Transitional metal oxides exhibit a wide array of functionalities, with applications as e.g. memristors, solid oxide fuel cells, and electrochromic devices. These functionalities are intrinsically controlled by the static and dynamic behavior of oxygen vacancies. The confluence of these effects can give rise to structural and metal-insulator transitions; characterization of these transformations is critical for understanding the materials behavior. Interestingly, many recent results illustrate that reversible vacancy redistribution in oxides is possible at room temperature and below in sufficiently high electric fields [1], suggesting that we can study these phenomena inside electron microscope.
Applying electrical current inside the microscope, we can observe the sequence of phases during forming of a memristor filament in amorphous TiO₂ thin films. We can also trace the improved performance of the lanthanum strontium cobaltite-based fuel cells to surface amorphization and observe “annealing” of a vacancy ordered system caused by bias cycling [2]. Interestingly, we can demonstrate that electron beam has a similar effect on the oxygen sublattice, inducing vacancy ordering and vacancy injection in controllable proportions. Finally, we will show how electron beam can be used to controllably grow crystalline oxide filaments from the amorphous matrix.
Research supported by the U.S. Department of Energy (DOE), Basic Energy Sciences (BES), Division of Materials Sciences and Engineering, and through a user project supported by ORNL&’s Center for Nanophase Materials Sciences (CNMS), which is sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. DOE.
References
[1] J. Fleig et al., Scripta Materialia 65 (2), 78 (2011)
[2] D.N. Leonard et al., Adv. Energy Mater., 3, 788 (2013)

In recent years the development of instruments for time-resolved transmission electron microscopy (TEM) on the nanosecond time scale has revolutionized the study of phase transformations, many of which occur very rapidly when viewed at nanometer length scales. This talk describes a new advance in the study of rapid phase transformations: the combination of nanocalorimetry and dynamic transmission electron microscopy (DTEM). Operating a chip-based nanocalorimeter within a DTEM enables time-resolved acquisition of temperature, reaction enthalpy, electron images, and electron diffraction patterns with 5 µs resolution, all while heating materials at rates from 100 K/s to 100,000 K/s. While the system is broadly applicable to a wide range of materials, its development was spurred specifically by an interest in reactive materials. Reactive materials are a broad class of materials systems designed to deliver large heat releases, typically from formation or oxidation-reduction reactions. As a case study we present results on the effects of heating rate on the phase transformation sequence in Ni/Al bilayers. The combination of time-resolved electron diffraction and heat evolution data reveals the suppression of one of the Ni/Al intermetallic phases as heating rate is increased. A preliminary explanation for this observation based on a changing balance between nucleation rate and growth rate will be presented, illustrating the importance of calorimetric data in the interpretation of time-resolved microscopy results.

Growth of titanium dioxide (TiO2) nanostructures is the subject of extensive research due to their potential in energy applications such as photocatalysts, solar-to-hydrogen production, methanol fuel cells, anodes for lithium rechargeable batteries, and photovoltaic cells. Rutile is reported to exhibit a high rate of recombination in comparison to the anatase while some mixed phases exhibit high photoactivity due to the transfer of electrons from rutile to anatase trapping sites, preventing charge recombination. Thus, controlling the phase of TiO2 and understanding its growth behavior is critical for exploiting the phase-function relationships. Moreover, precise control over morphology is required to utilize nanocrystalline materials for energy storage, photovoltaic, catalytic, and photonic applications. Highly branched nanostructures are of particular interest because they can have large absorption cross-sections, short electron mean free paths or complex patterns of optical interference. Using ex situ TEM, we showed that branched TiO2 forms through a process of oriented nanoparticle attachment in which particles of anatase, the stable phase at the nanoscle, attach to wires of rutile, the stable phase at the macroscale, on specific facets. Following attachment, the particles undergo a pseudomorphic transition to rutile, either extending the wire or creating a branch, depending on the direction of attachment. In order to understand the controls on the attachment and transformation process, we employed in situ TEM techniques to study both the phase transformation from anatase to rutile and the growth of branched TiO2 nanostructures. We used the TEAM0.5 microscope to perform high-resolution TEM/STEM imaging experiments of anatase particle transformation into rutile at temperatures of 600 to 900 degree C. We used two different sources of 5-10 nm anatase, one consisting of individual particles and the other composed of 50 to 100 nn clusters of co-aligned particles. The individual particles were observed to transform into rutile via an unidentified transitory phase that forms square particles. These then transform into round, rutile particles via Ostwald ripening. For the large cluster of anatase particles, no transitory phase was observed. STEM imaging revealed the detailed atomic rearrangements that took place during the transformation. In the second part, we employ in situ TEM to probe the mechanisms of branched nanocrystal nucleation and growth at the atomic level and quantify the kinetic and thermodynamic parameters that control the resulting morphologies and growth rates.

Traditionally, crystal-to-amorphous phase transformation in phase-change materials (PCM) used in non-volatile memory applications has been carried out by melting the crystalline phase, and quenching the melt to a glassy state, via the application of electrical or laser pulses. However, it has been recently realized that this transformation may be achieved through lower power consuming routes, which do not invoke the formation of the melt phase[1]. Nam et al.,[1] through in situ transmission electron microscopy (TEM) have shown that formation of dislocations and their subsequent dynamics during the application of electrical pulses (programming) is responsible for amorphization in Ge2Sb2Te5 nanowires. However, the role of intrinsic point defects in the evolution of extended defects such as dislocations and their effect on the electronic properties, leading to amorphization in PCM have remained elusive. Here, by performing in situ TEM we present a multi-scale structural analysis, and structure-property correlation on a simple binary GeTe single-crystalline nanowire system, upon programming to the amorphous phase.
A unique feature of crystalline GeTe is the presence of 1E19-1E20/cm3 structural Ge vacancies. Application of short electrical pulses (50 ns, < 3V) creates heat shocks in the material resulting in clustering of Ge vacancies, which beyond a certain size prefer to condense in the {111} plane. This leads to a local collapse of the adjacent atomic planes and the formation of an edge dislocation loop with an associated anti-phase boundary (APB), which contains series of ordered Te antisites. This process results in a reduction of Ge vacancy concentration, which was verified through peak-shift of the plasmon peak in the electron energy loss spectrum. We demonstrate the formation and migration of these APBs in the direction of hole-wind force using real space in situ TEM imaging, and reveal their dynamics further through in situ Fourier space imaging, and density functional theory calculations. Furthermore, we show that the APBs accumulate at a local region of inhomogeneity, and the system then activates other slip systems (along the non-growth direction), generating more APBs that intersect each other, creating random Te antisites template- along which the amorphization takes place. Thus microstructurally, we show the evolution of APBs and their subsequent jamming, which at the atomic scale relates to the evolution of intrinsic Ge vacancies to ordered Te antisites and finally to random Te antisites in single-crystalline GeTe nanowire devices. Through a structure-property correlation, we show that the accumulation of disorder changes the electronic properties of GeTe while still maintaining the single-crystalline long-range order, prior to this solid-state amorphization- suggesting the role of electronic instabilities in the phase change process.

Advances in electron microscopy have enabled the imaging of dynamics at atomic-level resolution. Nanocrystals present well-defined systems to study fundamental transient phenomena which are well defined in bulk materials. Cadmium chalcogenides (CdS, CdSe, and CdTe) are one of the most extensively studied and understood nanocrystals systems. These materials have been applied to a variety of optical and optoelectronic applications such as display phosphors, biological markers, and photovoltaics. Many first order phase transitions such as melting point and pressure-induced structural changes for these materials have been investigated through indirect spectroscopic methods; direct observation of phase changes in anisotropic structures have not been reported. In this work, we present the first direct observation of sublimation in CdSe nanorods. We observe the dynamics of sublimation in bright field TEM with atomic-level resolution at 10^-7 Torr at four different temperatures. We found that vaporization occurs exclusively from the (001) and (00-1) planes. At a temperature just below the sublimation point, the electron beam heats the rod inducing vaporization from both ends in process which is limited by nucleation rather than vaporization. At temperatures much higher than the sublimation point, vaporization proceeds rapidly from only one end of the rod and does not appear to be nucleation limited. We believe that at these elevated temperatures, the sublimation behavior may be strongly influenced by a roughening transition.

Our focus is on the development of integrated characterization and modeling tools and their applications appropriate for carrying out detailed studies on metallic nanoscale clusters comprised of a few to as many as 100 metal atoms. Two state of the art methodologies, synchrotron X-ray absorption fine-structure (XAFS) and quantitative scanning transmission electron microscopy (STEM) methodologies are used and specially designed for determining the 3D structure and structural habits, both individually and as an ensemble, critical for understanding metallic nanoclusters. The experimental work is integrated with theoretical calculations. It is now clear that the structural dynamics of small metallic clusters is actually quite complex. For example, we have shown that the structures of Pt NPs may be both ordered and disordered, depending on its size, support and adsorbates. While bulk amorphous Pt is unstable, its existence in NPs is a manifestation of their mesoscopic nature. Furthermore, theoretical simulations show that the Pt NPs are not static, but show highly fluxional dynamics. To bridge the theory-experiment gap, we are producing model Pt/γ-Al2O3 systems using oxidation of NiAl(110) to form a thin film of single crystal γ-Al2O3 . To bridge the complexity gap, we are developing an universal environmental cell that is compatible currently with synchrotron XAFS and environmental TEM.

Coherent electron nanodiffraction in the STEM has been used to study the static structure of amorphous materials at the nanoscale in a technique called fluctuation electron microscopy. Here, we report the use of time-resolved electron nanodiffraction to measure atomic dynamics in glasses and supercooled glass-forming liquids. In analogy to the corresponding technique with photons, photon correlation spectroscopy, we call this technique electron correlation microscopy. From the time autocorrelation function of the diffracted intensity, we derive the relaxation time tau; and stretched exponential parameter β for metallic glasses from 75% to 110% of the glass transition temperature, T_g. Well below T_g, the results may be dominated by relaxation of beam-induced atomic motions, but near and above T_g, the behavior appears to be intrinsic. tau; decreases monotonically above T_g, but β changes abruptly from <1 below T_g to >1 above T_g. Current measurements were performed at 6 nm spatial resolution and ~3 sec temporal resolution. We will discuss efforts to achieve sub-nanometer and millisecond performance.
We acknowledge support from the National Science Foundation (LH and PMV DMR-1205899 and PKL DMR-0909037, CMMI-0900271, and CMMI-1100080).

In-situ STEM experiments are now capable of observing chemical and biological processes with sub-nanometer spatial resolution [1, 2]. In order to understand these experiments, there is a growing demand for the development and optimization of image interpretation techniques that are sensitive to specific experimental conditions. In order to verify the accuracy of our image interpretation, it becomes necessary to simulate the images through modeling techniques. There are two key areas of understanding that need be addressed in order to perform successful simulation: (1) the atomic structure of observed specimens, and (2) the resulting electron-beam interaction with specimens. To this end, we have created a partnership between molecular dynamics (MD) simulation techniques and the multi-slice image simulation technique [3, 4, 5]. By employing these methods, it is possible to simulate realistic images of entire in-situ environments via million-atom models [5].
Various in-situ STEM observations can be explained through these methods. We have been able to employ simulation to understand such image features as resolution limits, interface contrast features, and physical nanoparticulate behavior. We show that contrast features due to solvent structural changes at a gold electrode-solution interface are qualitatively explained with simulation, and interesting electron channeling effects are identified. Additionally, we show that nanoparticulate-agglomeration behavior observed for silver nanorods is explained with these techniques.
References
[1] Evans, J. E. Jungjohann, K. L. Browning, N. D. Arslan, I. Nano Lett. 11. 2011. 2809.
[2] Ring, E. A. de Jonge, N. Microsc. Microanal. 16. 2010. 622.
[3] E. Kirkland. Image Simulation in Transmission Electron Microscopy. Cornell University. Ithaca. 2006.
[4] C. Koch. Determination of Core Structure Periodicity and Point Defect Density Along Dislocations. Dissertation. Arizona State University. 2002.
[5] Welch, D. A. Faller, R. Evans, J. E. Browning, N. D. Ultramicroscopy. 135. 2013. 36.
[6] This research was supported by the Department of Energy (Contract DE-AC05-76RL01830 and Grant DE-FG52-06NA26213) and by the National Institute of Health (Grant RR025032-01 and Grant 5RC1GM091755). The research described in this presentation is part of the Chemical Imaging Initiative; it was conducted under the Laboratory Directed Research and Development Program at PNNL, a multiprogram national laboratory operated by Battelle for the U.S. Department of Energy under Contract DE-AC05-76RL01830. A portion of the research was performed using EMSL, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory.

Dynamic processes such as solid state chemical reactions are ubiquitous in materials science. They are relied upon for applications ranging from materials synthesis to device operations. For instance, electrochemical energy systems rely on ion exchanges to store or release energy. Furthermore in devices such as batteries these exchanges often necessitate not only the transport of ions but also phase changes which involve their own transformation dynamics. Understanding how these processes occur can prove vital to advancing device performance, yet experimental methods have not previously provided direct atomic scale insight into such transformations. We demonstrate the use of Z-contrast annular dark-field electron microscopy to directly observe the atomic scale dynamics of a manganese oxide phase change. The energy of the electron probe in an aberration corrected scanning transmission electron microscope is used to transform Mn3O4 into MnO. A small region of MnO is first nucleated by prolonged exposure to the electron beam. By recording a time series of rapidly acquired atomic resolution images we uncover the detailed motions of the atomic columns as the phase front advances. Furthermore the atomic number contrast of the Z-contrast images also allows changes in the occupancy of the atomic columns to be quantified. Finally, by inputting the observations into density functional theory simulations we are able to determine the energetics of the atomic motions involved in the chemical reaction step-by-step.
Research sponsored by the UK Engineering and Physical Sciences Research Council through the UK National Facility for Aberration-Corrected STEM (SuperSTEM).

Grain boundaries are well known to enhance the strength of polycrystalline metals as they act as obstacles for dislocations. However, the blocking strength of individual grain boundaries may be very different depending on the orientation of grain boundary plane and the orientation of the slip systems in the adjacent grains. In addition some grain boundaries act as sinks, while others are sources of dislocations. In this talk we compare as a model system the deformation behavior of a general large angle grain boundary and a coherent twin boundary in a compression experiment of Cu micropillars. For comparison, the flow behavior of the adjacent single crystalline Cu micropillars is analyzed. In situ SEM, TEM and micro-Laue studies as well as DDD simulations are performed to shed light on the dislocation processes. The huge differences in mechanical behavior of the bicrystalline pillars are discussed based on the experimental results.

Mechanical properties in nano-sized metallic glasses have been widely investigated to clearly understand the fundamental deformation mechanism of metallic glasses. In particular, the change of yield strength and the occurrence of deformation mode transition (from heterogeneous to homogeneous) with sample size reduction have been reported in previous experimental studies through nanopillar test results. Research on nano-mechanical responses of metallic glasses could lead to an in-depth understanding of the deformation mechanism related to shear deformation. However, during the pillar fabrication using focused ion beam for nanopillar tests, Ga+ ion beam damage on pillar surface is difficult to avoid and the fabrication takes relatively long for multiple pillar preparations. To avoid the drawbacks of nanopillar tests, in the present study we performed compression tests of metallic glass nanoparticles using in-situ holder in electron microscope. In our experiments, metallic glass nanoparticles have been fabricated by the dealloying technique from phase separated metallic glasses. From the two-amorphous alloys with droplet structure, the reactive matrix phase has been selectively dissolved by chemical process. The shape of the remaining particle phases was clearly spherical, and the sizes of fabricated particles have distribution in 40~300 nm diameter range. The effect of particle size on mechanical properties of fabricated amorphous particles has been investigated from the compression test using in-situ tester with electron microscope imaging. Due to the distinct morphology of particles compared to that of nanopillars, the stress-strain relations from particle compression test results are derived based on contact mechanics theory and contact area calculation. These results provide us with insights on evaluation of nano-mechanical properties and understanding of fundamental deformation mechanism of metallic glasses.

The objective of this work is to elucidate the deformation behavior of materials at high temperatures - an essential step toward the design and manufacturing of a new generation of high-temperature materials. To do this, we developed an experimental setup that allows us to heat the specimen while applying uniaxial tensile loading. High temperature at the specimen is achieved by ohmic heating while uniaxial tensile loading is applied using electro-thermal (chevron) actuator. This device is fabricated by MEMS based micro fabrication techniques. Specimen is cofabricated with the device that will remove any misalignment and gripping problems. We carried out in-situ transmission electron microscope (TEM) experiments on 75 nm Pt thin film specimen at high temperatures and observed grain boundary sliding induced edge cavitation as deformation and failure mechanism.

The trend of microelectronics industry is moving from two-dimensional to three-dimensional integrated circuits (3D IC) which raises significant attention to the integration of chip technology and packaging technology. The formation of a large number of micribumps in 3D IC packaging with controlled orientation has been proposed from the technology with [111]-oriented and nanotwinned Cu (nt-Cu) which enhances the strength of materials with microstructure designs. [1] Cu with nano-sized twins has been found to have significant improvement on the strengths of materials which benefits to the engineering designs in metal and alloys. [2, 3] The typical strengthening mechanisms in metals include grain refinement, strain hardening, and impurity alloying. In this paper, we will discuss the strengthening mechanism on a [111]-oriented and nanotwinned Cu in the aspect of microstructures and twin orientations. We will show the aberration-corrected images of nanotwinned copper from Cs-corrected transmission electron microscopy (Cs-corrected TEM) which provides the atomic details. We will then present the results of the effects of external force and nano-indentation which attributes to dislocation motion and strain formation. The reactions at the grain boundaries and twin boundaries under the conditions will be shown and discussed as well as the microstructures and reactions at the triple point of grain boundary and twin boundary. Besides, we will present the video rate imaging of the motion of grain boundary.
[1] H. -Y. Hsiao et al. Science 336, 1007-1010, 2012.
[2] L. Lu et al. Science 304, 422-426, 2004.
[3] D. Kiener et al. Nature Materials 10, 608-613, 2011.

Si nanowire-based tunnel-FET characteristics are intensively studied as a function of nanowire diameter and doping [1]. A significant reduction of B diffusion with decreasing nanowires diameter and a non-uniform diffusion depth in wider nanowires are observed [2]. Using process simulations, this behavior was attributed to a reduced transient enhanced diffusion close to the nanowire sidewall caused by the recombination of excess interstitials. The shallower profile in narrower nanowires was assumed to be related to an enhanced interstitial annihilation.
High fluxes of high energy electrons are known to create {113}-defects in thin Si foils and consist of self-interstitial clusters. {113}-defects are also formed during low temperature ion implantation. They dissolve during subsequent thermal anneals thus forming a source of self-interstitials leading, for example, to (unwanted) transient enhanced diffusion of dopants. Electrically active dopants like boron and phosphorus, interfaces and local stress fields have an influence on the {113}-defect formation kinetics and stability.
In an Ultra High Voltage Electron Microscope (UHVEM), the formation of intrinsic point defect clusters can be studied in situ while varying in a controlled way experimental parameters such as e-beam intensity, irradiation temperature, impurity concentration, capping layers on the sample and even vacuum in the specimen chamber. In situ e-irradiation offers a unique possibility to investigate intrinsic point defect interactions with various sinks in the bulk or at the surface of the Si sample [3 and references therein].
Results are presented of a study of {113}-defect formation in Si nanowire structures with diameters varying between 40 and 500 nm. The Si nanowires, used for the processing of tunnel-FET's, are etched into an epitaxial stack, of which the top layer is in situ boron doped and the top contact is implanted. The nanowires are embedded in oxide. In situ studies are performed on FIB prepared cross-section samples. Irradiations are performed between room temperature and 375 °C, using a 2 MeV e-beam.
[1] A. Vandooren, D. Leonelli, R. Rooyackers, K. Arstila, G. Groeseneken, and C. Huyghebaert, Solid-State Electronics 72, 82 (2012).
[2] A. Schulze, A. Florakis, T. Hantschel, P. Eyben, A. S. Verhulst, R. Rooyackers, A. Vandooren, and W. Vandervorst, Appl. Phys. Lett. 102, 052108 (2013).
[3] J. Vanhellemont, H. Yasuda , Y. Tokumoto, Y. Ohno, M. Suezawa, and I. Yonenaga , Phys. Status Solidi A 209, 1902 (2012).

Yan Xin
National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310
The range of the applications of gold nanoparticles is expanding astoundingly in areas such as catalysis, optical-electronics, therapeutic agents, biological and medical applications. The particle size, shape and particularly the surface atoms are fundamentally important to its applications. Transmission electron microscopy (TEM) is probably the best characterization technique to obtain its structural information. There has been numerous TEM works studying their size, shape, surface, and structure, since the TEM microscope had good enough resolution to resolve the Au lattice [1]. The surface atoms diffusion, and Au nanopartcile coalescence have also been observed and studied extensively, but qualitatively. In this work, aberration-corrected scanning transmission electron microscopy high angle angular dark field (STEM-HAADF) imaging is used to observe the 4 nm Au nanoparticle coalescence and migration quantitatively, at atomic level. The core finding is that the surface atoms play the essential role in the coalescence and migration [2].
Reference:
[1] J.-O. Bovin, R. Wallenberg, and D. J. Smith, Nature, 317, 47 (1985).
[2] The TEM facility at FSU is funded and supported by the Florida State University Research Foundation, and the work is supported by the National High Magnetic Field Laboratory, which was supported in part by the National Science Foundation Cooperative Agreement DMR-1157490, the State of Florida, the U.S. Department of Energy, and Florida State University.

Noble metal nanocrystals are expected to play a significant role in areas such as catalysis and green energy technologies, due to the unique properties resulting from their size. One key attribute of nanocrystals is that the higher ratio of surface atoms can lead to increased reactivity. Another important factor is crystallographic orientation of the surface facet; where chemical reactivity varies from one facet to another. The desired facets can either be formed during synthesis or through selective etching. Here, we present a study of the dissolution of Pd nanocubes due to Br- ions in solution using in situ liquid cell transmission electron microscopy. The dissolution process was observed dynamically using a liquid flow specimen holder and scanning transmission electron microscopy. The etching process starts from the corners and edges of the nanocube, slowly transforming the nanocube into a nearly spherical polyhedron until it dissolves completely. The nanocubes are not etched in solutions devoid of Br-, but they were found to rotate under influence of the electron beam.

Graphene-nanoribbon nanopore (GNR-NP) devices, in which a NP lays next to or in the center of a GNR are promising candidates for DNA sequencing. DNA sensing in solution is achieved by measuring GNR conductivity as the molecule traverses the NP. The challenge of creating NPs [1] in or next to GNRs using an electron beam is that, to precisely locate the position for NP drilling relative to the GNR, it is necessary to image some part of the device at relatively high magnification and thus high current densities. A beam of sufficient current will drill NPs in silicon nitride (SiNx, the supporting film of the GNR) but damage graphene, so the exposure of the GNR to the beam must be kept to a minimum.
We present the fabrication of GNR-NP sensors with NPs with diameters in the range of 2-10 nm and GNRs with widths between 20 and 200 nm and a length of 600 nm, on 40 nm-thick SiNx films. GNR conductance was monitored in situ during NP formation inside a TEM operating at 200 kV. We show that GNR resistance increases linearly with electron dose and that GNR conductance and mobility decrease by one or more orders of magnitude when GNRs are imaged at relatively high magnification with a broad beam prior to making a NP.
By operating the TEM in scanning TEM (STEM) mode we were able to prevent electron beam-induced damage and make NPs in highly conducting GNR sensors. The resulting GNRs can sustain micro ampere currents at low voltages in buffered electrolyte solution and exhibit high sensitivity, with a large relative change of resistance upon changes of gate voltage, similar to pristine GNRs without NPs [2].
[1] Differentiation of short, single-stranded DNA homopolymers in solid-state nanopores. K. Venta, G. Shemer, M. Puster, J. A. Rodríguez-Manzo, A. Balan, J. K. Rosenstein, K. Shepard, M. Drndicacute;. ACS Nano, 7: 4629-4636 (2013).
[2] Towards sensitive graphene nanoribbon-nanopore devices by preventing electron beam induced damage. M. Puster, J. A. Rodríguez-Manzo, A. Balan, M. Drndicacute;. ACS Nano, in review (2013).

Vertical graphene is a kind of excellent field emission materials because it has atomic thin edge and two-dimensional heat dissipated area. It has a potential application on cold cathode vacuum electronic devices, such as travelling wave tube, X-ray tube etc. To achieve top performance of vacuum electronic device, the electron source needs high current and current density to gain high power output. In such high current situation, the graphene sheets easily come to vacuum breakdown and cause damage of graphene sheet. There are several explanations on the mechanism, such as current-heating, discharge, ion bombardment. However, direct evident on microscopic level is lacked to verify these explanations.
Here, we use a high resolution transmission electron microscopy combined with an in-situ nano probe system to direct observe field emission process of graphene in nano scale. A single graphene sheet is fabricated on a tungsten tip, and another tungsten tip move to get close the graphene. When a voltage is applied between the graphene and the tungsten tip, field emission current can be detected. Two phenomenons on the structure deformation of graphene are observed. Along with the increase of field emission current, the deformation first appears on the sharp tip on the two corners of graphene sheet which means that electron most emit from the two corners but not averagely emits from the whole edge of graphene. Further increase the current, a serious deformation happens and totally changes the graphene edge shape which means the high current could reshape the graphene and improve the field emission performance. Further theory model and explanation will be discussed in details.

In recent years, with the increasing demand of smart phones and tablets, integrated circuits become more important than ever. Copper interconnect plays an important role in integrated circuits. Electroless deposition is a promising technology to fabricate copper interconnect owing to the following characteristics : (1) coating on nonmetallic substrate, (2) good uniformity, and (3) low cost. Therefore, realizing the grain growth mechanism in electroless copper deposition to improve the quality becomes an important issue in this field.
In this study, we utilized a specimen named K-kit (ref.1) (provided by MA -tek) for the in-situ observation of copper grain growth in transmission electron microscope (TEM). Palladium particles were formed in K-kit by loading tin (II) chloride and palladium (II) chloride subsequently, and copper electrolyte was applied. The K-kit was then sealed and the copper grain growth process was observed in K-kit by TEM. By investigating the effect of palladium morphology on copper growth and the growth mechanism, it can be applied to optimize copper deposition process. Therefore, with the successful in-situ and real time observation technology, electroless copper growth process could be optimized and used for future interconnect application.
Ref.
[1] K. L. Liu et al. Lab Chip, 2008, 8, 1915-1921

Monolayer sheets of two-dimensional sp2-bonded materials such as graphene and hexagonal boron nitride (h-BN) have been investigated for use in future devices due to their properties including high mechanical strength, thermal conductivity, stability and interesting electronic properties. A structural understanding of atomic scale defects in these materials is important because they significantly affect the physical properties in these materials. In particular, understanding the dynamics of these defects explains much about the material&’s stability. We have synthesized h-BN and graphene using low pressure chemical vapor deposition and imaged defects using ultra-high resolution aberration corrected transmission electron microscopy.

Sintering process of nanoparticles represents an interesting topic in maintaining the stability of colloidal nanoparticles and synthesizing hybrid multiple functional nanomaterials. In this presentation, we will report the sintering of Au nanoparticles and interfaced Au/Ag heterodimers with quantum sizes studied by in-situ high-resolution transmission electron microscopy (HRTEM). The results reveal that pure Au nanoparticles simply merger together to form bigger particles upon electron illumination and orientated attachment is not observed among the fused particles. Similar electron illumination can force the Au/Ag dimers to form Au@Ag core-shell particles followed by sublimation of the Ag shells slowly. In contrast, the Au/Ag dimers are transformed into alloy nanoparticles at elevated temperature around 400°C.
This work was performed at the Center for Nanoscale Materials, a U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences User Facility under Contract No. DE-AC02-06CH11357.

The increasing demand for smaller, lighter, cheaper, longer-lasting power sources for portable electronics, aircrafts and vehicles impels intensive research of the lithium ion batteries. Implementation of the modern paradigm of rational battery engineering, including design of smart electrode materials, is impossible without in-depth understanding of the chemical and physical processes in galvanic cells at the microscopic, nanoscopic, and eventually, molecular levels. Reaction mechanisms, cathode expansion, formation of cracks and SEI layer, electrolyte decomposition etc., are being extensively studied with a variety of ex and in situ microscopic, spectroscopic and electrochemical techniques. In situ transmission electron microscopy of single-nanowire batteries is the most recent advancement of the battery characterization, allowing real-time monitoring of the electrochemical processes at the nano and atomic scales. However, the cathode materials chosen for studies so far - SnO2, ZnO, Si, Ge - do not manifest topochemical transformations during lithiation, but rather lose their crystalline structure irreversibly as a result of reduction or amorphization processes. This leads to significant expansion and loss of integrity of the nanostructured cathodes, and therefore, shortens battery lifetime. Vanadium pentoxide, on the contrary, is not reduced to metal during lithiation, but rather forms a continuous range of lithium bronzes LixV2O5 with 0We report here on the in situ SEM studies of a single V2O5 mesowire-based battery with LiCoO2 anode in vacuum-compatible ionic liquid electrolyte. Cyclic voltammetry and potentiometric curves were correlated with the SEM observed processes such as electromigration, formation of SEI and meso-wire expansion. It is shown that the V2O5 wire can reversibly intercalate lithium without structural integrity failure or cracks formation, and underwent only minimal shape distortions.
Research supported by the Materials Science and Engineering Division of the U.S. Department of Energy and through a user project supported by ORNL&’s Center for Nanophase Materials Sciences (CNMS), which is sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy. SIUC part of the research was supported through NSF ECCS-0925837 grant.

Metal silicide nanowires (NWs) are of great interesting materials with diverse physical properties. Among these silicides, manganese silicides nanostructures have been attracted wide attention due to their several potential applications, including microelectronics, optoelectronics, spintronics and thermoelectric devices. In this work, we exhibited the formation of pure manganese silicide and manganese silicide/silicon nanowire heterostructures through solid state reaction with line contacts between manganese pads and silicon NWs. The growth process, structure and composition analysis of manganese silicide NWs have been investigated by in-situ ultrahigh vacuum transmission electron microscopy (UHV-TEM) and energy dispersive X-ray spectroscopy (EDX), respectively. The growth rates and the formation of various manganese silicide phases under thermal effect were systematically studied. We also characterized the dynamic diffusion of manganese atoms in the growth process and discussed the formation mechanism. Furthermore, we have investigated the electrical transport properties and fabricated field effect transistors (FETs) of the manganese silicide/silicon/manganese silicide nanowire heterostructures based devices. In addition to fundamental science, the significance of the study will be helpful for future processing techniques in nanotechnology and related applications.

In this talk, we shall report on atomic resolution In-situ electron microscopy study of plasticity mechanism of metallic Cu-, Au-, and Ni- nano-materials. By employing of in-situ tensile and/or bending tests with simultaneous atomic-lattice resolution observations, we can study on some abnormal mechanical properties under external strain.
Firstly, we shall report on the size dependent of dislocation activities in deformation of single crystalline- and micro twinning-cupper nano wires [1]. Then we shall present an in situ TEM tensile test on single crystalline copper nanowires with an advanced tensile device, and report here a crystalline-liquid-rubber-like (CRYS-LIQUE-R) behavior in fracturing crystalline metallic nanowires. A retractable strain of the fractured crystalline Cu nanowires can approach over 35%. Then we shall show some atomic-scale observation of continuous lattice deformation in bending Ni nanowires (NWs) to a strain as high as 17.5%, which is about twice larger than the normally expected theoretical elastic limit [3]. The functioning deformation mechanism was revealed in a novel in situ nano wire bending experiment inside a transmission electron microscope. This hyper lattice strain was thermally reversible by heating, and can store elastic energy more than 100 times higher than in bulk samples.
References:
[1] Y. H. Yue, et al.; Nano Letters, 12 (2012),4050.
[2] Y. H. Yue, et al.; Nano Letters, 13 (2013), 3812.
[3] L. H. Wang. Et al.; Nat Commun 4 (2013), 2413.

In our present work, copper nanopillars that only contain a few twin boundaries (in absence of grain boundaries) were cut from a polycrystalline nanotwinned sample by focused-ion-beam technique. Subsequent in situ compression of the copper nanotwinned pillars in transmission electron microscope shows that the twin boundaries are not stable anymore and can migrate under ~300 MPa shear stresses. Interestingly, in some cases twin lamella thickens, while in some cases twin lamella becomes thinner and finally annihilates. Combined with molecular dynamics simulations, we demonstrate that the twin boundary migration arises from highly-correlated surface partial dislocation nucleation and the migration direction is determined by the relation between the Burgers vector of the nucleated partial dislocations and the direction of applied shear stress. Our quantitative findings should be relevant for assessing the twin stability and deformation characteristics of nanotwinned materials.

Plastic deformation of crystalline materials commonly proceeds by slips of dislocations. It is of primal importance to understand dynamic dislocation behavior in the course of deformation in order to fundamentally understand mechanical properties of materials. In the case of polycrystalline materials, the presence of grain boundaries significantly affects the dislocation dynamics during the deformation. Thus, the interaction between dislocations and grain boundaries is a key factor to understand the mechanical behavior in polycrystalline materials. However, the interaction processes, which are microscopic and dynamic, have not been well characterized by experiments and are still ambiguous so far. In the present study, we carried out nanoindentation experiments inside a transmission electron microscope (TEM) to directly and dynamically observe dislocation-G.B. interaction in SrTiO₃.
In situ TEM nanoindentation experiments were performed with JEM-2010 (JEOL Ltd.) operated at 200 kV, equipped with the double-tilt TEM-Nanoindenter holder (Nanofactory Instrument AB.). This holder enables nanoindentation experiments inside a TEM by controlling the specimen position using a piezo actuator. For the in situ nanoindentation experiments, we prepared two types of TEM specimens, that are single crystals and bicrystals. The single crystal specimens were used for revealing the dislocation behavior inside the crystal, while the bicrystal specimens were used for observing the dislocation-grain boundary interaction. The TEM specimens for the TEM nanoindentation are fabricated by the standard procedure using ion milling methods. During the nanoindentation experiments, the sequential TEM images, which were taken by the dark-field method to highlight the specific dislocations, were recorded as movies with the frame rate of 30 fps.
The SrTiO₃ single crystals were indented with the sharp diamond tip along the [001] direction and we observed the dynamic propagation process of dislocations^[1]. From the detailed ex situ analysis of the dislocations after the nanoinddentation, the introduced dislocations have the slip system of {110}<1-10>, which agrees with the primary slip system of SrTiO₃ at room temperatures reported previously. In the case of bicrystal sample, we directly observed the interaction between lattice dislocations and well-defined grain boundaries. The dislocation-grain boundary interaction and its dependence on the grain boundary characters will be discussed in the presentation.
[1]S. Kondo et al., Appl. Phys. Lett. 100, 181906 (2012).

Mechanical behavior of bcc iron in micro-pillar sample was characterized by in-situ deformation in a TEM (Transmission Electron Microscopy) in terms of the relationship between flow stress and dislocation density. The initial dislocation density was quite low and the yield stress was in an order of 1 GPa that is much higher than macroscopic one. After the yielding, the dislocation density increased gradually with strain and the corresponding flow stress decreased edgingly. A dislocation multiplication was observed, which is a major mechanism of dislocation density rise during deformation. All the dislocation lines are parallel to the direction of projection of <111>, which indicates screw component dominance. The flow stress was plotted as a function of the dislocation density and the stress exponent m on the Johnston and Gilman model was evaluated. The m value was much lower than that in the literature. This is reasonable because the m value in the literature is for edge dislocation with much higher mobility that that of screw dislocation in bcc structure.

A fundamental understanding of adhesion and wear is important for applications at all length scales, but is particularly critical in nanoscale devices and applications due to their high surface-to-volume ratio. Advancements in studying such tribological phenomena are typically hindered by the inaccessibility of the sliding interface. We will present nanoscale adhesion and wear measurements conducted inside of a transmission electron microscope (TEM), using a modified in situ nanoindentation apparatus. This tool provides new opportunities to observe, identify, and quantify tribological processes with unprecedented access and resolution. First, we have quantified adhesion by making and breaking contact between nanoscale silicon asperities and a flat diamond substrate. The snap-in distance and the pull-off force are measured with sub-nanometer and sub-nanonewton resolution, respectively. The shape of the Si asperity is determined with sub-nanometer resolution immediately before and after contact to verify that elastic conditions were maintained. A simple analytical model was used to determine the work of adhesion and range of adhesion. The range of adhesion is longer than commonly estimated, and the true work of adhesion is more than an order of magnitude larger than the result calculated using conventional continuum mechanics models. We furthermore find that roughness of tips can greatly reduce the pull off force and lead to severe underestimation of the work of adhesion [1]. These two results demonstrate the importance of applying in situ approaches to studies of adhesion.
We then present in situ studies of nanoscale wear. We find that silicon, silicon oxide, and amorphous hydrogenated carbon (a-C:H) all exhibit gradual nanoscale wear without fracture or plastic deformation.. For silicon and silicon oxide, the atomic-level wear process is well-described by stress-assisted chemical kinetics [2], while qualitatively different behavior is observed for a-C:H, suggesting a distinct mode of nanoscale wear, which has not been previously reported experimentally.
1. Jacobs, T.D.B., Ryan, K.E., Keating, P.L., Grierson, D.S., Lefever, J.A., Turner, K.T., Harrison, J.A. and Carpick, R.W. The Effect of Atomic-Scale Roughness on the Adhesion of Nanoscale Asperities: A Combined Simulation and Experimental Investigation. Tribol. Lett. 50, 81-93 (2013).
2. Jacobs, T.D. and Carpick, R.W. Nanoscale Wear as a Stress-Assisted Chemical Reaction. Nature Nanotech. 8, 108-112 (2013).

A key advantage of in situ TEM probing techniques is control over when the experiment begins so that clear before and after images or measurements can be obtained. For example, is possible to keep a material undeformed until contacted by a nanoindenter. This talk will present recent developments from a number of in situ TEM probing techniques, where deformation in metallic nanostructures or the actuation of phase transformations in functional oxides can be triggered either mechanically or electrically. In the field of dislocation plasticity, deformation is inherently a localized phenomenon so that combining digital image correlation with global stress and strain measurements makes it possible to measure the true local strain in a material. With functional materials, direct measurements of induced strain in the materials makes it is possible to probe the coupled electrical and mechanical properties of materials such as piezoelectric thin films and oxide nanowires.

A large number of energy absorption materials (e.g. composite materials, foams, and honeycombs) have been developed for isolating devices and personel from impacts, collisions or blasts. Nanosized cellular and porous structures provide an ideal opportunity to obtain large specific energy absorption. As one of the most elementary structures, hollow nanospheres afford the ability to gain insights into the fundamental deformation mechanisms associated with nanoporous materials at the nanoscale. Here, we report on the deformation and fracture of amorphous hollow carbon nanospheres (CNS) characterized by in-situ TEM mechanical compression. Nanostructuring suppresses brittle fracture to large strains and the CNSs exhibit enhanced strength and toughness compared with their solid counterparts. The deformation mechanisms include pre-buckling, post-buckling and collapse of the CNS. A size dependent strength model is proposed to understand the experimental results. This research is expected to provide a mechanical basis for developing high performance energy absorption and high density energy storage systems through assembling hollow nanospheres.

Nanoporous silicon (np-Si) is an attractive potential anode material for lithium ion batteries, as it offers a large amount of free volume for lithium insertion and de-insertion, allowing the anode to swell and contract without cracking during lithium cycling. Understanding the mechanical behavior of np-Si is challenging, as the nanoscale ligaments (20 nm wide) induce size effects and can change the fundamental deformation mechanism(s) in Si at this length scale. High-purity (100% Si content) np-Si was fabricated by dealloying precursor materials, and the mechanical behavior was measured for these specimens. In-situ nanoindentation in the TEM, performed on as-dealloyed thin film np-Si, revealed that this material can withstand extensive deformation without exhibiting brittle fracture. After significant compression under the indenter tip, np-Si fully recovered this deformation and the ligaments returned to their original configuration. This behavior will be discussed in the context of size effects on the plastic deformation behavior of nanoscale Si.

Carbon nanotube (CNT) and semiconductor nanowire (NW) materials are important building ma-terials for nanotechnology. These materials may be synthesized via a range of physical and chemical methods, and new nanotube and NW materials are being produced every day. Measurements on individual nanostructures remain, however, difficult and it is even more challenging to control the property of these nanomaterials via structure modification at near atomic resolution. A very promis-ing and perhaps the best method to tackle these problems is to combine the scanning tunnelling mi-croscope (STM) with the electron microscope (EM) so that manipulation and structure modification may be made via a highly controllable fashion on individual nanostructure [1], and their structures [2], real time electrical [3-7], mechanical [8], optical [9] and thermoelectric properties [10] can be measured in-situ inside the electron microscope simultaneously.
References
[1] L.-M. Peng et al., MICRON 35 (2004) 495
[2] C.H. Jin et al., Phys. Rev. Lett. 102 (2009) 205501; 101 (2008) 176102
[3] Y. Liu et al., Appl. Phys. Lett. 92 (2008) 033102; L. Shi et al., Nano Letters 7 (2007) 3559
[4] Z.Y. Zhang et al., Appl. Phys. Lett. 88 (2006) 073102; Adv. Func. Mater. 17 (2007) 2478
[5] M.S. Wang, Q. Chen, and L.-M. Peng, Adv. Mater. 20 (2008) 724; Small 4 (2008) 1907
[6] M.S. Wang et al., Adv. Func. Mater. 15 (2005) 1825; 16 (2006) 1462
[7] X.L. Wei et al., AIP Advances 2 (2012) 042130
[8] X.L. Wei et al., Adv. Func. Mater. 19 (2009) 1753; 18 (2008) 1555
[9] M. Gao et al., Appl. Phys. Lett. 92 (2008) 113112; W.L. Li et al., Appl. Phys. Lett. 93 (2008) 023117; Nanotechnology 20 (2009) 175703
[10] Y. Liu, Z.Y. Zhang, X.L. Wei, Q. Li and L.-M. Peng, Adv. Func. Mater. 21 (2011) 3900

Traditional electron microscopy studies solid samples in the vacuum environment of the microscope. But for a variety of experiments it is desired to the samples directly in their functional liquid environment, for example, for the study of nanoparticle growth, self assembly of nanoparticles, the functioning of nanoscale catalyst particles, solid:liquid interfaces of energy materials, and for research on biological cells and macromolecules [1]. A new approach was introduced in recent years combining scanning transmission electron microscopy (STEM) with the usage of silicon nitride (SiN) membranes as windows in a liquid compartment [2]. This so-called Liquid STEM approach can image nanoscale materials of high atomic number (Z) in low-Z liquids, resulting from the Z contrast of STEM. The spatial resolution depends on the microscope settings, the used materials, the location of the nanomaterials in the liquid, and the liquid thickness. For example, gold nanoparticles (AuNPs) can be imaged with a resolution as high as 1 nm on top of a liquid layer of 4 micrometers thickness. Dynamic STEM is capable of recording movies of flowing nanoparticles. The growth of gold dendrites can readily be observed [3]. In the area of biology, Liquid STEM presents a new technology to study the distribution of selected protein species in whole cells using AuNPs as specific labels. The labels provide information about the location of proteins in cells, and also about the assembly of proteins into complexes, i.e., about the stoichiometric distribution [4]. This principle works for fixed cells with nanoscale resolution [2]. Furthermore, live cells can also be imaged. The cells are not viable after electron beam irradiation on account of the electron dose. Nevertheless, a "snap shot" image reveals information about the native cell [5]. This presentation will describe the theoretical concepts behind Liquid STEM, introduce the key components of the instruments, and discuss examples of its usage in both biology and materials science.
References:
[1] de Jonge, N., Ross, F.M., Electron microscopy of specimens in liquid, Nature Nanotechnology 6, 695-704, 2011.
[2] de Jonge, N., Peckys, D.B., Kremers, G.J., Piston, D.W., Electron microscopy of whole cells in liquid with nanometer resolution, Proc Natl Acad Sci 106, 2159-2164, 2009.
[3] Kraus, T., de Jonge, N., Dendritic gold nanowire growth observed in liquid with transmission electron microscopy, Langmuir : the ACS journal of surfaces and colloids 29, 8427-32, 2013.
[4] Peckys, D.B., Baudoin, J.P., Eder, M., Werner, U., de Jonge, N., Epidermal growth factor receptor subunit locations determined in hydrated cells with environmental scanning electron microscopy, Sci Rep 3, 2626, 2013.
[5] Peckys, D.B., de Jonge, N., Visualization of gold nanoparticle uptake in living cells with liquid scanning transmission electron microscopy, Nano Lett 11, 1733-1738, 2011.

In-situ transmission electron microscopy (TEM) has seen a dramatic increase in interest in recent years with the commercial development of liquid and gas stages. High-resolution TEM characterization of samples in a liquid environment remains limited by radiation damage and loss of resolution due to the thick window-layers required by the in-situ stages. We introduce thin-window static-liquid cells that enable sample imaging with atomic resolution and electron energy-loss (EEL) spectroscopy with 1.3 nm resolution. Using this approach, high energy electron induced reactions is studied via nanometer resolution in-situ transmission electron microscopy experiments. Liquid, such as CuCl2 or Ferritin in solution are encapsulated using the static liquid cells with reduced window thickness. The integrity of the thin window liquid cell is maintained by controlling the electron dose rate, and local beam induced reaction can be initiated in the sample at nm resolution. Reactions, such as beam induced liquid/ gas phase transition (bubble formation and condensation), beam induced nanoparticle and nanowire growth, as well as biochemical reactions, such as valence change of the iron in a functioning ferritin, is observed and will be quantified. On the other hand, radiation damage of samples, such as liquid water and protein, is quantitatively studied to allow precision control of radiation damage level within the liquid cells.

Studying dynamic phenomena such as self-assembly, growth and nucleation of colloidal particles, conformational dynamics in biological systems, or the fundamental mechanisms of lithium-ion batteries in operation in non-aqueous electrolytes requires nanometer spatial resolution or better and reproducing a liquid environment around the specimen that must be controlled during the course of the experiment. Following the advances in nanofabrication of recent years, there has been a renewed interest in the use of environmental stages capable of creating a gas or a liquid reservoir around the sample separated from the high vacuum inside the microscope [1, 2]. Fluid stage holders are specifically designed to fit in any transmission electron microscope (TEM), allowing us to apply the distinct capabilities of each instrument to our experiment. For instance, if a dynamic TEM (DTEM) is used, a high temporal resolution in the nanosecond-microsecond range can be achieved [3, 4]. Critical to the quantitative interpretation of phenomena at the nanoscale is the evaluation of the magnitude of electron radiation damage resulting from beam-induced reactions with the liquid sample. Here we present our approach for studying dynamic processes in liquids by (S)TEM. We discuss our most relevant findings regarding the different experimental and technical challenges to be overcome for a truly quantitative analysis in the (S)TEM using an environmental liquid holder. As a direct application, a new methodology for more rapidly developing and identifying next-generation electrolytes for Li-ion batteries will be presented. This holder is being developed for its use with the second generation DTEM for high time resolution observations of nanomaterials [3]. The DTEM at PNNL has been designed to achieve a combined temporal and spatial resolution of ~10-6s and ~10-10m. The unique qualities of the DTEM that benefit the in-situ experiments with gas/fluid environmental cells will be also discussed.[5]
[1] M.J. Williamson et al., Nature Mater., 2 (2003) 532
[2] S. Mehraeen et al., Microsc. Microanal., 19 (2013) 470 ,P.V. Deshmukh et al., In Situ Holder Assembly, U.S. Patent 8178851 (2012)
[3] N.D. Browning et al., Current Opinion in Solid State & Mtrls. Sci., 16 (2012) 23
[4] J.E. Evans et al., Nano Lett., 11 (2011) 2809
[5] The research described in this presentation is part of the Chemical Imaging Initiative; it was conducted under the Laboratory Directed Research and Development Program at PNNL, a multiprogram national laboratory operated by Battelle for the U.S. Department of Energy under Contract DE-AC05-76RL01830. A portion of the research was performed using EMSL, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. Development of in-situ stages was supported by DOE NNSA-SSAA grant number DE-FG52-06NA26213, and DOE BES grant number DE-FG02-03ER46057.

In situ liquid cell electron microscopy has emerged as a powerful tool to study nanoscale phenomena in liquids. The electron beam interacts with the aqueous medium to produce a variety of reaction products such as hydrogen, oxygen, solvated electrons, and radicals. We compute the concentrations of radiolysis products as functions of beam intensity, beam size, time, position relative to the beam center, and solution composition, such as pH and dissolved gases. The theory predicts that the concentrations of radiolysis products do not increase unabated, but rapidly reach equilibrium levels. We present experimental observations made using liquid cell microscopy that support the existence of equilibrium. We then demonstrate that the electron beam can be used to induce aggregation of colloidal particles, to form (write) nanowires with complex patterns without a need for a mask, and to study the characteristics of single nanobubbles. Additionally, the liquid cell provides a unique tool for studying the radiolysis process itself and for examining the behavior of materials under extreme conditions. A better understanding of radiolysis effects should aid researchers to correctly interpret phenomena imaged with liquid cell electron microscopy, to develop methods to minimize and account for unwanted artifacts, and to profitably take advantage of beam effects.
Acknowledgment: The work was supported, in part, by grants # 1129722 and # 1066573 from the National Science Foundation.

Quantitative in situ electrochemistry experiments were performed with small-scale microfluidic electrochemical liquid cells using the TEM as an experimental platform. In this work, HAADF STEM imaging was used to directly image nanoparticle nucleation and growth that was directly correlated with the electrodeposition/electrodissolution conditions obtained by cyclic voltammetry measurements. CV scan rate was found to have a profound effect on the size scale and distribution of the electrodeposited nanoparticles, with higher scan rates resulting in smaller nanoparticles. Here we extract reaction rate parameters of nanoparticle diffusion-controlled nucleation and growth directly from CV data acquired at different CV scan rates. The compromise between HAADF STEM image acquisition parameters on spatial resolution and temporal resolution on elucidating nucleation and growth mechanism and kinetics will be discussed.
Research supported by the Fluid Interface Reactions Structures and Transport (FIRST) Center, an Energy Frontier Research Center funded by the Department of Energy&’s Office of Basic Energy Sciences Division and by the Center for Nanophase Materials Sciences, which is sponsored at Oak Ridge National Laboratory by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy.

Multi-metallic core-shell nanostructures with different shapes and architectures are of great interest, which may provide multiple functions through manipulating the metal distributions in alloys and structures. Although core-shell nanocrystals have been made by a variety of gas and solution growth processes, the theories on formation mechanisms are well known to fall into one of three categories: layer-by-layer growth, island growth or combination of those two modes. Recent developments in TEM, which use a liquid environmental cell to image through liquid environments, provide an opportunity to in-situ observe the crystal growth behavior during the synthetic process.(1) However, one critical challenge is to track the entire heterogeneous nucleation process of the shell materials on the existing seed as core. As such, the liquid containing the existing seeds and the solution of the precursor for the formation of shell need to be segregated to avoid any initial nucleation and growth before the solution is exposed under the electronic beam. We overcome this challenge by using the fluid liquid cell to inject the reagents and initialize the crystals growth to achieve the entire observation on the formation of shell on the existing core. This observation can exhibit the “real” crystal growth behavior and guide chemists to design and synthesize the core-shell structures with desired compositions.
1. H. Zheng et al., Science 324, 1309 (June 5, 2009, 2009).
The work is supported by DOE BES, NSF and University of Illinois.

The low-energy densities of lithium-ion batteries limit their storage capabilities and potential applications. As an alternative, rechargeable, nonaqueous Li-O2 batteries based on chemical reaction exhibit higher theoretical energy densities, which are comparable to gasoline [1]. These Li-O2 batteries are being considered for adoption in the next generation electric vehicles [2-4]. Their operation involves reduction of oxygen by lithium metal, which results in the formation of the discharge product lithium peroxide (Li2O2). Poorly conductive Li2O2 nanoparticle are usually found at the porous carbon cathode where they are oxidized during the charging process, forming O2 at the cathode and restoring Li metal at the anode. This reversible formation and oxidation of Li2O2 demonstrates the recharge mechanism and ultimately determines Li-O2 battery performance.
Despite the simplicity of Li-O2 battery operation and the high capacity values achieved for mesoporous carbon cathode, reversibility of the battery is limited by only a few discharge-charge cycles. Performance reduction is caused by degradation of both cathode and nonaqueous electrolyte into undesirable side products, resulting in fast capacity fading and high overpotential upon charging. In order to understand performance complications, application of the in-situ liquid electrochemical TEM cell enables monitoring of dynamic changes and structural evolution. The in-situ biasing microchip is modified with single walled carbon nanotubes (SWNTs) as the cathode and lithium metal as the anode. This creates a rechargeable Li-O2 nanobattery cell with both electrodes immersed in the high vapor pressure organic electrolyte (1 M LiTf in tetraglyme). We observe Li2O2 nanoparticles at the SWNTs/electrolyte interface in liquid electrolyte at high spatial and temporal resolution while imaging Li-O2 battery cycling. We demonstrate direct observation of Li2O2 formation during the discharge process as well as Li2O2 oxidation at the cathode during charging.
References:
[1] G. Girishkumar, B. McCloskey, A. C. Luntz, S. Swanson, W. Wilcke, J.Phys. Chem. Lett. 1, 2193, 2010
[2] M. Park, H. Sun, H. Lee, J. Lee, J. Cho, Adv.Energy Mat. 2, 780, 2012
[3] P. G. Bruce, S. A. Freunberger, L. J. Hardwick, J. M. Tarascon, Nat. Matt. 11, 1, 19 (2012)
[4] L. Zhong, R. R. Mitchell, Y. Liu, B. M. Gallant, C. V. Thompson, J. Y. Huang, S. X. Mao, Y. Shao-Horn, Nano Lett. 13, 2209 (2013)
The research described in this presentation is part of the Chemical Imaging Initiative at Pacific Northwest National Laboratory under Contract DE-AC05-76RL01830 operated for DOE by Battelle. This work is supported in part by the United States Department of Energy, Basic Energy Sciences Grant No. DE-FG02-03ER46057. A portion of the research was performed using EMSL, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory.

Structure of bio-molecules and cells determines their behaviors in a given environment. When they come to biological interactions and reactions, they host critical steps that require understanding in molecular, and sometimes, atomic level. Light microscopic studies have greatly facilitated structural analysis as well as direct observation of real-time phenomena that occur in a live cell, however, the spatial resolution of light microscopy restricts molecular level understanding. Electron microscopy, in contrast, provides a sub-nanometer level resolution of dried and fixed events. We develop a graphene liquid cell which can sustain an aqueous environment in a harsh imaging condition of electron microscopy. Graphene liquid cell microscopy opens an opportunity to study cellular behaviors in an aqueous environment by using correlative electron and light microscopies.

Electron holography (EH) is a powerful interferometric TEM method particularly efficient for the quantitative studies of local electrostatic and magnetic fields with a resolution of the order of few nanometers over a field of view as large as few microns. [1 - 4]
We have developed a new set-up that allows for the first time the quantitatively mapping in-situ, in a TEM, of the induction field generated by the write pole from a read/write head of a hard disk drive (HDD).
The use of EH allows for a complete mapping of the magnetic fields generated by the writer as a function of the applied electrical current. The resulting quantified field maps demonstrate the key features desired for in-situ magnetic studies, namely a directional magnetic field with low angular spread.
The magnetic induction maps obtained by EH for various applied currents have been successfully simulated using micromagnetic simulation using the geometrical parameters of the writer.
Further, since the writer&’s control electronics are designed to operate to GHz frequencies, we demonstrated the possibility of performing time resolved dynamic magnetic studies to obtain quantitative information about the damping of the magnetic induction as a function of the applied current frequency.
[1] Electron holography of nanostructured materials R.E. Dunin-Borkowski, M.R. McCartney and D.J. Smith.
Chapter in Volume 3 of the "Encyclopaedia of Nanoscience
[2] Magnetic configurations of 30 nm iron nanocubes studied by electron holography
E. Snoeck, C. Gatel, L.M. Lacroix, T. Blon, S. Lachaize, J. Carrey, M. Respaud, B. Chaudret
Nano Lett., 2008, 8 (12), pp 4293-4298
[3] Quantitative observation of magnetic flux distribution in new magnetic films for future high density recording media A. Masseboeuf, A. Marty, P. Bayle-Guillemaud, C. Gatel and E. Snoeck,
Nano Lett., 2009, 9 (8), pp 2803-2806

[4] Imaging the fine structure of a magnetic domain wall in a Ni nanocylinder
N. Bizière, C. Gatel, R. Lassalle-Balier, M.-C. Clochard, J.-E. Wegrowe and E. Snoeck
Nano Lett. 13, 2053-2057 (2013)

The cold field emission gun (C-FEG) is the brightest electron source available, which also exhibits the smallest energy spread [1]. This technology has been greatly improved over the years concerning the electron optics and the vacuum, but the same cathode materials are still in use [2]. We have recently developed a new C-FEG source using a carbon cone nanotip (CCnT) mounted on a standard tungsten cathode using a focused ion beam (FIB) [3]. This source exhibits very good spatial coherence properties, which could be useful for electron interferometry applications [4].
In this study, we have inserted a CCnT inside a biasing transmission electron microscope (TEM) sample holder incorporating a nanomanipulator (Nanofactory Instruments), in order to approach the CCnT towards an Au-anode plate to a defined distance. We then ramped up the voltage between the nanotip and the anode from 0 to 140 V until the electric field around the tip was strong enough to allow the electrons to tunnel through the barrier and a field emission current could be acquired. During the voltage ramping and the field emission, off-axis electron holography was performed and holograms were recorded at each voltage step. After extracting the phase images from these holograms, the electric field has been directly measured as a function of applied voltage.
We recently developed a new quantitative method to count the elementary charges with a precision of one elementary unit of charge from phase images [5]. We achieved this by applying at the nanoscale the elegance and power of Gauss&’s Law to aberration-corrected electron holograms. The method is therefore a direct measurement of charge and avoids the lengthy and non-unique fitting procedures which previously dogged electron holographic charge analysis. The extra sensitivity is achieved by the high signal-to-noise of aberration-corrected instruments and our new methodology. We applied this method on the phase images as a function of the applied voltage. The numbers of accumulated charges and the charge density on different places on the tip has been determined. We repeat this experiment for different tip-anode distances. We will show quantitative elementary charge measurements as a function of the applied voltage and the tip-anode distance, particularly the charge density at the beginning and during the field emission process. We will then discuss the importance of these values.

References
[1] O.L. Krivanek et al in “Advances in Imaging and Electron Physics” 153 (2008), ed. PW Hawkes, (Elsevier Academic Press, San Diego), p. 121.
[2] A.V. Crewe, Rev. of Sci. Inst. 39 (1968), p. 576.
[3] F. Houdellier et al, Carbon 50 (2012), p. 2037.
[4] F. Houdellier and M Monthioux, CNRS, International Patent Application PCT/FR2011/052135.
[5] C. Gatel et al, Phys. Rev. Lett. 111 (2013), 025501.

Developments in electron imaging and diffraction techniques now offer time resolution in three important regimes: 1) ultrafast from nanoseconds down to sub-picoseconds, 2) fast from 1/100 down to 1/1600 seconds, and 3) normal at video rate (~1/30 seconds). Each time resolution offers a unique opportunity for in-situ study of dynamic processes in materials science. Here we will report our efforts in developing ultrafast techniques for the study of laser-matter interaction and plasmonic excitation, fast electron imaging using direct electron detection CMOS camera, and in-situ deformation and observation of nucleation and growth in liquid cells. In the study of plasmonic excitation, Ag nanocrystals are deposited on rutile crystals, under ultrafast laser pulse irradiation, strong electron emissions are observed which can be directed probed by the pulsed electron beam. For in-situ deformation, a Hysitron indentation holder was used to investigate mechanic response of high entropy alloys at the normal rate. Serrations in the stress-strain curve were observed, which can be correlated with change in diffraction contrast. In the study of nucleation and growth using a liquid cell, initial events occur at minutes after initiation while low dose imaging condition is critical to the success of the experiment. Using the above results , we show that there is now an opportunity to combine all these capabilities in a dynamical environmental TEM (DETEM). The work is supported by the U.S. Department of Energy under grant DEFG02-91-ER45439 and NSF DMR 1229454.

Periodically branched, single-crystalline nanostructures (eg. nanocombs) have been synthesized and studied in the past as novel morphologies with interesting optical and electronic properties. However, the proposed mechanisms explaining the formation of these structures have been mostly speculative. We have observed that CdS nanobelts growing perpendicular to the c-axis (wurtzite, thickness (30-100 nm) and width (2-5 mu;m)) upon heating to 550 °C under moderate vacuum levels (25 mTorr) spontaneously transform into a periodically branched morphology. The resulting single-crystalline branched structures can be described as wurtzite nanobelts with 1-2 mu;m long nanowires protruding along the c-axis (along the two sides of the nanobelts), with a periodicity comparable to the nanowire&’s thickness. However, when the same heating experiments were performed in a conventional TEM under ultrahigh vacuum, only sublimation along certain crystallographic axes was observed. Therefore, in order to understand the mechanism of branching of nanobelts upon heating, an ideal experiment would be to observe the process in real time with high spatial resolution via in-situ TEM techniques but under “real” experimental conditions, i.e., at similar atmospheric conditions as our growth furnace. By performing in-situ heating of CdS nanobelts inside an environmental TEM (FEI Titan ETEM) and observing in real time their morphological transformations under different conditions (ultrahigh vacuum, inert and oxidizing atmospheres), it is observed that periodic branching only occurs under the presence of an oxidizing environment, while only sublimation along preferred crystallographic axes occurs under other conditions. An oxidizing atmosphere leads to the formation of periodic CdO domains on the surface of the nanobelts, which protect the underlying CdS from sublimation, whereas the unprotected CdS sublimates leaving behind a periodic pattern of branched nanostructures. The detailed atomistic mechanism of the transformation process and the role of strain in the formation of domains and subsequent periodic branching of CdS nanobelts will be described. The implication of these studies to understand structural and chemical transformations at the nanoscale for the precise engineering of novel nanoscale materials and devices will be discussed.

Metal hydrides are widely used in energy storage and gas sensing due to their high uptake capacity and catalytic ability. In bulk systems, most metal hydrides exhibit a miscibility gap in their M-H phase diagrams, indicating a first-order phase transition from a hydrogen-poor alpha phase to a hydrogen-rich beta phase. However, recent studies of metal nanoparticle ensembles suggest that metal hydrides deviate from bulk-like properties at nanoscale dimensions. In particular, sloped pressure-concentration isotherms observed in nanoscale systems have been attributed to modification of surface energies and band structure. It is still unclear if such behavior is intrinsic to the thermodynamics and kinetics of the nanoscale system, or a result of ensemble averaging.

In this presentation, we investigate hydrogen loading of individual metallic nanoparticles between 14 and 25 nm. As a model system, we consider palladium nanoparticles prepared by ascorbic acid-mediated reduction of an aqueous solution of CTAB and hydrogen tetrachloropalladate. Our synthesis yields both single-crystalline cubic nanoparticles and multiply-twinned spheroidal nanoparticles, which we compare with our single-particle studies.We use environmental scanning transmission electron microscopy combined with electron energy loss spectroscopy to monitor the bulk plasma frequency of palladium nanoparticles upon hydrogen loading. At low pressures, we observe a bulk plasmon at 8 eV, consistent with the dielectric function of palladium and thus alpha PdH. Upon increasing the pressure to ~1mbar at -27 C, we note a transition to 5.5 eV, corresponding to beta PdH. Single crystals exhibit an abrupt transition from the alpha to the beta phase that is reversible upon reducing the pressure. Larger nanocubes tend to load at higher pressures than smaller nanocubes. In contrast, multiply-twinned spheroids show a much more gradual transition and do not appear to fully load at the highest pressures attained in our system. This behavior is distinct from that of the single crystalline nanocubes.
Our results show that first order phase transformations persist in single crystalline nanoscale systems. Our presentation will discuss the likely origins of the sloped isotherms present in ensemble studies and also describe techniques to directly map the alpha and beta phases of PdH with high spatial resolution.

The interaction of a material with a gas phase can trigger a phase change and is of great technological importance to fields such as corrosion, catalysis, coatings and bonding. Well known examples include metal transformation to oxides in the presence of oxygen and oxide reduction to metal in the presence of hydrogen or carbon monoxide. The redox reactions are commonly activated with thermal energy to drive the reaction forward to equilibrium and this transformation pathway has been extensively studied. Energy can also be provided with ionizing radiation such as ultraviolet light or high energy electrons. Electron beam induced changes in materials under high vacuum conditions have received considerable attention over the years because of their relevance to radiation damage. Electron beam induced changes in the presence of reactive gasses have not been extensively studied, a significant exception being perhaps electron beam induced deposition but, in this application, interest has focused mainly on the dissociation of the gaseous precursor [e.g. 1] with very few studies of controlled changes in the underlying substrate resulting from the gas-electron-solid interaction [2]. Energy transfer via fast electrons or ultraviolet photons may involve significant ionization of both the sample and the gas phase adjacent to the sample as a result of secondary electron emission. The kinetic pathways for phase evolution under such conditions may be significantly different from those associated with thermal processes. Moreover, changes that take place during electron and photon irradiation may also show significant variations because of the different energy transfer channels activated in each case. An environmental transmission electron microscope modified to permit in situ UV light illumination is employed to compare the changes taking place in materials structure under a variety of different gases as a result of exposure to heat, light or electrons. The changes taking place in nanostructures such as nanoparticles, interfaces and surfaces will be of particular interest. The current study focusses primarily on metals undergoing oxidation and oxides undergoing reduction processes.

[1] W.F. van Dorp, C.W. Hagen, P.A. Crozier and P. Kruit, (2007) J. Vac. Sci. & Tech. B, 25(6), 2210-2214.
[2] P. A. Crozier, (2007), Nano Letters, 7(8) 2395-2398..
[3] The support from the National Science Foundation (NSF-CBET 1134464, NSF-DMR 1308085), 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.

Characterization of catalytic reactions is often hindered by the fact that the behavior the system is mesoscopic, while the materials involved are nanoscale, with features that can span a broad range of temporal and spatial scales and which involve a broad range of competitive interactions. As a result, the description of a catalytic system requires interrogation with a variety of techniques, involving imaging, diffraction and spectroscopy, to describe the dynamic changes in structure that can occur during reactions. Commonly, this is done by simple use of standard techniques, and inference of how the results relate to the working condition of the system. It is, however, preferable that multiple probes are used to characterize physical and electronic structure of the catalyst during reaction, over multiple time and length scales. To date it has not been possible to directly link the observations across these techniques in such a way as to confirm that the data (imaging, diffraction, spectroscopy) is obtained from the system in the exact same “working” state.
Here we report an experimental approach that allows: (1) characterization (via x-ray absorption spectroscopy, extended x-ray absorption fine structure, x-ray fluorescence, Raman spectroscopy, transmission electron microscopy, scanning transmission electron microscopy, electron energy loss spectroscopy and energy dispersive electron microscopy) from the same sample, (2) characterization at atmospheric pressures in reactive environments, and (3) simultaneous, real-time and on-line analysis of the reaction products, i.e. “operando” experimentation
We take advantage of recent developments in sample holders for transmission electron microscopy that allow catalysts to be confined between two, thin nitride membrane supports that are separated by a narrow gap, and that allow continuous flow of liquid or gas through the system. We exploit the simplicity of this system in such a way as to allow utilization in both synchrotron x-ray beamlines and transmission electron microscopes. We have chosen a simple, model catalyst reaction for the demonstration phase of this work, the catalyzed conversion of ethylene to ethane, though the use of Pd/SiO2 and Pt/SiOnot;2 heterogenous catalysts. This reaction occurs at room temperature, thereby greatly simplifying the initial experimentation. We demonstrate the ability to measure reactive products in this system, and demonstrate that the measurements made in each technique are from the same “working” catalytic system. The combination of measurement approaches allows us to directly correlate “ensemble-average” properties (such as can be obtained with x-ray absorption and Raman approaches) with measurements of individual particles, at the atomic scale.

In situ imaging, using an environmental scanning transmission electron microscope (ESTEM), has been successfully used to reveal and understand the crucial chemical and physical processes occurring at the nanoscale in many important phenomena, e.g. oxidation/reduction, coalescence, Ostwald ripening, surface reconstruction, substrate/catalyst interaction, etc. However, the relevance of such ETEM studies, and the ability to derive quantitative information from them, can be diminished if the following two questions cannot be satisfactorily answered: i) Do high energy electrons alter the reaction mechanism? ii) What is the sample temperature in the gaseous environment?
Here, we present a unique instrument that helps to address both of these issues by allowing the collection of Raman data during high-resolution ESTEM observation. Such coupled measurements are made possible thanks to the insertion of a parabolic mirror in between the sample holder and the lower pole piece of the microscope (a 1.65 mm tall confined space). The mirror focuses the incoming laser on the sample and collects the scattered Raman photons. A set of optics then carries the Raman signal up to the spectrometer. This new platform enables us to combine and compare the structural information and kinetics from micrometer-scale areas obtained by Raman spectroscopy with the local information collected by the ETEM at the nanometer-scale (near atomic). This system also permits us to simultaneously monitor the temperature of the probed material (at micrometer scale) by analyzing shifts in Raman peak frequency. Moreover, this versatile optical setup can also be used i) to investigate light/matter interactions (the current 532 nm laser can be easily replaced by any IR/Vis/UV wavelength) ii) as a heating source: the sample can be heated up to 1000°C at 25 mW with a 532 nm laser, iii) for general spectroscopy (photoluminescence, cathodoluminescence, etc.). Detailed design, functioning, capabilities and application to carbon nanotube synthesis will be presented.

It is now recognized that atomic level in situ observations of catalytic nanomaterials are critical for understanding structure-reactivity relations because the active form of the material may exist only under reaction conditions. TiO2 is a semiconducting oxide used as a UV-light photocatalyst with potential applications to degradation of organics and solar fuel generation. The photocatalytic activity can be significantly enhanced via the deposition of metal particles onto the oxide surface. The photochemical reactions that take place in these composite systems are not well understood. We have undertaken a series of in situ TEM experiments to develop a fundamental understanding of metal particle/TiO2 structure evolutions under a variety of reaction conditions. Such an analysis is performed under in situ conditions in the presence of light and reactants in an environmental transmission electron microscope (ETEM). Here we employ a modified ETEM with a broadband light source to study the behavior of metal particles on TiO2 semiconductor surfaces under photoreaction conditions. Preliminary experiments showed that the surfaces of anatase nano particles becomes disordered in water vapor under light exposure in the electron microscopes. In this study we investigate the light induced changes that occur in a variety of supported metal systems including Ni, Cu, Pt and Ag in atmosphere such as H2, O2, and H2O. Light induced surface and interface changes during reactions will be captured by TEM images and electron energy loss spectrums (EELS). Insights from these experiments can help in the design of photocatalysts with better performance and stability.

Significant progress has been made in the past few years on the development of in situ electron microscopy for probing nano-scale electrochemistry. In situ TEM observations of electrochemistry were not possible in the past due to several key challenges such as the lack of suitable biasing sample holder and lack of beam damage control. To this end, we have developed a novel in situ instrumental system combining analytical electron microscopy with advanced spectroscopy to probe the dynamic phenomena in an all solid-state nano-battery. In situ electron microscopy can be a versatile technique and provide us answers to questions that could not be provided using other techniques. However in order to fully exploit the capabilities and obtain reliable and quantitative data, a very carefully thought-out plan of action is essential. A complete experimental set-up, including choice of Focused Ion Beam (FIB) operation conditions, specimen holder for biasing, grid materials and design as well as microscope environment must be thoroughly considered. We will present the main challenges that have been overcome to enable in situ biasing, and demonstrate a novel method of studying nano-electrochemistry in the TEM for applications beyond battery research.

Rechargeable Li-ion batteries using Si electrodes have attracted considerable attention over the past decade due to the high capacities that can be achieved (>3,500 mA/h). However, the short lifetimes of such batteries, related to the large lattice expansion/contraction and eventual breakdown of the Si electrode upon cycling, has limited their performance and commercial utility. Recent studies have shown that specific nanoscale Si geometries, such as nanowires (NWs), nanotubes, or nanoparticles, can withstand these large changes in volume without degrading. In order to develop improved Si electrode morphologies that optimize performance, the fundamental mechanisms of strain accommodation and Li+ intercalation and removal during charging/discharging must be understood.
In this work, we have developed and employed a novel “closed-cell” approach for in situ (scanning) transmission electron microscopy ((S)TEM) studies of nanoscale Li-ion battery electrodes, based on the in situ liquid stage platform, using battery relevant liquid electrolytes and a lithium metal counter electrode. Using this closed-cell approach, the structural evolution of a single Si NW, fully immersed in electrolyte, is observed in operando during electrochemical charging/discharging with controlled battery operating conditions. Most significantly, the intercalation of Li+ into the Si NW occurs uniformly along the entire nanowire length without an advancing radial lithiation front. Conversely, the Si nanowire delithitiation is highly nonuniform over its length. The base of the wire does not fully delithiate, resulting in a needle-like morphology and the loss of contact of some Si at the tip.
Additionally, we find that the closed-cell platform uniquely enables direct in situ observation of the dynamic electrode-electrolyte interactions that are critical to battery performance but are not well understood, such as the solid electrolyte interphase (SEI). The SEI layer formed at the Li-ion battery electrode surface is beneficial to device performance by passivating and protecting the electrode from continuous reactions with the electrolyte solvent, while allowing Li+ migration through to the electrode. However, an effective SEI layer must be spatially homogeneous and elastically resilient to the large changes in volume of the Si electrode. We use the in situ closed-cell to study the SEI layer formation at the Si NW surface, and its behavior over subsequent lithiation/delithiation cycles of the Si NW electrode.
This research is part of the Chemical Imaging Initiative at PNNL under Contract DE-AC05-76RL01830 operated for DOE by Battelle. A portion of the research was performed at EMSL, a national scientific user facility sponsored by the DOE's Office of Biological and Environmental Research and located at PNNL.

When crystalline particles are dispersed in their matrix, it is readily observed that particles larger than those of average size grow, accompanying the dissolution of smaller particles into the matrix at the same time. This particle coarsening process has generally been referred to as Ostwald ripening. since a report by Liesegang in 1911. As the physical properties of crystals significantly vary with their ultimate size and shape, observation and appropriate control of their growth and dissolution behavior during the ripening process have been recognized as important issues in crystallization studies over the past several decades. Recent advances in transmission electron microscopy (TEM) enable atomic-scale imaging in Li intercalation compounds for direct visualization of lattice defects, phase transition, and structural evolution (S.-Y. Chung et al., Angew. Chem. Int. Ed.48, 543 (2009); S.-Y. Chung et al., Adv. Mater.23, 1398 (2011)). In particular, a variety of techniques have been utilized for real-time observations in TEM, providing unexpected and new experimental findings (S.-Y. Chung et al., Nature Phys.5, 68 (2009); Nano Lett.12, 3068 (2012)). Using in situ high-resolution electron microscopy (HREM) with a heating specimen holder, in this study we demonstrate, for the first time, the atomic-level evaporation behavior of LiFePO₄ crystals in real time at high temperature. Prior to detailed observation of crystal evaporation, we also investigated the growth behavior of atomically flat low-index surfaces. A systematic comparison with image simulations along with density-functional theory calculations demonstrated that the cations evaporate preferentially over the [PO₄]^3- oxyanions, accompanying fast charge transfer from the nearest-neighboring Fe and O. The present study thus shows that our combined technique based on high-temperature HREM and systematic image simulations is a powerful tool to understand the dynamic characteristics of crystal growth and evaporation.

Resistance of various insulating materials could be changed by external electric stimulus. This phenomenon has attracted considerable interest due to its technological potential for non-volatile memories and its scientific challenges in identifying mechanism.
Here, we study the unipolar switching system, where “on” and “off” states can be set by the same polarity of the applied bias. Most convincing model to explain this system is the filamentary model which attributes the origin of resistive switching to formation and rupture of highly localized filaments in dielectric matrix. The nature of real conducting channels, however, has been in debates. For example, metallic 2nd phase, grain boundaries, and defect percolation have been considered conducting paths. In the case of TiO2 thin film unipolar system, we have reported that metallic 2nd phase was formed as a conducting channel. It has been observed directly by transmission electron microscopy (TEM) that Ti4O7 crystal structures, called Magnéli phase, were generated and ruptured according to resistance state of the system. We extend the same approach to polycrystalline SrTiO3 thin films to unveil conducting channels in this system.

SrTiO3 thin film of 60 nm was deposited by pulsed laser deposition process under oxygen atmosphere. Platinum pad was exploited for both top and bottom electrodes. The samples in three different states, “on&’, “off&’ and pristine, were examined. Cross section TEM samples were prepared by focused ion beam at the “on” state sample where the channel is generated. Furthermore, in-situ scanning tunneling microscope/TEM and electron energy-loss spectroscopy were employed to probe conducting channel and correlate with the electronic structure. In addition, microstructures of channel were analyzed by high-resolution TEM.

The development of safe, high-energy batteries with long cycling life, requires an improved understanding of the mechanisms for lithium-ion transport and reactions with active components of a working electrode. Hard X-ray based techniques are well suited to in situ studies of electrochemical reaction in bulk electrodes due to their high penetration depth. However, the spatial resolution is often inadequate for exploring nanoscale morphological and structural changes and determining where and how new phases nucleate and propagate. Transmission electron microscopy (TEM), coupled with electron energy-loss spectroscopy (EELS) is one of the powerful techniques for local structural and chemical analysis with extraordinary spatial resolution (down to atomic level) and high sensitivity to lithium [1]. We have recently custom-built an electrochemical cell for operation inside the transmission electron microscope, and with which real-time lithium transport and reaction in individual nanoparticles and across composite electrodes (spanning from sub-nm to micron-scales) can be tracked by in-situ TEM imaging, EELS and electron diffraction [2]. We will present some of recent results from studies of electrochemical reactions in a few different types of electrodes. The electronic and ionic transport mechanisms and reaction kinetics in these systems will be discussed. [1] F. Wang, et al., “Chemical distribution and bonding of lithium in intercalated graphite: Identification with optimized electron energy loss spectroscopy”, ACS Nano, 5, 1190 (2011); [2] F. Wang, et al. "Tracking Lithium Transport and Electrochemical Reactions in Nanoparticles." Nature Communications 3, 1201(2012).
Acknowledgement This work is supported by the U.S. DOE under contract DE-AC02-98CH10886 with funding from DOE/BES-EFRC-NCCES.

Transition metal oxides (TMOs) have attracted attention for solid oxide fuel cell, gas sensor and catalytic applications. [1] In many of these cases, material functionality is dependent on the distribution and transport behavior of oxygen ions. It has recently been demonstrated that, for a static case, oxygen vacancy distribution and vacancy ordering can be characterized at an atomic scale using quantitative aberration-corrected STEM. [2] In this work, we take this approach to the next level by observing the dynamics of vacancy ordering and vacancy injection under the electron beam in LaCoO3/SrTiO3 (LCO/STO) superlattices and LaCoO3-x thin films using high angle annular dark field (HAADF) and annular bright field (ABF) STEM.
We find that while before electron beam exposure films and superlattices do not show any signs of vacancy ordering, they nevertheless contain a substantial amount of vacancies; the ordering is quickly induced by electron beam exposure. We can monitor vacancy ordering by tracking local interatomic spacings, and vacancy injection by tracking global average of the spacings as per Vegard&’s law. The rate of ordering shows a strong dependence on the specimen thickness. ABF images show that one-dimensional (110) vacancy channels form in the depleted layers. The effects associated with vacancy injection are very limited, but are influenced by the composition of the surface (i.e. more vacancy injection is observed for pure LCO films than for LCO/STO superlattices), suggesting that surface modification will enable us to control the rate of injection with high precision. In the case of 15 u.c. LCO film, beam exposure leads to a sequence of different phases, starting from disordered perovskite LaCoO3-x to a brownmillerite polytype La3Co3O8-x (2 perovskite layers), to eventually brownmillerite La2Co2O5-x, which is similar to the phase evolution observed in the bulk [3]. Kinetics of the ordering and vacancy injection, as well as implications for beam-driven material modification at an atomic scale, will be discussed.
* Research supported by the U.S. Department of Energy (DOE), Basic Energy Sciences (BES), Division of Materials Sciences and Engineering, and through a user project supported by ORNL&’s Center for Nanophase Materials Sciences (CNMS), which is sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. DOE.
References
[1] Maier, J. Nature Mater. 4, 805 (2005)
[2] Young-Min et al., Nat. Mater. 11 888 (2012)
[3] Ole H. Hansten et al., J. Mater. Chem. 8(9) 2081 (1998)

The application of electrical fields can enable the accelerated consolidation of materials during spark plasma sintering or flash sintering. Although such techniques are already employed for the synthesis of a wide variety of microstructures with unique macroscopic properties, we lack a fundamental understanding of the atomic-scale mechanisms that lead to enhanced densification in the presence of electrical fields and/or currents. In this presentation, recent in situ transmission electron microscopy experiments will be reported that were designed to directly observe and, hence, clarify densification mechanisms. For metallic powders, it was found that previously postulated “surface cleaning effects” can be correlated with either electric field induced dielectric breakdown of surface oxide layers or reduction-oxidation reactions at the inter-article contact areas. In addition, we will demonstrate on a particle-by-particle basis that the application of electrical fields to yttrium-stabilized zirconia in the absence of current has the ability to lower the onset temperature for consolidation. In situ TEM experiments were used to quantitatively determine three-dimensional consolidation curves of particle agglomerates spanning nano- and meso-scales. Initial experimental results reproduce macroscopic shrinkage curves measured during conventional and flash sintering. Research is supported by the University of California Laboratory Fee Program (12-LR-238313) and the Army Research Office (program manager: Dr. S. Mathaudu) under grant W911nf-12-1-0491-0.

High Resolution Electron Microscopy (HR-EM) has been considered as an inseparable part of nanoscience and nanotechnology due to the miniaturization of the novel materials, structures and systems down to atomic-scale. As far as energy materials with porous network in three dimensions are concerned, 3D analysis and tomography based EM applications can be performed for detailed characterization of e.g. solid oxide fuel cells, hydrogen storage materials and solar cells. Especially, in order to reveal the geometric and chemical information distribution of material systems that are based on nanostructures, advanced TEM and FIB imaging and tomography modes are being extensively used. In order to achieve reliable data during TEM investigations, ion milling based specific samples preparation techniques that keep the original structures of the sections are often required. Dual-beam technologies provide material dependent and TEM analysis spectrum based solutions that are highly rapid, practical, creative and reliable.
The components of Solid Oxide Fuel Cells are composed of hard materials/matrices, and therefore it is highly required to process them by ion milling techniques. In this study, dual-beam instruments were mainly used for: 1. Developing novel sample preparation methodologies for TEM imaging and tomography applications; 2. FIB tomography on similar material systems. The complimentary analysis on corresponding materials were presented using HR-TEM imaging coupled with HR-SEM imaging from micron to atomic scale, revealing the distribution of the morphology and chemistry of various energy materials in three dimensions.
The sponsorship by TUBITAK for Dr. Sezen&’s Carreer Development Grant (Project No: 112M195) is highly acknowledged.