Materials Research and Engineering, Singapore Singapore
Show AbstractGalvanic replacement (GR) is a simple and versatile way to derive hollow noble metal nanostructures from nanoparticle templates. These hollow structures have possess promising properties for applications that range from catalysis to plasmonics. Here, we use liquid cell transmission electron microscopy to follow the morphological evolution of Ag nanocubes as they undergo galvanic replacement during the introduction of HAuCl4 solutions. These reactions were studied at three temperatures, 22°C, 70°C and 90°C. We observed significant differences in how the nanostructures changed at the three temperatures. At 22°C, the reaction was dominated by etching at the nanocube corners and precipitation of AgCl. At elevated temperatures, the entire nanocube dissolved through outward diffusion of Ag and void propagation through the nanocube. We will further discuss how these in situ observations impact our understanding of the mechanisms involved in galvanic replacement.
This work is supported by the Singapore Ministry of Education Academic Research Fund Tier 2 (MOE2015-T2-1-07).
CM4.3: Poster Session
Session Chairs
Wednesday AM, April 19, 2017
Sheraton, Third Level, Phoenix Ballroom
9:00 PM - CM4.3.01
Nucleation and Growth Analysis of In Situ Electrochemical Deposition of Poly(3,4-ethylenedioxythiophene) (PEDOT)
Vivek Subramanian 1 , Jinglin Liu 3 , Bin Wei 1 , Chin-Chen Kuo 1 , Aniruddha Dutta 1 , David Martin 1 2
1 Materials Science and Engineering, University of Delaware, Newark, Delaware, United States, 3 , Dow Agrosciences LLC, Indianapolis, Indiana, United States, 2 Biomedical Engineering, University of Delaware, Newark, Delaware, United States
Show AbstractOver the past several years, conjugated polymers have been considered for a variety of applications such as neural interfaces, solar cells and antistatic coatings. Poly(3,4-ethylenedioxythiophene) (PEDOT) is especially attractive because of its excellent chemical and mechanical stability. In addition, it has the ability to conduct both electrons and ions and has shown cytological compatibility important for biomedical applications. Techniques like Optical Microscopy, Scanning Electron Microscopy, and Atomic Force Microscopy have been previously used to characterize these materials. However, the detailed dynamics of certain processes during film formation were not yet known. We have used in-situ, liquid-flow, low dose Transmission Electron Microscopy (TEM) to study the dynamics of these processes during electrochemical polymerization of PEDOT. This technique made it possible for us to directly image the nucleation and growth events involved in PEDOT film formation. PEDOT is electrochemically polymerized from an EDOT monomer solution in the TEM sample chamber. The device has a glassy carbon working electrode that is supported on an electron transparent silicon nitride membrane. The electrochemical deposition was carried out at 1.2 V while the electron doses were limited to 0.1-1 mC/cm2. The polymerization, solidification and precipitation of PEDOT were analyzed in detail, including the nucleation and growth of individual clusters. While most of the clusters grew with time, the growth rates were somewhat irregular, and individual clusters could also decrease in size. This analysis provides new insights about the local mechanism of the nucleation and growth of PEDOT clusters and the effect of changing dopants or introducing a gel matrix.
9:00 PM - CM4.3.02
Transmission Electron Microscope Beam-Induced Delithiation of Lithiated Metal Silicate
Frederic Voisard 1 , Bin Wei 1 , Michel Trudeau 2 , George Demopoulos 1 , Raynald Gauvin 1
1 Mining and Materials Engineering, McGill University, Montreal, Quebec, Canada, 2 , IREQ, Varennes, Quebec, Canada
Show AbstractLithiated metal orthosilicates, Li2FeSiO4 (LFS) and Li2MnSiO4 (LMS) are seen as potential candidates for the future generation of rechargeable batteries, due to these materials high theoretical power density. In order to understand if the litihiation-delitihiation cycles will affect these materials, electron energy loss spectroscopy (EELS) is used to measure the presence of lithium in a sample. Experiments with this material in both scanning electron microscope and transmission electron microscope has shown that the lithiated metal silicates undergoes a strong phase change during observation. EDS (X-Ray energy dispersive) analysis shows that the metal, oxygen and silicon remain in the sample after electron beam analysis. However, the element of interest for batteries, lithium, with an ionization energy of 55 eV, is not detectable with the vast majority of commercially available EDS detector. The ionization energy of lithium of 55 eV is detectable by electron energy loss spectroscopy. The other elements in lithiated metal orthosilicates have sub-keV ionization edges at 99 eV for silicon, 532 eV for oxygen, 640 eV for manganese, and 708 eV for iron. All of these edges are in energy ranges favorable to EELS analysis. However, both iron and manganese also have their M-edges at 54 and 49 eV, respectively. Because of the proximity of these edges to that of lithium, the quantitative analysis of lithium in lithiated metal orthosilicates is non-trivial. However, the shape of the metal and lithium edges are very different. Therefore, the analysis of the near edge structures allows the identification of lithium within the tail of iron and manganese M-lines.
In this work, a 300 keV scanning transmission electron microscope (STEM) is used to repeatedly probe the same area on a sample and record time-resolved EELS spectra. The microscope used for these experiments is a 300 keV Hitachi HF-3300 S-TEM equipped with a GIF Quantum ER spectrometer.
The analysis the fine structure of the lithium K and metal M edges shows that the electron microscope induces a delithiation in the lithiated metal orthosilicates. In both LFS and LMS, the initial fine structure of the metal-lithium edge is composed of the metal M edge, a single peak on the ionization edge and the lithium edge, which is characterized by multiple peaks, the number, location and shape of which are dependent on the local chemical bonding of the lithium atoms. The strength of the signal associated with the lithium decreases with exposure time, indicating a loss of lithium. Chemical information of the iron and manganese atoms, however, is mostly present in the L edges of these atoms. A gradual shift of the L3 line is seen in LFS during exposure of the sample to the electron beam.
The loss of lithium and change of oxidation state of the metal elements indicates that the particle undergoes beam-induced delithiation and that the chemical process is similar to that of cycling a battery.
9:00 PM - CM4.3.03
In Situ Observation of High Temperature CO2 Capture over Eutectic Mixture Promoted Magnesia-Based Composites
Soonha Hwang 1 , Hyeongbin Jeon 1 , Jeong Gil Seo 1
1 Energy Science and Technology, Myongi University, Yongin Korea (the Republic of)
Show AbstractEutectic mixture (EM) promoted MgO has been proposed as promising solid sorbent due to its high CO2 capacity at high temperature. The chemistry behind this has recently been revealed that EM might be able to facilitate sorption-mediated carbonation due to its strong solvation effect. However, direct observation for the CO2 sorption mechanism with EM-MgO cannot been proceeded easily due to structural deformation of sorbent in the sorption-regeneration process. In the cyclic process, CO2 capacity of EM-MgO decreased drastically. In addition to that, too strong solvation of the sorbent resulted in agglomerates, blocking surface rapidly during sorption-regeneration. For that reason, EM promoted MgO-Al2O3 composites were synthesized using magnesium acetate and aluminium tetra butoxide as precursors in ethanol solution. The sorbent which was thoroughly dispersed and coated with Al2O3 as support was observed during balance stability and cycling performance of CO2 under sorption-regeneration process. In order to explain this phenomena more clearly, direct observation was performed using in situ transmission electron microscopy (TEM). In this study, triacetylcellulose (TAC) coated carbon film which was attached on 7 hole grids is used to endure over 70 mbar in the holder. Also, EM promoted MgO-Al2O3 sorbent was analyzed by in-situ TEM with respect to the interfacial transformation by CO2 sorption and regeneration at high temperature (> 400oC). The morphological and crystallogrophical changes will be discussed in detail in comparison to EM-MgO sorbent. This work was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning (NRF-2016R1C1B2008694).
9:00 PM - CM4.3.04
Solid Phase Crystallization of High Mobility Transparent Conducting Oxide
Sebastian Husein 1 , Laura Ding 1 , Martial Duchamp 2 , Michael Stuckelberger 1 , Mariana Bertoni 1
1 , Arizona State University, Tempe, Arizona, United States, 2 School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798 Singapore
Show AbstractTransparent conducting oxides (TCO) are a crucial layer offering both optical transparency and electrical transport for a broad range of opto-electronic devices, including LEDs, LCD displays, photovoltaics, and electrochromic windows. The state-of-the-art TCO most widespread in industry, indium tin oxide (ITO), is characterized by high carrier density (N) (~1021 cm-3) and mobilities (µ ) (~40 cm2/Vs) to achieve acceptable resistivities (1-2 x 10-4 Ω-cm). Minimization of power loss requires lower resistivity of the TCO layer. However, for devices requiring an electrode with high red to near-infrared (nIR) transparency, N cannot be increased to reduce resistivity, as this increases free carrier absorption and parasitic light absorption. Moreover, changes to thickness to enable lower sheet resistance cannot be tolerated due to antireflection requirements in some devices, such as photovoltaic cells. Therefore, in order to improve conductivity without impacting optical transparency, many efforts are driven toward development of high-mobility TCOs.
Introduction of hydrogen during deposition, rather than tin, yields hydrogenated indium oxide (IO:H). IO:H offers a 3-fold improvement in µ at far lower N than ITO: µIOH ~ 130 cm2/Vs at N ~1020 cm-3, resulting in similar resistivity with much improved nIR transparency. While these astounding mobilities are readily repeatable (RF magnetron sputtering [1], atomic layer deposition [2]), the underlying cause of µ increase is not fully understood.
One crucial aspect in obtaining IO:H thin films with high µ is the solid-phase crystallization by mild-temperature annealing post-deposition. Prior studies have focused on structural characterization of the material before and after annealing, but little is known about the process itself and its dependency on hydrogen content.
Here we characterize the solid-phase crystallization of IO:H in-situ utilizing transmission electron microscopy (TEM) on RF magnetron sputtered films optimized for high mobility. We compare resulting select area electron diffraction (SAED) and high resolution TEM with ex-situ x-ray diffraction (XRD) on a series of films having increasing hydrogen content to reveal the evolution of the crystallographic structure of these films. We investigate the influence of hydrogen content (measured ex-situ via Rutherford Backscattering) on grain growth, phase changes, and preferred grain orientations.
SAED and XRD reveal two distinct regimes with hydrogen content upon deposition. Samples with low hydrogen content deposit with a large crystalline fraction, while increased hydrogen content results in a more distinct amorphous fraction. Upon annealing, samples which deposit crystalline undergo texturing to a preferred orientation. Samples with an increased amorphous fraction experience grain growth out of the amorphous phase.
[1]: T. Koida et al., Jpn. J. Appl. Phys., Vol. 46, No. 28 (2007)
[2]: B. Macco et al., ACS Appl. Mater. Interfaces 7 (2015)
9:00 PM - CM4.3.05
In Situ Calcination of Palladium Nanoparticles on Delta Alumina versus Ex-Situ Calcination
Siddardha Koneti 1 , Lucian Roiban 1 , Anne-Sophie Gay 2 , Amandine Cabiac 2 , Florent Dalmas 1 , Thierry Epicier 1
1 , MATEIS, INSA de Lyon, Villeurbanne France, 2 , IFP Energies Nouvelles, Solaize France
Show AbstractSustainable chemistry, reduction of pollution, greenhouse gases control, oil refinery, liquid and solid waste management, are essential societal topics related to what is called Environmental catalysis, a sector which is booming rapidly for the past 10 years. So, developing innovative catalysts is a very important aspect ahead of us. To develop more advanced catalysts, we have to understand the catalysts genesis in all the stages of preparation (impregnation, drying, calcination and reduction of the active phase). Nowadays Environmental Transmission Electron Microscopy (ETEM) enables dynamic studies of the catalytic activity down to the nanometer and even atomic scale.
This contribution shows the dynamic evolution of palladium nanoparticles (NP) supported by alumina during the catalysis preparation process. Here, the calcination step is studied in a FEI TITAN-ETEM microscope operated at 300 kV. A Pd/delta alumina catalyst was investigated at different temperatures and under different gas pressures in order to follow the particles size evolution. Owing to the small size of the Pd NPs in the range of 1-3 nm, we mainly used the STEM-ADF imaging mode. we performed in-situ in order to ascertain the chemical nature of the observed particles. During this work essential measurements were performed systematically on the same areas at different temperatures. Same area observation facilitates to understand the growth behavior and other physical dynamics of nanoparticles. later, the nanoparticles size evolution was quantified and compared with post-mortem TEM observations after ex-situ experiments performed at same temperatures under atmospheric pressure in the course of the catalyst synthesis. This comparison shows that all measurements appear to be consistent except those performed in the bright field TEM imaging mode, where larger particles sizes are obtained, most probably due to irradiation effects which were further evidenced by a high-induced mobility of NPs on their supporting media. This environmental study brings direct in situ information on the transient stages that cannot be followed by post mortem experiments after ex-situ treatment.
9:00 PM - CM4.3.06
In Situ TEM Environmental Cell Optimized for EDS Studies
Marco Cordeiro 2 , Khim Karki 2 , Julio Rodriguez Manzo 1 , Daan Hein Alsem 1 , Norman Salmon 1
2 Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York, United States, 1 , Hummingbird Scientific, Lacey, Washington, United States
Show AbstractIn situ and operando transmission electron microscopy (TEM) have been pointed out as promising experimental avenues towards the understanding of fundamental dynamic processes at the nanoscale in real time [1,2]. Although in situ TEM has provided valuable data, there is a great need for methods and tools that provide greater data acquisition speeds to decrease electron beam induced effects in samples. One of the most challenge techniques during in situ TEM is chemical analysis. Notably, the x-rays energy dispersive spectroscopy (EDS) of dynamical samples in gas or liquid environments, because traditional EDS data acquisition takes relative long times and usually has poor signal-to-noise ratio. However, the advent of new instrumentation such as the super-x EDS detector, which combines four windowless silicon drift detectors symmetrically spaced around the sample plane, has renewed the chemical analysis field with mapping speeds improvements of up to 50 times when compared against traditional EDS Si(Li) systems. Hence, the next needed improvement must come from in situ TEM sample holders that allow the acquisition of reliable EDS data with speeds comparable to those of the dynamics of in situ TEM experiments.
In a TEM environmental cell, the fluid is enclosed in a microchannel between two silicon chips typically separated by 50-500 nm, which have facing silicon nitride electron transparent membranes. For TEM observations the cells are assembled in a sample holder tip with conical entrance and exit openings. In non-optimized standard TEM enclosed environmental cell holders, a substantial amount of the x-rays generated by the interaction between the electron beam and the sample are blocked from reaching the EDS detector by the metal enclosure sealing the liquid cell or the cell geometry. Moreover, the metal enclosure acts like an aperture whose edge can potentially contribute with x-rays increasing the EDS signal’s background.
Here we present a new enclosed environmental cell TEM holder optimized for EDS studies. Specifically, we present results from a liquid cell TEM holder designed to exploit the advantages of the super-x EDS detector in a FEI Talos F200X TEM. An increase in the conical entrance of the metal enclosure at the sample holder’s tip increases the solid angle that the x-rays can access markedly, effectively increasing the EDS signal-to-noise ratio for this specific experimental setup, when compare with traditional environmental cell TEM holders. This new tool provides opportunities for in situ TEM studies that capture both the structure and chemistry of a sample in liquid/gas state in real time.
[1] P. A. Crozier, et al. MRS Bulletin 2015, 40, 38.
[2] P. J. Ferreira, et al. MRS Bulletin 2008, 33, 83.
9:00 PM - CM4.3.07
A Modelling Approach to Determine Gas and Temperature Profiles during Catalytic Reactions in Environmental Transmission Electron Microscopy
Jayse Langdon 1 , Peter Crozier 1
1 , Arizona State University, Tempe, Arizona, United States
Show AbstractThe advent of operando transmission electron microscopy (TEM) has opened up significant potential for the study of catalysis [1-3]. With this technique, a catalyst can be subjected to heat as well as reactive gasses, the gaseous products of the reaction can be measured, and the catalyst surface structure can be imaged all concurrently. In principle, this allows for correlation between the most active surface structures and the conditions which produce them.
However, this kind of quantitative analysis depends on several assumptions. If the gas in the microscope is perfectly homogenous, as in a continuously stirred tank reactor (CSTR), then current measurement techniques sufficiently describe gas composition around the catalyst. However, current techniques (RGA, EELS) are unable to measure composition directly next to the catalyst [2], and thus cannot verify this assumption. The temperature distribution is also not easy to determine. It is generally assumed that modern sample heaters keep catalyst temperature at their set points, and this is corroborated by recent models [4], but no account has yet been made for enthalpies of reaction during catalysis.
In order to improve the quantification of operando TEM, we have used the finite element method to model the differentially pumped reaction cell of the ETEM, to investigate gas and temperature profiles. The model (generated in COMSOL Multiphysics) combines the relevant physics phenomena: the Navier-Stokes equation for gas flow; Maxwell-Stefan equations for gas diffusion; equations for heat transfer by convection, conduction, and radiation; and equations for chemical reaction kinetics, among others. The model has been applied to investigate CO oxidation over a ruthenium catalyst, in a cell geometry relevant to the FEI ETEM systems.
The model has already revealed several interesting phenomena on transport and thermal behavior in the operando ETEM. First, it appears that the low pressure and thus high diffusion lead to good mixing of the gas inside the cell, but that reactant concentrations are still significantly lower in the porous pellet. In addition, the negative heat of reaction leads to a higher temperature in the pellet than is measurable by the heater thermocouple. The presentation will describe the model in detail and give a discussion of the overall findings as they relate to operando ETEM.
[1] Chenna, S. and P.A. Crozier, ACS Catalysis, 2012. 2: p. 2395-2402.
[2] Miller, B. K.; Crozier, P. A. Microsc. Microanal., 2014. 20 (3): p. 815–824.
[3] F. Tao, and P.A. Crozier, Chemical Reviews, 2016. 116 (6): p. 3487-3539.
[4] Mølgaard Mortensen, P. et al, Ultramicroscopy, 2015. 152: p. 1–9.
[5] The support from the National Science Foundation (NSF-CBET 1134464); the MSA Undergraduate Research Scholarship Program; Barrett, the Honors College at ASU; the Gore Funding Grant; and the use of TEMs at the John M. Cowley Center for High Resolution Microscopy at Arizona State University are gratefully acknowledged.
9:00 PM - CM4.3.08
Addressing In Situ TEM Challenges Using Integrated Hardware and Software
Benjamin Miller 1 , Stephen Mick 1
1 , Gatan, Inc., Pleasanton, California, United States
Show AbstractThe prevalence of in-situ TEM has increased dramatically in the past 5 years1. This is an indication of progress toward making in-situ experiments more accessible to researchers and an increased awareness of the value and importance of performing in-situ investigations.
However, there remain significant challenges to acquiring high quality data and gleaning meaningful knowledge from this data. Some of the challenges include, capturing dynamic events, reducing beam damage and sample drift, aggregating and organizing in-situ data, accurately reproducing ex-situ conditions, accurately measuring in-situ conditions, determining the effect of the electron beam, and observing a representative sample. Specific issues underlying these challenges range from straightforward technical difficulties, to pervasive problems, for which comprehensive solutions are not currently known.
Nevertheless, some issues within several of the in-situ challenges indicated above have been jointly addressed by Gatan and DENSsolutions recently. Specifically, the high frame rate, large field of view, and lookback capability of the Gatan OneView camera are enabling researchers to capture dynamic events. This is demonstrated by a video sequence with a field of view of over 27000 nm2 in which lattice fringes of just 0.2 nm are clearly resolved and a particle transforms over the course of 10.9 s, with 272 frames recording this transformation. In addition, the excellent stability of the DENSsolutions MEMS-based Wildfire heating holder significantly reduces undesired sample drift, as demonstrated by a video acquired at 1100°C in which the sample moves just 1.6 nm during the 39 seconds recorded. Recent Digital Micrograph integration of the DENSsolutions Wildfire holder with image data from the Gatan OneView camera has simplified aggregation and organization of this data significantly, as can be seen in unprocessed screenshots of an in-situ acquisition of a reversible phase transformation observed while oscillating the temperature using the most recent GMS software. While other challenges remain, these successes demonstrate real progress toward making in-situ techniques more accessible.
References:
1. Koh, A. L., Lee, S. C. & Sinclair, R. in Controlled Atmosphere Transmission Electron Microscopy (eds. Hansen, T. W. & Wagner, J. B.) 3–43 (Springer International Publishing, 2016).
9:00 PM - CM4.3.09
Characterizing the Effects of Grain Size on Electron Beam Induced Artifacts during In Situ TEM Deformation of Al Films
Rohit Sarkar 1 , Jagannathan Rajagopalan 1
1 , Arizona State University, Tempe, Arizona, United States
Show AbstractThe TEM electron beam (e-beam) is known to cause radiation damage to nanostructured specimen during in situ experiments. It has been previously shown that at low e-beam intensities, the most prominent damage mechanism in nanocrystalline thin films during in situ straining is stress relaxation brought about by the depinning of dislocations. This is caused by inelastic scattering of the e-beam at crystal defects like grain boundaries which create local lattice vibrations or phonons. These phonons lead to increased dislocation mobility causing a relaxation in stress. To further study this behavior and analyze the effects of grain boundary area on such inelastic scattering event mediated stress relaxations, we fabricated Al films with identical thicknesses and textures but varying grain sizes. Systematic experiments were then carried out to quantify the effects of grain boundary area on the e beam induced artifacts during in situ straining.
250 nm thick Al films were deposited on Si substrates by magnetron sputtering. MEMS based tensile testing stages were subsequently co-fabricated with the freestanding thin film specimens to carry out in situ TEM straining. Each device containing the thin film specimen was subjected to annealing at varying temperatures to induced controlled grain growth. Films with increasing grain sizes were then subjected to in situ TEM stress-relaxations experiments. In these experiments, the specimens were exposed to an e- beam of identical intensity and area for an equal period of time at two points during loading. The percentage drop in stress was measured to quantify the effect of the e-beam on the mechanical behavior of films with different grain sizes.
9:00 PM - CM4.3.10
In Situ Observation of Au Nanoparticles Nucleation and Growth on Ultrathin MoS2 Substrate
Boao Song 1 , Kun He 1 , Yifei Yuan 2 1 , Soroosh Sharifi-Asl 1 , Meng Cheng 1 , Jun Lu 2 , Wissam Saidi 3 , Reza Shahbazian-Yassar 1
1 , University of Illinois at Chicago, Chicago, Illinois, United States, 2 Chemical Science and Engineering Division, Argonne National Laboratory, Lemont, Illinois, United States, 3 Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
Show AbstractTwo-dimensional substrates decorated with metal nanoparticles offer new opportunities to achieve high performance catalytic behaviors. However, little is known on how such substrates control the nucleation and growth processes of nanoparticles. This paper presents a direct observation of gold nanoparticles nucleation and growth on ultrathin MoS2 nanoflakes by in situ liquid-cell transmission electron microscopy. Our findings demonstrate that the size and orientation of gold nanoparticles depends on the nucleation sites. In general, the nanoparticles forming on the interior of MoS2 nanoflakes have smaller size than the ones along MoS2 edge. In addition, the nanoparticles formed on MoS2 interior maintain {111} orientations, while the nanoparticles on the MoS2 edge exhibit other orientations. Density functional theory calculations show that this difference is because exposed molybdenum atoms at the edge with dangling bonds can strongly interact with gold atoms despite the inert nature of gold, while as sulfur atoms on MoS2 interior have no dangling bonds and weakly interact with gold atoms. The present results facilitate the design of two-dimensional materials substrates where the mismatch strain can be used to control the nanoparticles size and orientation during nucleation and growth processes.
9:00 PM - CM4.3.11
In Situ Crystallization of YIG Thin Films on Non-Garnet Substrates
Thomas Gage 1 , Bethanie Stadler 1 , David Flannigan 1
1 , University of Minnesota, Minneapolis, Minnesota, United States
Show AbstractThe amorphous to crystalline phase transition of yttrium iron garnet (YIG) on non-garnet substrates is investigated using transmission electron microscopy (TEM) and in situ annealing techniques. The ability to crystallize high quality YIG films directly on non-garnet substrates is of high current interest to the photonics and spintronics communities because of YIG’s use in faraday rotating devices and low magnon damping coefficient. While high quality YIG can be grown on garnet substrates, this limits device design and application of new technologies where integration with silicon technology is needed. Current research in the field of annealing YIG thin films on non-garnet substrates shows the process often leads to incomplete crystallization or unwanted phases, hampering device functionality. Understanding the crystallization process of YIG on non-garnet substrates will allow for better control of crystal growth and phase purity, leading to better device performance.
Two in situ annealing techniques are employed in this study. An in situ heating holder is used to control the temperature of the entire specimen and provide information about film crystallization behavior at specific temperatures during the crystallization process, while an in situ laser anneal is used to provide information about higher temperature regimes as well as the effect of high spatiotemporal temperature gradients. Bright-field TEM shows crystallization front velocities of 280 nm/sec as well as the nucleation and growth mechanisms of the film. From the in situ heating holder annealing of the film, crystallization kinetics such as the Avrami constants and specific phase evolution are determined. High electron fluence during annealing is shown to disrupt the crystallization process, preventing formation of the garnet crystal structure.
9:00 PM - CM4.3.12
In Situ EBSD Investigation of Cold Rolling Reduction Effect on Microstructure and Texture Evolution during Recrystallization of Commercial Pure Aluminum Alloy
Khaled Adam 1 , David Field 1 , Mohammed Anazi 1
1 Mechanical and Materials Engineering , WSU, Pullman, Washington, United States
Show AbstractAn investigation of annealing behavior is important from an industrial standpoint, since restoration processes may be necessary to make a balance between high strength and better ductility in metals. In the present work, the evolved microstructure and texture of recrystallization in high purity aluminum under different cold rolled reductions of 20–70% were studied by in-situ EBSD heating stage. Furthermore, the effects of microstructural and orientational changes that occur during recovery determine the recrystallization behavior in terms of the evolved structure. Texture evolution is also taken into account in this investigation.
9:00 PM - CM4.3.13
In situ TEM Visualization of Superior Nanomechanical Flexibility of an Individual Hydroxyapatite Nanobelt
Meili Qi 1
1 , University of Illinois at Chicago, Chicago, Illinois, United States
Show AbstractRecently discovered hydroxyapatite (HA) fibers with improved biomechanical and biological properties hold great promise for biomedical applications. The way to describe the flexible behavior of HA fibers is mainly through the bent morphology and static microstructures，or based on macroscopic tensile testing for bulk measurements. Experimentally identifying and characterizing the nanomechanical properties of a single HA fiber are rather challenging but potentially rewarding. Here, for the first time, we visualize the nanomechanical compressive responses of individual HA nanobelt and nanorod using in situ transmission electron microscopy. We demonstrate that the HA nanobelt offers high mechanical flexibility than the nanorod. In situ bending induced deformations in the nanobelt can spontaneously return to its original shape after severe deformations of approximately 180°. However, the HA nanorod fractures at the first cycle of the bending test with a maximum strain value of 7.2%. High surface area-to-volume ratios and multi-layered structures in HA nanobelt makes dislocation slip in this bioceramic material available and contributes to the stress distribution during bending. We will provide several images and interesting videos if possible, to show the bending and fracture processed of the nanobelt and nanorod, respectively. This study provides important insights into the design of HA nanobelt/nanowire reinforcements for biomedical applications as well as the mechanical behavior of ceramic materials at the nanoscale.
Symposium Organizers
Haimei Zheng, Lawrence Berkeley National Laboratory
Dongsheng Li, Pacific Northwest National Laboratory
Judith Yang, University of Pittsburgh
Henry Zandbergen, Delft University of Technology
Yimei Zhu, Brookhaven National Laboratory
Symposium Support
Direct Electron, LP
Henan University
Hitachi
CM4.4: Gas Environmental TEM and Imaging of Beam Sensitive Materials
Session Chairs
Wednesday AM, April 19, 2017
PCC North, 100 Level, Room 127 B
9:30 AM - *CM4.4.01
In Situ Environmental TEM of Carbon Nanotube Oxidation, Molybdenum Sulphide Hydrogenation and the Influence of an Imaging Electron Beam
Robert Sinclair 1 , Sangchul Lee 1 , Ai Leen Koh 1
1 , Stanford University, Stanford, California, United States
Show AbstractOur recent environmental transmission electron microscopy (ETEM) work concerns basic oxidation and hydrogenation reactions. The oxidation of carbon nanotubes (CNT) is important as this is the process whereby field-emitting CNTs (their major application) dissipate over time in a non-ideal vacuum. We have shown that the natural oxidation mechanism (attack of the outer CNT walls) in molecular oxygen is significantly altered when the oxygen is ionized by the TEM imaging electron beam [1], resulting in oxidation of the CNT caps preferentially. This occurs also when the CNTs are field emitting, as demonstrated by in situ observations. Likewise exposure of amorphous molybdenum sulphide in a hydrogen environment in the ETEM results in its reduction at room temperature, which does not take place until the material is heated when the beam is blanked [2]. Accordingly, quantification of, and attention to, the influence of the electron beam is critical to performing reproducible observations in the ETEM.
10:00 AM - CM4.4.02
The Role of Graphene in Mitigating Electron Beam-Induced Damage in Liquid Phase Electron Microscopy Investigated Using DNA-AuNP Conjugates
Hoduk Cho 1 , Matthew Jones 1 , Son Nguyen 1 , Matthew Hauwiller 1 , Alex Zettl 1 , A. Paul Alivisatos 1
1 , University of California, Berkeley, Berkeley, California, United States
Show AbstractUse of liquid phase transmission electron microscopy (TEM) for biological applications has been limited by the specimen’s vulnerability to radiation-induced damage. The strongly ionizing electron beam is known to induce radiolysis of water, leading to formation of reactive radical species which are highly damaging to biological specimens. Here, we show that graphene can play a protective role in reducing radiation damage to sensitive samples using DNA-AuNP conjugates as a model system. In this study, we observed that DNA-AuNP conjugates can be imaged in their native aqueous environment when encapsulated in graphene liquid cells but not in silicon nitride liquid cells. In the latter, initial dissociation of DNA-assembled nanoparticles was observed, followed by their random aggregation and etching. We carried out a correlative Raman spectroscopy and liquid phase TEM study to analyze the state of graphene before and after exposure to the electron beam and confirmed that graphene is reacting with water radiolysis products. We conclude that the observed protective effect is attributable to graphene’s ability to efficiently scavenge radical products of water radiolysis, including hydroxyl radicals which are known to cause DNA strand breaks. Our study shows that we can reduce radiation-induced damage in silicon nitride liquid cells by incorporating graphene as a biocompatible radical scavenger for investigating biological phenomena at the nanoscale.
10:15 AM - CM4.4.03
The Low-Energy Electron Beam Does Not Damage Carbon Nanomaterials
Jae Hong Choi 1 , Chang Young Lee 1
1 , Ulsan National Institute of Science and Technology (UNIST), Ulsan Korea (the Republic of)
Show AbstractScanning electron microscopy (SEM) is a principal tool for studying nanomaterials, including carbon nanotubes and graphene. Imaging carbon nanomaterials by SEM, however, increases the disorder mode (D-mode) in their Raman spectra. Early studies, which relied on ambiguous ensemble measurements, claimed that the D-mode indicates damage to the specimens by the low-energy electron beam (e-beam). This claim has been accepted by the nanomaterials community for more than a decade without thorough examination. Here we demonstrate that a low-energy e-beam does not damage carbon nanomaterials. By performing measurements on single nanotubes, we independently examined the following factors: 1) the e-beam irradiation itself, 2) the e-beam-deposited hydrocarbon, and 3) the amorphous carbon deposited during synthesis of the material. We concluded that the e-beam-induced D-mode of both carbon nanotubes and graphene originates solely from the irradiated amorphous carbon and not from the e-beam itself or the hydrocarbon. The results of this study should help minimize potential ambiguities for researchers imaging a broad range of nanomaterials by electron microscopy.
10:30 AM - *CM4.4.04
Imaging Beam-Sensitive Nanostructures by Transmission Electron Microscopy
Yihan Zhu 1 , Jim Ciston 2 , Ming Pan 3 , Yu Han 1
1 , KAUST, Thuwal Saudi Arabia, 2 , Lawrence Berkeley National Laboratory, Berkeley, California, United States, 3 , Gatan, Inc., Pleasanton, California, United States
Show AbstractTransmission electron microscopy is a powerful tool studying not only periodic structures but also local and nano-sized structural features, such as defects, surface terminations, interfaces and disorder, which are, from an application perspective, equally important as the crystallographic structure and can dominate the overall properties of the materials. Imaging beam-sensitive nanostructures is more challenging but especially important.
As an example, we report the direct imaging of ultrathin Au nanowires (NWs) with an atomic packing mode that is close representation of the Boerdijk-Coxeter-Bernal (BCB) tetrahelix, where the Au atoms are densely packed, forming a linear stack of regular tetrahedra as an overall chiral structure. This is an excellent example of a chiral structure made of totally symmetrical gold atoms, created in nanowires by direct chemical synthesis. Detailed study by high-resolution electron microscopy illustrates their elegant chiral structure constructed by multiple twinning of consecutive tetrahedral domains, fragmentary tetrahedra defects that effectively smooth the surface and the unique one-dimensional “pseudo-periodicity”. These observations demonstrate the chiral atomic packing mode is formed as a result of the competition and compromise between the lattice and surface energy. The BCB Au NWs are vulnerable to electron beam irradiation, which is more remarkable under low voltage due to the more pronounced ionization effect that damage the surface ligands. Combining in situ electron microscopy with theoretical simulations, we show that the surface ligands play a key role in stabilizing the unusual Au NWs. Such a structure demonstrates the feasibility of chirality in densely packed non-alloy NWs, and represents a good example where the interplay of fundamental interactions leads to exotic structures at the nanoscale.
CM4.5: Gas Environmental TEM and Catalysis
Session Chairs
Wednesday PM, April 19, 2017
PCC North, 100 Level, Room 127 B
11:30 AM - *CM4.5.01
Heat, Light and Electric Field Stimuli in the Environmental TEM
Peter Crozier 1
1 , Arizona State University, Tempe, Arizona, United States
Show AbstractIn situ electron microscopy experiments conducted in the environmental transmission electron microscope (ETEM) allow gas-solid interactions to be explored with potential impacts in fields such as catalysis [1]. The range of stimuli available in the ETEM continues to grow and we are now performing experiments in gas, heat, light and electric fields. The application of heat and gas allows fundamental structure-reactivity relations in thermal catalytic processes to be explored. By performing simultaneous measurement of the surrounding gas phase with electron energy-loss spectroscopy (EELS), we are able to confirm that gas-phase catalysis is actually taking place and make an estimate of chemical kinetics [2-4]. This operando measurement correlates surface structure with catalysis and allows catalytically irrelevant spectator structures to be identified as we demonstrate in CO oxidation on Ru. To improve the rigor of the reaction kinetics, detailed calculations of the mass and heat transfer processes are currently being carried out to make the operando approach more quantitative. The ability to expose the sample to light and reactive gases allows surface processes in model water splitting photocatalyst to investigate structural evolution under reaction conditions [5]. In addition to imaging, monochromated aloof beam EELS has potential to probe the electronic surface structure of the materials under a variety of different reaction conditions. The advantage of the aloof beam approach is that the electron beam induced effects are dramatically reduced or even eliminated [6,7]. This is particularly important for the investigation of catalytic particles because the surface of materials typically damage and change faster than the bulk. Electroceramics such as CeO2 have interesting catalytic and ionic conduction properties making them interesting to investigate under a variety of gases in the presence of electric fields [8]. With the ability to bias materials we are able to extend our in situ observation to ionics and photoelectrochemical processes.
References
1. F. Tao, and P.A. Crozier, Chemical Reviews, 2016. 116(6): p. 3487-3539.
2. S. Chenna and P.A Crozier, ACS Catal. 2 (2012) 2395.
3. B.K Miller et al, Ultramicroscopy 2015. 156: p. 18-22.
4. Miller, B.K. and P.A. Crozier, Microscopy and Microanalysis, 2014. 20(3): p. 815-824.
5. L. Zhang et al, Nano Letters, 2013. 13(2): p. 679-684.
6. P.A., Crozier et al, Ultramicroscopy, 2016. 169: p. 30-36..
7. Q. Liu et al, Ultramicroscopy (in press), 2016.
8. Bowman, W.J., et al., Solid State Ionics, 2015. 272: p. 9-17.
9. The support from the National Science Foundation (NSF-CBET 1134464, DMR-1308085 CHE-1508667), US Department of Energy (DE-SC0004954) and the use of TEMs at the John M. Cowley Center for High Resolution Microscopy at Arizona State University are gratefully acknowledged.
12:00 PM - *CM4.5.02
Time Resolved Measurements to Reveal Atomic Scale Reaction Pathways Under Non-Equilibrium Conditions
Renu Sharma 1
1 , National Institute of Standards and Technology, Gaithersburg, Maryland, United States
Show AbstractThe interaction of gases with a solid catalyst nanoparticle during catalysis is a non-equilibrium system that requires high spatial and temporal resolution measurements to elucidate underlying mechanisms. State-of-the-art environmental transmission electron microscopy (ETEM) enables in situ measurements of the dynamic changes occurring under reaction conditions These changes usually take place rapidly at the nanometer scale. In order to record them in real time, high image resolutions and frame rates are needed, resulting in large video data sets (≈ GB s-1). Recently, direct electron detection cameras, have enabled us to record atomic resolution images with ms time resolution. To follow the atomic-level changes occurring under reaction conditions over time, the structure and phase of the nanostructure under observation must be analyzed for each individual frame. It is laborious to analyze such large videos frame by frame. An automated image processing scheme (AIPS) is therefore desirable to increase the speed and reliability of the analysis. There are two major inherent problems for such an automated structural analysis: (a) individual frames are noisy due to the short frame acquisition time and (b) the sample drifts during video recording periods that can range from seconds to minutes. In order to overcome these problems, we have developed an automatic method to obtain structural information from the images extracted from videos using a combination of publicly available and NIST-developed algorithms. We have successfully measured the interatomic distances with a precision of 0.07 pm and have used it to measure phase transformation rates in a catalyst nanoparticle during the growth of single-walled carbon nanotube (SWCNT) and reduction of iron oxide nanowires. Videos recorded using two different cameras have been analyzed. Details of the image processing scheme and its application will be presented.
12:30 PM - CM4.5.03
Aberration-Corrected Environmental TEM Investigation of Ag Catalyzed Oxidation of Carbon Nanotubes
Datong Yuchi 1 , Yonghai Yue 3 2 , Jia Xu 1 , Jingyue Liu 3
1 School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, Arizona, United States, 3 Department of Physics, Arizona State University, Tempe, Arizona, United States, 2 School of Chemistry and Environment, Beihang University, Beijing China
Show AbstractThe emissions of soot formed during combustion of carbonaceous fuels is a major source of air pollution. Development of highly efficient oxidation catalysts at low temperatures is crucial to dramatically reduce the emissions of particles into the environment [1]. Metal and metal-based nanoparticles (NPs) have captured broad attention, especially for their potential applications in solving environmental problems. The aberration-corrected environmental transmission electron microscope (AC-ETEM) can be used to probe the nature of metal-catalyzed processes on an atomic scale. Such a fundamental understanding of the catalytic processes can help design better catalysts with improved catalytic performances. We recently conducted detailed investigations on the atomic scale processes of the Ag NP catalyzed oxidation of multi-wall carbon nanotubes (MW-CNTs) [2]. Based on the AC-ETEM study, a mechanism similar to the Mars–van Krevelen process was proposed to understand the Ag NP catalyzed oxidation processes of MW-CNTs: Oxygen molecules first dissociate upon adsorption on the Ag NPs and then the oxygen atoms diffuse through the Ag NP to reach the Ag/MW-CNT interfaces to react with carbon to form CO/CO2. The atomic scale processes of the dynamic evolution of Ag NPs and the MW-CNTS, the effects of the size of the Ag NPs and reaction temperature on the oxidation reaction of the MW-CNTs, and the effect of the gas environment will be discussed [3].
1. Leino, A.; Mohl, M.; Kukkola, J.; Maki-Arvela, P.; Kokkonen, T.; Shchukarev, A.; Kordas, K. Carbon 2013, 57, 99-107.
2. Yue, Y.; Yuchi, D.; Guan, P.; Xu, J.; Guo, L.; Liu, J. Nat Commun. 2016, 7, #12251.
3. This work was supported by the College of Liberal Arts and Sciences of Arizona State University. The authors gratefully acknowledge the use of facilities within the LeRoy Eyring Center for Solid State Science at Arizona State University.
12:45 PM - CM4.5.04
Cathodoluminescence Characteristics of Stacking Faults in Semipolar InGaN/GaN Quantum Wells Structure
Mi-Hyang Sheen 1 , Wi joo Hoang 1 , Sung-Dae Kim 1 , Jongjin Jang 2 , Okhyun Nam 2 , Young-Woon Kim 1
1 , Seoul National University, Seoul Korea (the Republic of), 2 , Korea Polytechnic University, Siheung Korea (the Republic of)
Show AbstractSemi-polar InGaN/GaN multi-quantum well (MQW) system can be a strong candidate to replace the polar MQW system because of its high efficiency originated from low internal electrical field. Growth of semi-polar GaN thin film, however, involves high density of extended defects, i.e. basal plane stacking faults (BSFs), partial dislocations (PDs), prismatic stacking faults (PSFs), and stair-rod dislocations (SRDs), due to low crystal symmetry on the growth plane. Even with the high density of the defects, the MQWs on the semi-polar GaN thin film show remarkable internal quantum efficiency (IQE), compared to the one from c-plane GaN thin film. In this point of view, it is a critical step to identify defect distribution and the influence of them on the QW performance to refine and develop beneficial microstructure for higher efficiency LED design. In this presentation, results from luminescence characteristic of microstructural defects, formed in InGaN/GaN QWs on (11-22) semi-polar GaN thin film will be reported. The semi-polar GaN film was grown on hemisphere-patterned sapphire substrates (HPSS) by metal organic chemical vapor deposition (MOCVD). A home-built cathodoluminescence (CL) stage for transmission electron microscopy (TEM) was used to correlate the luminescence wavelengths and the types of defects with position specific mapping of spectrum. Plan-view and cross-sectional view revealed the formation of faceted QWs, which affected the luminescence characteristics. Dead luminescence of near-band edge peak was observed when the defects cross the QW. In addition, type-1 and type-2 BSFs were clearly identified with their unique luminescence wavelengths and the distribution of the defects were visualized.
This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Ministry of Science, ICT & Future Planning (MSIP) (NO. NRF-2015R1A5A1037627)
CM4.6: In Situ TEM of Nucleation, Growth and Assembly in a Liquid Phase
Session Chairs
See Wee Chee
Haimei Zheng
Wednesday PM, April 19, 2017
PCC North, 100 Level, Room 127 B
2:30 PM - *CM4.6.01
Liquid-Phase TEM Investigations of Nucleation
James De Yoreo 1 , Zhaoming Liu 1 2 , Paul Smeets 3 4 , Mike Nielsen 5 , Nico Sommerdijk 4 , Ruikang Tang 2
1 Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington, United States, 2 Department of Chemistry, Zhejiang University, Zhejiang China, 3 Lawrence Berkeley National Laboratory, Molecular Foundry, Berkeley, California, United States, 4 Laboratory of Materials and Interface Chemistry and Soft Matter CryoTEM Unit, Eindhoven University, Eindhoven Netherlands, 5 Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, California, United States
Show AbstractMany long-standing questions about the mechanisms of nucleation remain unanswered due to a lack of experimental tools that can probe this process with adequate spatial and temporal resolution. In the case of biologically-directed nucleation, understanding the added role of macromolecules poses additional challenges. To address these questions we used liquid phase TEM to investigate nucleation pathways in the CaCO3 system using a dual-inlet fluid stage that allowed us to mix calcium and carbonate reagents. In pure solutions at moderate-to-high supersaturations, we observed both direct formation of amorphous calcium carbonate (ACC), as well as the three predominant crystalline phases: calcite, vaterite, and aragonite, even under conditions where ACC readily forms. In addition, we observed indirect pathways in which ACC precursors transform into crystalline phases that exhibit their typical morphologies. These results are consistent with the classical picture in which the high supersaturation needed to overcome the free energy barrier to formation of the stable calcite phase should open the pathway to all other phases. Addition of small organic additves such as citrate and polyacrylic acid increased ACC lifetimes, but left the basic pathway unchanged. In contrast, addition of Mg, the initial phase that formed at high supersaturation exhibited low electron contrast, which increased over time independent of particle size and absent any change in spheroidal morphology. Diffraction analysis indicated an initial amorphous phase followed by transformation to calcite. IR spectroscopy confirmed an evolution from an amorphous phase to either Mg-rich calcite or monohydrocalcite. Consequently, we hypothesize that, due to its strong hydration state, Mg stabilizes a dense liquid phase, which then dehydrates and transforms over time into a crystalline product. To understand how a macromolecular matrix impacts nucleation, we performed a similar set of experiments in solutions containing the polyelectrolyte polystyrene sulfonate (PSS). In its absence, vaterite formed randomly throughout the cell. When PSS was introduced, it complexed more than half of the Ca2+ ions and formed a globular phase. As carbonate diffused into the cell, ACC appeared instead of vaterite and nucleated only within the globules. Analysis of growth rate data shows that, while PSS stabilizes ACC, it is an inhibitor of its nucleation. The results demonstrate that ion binding can play a significant role in directing nucleation, independent of changes in the free energy barrier to nucleation, which is usually inferred to be the primary factor leading to matrix-controlled nucleation. These results highlight the diverse pathways accessible during nucleation, as well as the opportunity liquid-phase TEM provides to decipher underlying mechanisms.
3:00 PM - CM4.6.02
The Control of pH over Au Nanocrystal Growth—From Classical to Non-Classical Pathways
Yingwen Chen 2 , Jinhui Tao 2 , Guomin Zhu 1 2 , Jennifer Soltis 2 , Maria Sushko 2 , James De Yoreo 1 2 , Jun Liu 2
2 , Pacific Northwest National Laboratory, Richland, Washington, United States, 1 , University of Washington, Richland, Washington, United States
Show AbstractThe process of nucleation and growth of crystals from solution is fundamental to many natural and synthetic systems. The solid-liquid interface is actively involved in both stages, but its role in controlling pathways is poorly understood. This is especially true in the case of nanocrystals, where the surface structure is more complex and challenging to characterize than that of large single crystals due to their high surface curvature and the common use of stabilizing ligands. In this study we use citric acid-coated gold seeds as a model system to study the influence of interfacial properties on nanoparticle growth by utilizing the solution pH as a control variable to tune the speciation and the charge state of the adsorbed, charged solution species. Liquid phase TEM (LP-TEM) was combined with in situ AFM and UV-vis spectroscopy, cryo-TEM and zeta potential measurements to determine the effect of pH of the growth pathway and dynamics. Our results show that at acidic conditions the gold seeds grow continuously by monomer attachment to produce spherical or triangular nanoparticles. However, at near-neutral pH, growth proceeds via nucleation of new nanoparticles almost exclusively on existing seed particles or at the interfaces between these particles and the surrounding solution. Those that nucleate next to the seed particles either undergo local diffusive motion within the interfacial region until they attach to the seeds or close the gap via growth of a neck between the seed and the new particle. This process results in generation of particle clusters that appear to have formed through aggregative processes and often exhibit small protrusions produced by the new nuclei. Finally, in basic solutions, there is almost no growth of existing particles and nucleation of new particles occurs uniformly throughout the solution independent of the existing seeds. A theoretical analysis is presented that explains the observed evolution in growth pathways through competitive absorption of citric and auric anions, producing differences in the driving force for nucleation in the interfacial region relative to the bulk, and accounts for both the promotion of nucleation near the seeds and attachment to the seeds in near-neutral conditions. The abrupt change in the pathway of gold nanoparticle growth and the resulting morphology observed in this study suggests that significant variations in the properties of the solid-liquid interface achieved through simple control parameters like solution pH can be used to direct the synthesis of hierarchical inorganic crystals with potential application to a wide range of materials.
3:15 PM - CM4.6.03
Real Time Liquid Phase TEM Observations of Chain-Like and Rod-Like ZnO Formation via Oriented Attachment
Lili Liu 1 2 , Jharna Chaudhuri 2 , James De Yoreo 1 3
1 Physcial Sciences Division, Pacific Northwest National Laboratory, Richland , Washington, United States, 2 Mechanical Engineering, Texas Tech University, Lubbock, Texas, United States, 3 Department of Materials Science and Engineering, University of Washington , Seattle , Washington, United States
Show AbstractOriented attachment (OA), an important crystal growth mechanism, involves collision of nanocrystals followed by attachment and coalescence with a common crystallographic orientation on planar interfaces to produce lower energy configurations. Up till now, OA has been cited as responsible for particle growth in many systems and for exerting control over the size, shape and morphology of the resulting materials. These systems include oxides, semiconductor compounds, metals and metal alloys, and carbonates. However, controlling crystal morphology via this process is still a tremendous challenge owing, in part, to the complex impact of growth conditions, such as the influence of ions in solution. Zinc oxide (ZnO) is an attractive II-VI compound semiconductor material with a direct band-gap (Eg = 3.37eV) and a large exciton binding energy (60 meV). Owing to their wide application in electronics, photonics and piezoelectric devices, one-dimensional ZnO nanostructures have attracted significant attention. Consequently, an understanding the fundamental mechanisms and controls underlying the process of shape-controlled ZnO crystal growth could have a significant impact on these technologies. There are only a few reports of preparing ZnO nanorods in a controllable manner by solvent evaporation. For example, reflux methods have been used to induce assembly of ZnO nanoparticles into a “chain-of-pearls” architecture in which the lattice planes are well-aligned, and eventually evolve into single crystal nanorods. However, little mechanistic information about the formation process, particularly the nanoscale-to-atomistic dynamics of the OA process has been reported for the ZnO system. Here we report the results of a liquid phase (LP)-TEM investigation aimed at filling these knowledge gaps. We observed the growth of chain-like ZnO from primary particles in both methanol and aqueous solution. In the absence of added Zn salts, even at the lowest electron doses possible, the primary particles underwent dissolution, presumably owing to the effects of electron-beam induced radiolysis on solution speciation. None-the-less, coalesence events did occur, resutling in chain-like ZnO structures with a high degree of crystallographic co-alignement. Addition of Zn2+ions to solution prevented dissolution enabling imaging of both classical nanocrystal growth and oriented attachment, but the concentration requied in the aqueous system was 100 times that need for methanol solutions. In addition, the plane of attachment was not necessarily a low energy face; for example, in at least one instance the attachment direction was 60o off the ZnO c-axis (002). As in past studies, observations of OA and near-OA events provided kinetic data to evaluate the forces driving attachment. The approach reported here overcomes the problem of dissolution common to LP-TEM studies of mineral systems and the results provide insights into the growth of this important oxide semiconductor.
4:30 PM - *CM4.6.04
Colloidal Nanostructures—In Situ Electron Microscopy of Plasmon-Mediated Synthesis, Chemistry and Self-Assembly
Eli Sutter 1
1 , University of Nebraska–Lincoln, Lincoln, Nebraska, United States
Show AbstractIn-situ transmission electron microscopy (TEM) can be used to follow the behavior and measure the properties of nanostructures over a wide range of environmental conditions with resolution down to the atomic scale. Liquid-cell electron microscopy (LCEM), in particular, is the only technique that allows direct imaging of nanometer-scale processes in liquids. It has been successfully applied to imaging various processes in liquids, solutions, and colloidal suspensions that were typically investigated ex-situ on samples taken at different process stages, or in some cases in-situ using reciprocal space techniques.
Here I will demonstrate the power of LCEM to probe complex solution-phase processes in real space, including plasmon-mediated colloidal synthesis of nanostructures, galvanic replacement reactions, and the self-assembly of nanocrystal superstructures in solution. Our results demonstrate that real-time electron microscopy can substantially advance our understanding of a wide range of processes involving nanoscale objects in bulk liquids.
5:00 PM - CM4.6.05
In Situ TEM Observation of New Biomineralization Pathways in Calcium Phosphate Crystals
Kun He 1 , Yifei Yuan 1 2 , Cortino Sukotjo 3 , Reza Shahbazian-Yassar 1 , Tolou Shokuhfar 4 , Boao Song 1
1 The Department of Mechanical & Industrial Engineering , University of Illinois at Chicago, Chicago, Illinois, United States, 2 Chemical Science and Engineering Division, Argonne National Laboratory, Argonne, Illinois, United States, 3 College of Dentistry, University of Illinois at Chicago, Chicago, Illinois, United States, 4 Department of Bioengineering, University of Illinois at Chicago, Chicago, Illinois, United States
Show AbstractThe continuous demineralization and remineralization processes happen on the dental enamel. Once the balance between these two processes is broken, dental erosion or dentine hypersensitivity will be developed. Therefore, elucidation of the biomineralization pathway in vitro will help dentists to find out a more precise strategy to maintain the oral health. In fact, the biomineralization of apatite, the core building block of the enamel, has been studied for decades. Due to resolution limit during observation, however, sub-micron level details of this process are still not clear. Now it is generally accepted that Ca2+ and PO43- ions in aqueous solution first form metastable clusters, like Posner clusters (Ca9(PO4) 6)1, then the ion-dense clusters form amorphous calcium phosphate (ACP), which finally transforms to crystal structure2, 3. To date, the details describing how ACP transforms to crystal phase are still unknown. To answer these questions, real time high-resolution observation is needed to investigation the possible apatite mineralization pathways. Fortunately, in recent years, liquid cell (Scanning) Transmission Electron Microscopy ((S)TEM) has enabled the investigation of such dynamic biological processes. In this research, liquid cell STEM imaging was used to investigate the biomineralization process. A mineral solution is first encapsulated in a liquid cell that is transparent to electron beam. During the observation, particles sized in 10-15 nm are found to nucleate from the solution and then they attach with each other to form a larger loosely bound cluster. In addition, the second pathway, namely the direct nucleation rooted on the ACP sphere, is also captured. For both pathways, the whole processes are captured in real time. Electron Energy Loss Spectroscopy (EELS) and Selected Area Electron Diffraction (SAED) are carried out to identify the chemical composition and crystal structure of the newly formed crystals, where the existence of calcium ions is confirmed. Our results partially disagree with the previously proposed pathway for the crystallization of calcium phosphate, which insists that crystalline phase calcium phosphate is formed via intermediate stages such as metastable ion clusters, amorphous phase, and then the amorphous-crystalline transition. From our research, we propose that, for the crystallization process, both direct nucleation and indirect nucleation pathways for the mineralization process exist. For both pathways, the size of new formed crystal particles is similar (10-15 nm). And no matter via which path the crystal particles are formed, finally, these small particles aggregate to form crystal phase in a larger size (around hundreds of nanometers).
1. Posner, A. S.; Betts, F. 1975, 8, 273-281.
2. Dey, A.; Bomans,et. al. Nature materials 2010, 9, 1010-1014.
3. Pouget, E. M.;et.al. Science 2009, 323, 1455-1458.
5:15 PM - CM4.6.06
Studying Polymer Self-Assembly by Combined Liquid Phase and Cryogenic Transmission Electron Microscopy
Joseph Patterson 1 , Alessandro Ianiro 1 , Mark van Rijt 1 , Catarina Esteves 1 , Remco Tuinier 1 , Nico Sommerdijk 1
1 , Eindhoven University of Technology, Eindhoven Netherlands
Show AbstractLP-EM is an emerging analytical technique for the study of materials formation, but has already begun to revolutionize our understanding of nanocrystal formation. Many experiments have been performed by the electron beam reduction of metal precursors, which initiates nanoparticle formation.[4] This convenient method of synthesis, along with the high convenient of the metal nanoparticles has greatly aided the success of LP-EM in this area. However, the synthesis of most materials is typically performed by controlled solution mixing, which is still a challenge in the liquid cells available for LP-EM experiments. Furthermore, to study the aqueous solution self-assembly of polymers it is necessary to ensure the liquid layer thickness is on the order of the particle thickness, as the electron density of the macromolecular materials is not vastly different from water. Therefore, we must create new experimental set ups for LP-EM which allow thin cells to be created and either create structures without controlled solution mixing, or allow controlled solution mixing to occur inside the cell.
In this paper we will discuss our efforts to perform block copolymer self-assembly using a solvent switch inside the liquid cell. The system we have chosen comprises poly(caprolactone)-b-poly(ethylene oxide) PCL-b-PEO, and a solvent switch from acetone to water, which based on ex-situ cryo-TEM and self-consistent field (SCF) theory should form vesicles upon increasing water content. PCL-b-PEO is a well-studied system, however little is currently known about the dynamics of assembly, or how the assembly route can be effected by changing experimental conditions. Adam et. al. studied the formation of PCL-b-PEO vesicles by scatting and cryo-TEM, [5] showing evidence of the conventionally accepted micelle à cylinder à vesicle formation route. However they also suggested the possibility of a precursor phase, based on turbidity measurements and dynamic light scattering which is characterized as being large and of high dispersity. Here we show direct evidence for the formation of this precursor phase by LP-EM and cryo-TEM, which we characterize as a polymer-rich dense liquid phase. We discuss the role of this precursor phase in the formation of vesicles, and we link this process to our SCF theory calculations.
[1] J. J. De Yoreo & N. A. J. M, Sommerdijk. Nature Reviews Materials, 16035, (2016) doi:10.1038/natrevmats.2016.35.
[2] P. J. Smeets et. al, Nature Materials 14 (2015), p. 394.
[3] M. W. P. van de Put et al, Small 11 (2015), p. 585.
[4] J. P. Patterson, et. al, Perspectives in Science 6 (2016), p. 106.
[5] J. P. Patterson, et. al, Microscopy and Microanalysis 22 (2016) p. 507.
[6] D. J. Adams, et al, Soft Matter 5 (2009), p. 3086.
5:30 PM - CM4.6.07
A Time-Resolved View of Protein Aggregates in Pharmaceutical Formulations Using In Situ Liquid Cell Transmission Electron Microscopy
Madeline Dukes 1 , Lynn Dimemmo 2 , A. Varano 3 , Jonathan Haulenbeek 2 , Yanping Liang 3 , Kaya Patel 3 , Songyan Zheng 2 , Mario Hubert 2 , Steven Piccoli 2 , Deborah Kelly 3
1 , Protochips, Inc., Morrisville, North Carolina, United States, 2 , Bristol-Myers Squibb Company, New Brunswick, New Jersey, United States, 3 , Virginia Tech Carilion Research Institute, Roanoke, Virginia, United States
Show AbstractProtein based therapeutics, such as immunotherapies, are a promising tool in the treatment of disease. Aggregation of a drug's protein components represents a significant challenge when characterizing the efficacy and safety of these pharmaceuticals. Protein aggregates cause reduction in both drug stability and efficacy and can result in an immunogenic effect during drug therapy. In order to understand these effects, direct observation of small proteins or therapeutic agents in a physiologically relevant environment is necessary. In situ transmission electron microscopy (TEM) imaging performed in a liquid environment permits us to observe the dynamics of bio-macromolecules at the nanoscale. The work described here uses in situ TEM to examine a representative drug-conjugate system, PEGylated Interferon α2a, in both its native conformation and aggregate state in a time-resolved manner. Combined with quantitative analyses, this study provides new information for how a model drug-conjugate behaves in solution, including under stress conditions, in association with immune proteins, and under aggregating conditions. These results provide insight for future pharmaceutical development and new characterization methods for protein-based therapeutics.
5:45 PM - CM4.6.08
Probing Ferroelectric/Ferroelastic Nanodomain Structures at Atomic Resolution with In Situ TEM
Yu Deng 1 , Christoph Gammer 4 , Jim Ciston 2 , Peter Ercius 2 , Colin Ophus 2 , Andrew Minor 2 3
1 , Nanjing University, Nanjing China, 4 , Erich Schmid Institute of Materials Science, Leoben Austria, 2 National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 3 Department of Materials Science & Engineering, University of California, Berkeley, California, United States
Show AbstractFerroelectric/Ferroelastic nanodomain structures are attractive due to their applications in ultra-small actuator and memory devices [1-3]. With a quantitative in situ mechanical system in an aberration-corrected transmission electron microscope, we studied the evolution of nanodomain structures in a free-standing single-crystal BaTiO3 sub-micrometer pillars under mechanical loading at atomic resolution, directly measuring the recoverable large local strains at the domain boundaries by a scanning nanobeam diffraction technique [4-5]. Our observations revealed the coexistence of multiple phases and a greatly accelerated mobile-point-defect redistribution behavior in the nanodomain structures. The domain evolution mechanism and the unique properties of the nanodomain structures are also investigated.
ACKNOWLEDGEMENTS
The authors acknowledge support by the Natural Science Foundation of Jiangsu Province, China (Grant No.BK20151382), the Austrian Science Fund (FWF):[J3397] and the Molecular Foundry, Lawrence Berkeley National Laboratory, which is supported by the U.S. Dept. of Energy under Contract # DE-AC02-05CH11231.
REFERENCES
1. G. Catalan, J. Seidel, R. Ramesh, J. F. Scott, Rev. Modern Phys. 84, 119 (2012).
2. J. F. Scott, Science 315, 954 (2007).
3. Y. L. Tang, Y. L. Zhu, X. L. Ma, S. J. Pennycook, et. al. Science 348, 547 (2015).
4. C. Gammer, V. B. Ozdol, C.H. Liebscher, and A.M. Minor, Ultramicroscopy, 155, 1 (2015).
5. V.B. Ozdol, C. Gammer, X.G. Jin, P. Ercius, C. Ophus, J. Ciston, A.M. Minor, Applied Physics Letters, 106, 253107 (2015).
Symposium Organizers
Haimei Zheng, Lawrence Berkeley National Laboratory
Dongsheng Li, Pacific Northwest National Laboratory
Judith Yang, University of Pittsburgh
Henry Zandbergen, Delft University of Technology
Yimei Zhu, Brookhaven National Laboratory
Symposium Support
Direct Electron, LP
Henan University
Hitachi
CM4.7: In Situ TEM of Mechanical Properties
Session Chairs
Thursday AM, April 20, 2017
PCC North, 100 Level, Room 127 B
9:15 AM - CM4.7.01
Quantified In Situ TEM Tensile Test Experiments on Ni Thin Films Prepared by New Optimised Techniques
Vahid Samaeeaghmiyoni 1 , Hosni Idrissi 1 2 , Jonas Groten 3 , Ruth Schwaiger 4 , Dominique Schryvers 1
1 EMAT, Physics, University of Antwerp, Antwerpen Belgium, 2 Institute of Mechanics, Materials and Civil Engineering, Université catholique de Louvain, Louvain-la-Neuve Belgium, 3 , Joanneum Research, Graz Austria, 4 Institute for Applied Materials, Karlsruhe Institute of Technolog, Karlsruhe Germany
Show AbstractOwing to its site selectivity and its micro machining ability, Focused ion beam (FIB) is an almost unique technique to produce small-sized objects for nano/micro mechanical testing. However, the effects of the FIB induced damages on the mechanical behaviour and the plasticity mechanisms cannot be neglected.
The present work focuses on adopting different sample preparation methods in order to improve the in-situ TEM nanomechanical characterizations by minimizing the effect of FIB damages and artefacts. Twin jet electro-polishing, FIB, flash electro-polishing as well as vacuum heat treatment were used to produce micro/nano-scale Ni gages for in-situ TEM nanotensile testing using the Pi 95 PicoIndenter holder (Hysitron. Inc) equipped with a special MEMS device called ‘Push-to-Pull [1].
First, in order to minimize the effect of the FIB induced damages on the in-situ experiments, an original sample preparation method combining twin jet electro-polishing and FIB was used, the former for thinning and the latter for cutting the edges.Having a sample with a specific defined orientation, with specific defects, such as grain boundaries, twin boundaries, precipitations and etc. and with a specific dislocation density are the main advantages of this technique.
The results showed that a FIB-damage-free area suited to investigate the pristine plasticity mechanisms can be obtained. The effect of the FIB induced defects at the edges of the samples on the mechanical response was elucidated. Efforts are now made to use vacuum heat treatment and flash electro polishing to produce fully FIB damage-free samples also removing the FIB induced defects at the edges of the samples.
[1] https://www.hysitron.com/
9:30 AM - *CM4.7.02
In Situ TEM Study of the Mechanical Behavior of Submicron-Sized Si
Yuecun Wang 1 , Zhiwei Shan 1
1 , Xi'an Jiaotong University, Xi'an China
Show AbstractIn this talk, I will review our recent progress in exploring the mechanical behavior of Si [1,2,3] . Si pillars fabricated by galium based focused ion beam (GAFIB) had been reported to have a critical size of 310–400 nm, below which their deformation behavior would experience a brittle-to-ductile transition at room temperature. We demonstrated that the size-dependent transition was actually stemmed from the amorphous Si (a-Si) shell introduced during the FIB fabrication process. Once the a-Si shell was crystallized, Si pillars would behave brittle again with their modulus comparable to their bulk counterpart. The analytical model we developed has been proved to be valid in deriving the moduli of crystalline Si core and a-Si shell [1]. Inspired by above findings, we have devised a novel core/shell configuration to impose confinement on the sample to circumvent early cracking during uniaxial compression of sub-micron sized Si pillars. This has enabled large plastic deformation and in situ monitoring of the crystalline-to-amorphous transition (CAT) process inside a transmission electron microscope (TEM). We demonstrate that diamond cubic Si transforms into amorphous silicon through slip-mediated generation and storage of stacking faults, without involving any intermediate crystalline phases. By employing density functional theory simulations, we find that energetically unfavorable single-layer stacking faults create very strong antibonding interactions, which trigger the subsequent structural rearrangements. Our findings classify the considerable debate on the mechanism responsible for deformation induced CAT in silicon and shed light on the mechanism underlying deformation-induced CAT in general [2]. In addition, we found that helium ion microscope fabrication can change the structure and mechanical behavior of silicon micropillars significantly [3].
References
[1] Y. C. Wang, D. G. Xie, X. H. Ning, and Z. W. Shan, Thermal treatment-induced ductile-to-brittle transition of submicron-sized Si pillars fabricated by focused ion beam, Applied Physics Letters, 106 (2015).
[2] Y.-C. Wang, W. Zhang, L.-Y. Wang, Z. Zhuang, E. Ma, J. Li, Z.-W. Shan, In situ TEM study of deformation-induced crystalline-to-amorphous transition in silicon, NPG Asia Materials, 8, e291 (2016, Jul.)
[3] Yue-Cun Wang, Lin Tian, Fan Liu, Yuan-Bin Qin, Gong Zheng, Jing-Tao Wang, Evan Ma,and Zhi-Wei Shan, Helium Ion Microscope Fabrication Causing Changes in the Structure and Mechanical Behavior of Silicon Micropillars, Small, DOI: 10.1002/smll.201601753 (2016)
10:00 AM - CM4.7.03
In Situ High Strain Rate Mechanical Testing in the Dynamic TEM
Thomas Voisin 1 2 , Michael Grapes 1 2 , Yong Zhang 2 , Nicholas Lorenzo 3 , Jonathan Ligda 3 , Brian Schuster 3 , Tian Li 1 , Melissa Santala 1 , Geoffrey Campbell 1 , Timothy Weihs 2
1 Materials Science Division, Lawrence Livermore National Laboratory, Livermore, California, United States, 2 Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland, United States, 3 Weapons and Materials Research Directorate, Army Research Laboratory, Aberdeen Proving Ground, Maryland, United States
Show AbstractIn situ TEM tension tests are powerful methods for imaging defection nucleation and propagation when metals are deformed at low strain rates, but we lack such capability at high strain rates above 10^3/s due to the 30 frames per second time resolution of conventional TEM. Even the new high speed electron detectors, operating around 1000fps, are too slow. Here we present a new technique that over comes this limitation and enables in situ observation of dislocations and twins in metals as they are deformed at high strain rates in a TEM.
To achieve the needed time resolution for high strain rates, we use the Dynamic TEM at the Lawrence Livermore National Laboratory which is able to record a set of 9 pictures with delays between each picture as short as 50ns. We also designed and built a new TEM holder capable of deforming samples at strain rates ranging from quasi-static up to 4x10^3/s. The straining stage uses two piezoelectric actuators that bend to load samples in tension, and rectangular specimens with 400µm widths and 25-µm long gauge sections are laser machined and ion milled to achieve the desired strain rates. We will present the latest results of high strain rate, in situ TEM tension tests conducted on copper and magnesium alloys specimens. In addition, we will identify the impact of strain rate on defect nucleation and propagation by comparing the high strain rate results with similar results obtained from in situ TEM experiments conducted on identical specimens at quasi-static strain rates.
10:15 AM - CM4.7.04
In SituTensile and Fatigue Tests on Mild Notched Oligocrystalline 316L Wires
Bojan Mitevski 1 2
1 , University of Duisburg-Essen, Duisburg Germany, 2 Materials Science and Engineering, BTU Cottbus-Senftenberg, Cottbus Germany
Show AbstractDue to large grain size and a low number of grains in the cross section of thin metal components like stents, steels show for such oligo-crystalline distributions a deviating behavior. The mechanical material parameters can differ dependent on their crystallographic texture compared to components with a low grain size to thickness ratio in relatively thick components. Electron backscatter diffraction (EBSD) measurements within a scanning electron microscope (SEM) were conducted during tensile and fatigue tests in this study for the reason of analysis of the crystallographic orientation and grain size distribution of the wires after specimen failure. The tests were conducted on notched thin wires made of 316L medical alloy. The tensile tests show a fundamental difference for the monotone mechanical properties compared to non-notched and notched polycrystalline wires and non-notched oligocrystalline wires. The in situ low-cycle fatigue tests show the crystallographic grain orientation dependent deformation behavior for oligocrystalline specimens.
All tests were conducted on solution annealed (at 1150°C / for 320 seconds / quenched in water) notched wires made from 316L austenitic steel. Annealing was made with a self-made conductive heat treatment fixture under argon atmosphere. The mild notches were made for the reason to provoke slightly different stress conditions / triaxialities that can occur in components like stents (f.e. during the dilatation). For this study 53 notched wires (with 7 different crystallographic main orientations) were prepared with four different mild notch dimensions (initial wire diameter without notch 0,95mm): 2/4mm notch width – 0,5/0,75mm diameter at notch ground.
The mild notches were corroded with the help of a current source and a phosphor-sulfur acid mixture as electrolyte. The part of the wire that shall not be corroded was protected with an acid resistant varnish. The tensile and fatigue tests were conducted with a micro tensile/fatigue testing device (Kammrath & Weiss, Dortmund, Germany) with 5 µm/s drawing speed. Macroscopic photos were taken in regular intervals in order to get the recent diameter for the true stress calculation. After fracture the wires were mechanically and electrolytically polished so that the middle section along the rolling direction could be observed in the SEM with the help of the EBSD technique, that requires a flat surface.
It can be shown that notching in combination with a low amount of crystals in the cross section can increase the monotone mechanical properties, if the total tension is low. The deformation of the tensile and fatigue tested specimens can be found preferably in a low amount of grains with an unfavorable crystallographic orientation and favorable Schmid factor. The effect of the crystallographic orientation of the oligocrystalline wires is low compared to the geometrical influence of the mild notch.
10:30 AM - *CM4.7.05
In Situ TEM Deformation of Lightweight Alloys and Local Strain Measurements with Diffraction Imaging
Andrew Minor 1 2
1 , University of California, Berkeley, Berkeley, California, United States, 2 , Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractBesides the important results related to the effect of size on the strength of individual nanostructures, the ability to systematically measure the mechanical properties of small volumes through nanoscale mechanical testing allows us to test samples that cannot easily be processed in bulk form, such as a ion-irradiated materials or single crystals of very specific alloys. This talk will highlight recent advances with in situ Transmission Electron Microscopy (TEM) nanomechanical testing techniques that provide insight into small-scale plasticity and the evolution of defect structures in lightweight alloys such as Mg, Al and Ti. In addition to measuring the strength of small-volumes, measuring the evolution of strain during plastic deformation is of great importance for correlating the defect structure with material properties. Here we demonstrate that strain mapping can be carried out during in-situ deformation in a TEM with the precision of a few nanometers without stopping the experiment. Our method of local strain mapping consists of recording large multidimensional data sets of nanodiffraction patterns using a high-speed direct electron detectors. This dataset can then be reconstructed to form a time-dependent local strain-map with sufficient resolution to measure the transient strains occurring around individual moving dislocations.
CM4.8: Atmosperic Pressure TEM
Session Chairs
Thursday PM, April 20, 2017
PCC North, 100 Level, Room 127 B
11:30 AM - *CM4.8.01
Transmission Electron Microscopy with Atomic Resolution at Atmospheric Pressure
Xiaoqing Pan 1 2 , Sheng Dai 1 , Shuyi Zhang 1 , George Graham 1
1 Chemical Engineering and Materials Science, University of California, Irvine, Irvine, California, United States, 2 Physics and Astronomy, University of California, Irvine, Irvine, California, United States
Show AbstractThe ability to monitor the dynamic evolution of catalysts under reaction conditions is crucial for understanding structure-property relationships. In the past decade, the majority of atomic-scale transmission electron microscopy (TEM) studies involving gas-solid interactions were conducted in an environmental transmission electron microscope (ETEM), where the gas pressure is typically limited to no more than 1/100 of atmosphere. Recently, it has become possible to overcome this limitation through a MEMS-based, electron-transparent closed cell with a heating stage. In this talk, we report our results obtained using this device (the Protochips AtmosphereTM system) for two important catalyst systems: 1) the structural evolution of supported Pd@CeO2 and 2) the core-shell formation in Pt3Co nanoparticles (NPs).
Core–shell structures consisting of modular palladium-ceria core-shell subunits (Pd@CeO2), assembled in solution from discrete 2 nm crystallites of Pd and CeO2, have shown exceptional activity for methane combustion. We found that the sample consists of loosely assembled clusters of Pd and CeO2 NPs, each about 2–3 nm in diameter, in close proximity after air calcination at 500 °C for 5 h. In-situ TEM observations performed in 150 Torr O2 revealed that an unexpected structural transformation occurs upon further heating at temperatures between 500 and 800 °C. As temperature increased above 500 °C, atoms on the corners of smaller CeO2 NPs started to leave the NPs, causing them to shrink, while atom clouds consisting single atoms form in the sample. As temperature increased to 650 °C, the atomc “cloud” starts to contract, accompanied by the growth of the surrounding CeO2 NPs. Eventually, the system reached a stable state, where large CeO2 NPs, about 5-10 nm in diameter, together with very small entities, about 1-2 nm across, are both present in the sample. This reveals that the newly formed structure, comprised of an intimate mixture of palladium, cerium, silicon, and oxygen with extremely high dispersion, is more likely to account for the exceptional catalytic properties that have been reported.
Using the similar techniques, we also studied the core-shell platinum-metal (Pt-M) nanoparticles which show a catalytic performance in the oxygen reduction reaction (ORR) superior to that of pure Pt nanoparticles. To understand the formation mechanism of the Pt shell, we studied thermally activated core-shell formation in Pt3Co nanoparticles via in-situ electron microscopy with the gas cell. The disordered Pt3Co nanoparticle was found to transform into an ordered intermetallic structure after annealing at high temperature (725 °C) in 760 Torr O2, followed by layer-by-layer Pt shell growth on (100) surfaces at low temperature (300 °C). The apparent ‘anti-oxidation’ phenomenon promoted by the ordered Pt3Co phase is favorable to the ORR catalyst, which operates in an oxidizing environment.
12:00 PM - CM4.8.02
Study of Copper Nanocrystal Redox at Atmospheric Pressure by In Situ TEM
Yuzi Liu 1 , Jun Tian 1
1 , Argonne National Laboratory, Lemont, Illinois, United States
Show AbstractCopper (Cu) is a 3d transition metal and has interesting physical and chemical properties. Cu is inherent instable (prone to oxidation) under atmospheric conditions. Cu can undergo a variety of reactions owning its wide range of oxidation states (Cu (0), Cu (I), Cu (II), and Cu (III)), which enable reactivity via one- and two-electron pathways. The studies of Cu and its oxides nanoparticles, earth-abundant and inexpensive materials, have attracted tremendous effort for their numerous applications especially in the field of catalysis. Here we report the results of Cu redox process in different gas environments at atmospheric pressure by using gas flow in situ transmission electron microscopy (TEM) to study the structure and the electronic state evolution process.
The as prepared Cu nanoparticles were loaded to the gas flow cell made from a pair of SiN membranes. There is a MEMS heating coil patterned on one of the SiN membranes which provide the heating capability during gas flow. From the bright field images, we found that Cu nanoparticles were oxidized after the compressed air flow through the cell at rate of 0.5sccm for 80 mins at 320oC. The oxides layer, which was confirmed by energy-filtered TEM, emerges slowly on the nanoparticles. The particles morphology didn’t change except a shell layer growth on the particles. The oxidization rate of the sphere is higher than which of the nanocubes. It indicates that the low index facets on nanocubes are less active than the high index facets of the spheres. The shell layer disappeared after hydrogen flow at 0.5sccm for 5mins at 310oC. It means the Cu oxides were reduced to Cu. Then upon the flow of mixture of H2 and CO2, we found the Cu electronic state shift due to the gas molecules adsorption on the nanoparticles by using electron energy loss spectra. This is an indication that the Cu is an efficient catalyst for the hydrogenation of CO2 to methanol.1
1. C. Liu et al. J. Am. Chem. Soc., 2015, 137 (27), pp 8676–8679
12:15 PM - CM4.8.03
Unveiling the Atomistic Processes of the Accelerated Decomposition of Y2O3–Stabilized ZrO2 by Environmental TEM
Benjamin Butz 1 3 , Ai Leen Koh 2 , Robert Sinclair 1
1 Department of Materials Science and Engineering, Stanford University, Stanford, California, United States, 3 Institute of Micro- and Nanostructure Research, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen Germany, 2 Stanford Nano Shared Facilities, Stanford University, Stanford, California, United States
Show AbstractYttria-stabilized Zirconia (YSZ) has been widely used as structural or functional ceramic in harsh chemical environments or at high operating temperatures. For application, its long-term stability is of importance. As the ternary Y2O3-ZrO2 system exhibits a miscibility gap, spinodal decomposition occurs depending on the Y2O3 content and the applied conditions. This particularly holds for 8–8.5 mol% YSZ, which is a common electrolyte material for, e.g., solid oxide fuel cells (SOFC). During operation around 900 °C, the spinodal decomposition, which is characterized by microstructural coarsening and accompanied evolution of drastic chemical variations, leads to a significant degradation of the oxygen-ion conductivity (e.g., 40% within 5000 h at 950 °C)[1, 2]. Besides the temperature-dependency of the decomposition rate, it may strongly be enhanced by trace elements, which possess different solubility in 8YSZ under oxidizing or reducing atmosphere. Here, the accelerated decomposition of Ni-containing 8YSZ, as it commonly forms during SOFC manufacturing, is investigated in detail. It proceeds more than 50 times faster than the degradation of pure 8YSZ[3]. In order to understand the underlying mechanism, the fundamental processes like Ni indiffusion (oxidizing atmosphere) and Ni exsolution/precipitation (reducing atmosphere) are investigated. The comprehensive investigation is based on the local analysis of the behaviour of the dissolved Ni, meaning the evolution of its oxidation state and atomic configuration at different oxygen partial pressures, by in situ electron energy-loss spectroscopy (EELS) in an environmental transmission electron microscope (ETEM). The study is complemented by global in situ X-ray absorption measurements.
[1] B. Butz, P. Kruse, H. Störmer, D. Gerthsen, A. Müller, A. Weber, E. Ivers-Tiffée, SSI 177 (2006) 3275
[2] B. Butz, R. Schneider, D. Gerthsen, M. Schowalter, A. Rosenauer, Acta Mater. 57 (2009) 5480
[3] B. Butz, A. Lefarth, H. Störmer, A. Utz, E. Ivers-Tiffée, D. Gerthsen, SSI 214 (2012) 37
BB gratefully acknowledges provision of sample materials by the IWE at KIT (Prof. E. Ivers-Tiffée, Germany) and the IEK-1 at FZ Jülich (Germany). The research is financially supported by the German Research Foundation, DFG grant no. BU 2875/2-1. Part of this work was performed at the Stanford Nano Shared Facilities.
12:30 PM - CM4.8.04
In Situ TEM Monitoring of Growth Dynamics of Nanocrystalline Molybdenum Carbide Nanosheet
Ziyuan Lin 1 , Yang Chai 1
1 , The Hong Kong Polytechnic University, Hong Kong Hong Kong
Show AbstractEfficient carbon capture and storage are increasingly important for the reduction of carbon dioxide (CO2) emission, which is responsible for the climate change and ocean acidification. Active catalytic systems for the re-use of CO2 have been extensively studied, but most of them are based on scarce and noble metals.1 Transistion metal carbides (TMCs) have been reported to have comparable catalytic properties with platinum-group metals.2 They are appealing to catalyze various reactions as an alternative to noble metals due to their abundance, low cost, and relative small activation energy barriers. Molybdenum monocarbide with face-centered cubic structure (δ-MoC) is predicted to exhibit a promising behavior for activating CO2 with high selectivity and excellent resistance to oxygen poisoning compared with other TMCs.3-4 However, δ-MoC is a metastable phase of molybdenum carbide. The as-prepared molybdenum carbide is usually Mo2C with thermodynamically stable phase.5-6 It is required to develop an understanding on controlling the phase of molybdenum carbide and the growth of δ-MoC for efficient catalysis.
The direct carburization of molybdenum oxide (MoO3) in the presence of carbon is widely used to grow molybdenum carbide. We performed the carburization inside the transmission electron microscope (TEM) to monitor the growth dynamics. MoO3 was decomposed from the molybdenum peroxide. When the MoO3 only reacted with the amorphous carbon film on the E-chips, the Mo2C in hexagonal-closed packed (hcp) arrangement was grown. The metastable δ-MoC was not grown in this process. After we introduced additional carbon source, sucrose, which can be decomposed into activated carbon, the phase was thransformed to δ-MoC. The as-grown products have a grain size of ~ 50 nm. The SAED evolution with temperature indicates the formation of molybdenum oxycarbide at the initial stage, which provides a cubic structure template and leads to the growth of δ-MoC. This intermediate phase of TMC was grown at a relative low temperature (500 °C) because of the higher C/Mo ratio and the lower activation energy barriers of the carbon from the sucrose. Direct observation with the TEM allows us to investigate the controllable growth of different phases of MoxC, which is primary for further applications.
References
1.Espinal, L.; Poster, D. L.; Wong-Ng, W.; Allen, A. J.; Green, M. L., Environmental science & technology 2013, 47 (21), 11960-11975.
2.Levy, R.; Boudart, M., science 1973, 181 (4099), 547-549.
3.Kunkel, C.; Viñes, F.; Illas, F., Energy & Environmental Science 2016, 9 (1), 141-144.
4.Posada-Pérez, S.; Ramírez, P. J.; Evans, J.; Viñes, F.; Liu, P.; Illas, F.; Rodriguez, J. A., Journal of the American Chemical Society 2016, 138 (26), 8269-8278.
5.Hwu, H. H.; Chen, J. G., Chemical reviews 2005, 105 (1), 185-212.
6.Oyama, S., Catalysis today 1992, 15 (2), 179-200.
12:45 PM - CM4.8.05
Structural Phase Transitions and Dynamics of Solid-Supported Interfacial Assemblies
Ding-Shyue (Jerry) Yang 1
1 Chemistry, University of Houston, Houston, Texas, United States
Show AbstractDue to their large scattering cross sections with matter, electrons are suitable for contactless probing of surface assemblies at heterogeneous interfaces, especially in a reflection geometry. Direct probing of assembly structures through electron diffraction further enables studies of ultrafast structural dynamics through the pump-probe scheme as well as discoveries of hidden phase changes in equilibrium that have been obscure in spectroscopic measurements. In this presentation, our first observations of the ordered structure of an ionic liquid on a terraced graphite surface [1] and the unique two-stage transformations of interfacial methanol on smooth hydrophobic surfaces [2] will be discussed. The latter finding may reconcile the inconsistent reports of the crystallization temperature of interfacial methanol using various indirect methods. Dynamically, energy transfer across a solid-molecule interface following photoexcitation of the substrate is found to be highly dependent on the structure of an interfacial assembly. As the film thickness increases, an onset delay and a prolonged time scale in the decrease of diffraction intensity are observed, signifying an inefficient vibrational coupling due to the lack of crystalline order in the surface normal direction. Implications of the dynamics results and an outlook of interfacial studies using time-resolved and averaged electron diffraction will be discussed.
[1] He, Wu, Rajagopal, Punpongjareorn, and Yang, Phys. Chem. Chem. Phys. 18, 3392 (2016).
[2] He, Wu, and Yang, J. Chem. Phys. 145, 171102 (2016).
CM4.9: Advanced In Situ Methods, Multimodal Characterization and Data Processing
Session Chairs
Thursday PM, April 20, 2017
PCC North, 100 Level, Room 127 B
2:30 PM - *CM4.9.01
Using Real Time Characterization Methods to Understand Surface Phase Transitions in Layered Oxide Cathode Materials
Khim Karki 2 1 , Yiqing Huang 2 , Sooyeon Hwang 1 , Andrew Gamalski 1 , M Stanley Whittingham 2 , Guangwen Zhou 2 , Eric Stach 1
2 , SUNY Binghamton, Binghamton, New York, United States, 1 , Brookhaven National Laboratory, Upton, New York, United States
Show AbstractLithium ion batteries find ubiquitous use in mobile devices such as smartphones, tablets and laptops, and are being increasingly considered for use in both transportation and Smart Grid applications. In all of these applications, there is a demand for higher capacity, faster charging rate and improved safety.
In this presentation, I will describe how we use real time transmission electron microscopy methods to understand how phase transitions occur at the surface of a layered oxide cathode material (LiNi0.8Co 0.15Al0.05O2 (NCA). These materials suffer from thermal runaway caused by deleterious oxygen loss and surface phase transitions at highly overcharged and overheated conditions, prompting serious safety concerns. Using in situ environmental transmission electron microscopy techniques, we demonstrate that surface oxygen loss and structural changes in the highly overcharged NCA particles are suppressed by exposing them to an oxygen-rich environment. The onset temperature for the loss of oxygen from the electrode particle is delayed to 350 °C at oxygen gas overpressure of 400 mTorr. Similar heating of the particles in a reducing hydrogen gas demonstrated a quick onset of oxygen loss at 150 °C and rapid surface degradation of the particles.The results reported here illustrate the fundamental materials science governing the failure processes of electrode particles and highlight possible strategies to circumvent such issues.
3:00 PM - CM4.9.02
In Situ Imaging with Electrons and X-Rays to Track the Conversion of Organic Inorganic Perovskite Solar Cells
Jeffery Aguiar 1 2 3 , Maulik Patel 4 , Sarah Wozny 5 2 , Nooraldeen Alkurd 5 9 2 , Libor Kovarik 8 , Terry Holesinger 6 , Toshihiro Aoki 7 10 , Mengjin Yang 2 , Mowafak Al-Jassim 2 , Weilie Zhou 5 , Joseph Berry 2 , Kai Zhu 2
1 , Idaho National Laboratory, Idaho Falls, Idaho, United States, 2 , National Renewable Energy Laboratory, Golden, Colorado, United States, 3 Materials Science and Engineering, University of Utah, Salt Lake City, Utah, United States, 4 Materials Science and Engineering, University of Tennessee Knoxville, Knoxville, Tennessee, United States, 5 Advanced Materials Institute, University of New Orleans, New Orleans, Louisiana, United States, 9 , Colorado School of Mines, Golden, Colorado, United States, 8 , Pacific Northwest National Laboratory, Richland, Washington, United States, 6 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 7 , Arizona State University, Tempe, Arizona, United States, 10 , University of California, Irvine, Irvine, California, United States
Show AbstractPhotovoltaic materials development is entangled with major technological achievements in energy and semiconductor device fabrication. Today’s photovoltaics have similar requirements for energy and semiconductor fabrication including high efficiency (>15%), a large capacity for long-term manufacturing (> 5 years), and extended lifetimes (>20 years). Perovskite-based solar cells are attractive low-cost, industry-scalable energy materials due to their ability to be excellent electro-optical transistors and light harvesters. The materials basis and understanding surrounding their crystallization and stability however is ongoing in the literature. Elucidating the relationships between chemistry, crystal structure, device stability, functional properties, processing environment (surrounding gases, relative humidity, temperature, pressure), and fabrication history are all thereby vital to future of this emerging technology.
A need to apply in-situ microscopy to report on the transient and final material chemistry and structure regarding incorporating different chemistries, environments, and processing steps is important to the future fabrication goals of these energy materials. For example, intermixing halides into perovskites are shown in the literature to improve on device properties including carrier lifetimes, open-circuit voltages, and short circuit currents. However, the final mixed halide concentration in FAPbI3-xClx has been reported in various ways, where there are remaining questions concerning whether the halide remains inside the perovskite host at all, and acts as a volatile crystallizing agent.
In this presentation, we highlight the use and interpretation of in-situ microscopy and X-ray diffraction (XRD) to track the material chemistry and structure of organic inorganic perovskites. In order to accomplish this task, joint growth studies using environmental transmission electron microscopy and XRD focused on the evolving material chemistry and structure as function of temperature and processing environment. Improvements on the current device growth methods to fabricate solar cells based on the collected data have not only been suggested, but applied to generate solar cells reaching above 17% efficiency.
3:15 PM - CM4.9.03
Dynamic XPS Measurements for Observing and Monitoring Surface Reactions
Christian Kaiser 1 , Burkhard Krömker 1 , Georg Prümper 1 , Jessica Hilton 2
1 , Sigma Surface Science GmbH, Taunusstein Germany, 2 , Mantis-Sigma USA, Denver, Colorado, United States
Show AbstractX-ray Photoelectron Spectroscopy (XPS) is a mature and popular measurement technique for studying surface chemical and physical properties. The ability to gain chemical state and quantitative elemental information with high surface sensitivity is widely used with applications in many research fields, such as semiconductors and 2d materials, thin films for electronics and photovoltaics, nano materials, catalysis or metallurgy. Typically, XPS measurements are carried out with the premise that the sample is not altered during the data acquisition.
Often, however, XPS is used to analyse surfaces before and after a particular process (e.g. heating, process gas exposure, oxidation) to determine the alteration due to the applied process. This can be a laborious procedure and misses out the observation of the transformation itself.
Furthermore, in many cases sample preparation requires a careful procedure followed by an analysis to verify the required outcome of the preparation. This is often time consuming and the outcome is not always guaranteed to be satisfying.
Here, we present a unique acquisition mode, Multi Peak Monitoring, on the basis of multi-channel snapshot detection and the ability for changing the spectrometer voltages fast. Important parameters for using this acquisition mode to study dynamic processes down to the millisecond range are discussed and the capability of this measurement technique demonstrated.
Utilising the benefits of XPS on a sample under controlled and variable process conditions presents a whole new tool set for observing, monitoring and even tailoring surface reactions. Dynamic XPS measurements can be used not only to find and optimise parameters for controlled and reproducible processes, but also to gain fundamental understanding of the underlying dynamics of reactions.
3:30 PM - CM4.9.04
Evolution of Electronic Structure on Transition Metal and Transition Metal Doped Titanium Disulphide by High Resolution Photoemission Spectroscopy Study
Xiaoyu Cui 1
1 , Canadian Light Source, Saskatoon, Saskatchewan, Canada
Show AbstractI will also present our high-resolution photoemission measurements on the transition metal doped dichalcogenides system. TiS2 is proved to be a semiconductor with indirect gas around 600 meV. We confirmed that there is no CDW transition happen. Upon iron atoms intercalation, the strong modification of the valence band structures and the band dispersions in the intercalated compound are observed. The hybridization of the S derived states with Fe 3d states is thought to be predominantly the reason. The mechanism of these hybridized bands’ modification has been explained well by Vienna ab initio simulation program and the projected augmented wave potentials; the Perdew-Burke-Ernzerhof exchange correlation functional.
Finally I will present some of our latest photoemission work in Canadian Light Source Inc.
3:45 PM - CM4.9.05
In Situ Probing of Surface States on Nanoparticles
Qianlang Liu 1 , Peter Crozier 1
1 , Arizona State University, Tempe, Arizona, United States
Show AbstractThe electronic structure on the surface and near-surface region of a nanoparticle can vary considerably from that in the bulk. This is critical to heterogeneous catalysts as chemical reactions occur only on the catalyst surfaces, and electronic states control the thermodynamic driving force for redox reactions. Thermal treatments are usually required during material preparation which may introduce defects and impurities on the surfaces of catalysts, leading to extrinsic electronic states. Also, exposure to reactants may alter the surface atomic and electronic structures, thus influencing the catalytic performance. An environmental transmission electron microscope (ETEM) coupled with monochromated electron energy loss spectroscopy (EELS) opens up the opportunity of simulating material synthesis steps or near-reaction conditions while observing the corresponding surface electronic structural evolutions. An aloof beam EELS technique is employed where the electron beam is a few nanometers outside the nanoparticle surface to reduce beam damage. TEM has an advantage of high spatial resolution over many other surface sensitive techniques, therefore it can be used to probe the heterogeneity existing in nanoparticle systems. Furthermore, monochromated EELS offers high energy resolution enabling observation of small features in the low-loss part of the spectrum associated with states in the bandgap. By following the transformation of surface states and correlating them with different stimuli, insights into activation and/or deactivation mechanisms of the catalysts may be gained.
MgO nanocubes will be used as a model material as they have well-defined morphology and large bandgap. Previous ex situ work on MgO that was exposed to water vapor showed a plateau feature in the bandgap region of the EELS spectrum. Spectral simulations showed this feature is consistent with a broad filled surface state at 1.1 eV above the MgO valence band maximum and a thin hydroxide surface layer [1]. In situ exposure to water vapor will be conducted on MgO nanocubes and surface state changes will be monitored. TiO2 anatase nanoparticles, which is a photocatalyst, will also be investigated upon exposure to oxidizing and reducing environments to explore surface states changes related to oxygen vacancy formation.
[1] Q. Liu, K. March and P.A. Crozier, Ultramicroscopy, in press.
[2] The support from US Department of Energy (DE-SC0004954) and the use of Titan microscope at John M. Cowley Center for High Resolution Microscopy at Arizona State University is gratefully acknowledged.
4:30 PM - *CM4.9.06
5D Imaging of Multi-Element and Multi-Valence Material Evolution in In Situ Environmental TEM by On-the-Fly and Analytical Electron Tomography
Huolin Xin 1
1 , Brookhaven National Lab, Upton, New York, United States
Show AbstractThe spatial, compositional, bonding, and time-domain complexity of materials transformation under the solid/gas reaction [1-3], particularly with heterogeneous nucleation involved, highlights the need to increase the dimensionality of electron microscopy data sets beyond conventional projection imaging and the acquisition of image series, i.e. x-y-t. Because projection images can be misleading or inconclusive for inhomogeneous systems, it is much desired to include all three spatial coordinates, x, y, and z, into the data set without losing the time and energy resolution. However, a key stumbling block that had held back progress in achieving this is the rather slow process in acquiring electron tomography data for the retrieval of depth information. In this talk, I will report the realization of high-throughput electron tomography, on-the-fly reconstruction, and the first attempt to achieve 5-D electron microscopy data sets under reaction conditions. The five-dimensional data sets visualize the oxidation of a Co-Fe catalyst with unprecedented 3-D and chemical details and transform our understanding of adsorbate induced segregation in bimetallic systems. [4]
[1] R. Sharma and K. Weiss, Microscopy Research and Technique 42 (4), 270 (1998).
[2] HL Xin et al, Microscopy and Microanalysis 19 (06), 1558 (2013).
[3] HL Xin et al, Nano Letters 14 (6), 3203 (2014).
[4] Research carried out at the CFN/BNL, which is supported by the U.S. Department of Energy, Office of Basic Energy Sciences, under Contract No. DE-SC0012704.
5:00 PM - CM4.9.07
Rapid Tomography in Environmental TEM—Solutions for a Fast Analysis of Nano-Materials in 3D under In Situ Conditions
Siddardha Koneti 1 , Lucian Roiban 1 , Voichita Maxim 2 , Thomas Grenier 2 , Anne-Sophie Gay 3 , Florent Dalmas 1 , Philippe Vernoux 4 , Thierry Epicier 1
1 MATEIS, CNRS UMR 5510, Univ Lyon, INSA-Lyon, Villeurbanne France, 2 CREATIS, CNRS UMR 5220, Inserm U1044, Univ Lyon, INSA-Lyon, Villeurbanne France, 3 , IFP Energies nouvelles, Solaize France, 4 IRCE lyon, CNRS UMR 5256, Univ Lyon, Université Claude Bernard Lyon 1, Villeurbanne France
Show AbstractEnvironmental Transmission Electron Microscopy (ETEM) is a dedicated instrument has been the subject of recent considerable developments allowing to follow chemical reactions under environmental, e.g. gas and temperature conditions even at atomic resolution. A typical domain of applications concerns catalysis, where supported nanoparticles (NPs) can be followed during synthesis and evolution (activation / de-activation) in the presence of various gases. Whereas numerous works have now been published in conventional imaging, that is, 2D projection, little work is reported on 3D investigations performed under in situ. It is easy to understand why such an approach is difficult: since TEM tomography consists in reconstructing numerically a tilt series of images projected over a wide angular range, the time to acquire these data is generally too important as compared to the speed of the sample evolution, or the kinetics of the studied chemical reaction. The duration of the conventional acquisition step is typically one hour, or close to one hour, making it impossible to get tilt sequences during the intermediate stages of catalytic synthesis.
In this work we aimed at understanding the possibilities and limitations for acquiring fast tilt series under BF-TEM conditions in terms of speed and proper signal to noise ratio with the help of equipment available today. The main interest is to reduce the acquisition time from few tens of minutes to few minutes or even to seconds. Vivid nano-materials were studied to estimate and discuss the possibilities for rapid tomography under environmental conditions. Firstly, simulations performed on a ghost model will address the question of the blur induced by a continuous rotation while recording images. Secondly, tomographic results on alumina catalysts will be shown to understand the capabilities of a rapid tomography approach (Palladium nano particles grafted on alpha and delta alumina). Thirdly, the possibility and reliability of using rapid tomography approach under environmental condition will be demonstrated with the example of catalysts for soot particles abatement in Diesel engines exhausts. The 3D evolution of soot onto Yttria-Stabilized Zirconia (YSZ) catalysts is followed during its consumption under 1.7 mbar of oxygen at different temperatures. This fast tomography approach opens the way to study beam sensitive materials like polymers and biological samples even at 300 keV without any special treatments. As a further illustration, tomographic studies performed on polymer (Mg3AlCO3 LDH nano-platelets dispersed in Latex) and on biological sample (Magnetotactic bacteria) will also be shown.
5:15 PM - CM4.9.08
In Situ STEM-EELS Study on Cation Exchange Reactions at Nanoscale
Alessandro Genovese 1 , Alberto Casu 1 , Andrea Falqui 1
1 , King Abdullah University of Science and Technology, Thuwal Saudi Arabia
Show AbstractColloidal cation exchange (CE) reactions in liquid solution are a well-established tool to modify the chemical composition of nanomaterials by substituting with different cation species their cationic sublattices, partially or wholly, and tuning their chemical-physical properties consequently. A significant benefit of the colloidal CE is the possibility to synthesize new compounds hardly obtainable otherwise, and with important technological applications. In particular, these reactions take place quickly in the liquid phase. As a consequence, monitoring in detail the materials formation and evolution over time in the liquid medium is not possible. Thus, it is feasible characterizing the pre- and post-reaction compounds, but not to the intermediate ones, resulting in a lack of meaningful information about the reactions progress. To overcome these limitations, we recently proved that CE reactions between nanoparticles could be directly activated at the solid-state via thermal annealing using cation-donor and cation-acceptor materials, and directly monitored through in situ TEM analysis [1].
In this direction, we performed STEM-EELS investigation to study in-situ thermally driven CE experiments more in detail by using a low-drift heating holder based on MEMS technology. Cu2Se nanocrystals (NCs) and CdSe nanowires (NWs) were used as Cu-donors and Cu-acceptors cation species, respectively. CE reaction occurred at a temperature of 400 °C. Once reached this temperature, in-situ time-resolved STEM-EELS investigation was performed directly on the cation-acceptor nanomaterial, i.e. CdSe NWs, and exhibited the onset of the CE reaction and its resulting progress over time. Specifically, we investigated the Cu core loss region (the L2,3 edge at 931 eV) and monitored its evolution, while maintaining the electron probe stationary on a sector of a single CdSe NW surrounded by several Cu2Se NCs, not in direct contact with it. Spatially-resolved spectrum-imaging EELS analysis also revealed how the free Cu atom species, thermally-expelled from Cu2Se NCs, approached the Cu-acceptor CdSe phase and gave rise to the CE reaction. At first, Cu atoms formed a layer thick less than 1 nm around the CdSe NWs, then diffused into the CdSe crystal structure from a single and distinct entry point. Subsequently, the Cu CE front advanced by substituting Cd cations and converting the CdSe NW into the corresponding Cu2-xSe phase, keeping unaltered its habit. Moreover, the Cu diffusion was observed to occur at different rates along the CdSe NWs in the two opposite directions. These results shed further light about how the CE takes place in nanosized crystalline structures at solid state while highlighting the power of in situ STEM-EELS-based techniques.
References
[1] Casu et al., ACS Nano 2016, 10,, 2406-2414.
5:30 PM - CM4.9.09
Big Data Analytics for Scanning Transmission Electron Microscopy Ptychography
Alex Belianinov 1 , Stephen Jesse 1 , Miaofang Chi 1 , Albina Borisevich 1 , Sergei Kalinin 1 , Eirik Endeve 1 , Richard Archiblad 1 , Christopher Symons 1 , Andrew Lupini 1
1 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractThe scanning transmission electron microscopy (STEM) is a powerful platform for studying materials and their many varied properties (including structural, electronic, magnetic, ferroic etc.) locally and at their fundamental length-scales. In its current standard implementation, STEM imaging is severely restricted by the instrumental linkage in which the information rich electron diffraction pattern (Ronchigram) is reduced to a single value (e.g. through the integrated intensity over a relatively large detector) at each beam location resulting in loss and distortion of information about important but subtle aspects of material properties. Previous theoretical and experimental work suggests that full acquisition of the Ronchigram at each spatial location during a scan can enable super resolution, phase-contrast imaging, imaging of internal fields, and 3D sample reconstruction.
In the current work we have utilized the DE-12 camera installed on an aberration corrected FEI Titan operating at 300 kV combined through a custom FPGA control system to synchronize frame capture and beam positioning to acquire 4D scanning-scattering data sets. Typical scans of 192×192 pixel images containing 384×384 Ronchigrams at every pixel were captured in less than 1 minute. A host of multivariate statistical methods can be brought to bear to extract meaningful information from these large data sets. Statistical methods can be advantageous in that they are parallelizable and can be efficiently implemented on large-scale computing platforms, are model-free and operate with no pre-imposed expectation or bias, and are capable of elucidating inter-pixel correlations unlikely to be noticed by human observation alone.
Though PCA can be used to reduce the dimensionality of information within a data set, it may not always be the most efficient means to compress the and the output of PCA it is often not well suited for finding clusters that exist in subspaces of the data. In order to simultaneously address the difficulty of defining and finding neighbors in extremely high dimensions and the desire to find clusters that are locally defined, we utilize an approach that creates local, patch-based Multidimensional Spectral Hashing (MDSH) codes for dimensionality reduction. MDSH is used to generate small set of dimensions in which similarity among close points is preserved, while allowing distinctions between larger distances to become indistinguishable. This enables us to create a space with many fewer dimensions in which local clustering is preserved. Here, we will explore the use of high-dimensional techniques that automatically select an appropriate number of clusters, to visualize domains in Bismuth Ferrite (BFO), as well as explore how variations in the stride and receptive field of the patches impact the imaging results.
Symposium Organizers
Haimei Zheng, Lawrence Berkeley National Laboratory
Dongsheng Li, Pacific Northwest National Laboratory
Judith Yang, University of Pittsburgh
Henry Zandbergen, Delft University of Technology
Yimei Zhu, Brookhaven National Laboratory
Symposium Support
Direct Electron, LP
Henan University
Hitachi
CM4.10: In Situ TEM of Nanostructured Materials
Session Chairs
Friday AM, April 21, 2017
PCC North, 100 Level, Room 127 B
9:30 AM - CM4.10.01
In Situ Electron Beam Amorphization of Sb2Te3 Nano-Confined Phase Change Material within Single Walled Carbon Nanotubes
Jeremy Sloan 1 , Samuel Marks 1 , Krzysztof Morawiec 2 , Piotr Dluzewski 2 , Slawomir Kret 2
1 , University of Warwick, Coventry United Kingdom, 2 Instytut Fizyki, PAN, Warsaw Poland
Show AbstractDriven by a growing demand for high-density data storage materials, local phase change behaviour in nanoscale 'Phase Change Materials' (PCMs) have been studied by scanning probe microscopies based on conductance modification, ferroelectric polarization and topographic transformation. Recently, a variety of PCMs, including GeTe, SnSe and PbTe have been incorporated into single walled carbon nanotubes (SWNTs) to produce, in effect, 'nano-Confined' PCMs or nC-PCMs. These confined systems have several significant advantages over many other composites embedded in comparable templating systems: (i) the internal van der Waals surface of SWNTs constrains the size of the nC-PCMs to atomically smooth nanopores with confining surfaces as small as ca. 1nm2 in cross section; (ii) by comparison with porous templates fabricated from, for example, anodic alumina or nanoporous or mesoporous silica, SWNTs are thermally robust to 1400K and, crucially, do not sinter over the metling temperature of many if not all important PCMs; and (iii) are only selectively sensitive to electron beam irradiation under moderate to medium electron beam dose conditions below the threshold for knock on electron beam damage, i.e. 86 keV. In this study, we reveal the crystallography, crystallinity and amorphisation of low-dimensional crystals of the Topological Insulator/nC-PCM Sb2Te3 within both discrete and bundled SWNTs with a diameter spread spanning 1.3-1.7 nm by a combination of electron diffraction, aberration-corrected high resolution imaging and variable dose electron beam irradiation. We further reveal that electron diffraction and imaging indicates that the crystallinity of the host SWNTs is largely unaffected by this process indicating that this in situ glass transition can effectively be made reversible.
9:45 AM - *CM4.10.02
Nanotube, Nanowire and Nanosheet Manipulations and Physical Property Analysis in a High-Resolution TEM
Dmitri Golberg 1 2 , Ovidiu Cretu 1
1 , National Institute for Materials Science, Tsukuba, Ibaraki, Japan, 2 , Queensland University of Technology, Brisbane, Queensland, Australia
Show AbstractPhysical property studies of inorganic nanotubes, nanowires and nanosheets, e.g. their mechanical, optoelectronic, thermal and/or cathodoluminescence performances, are carried out under delicate manipulations with diverse nanoscale objects in a 300 kV high-resolution transmission electron microscope (HRTEM) equipped with a variety of in situ TEM holders. The objects of interest include, but are not limited to, carbon and boron nitride nanotubes, nitrogen doped graphene, boron nitride and molybdenum sulfide nanosheets and cadmium sulfide, and silicon-germanium nanowires. Various mechanical and electrical characteristics, like Young's modulus, ultimate tensile strength, conductance, are determined as a function of carbon nanotube morphology and/or its defectiveness (as revealed by direct HRTEM imaging). Optoelectronic and cathodoluminescence parameters of cadmium sulfide nanowires with and without elastic bents are analyzed as a function of bending ratios or existence of localized structural defects. The conclusions are supported by density functional tight binding (DFTB) simulations. Statistically unchanged values of on/off (photocurrent/dark current) ratios in bent nanowires are documented. Performance of doped graphenes/amorphous phosphorus sandwiches as electrodes in sodium-ion batteries is also investigated via construction of prototype ion battery cells in HRTEM. All these works have been performed through key contributions of the numerous authors’ colleagues effectively participating in the diverse in situ TEM projects, namely Drs. Chao Zhang, Katherine Elizabeth Moore, Xin Zhou, Ming-Sheng Wang, Konstantin Firestein, Dmitry Kvashnin, Pavel Sorokin, Xi Wang, Wenlong Wei, Dai-Ming Tang, Naoyuki Kawamoto, Yohei Kakefuda, Isamu Yamada, Renzhi Ma, Masanori Mitome, Naoki Fukata, Takao Mori, Takaoshi Sasaki, Yoshio Bando, and John Bell.
10:15 AM - CM4.10.03
In Situ Observation of Domain-Confined Growth of Hollow Nanocrystals
Luping Tang 1 , Longbing He 1 , Litao Sun 1
1 , Southeast University, Nanjing China
Show AbstractThe design and synthesis of hollow nanocrystals (NCs) have been rapidly developed due to their large surface area, low density, and high loading capacity. Although different synthesis approaches such as templating method, Kirkendall effect, Ostwald ripening, and galvanic replacement have been proposed to construct a desirable shell structure with an interior void space, most of these hollow structures are obtained in solution and it is hard to manipulate or acquire only partial hollow structures from the ensemble, even in single-NC mode. Heat or electron beam irradiation treatment has recently become a new strategy for fabricating unique structured nanomaterials. For example, Feng et al. reported NaYF4:Yb,Er hollow structures can be fabricated from an assembled solid NaYF4:Yb,Er nanocrystal monolayer by electron beam lithography, which can be used as a kind of information-storage medium through "writing" with the electron beam and "reading" with TEM [1]. Therefore, understanding the occurrence and evolution of material restructuring induced by electron beam irradiation is of both scientific and technical importance for developing advanced materials.
Here, we report our in situ observation of electron-beam-irradiated domain-confined growth of partially sublimed core-shell CdSe/CdS to hollow CdSeS NCs. The CdSe/CdS NCs were chosen as a model to investigate the irradiation processing of semiconductor NCs which were always used in nano-device. The mechanisms of the structure evolution of CdSe/CdS NCs are also discussed. In this mechanism, partially sublimed nanocrystals (NCs) were irradiated with an electron beam. These NCs then evolved into a hollow structure as a result of shell regeneration. The remaining volume of the partially sublimed CdSe/CdS core-shell NCs should be approximately greater than 20% and less than 80% of the original volume to provide sufficient generation space and source. Under electron beam irradiation, when the transferred energy reached their surface binding energy, the Cd, Se, and S atoms on the partially sublimed CdSe/CdS NCs surfaces possibly ejected and recrystallized in the inner surface of the carbon shell. As a result, a hollow structure with CdSeS shell was produced, as indicated by high-sensitivity energy-dispersive X-ray spectroscopy. Therefore, the molecular layer of surfactants on their surfaces should be transferred to an amorphous carbon shell via electron beam irradiation and be utilized as a template during subsequent generation. These physical manipulations of NCs can be targeted on only some of the hollow structures from the ensemble, even in single-NC mode, providing an interesting pathway in precision machining of single structure for nano-device fabrication.
References
[1] W. Feng et al., Small 5, 2057 (2009).
10:30 AM - CM4.10.04
In Situ HRTEM Investigation of Phase Transformation from Anatase to Rutile
Miao Song 1 , James De Yoreo 1 , Dongsheng Li 1
1 Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington, United States
Show AbstractTitanium dioxide (TiO2) has been used in various fields, such as photocatalysis, sensors, pigments, solar hydrogen, methanol fuel cells, and electronics. Most of those applications are closely associated with different structures, typically including brookite, anatase and rutile. For example, Degussa P-25 (80% anatase, 20% rutile) has high photoactivity due to the transferring of electrons from rutile to anatase trapping sites, which hinders the electron-hole recombination. Thus, controlling the phase of TiO2 and understanding growth behavior of these materials are critical for designing and controllably manipulating structures for more efficient application. Herein, we investigate the phase transformation from anatase to rutile at atomic level by in situ TEM combined with electron diffraction patterns (EDPs). Nano particle (~ 10 nm), platelet with (001) facet and octahedron with (101) facet have been employed in our experiment, and orientation relationships of different phases are determined by real-time EDPs. The results show that transformations from anatase to intermediate phases (e.g. brookite and/or TiO2 with a different structure) are essential before completing the rutile phase transformation. Possible mechanisms for the phase transformation path are discussed. Moreover, a significant number of particles can be reduced into Ti2O3 for a long duration electron-beam activation.
11:15 AM - *CM4.10.05
A Nanolab inside a TEM for Nanoresearch
Litao Sun 1
1 , Southeast University, Nanjing China
Show AbstractBased on the idea of "setting up a nanolab inside a TEM", we present our recent progress in nanoresearch including in situ growth, nanofabrication with atomic resolution, in situ property characterization, nanodevice construction and possible applications (e.g. a 5nm-diameter hole on graphene for third-generation gene sequencing, the spongy graphene as an ultra-efficient sorbent for oils and organic solvents, etc.). The electron beam can be used as a tool to induce nanofabrication on the atomic scale. Additional probes from a special-designed holder provide the possibility to further manipulate and measure the electric/mechanical properties of the nanostructures in the small specimen chamber of a TEM. Recently, the optical signal also was introduced into the electron microscope to enrich the coverage of investigation inside the “multifunctional nanolab”. All phenomena from the in-situ experiments can be recorded in real time with atomic resolution.
References:
[1] L. Sun, F. Banhart, et. al., Science 312, 1199 (2006)
[2] J. R-Manzo, M. Terrones, et.al., Nature Nanotechnology 2, 307 (2007)
[3] X. Liu, T. Xu, et al., Nature Communications 4, 1776 (2013)
[4] H. Qiu, T. Xu, et al., Nature Communications 4, 2642 (2013)
[5] X. Li, X. Pan, et al., Nature Communications 5, 3688 (2014)
[6] X. Guo, G. Fang, et al., Science 344, 616 (2014)
[7] J. Sun, L. He, et al., Nature Materials 13, 1007 (2014)
[8] W. Zhou, K. Yin, et al., Nature 528, E1 (2015)
11:45 AM - CM4.10.06
Formation of Multi-Functional Heterostructure Nanowires through Solid-State Cation Exchanging Reaction
Jo-Hsuan Ho 1 , Chun-Wei Huang 1 , Ting-Yi Lin 1 , Tsung-Chun Tsai 1 , Yi-Hsin Ting 1 , Jui-Yuan Chen 1 , Wen-Wei Wu 1
1 Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu Taiwan
Show AbstractDynamics of atomic diffusion have been studied for many years. In addition, in-situ TEM observations can help us to understand diffusion behaviors in nanoscale directly. Here, we report a successful transformation from single crystalline ZnO to porous Fe3O4 nanowire in ultra-high vacuum transmission electron microscope (TEM) by cation exchange reaction at 600K for 10 min. The diffusion process was systematically analyzed, which can be seen in the in-situ video. Furthermore, the structure and composition of the Fe3O4 NWs were analyzed by Cs-corrected STEM equipped with EDS. Interestingly, ZnO nanowires will turn into different morphologies of porous Fe3O4 nanowires through different growth behaviors. The grown porous Fe3O4 nanowires are single crystalline, and the pores are either in the center of the nanowire to form a spine-like structure, or randomly distributed over the whole nanowire. By in-situ TEM observation, we can easily control the diffusion length, getting the multi-functional one-dimensional heterostructures. Such ZnO/Fe3O4 and ZnO/Fe3O4/ZnO heterostructure nanowires are promising for the potential application in resistive random-access memory.
12:00 PM - CM4.10.07
In Situ TEM Studies of Anisotropic Sublimation and Solid State Intercalation in Two-Dimensional Colloidal Bi2Se3 and Bi2Te3 Nanocrystals
Joka Buha 1 , Liberato Manna 1
1 Nanochemistry, Istituto Italiano di Tecnologia, Genova Italy
Show AbstractThe phenomenon of anisotropic phase transformation (sublimation) observed in two-dimensional (2D) colloidal Bi2Te3 and Bi2Se3 nanocrystals (NC) has been studied by in situ annealing in TEM. Similar in situ experiments have been pursued to demonstrate solid state intercalation of Cu into Bi2Te3 and Bi2Se3 NCs. EFTEM, EDX and EELS have all be employed for a detailed characterization of the NCs and the processes studied.
Bismuth chalcogenides, such as Bi2Te3 and Bi2Se3, are among the best established thermoelectric materials. Nanostructured forms of these materials are particularly advantageous as this allows for their electrical and thermal transport properties to be tuned independently. Thermal stability and basic phase transformations, such as sublimation, have not been studied in these materials before on an atomic scale. Recently, Bi2Te3 and Bi2Se3 are attracting even more attention as topological insulators, and as superconductors when intercalated/doped with certain metals, Cu in particular.
The present study has found that the sublimation process in 2D Bi2Te3 and Bi2Se3 NCs induced by annealing is structurally and chemically anisotropic and takes place through the preferential dismantling of the prismatic type planes, as well as the preferential sublimation of Te (or Se). The observed anisotropic sublimation process is independent of the method of nanocrystal’s synthesis, their morphology, or the presence of surfactant on the nanocrystal surface. A thickness-dependent reduction of the sublimation point has also been observed with nanocrystals thinner than about 15 nm. The platelet-like Bi2Se3 NCs sublimate even below 280°C, while the Bi2Te3 ones sublimate at temperatures between 350°C and 450°C, depending on their thickness, under the vacuum conditions in TEM column.
Intercalation into these and similar layered materials is usually achieved by either electrointercalation in an electrolyte containing the intercalant, self-intercalation during solidification of a melt containing the intercalant, or by diffusing the intercalant deposited/grown on the surface of a thin film. The present study demonstrates solid state intercalation into colloidal 2D Bi2Te3 and Bi2Se3 NCs, whereby the NCs and the source of intercalant are placed on the common solid substrate. Cu can be readily introduced into 2D Bi2Te3 and Bi2Se3 NC by a thermally-driven solid state intercalation. In the case of Bi2Se3, high levels of intercalated Cu and strong interaction between Se and Cu may additionally lead to solid state cation exchange transforming the rhombohedral Bi2Se3 to a cubic Cu2-xSe e. The 2D morphology of the NCs is preserved though both the intercalation and cation exchange processes. These experiments demonstrate that structure, composition and hence the properties and or functionality of colloidal NCs already utilized in solid state (e.g. in a device) may be locally modified.
12:15 PM - CM4.10.08
In Situ Imaging and Spectroscopy of Carbon Deposition on a Ni/CeO2 Catalyst
Ethan Lawrence 1 , Peter Crozier 1
1 , Arizona State University, Tempe, Arizona, United States
Show AbstractCorrelating structural and chemical changes observed at the nanoscale can provide more detailed insights into improving the stability of catalysts. Environmental transmission electron microscopy (ETEM) provides the ability to observe structural changes under simulated reaction conditions which can be correlated with nanomaterials’ performance through in situ techniques [1]. In situ electron energy-loss spectroscopy (EELS) has also allowed dynamic changes in the local oxidation state of nanomaterials to be determined during catalysis [2]. Long-term stability of solid oxide fuel cells (SOFC) may be limited by carbon deposition onto the active anode (fuel oxidation) catalyst, causing deactivation or destruction of the ceramic-metal (cermet) composite catalyst structure. In situ studies detailing fundamental processes occurring during carbon deposition are essential to designing better catalysts. Ni/ceria (Ni/CeO2) cermets have been shown to impede carbon deposition while maintaining favorable catalytic properties [3]. A fundamental study of the metal-oxide interaction in the cermet under reaction conditions will provide information on how the Ni/ceria catalyst is able to inhibit carbon deposition.
An FEI Titan ETEM was used to study gas-solid interactions of model Ni/CeO2 and Ni/SiO2 catalysts with two carbon source gases, ethane (C2H6) and ethylene (C2H4), to gain insight into carbon deposition processes relevant to SOFCs. During gas exposure, in situ EELS was used to monitor the valence state of Ce3+/4+, which varies with the oxygen content of the ceria according to Ce3+xCe4+1-xO2-2-x/2. Ce valence can thus be used to interpret carbon deposition behaviors in terms of oxygen deficiency of the ceria support. SiO2 was selected as a control support as it does not release oxygen, and thus enables comparison of metal-support interactions. When exposed to ethylene, carbon was deposited in the form of graphite layers on Ni particles supported by both CeO2 and SiO2. During ethane exposure under identical conditions, however, no carbon deposition was observed on Ni/CeO2. Therefore, ceria was able to inhibit carbon deposition during ethane exposure but not during ethylene exposure. Further in situ results and spectroscopic data will be presented.
[1] Tao, F. and P.A. Crozier, Chemical Reviews 116 (2016), p. 3487-3539.
[2] Sharma, R., et al, Philosophical Magazine 84 (2004), p. 2731-2747.
[3] Wang, W., et al, Chemical Reviews 113 (2013), p. 8104-8151.
[4] We gratefully acknowledge support of NSF grant DMR-1308085 and ASU’s John M. Cowley Center for High Resolution Electron Microscopy.
12:30 PM - CM4.10.09
Dynamic Observation of the Growth Behaviors in Cr3Si/Si Heterostructure Nanowires
Wan-Jhen Lin 1 , Chun-Wei Huang 1 , Jui-Yuan Chen 1 , Tsung-Chun Tsai 1 , Wen-Wei Wu 1
1 Materials Science and Engineering, National Chiao Tung University, Hsinchu Taiwan
Show AbstractTransition metal silicide nanowires exhibit low resistance,great thermal stability and excellent mechanical strength and therefore can be applied as interconnect and contact materials for future integrated circuits devices. In this work,we successfully fabricated two kinds of heterostructure nanowires,bare Si/Cr3Si nanowires and Si/Cr3Si nanowires covered with Al2O3 as outer shell that let the nanowires growth more perfectly straight. The growth behaviors and diffusion mechanisms of these two kinds of silicide heterostructure nanowires were observed by in-situ TEM at 620°C and discovered that different growth rates correspond to different annealing temperatures;therefore,the activation energy of Cr3Si heterostructure nanowires could be calculated. We also studied the crystal structure and the electrical transportation properties of Cr3Si nanowires; and the results of TEM, EDS and SAED confirmed the single-crystalline A15 type structure of the intrinsic Cr3Si nanowires. These result provide that phase transformation is influenced by the stressed structure at nanoscale.
12:45 PM - CM4.10.10
In Situ Visualization of Hydrogen-Induced Phase Transformations in Individual Palladium Nanorods
Fariah Hayee 1 , Tarun Narayan 2 , Andrea Baldi 3 , Ai Leen Koh 4 , Robert Sinclair 2 5 , Jennifer Dionne 2
1 Electrical Engineering, Stanford University, Stanford, California, United States, 2 Materials Science and Engineering, Stanford University, Stanford, California, United States, 3 , FOM Institute DIFFER, Eindhoven Netherlands, 4 Stanford Nano Shared Facilities, Stanford University, Stanford, California, United States, 5 Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Stanford, California, United States
Show AbstractNanoparticle phase transitions based on ion intercalation are ubiquitous in numerous energy- and information-processing devices, including batteries, fuel cells, and memory devices. Many of these systems rely on one-dimensional nanostructures, such as nanowires and nanorods, owing to their high surface-area to volume ratio. However, their intercalation thermodynamics and kinetics remain largely unknown, due to the difficulty in visualizing nanoparticle phase transitions in reactive environments. Here, we use in-situ electron microscopy and spectroscopy to investigate solute ion-driven phase transitions in nanorods, focusing on the hydrogenation of Pd. First, we colloidally synthesized nanorods of varying aspect ratios, with lengths ranging from 40 nm to 500 nm and diameters of ~20 nm. Each nanorod is a five-fold twinned structure enclosed by five (100) side surfaces and capped by ten (111) surfaces. We then used focused electron energy loss (EEL) spectroscopy to probe the hydrogen-induced phase transformation with ~3 nm spatial resolution and at hydrogen pressures ranging from 0Pa to 600Pa. EEL spectra collected at different points along the nanorod at different pressures show that the lattice-expanded hydrogenated phase preferentially nucleates at the (111)-terminated caps, regardless of nanorod length. However, shorter rods tend to nucleate the hydrogenated phase at only one cap, while longer rods tend to show nucleation at both caps. With increasing hydrogen pressure, the phase boundary propagates along the length of the nanorod. Dark field imaging and diffraction confirm phase separation within individual crystallites of the nanorod. These results are in contrast with our studies of single-crystalline nanoparticles, which do not exhibit equilibrium phase coexistence. We rationalize our results using a combination of mechanical strain modeling and kinetic analysis. Together, our EEL spectroscopy and diffraction techniques reveal preferential spatial nucleation and near-equilibrium phase coexistence in nanorods, and point toward design principles for next-generation nanorod-based energy and memory storage systems.
CM4.11: Ultra-Fast Electron Microscopy and Solid-State Materials Dynamics
Session Chairs
Friday PM, April 21, 2017
PCC North, 100 Level, Room 127 B
2:30 PM - *CM4.11.01
Spatio-Temporal Visualization of Phonon and Plasmon Dynamics in Low-Dimensional Materials
Giovanni Vanacore 1 , Fabrizio Carbone 1
1 Institute of Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne Switzerland
Show AbstractUnderstanding the ultrafast evolution of low-dimensional materials under non-equilibrium conditions plays a fundamental role in deciphering the mechanism governing chemical and physical functions. With direct visualization, the technological development of new generation nanoscale devices would become feasible.
Although an enormous effort has been devoted to the comprehension and improvement of these materials and devices, the capability of investigating their dynamic behavior is hindered by the difficulty of simultaneously studying their evolution in space and time at the appropriate scales. The traditional characterization techniques and the steady-state theoretical models are both not adequate for describing their non-equilibrium behavior. Instead, a novel approach for visualization of matter with high temporal and spatial resolutions, together with momentum and energy selection, is indispensable to fully exploit their potential.
Ultrafast electron microscopy (UEM) has been recently developed with the capability of performing time-resolved imaging, diffraction and electron-spectroscopy [1]. The high scattering cross-section for electron/matter interaction, the high spatial resolution (down to the atomic scale), the ultrafast temporal resolution and the high energy selectivity of UEM represent the key elements that make this technique a unique tool for the dynamic investigation of surfaces, interfaces and nanostructures.
In this contribution, we will address several recent applications to the investigation of elementary excitations, such as plasmons and phonons, in low-dimensional nanosystems, highlighting for each case the challenges that had to be overcome and the main scientific contribution. In particular, using the near-field variant of UEM, called Photon-Induced Near-Field Electron Microscopy (PINEM), it is now possible to visualize and control the dynamics of the plasmonic near-field optically created in the vicinities of single nanostructures or arrays of nanocavities with nanometer spatial and femtosecond temporal resolutions [2-3]. Also, ultrafast diffraction, which provides atomic-scale resolution at a femtosecond time scale, is used to unveil the effect of the reduced dimensionality on the non-equilibrium dynamics of lattice vibrations (phonons) and their transport regimes [4].
The highly inter- and multi-disciplinary approach presented here will pave the way for an unprecedented insight into the non-equilibrium phenomena of advanced materials, and should play a decisive role in the rational design and engineering of future applications.
[1] G.M. Vanacore et al., Nano Today 11, 228-249 (2016).
[2] L. Piazza et al., Nat. Commun. 6 6407 (2015).
[3] T.T.A. Lummen et al., Nat. Commun. 7 13156 (2016).
[4] G.M. Vanacore et al., Nano Lett. 14 6148-6154 (2014).
3:00 PM - CM4.11.02
Development of Sandia National Laboratories’ In Situ Ion Irradiation Dynamic TEM
Patrick Price 1 , Richard Sisson 1 , Michael Abere 1 , Sang Park 2 , Bryan Reed 2 , Daniel Masiel 2 , David Adams 1 , Khalid Hattar 1
1 , Sandia National Laboratories, Boise, Idaho, United States, 2 , Integrated Dynamic Electron Solutions, Inc., Pleasanton, California, United States
Show AbstractTraditional in situ transmission electron microscopy (TEM) is capable of imaging structure and morphology, characterizing defects, and chemical analysis with high spatial resolution in a range of applied thermal, mechanical, and environmental loads, but is limited by the temporal resolution of the camera system, typically 33 ms. Higher temporal resolution is required to characterize many dynamic phenomena in materials systems such as defect formation and growth, phase transformations, and structural changes. Dynamic TEM (DTEM) has been developed to investigate materials under these transient conditions using a pulsed laser to illuminate a photocathode source to achieve nanosecond-scale time resolution, but all current DTEM systems have limited control over the sample environment. We are addressing this issue by adding DTEM capabilities to the In-situ Ion Irradiation Transmission Electron Microscope (I3TEM), a unique instrument designed for the investigation of materials in a range of overlapping extreme environments including radiation effects, gas and liquid interactions, corrosion, temperature extremes, and mechanical strain, fatigue, or creep. This ongoing development will combine in-situ imaging in extreme environments with high spatial and temporal resolution in order to better understand the transient behavior in materials under challenging real-world conditions. This talk will highlight the current status of the I3DTEM including: a movie mode deflector system, an in-situ specimen drive laser, a pulsed laser cathode system, addition of a C0 lens, a tantalum cathode source, a laser control system, and associated synchronization software between the environmental holders, laser systems, and ion accelerators. Finally, preliminary results of in-situ characterization of materials using the I3DTEM will be presented.
This work is supported partially by the Division of Materials Science and Engineering, Office of Basic Energy Sciences, U.S. Department of Energy. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.
3:15 PM - *CM4.11.03
In Situ Imaging of Complex Phase Transitions in Functional Transition Metal Compounds at Ultrafast Timescales
Chong-Yu Ruan 1 , Faran Zhou 1 , Joseph Williams 1 , Tianyin Sun 1 , Christos Malliakas 2 , Mercouri Kanatzidis 2 , David Torres 3 , Nelson Sepulveda 3 , Phillip Duxbury 1 , Subhendra Mahanti 1
1 Physics and Astronomy, Michigan State University, East Lansing, Michigan, United States, 2 Chemistry, Northwestern University, Evanston, Illinois, United States, 3 Electrical and Computer Engineering, Michigan State University, East Lansing, Michigan, United States
Show AbstractPhase transition is often discussed within the context of thermal equilibrium where distinct phase change processes are described by the complex phase diagram where temperature, chemical doping, and pressure are steady-state tuning parameters. Much less is understood in dynamical phase transitions induced under a sudden interaction quench, where the thermodynamic ground state may become less stable than its counterparts and metastable new functional phases may emerge. Characterizing the nonequilibrium transformations may provide valuable insight regarding the nature of these states, and their interactions, which may open new pathways for active controls of these phases transformations with significant technological ramifications.
We discuss the different prospects of implementing ultrafast pump-probe experiments using ultrashort and coherent electron beams, and the ideas of photo-doping and using intense electron pulses as excitation sources to instigate the material transformations. We report case studies of phase transitions in transition metal chalcogenide charge-density wave compounds and vanadium dioxide, in which the electronic transition and structural transition are strongly coupled. Through the in situ direct observation of transient intermediate state structures under controlled excitations, we illustrate the keys mechanisms involving different roles of charge-carrier and lattice instabilities in directing unconventional phase transformations at ultrafast timescales.
In the case of transition-metal dichalcogenide materials, a succession of different phases was introduced transiently using femtosecond mid-infrared pulses and the local atomic scale charge-density-wave dynamics and morphological evolution of the long-range textured domains were characterized using the ultrashort coherent electron pulses. The various metastable and hidden states emerging under the controlled nonthermal, nonadiabatic driving highlight the interaction-driven nature of these transitions with limited involvement of lattice entropy.
In the case of vanadium dioxide, the dynamical phase transitions defined by sharp crossover into metastable phases and their distinct decay driven by lattice instabilities were closely examined from the perspectives of nonequilibrium dynamics. The emergent state with unusual transient electronic metastability instigated by carrier effects and its unusually long lifetime ameliorable by lattice strain and instabilities highlight the unique functional properties of VO2 for metastable memory and gating under controlled settings.
The methodology introduced here could be generally applied to survey the functional energy landscape in electronic materials. In particular, the observation of robust non-thermal switching at meso-scales and at ultrafast timescales, provides a platform for designing high-speed low-energy consumption nano-photonics and electronics devices.
CM4.12: Advanced In Situ Methods and Multimodal Characterization
Session Chairs
Friday PM, April 21, 2017
PCC North, 100 Level, Room 127 B
4:15 PM - *CM4.12.01
High Performance Direct Electron Camera for In Situ TEM Imaging
Liang Jin 1 , Benjamin Bammes 1 , Michael Spilman 1 , Robert Bilhorn 1
1 , Direct Electron, LP, San Diego, California, United States
Show AbstractIn-situ testing experiments using Transmission electron microscopy (TEM) can provide important direct evidence about materials deformation mechanisms and chemical reactions at high resolution, but it also introduce new instrumentation challenges. These include undesired dynamic specimen processes (e.g., drift, beam-induced motion, charging, radiation damage, etc.), insufficient field of view, insufficient frame rates, and inefficient electron detectors.
With the goal of overcoming many of these obstacles, Direct Electron (San Diego, CA, USA) has expanded the direct electron camera product line recently and introduced a new camera, DE-16. The 16 megapixel high speed camera represents the latest sensor innovation and can provide unrivaled signal to noise ratio (SNR) and dynamic range of any available TEM direct detection camera. In this report, we will show results from the DE-16 DDD camera demonstrating the sensor’s unique features. The data analysis is performed using the latest GPU-accelerated in-situ movie processing software tools from Direct Electron.
4:45 PM - CM4.12.02
Direct Observation of Transversely Propagating Exothermic Processes in Nanoscale Thin Films
Garth Egan 1 , Tian Li 1 , John Roehling 1 , Joseph McKeown 1 , David Adams 2 , Geoffrey Campbell 1
1 , Lawrence Livermore National Laboratory, Livermore, California, United States, 2 , Sandia National Laboratory, Albuquerque, New Mexico, United States
Show AbstractSelf-propagating reactions in thin film materials are important to a wide range of fields and applications. Common examples include the crystallization of amorphous semiconductors in electronic materials processing and alloying reactions in multilayer thin films for heat generation or materials synthesis. Under certain conditions, the reaction front of these processes will become unsteady, which can lead to propagation that occurs primarily in the direction transverse to the net growth of the reacted zone. Often this produces spiral-like patterns as multiple small (1-10 µm wide) reaction fronts circle around the point of origin. For this paper, the kinetics and mechanisms of transverse propagation during crystallization of amorphous Ge and reaction of Al/Co multilayers were studied using the Movie Mode of the Dynamic Transmission Electron Microscope (DTEM) at Lawrence Livermore National Laboratory. This enabled the recording of 9 frames with 50 ns exposures and submicron resolution of a reaction initiated with a ~12 ns laser pulse. During reaction, the net radial growth rate was found to be 0.1-1 m/s depending on the system, with transversely propagating reaction fronts moving at 7-10 m/s. In situ heating and cooling holders were also employed to determine the impact of substrate temperature on propagation behavior and rate. Along with post mortem analysis of resulting crystalline structures, this data was used to better understand the origin and mechanisms of transverse propagation in these two very different reactive systems. This work was performed under the auspices of the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering for FWP SCW0974 by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
5:00 PM - CM4.12.03
High-Speed Observation of Reversible Phase Transformations Using a Direct Detection Camera
Benjamin Miller 1 , Stephen Mick 1
1 , Gatan, Inc., Pleasanton, California, United States
Show AbstractTraditional digital TEM cameras have been capable of capturing only tens of frames per second, limiting the temporal resolution with which dynamic processes can be observed in the TEM. This was due to a combination of slow digital processing and rate-limiting detective quantum efficiency (DQE). Today, direct detection cameras with significantly enhanced DQE are available, extending the possible temporal resolution to millisecond time scales.
In this work, the K2 IS direct detection camera was used to collect high speed videos of reversible phase transformations within clusters of copper-tin nanoparticles. This was enabled by the use of a MEMS-based Wildfire heating holder from DENSsolutions which minimized the spatial drift usually associated with heating a sample in the TEM.
Using the stable holder and fast camera, videos were acquired with a spatial resolution of less than 1 Å and a temporal resolution of 5 ms. An analysis of the lattice spacings present in the video frames clearly indicates that the expected phase transformation did take place. However, Fourier filtering of the videos revealed that the phase transformation was inhomogeneous across <100 nm diameter clusters of particles. This emphasizes the importance of techniques like TEM which can provide the high spatial resolution necessary to resolve this inhomogeneity, and with direct detection cameras, the temporal resolution needed to observe the dynamics of the transformation.
5:15 PM - CM4.12.04
In Situ TEM Observation of Oxygen Vacancy Driven Structural and Resistive Phase Transitions in La2/3Sr1/3MnO3
Lide Yao 1 , Sampo Inkinen 1 , Sebastiaan van Dijken 1
1 , Aalto University, Espoo Finland
Show AbstractOxygen defects can have a profound effect on the physical properties of transition metal oxides. Electric-field driven migration of oxygen vacancies provides a viable mechanism for the formation, rupture and reconstruction of conducting filaments in insulating oxides, an effect that is used in nanoscale resistive switching devices [1,2]. In complex oxides where magnetic, ferroelectric and superconducting phases emerge from strong correlations between localized transition metal valence electrons, oxygen vacancies can radically alter a plurality of intrinsic properties via valance changes and structural phase transitions [3]. The ability to reversibly control the concentration and profile of oxygen vacancies in oxide nanostructures would thus open up comprehensive prospects for new functional ionic devices. Advancements in this direction require experimental techniques that allow for simultaneous measurements of oxygen vacancy dynamics, atomic-scale structural effects and macroscopic physical properties.
Here, we use in situ transmission electron microscopy (TEM) to demonstrate reversible switching between three resistance states in epitaxial La2/3Sr1/3MnO3 films. Simultaneous high-resolution imaging and resistance probing indicate that the switching events are caused by the formation of uniform structural phases. Reversible horizontal migration of oxygen vacancies within the manganite film, driven by combined effects of Joule heating and bias voltage, predominantly triggers the structural and resistive transitions. Our findings open prospects based on dynamic control of physical properties in complex oxide nanostructures.
[1] R. Waser and M. Aono, Nature Mater. 6, 833 (2007).
[2] J.J. Yang, D.B. Strukov, and D.R. Stewart, Nature Nanotech. 8, 13 (2013).
[3] S.V. Kalinin and N.A. Spaldin, Science 341, 858 (2013).