The behaviour of water and ions at the interface with immersed solids plays a central role in processes such as crystal growth and dissolution and biomineralisation. Gaining insights into the molecular mechanism underlying these processes remains challenging, partly because of the need to probe the system in-situ, locally and with sub-nanometre resolution.
Atomic force microscopy (AFM) can in principle overcome these difficulties, with recent developments making it possible to map sub-nanometre details of the interfacial liquid [1] and gather quantitative information about its local dynamics [1-2]. Here AFM is used to create images of single metal ions close to the surface of minerals immersed in aqueous solutions [3-4]. The behaviour of the water molecules controls the organisation of ions at the interface and can considerably slow down their dynamics, depending on their hydration properties. Results obtained near surface singularities such as atomic steps, or adsorbed organics highlight the impact that these local perturbations have on the behaviour of the interfacial water and ions, with consequences for the fate of the mineral.
References:
[1] Voitchovsky et al., Nat. Nanotechnol., 5, 401, (2010)
[2] Ortiz-Young et al., Nat. Commun., 4, 2482, (2013)
[3] Ricci et al., Langmuir, 29, 2207, (2013)
[4] Ricci et al., Nat. Commun., 5, 4400, (2014)

In the classical picture of nucleation, density fluctuations that are inherent at finite temperature form unstable clusters of the new phase through monomer-by-monomer addition. Clusters transition from unstable to stable if they exceed a critical size, beyond which the free energy cost of creating the new phase boundary is compensated by the drop in chemical potential. In recent years, hierarchical pathways involving assembly of species more complex than monomers have been proposed for numerous systems. Amongst these pathways, a “two-step nucleation” process was proposed whereby macromolecular crystals nucleate within monomer-rich, non-crystalline clusters. However, reports of such pathways are almost entirely based on computational models or interpretations of indirect observations. Moreover, little is known about two-step nucleation dynamics, and whether the monomers in the clusters are one and the same as those that comprise the crystal nucleus or are act instead to provide an environment for heterogeneous nucleation is uncertain, as is the extent to which two-step pathways are general features of either macromolecular or inorganic materials. To address these knowledge gaps, we have used in situ TEM and AFM to investigate nucleation in numerous systems.
To examine nucleation pathways of macromolecules, we synthesized a biomimetic polymer sequence that forms 2D ordered structures and used in situ AFM to observe nucleation. Our results show that the nucleation occurs along a two-step pathway that begins with creation of disordered clusters containing ~ 10-20 molecules. These clusters transform directly into ordered nuclei that grow via molecule-by-molecule addition, with the kinetics of transformation strongly dependent on Ca concentration. However, when a small aggregation-promoting hydrophobic region is deleted, even though the same final structure is obtained, nucleation occurs in a single step and the kinetics are dramatically altered.
To investigate nucleation of simple inorganic materials, we used in situ TEM to observe nucleation of CaCO3. Formation pathways are confirmed in most cases by collecting diffraction information of the observed phases. We find that amorphous calcium carbonate (ACC), as well as the three predominant crystalline phases: calcite, vaterite, and aragonite, can form directly even under conditions in which ACC readily forms. In addition to these direct formation pathways, we observe two-step nucleation of aragonite and vaterite from ACC. Here, ACC transforms directly to the crystalline phases through distinct nucleation events on or just beneath the surface followed by consumption of the parent ACC particle.
The results demonstrate that two-step pathways are possible in both inorganic and macromolecular systems, but are not universal. They can be accompanied by direct nucleation pathways and, in the case of macromolecules, their existence can depend on the specific sequence of the molecule.

In recent years, significant efforts have been mounted to directly image and quantify the population subcritical nucleation clusters that participate in crystal nucleation from solution. Such an achievement would provide great insight into the energy landscape for nucleation of new particles. However, the critical structures involved in nucleation are typically either too small or too scarce to be unambiguously detected using techniques such as in situ electron microscopy or X-ray scattering. However, recent advances in atomic force microscopy have demonstrated the ability to image in fluid with true atomic resolution, including the adsorption of single ions on atomically flat surface such as mica. We will report on efforts to directly image adsorbate structures on atomically flat surfaces, with interest in these adsorbates as precursors to heterogeneous nucleation. Our work focuses on alkali halide solutions, which are known to form epitaxial crystals on mica surfaces. We have developed an approach by which rubidium iodide crystal nucleation can be induced and observed in-situ with optical microscopy, and the site of nucleation can be investigated in detail with AFM. Unsurprisingly, nucleation is often found to occur at preexisting structural defects. Furthermore, our efforts to investigate the process of nucleation with atomic resolution have indicated the frequent occurrence of nanometer-scale surface heterogeneities. When sufficiently soft imaging forces are used (i.e. subnanometer tip oscillation amplitudes), we can observe the formation of adsorbate islands with thicknesses on the order of several angstroms, even in subsaturated salt solutions. These islands appear to coarsen slowly over time, and can be removed with sufficiently aggressive imaging forces.

Phase contrast x-ray microscopy, which is appropriate in dynamic studies at extreme conditions of high spatial (~ nm) and/or temporal (~mu;s) resolutions in bulk systems, was applied to ultrafast and nanoscale dynamic studies of ‘drop impact&’ and ‘wetting&’, respectively. In a drop impact on a solid surface, we directly visualized the profile of an entrapped air film and its evolution into a bubble during drop impact, using ultrafast (~mu;s) x-ray microscopy, and identified the complicated evolution process of the air into a bubble [1]. Using ultrafast x-ray microscopy in drop impact, we also investigated the dynamics of bubble bursting at an air-liquid interface and identified the jetting mechanism during bubble bursting [2]. Our results demonstrate that jetting in bubble bursting is analogous to pinching-off in liquid coalescence. Finally, we applied nano-resolution (~ 30 nm) X-ray microscopy to study wetting on soft solids [3]. We directly visualized wetting ridges with a high spatio-temporal resolution and revealed a universal wetting principle from the tip geometry of ‘wetting ridges&’. On-going dynamic studies of vortex formation and wetting-ridge dynamics using ultrafast and nanoscale X-ray microscopy will be shortly introduced.
References
[1] J.S. Lee et al, Phys. Rev. Lett, 109, 204501 (2012).
[2] J.S. Lee et al, Nat. Comm.2, 367 (2011).
[3] S.J. Park et al, Nat. Comm., 5, 4369 (2014)

We introduce a new reconstruction method, 3D SINGLE (Structural Identification of Nanocrystals by Graphele Liquid cell Electron microscopy), for identifying 3D atomic structures of individual heterogeneous nanoparticles in their native solution. The combination of techniques from the soft and hard matter sciences, high-resolution graphene liquid cell electron microscopy, new direct electron detection technology, and algorithm for ab initio single-particle 3D reconstruction, is applied to separately reconstruct 3D structure of individual Pt nanocrystals freely-moving in the solution at atomic-scale. Particle by particle 3D reconstruction discloses the heterogeneous structural nature of individual Pt nanocrystals grown in a solution.

In situ three-dimensional (3D) imaging of deforming as well as moving micro-objects is highly important to better understand dynamic study of organic or biological materials. For deforming micro-objects, it is feasible to perform in situ 3D imaging if the microtomographic speed can be much faster than the deformation rate. For deforming and moving micro-objects, however, it is a challenge to in-situ image micro-objects in 3D. Pulmonary alveoli that inflate (deflate) and simultaneously move significantly in inspiration (expiration) are a typical example of deforming and moving micro-objects. In situ 3D imaging of pulmonary alveoli in live animals has been therefore hampered mostly by this active lung movement in respiration. Recently, we developed a tracking X-ray microscopy that enables us to perform in situ microtomography of alveoli during 180° rotation of a live mouse in respiration, based on inspiratory and expiratory triggering [1]. However, automatic segmentation, an essential step toward 3D volume-rendering, which is a challenging task for deforming and moving micro-objects, has yet to be developed. Here, we complete in situ 3D X-ray imaging of inflating (deflating) and moving alveoli in respiration by developing an automatic segmentation algorithm. An unavoidable critical issue in microtomography of deforming and moving micro-objects is the image-blurring problem. The key idea to resolve this issue is based on a self-developed binary image processing algorithm that applies iteration operators containing a series of pre-processed reconstruction images. From in situ 3D image data of alveoli, we identify each acinar unit with ducts and alveoli in live mice and analyze alveolar dynamics (geometry and expansion rate) during respiration. This analysis in alveolar dynamics would be significant for better understanding the mechanisms leading to alveolar- damage, for instance, during ventilator induced lung injury (VILI) commonly occurring in patients treated for acute respiratory distress syndrome (ARDS). We believe that our in situ 3D X-ray imaging technique can be applied to various 3D dynamics studies involving deforming and moving micro-objects.
References
[1] S. Chang, N. Kwon, B.M. Weon, J. Kim, C.K. Rhee, H. S. Choi, Y. Kohmura, M. Yamamoto, T. Ishikawa, and J. H. Je, Scientific Reports 3 (2013) 1304.

The production of high-performance carbon nanotube (CNT) materials demands understanding of the growth behavior of individual CNTs as well as collective effects. We aim to understand the cooperative mechanisms and kinetics of CNT self-organization and how this may limit density and alignment in vertically aligned CNT “forests”. We use synchrotron radiation in combination with a high-frame-rate (100 Hz) pixel array detector to uniquely study in situ the intrinsically rapid processes during nucleation and self-organization of CNT films made by chemical vapor deposition.[1] We calculate an order parameter from time-resolved, grazing-incidence small-angle X-ray scattering (GISAXS) images in order to quantify the evolution of CNT morphology as a function of growth time. Further, we elucidate the mechanisms of CNT self-organization by correlating the order parameter with real-time film height kinetics and qualitative CNT density measurements (from X-ray scattering intensity). We study a set of canonical CNT growth experiments (various thermal and chemical conditions) using a bilayer Fe/Al2O3 catalyst thin film on a Si wafer with C2H4/H2 precursors near atmospheric pressure and high temperatures (up to 825 deg C). Our results show that the kinetics of CNT self-organization are proportional to the vertical growth rate of the forest. This suggests that the disorder-order transition is the result of excluded volume interactions,[2] which are in part governed by the lengthening rate of constituent CNTs, in conjunction with increasing number density of CNTs. We draw analogies with the isotropic-nematic (aligned) phase changes previously observed in CNT solutions and liquid crystals. Further, the beginning of upward forest growth marks the onset of vertical self-alignment, which occurs as the order parameter begins to saturate with time. However, both the final value of the order parameter and the kinetcs depend on processing conditions (e.g., catalyst annealing gases, temperature), indicating that inherent limits to the straightness (and thus defects) of the CNTs are linked to the nucleation conditions. [1] E. R. Meshot, E. Verploegen, M. Bedewy, S. Tawfick, A. R. Woll, K. S. Green, M. Hromalik, L. J. Koerner, H. T. Philipp, M. W. Tate, S. M. Gruner, A. J. Hart, ACS Nano 2012. [2] L. Onsager, Annals of the New York Academy of Sciences 1949, 51, 627-659.

Understanding the synthesis process of any nano-material, including ceria, is a key point for the tailoring of properties and scaling for production. Here, we present the in-situ study of hydrothermal synthesis of nano-ceria by a combination of several x-ray scattering techniques on a laboratory diffractometer; X-ray diffraction (XRD) and small angle x-ray scattering (SAXS) are used to provide information about the crystal structure, crystallite size and particle size. Pair distribution function (PDF) analysis is used to provide information on the atomic ordering at various length scales. Combining these techniques, we are able to demonstrate that the lattice parameter, crystallite size and particle size of the nano-ceria all increase during the initial stages of growth. After a certain period, the lattice parameter stabilizes while the crystallite and particle size continue to increase at a diminished rate. In addition, we observe that the particles are formed from more than one crystallite, as the particle size is always greater than the crystallite size. Particular attention shall be given to the PDF results, as this technique is not typically associated with in-situ studies on laboratory diffractometers.
Cerium dioxide has numerous applications including use as a catalyst for petroleum refining, as a polishing agent, in coatings and as an electrolyte material for intermediate temperature solid oxide fuel cell. Although yttria stabilized zirconia is still the preferred electrolyte material, cerium dioxide offers an alternative, enabling operation at lower temperatures (500-600 °C). The ionic conductivity of ceria is approximately an order of magnitude greater than that of yttria stabilized zirconia for comparable doping conditions, especially if it is nano-crystalline. An additional advantage of nano-crystalline ceria is the lower sintering temperature due to the high surface energy of the nanoparticles.

Morphological transformations of nanocrystals in response to the heating and gas environments are crucial to understand heterogeneous catalysis. Although a myriad of progresses have been made in the past, large pressure gap still poses since most conditions nanocrystals encountered in previous work were far removed from the realistic catalytic reactions. Here, we controllably expose PdCu nanocrystals to H₂ at pressures from 0.1 mbar to 1 bar above in a gas reactor. In situ atom-resolved transmission electron microscopy (TEM) studies reveal that when heating to 300 #730;C, the as-synthesized spherical PdCu nanocrystals preferentially transform into edge-truncated cubes with sharp facets, which is not observed in the low-pressure environment. Our work suggests the great influence of pressures on the nanocatalysts and proves the significance of the study on nanocrystal behaviors at realistic conditions.

Among the commercial aluminum alloy castings, hypereutectic Al-Si and Al-Si-Cu alloys are the most commonly used owing to their excellent hardness, corrosion resistance, and machinability. These properties depend strongly on the characteristics of the microstructure, e.g., the size, shape, and distribution of the highly anisotropic Si particles. The mechanisms controlling the growth and coarsening behavior of such particles above the eutectic temperature, which are critical to the semi-solid processing of the alloy, have been difficult to determine due to the lack of real-time experiments that can capture the 3D morphology of the particles. Thus, we probe the microstructural evolution of primary Si particles in an Al-32wt%Si-15wt%Cu alloy via in situ synchrotron#8209;based X-ray tomography. In order to assess the extraordinary morphological and topological complexity of the Si particles, we calculate curvatures, orientations, and velocities from the 4D (time and space resolved) data and track their evolution during the phase transformation. The results indicate that at long times, growth and coarsening are both diffusion-limited, despite the highly anisotropic particle morphology. This trend can be rationalized by postulating that twin defects provide the kink sites necessary for interfacial propagation. Other insights into the mechanisms responsible for the evolution of these complex systems that are attainable only through in situ 3D experiments will be given.

In situ liquid cell transmission electron microscopy (TEM) was used to observe nanostructural platinum (Pt) growth under electron beam irradiation in amphiphilic block copolymer solutions. Certain amount of K₂PtCl₄ and Pluronic F127 were dissolved in high purity water and loaded into the in situ liquid cell. A JEOL2100 LaB6 transmission electron microscope was used for the in situ observation. Platinum nanostructures were observed to grow under spread electron beam. With electron irradiation, Pt nano particles were observed to appear, grow up, dance around, connect to each other, and finally self-assembled into chain-like and branched nanostructures. The morphorlogies of the Pt nanostructures were found to be associated with the liquid layer thickness. With ~100 s beam irradiation, the resulted Pt particles and nanostructures in the thicker liquid region were of bigger sizes (~30 nm and ~200 nm), and appeared to be fluffier; while in the thinner liquid resion, they were of smaller sizes (~10 nm and ~50 nm), and appeared to be denser. The effects of the copolymer and the liquid layer thickness for the nanostructural Pt formation are discussed.
Acknowledgment: The helps from Prof. S. Dillon and Dr. J. G. Wen are greatly acknowledgd. This work was supported by the Science and Technology Commission of Shanghai Municipality (11nm0507000), the Shanghai Pujiang Program (13PJ1401700), Shanghai Leading Academic Discipline Project (B502), and Shanghai Key Laboratory Project (08DZ2230500).

Research into the structural and magnetic response of optomagnetic materials and devices irradiated with femtosecond (fs) laser pulses has attracted a great deal of attention from both academia and industry owing to a variety of fundamental and applied aspects. Rare-earth transition-metal alloys are currently being explored for their ultrafast magneto-optical response to fs laser pulses in a process known as all-optical switching (AOS). The phenomenon of AOS is very promising for next-generation extremely high-density magnetic recording. Typically, techniques for characterizing AOS and domain-wall dynamics are based on optical-microscopy methods which can suffer from diffraction-limited resolutions in the far field. Here, we describe a new approach that combines in situ laser irradiation with Fresnel imaging in a transmission electron microscope (TEM) to characterize the effects of fs optical pulses on the magnetic and crystallographic structure of TbCo thin films. Preliminary results indicate that sustaining the single-domain magnetic and amorphous structure necessary for achieving the AOS phenomenon at industrially-feasible working parameters poses a challenge for future device applications. Specifically, we found a difference in the repeatability of AOS for the accumulation and single-pulse responses. Accumulation of the AOS phenomenon was found to be repeatable less than 20 times, whereas the single-pulse-induced AOS was repeatable well over 10⁵ times. Future work will focus on further quantifying and exploring this variability in the number of reversible cycles attainable for different laser parameters via this in situ Fresnel TEM method in order to identify industrially-pertinent parameter space necessary for AOS.

We studied the αharr;γ phase transformation in Fe and Fe-Au thin films and nanoparticles employing in-situshy; X-ray diffraction by varying the temperature (from room temperature up to 1100°C), film thickness, particle size and composition. In pure Fe particles the transformation did not occur, whereas in the respective thin films a “reverse size effect” was observed shy;- only the thinnest and the thickest films underwent the transformation. In contrast, the γ-Fe phase was observed in all Fe-Au samples (bi-particles and thin films), and remained metastable at room temperature. γ-Fe particles as large as 300 nm in diameter were observed by electron microscopy. The results are discussed in terms of the difference in available nucleation sites in the particles, bi-particles and films; critical nucleus size; and the facilitating presence of Fe/Au interfaces. The reverse size effect challenges the paradigm that phase stability at the nanoscale changes monotonously with a decrease of the system&’s characteristic dimensions.

The Incoatec microfocus source IµS is a low power air cooled X-ray source for diffractshy;tometry applications. It is available with Cr, Co, Cu, Mo, and Ag anodes. The source is equipped with a two dimensional beam shaping multilayer optics. Therefore, we can form either a highly collimated beam with a low divergence (below 0.5 mrad) or a focusing beam with higher divergence (up to 10 mrad) and very small focal spots (diameter below 100 µm).
Equipped with a collimating optics it can be used for GISAXS, SAXS and X-ray reflecshy;toshy;meshy;try studies. When using focusing optics all those experiments can be carried out in transshy;mission geometry, especially in powder diffraction applications. With the Mo-IµS highly absorshy;bing and radiation-damage sensitive materials can be investigated. Consequently, this source is often used for single crystal diffractometry in the chemical crystallography and becomes more and more interesting for investigations of soft matter samples.
In our presentation we will give an overview of representative experimental setups and results demonstrating the potential of our IµS in XRD studies. These take advantage of the brilliance and outstanding beam quality of this low-maintenance microfocus source. It is shown how the IµS can be used to achieve excellent results in both home-lab and synchrotron pre-characterization experiments, e.g. the investigation of in-situ thin film deposition in UHV chambers by using GISAXS or the structure of oriented two-dimensional liquid crystalline samples.
We will be presenting two applications in more detail, both measured at the Slovak Academy of Sciences:
1) Nanoparticles on a liquid sample were investigated with a special GISAXS setup equipped with a Cu-IµS producing a 5 mrad focused beam and with a Pilatus pixel detector. Ordering phenomena could be observed in-situ during an increase of surface pressure. The particles were transformed from single islands to an almost vertically ordered structure of connecting particles.
2) By using in-situ GISAXS in the home-lab we investigated how a multilayer grows during thin film deposition. This kind of experiments is typically done only at synchrotrons. With an IµS it is now also feasible in the home-lab.

Nanoparticles can easily be fabricated by different physical and chemical processes and can also be arranged in many different patterns and shapes, by micellar techniques for example. However, the synthesis is usually restricted to thermally equilibrium conditions. Ion beam irradiation, a non-equilibrium method, is one possible subsequent approach to tune the properties of such nanoparticles. An important effect in this case is sputtering, especially when the ion range is in the range of the size of the nanoparticle. For different purposes, it is important to understand the quantity of the sputtering effects on nanoparticles and the nanoparticle-substrate interaction. Gold nanoparticles with diameters of around 50 nm on top of silicon substrates with native oxide layer were irradiated by gallium ions of various energies in a focused ion beam system. Using high resolution in-situ SEM imaging, the size dependence of the sputter yield was measured by image analysis. These results were compared with the simulation results by iradina [1], a new Monta-Carlo-code, which takes the specifics of the nanogeometry into account. We observe enhanced sputtering in the nanostructures compared to bulk-like structures or films.
[1] C. Borschel, C. Ronning: Ion beam irradiation of nanostructures - A 3D Monte Carlo simulation code, Nuclear Instruments and Methods in Physics Research B 269 (2011) 2133-2138

Vanadium oxides (VO_x) exist as a variety of metastable and stable crystalline phases, many of which exhibit a metal-to-insulator transition (MIT) within a narrow temperature range. The sharpness of the MIT has been shown to be heavily influenced by the synthetic method and conditions. Such dramatic phase changes make VO_x films excellent candidates for "smart material" applications such as thermochromic windows, electrical and optical switches and sensors, and energy storage devices. Electrochemical synthesis represents a powerful synthetic approach that is well suited to the desired practical applications of vanadium oxides; it offers an inexpensive, scalable, and highly tunable technique with which to make VO_x films. By exploiting the inherent modularity of electrosynthesis, we show that the structural and electronic properties of electrodeposited vanadium oxide films may be carefully controlled by growth conditions such as deposition potential, temperature, time (film thickness), and electrolyte composition. As part of the Center for Next Generation Materials by Design EFRC, we combine synthetic insight with in-situ characterization studies conducted at the Stanford Synchrotron Radiation Lightsource facilities to shed light on how the structural order of electrodeposited VO_x polymorphs may direct the properties of the highly useful phase changing crystalline structures.

We report on the development of a new laser diagnostic for the in situ characterization of gaseous clusters. Additionally, we aim to use this diagnostic in order to detect nanoparticle formation in an arc discharge environment. Already succesfully demonstrated in atomic and molecular gaseous environments, this four wave mixing diagnostic technique exploits the strong interaction between a particle&’s polarizability with intense laser fields. Though this interaction, we can detect the temperature, pressure, relative density and speed of sound of the gas particle. In nanoparticles, we aim to validate their presence, differentiate between the different types of nanoparticles (nanotubes, fullerenes etc) and also provide with relative density measurements of nanoparticles in the arc discharge environment. The anticipated spatial resolution of this technique is ~150 mu;m while the spectral acquisition time is in the order of ~200 ns, rendering the technique ideal for fast changing environments, such as arc discharges, combustion and transient flow environments.

Manganese containing spinels are of interest as important catalysts towards oxidation and reduction reactions as well as for battery materials, both for the versatility of the spinel-type crystal structure with its many interstices, and for the multiple oxidation states. Nano-sized manganese spinels are especially desirable for catalytic processes taking place at active surfaces, since they have larger surface-to-volume ratios than bulk spinels. Though some reports exist on the synthesis of manganese-containing spinels with nanoparticle and nanorod morphology, synthesizing these compounds with a nanowire morphology is still challenging. Here, we report a new route to synthesize single-crystalline manganese-containing spinel nanowires by the solid-state reaction of manganite nanowire precursors with metal oxides or hydroxides; this represents the first report of the synthesis of Mg₂MnO₄ or CuMn₂O₄ in single-crystalline nanowire morphology and we believe this synthetic route may be extended as a general way to synthesize manganese containing spinel NWs. In both cases the wires show electrochemical catalytic activity with regards to the oxygen evolution reaction. To further understand the reaction mechanism, we performed in situ heating experiments in the transmission electron microscope (TEM), in which we place Mg(OH)₂ and γ-MnOOH reactant crystals in contact with each other on a TEM heating substrate, and observe the solid-state reaction directly as it progresses. As the temperature is ramped, a single-crystalline to polycrystalline to single-crystalline structural progression is observed within an individual γ-MnOOH nanowire, and the wire is seen to develop a measureable magnesium content via contemporaneous spectroscopic measurements. Compositional maps collected from nanowires during heating show a magnesium front migrating along the nanowire during the polycrystalline stage. We speculate that magnesium diffusion into and reaction with the γ-MnOOH wire may be aided by the transient nanocrystalline grain boundary formation.

As the device dimensions are scaled down, transport of matters induced by the electrical current drew much attention in the metal inter-connects. High current density of ~10⁶ A/cm², may invoke voids and hillocks in the copper interconnects, resulting in the device failure. It is one of important factors to identify the dominant diffusion paths to improve the reliability of the interconnects. Surface, Cu/Si₃N₄ interface, and grainboundaries were proposed as a preferential diffusion paths as per previous studies. In order to identify the preferential diffusion path of the copper atoms under the electrical field, in-situ electromigration steps were quantified by observing and recording under transmission electron microscopy (TEM).
Cu film of 50nm thickness was deposited by an ultrahigh vacuum DC magnetron sputtering, and patterned into a line with 3mu;m-width by photolithography followed by wet etching. Electric current was applied to the both ends of Cu line and the electro-migration induced microstructural changes of the Cu line were recorded for up to 10 hours using a specially designed in-situ TEM stage with 1×10⁶ A/cm² applied. Crystallographic orientations from each copper grains were mapped using diffraction-scanning transmission electron microscopy (D-STEM) technique (ASTER system) to visualize the distribution of the grain orientations. Migration path and grain growth steps with the defect generation were pile to play movie at 1000 times of speed.
Changes of the surface contour was overlaid with time to check the fast volume reduction path and confirm the fast migration path. It was found that the fast diffusion occurs along the grain boundaries exposed to the free surface in both side walls and voids. In the hillock region, on the other hand, grain growth was observed with the formation of internal defects. Driving force of the grain growth might be the stress accumulated by the hillock formation, which occurred in a very short time frame. Low angle boundaries appeared with the grain growth were Σ3 and Σ7 defects. Σ3 boundary is known as twin boundary, which commonly appeared in the pure copper and copper alloy and mainly observed in the hillock region. Σ7 has high interfacial energy and is known to be a fast moving boundary.

Nanoscale materials have received a great attention over the past few decades in the application areas of medicine, catalysis, sensing, and photonics. The properties of metal nanoparticles are significantly affected by their size distribution and aspect ratio, as well as faceting of the crystallographic surfaces. Since the first report of electroplating of copper nanoparticles from a liquid cell using transmission electron microscopy (TEM), liquid TEM has marked as an important research field that enables observations of particle nucleation, growth, and dissolution in real time.
The aim of this presentation is to gain insight into the inhomogeneous growth and dissolution of silver nanoparticles using real-time liquid transmission electron microscopy. The solution used to fill the liquid cell was prepared by dissolving silver nitrate (AgNO₃) in deionized (D.I) water. The assembled custom-built liquid cell stage was loaded into the TEM (JEOL, JEM-2010F), which was operated at 200 kV. It was reported that the Scanning TEM (STEM) and CTEM modes provide different results in liquid TEM because of the difference in current density and illumination area of the electron beam. Parallel illumination in conventional TEM (CTEM) was used in this experiment.
Small equiaxed silver nanocrystals were observed for the first 5 seconds with electron beam irradiation. Inhomogeneous, preferential growth was observed started from one corner of the frame after 35 seconds. Unlike the typical nano-particle growth, growth of the silver nanoparticles from seeds was anisotropic, with unidirectional growth. Subsequently, growth of nano-partlicles located at the center of the screen occurred after 55 seconds. In the same region of unidirectional growth, dissolution of nanoparticles was also observed. After 75 seconds of exposure, reactions of particle growth were occurred in the region of the unchanged. Finally, after 95 seconds, growth saturated, and silver nanoparticles covered the entire observation area. The interpretation of the inhomogeneous growth and dissolution of silver nanoparticles were to be discussed using the preferential reaction by the radiolysis.
This research was supported by the Nano-Material Technology Development Program (Green Nano Technology Development Program) through the National Research Foundation of Korea funded by the Ministry of Science, ICT & Future Planning (2011-0019984).

Assemblies of ligand stabilized gold nanoparticles have demonstrated remarkable potential for vapor sensing applications. The main features of gold nanoparticle based chemiresistors are their high sensitivity, adjustable selectivity, fast and reversible responses, low power consumption and the tunability of their underlying electrical properties.^[1,2] It is generally accepted that the sensing mechanism involves (at least) both swelling and sorption induced changes in permittivity. While swelling leads to higher resistivities, due to increased tunnel distances between neighboring particles, an increase in permittivity counteracts, and sometimes even over-compensates, this effect.^[3]However, repeatedly, findings have been reported which are difficult to explain by this model.^[4] Thus, to enable the rational development and target specific optimization of such sensors, a deeper and more quantitative mechanistic understanding is indispensable. On the experimental side, this requires measurements enabling the correlation of the chemiresistive response with the actual change in interparticle distance and the absolute amount of sorbed analyte. As shown previously, swelling of ordered nanoparticle assemblies can be probed in situ via grazing incidence small angle x-ray scattering (GISAXS).^[5,6] Here, we use GISAXS to study simultaneously swelling and resistive responses of supercrystals assembled from dodecanethiol stabilized gold nanoparticles. Additionally, the mass uptake due to analyte sorption was quantified using quartz crystal microbalances. When exposed to toluene, 4-methyl-2-pentanone or 1-propanol vapors, with concentrations ranging from 1000 to 10000 ppm, the supercrystals responded with a fast reversible increase in resistance and interparticle distance. All three measurements revealed the same trend concerning the selectivity, which was controlled by the solubility match between the dodecanethiol ligand and the solvent. The measurements allow us to test and further develop the above mentioned model. Further, it was observed that contaminants originating from the particle synthesis can have a considerable effect on the lattice constants, the swelling and the chemiresistive responses.
[1] F. J. Ibañez, F. P. Zamborini, Small2011, 8, 174.
[2] N. Olichwer, E. W. Leib, A. H. Halfar, A. Petrov, T. Vossmeyer, ACS Appl. Mater. Interfaces2012, 4, 6151.
[3] Y. Joseph, A. Peic, X. Chen, J. Michl, T. Vossmeyer, A. Yasuda, J. Phys. Chem. C2007, 111, 12855.
[4] A. W. Snow, M. G. Ancona, D. Park, Langmuir2012, 28, 15438.
[5] Y. Wan, N. Goubet, P.-A. Albouy, N. Schaeffer, M.-P. Pileni, Langmuir2013, 29, 13576.
[6] M. C. Dalfovo, L. J. Giovanetti, J. M. Ramallo-Loacute;pez, R. C. Salvarezza, F. G. Requejo, F. J. Ibañez, J. Phys. Chem. C2015, 119, 5098.

Nanoparticles (NPs) have shown tremendous potential for the targeted delivery of therapeutics and diagnostics to sites of diseased or cancerous tissue in vivo. Organic block copolymer amphiphile nanoparticle assemblies are of particular interest as active drug nanocarriers due to their general biocompatibility and the high degree of synthetic tunability of their size, morphology, and surface chemistry, and of their stimuli-responsive functionality. The synthesis of uniform micelle NP architectures is typically controlled via methods involving cosolvent mixtures, with the assumption that the macromolecular structures produced are stable following transfer to aqueous solution. However, recent studies suggest that ongoing dynamic interactions occur in amphiphilic micelle NPs in solution, including fusion/fission events and unimer exchange, that can result in unexpected particle size evolution and step-change shifts in size distribution. However, these dynamic nanoscale growth processes have not been directly observed and are not well understood, largely due to the inherent challenges of imaging organic nanostructures in liquid. For in vivo applications, NP size and dispersity are critical parameters in dictating functional properties. Understanding the fundamental mechanisms and kinetics involved in micelle NP formation and size evolution is essential in order to effectively design amphiphilic polymer NP systems with controlled functionality.
In this work, we use in situ liquid cell transmission electron microscopy (LCTEM) to directly observe the dynamic evolution of organic zwitterionic polymer micelle NPs in aqueous solution. The results from this study represent the first real-time imaging characterization of organic micelle NP dynamics, and provide unprecedented insight into the fundamental mechanisms and kinetics involved in micelle assembly and growth. We observe the formation of larger (~150 nm), bicontinuous spherical NPs, by a combination of fusion events between smaller NPs (<100 nm) and unimer attachment from solution. Using multiparticle tracking algorithms and computational modeling we are able to quantify the kinetics of individual particles, such as fusion event relaxation rates, unimer attachment growth rates and the rate and magnitude of motion for a spectrum of particle sizes, and begin to understand the energetics involved in particle fusion and other particle interactions. We find that only small percentage of particle proximity interactions result in fusion events. We correlate the in situ LCTEM results with cryo-TEM imaging of the system as-synthesized and after several treatments that have been shown to increase system kinetics, such as mild heating, solution agitation, and slight modifications in pH, to demonstrate that the growth processes observed by LCTEM are not beam induced artifacts, and represent the natural rearrangement of the kinetically trapped system to a more stable structural configuration.

Many researchers are interested in observation of chemical reactions using transmission electron microscope (TEM), because it reveals the details of the reaction, such as reactive sites and elementary processes of the reaction. For instance, Yuk et al. [1] have succeeded in in-situ observation of coalescing of the two platinum nanocrystals in liquid using graphene cell. However, the graphene cells may not be suitable for aqueous solutions, since graphene is hydrophobic. Therefore, another cell for aqueous solution is required. A liposome, which is composed of dipalmitoylphosphatidylcholine (DPPC) bilayers, is one of the candidates for such cell. In this study, using liposomes, the precipitation of rock salt crystal from aqueous solution is in-situ observed using TEM.
The liposomes were synthesized using Bangham method [2]. DPPC layer reinforced with cholesterol were fabricated and the ultrasonic treatment was conducted in sodium chloride aqueous solution to form the liposomes filled with the aqueous solution.
The prepared liposomes were observed using phase contrast Cryo-TEM (JEM-2200FS , JEOL) and conventional TEM (JEM-2000FX and JEM-2000EX, JEOL) operated at 200kV. It is confirmed by Cryo-TEM that the liposomes are successfully fabricated. Using conventional TEM, the effects of electron irradiation heating on the liposome filled with aqueous solution are investigated, and the contrast fluctuation of the liposome during electron irradiation is firstly observed. The gases evaporated from the liposome are also analyzed using a mass spectrometer (835 Vacuum Quality Monitor System, MKS instruments), which is attached to conventional TEM. In the final state, the precipitation of square nanocrystals is confirmed. According to the selected area electron diffraction pattern, the precipitated nanocrystals are sodium chloride single crystal. Thus, liposomes can be employed for in-situ TEM observation of chemical reactions in aqueous solution and, in this study, the precipitation of rock salt crystal from aqueous solution is observed.
[1] J. M. Yuk, Jong Min, et al. Science 336.6077 (2012): 61-64.
[2] A.D. Bangham et al. J. Mol. Biol. 13 (1965) 238.
Acknowledgement: This research is supported by a Grant-in-Aid for Exploratory Research (No.
25630269) from the Japan Society for the Promotion of Science (JSPS) and General collaborative project (No. 133) of National Institute for Physiological Sciences of Japan.

Scanning Electron Microscopy (SEM) can be performed at ambient pressure if certain conditions are met. Such an apparatus opens up the possibility of characterizing vapor-solid or solid state chemical reactions in-situ and at the nanoscale using electron beam-based techniques such as imaging, energy dispersive x-ray spectroscopy (EDS), or cathodoluminescence. Using a commercial airSEM^trade; (B-nano Ltd.) and a custom-built heating chamber which seals to the SEM chamber, the reaction between lead iodide (PbI₂) and methyl ammonium iodide (CH₃NH₃I, MAI) vapor to form the perovskite MAPbI₃ is explored by SEM imaging and EDS. This reaction was chosen because of the photovoltaic community&’s intense focus on MAPbI₃ as an active layer material in solar cells. Beginning with a polycrystalline film of PbI₂ with grain size below the imaging resolution, formation of cubic grains is observed upon exposure of the film to MAI vapor. Grain formation was concurrent with incorporation of iodine into the sample as verified by EDS, with the iodine to lead ratio increasing as exposure to MAI progressed, suggesting that the perovskite compound was indeed formed. In-situ observation requires that the effects of the measurement itself be considered. While some form of the reaction between PbI₂ and MAI was apparent, even minimized exposure to electron beam irradiation changed the outcome of the reaction as evidenced by comparison to un-imaged areas. Future work will explore other systems that are less prone to electron beam damage for in-situ observation experiments.

In-situ liquid cell microscopy combining multiple imaging tools is a powerful technique for probing next generation battery materials. TEM observations are uniquely able to view dynamic nanoscale phenomena while X-ray microscopy provides the ability to make links between nano-, meso-, and bulk scale phenomena. X-ray makes this possible through the application of probes including x-ray diffraction, x-ray absorption spectroscopy, and scanning transmission x-ray microscopy (STXM). The recent development of liquid sample holders enables imaging through liquids in these tools while applying a bias and is directly applicable to the study of next generation liquid cell batteries. Through a cross correlative approach, a better understanding of the ion insertion and extraction mechanisms in the cells, the evolution of the electrode interface, and SEI layer growth dynamics can be achieved. Here we present details on the cross correlative tools and techniques used in this research into next generation battery materials. Initial results from the application of this approach to the study of lithiation of lithium iron phosphate particles will be discussed. The results yield state-of-charge maps as the battery is cycled and demonstrate the usefulness of liquid cell microscopy in the characterization of future battery cathode materials.

Understanding the processes by which pharmaceuticals disintegrate, dissolve, and release their drug payload is a key requirement for targeted drug delivery, rational formulation, etc. We have recently employed a range of techniques including rapid in-situ Raman chemical imaging, UV-vis spectroscopy, rotating disk dissolution rate experiments, MRI imaging and conventional solution-state NMR to investigate this process for several model pharmaceutical formulations. We show that transformations including amorphous-crystalline, and crystalline-crystalline, can be identified spatially and temporally for model tablets in a flow-cell apparatus. Modelling of the results allows the mechanism of the transformation to be understood. Results from several studies will be presented, and future developments outlined.

The observation and evaluation of lattice defects such as vacancies, dislocations, and grain boundaries are very important in materials design. Electrical resistivity measurement is superior to electron microscopy for obtaining average microstructural information, including density and type of lattice defects. Electrical resistivity can generally be measured using a well-shaped cylindrical or tabular specimen. The dimensions of the specimen must be accurately measured in order to obtain the electrical resistivity from four-point DC electrical resistance measurements. This means that the resistivity cannot be measured in irregularly shaped specimens, for example, under tensile deformation. However, resistivity can be estimated using the empirical relationship. The purpose of this study was to determine Matthiessen&’s empirical relationship by using tensile-deformed specimens and to estimate changes in electrical resistivity during the tensile deformation of pure Fe. The electrical resistivities of tensile deformed Ti specimens were measured at 77 K (ρ₇₇) and 300 K (ρ₃₀₀) along the tensile direction using a direct current (DC) four-point method in order to determine Matthiessen&’s empirical relationship, ρ₇₇ = α/(R - 1) + β, R = ρ₃₀₀/ρ₇₇. Plots of ρ₇₇ versus 1/(R-1) showed a linear relationship, and the values of α and β were determined to be 0.1104 and -0.001465 (mWm), respectively. Changes in ρ₇₇ during tensile deformation were estimated by substituting the resistance ratio R into Matthiessen&’s empirical relationship. Basically resistance increased with the tensile deformation in both elastic and plastic regions. Although the stress-strain curve showed uniform elastic deformation, the increment rate of resistance changed drastically around 20 MPa. It assumes to be attributed to micro-yielding. In addition, the resistivity change in the loading/unloading process can be separated into vacancy or dislocation-derived one by monitoring the change at 273 K for a while, since vacancies can disappear but dislocations can&’t at 273 K. Vacancy might be induced even in elastic deformation and the density was almost proportional to applied strain. Drastic increase in resistivity related to dislocation density was confirmed to appear in the Lüders deformation.

Transition metal oxides (TMOs) with ABO₃ perovskite structures are a playground for interesting physics, driven by electron localization and competition between electron-electron and electron-lattice couplings. Unlike traditional semiconductors, the high electron localization in TMOs renders them more complex to study and suggests structure property relations should be determined at the unit cell or single reconstruction level, requiring atomically resolved studies. In this talk, I will describe our recent work on in-situ studies of TMOs, focusing on pulsed laser deposition growth and atomically resolved imaging of La_xCa_1-xMnO₃ (LCMO). It will be shown that the surface segregation and morphology of the films can be controlled by suitable changes in oxygen pressure or chemical doping, while barrier heights for diffusion of adatoms can be determined via determination of atomic positions and theory-experiment matching utilizing a Monte-Carlo model based on Boltzmann statistics. Density functional theory calculations show half-metallicity of both terminations of LCMO, and suggest a tunable gap determined by oxygen overlayer concentration, confirming experimental studies. These insights show the power of the in-situ approach in determining novel physics and identifying the relevant structure-property relations in TMOs.
This research was supported by the US Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), Materials Sciences and Engineering Division (RKV, AT, SVK, HD, VRC) and the Office of Science Early Career Research Program (V.R.C). This research was conducted at and partially supported by (APB, PG) the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility. AGG acknowledges fellowship support from the UT/ORNL Bredesen Center for Interdisciplinary Research and Graduate Education.

Manipulation the matter at the atomic level is one of the ultimate goals in nanoscience. Demonstration of atomic manipulation at surfaces by Scanning Tunneling Microscopy (STM)¹ opened the possibilities for the fabrication of novel atomic structures including quantum corrals,² standing electronic waves,³ atomic switches,^[4] molecular cascades for atom based computing,⁵ and quantum holographic devices.⁶ While the STM and non-contact AFM approaches are limited to material surfaces, an alternative paradigm for nano-patterning in bulk material is offered by electron beams. E-beam lithography in scanning electron microscope (SEM) geometry⁷ have been demonstrated to fabricate three dimensional structures at the nanometer scale. However atomic-level fabrication is only expected with highly energetic e-beams in (scanning) transmission electron microscope ((S)TEM). Recently, atomic rearrangements in amorphous materials have been reported.⁸ These observations suggest that (S)TEM beam can in principle be used to achieve sub-nanometer level bulk nanofabrication.
In this work, we demonstrate atomic-level sculpting of 3d crystalline oxide nanostructures from amorphous precursor in a STEM. SrTiO_shy;3 nanowires can be fabricated epitaxially from the crystalline substrate following the beam path. This method can be used for producing crystalline structures as small as 1-2 nm, and the process can be observed in situ with atomic resolution. Heating of the specimen by electron beam is judged unlikely to contribute to the process; even assuming exceedingly low thermal conductivity of the amorphous SrTiO₃ material, the relevant temperature increase was estimated to be at most 50K, which is still too low to be responsible for the phase transformation. The energy transfer could therefore be knock-on in nature. Atomistic molecular dynamics (MD) simulations verified the feasibility of beam-induced crystallization if the high-energy excitation is applied in the vicinity of the amorphous-crystalline interface.
We further demonstrate fabrication of arbitrary shape structures via control of the position and scan speed of the electron beam. Combined with broad availability of the atomically resolved electron microscopy platforms, these observations suggest the feasibility of large scale implementation of bulk atomic-level fabrication as a new enabling tool of nanoscience and technology, providing a bottom-up, atom-by-atom approach, which could be complementary to 3D printing.
[1] D. M. Eigler, et al.,Nature 1990
[2] M. F. Crommie et al.,Science 1993
[3] M. F. Crommie et al.,Nature 1993
[4] D. M. Eigler et al.,Nature 1991
[5] A. J. Heinrich et al.,Science 2002
[6] C. R. Moon et al.,Nature Physics 2008
[7] C. Vieu et al., Applied Surface Science 2000
[8] K. Zheng et al.,Nature Communication 2010
Supported by the Materials Science and Engineering Division, Office of Basic Energy Sciences, U.S. DOE., and Oak Ridge Leadership Computing Facility, sponsored by Office of Science, U.S. DOE.

As the start point of solidification, the effect of particle size, location, distribution and the potency of the nucleus are of importance in nucleation behaviour and the following solidification process. Since last 50s, the nucleation behaviour of metals has been extensively investigated. But due to the restriction of the observation facility, the direct observation on the nucleation of liquid metal is still not practical. In this study, single crystal substrates were used as catalyser. The nucleation behaviour of liquid Al on different substrates was investigated through cooling curves, nucleation interface and liquid structure adjacent to liquid/substrate interface under synchrotron radiation facility. From the observed results, the nucleation behaviour of liquid Al were related to the lattice misfit between new crystal and substrate. Combining with previous published results and our experimental data, the relationship between misfit and undercooling can be formulated by van der Mere model, natural lattice misfit model and coincidence lattice misfit model, respectively, as misfit less than 13%. Above 13% misfit, the nucleation is dominated by stack fault energy of new crystal adjacent to substrate. Apart from lattice misfit, the chemical reaction between substrate and liquid also affects nucleation, where Al reacted with MgO and MgAl2O4 substrate forming α-Al2O3. Further investigation shows, the similarity between liquid atomic clusters and the lattice structure of substrate dominate heterogeneous nucleation behaviour of liquid metal.

Heterogeneous catalysts often undergo dramatic changes in their structure as the mediate a chemical reaction. Multiple experimental approaches have been developed to understand these changes, but each has its particular limitations. Electron microscopy can provide analytical characterization with exquisite spatial resolution, but generally requires that the sample be imaged both ex situ and ex post facto. Photon probes have superior depth penetration and thus can be used to characterize samples in operando (i.e when they are actively working). But they generally lack spatial resolution and thus give only ensemble average information.
We have taken advantage of the recent developments in closed-cell microscopy methods to develop an approach that allows us to successfully combine electron, x-ray and optical probes to characterize supported nanoparticle catalysts in operando. By measuring the reaction products at each stage of the reaction, we can directly correlate the information that can be obtained from each approach, and thus gain a deep insight into the structural dynamics of the system.
We will describe how we can use this approach to correlate x-ray absorption spectroscopy (both near-edge and extended fine structure), scanning transmission electron microscopy and infrared microspectroscopy to understand how Pt and Pd nanoparticles supported on silica undergo structural changes during the room temperature hydrogenation of the ethylene, and how we can direct measure and describe the reaction products on the surfaces of the nanoparticles as the reaction proceeds. By combining these approaches, we can track the interplay between nanoparticle reduction, coarsening, and the specific surface species at different stages of the reaction. We will also show how this approach can be used to understand the partitioning that occurs in bimetallic nanoparticles during oxidation and reduction at elevated temperatures, with a focus on the NiPt system.
The presentation will focus on the development and application of experimental methods, including the high temperature atmospheric pressure electron microscopy, the direct measurement of reaction products using gas chromatography-mass spectrometry and the ability of a newly developed electron microscope for operando microscopy (based on the FEI Talos platform) to characterize bimetallic nanoparticles through energy dispersive x-ray spectroscopy.

Improving the efficiency of gas turbine engines necessitates the development of structural alloys that can operate at higher temperatures. The alloys must maintain structural integrity while possessing excellent high-temperature oxidation resistance. The formation of a stable oxide scale is needed to protect the material from aggressive oxidizing environments. Understanding the mechanisms of growth of the oxide under various reaction conditions is critical for improving an alloy&’s resistance to high temperature oxidation in aggressive environments.
50.3Ni-49.7Al (at. %) powder was used to study oxidation reactions in an aberration-corrected JEOL 2200FS scanning transmission electron microscope, under static air conditions at 300 Torr, with heating up to 800°C. A closed-cell TEM specimen holder based on MEMS-fabricated heater devices (Protochips “Aduro^TM” E-chips) was used to carry out oxidation experiments. The Protochips Atmosphere 200^TM Gas E-cell system incorporates a fully automated, computer-controlled gas delivery manifold with near-instantaneous closed-loop temperature control, independent of the gas pressure and composition. Atomic-resolution STEM imaging and x-ray energy dispersive spectroscopy (EDS) were used to identify oxidation products. After heating the powders e.g. to 800°C, the sample was “quenched” in a few seconds to 200°C for subsequent imaging (to avoid contamination). Several oxidation reactions were carried out in the gas cell, with the Aduro E-chip removed and mounted in a standard heater holder for EDS work between each oxidation experiment. Thin NiAl alloy grains showed formation of mainly Al₂O₃ on the surface of the NiAl powder particle after oxidation at 800°C. Additional heating was carried out at lower temperatures; reaction products and their mechanism of formation were characterized, and will be discussed.
shy;__________________________________
Research supported by Research supported by the U.S. Department of Energy, Office of Coal and Power R&D, Office of Fossil Energy.

Dynamic composition distribution of carbon-supported Pt₃Ni octahedral (Oh) nanocrystal was studied using environmental transmission electron microscope (ETEM) under thermal annealing conditions. The as-made Pt₃Ni Oh nanocrystal was inhomogeneous in atomic distribution with a Pt rich shell and PtNi alloy core. Dislocations exist at the boundaries between the core and shell. Upon mild annealing in vacuum at enhanced temperatures, the migration of a paired dislocation towards the surface was observed over time. Coinciding with this structural change, dramatic enhancement of the reduction of oxygen electrochemically was observed for this Pt-Ni catalyst. The migration of dislocations was found to follow first order decay as a function of time, suggesting a Fick&’s law like behavior. Since the post-synthesis processing for the Pt₃Ni catalysts was performed under similar vacuum condition, the movement of dislocations should reflect the redistribution of Pt and Ni in the catalyst particles. The outward migration of dislocations suggest the inward diffusion of Pt atoms from the shell towards the core proceeded faster than the outward net diffusion of Ni atoms, i.e. Kirkendall effect, resulting in an Oh nanocrystal with higher surface Ni content. XPS study on as-made and post annealed (under vacuum) Oh Pt₃Ni nanocrystals agreed with the observation in the in-situ ETEM where the treated Oh nanocrystals showed much higher Ni ratio than the as-made sample. The thermally treated Pt₃Ni Oh nanocrystal showed significant improvement in catalyzing oxygen reduction reaction (ORR) as compare to the as-made nanoparticles. Our result indicates that optimization of Pt and Ni atom distribution can be achieved through thermal treatment under vacuum in a controllable and quantitative fashion.

This presentation will demonstrate the power of neutron powder diffraction (NPD) using high intensity neutron fluxes for obtaining unique and reliable information concerning real time structural and chemical changes in oxide materials. The focus will be on low-dimensional non-stoichiometric oxides where oxygen migration occurs in planes in layered materials or within one-dimensional channels in a new class of oxygen excess phases. The data to be discussed were obtained on the instrument D20 (ILL, Grenoble) with complete data sets being obtained in time intervals of 1-5 minutes with a corresponding temperature resolution of 1-5^oC . The presentation will focus on how the in situ approach can yield additional, reliable structural information that is easily missed using conventional ex situ refinement methods. The presentation will primarily consider a 1-D channel structure which has not previously been reported to accommodate interstitial oxygen, and therefore is of significant interest for catalytic and electrocatalytic applications.
The new oxygen excess phases are related to ASb₂O₄ (A=Mn, Fe, Co , Zn etc.) which has a tetragonal structure with empty 1-D channels (diameter ~ 4 A) directed along [001]. Lone pairs of electrons on the Sb³⁺ ions are directed into the channels, and chains of edge-linked AO₆ octahedra separate the channels. Appropriate chemical modification of this parent structure results in materials which can absorb oxygen at relatively low temperatures (350^oC) to give, for example, ASb₂O_4.4 with no major structural changes. The process can be reversed by heating in hydrogen at 500^oC. Although the location of the interstitial oxygen within the channels was suggested by an ex situ NPD study and appeared chemically sensible, the refinement statistics were insensitive to the structural details. Real time oxidation and reduction were therefore performed while collecting NPD data. In this way, the location of the oxygen within the channels was confirmed; however, by monitoring subtle changes in bond lengths and oxygen site occupancies, additional details of the chemistry involved have been revealed. In particular, the inserted oxygen ions bond directly to the Sb³⁺ ions and cause a change in the coordination environment to retain space for the lone pair of electrons; charge balance occurs via oxidation of A cations. Moreover, the oxygen seems not to enter simply as O^2- ions, since the oxygen stoichiometry is higher than expected for the change occurring in the A oxidation state. Indeed, it seems likely that some peroxide O₂^2- species are present. Additional support for the presence of peroxide ions will be presented. Related materials may therefore be candidates as electrocatalysts for partial reduction of O₂ molecules.

There has been a steady growth in the applications and breadth of in situ transmission electron microscopy (TEM) since the 1980&’s [1]. At that time, the procedures to carry out meaningful experiments were described (e.g. [2]) but it was thought that high voltage TEM and thick specimens were required to reproduce bulk behavior. However, in a series of studies, we established that this was not necessarily the case and that high resolution TEM recordings could be made in real time, in situ and that the atomic behavior associated with materials reactions at interfaces could be deduced (e.g. [3]-[5]). Moreover, with the advent of thin film and nanotechnology, the investigation of thin and nano-scale materials became a necessity (e.g. [6]). In recent years, there has been an additional proliferation, most notably from in situ TEM in controlled environments such as in gases and liquids (e.g. [1], [7]).
This paper therefore reviews the application of in situ TEM to investigate material reactions, particularly those associated with interfaces important in electronic applications. An overarching theme of our work has been to ensure that the in situ studies are truly representative of the real behavior of the material system, and we have advanced a number of guidelines to ensure this. Moreover, we have also expanded our approach to environmental material-gas reactions such as carbon nanotube oxidation [8], magnesium hydrogenation and the hydrogen reduction of amorphous molybdenum sulfide for water splitting reactions. The influence of the imaging electron beam is more important for the gaseous reactions, as it ionizes the reacting gas species, and it is necessary to develop protocols to take this into account. The procedures we have adopted to do this will be carefully described.
References:
[1] R. Sinclair, Mats. Res. Soc. Bull. 38 (2013), p 1065-1071
[2] E. P. Butler and K. F. Hale, “Dynamic Experiments in the Electron Microscope” Vol. 9 of “Practical Methods in Electron Microscopy”, ed. A. M. Glauert, (North-Holland Pub. Com., New York).
[3] R. Sinclair, T. Yamashita, M.A. Parker, K. B. Kim, K. Holloway and A. F. Schwartzman, Acta Crystallogr. Sec. A 44 (1988), p. 965-975.
[4] T.J. Konno and R. Sinclair, Philos. Mag. B 71 (1995), p. 179-199.
[5] D. H. Ko and R. Sinclair, Ultramicroscopy 54 (1994), p. 166-178.
[6] K. H. Min, R. Sinclair, I. S. Park, S. T. Kim, and U. I. Chung, Philos. Mag. 85 (2005), p. 2049-2063.
[7] A. L. Koh, S. C. Lee and R. Sinclair, “A Brief History of Controlled Atmosphere Transmission Electron Microscopy”, in: “Controlled Atmosphere Transmission Electron Microscopy - Principles and Practice”, ed. T. W. Hansen and J. B. Wagner, (Springer Publishing Company, New York) (in press).
[8] A. L. Koh, E. Gidcumb, O. Zhou and R. Sinclair, ACS Nano 7 (2013), p. 2566-2572.

Mo-Si-B alloys are a good candidate for high temperature application due to the striking alloy properties of high strength, creep resistance and phase stability. However, their oxidation resistant depends on creation of the continuous outer layer of glass upon elevated temperature exposure. Therefore the limited knowledge of the very early stage of the oxidation process needs to be expanded due to the design for oxygen resistant high temperature alloys. In this work we utilize environmental transmission electron microscopes (ETEM) (Hitachi H-9500 ETEM) which enables atomic resolution visualization of structural transformation in gas environment and tunable temperature in real time and insitu ultra high vacuum (UHV) microscope (Hitachi UHV H-9000) connected to the surface preparation and analysis system (SPEAR) which combines the high resolution imaging with insitu oxidation, heating and surface characterization by XPS while preserving UHV conditions at all times. Additionally, ex-situ oxidized samples are investigated by using aberration corrected scanning transmission electron microscope (STEM) (JEOL JEM ARM200CF) to get atomically resolved images and chemical maps. In this work, we show the very early stage of oxidation of Mo-Si-B alloys of which mechanism is not as yet very well understood. We observed the first 2-3 nm of oxidation layer in real time.

The development of magnesium alloys offers promise for high specific strength applications, but can suffer from a susceptibility to corrosion, in which the mechanisms and degradation processes are not well understood. The progression of the corrosion can be dependent on such features as the alloy grain size, the different alloying elements present, as well as the possibility of intermetallic phases and impurities. Furthermore, the physical degradation effects can take a variety of different forms, spanning from isolated pitting corrosion, to inter and intra granular corrosion, and material fracture. To help gain more understanding of the microstructural evolution of the material in three dimensions, an in situ 3D X-ray tomographic imaging study has been performed. A custom in situ chamber has been designed and implemented to contain a small sample of Mg alloy with a controlled surface exposed to a 0.1molar solution of NaCl. The chamber was mounted in a commercial laboratory X-ray microscope to perform 1µm/pixel tomographic imaging while the corrosion process evolved over the time scale of hours. Multiple tomographic data sets were collected during the degradation process. The results reveal initial widespread pitting corrosion across the surface of the sample, with pits subsequently serving as initiation sites for filament growth spreading across the surface, denoted as ‘Stage 1&’ corrosion. A critical point was reached where the dominant degradation process changes to so-called ‘Stage 2&’ corrosion, in which further surface damage appears to slow in favor of increased expansion of the corrosion front into the depth of the material. The in situ observations were used to simultaneously characterize the extent of the surface and near-surface damage, as well as identify the transition from ‘Stage 1&’ to ‘Stage 2&’ corrosion. Soon after recognizing the transition, the process was halted and the sample was removed from the corrosive environment, and subsequently characterized with additional high resolution imaging tools including nanoscale X-ray microscopy and focused ion beam - scanning electron microscopy 3D tomography. The high resolution techniques revealed additional detail with regards to the structure of the corrosion products, as well as the progression of the corrosion front, specifically the impacts of the grain structure of the alloy and the effects of dispersed intermetallic inclusions.

Lithium (Li)-ion batteries are currently used for a wide variety of portable electronic devices, electric vehicles and renewable energy applications. In addition, extensive worldwide research efforts are now being devoted to more advanced “beyond Li-ion” battery chemistries - such as lithium-sulfur (Li-S), lithium-air (Li-O₂) and replacing Li⁺ with cost effective bivalent metals, such as Mg to improve gravimetric storage capacity and energy density. However, the practical application of these new systems has been highly problematic. For example, the main challenges for Li based systems involve controlling the formation of a solid-electrolyte interphase (SEI) layer and the suppression of Li dendrite growth during the charge/discharge process (achieving “dendrite-free” cycling). The SEI layer formation continuously consumes the electrolyte components creating highly resistive layer, which leads to the rapid decrease of cycling performance and degradation of the Li anode. The growth of Li metal dendrites at the anode contributes to rapid capacity fading and, in the case of continuous growth, leads to internal short circuits (the dendrites contact the cathode) and extreme safety issues. One of the key challenges for Li-S battery is the understanding of lithium polysulfide dissolution process and subsequent evolution of transient polysulfide species and their reactivity with electrode and electrolyte during the cycling. On the other hand, the bivalent Mg battery exhibits large difficulties with transport of Mg²⁺ion within electrode, incompatibilities of the electrolyte with the electrode surface, and the formation of passivating solid electrolyte interphase (SEI) layers, which leads to fast capacity fading during cycling. Here we demonstrate the application of an operando electrochemical scanning transmission electron microscopy (ec-(S)TEM) cell to study the SEI layer formation in Li⁺ ion and Mg²⁺ systems, the initial stages of Li dendrite growth and formation/dissolution of lithium polysulfide species. From these observations, we can precisely quantify the total volume of Li deposition, the thickness of the SEI layer (observed as a ring of positive contrast around the electrode) and alloy formation due to Li⁺ ion insertion during each cycle. Furthermore, at the end of each discharge cycle we can quantify the presence of “dead Li” detached from the Pt electrode, thereby demonstrating the degree of irreversibility (and degradation of Pt electrode) associated with insertion/removal of Li⁺ during this process. Such analyses provide significant insights into Li metal dendrite growth, which is critical to understand the complex interfacial reactions needed to be controlled for future Li-based and next generation energy storage systems. The differences and similarities between these results and more recent observations for Li-S, Li-Air and Mg based battery systems will also be discussed.

Behaviors of functional interfaces are crucial factors in the performance and safety of energy storage and conversion devices. In perovskite solar cells, careful engineering of component interfaces suppresses carrier recombination and boosts conversion efficiency. In lithium ion batteries, side reactions and phase transformations that occur at electrode-electrolyte interfaces are often the cause of inefficiencies and eventual failure. However, the dynamic analytical characterization of interfacial behavior far from equilibrium has not yet been demonstrated, and would be instrumental in designing advanced functional systems in many fields. Here, we present a study uncovering the unique interfacial phenomena related to lithium ion transport and its corresponding charge transfer in all-solid-state batteries by in situ scanning transmission electron microscopy (STEM), coupled with electron energy loss spectroscopy (EELS). With appropriate focused ion beam (FIB) fabrication conditions and design, electrochemically active samples can be galvanostatically biased in the TEM column avoiding air exposure and relaxation. The high spatial and spectral resolution of this coupled technique enabled the first observation of dynamic compositional and electronic bonding changes at the interface between solid electrolyte and solid electrode. An unexpected structurally disordered interphase layer was discovered between LiCoO₂ cathode and LiPON solid electrolyte. During in situ charging, this interfacial layer evolved to form highly oxidized Co ions and lithium oxide species. The insights gained from this novel technique will facilitate the improved engineering of various interfaces far from equilibrium.

I will describe recent experiments using ultrafast x-ray and electron pulses as dynamical probes of the atomic-scale structural dynamics underlying how materials transform. The focus will be on three specific examples: (1) I will describe studies of the dynamic deformations associated with monolayer transition metal dichalcogenides following optical excitation, using femtosecond electron scattering approaches to resolve both the in-plane disordering dynamics and out-of-plane rippling dynamics developing on picosecond time-scales. (2) I will describe femtosecond x-ray studies of nanocrystal transformations driven by both optical excitation and by high pressure shocks, probing both solid-solid transformations and solid-liquid transformations and associated intermediate states occuring on ultrafast time-scales. (3) I will describe recent experiments probing optical and field-induced amorphous-crystalline transitions in phase-change materials, investigating the fundamental time-scales for threshold switching and crystallization processes.

Precipitation hardening is an important heat treatment technique used to increase the yield strength of most structural alloys based on Al, Mg, Ni and Ti. Understanding of the precipitation kinetics and atomic structure and microstructure of the precipitates not only establishes the structure-performance relationships but also leads to a rational design of optimal alloys for specific applications.
Despite its obvious importance, acquisition of comprehensive knowledge on the in situ evolution of precipitate structure and morphology presents major challenges due to the sub-angstrom to micrometer scale ranges involved. Recently, we have developed a methodology that combines synchrotron ultra-small-angle X-ray scattering, small angle X-ray scattering, and X-ray diffraction to enable detailed interrogation of in situ and in operando evolution of precipitates, and in a broader sense, structural transformations within a wide range of engineering materials.
We have investigated the precipitation kinetics of a number of industrially important precipitation-hardened alloys. In one example, we present an in-depth study of Al-Cu-Mg based aluminum alloy (AA2024) which is one of the most widely used alloys in the aviation industry. Our results reveal details about the simultaneous formation kinetics of the S-phase precipitates and dissolution kinetics of Guinier-Preston-Bagariastkij (GPB) zones in AA2024, including the kinetic time scales and evolution of precipitate size and volume as functions of temperature. Based on these findings, we determined the kinetic energies related to the dissolution of GPB zones and growth of S-phase precipitates. These results are further validated by thermodynamic modeling efforts.
Our second example addresses structure characterization challenges encountered in additive manufacturing (AM). By combining digital modeling with emerging fabrication techniques, AM has the potential to revolutionize the design and production of complex components and parts. For metal-based AM products, rapid laser melting and cooling produces nonequilibrium heterogeneous material structures and microstructures, which often require annealing to optimize their material performance characteristics. In our study, we investigated the detailed microstructure and atomic structure evolution of the δ-phase precipitates in additively manufactured Ni-based Inconel 718+ superalloys under different annealing conditions. We found the time- and temperature-dependent evolution of the nominal dimensions of the precipitates, which occurs simultaneously with a shift in the lattice parameters of the δ phase precipitates. This is indicative of stress relaxation occurring within the sample.
Fan Zhang, Lyle E. Levine, Andrew J. Allen, Carelyn E Campbell, Adam A. Creuziger, Nataliya Kazantseva, and Jan Ilavsky, "In Situ Structure Characterization of Ageing Kinetics in Aluminum Alloy 2024 Across Length Scales", to be submitted to Acta Materialia, 2015.

The fabrication of aluminum alloys involves a number of thermomechanical steps, including solute-heat treatment followed by fast cooling, i.e., quenching. It is well known that the cooling rate influences the homogeneous and heterogeneous formation of precipitates, which in turn may have a significant effect on the local mechanical properties. When producing thick Al alloy plates, the resultant precipitation size, density, and volume fraction are expected to differ across the plate because of the difference in cooling rates. This causes the presence of residual stresses, which may lead to machining distortions. To investigate the influence of precipitation on residual stresses, thermomechanical models linking solid-state transformations to the final stress distribution have to be developed. Such simulation schemes need input on size, density, and volume fraction of precipitation as function of cooling rates.
In order to follow the formation of precipitates during quenching, time- and temperature-resolved in-situ measurements are required. To this aim, a laser-based heating system, which had been designed for the TOMCAT beamline of the Swiss Light Source (SLS), was installed at the cSAXS beamline of the SLS. This allows performing thermal treatments and small-angle scattering measurements simultaneously and in real time.
In this work we report on homogeneous and heterogeneous nucleation and growth of precipitates in an Al-Zn-Mg-Cu alloy during in situ rapid cooling. Various experiments with different cooling rates were performed. Two kinds of precipitates can be observed at two different temperature ranges. In the temperature regime between 400°C and 200 °C, larger heterogeneous eta; phase precipitates form. This is most pronounced at lower cooling rates. At lower temperatures fine hardening precipitates appear with sizes in the nanometer range. The average size of the clusters at room temperature strongly depends on the cooling rate, where larger cluster sizes occur at slower cooling rates. The cluster density increases with faster cooling rates, which can be ascribed to the higher number of excess vacancies when cooling speed is increased. Interestingly, the evolution of the volume fraction of clusters during cooling is very similar for all cooling rates.
The obtained results bring new insights into homogeneous and heterogeneous nucleation and growth of precipitates, which provides valuable input for simulations that attempt to predict the formation of residual stresses in thick plates.

A longstanding problem in materials exploration has been the inability to directly image evolving structures in complex environments with high resolution across multiple length scales. While transmission electron microscopy has clearly made great strides toward this goal, hard x-rays are unique in their ability to penetrate complex environments to visualize atomic-scale structures within buried layers. Considerable progress has been made in the development of in situ X-ray techniques to understand structural evolution in real time or diverse areas, such as, catalysis, deformation, and crystal growth. However, researchers typically monitor a single position in reciprocal space for such studies, even though evolution in the scattering is expected everywhere: in effect, much of the information in reciprocal space is completely ignored. Furthermore, the scattering is laterally averaged over the coherence length of the beam such that changes in the meso/nanoscale structure during materials evolution may be impossible to observe. In this talk, we will demonstrate a novel high-energy synchrotron X-ray technique to overcome these limitations and enable the rapid capture of large volumes in reciprocal space with high spatial resolution to meet the grand challenge of gaining a transformational understanding of matter. When applied in situ to epitaxial thin films and heterostructures with heterogeneity on the mesoscale, this will allow simultaneous imaging of atomic-level and mesoscale structure in real time and in real conditions.
The new X-ray probe is capable of multiscale imaging by combining several existing but disparate capabilities: 1) rapid 3D data acquisition of reciprocal space (e.g. crystal truncation rods (CTRs) or Bragg rods) enabled by the high-energy X-rays produced at a third-generation synchrotron like Advanced Photon Source; 2) state-of-the-art focusing optics optimized for high-energy X-rays; 3) Fourier phase retrieval atomic mapping of epitaxial systems. Along the surface normal direction, it can render electron density mapping with sub-Ångstrom resolution, as well as resolving submicron-scale features along lateral directions. By virtue of its ability to access this information in real time and in real environments, this high-energy X-ray probe will be a new science enabler, allowing for the study of novel interfacial phenomena and functionalities that would be otherwise inaccessible by existing techniques. Such individual measurements are the crux to the development of advanced interfacial materials with improved information manipulation and energy performance. The future opportunities such as integrating this rapid X-ray mapping probe with thin film growth system, ultrafast pump-probe aperatus, and predictive computational modeling will also be discussed.

Directed nanolithographic patterning from liquid phase precursors enables the fabrication of nano-scaled structures with tailored chemistries and functionalities. A custom-built electron-beam nanopositioning and scan generator system has been developed to precisely control the position, dwell time, velocity, and trajectory of the focused electron beam in an aberration-corrected scanning transmission electron microscope (STEM). A precursor liquid-phase solution is encapsulated between two electron transparent silicon nitride membranes in an in situ liquid-cell platform, and the scan control system is used to position the electron beam to controllably deposit metallic Pd from an aqueous solution of H₂PdCl₄. A critical electron dose for Pd reduction was determined and the influence of electron dose on the radiolytic deposition of Pd metal was quantitatively explored. The nanolithography patterning capabilities of this system are further demonstrated by fabricating arbitrary shaped nanostructures directly from the growth solutions. The concept of a feedback-control system that provides real-time monitoring and automated adjustment of deposition parameters to actively control feature size of the nanolithographically patterned structures will be discussed. This approach enables fundamental electron beam interaction studies and opens a new pathway for direct-write nanolithography from liquid phase solutions.
Acknowledgements. Research supported by Oak Ridge National Laboratory&’s Center for Nanophase Materials Sciences (CNMS), which is a U.S. Department of Energy, Office of Science User Facility. Research supported in part by the Division of Materials Sciences and Engineering, Office of Basic Energy Sciences, U.S. Department of Energy.

In-situ neutron and synchrotron X-ray diffraction deliver unique and complementary insight into the microstructural evolution of metals at high temperature. Neutrons illuminate a larger bulk volume and reveal quantitative phase abundance, bulk texture, lattice parameter changes and other ensemble averaged quantities. Applications are presented on phase transformation and the defect kinetics in metals at high temperature. In contrast, fine-bundled high-energy X-rays deliver reflections from a number of individual grains. For each constituting phase, their statistics and behavior in time reveal information about grain growth or refinement, subgrain formation, static and dynamic recovery and recrystallization, slip systems, twinning, etc. The concept of the Materials Oscilloscope has been developed, where multi-dimensional diffraction patterns are streaked in time, distinguishing such physical processes in a variety of metallic systems, undergoing room- and high temperature plastic deformation, in co-existing phases and across phase changes.

Core-shell structures, such as noble-metal (Ag, Au, Pd, Pt) particles in a carbon sphere, Pt@CoO yolk/shell nanoparticles, Pt@mSiO₂, and Au nanoparticles in hollow ZrO₂ and hollow SiO₂ spheres, comprise a broad class of nano-engineered catalysts. Another recent example, consisting of modular palladium-ceria core-shell subunits, assembled in solution from discrete 2 nm crystallites of Pd and CeO₂, then supported on silicon-functionalized alumina, shows exceptional activity for methane combustion, and it has thus attracted widespread interest from the catalysis community. In an attempt to better understand the connection between structure and activity of this catalyst, we have performed a detailed electron microscopy study of supported Pd@CeO₂, including planar forms of the catalyst, using state-of-the-art ex-situ and in-situ transmission electron microscopy (TEM) with sub-angstrom resolution. Our results reveal that a wholly unexpected transformation occurs upon air calcination at temperatures between 500 and 800 °C, leading to the formation of a new structure comprised of an intimate mixture of palladium, cerium, silicon, and oxygen, with extremely high dispersion. Based on the newly found structure, we propose an alternative explanation for the exceptional catalytic properties that have been observed.

When polycrystals are dispersed in the matrix, such as a solution or vapor, 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. As the entire microstructure of polycrystalline materials consists of both growing and shrinking crystals, scrutiny of shrinking (or evaporating) characteristics is essential for a complete understanding of the kinetic evolution of microstructure. Recent advances in TEM enable atomic-scale imaging for direct visualization of lattice defects, phase transition, and structural evolution. In particular, a variety of techniques have been utilized for real-time observations in TEM, providing unexpected and new experimental findings in LiFePO₄ (S.-Y. Chung et al., Nature Phys.5, 68 (2009); Nano Lett.12, 3068 (2012); J. Am. Chem. Soc.135, 7811 (2013)). By capturing real-time in situ high-resolution electron micrographs at high temperatures, in this presentation we demonstrate the evaporation behavior of LiFePO₄ crystals embedded in a solid crystalline matrix, instead of crystals in a vapor, during recrystallization. Low-energy grain boundaries between an embedded nanocrystal and a matrix are clearly observed transitioning into comparatively high-energy surfaces before substantial evaporation begins (S.-Y. Chung et al., ACSNano.9, 327 (2015)), creating unavoidable free energy instability at the early stage of evaporation. Additionally, post-transition evaporation behavior is discussed in terms of the local strain field distribution inside the crystal and the anisotropic grain-boundary energy. This study suggests that the initial energy instability induced by the boundary transition strongly influences the overall evaporation rate of crystals that are geometrically confined by a solid phase.

Synthesis of metallic or bimetallic (BM) nanoparticles (NPs) with a desired shape is of importance to nanoscience and nanotechnology and can be controlled by regulating the nucleation and growth of the solution-derived NPs. The real-time in situ STEM liquid cell imaging is an important technique uniquely suitable for investigation of the nucleation and growth phenomena in NP systems.^{1, 2} It is worth noting that the majority of the reported in situ STEM studies aimed at the nucleation and growth of NPs, utilized the electron beam as the reducing agent, which is different from the chemical reducing agents, such as sodium borohydride or ascorbic acid (AA), used in many synthesis. This difference makes it hard to directly compare the reactions observed in the course of in situ liquid cell experiments with the solution-based synthesis carried out ex situ. In this report, we present the ex situ and in situ investigation in shape modification of Au octahedral NPs to Au-Pd core-shell nanocubes, followed by their transformation to nanostars, and finally to multilayered Au-Pd-Au core-shell hexagonal platelets in the presence of T30 DNA. The entire study was carried out using FEI Tecnai G² F20 STEM operated at 200 kV, using the HAADF-STEM imaging mode. The in situ experiments were carried out using low electron dose, to minimize the effect of electron beam on the reaction.
The ex situ investigations showed the nanocubes were formed from Au octahedral NPs with fast growth of Pd along <111> directions than along <100> direction, in a good agreement with the previous reports. The clear changes in the shape from nanocubes to nanostars and finally to hexagonal platelates were observed. The in situ STEM study were carried out using a Continuous Flow Fluid Cell holder platform with the AuPd core-shell nanocubes incubated with DNA sealed between the two 50 nm-thick electron-transparent silicon nitride (SiN) membranes. The Au precursors and reducing agent (AA) were flown into the system using the syringe pump and the changes in nanostructures were recorded using STEM at low electron dose conditions. The results from in situ and ex situ are compared. Reproducing the native reaction environment during imaging will direct the investigation towards the more realistic and accurate information, free of the artifacts associated with undesired reduction of precursor induced by the electron beam.
References
1. K.L. Jungjohann et al., Nano Letters13, 2964 (2013).
2. H.-G. Liao et al., Science336, 1011 (2012).
3. T.P. acknowledges support from the Department of Energy Office of Science Early Career Research Award, Biomolecular Materials Program. This work was supported by the U.S. Department of Energy, Office of Basic Energy Science, Division of Materials Sciences and Engineering. The research was performed at the Ames Laboratory, which is operated for the U.S. Department of Energy by Iowa State University under Contract No. DE-AC02-07CH11358.

Mediating electrochemical deposition with under potentially deposited (UPD) monolayers of another elemental metal provides a controllable means of affecting the growth mechanism and microstructure of the deposited film. The technique has been previously demonstrated for silver deposition on a single crystal gold substrate. [1,2]
In this study, we extend the process to UPD electrodeposition of silver on polycrystalline gold and perform in-situ characterization of stress evolution in the growing films by curvature measurements. We report the effects of mediation on the stress evolution in the electrodeposited Ag films and show that UPD deposition can significantly alter the intrinsic stresses in deposited films. We also report the effects of interrupted deposition on the stress evolution. Atomic force microscopy images of the films are also presented to show the effects of UPD on the microstructures of the deposited films. Based on experimental results, we discuss how this deposition technique might be applied to other film/substrate systems as a means to tailor intrinsic stresses and microstructures of electrodeposited films.
1. K. Sieradzki, S.R. Brankovic, and N. Dimitrov, Electrochemical Defect-Mediated Thin-Film Growth, Science, Vol. 284, pp. 138-141 (1999).
2. S.R. Brankovic, N. Dimitrov, K. Sieradzki, Surfactant Mediated Electrochemical Deposition of Ag on Au(111), J. Electrochem. Soc., Vol. 2, pp. 443-445 (1999).

While the growth of pits in passive metals exposed to chloride solutions is reasonably well understood and has been attributed to changes in chemistry in occluded cavities in the metal surfaces, the initiation of pits is still a matter of some conjecture. In particular, the processes associated with the propagation of stable pits, versus pits that form and apparently re-passivate, are not well understood. At potentials active to the pitting potential, where pitting is not a stable process, pitting and re-passivation events have been observed as electrochemical noise, i.e. current transients¹. The goal of this work is to investigate the mechanisms of pit initiation by observation in situ to the TEM. A major challenge in observing the microstructural effects in pit initiation by electron microscopy in the past has been that there are structural and chemical changes between the hydrated passive film on aluminum, in situ to the corrosive medium, and the film after exposure to air during transfer to the electron microscope. The use of a microfluidic TEM holder allows us to observe the microstructure of an oxide film in its hydrated state and the microstructural detail of the metal from which the film is formed, with the intent of directly correlating local microstructure to stable pit initiation. A three-electrode thin film cell for in situ electrochemical polarization, in conjunction with a commercial TEM liquid cell, was developed as a part of this program. Pits were observed to initiate under potentiostatic polarization within the thin film cell. Polarization curves developed in the cell show good agreement with those observed under conventional electrochemical experimental conditions and show evidence of metastable pitting. Results obtained in this study have shown that the pit initiation process is a function of the chloride concentration of the environment, in contrast to the work of McCafferty². At chloride concentrations less than 0.001M the relationship between chloride concentration and pit susceptibility takes on a different slope, suggesting a different interaction between chloride and the oxide film. Angle-resolved XPS experiments show that chloride is not incorporated into the oxide near the surface of the oxide for higher concentrations. We hope to be able to provide significant insights into the parameters associated with localized corrosion for improved control over degradation of pitting-susceptible materials.
This work was supported by the National Science Foundation, grant number DMR-1309509.
1. Gupta, R. K., et al. (2012). Metastable pitting characteristics of aluminium alloys measured using current transients during potentiostatic polarisation. Electrochemica Acta. 245-254.
2. McCafferty, E. (2003). Sequence of steps in the pitting of aluminum by chloride ions. Corrosion Science, 1421-1438.

The use of select rare earth orthophosphates (REPO₄) as experimental oxide fiber coatings has proven their ability to enhance strength, toughness, and creep resistance in ceramic matrix composites. Ex situ TEM of the fiber coating following fiber push-out has provided evidence that xenotime REPO₄ compositions located close to the xenotime-monazite phase boundary undergo phase transformation as a result of the deformation due to sliding. We have synthesized a range of REPO₄ powders with similar compositions and report their behavior under high-pressure conditions in a diamond anvil cell. In situ Raman spectroscopy is performed concurrently to monitor the behavior of the materials under hydrostatic pressure, revealing information about pressure-induced phase transformation from the xenotime to monazite phase and its reversibility when pressure is released. These efforts represent the first steps in establishing the kinetics of the pressure-induced phase transformation in this system and contribute to a greater understanding of the factors that control phase transformation.

Liquid Cell Transmission Electron Microscopy (LCTEM) can provide direct observations of solution phase nanoscale materials, and holds great promise as a tool for monitoring dynamic self-assembled nanomaterials. Control over particle behavior within the liquid cell, and under electron beam irradiation, is of paramount importance for this technique to contribute to our understanding of chemistry and materials science at the nanoscale. However, this type of control has not been demonstrated for complex, organic macromolecular materials, which form the basis for all biological systems, all of polymer science, and encompass important classes of advanced porous materials. Here we show that by controlling the liquid cell membrane surface chemistry and electron beam conditions, the dynamics and growth of metal-organic frameworks (MOFs) can be observed. Our results demonstrate that hybrid organic/inorganic beam sensitive materials can be analyzed with LCTEM and at least in the case of ZIF-8 dynamics, the results correlate with observations from bulk growth or other standard synthetic conditions. Furthermore, we show that LCTEM can be used to better understand how changes to synthetic conditions result in changes to particle size. We anticipate that direct, nanoscale imaging by LCTEM of MOF nucleation and growth mechanisms, may provide insight into controlled MOF crystal morphology, domain composition, and processes influencing defect formation.

Material performance in extreme radiation environments is central to the design of future nuclear reactors. Radiation induces significant damage in form of dislocation loops and voids in irradiated materials and continuous radiation often leads to void growth and subsequent void swelling in metals with low stacking fault energy. Here we show that by using in situ heavy ion irradiation in a transmission electron microscope, pre-introduced nanovoids in nanotwinned Cu efficiently absorb radiation-induced defects accompanied by gradual elimination of nanovoids, enhancing radiation tolerance of Cu. In situ studies and atomistic simulations reveal that such remarkable self-healing capability stems from high density of coherent and incoherent twin boundaries that rapidly capture and transport point defects and dislocation loops to nanovoids, which act as storage bins for interstitial loops. This study describes a counterintuitive yet significant concept: deliberate introduction of nanovoids in conjunction with nanotwins enables unprecedented damage tolerance in metallic materials. This work is funded by NSF-DMR-Metallic Materials and Nanostructures Program under grant no. 1304101

In situ transmission electron microscopy (TEM) through liquids is a promising approach for exploring fuel cell processes in alkaline conditions as they occur on the nanometer scale. While there is an extensive database on characterization and degradation analysis of PEM fuel cell components, very little has been done on alkaline fuel cells (AFCs) systems. One of the major challenges in AFCs conditions is the formation of carbonate crystallites. Carbonation occurs when trace amounts of CO₂ in the reactant feed streams is converted into CO₃^2-. Over time, CO₃^2- can accumulate, combine with free cations in solution and precipitate into a carbonate salt. The formation of CO₃^2- consumes hydroxides in the electrolyte and thus its ionic conductivity is lowered. This precipitate can coat the electrodes and the gas diffusion layers, restricting the transport of reactants, including hydroxide to the electrode surface. Here, we use TEM to examine different systems in alkaline fuel cell conditions using an electrochemical liquid cell holder to study these processes in situ. We experimentally observe the formation of sodium carbonate upon methanol oxidation in alkaline media near the platinum catalyst.

Ultrafast electron microscopy (UEM) allows for direct visualization of materials dynamics with unprecedented combined spatiotemporal resolutions. Generally, UEM instruments consist of a transmission electron microscope (TEM) that has been modified to accept optical pulses from a short-pulsed laser. Access to both the electron gun and specimen region are enabled via side-mounted optical periscopes such that stroboscopic pump-probe experiments can be performed. Currently, the most widely-used photoelectron emission source is lanthanum hexaboride (LaB₆) owing to its relatively low work function, and the electron gun configuration typically employed is a Wehnelt triode assembly, the same type used in thermionic TEMs. Here, we discuss the significant differences between photoelectric and thermionic emission from a LaB₆-based electron gun, especially as related to the lensing effect of the Wehnelt aperture which controls the position of the beam crossover and ultimately the collection efficiency of the instrument. Further, we show via systematic experiments (informed by simulations) how precise configuration of the electron gun - that is, the LaB₆ source and aperture size - greatly affects UEM beam current and ultimately the materials dynamics that can be imaged. Our results indicate there are optimum settings for both the single-electron and single-shot regimes for the unbiased (i.e., cold LaB₆) Wehnelt assembly that result in unity collection efficiency. We also discuss commensurate effects on the energy and temporal distributions and the result of varying laser-pulse durations on these parameters.

Zirconium based alloy is widely used as fuel cladding materials and some other structural materials in water-cooled reactors. However, degradation of zirconium alloy by waterside corrosion in harsh conditions severely limits the burnup and thus cycle life of nuclear fuels. Extensive researches have been done to understand this problem; however, several key aspects of knowledge related to the corrosion mechanisms of zirconium alloy still remain unclear. So far, most microstrutural analysis of corrosion behaviors of zirconium alloy is performed ex-situ, making it difficult to know what is taking place during corrosion.
We performed in-situ environmental transmission electron microscope (E-TEM) study of zircaloy-4 corrosion in gas environments at ~500#730;C. This enables direct observation of the microstructure evolution during reaction, with a very high resolution (~0.8 Angstrom). The preliminary analysis of the results has shown that porous oxide was formed during corrosion, and there were preferable sites for crack nucleation and propagation. Our study may help discover new corrosion mechanisms of zirconium alloy, and thus provide insights on prediction and prevention of zirconium alloy corrosion in nuclear reactors.

Identification and control of the chemical ordering in multi-component crystalline systems have been critical issues in solid-state science. Many compounds of alloy and oxide system represent different physical properties depending on the existence of the chemical ordering [1-2]. The Li(Mn_1.5Ni_0.5)O₄, one of these compounds, shows different electrochemical properties in accordance with chemical ordering. The Li(Mn_1.5Ni_0.5)O₄ is crystallized in a AB₂O₄-type spinel where Ni and Mn ions are both located in octahedral B sites. It shows a phase transition from cation disordered state (Fdm) to ordered state (P4₃32) when it post annealed at 700. Each of the phases has been actively studied with regard to their crystal structures and physical properties.
In this study, the transient state model during chemical ordering was demonstrated in Li(Mn_1.5Ni_0.5)O₄. We synthesized Li(Mn_1.5Ni_0.5)O₄via a solid state reaction and quenched at high temperature. In order to create a transient state during phase transition, we obtained atomic-scale images using high resolution electron microscopy (HREM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF STEM). In addition, we conducted micro-scale investigations through in situ X-ray diffraction (XRD) consistent with ab initio calculations. Consequently, we critically reveals that the chemical ordering transition occurs through the formation of Frenkel-type defects as entail the displacement of Mn and Ni from their normal B sites on to vacant octahedral interstitials in the lattice. We also clarified the key role of point defects in chemical ordering transition [3].
Reference
[1] S. -Y. Chung, S. -Y. Choi, T. Yamamoto, Y. Ikuhara, Phys. Rev. Lett.100, 125502 (2008).
[2] S. -Y. Chung, S. -Y. Choi, T. -H. Kim, S. Lee, ACS nano9, 850-859 (2015).
[3] H. Ryoo, H. B. Bae, Y. -M. Kim, J. -G. Kim, S. Lee, S. -Y. Chung, Angew. Chem. Int. Ed. 54, 1-6 (2015).

Photoelectron spectroscopy (PES) is perhaps the most direct probe of electronic structure available to the physical scientist, as well as an invaluable tool for elucidating bulk and surface chemical composition. It is commonplace to use PES for the characterization of samples held in high or ultra-high vacuum (HV, UHV), yet what is gained in understanding the fundamental surface physics of a material, is lost when this knowledge needs to be transferred to the material operating in real-world conditions. This so-called “pressure-gap” has been the focus of intense technological development over the last 40 years, culminating in the latest generation of high-pressure photoelectron spectroscopy (HiPPES) instruments [1]. Recently a state-of-the-art laboratory-based high-pressure photoelectron spectroscopy (HiPPES) system housed in the Department of Materials, Imperial College London has been developed and commissioned. The system allows key in-situ and in-operando XPS analysis of the surfaces of materials in a wide range of technologically relevant areas including energy, catalysis, electronic materials and biomaterials.
The system is equipped with state of the art monochromatic X-ray and ultraviolet light sources and a R4000 HiPP-2 analyser. This dual capability instrument can operate at pressures from UHV (10^-10 mbar) up to 30 mbar using a variety (and controllable mixtures) of gases (air, N₂, O₂, H₂, H₂O, CO₂, etc) and over a wide temperature range (110 K to over 1100 K). This is achieved using a two-piece titanium reaction-cell in-built with the cone and aperture necessary for HiPPES measurements. The high-pressure retractable reaction-cell is designed to provide flexibility between near-ambient pressure and UHV conditions. A specially designed “BioCell” has been developed for the study of biomaterial surfaces, and enables the transfer and measurement of vacuum sensitive materials without ever exposing the surfaces to vacuum conditions.
We will present benchmarking data highlighting the exceptional capability of the instrument including (i) stability of the gas pressure in the reaction cell during annealing and (ii) the transmission of the analyser at high pressure using the newly developed “swift-mode” [2]. The measurement of a number of different material systems will be highlighted, including the behaviour of oxygen deficient metal oxide PbO₂, the surface chemistry of CO₂ on reduced Cu₂O surfaces and the protonation level of PANI under physiological conditions measured using the BioCell.
[1] S.K. Eriksson, (...), D.J. Payne, Rev. Sci. Instrum.85 075119 (2014).
[2] M.O.M. Edwards, (...), D. J. Payne, J. Åhlund, Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 785 191 (2015).

Hydrothermal synthesis is an excellent route to the fabrication of oxide nanostructures including nanoparticles and hierarchical structures.^{1, 2} This synthesis is performed in an autoclave at high pressure and elevated temperature. Knowledge about the nucleation and growth mechanisms under these hydrothermal conditions is in most cases unknown but is detrimental for the development of new synthesis routes not based on a trial and error approach. Hence in situ studies of the nucleation and growth mechanisms during the synthesis are important to reveal this information. We are studying the hydrothermal synthesis of nanostructures of potassium niobate- and sodium niobate-based materials. Materials in the potassium sodium niobate system have good piezoelectric properties and are alternative lead-free materials to Pb[Zr_xTi_1-x]O₃ (0le;xle;1)(PZT). Both end members of potassium sodium niobate, KNbO₃ and NaNbO_3, have the orthorhombic perovskite structure at ambient temperature, but KNbO₃ becomes tetragonal and then cubic at 225 °C and 418 °C. ³ Similar transitions for NaNbO₃ occur at 575 and 614 °C. Here we present X-ray diffraction data from the in situ investigation of hydrothermal synthesis of KNbO₃ and NaNbO₃ nanoparticles. The measurements were performed at MAX II in Lund, Sweden using a reaction cell involving a sapphire capillary to contain the reaction medium.⁴ After heating was initiated the Nb₂O₅ precursor dissolved and after a short time tetragonal KNbO₃ nanoparticles were formed at 250 bars and temperatures ranging from 250 to 400 °C. The c/a ratio of KNbO₃ decreased with increasing temperature and increased with time at a given temperature showing the finite size effect. At the same pressure, orthorhombic NaNbO₃ nanoparticles were formed at temperatures between 225 °C and 325 °C after going through several phases. The Nb₂O₅ precursor dissolved in the highly alkaline solution at ambient conditions and formed HNa₇Nb₆O₁₉(H₂O)₁₅. After reaching hydrothermal conditions the layered structure Na₂Nb₂O₆middot;H₂O was formed before the final orthorhombic NaNbO₃ was formed.
References
[1] M.-A. Einarsrud and T. Grande, Chem. Soc. Rev.43, 2187 (2014).
[2] P. M. Roslash;rvik, T. Grande, and M.-A. Einarsrud, Adv. Mater.23, 4007 (2011).
[3] A. M. Glazer and H. D. Megaw, Acta. Cryst.A 29, 489 (1973).
[4] M. Bremholm, H. Jensen, S. B. Iversen, and B. B. Iversen, J. Supercrit. Fluids44, 385 (2008).

Multilayer foils comprising nanoscale layers formed from pairs of elemental metals with negative heats of mixing can sustain rapid self-sustaining reactions in which high temperatures (>1800 °C) can be attained in a millisecond or less. Typically the intermetallic formation reaction reaches completion in approximately one second, but in some applications it is desirable to extend the time at temperature. One way to do this is to make the multilayer of elements that will combust with atmospheric oxygen and nitrogen. The oxidation and nitridation reactions begin after intermetallic phases have formed and the sample reaches elevated temperatures. We seek to characterize this complex set of reactions involving interdiffusion of the metallic multilayer, possible melting of one or both elemental metals, competitive nucleation and growth of two or more intermetallic phases, and growth of oxide and nitride layers using high-speed in situ synchrotron x-ray diffraction.
We have studied the formation reactions and combustion in Al/Zr reactive multilayers using high-speed in situ synchrotron x-ray diffraction. Using a mixed-mode pixel array detector (MMPAD) framing at 1 kHz we observe the evolution of peaks from the elemental metal parent phases to track interdiffusion during uniform Joule heating prior to ignition of the self-sustaining reaction. Over longer times we track the progress of the intermetallic formation and combustion reactions with a large-format amorphous silicon detector framing at 30 Hz. During the combustion reaction the primary product (orthorhombic zirconium dioxide) grows linearly with time, indicative of interface-limited growth. The maximum temperature is reached shortly before growth of this phase ends. We see no evidence for the formation of crystalline nitride phases, which have been observed in ex situ studies and which are hypothesized to contribute to the total heat released in the reaction. During cooling we observe formation of new intermetallic and oxide phases. Combining these in situ observations with ex situ TEM observations of the reacted materials, we describe the progress of the reaction in terms of competitive growth of the surface oxide and the two primary intermetallic phases.#8203;

Hafnia (HfO₂) is a wide-band gap and high dielectric constant material that is thermally stable on silicon, and is already finding extensive use in highly scaled device components. The high temperature tetragonal phase of hafnia - occurring in bulk at 1720°C - has a larger band gap and higher permittivity than the room temperature monoclinic phase, making the tetragonal phase more desirable for device implementation. In its bulk form, however, the tetragonal phase has yet to be stabilized at room temperature. Scaling solids to finite, nanoscale dimensions can dramatically alter phase stabilities, allowing for room temperature stabilization of high temperature bulk phases. This is seen in ZrO₂, an isomorph of HfO₂; below the critical size of 15-30 nm the tetragonal phase of ZrO₂ can be stabilized with respect to the monoclinic phase. It is estimated, however, that the critical size of stabilization of the tetragonal phase of HfO₂ is sub-10 nm, and it is therefore much more difficult to achieve. Because the tetragonal phase of hafnia is more important for technological applications than the monoclinic phase, finding a way to stabilize the tetragonal phase of HfO₂ at low temperatures is paramount. In this research, we utilize in situ heating to observe the phase transformations of a single hafnia nanorod on an atomic scale to elucidate factors crucial to stabilizing a low temperature, tetragonal phase of hafnia.
High aspect ratio, monoclinic HfO₂ nanorods are grown via a nonhydrolytic sol-gel synthesis with tri-n-octylphosphine oxide (TOPO) as the coordinating solvent and passivating ligand. When heated in situ in a scanning transmission electron microscope (STEM) we observe a unique phase transformation, with evolution from the monoclinic phase to the tetragonal as well as the emergence of a defect-nucleated cubic phase. Upon slow cooling we see complete transformation of the nanorod to the hafnia cubic phase and ultimately reduction to hafnium metal. This later transformation is likely due to the low oxygen, high vacuum environment of the STEM column. The cubic phase occurs in bulk at 2700°C and under oxygen-rich conditions, and was therefore unexpected. Using these in situ techniques, we are able to study these hafnia transformation mechanisms in real time, and with single-atom resolution, providing fundamental insight into the atomic pathways of classical Martensitic processes. This is the first step towards stabilizing tetragonal HfO₂ nanocrystals under atmospheric conditions through control of defect dynamics.

One of the main limiting factors in using zinc for large scale electrochemical energy storage devices are the morphological inconsistencies in the electroplating and dissolution of zinc during the charge/discharge process. This leads to degradation of the electrodes, the growth of zinc dendrites, and eventual failure of the system. In a recent publication^[1], a novel method of Electrochemicalshy;-Acoustic Time-shy;ofshy;-Flight (EAToF) analysis has demonstrated the ability to use acoustic waves to determine physical changes in a battery by taking advantage of the inherent changes in density distribution during cycling in traditional battery geometries. This not only serves as a novel method for non-destructive, in operando characterization of the physical processes in the battery, but also a good indicator of its state of health.
This study presents a simple bottom-up EAToF analysis of zinc electroplating on a brass electrode. We demonstrate the use the EAToF technique to analyze density shifts and thickness variations in the electrode indicative of zinc formation along the surface of the electrode in a battery. We discuss how differences in the movement of sound through the electrode during the plating process correlate to the evolution of zinc during the charge/discharge process in a flooded system. We also discuss the differences in the EAToF analyses for different morphologies of zinc that form under varying operating conditions. Differences in the acoustic fingerprints can be used to characterize the morphology of electroplated zinc, which provides direct determination of the state of health of a zinc -based electrochemical system.
Finally, we provide an example of EAToF used as a part of a control loop to control the structure of zinc during electrodeposition by choosing operating conditions based on observed EAToF profiles.
References:
[1] A. Hsieh et al., Energy Environ. Sci. (2015) 8, 1569

Engineering nanocrystalline structures into refractory metals has gained significant attention in recent years as a pathway to improving strength and radiation tolerance for next-generation nuclear reactor materials. At the forefront of characterizing nanostructured materials are in situ techniques, which enable precise probing of structure and phase stability at the nanoscale. In this study, in situ transmission electron microscopy (TEM) was used to characterize phase stability and microstructural evolution during the heat treatment of nanocrystalline and amorphous tantalum films. Nanocrystalline tantalum samples were prepared by pulsed laser deposition (PLD) with a nominal thickness of 100 nm to provide electron-transparent films for in situ TEM imaging during heat treatment. The as-deposited films exhibited a mean grain size of approximately 10 nm, and selected-area diffraction (SAD) analysis confirmed the presence of the BCC α-tantalum phase. These films remained nanocrystalline with no discernible change in grain size upon heating to 1000°C. What&’s more, increasing the temperature to 1200°C, which represents 40% of the melting point of BCC tantalum, produced only a modest increase in the grain size to about 30 nm. This exceptional thermal stability was attributed to oxygen stabilization of the nanograins as confirmed by electron energy loss spectroscopy (EELS). Additional films were deposited to a thickness of 20 nm while varying the PLD chamber pressure to tailor the degree of oxygen stabilization; however, bright field imaging and SAD analysis indicated these films were amorphous. In situ heat treatments at temperatures over the range of 800 - 1200°C were employed to crystallize the amorphous Ta films for a study of structural evolution through devitrification. Quantitative image analysis of the in situ SAD patterns revealed a complex multi-phase nanostructure following devitrification that contained metallic α- and β-tantalum nanocrystalline grains as well as a series of metastable oxide precipitates. These nanoscale grains and precipitates exhibited limited growth following ex situ TEM analysis of films subjected to isothermal anneals for up to 100 hours. Complementing the in situ analysis with focused ex situ studies thus demonstrated the utility of complex multi-phase structures for stabilizing nanocrystalline grains in refractory metal alloys.

Chemical bath deposition (CBD) of semiconductor materials is an excellent way to reduce the cost of manufacturing solar cells. An understanding of the CBD deposition technique, especially during early stages of deposition can lead to better control of morphology and eventually, photovoltaic properties. Here we have used localized surface Plasmon resonance (LSPR) spectroscopy to monitor the in situ kinetics of early stage growth of cadmium sulfide (CdS) thin films on Ag nanoparticle(NP) on quartz substrates. Real-time shift during CdS deposition showed that the LSPR wavelength red-shifted rapidly due to random deposition of CdS on the substrate but saturated at longer times. LSPR modeling showed that these features could be interpreted as an initial deposition of CdS islands followed by preferential deposition of CdS onto itself. The CdS also showed significantly enhanced Raman signals up to 170 times due to surface-enhanced Raman scattering (SERS) from the CdS/Ag NP regions, indicating that our Ag NP on quartz have potential application as SERS substrates. The ex situ SERS effect supported the behavior of the LSPR shift, suggesting that these techniques could be used to understand nucleation and growth phenomena from the liquid phase.
This work was supported by TN-SCORE Grant NSF-EPS-1004083, while A. Malasi was supported by grant ARMY W911NF-13-1-0428. J.N. and R.E.R. acknowledge support from the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UTBattelle, LLC, for the U.S. Department of Energy. R.K. and H.T. also acknowledge CNMS2013-284 at the Center for
Nanophase Materials Science, which is sponsored at ORNL by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy for SEM characterization.

A DC arc discharge with a consumed graphite, anode electrode is commonly used for synthesis of carbon nanoparticles, including graphene and carbon nanotubes (CNTs) [1-3]. The graphite electrode is physically vaporized by high currents (20-60 A), leading to nanoparticle synthesis in a background low temperature (0.1 - 1 eV), atmospheric pressure plasma. Utilizing atmospheric pressure plasmas has resulted in the synthesis of higher quality nanomaterials [4]. However, the formation of nanoparticles in arc discharge plasmas - for example, where in the arc discharge nanoparticles nucleate and grow - is poorly understood.
A laser-induced incandescence (LII) diagnostic is currently being constructed to study the physics behind nanoparticle synthesis in a background plasma. The LII diagnostic involves heating the particles with a short-pulsed laser, and measuring the resulting spatial and temporal incandescence profiles on longer timescales [5]. By appropriately interpreting the induced spatiotemporal incandescence profiles, one can measure particle sizes and spatially-resolved volume fraction in situ. LII diagnostics have been extensively used to study soot particles in various backgrounds, including laboratory flames and diesel engines. However, LII has only recently been applied to study engineered nanoparticles, and has never been applied in a strongly coupled plasma background, such as a carbon arc discharge. Therefore, great care is interpreting results from an LII diagnostic applied to monitor nanoparticle synthesis in a background, atmospheric pressure plasma. Preliminary results of this study will be discussed.
1. C. Journet et al. Nature388, 756-8 (1997);
2. A. J. Fetterman et al. Carbon46 1322-6 (2008);
3. M. Keidar et al. Phys. Plasmas17, 057101 (2010);
4. M. Sankaran. Plasma Processing of Nanomaterials, Boca Raton: CRC Press, 2011.
5. C. Schultz et al. Appl. Phys B83, 333-54 (2006);

To date, electromigration and its origins have been widely studied due to its substantial impact on the semiconductor device industry. Much of the work that has previously been conducted focuses on the statistical analysis of interconnect reliability, to fit Black&’s mean time to failure MTF equation.¹ Despite an extensive literature also on microstructural origins of electromigration-induced failure, open questions remain. We use in-situ TEM to extend understanding of these microstructural phenomena. We use a Gatan TEM heating holder with multiple electrical feed-throughs to pass a current through metal lines patterned over electron transparent silicon nitride windows. The patterned structures can be chemically and physically tailored by standard lithographic processing techniques, and subsequent to fabrication by localized focused ion beam (FIB) modification using a wide range of incident ion species available through our mass-selecting FIB instrumentation. This allows for deterministic control of electromigration pathways through the conductor.
The results of preliminary finite element model calculations show that the temperature rise due to Joule heating in the samples is less than 10 K for current densities up to 10⁵ A/cm² (and silicon nitride membrane thicknesses of 200 nm), allowing direct control over the temperature of the sample by external heating. Thus it is possible to access a wide range of both current and temperature, over several orders of magnitude in current density and from ambient temperatures to many hundred degrees C.
Our initial studies to date have been on Titanium. The electromigration response of this material has been far less studied than that of Aluminum and Copper, the two classic interconnect materials in IC circuits. It has a different crystal structure (hcp vs fcc for Al, Cu). It has a higher resistivity which tends to promote electromigration failure at lower current densities², allowing for easier study in-situ to the TEM, and it has a high melting temperature[RH1] , mitigating the effect on electromigration of unintentional temperature increases due to Joule heating. We will present our initial observations on grain size evolution and in-situ electromigration failure in Ti (for example extensive voiding at grain boundaries observed at a current density of 2.5 x 10⁵ A cm^-2) observed at the nanoscale as well as our continuing work in controlling and observing electromigration failure. In conclusion, we will demonstrate the viability of this technique for acquiring real time information about nanoscale electromigration failure mechanisms.
This work was supported by the NYSTAR Focus Center at RPI, C100117.
¹Black, J.r. "Electromigration; A Brief Survey and Some Recent Results." IEEE Trans. Electron Devices IEEE Transactions on Electron Devices 16.4 (1969): 338-47.
²Ho, P. S., and T. Kwok. "Electromigration in Metals." Rep. Prog. Phys. Reports on Progress in Physics 52.3 (1989): 301-48.

Phase transitions in reactive environments are crucially important in energy and information storage, catalysis, and sensors. However, establishing the causal link between structure and function is challenging for nanoparticles as ensemble measurements convolve intrinsic single particle properties with sample size and shape diversity. Here we study the hydriding phase transformation in individual palladium nanocubes under operando conditions using coherent X-ray diffractive imaging. We directly observe two-phase coexistence in the single particle diffraction data. The phase transformation initiates as an incoherent precipitate at a cube corner and then further penetrates further into the particle. The strain distributions of the α and β phases are markedly different, indicating elastic, concentration, and surface effects all play a role. A phase field model is constructed to interpret the phase transformation. Our results provide a general framework for understanding phase transformations in individual nanocrystals under operating conditions in reactive environments while highlighting the utility and importance of single particle investigations to understand important systems.

An ultrahigh vacuum (UHV) surface diffractometer system equipped with molecular beam epitaxy (MBE) capabilities has been in use at the 33-ID of the Advanced Photon Source. The system has been upgraded for oxide MBE. The upgrade provides in-situ x-ray diffraction capability with synchrotron radiation for a wide range of oxide materials synthesis in addition to investigation on surfaces/interfaces structures in UHV. The in-situ synchrotron x-ray scattering capability helps us to expand the knowledge in the fundamental physics of layered oxide growth. This has been demonstrated in our study of dynamic rearrangement of oxide layers, which leads to structures that are highly unexpected based on the layer sequencing. This rearrangement can occur in many layered oxide systems and suggest a general approach that may be essential for the construction of metastable Ruddlesden-Popper phases.

Growth and transformation of colloidal nanoparticles are important for synthesizing functional nanoparticles with tailored properties that represent the foundation for enabling nanotechnology. However, the involving chemical and physical processes are very complicated and barely understood, which limits the precise control over the properties of the nanoparticles. In this presentation, high-energy x-ray scattering techniques will be discussed to serve as unique in-situ approach to monitor these processes in real time. High-energy x-rays have strong penetration in reaction solutions, enabling the possibility to probe the solid colloidal nanoparticles with small volume fractions. In addition, the weak absorption of high-energy x-rays in materials can eliminate the possible side reactions. A couple of reaction systems, including the synthesis of silver nanocubes, have been successfully studied with the high-energy x-ray scattering at the beamline 1ID of Advanced Photon Source (APS).
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.

One of the major scientific aims over times has been gaining control of matter during its formation. For this, it is of prime importance to understand and control the local atomic order phenomena. Fundamental processes in material sciences, like nucleation and growth events, or mass transport can be successfully studied in nanoscaled materials due to their unique characteristic of possessing a large surface to volume ratio, which triggers a change on the kinetic and thermodynamic processes compared to extended solids, a more well-defined boundary conditions and a surface-controlled reactivity. The study of the dynamics of the local atomic order phenomena in nucleation or mass transport events requires an in-situ investigation in the milliseconds time scale. The combination of a continuous-flow-device (CFD) for the synthesis of NCs with cutting edge characterization techniques opens up tremendous perspectives to describe the underlying mechanisms governing the outlined processes. Here we present a highly versatile CFD, able to reach residence times down to 9 ms. It is coupled with optic flow cells and/or microfluidic X-ray cells for in-situ optical characterization and synchrotron X-ray characterization, respectively. We have studied the influence of reaction parameters (temperature, nature and ratio of capping ligands and surfactant molecules) in the nucleation and growth of CdSe NCs. By changing the ratios of capping ligands and surfactants, the nucleation and growth events can be tuned. In our experiments we have observed that higher amounts of the surfactant TOP slow down the nucleation and growth processes, in such a way that below 0.45 s of reaction time, no absorption peak has been observed. However, when the amount of surfactant is diminished, small CdSe NCs are observed with reaction times from 0.25 s. Analogous studies carried out in a typical batch synthesis lead to no differences between these two amounts of surfactants. This points towards a key role played by surfactant molecules, only in the very beginning of the reaction.

Semiconducting nanoparticles (quantum dots) have attracted an increasing scientific and industrial interest during the last decades, due to their unique and size dependent physical and chemical properties. In order to manufacture those particles in an industrial scale with a narrow size distribution and a well-defined shape, it is a major issue to understand the principals of the formation mechanisms of these materials. To get those fundamental insights into the undisturbed formation in aqueous solution, we have developed a free liquid jet setup in order to access reaction times from below 100 µs up to 10 ms. Via SAXS experiments the morphology of the early particle states are accessible while simultaneously acquired WAXS pattern give an insight into the crystalline structure. The key advantages of this setup compared to capillary based setups are the high time resolution (down to 10 µs), the negligibly small influence of radiation damage induced to the sample and the dead time of the reaction of about 100 µs, thus the formation can be investigated starting at very early states. The results of both SAXS and WAXS studies show, that CdS quantum dots precipitate in a diffusion-limited formation mechanism of primary clusters, which already form below 100 µs due to a fast diffusion of cadmium and sulfur ions in water. This also confirms a non-classical two-step nucleation pathway for CdS as it is already assumed for calcium carbonate and gold. During the entire observation period the growing particles are not jet fully crystalline which can be concluded from the missing CdS Bragg peak in the WAXS signal. Beyond that, a temperature dependent study on this formation mechanism gives access to an energy barrier for Arrhenius-like diffusion of the primary clusters in water of E_g=0.6 eV. The diffusion of the primary clusters towards the surface of the growing particles is limiting the particle growth for all temperatures.
In summary the study gives direct access via scattering techniques to the precipitation mechanism of a representative semiconducting material (CdS) at a so far unexplored time scale.

The brilliant beams of modern synchrotron sources allow to study in-situ many wet chemical processes used e.g. for the synthesis of colloidal nanocrystals NCs [1], but allow also to follow in-operando the electro-chemistry within nanostructures of working devices [2]. Colloidal supercrystals using designed NCs as building blocks offer the opportunity for realising solids with tailored properties [1].
In this study, we have investigated with in-situ synchrotron small angle x-ray scattering (SAXS) the template free self-assembly of colloidal supercrystals based on nearly monodisperse NCs [3]. Synchrotron SAXS can probe rather large sample volumes in short time steps and thus give mean particle dimensions of a large ensemble of NCs, that are complementary to the values derived by locally sensitive techniques like in-situ TEM [4].
We studied by in-situ SAXS the crystallization by diffusion of a non-solvent into the colloidal dispersion of Bi NCs [3]. The SAXS patterns of the NC ensembles were recorded below the NC-solvent/non-solvent interface at the SAXS beamline at ELETTRA (Italy). Hence, we could follow the onset of the crystallization process in short time steps as a function of the non-solvent concentration. Many sharp Bragg peaks proved the formation of well-ordered superlattice structures, but could not be related to the expected spherical shape of the Bi NCs as derived by probing individual NCs on a flat substrate by TEM [3].
Thus we developed a method to retrieve the mean particle shape of a large ensemble (about 10⁸) of slightly polydisperse NCs in 3D by advanced SAXS analysis [5]. The retrieved 3D mean shape of the BI NCs can be described by a strongly facetted oblate ellipsoid with two main axis of about 22 nm and 18 nm, related to the rhombohedral crystal structure of Bi with the short axis along the c-axis of Bi.
With this shape as an input we were able to index the measured Bragg peaks and to reveal the coexistence of two crystal structures: The lateral ordering is in both cases hexagonal, but the vertical alignment only along the short axis of the Bi NCs follows either an ABAB (hcp-like) or AAAA stacking (simple hex).
Furthermore, recording the peak positions and intensities as a function of growth time allowed to investigate the dynamics of the supercrystal formation and the change in the crystal phase fractions. Additionally, we used the derived Bi NC shape also as an input for a theoretical modelling of the super-crystallisation process based on molecular dynamic simulations [6].
[1] M. V. Kovalenko, L. Manna, A. Cabot, Z. Hens, et al., ACS Nano 9, (2015)
[2] C. Prehal, D. Weingarth, E. Perre, R.T. Lechner, et al., Energy Environ. Sci. 8, (2015)
[3] M. Yarema, M.V. Kovalenko, G. Hesser; D.V. Talapin, et al., JACS 132, (2010)
[4] Y. Liu, X.M. Lin, Y. Sun, T. Rajh, JACS 135, (2013)
[5] M. Burian, G. Fritz-Popovski, M. He, M.V. Kovalenko, O. Paris, R.T. Lechner, J. Appl. Cryst.48, (2015)
[6] M.Burian, C. Karner, R.T. Lechner, to be submitted

We have developed a graphene liquid cell for the transmission electron microscope, in which a thin specimen of liquid, ~100nm in thickness, is encapsulated by two windows of graphene. In this cell we can observe motions and dynamics of nanocrystals, DNA directed nanocrystal assemblies, and protein shells and capsids. We are able to observe the growth of colloidal nanocrystals, as well as the structure of individual nanocrystals at a high level of detail.

Liquid cell transmission electron microscopy (TEM) has attracted a lot of attention recently since it provides the unique opportunity of imaging many material processes in liquids. For instance, using liquid cell TEM we can study nanocrystal growth mechanisms at the nanometer or atomic level by real time observation, from which many unseen colloidal nanocrystal growth trajectories have been revealed. So far, there have been numerous studies on metals and alloys, whereas only limited work has been reported on oxides. In this talk, I will show our systematic study of transition metal oxide nanocrystal growth in a liquid cell under TEM. A series of binary systems, i.e., Ni-Fe, Mn-Fe, Co-Fe, Cr-Fe and Pt-Fe, were studied, in which a growth solution of Ni, Fe, Mn and/or Cr metal acetylacetonates precursors dissolved in oleylamine, oleic acid and benzyl ether was used. We found transition metal oxide particles are formed under electron beam irradiation of the precursor solution in a liquid cell where a reductive environment is assumed to prevail. The incorporation of multicomponent transition metal ions in the oxide nanostructures varies depending on the combination of metal ions. For example, the spinel nickel iron oxide structures were obtained in Ni-Fe system, in contrast iron oxide nanocrystals were achieved with manganese remaining in the solution in Mn-Fe system. Factors such as differences in the reduction potential of metal ions, thermal decomposition temperature of the precursors, thermodynamic equilibrium phases will be discussed. Such study of the nanostructure growth mechanisms shed light on the control of solution chemistry of complex oxide nanoparticle formation for advanced functions.

Currently, nanoparticles and nanocrystals remain one of the central objects of study in many experimental and theoretical fields of science. Their unique intrinsic properties enable a great number of practical applications, including semiconductor and magnetic materials, energy storage and generation, catalysis and biomedicine, but also remain of great interest for fundamental science.
Recent advances in liquid cell platforms for in situ (scanning) transmission electron microscopy (S)TEM has provided direct observations and quantitative analysis of nanocrystal nucleation and growth. However, the analysis of the data acquired by in-situ (S)TEM is a nontrivial problem. Studies performed to date are mostly limited to visualization and quantification of the individual particles or macroscopic averages of the systems of particles. However, collective dynamics and proximity effects remained insufficiently explored and extracting useful data form real space observations is still to be achieved.
Here, we developed a framework for the systematic analysis and interpretation of time-resolved (S)TEM in situ observations of platinum nanocrystal nucleation and growth from K₂PtCl₆ aqueous solution. We introduce three levels of data analysis, including: average statistical level; network level; and local level. These approaches allowed us to extract of information otherwise unavailable for most common analysis methods, for instance interaction between neighboring particles.
This phenomenon was considered in details in terms of growth defined by the concentration of Pt⁰ and its diffusional transport properties. Computer simulations showed a posteriori that this simplified approach can be used to describe nontrivial dynamics of nanoparticles formation and growth as simulation results showed good agreement with the experiment.
The obtained results are important for optimizing the conditions for metallic nanocrystals and nanostructures synthesis.
A portion of this research was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility.

Liquid cell electron microscopy is a powerful tool to study nanoscale phenomena in liquids in situ. A key feature of liquid cell electron microscopy is the transfer of energy from the fast-moving electrons to the irradiated material. The radical and molecular species generated may either drive chemical reactions or may change the material or process under study. Radiolysis effects in liquid cell electron microscopy have been intensively studied in order to understand their effects on experimental data. In water, for example, species such as hydrogen, oxygen, hydrated electrons and hydrogen peroxide are generated by the electron beam. It is well known that the production rate of these species depends on the beam current and the dimensions of the illuminated area. Here, we examine in detail how the production rate also depends on the particular materials present in the liquid cell, especially given the unavoidable presence of interfaces and discontinuities in the irradiated medium. We use a liquid cell geometry that is typical for TEM and STEM experiments in which a 200 nm water layer is enclosed by 50 nm thick silicon nitride windows. We then use the electron trajectory simulation software CASINO to compute the spatially varying dose rate (energy deposition rate) due to the passage of electrons. We find that the dose rate can vary greatly in different regions of the irradiated volume. For example, at the interface between the window material and the confined liquid, scattering events cause the emission of secondary electrons that increase the local dose rate by factors in the range 3 to 5. The effects are magnified by the presence of highly scattering materials such as metallic electrodes at the water/window interface. Since the range of these low energy electrons is extremely short, effects are localized to a region within a few nanometers of the interface itself. We use the simulated results to interpret experimental results such as nucleation and growth of nanocrystals at the windows, the charging of surfaces, and the asymmetry between the top and bottom faces of the liquid cell.
Acknowledgements: The study was supported, in part, by the National Science Foundation through grants 1129722 and 1066573. Device fabrication was carried out at the Cornell NanoScale Facility (NSF Grant ECS-0335765), a member of the National Nanotechnology Infrastructure Network.

Molybdenum disulfide (MoS₂) materials have remarkable structure-sensitive properties [1]. For instance, atomically thin MoS₂ sheets are considered for electronics and optoelectronics and MoS₂ nanocrystals are extensively utilized to catalyze industrial oil refining, hydrogen evolution and photo-oxidation reactions [2]. Consequently, the development of reliable and scalable synthesis routes of well-defined MoS₂ crystals is key. A particular prominent procedure is the chemical transformation of molybdenum oxide precursor materials into MoS₂, accounting for the formation of approx. 25000 tons/year MoS₂ nanocrystals in the oil refineries worldwide [3]. However, the sulfidation process of such materials is only vaguely understood due to the difficulties of directly observing nanomaterials in sulfiding atmospheres. Here, we present in situ transmission electron microscopy (TEM) movies revealing unprecedented atomic details about the formation of MoS₂ nanocrystals by sulfidation of molybdenum oxide precursors.
In recent years TEM has become an indispensable tool for studying nanomaterials [4]. In conjunction with a differentially pumped vacuum system, TEM enables atomically and temporally resolved observations of materials during exposure to reactive gas environments [5]. Similar observations during growth of MoS₂ materials have not been available and represent a challenge because the sulfiding gas is highly corrosive to the microscope. Recently, we have overcome this problem by modifying a TEM to enable in situ studies under exposure to sulfur-containing gases [3].
This unique microscope has been used to acquire movies of MoS₂ growth by sulfidation of two distinctly different precursors. First, molybdenum oxide, atomically dispersed on an inert support, is observed to preferentially transform into single-layer MoS₂ nanocrystals whereas multi-layer MoS₂ emerge late in the process. The single-layer MoS₂ nanocrystals can nucleate at steps in the support and grow exclusively along the support surface. The multi-layer MoS₂ nanocrystals form in a layer-by-layer mode by homogeneous nucleation of MoS₂ on already formed single-layer nanocrystals. These observations are complemented with in situ TEM movies of the sulfidation of nanometer-sized molybdenum oxide particles. In this case, the MoS₂ nanocrystals form by either contouring or extending perpendicular to the nanoparticle surface. Atomic-resolved TEM images reveal that a lattice-matching between the molybdenum oxide and sulfide structures is decisive for the MoS₂ orientation. Thus, the in situ TEM studies disclose mechanisms responsible for the size, stacking and orientation of MoS₂ nanocrystals which enable tailoring of MoS₂ structures with optimal morphology for catalytic reactions.
[1] M. Chhowalla et al., Nat. Chem. 5, 2013
[2] F. Besenbacher et al., Catal. Today 130, 2008
[3] L. P. Hansen et al., J. Phys. Chem. C 118, 2014
[4] Y. Zhu et al., Angew. Chem. Int. Ed. 53, 2014
[5] S. Helveg, J. Catal. 328, 2015

As the dimensions of magnetic materials decrease to the nanoscale, novel distributions of spin can be created. We are exploring the formation of these novel distributions and ways to control them through gaining an understanding of the local energy landscape of the nanostructures. We use a combination of Lorentz TEM and in-situ magnetizing experiments, together with magnetic force microscopy (MFM), to study the micromagnetic behavior at the sub-micron scale in magnetic nanostructures such as heterostructures composed of coupled, patterned magnetic disks, and artificial spin ice arrays. Quantitative analysis of the Lorentz TEM data has been carried out using the transport of intensity equation (TIE) approach, which we have extended to allow us to visualize the magnetic structure in three dimensions. By comparing these data with the results of simulations, we are able to gain a fuller understanding of the various energy terms that contribute to the behavior that we observe. Further results will also be presented that show the ways in which Lorentz TEM can also be used to understand phase transitions between different magnetic states in materials such as manganites and shape memory alloys. Some comments will be made addressing the type of materials that are suitable for Lorentz TEM studies.

Resistive switching devices, where the resistance states of capacitor-like metal-insulator-metal structures are reversibly switched by an applied electric field, are promising for a wide range of applications including non-volatile random access memories and bio-inspired neuromorphic computing. However, the underlying atomic mechanisms governing the change in resistance are still unclear, which prevents their widespread application. In-situ X-ray investigations of devices at real operation conditions with chemical specificity and structural sensitivity are extremely valuable for clarifying the mechanisms. Here we report on an in-situ study of resistive switching processes in epitaxial WO₃ thin films by synchrotron X-ray scattering at the Advanced Photon Source.
The mechanisms behind resistive switching of oxide thin films are believed to be redox reactions that create or annihilate oxygen vacancies and migration of those oxygen vacancies under an electric field. In-situ X-ray characterization has the capability to test this hypothesis. The valence state change of tungsten ions during redox reactions is shown by micro-fluorescence imaging around tungsten absorption edge. At the same time, the lattice distortions and changes in oxygen content/octahedral tilt during the formation and migration of oxygen vacancies are monitored by changes to the integer-order and half-order diffraction peaks. The length scale of real space features during resistive switching is on the order of ~ 10-50 mu;m, which is well resolved with a sub-micron focused X-ray beams. The insights gained from these in-situ experiments will be discussed in the context of improved performance and new device design.

Ferroic materials play a key role in a wide range of technologically relevant devices. They all share the common feature that the microstructure and domains determine to a great extent their functionality. Among the promising piezoelectric materials for actuation applications is the solid solution Bi_0.5Na_0.5TiO₃ (BNT)-SrTiO₃ (ST). Recently it was found that this material is characterized by a core-shell microstructure that largely determines its electromechanical and dielectric properties [1], however, the microstructure formation and the mechanisms are poorly understood. In this contribution, we reveal the core-shell and domain formation in nanoparticles during a calcination process by means of in-situ high resolution TEM experiments. The solid state chemical reactions occurring upon heating could be followed in real time and the temperature-dependent core-shell formation and structural evolution was investigated. A series of combined electron diffraction, diffraction contrast, and high-resolution imaging experiments at temperatures varying from 300 °C up to 800 °C were carried out using a dedicated in-situ TEM holder and a MEMS heating chip. Domain nucleation processes in the nanoparticles were observed. A domain-like structure was observed at T = 800 °C and atomic resolution was possible due to the high thermal stability and low-drift conditions. In addition, thermo-gravimetric analysis (TG/DTA) and ex-situ X-ray diffraction (XRD) were also performed. The reaction was found to take place in two steps: first traces of the perovskite phase, identified as the BNT-rich cores, are formed between 450 and 600 °C, while the ST-rich shell is formed between 600 °C and 800 °C.
[1] M. Acosta, L.A. Schmitt, L. Molina-Luna, M.C. Scherrer, M. Brilz, K. G. Webber, M. Deluca, H.-J. Kleebe, J. Rödel, and W. Donner. Core-shell lead-free piezoelectric ceramics: current status and advanced characterization of the Bi_0.5Na_0.5TiO₃-SrTiO₃ system. Journal of the American Ceramic Society. Submitted.

To gain a greater understanding of the mechanisms that control material properties, researchers often turn to in situ TEM. This technique provides insight into many processes that are otherwise unclear in static experiments. Dynamic microscopy can potentially fill in gaps in the current understanding interfacial phenomena in a wide variety of materials. In this talk, the exploration of ferroelectric domain behavior in select oxide structures is presented [1-3]. Utilization of ferroelectrics for device applications requires precise control of domain structure. To facilitate device integration, an understanding of the microstructural factors that affect ferroelectric domain switching, and in most cases, ferroelastic relaxation, must be developed. In-situ transmission electron microscopy is an ideal tool for studying domain dynamics due to its inherent high spatial and temporal resolution.
Specifically, we present quantitative dynamic studies of ferroelectric domain motion in two systems: a uniaxial ferroelectric, RbKTiOPO₄ (RKTP), and a multiferroic, BiFeO₃ (BFO), using in situ biasing in a TEM. In RKTP, we show that by manipulating the electron beam, we can reverse the direction of domain propagation, and by using a condensed probe we can locally nucleate domains; this process is dependent on both the sample geometry and electron beam condition. In BFO, the evolution of ferroelastically switched ferroelectric domains during many switching cycles is investigated, and the role of local defects and other factors, such as local strain, on the reversibility of domains during cycling is discussed. The results of these time-resolved biasing experiments are compared to theoretical results. This body of work provides a real time and multiscale view of the complex dynamics of domain switching and complement scanning probe techniques and are critical to the development of improved ferroelectric devices.

Ferroelectric domains, surface termination, average lattice parameter and bilayer thickness were monitored using in-situ synchrotron x-ray diffraction during the growth of BaTiO₃ /SrTiO₃ (BTO/STO) superlattices by off-axis RF magnetron sputtering. A new x-ray diffraction technique was employed which makes effective use of the custom growth chamber, pilatus detector and synchrotron radiation available at beamline X21, NSLS, BNL. The technique allows for scan times substantially faster than the growth of a single layer of material, enabling continuous monitoring of multiple structural parameters as the film grows. Due to the large compressive strain experienced by the BTO layers in these substrates these superlattices are ferroelectric when grown and display continuous evolution of the polarization during growth. The effect of electric boundary conditions was investigated by growing the same superlattice alternatively on STO substrates and 20nm SrRuO₃ (SRO) thin films grown on STO substrates. The experiments provide insight into the formation and evolution of ferroelectric domains in the situation when the sample is ferroelectric during the growth process.
Analysis of the data shows several interesting features. Firstly, the domain structure of superlattices grown on SrRuO₃ bottom electrodes evolves differently from those grown on SrTiO₃ alone. While the fact that electrostatic boundary conditions have an effect on ferroelectric domain structure is hardly surprising, being able to monitor the evolution of this structure during the growth presents an excellent opportunity to monitor how this structure evolves as a function of the individual layer thicknesses and the total thickness of the evolving structure. Secondly, it was found that while the measured lattice parameters suggest strong coupling between ferroelectric layers, the size of domains did not evolve as much with thickness as expected, suggesting that domain size is locked in fairly early in the growth process. Finally, besides the fundamental knowledge gained from these studies, being able to monitor the structural parameters of a growing ferroelectric superlattice at this level of detail, provides numerous insights which can guide the growth of higher quality ferroelectric superlattices in general.

Ferromagnetic shape memory alloys (FSMA) have shown great potential as active components in next generation smart devices due to their exceptionally large magnetic-field-induced strains and fast response times. During application of magnetic fields in FSMAs, as is common in several magnetoelastic smart materials, there occurs simultaneous rotation of magnetic moments and reorientation of twin variants, resolving which although critical for design of new materials and devices, has been difficult to achieve quantitatively with current characterization methods. At the same time, theoretical modeling of these phenomena also faced limitations due to uncertainties in values of physical properties such as magnetocrystalline anisotropy energy (MCA), especially for off-stoichiometric FSMA compositions. Here, in situ polarized neutron diffraction is used to measure directly the extents of both magnetic moments rotation and crystallographic twin-reorientation in an FSMA single-crystal during the application of magnetic fields. In addition, high-resolution neutron scattering measurements and first-principles calculations based on fully relativistic density functional theory are used to determine accurately the MCA for the compositionally disordered alloy of Ni₂Mn_1.14Ga_0.86. The results from these state-of-the-art experiments and calculations are self-consistently described within a phenomenological framework, based on which the energy for magnetoelastic twin boundaries propagation is furthermore estimated to be ~150 kJ/m³.

The physical properties and functional efficiency in many real systems are intimately related to their internal stresses and strains caused through texture, constraint or other microstructural attributes. Recently, there has been considerable research effort devoted to understanding the complex interplay between material structure (atomic, lattice, domain etc) and internal strains resulting, for example, in ferroic order or externally applied electrical or magnetic fields. Strong effects have been observed in a wide range of materials including (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT) and PbZr(1-x)TixO3 (PZT). The origin of the remarkable large piezoelectric constants and strain observed in these materials is still under debate, with many studies aiming to map the crystallographic structure to the piezoelectric behaviour. It has become clear over the years that a new way of characterising these complex materials was required so that structure, field, and functional response (such as polarisation) could be mapped out with respect to time, excitation type, level and frequency. In this way origins of the extrinsic response of piezo and related ferroic (hysteretic) materials could be coupled to the structure of the material allowing new ways of accessing useful materials for sensors, transducers and actuators. At the UK&’s National Physical Laboratory, NPL, we have developed a series of in-situ and in-operando dynamic electrical and structural characterisation measurement facilities for functional materials, to explore this important set of relationships that is pertinent to these industrially relevant materials. In this talk, I will describe these capabilities -open to all - which we have designed, tested and commissioned at three world class materials user facilities, including two X-Ray synchrotron sites - Diamond Light Source (Oxfordshire, UK) and ESRF (XMaS beamline BM28 - Grenoble, France), and one neutron facility - the STFC-ISIS neutron facility (RAL, Harwell Research Centre, Oxfordshire UK). Unique, real time data collection methods on single crystal, epitaxial thin films and polycrystalline ceramic samples are employed as a function of electrical field, frequency and temperature to characterise the intrinsic and extrinsic contributions to the piezoelectric response. In these experiments, we have probed the dynamics of the ferroelectric response and, through successful integration of a metrological laser interferometer onto the XMaS beamline at ESRF, for the first time provided a method to simultaneously measure the electrical polarisation, lattice parameters and deformation allowing new insights to be gleaned on the correlation between induced strain and material properties of this industrially important class of materials.

In many lead-free ABO₃ compounds, the ferroelectric polarization vectors are modulated by nanoscale-disordered displacements of B atoms that tilt away from the average polarization direction. The electric-field-induced effects on such local atomic displacements are currently unknown. We observed from in situ high-energy X-ray scattering experiments that the correlation lengths for partially ordered B atom displacements can be dramatically increased under the application of electric fields. Such an increased ordering of B atom displacements, in turn, has dramatic effects on lattice vibration modes as observed from in situ neutron scattering experiments, including a large dampening of the TA (transverse acoustic) modes and enhanced coupling between TA and TO (transverse optic) modes. These results elucidate the underlying mechanisms for highly enhanced piezoelectric properties along nonpolar crystallographic directions in several lead-free ferroelectrics such as BaTiO₃ and KNbO₃. More generally, they help to establish a general correlation between atomic displacements ordering and lattice instability, which could be an useful tuning parameter for engineering enhanced multi-functionalities in non-lead ferroelectric oxide alloys.

A metastable phase of vanadium sesquioxide (V₂O₃) with a cubic bixbyite structure was recently discovered. This new polymorph has been the subject of several theoretical papers in the last few years. However, experimental studies are less common, likely due to difficulty of stabilizing the pure phase. We previously reported on a synthetic route to colloidal nanocrystals with a bixbyite crystal structure.¹ This nanocrystalline bixbyite has been shown to have enhanced stability relative to the bulk, which could be due to the increased influence of surface energy on Gibbs free energy at the nanoscale. Recently, we observed that these nanocrystals experience a change in structure upon air exposure. Heating the nanocrystals in air increases the kinetics of the process, resulting in structural changes as observed by in situ X-ray diffraction (XRD) and weight gain as measured by thermogravimetric analysis (TGA), indicating oxygen uptake by the V₂O₃ lattice. Furthermore, the oxidation process is reversible upon heating in an inert atmosphere, as also observed by in situ XRD and TGA. The energetics of oxygen interstitial formation have been modeled using Density Functional Theory, the results of which rationalize the energetic driving force for reversible interstitial formation as a function of temperature and oxygen partial pressure. Bixbyite nanocrystals therefore exhibit unusually low-temperature reversible oxygen storage properties as a consequence of their atomic and nanoscale structure.
(1) Bergerud, A.; Buonsanti, R.; Jordan-Sweet, J. L.; Milliron, D. J. Chem. Mater.2013, 25 (15), 3172-3179.

Reaction-Diffusion processes are prevalent in nature. They permeate the non-equilibrium configurations of various systems of interest to diverse disciplines such as chemical physics, biophysics, and geochemistry. Reaction-Diffusion processes span multiple spatiotemporal scales, requiring local and dynamical information on the probed system, and precise experimental control over its thermodynamic state.
In this work, we show that modern structural beam-probes such as in situ electron and X-ray microscopes, with their exquisite spatial and spectral properties, offer unprecedented opportunities to simultaneously observe and control reaction-diffusion phenomena. In particular, we describe a new approach to controllably drive the dissolution of the calcium carbonate-aqueous interface by the intense radiation fields of synchrotron X-rays, and simultaneously probe the dynamics of propagating surface reaction fronts using surface X-ray microscopy. Evolving structures of the reactive surface are related to the time-dependent solution composition by a reaction kinetics model. Reaction front instabilities are observed at extreme disequilibria with front velocities of tens of nanometers per second, and are identified as a dynamical signature of transport-limited reaction dynamics. The presented approach enables new opportunities in investigating the behavior of materials under extreme environmental conditions; conditions that are simulated and finely tuned by high-energy microscopic beams.

In using liquid cell microscopy to examine processes and structures in liquids, we generally aim to confine a well-controlled layer of liquid between thin membranes to achieve a stable system for observation in the electron microscope. The failure of the hermetic seal, for example by rupture of a membrane, usually marks the end of the experiment. However, controlled release of fluid from the cell can provide a unique means of examining liquid processes far from equilibrium with good spatial and temporal resolution. Here we describe a custom-made liquid cell in which one of the observation windows, made of 50 nm thick silicon nitride, is perforated using focused ion beam patterning to form a nanopore of approximately 500 nm. This enables a controlled flow rate of volatile phases into the column vacuum at a leak rate that can be chosen to be compatible with operation of the electron microscope. The window is robust enough to maintain its integrity even with the presence of the pore and its presumed stress field. Using water as the working fluid, we record images as the liquid discharges through the nanopore into the low pressure environment. We will describe observations of low pressure boiling, void formation and sublimation of ice at low pressure. We have also observed phase separation in the thin, confined film and the faceting of thin liquid/ice in extremely confined geometries and we will discuss the phenomena that may be driving these processes. We finally consider the opportunities provided by this type of perforated liquid cell device in examining other materials systems under extreme conditions.
Acknowledgments: The study was supported, in part, by the National Science Foundation through grants 1129722 and 1066573. Device fabrication was carried out at the Cornell NanoScale Facility (NSF Grant ECS-0335765), a member of the National Nanotechnology Infrastructure Network and at the Krishna P. Singh Center for Nanotechnology at the University of Pennsylvania.

In this work two poly(p-phenylene-ethynylene)-alt-poly(p-phenylene-vinylene) (PPE-PPV) polymer systems with defined side chain configurations are examined. Besides the solubilization, the configuration and the distribution of side chains can also have an impact on optical and physical properties of conjugated polymers. More distinct effects can be realized by altering the conjugated system itself. We went beyond present studies and compare profoundly the behavior upon doping of an anthracene-containing PPE-PPV with a solely phenylene-based PPE-PPV derivative by using in situ spectroscopic techniques ranging from UV-VIS to mid-IR. In UV-VIS measurements the HOMO-LUMO transition for the PPE-PPV polymer decreases upon chemical doping using iodine as an oxidation agent. Additionally, a new absorption band arises. Further, in situ mid-IR experiments in attenuated total reflection (ATR) mode are performed. Upon doping a broad absorption band appears and new infrared active vibration (IRAV) modes are detectable. All these data are correlated with electron paramagnetic resonance (EPR) measurements which show a simultaneously increasing EPR-signal. These data suggest the formation of polarons. Interestingly, for the anthracene-containing PPE-PPV polymer a different behavior upon chemical doping is observed. Although we obtain similar results in the UV-VIS range, in the mid-IR a broad absorption band arises upon doping, which shifts and simultaneously decreases its maximum as oxidation proceeds. Additionally, the vibrational absorption band for the triple bond of the PPE units decreases. In situ EPR measurements clarify the formation of radical cations saturating with increasing oxidation. Possibilities for these different spectroscopic behaviors of the anthracene-containing PPE-PPV polymer are explained and a model on a molecular level is presented.

Earth abundant compound semiconductors are promising candidates for the fabrication of high-quality thin film solar cell absorber. In particular, these compound (I2-II-IV-VI4) semiconductor material possess high optical absorption coefficients (10⁵ cm^-1), high power conversion efficiencies, offer good photostability against long-term radiation, and cause less environmental problems due to their relatively low toxicity.[1,2] However, device efficiencies for these materials are significantly lower than the best efficiencies achieved for chalcopyrite based solar cells. Low device efficiency for earth abundant semconductors have been attributed to difficulties in achieving large grained, single phase thin films with controlled stoichiometry using vacuum-based deposition or precursor annealing techniques. These techniques can also result in the unintentional formation of a large number of secondary phases in the Cu-Zn-Sn-S system that significantly reduces the device performance.[1] Nanocrystal based methods for the fabrication of thin film photovoltaics are an attractive alternative to vacuum deposition processes due to their simplicity and cost effectiveness.[3,4] Here, we develop a simple and reliable solution approach to process large grained, single phased kesterite Cu2ZnSnS4 films via thermal treatment of nanocrystal-precursor films consisting of wurtzite Cu2ZnSnS4 nanorods. In-situ analyses by means of energy-dispersive x-ray diffraction reveal that the transition from the wurtzite to the kesterite structure and the transition from the nanocrystal to large crystallites take place simultaneously within a few seconds. The crystal structure, composition and electrical properties of the final film were investigated with Scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman and Hall effect measurements.
1) M. F. A. M. van Hest, D. S. Ginley, Solution Processing of Inorganic Materials (Ed.: D. B. Mitzi), Wiley-VCH, Hoboken, NJ, 2008.
2) H. Katagiri, Thin Solid Films2005,480, 426.
3) Q. Guo, G. M. Ford, W. C. Yang, C. J. Hages, H. W. Hillhouse, R. Agrawal, Sol. Energy Mater. Sol. Cells, 2012, 105, 132.
4) T. K .Todorov, J. Tang, S. Bag, O. Gunawan, T. Gokmen, Y. Zhu, D. B. Mitzi, Adv. Energy Mater., 2013, 3, 34.

Mechanically driven phase transformations have elicited intensive attention as stress induced phase transformation could largely tailor the mechanical properties (strength and ductility) of materials. There are numerous in situ techniques that can reveal the structure-property relationships at a macroscopic level. However a clear understanding on the initial stage of the phase transformation (such as nucleation) is lacking, which is important to understand the physics of the phase transformation. Here, by using two examples, we demonstrate the utility of an in situ nanoindentation technique inside a transmission electron microscope, through which we can capture the phase transformation process at sub-micro length scale and reliably determine the critical stress necessary for phase transformations. In the amorphous Cu based alloy, we captured the nucleation of nanocrystals at very low stresses manifested by prominent load drop. In the Ni based shape memory alloy, we observed the two distinct types of martensitic phase transformations: a reversible gradual phase transformation at low stress, and an irreversible abrupt phase transition at higher stress levels. This work was supported by NSF.

Many technologically relevant materials are in fact kinetically stabilized and not at their true thermodynamic free energy minimum, i.e., they are metastable. These kinetically stabilized materials can show improved functionality over their thermodynamically stable counterparts. However, it is difficult at best to predict formation pathways for such metastable materials. In this work, we aim to understand how the initial state of amorphous thin films of VO_x influences the final crystalline form or polymorph. We employ a range of synchrotron based techniques: grazing incidence pair distribution function (GIPDF), x-ray absorption spectroscopy (XAS), and x-ray diffraction (XRD) during in-situshy; crystallization. We focus on amorphous VO_x films deposited by pulsed laser deposition with varying laser repetition rates and oxygen partial pressures and subsequently crystallized by annealing under different conditions. These different synthesis conditions create several different amorphous structures, as identified from GIPDF and XAS analysis. In-situshy; 2D-XRD during film crystallization shows that the different starting amorphous structures result in the formation of different polymorphs. We use these results to relate the local structure of the initial amorphous structures to the VO_x polymorph structure. This work is part of a larger effort to help better understand the pathways needed to synthesize different polymorphs.

In-situ direct writing by electron beam from solutions opens a pathway for resistless fabrication of nanostructures at high throughput. However, when using electrons to direct write in solution the minimal size of the created structures is limited to the micron scale due to fundamental physics of the interactions between the electron beam and the liquid, including the lateral transport of solvated electrons and ionic species. Use of the helium beam with the opposite charge and shorter mean free path offers the potential for the localization of the reaction zone on the single digit nanometer scale. Here we will present our results demonstrating writing of platinum structures from liquid (beam induced electroplating) in a platinum chloride solution using helium ions with sub-10 nm resolution. Using data analytics on acquired in-situ growth movies we are able to elucidate the main statistical descriptors for helium ion beam initiated platinum structure growth. The possible mechanisms of beam induced growth and ultrahigh localization of reaction zone are discussed. Furthermore, we will discuss optimization of solution chemistry and instrumental parameters as they relate to the quality and thickness of structures and the extension to device fabrication on a single digit nanometer level.
This work was conducted at the Center for Nanophase Materials Sciences, which is a Department of Energy (DOE) Office of Science User Facility

Nanometer-sized semiconductor crystals, (known as quantum dots, QDs), with size-dependent physicochemical properties have enabled a wide range of applications in biological imaging, light emitting diodes, solar cells and displays. The batch scale technique for the solution-phase preparation of QDs which was introduced ~ 20 years ago and still remains as the main strategy for characterization and discovery of new class of nanomaterials. The batch scale strategies, owing to the poor heat and mass transfer rates and inaccurate control over the reaction conditions present deficiencies for consistent preparation of QDs. Reducing the reaction volumes from milliliters to microliters and characteristic length scales from centimeters to hundreds of microns can significantly improve the rates of heat and mass transfer during the synthesis process of QDs. During the past 15 yrs, different droplet-based microscale platforms have been developed as an alternative route to the manual batch scale synthesis for reproducible and high-throughput screening of QDs. However, the inter-related flow properties of continuous droplet-based strategies (i.e., mixing and residence time via average flow velocity) makes it challenging to replicate the same degree of mixing for different QD synthesis times. In this work, inspired by our previously developed oscillatory flow strategy, we developed an integrated droplet-based strategy for in-situ characterization and fundamental studies of colloidal synthesis. The automated oscillatory flow strategy consists of a 12 cm long Teflon tubular reactor embedded within a custom-machined aluminum chuck and a fiber-coupled UV-Vis light source and a miniature spectrometer. The integration of the droplet-based oscillatory flow platform with spectral characterization tools enables real-time in-situ monitoring of the in-flow synthesized semiconductor nanocrystals during the nucleation and growth stages, which is otherwise challenging to accomplish in batch scale synthesis. The developed oscillatory flow technique, enabled in-situ studies of the kinetics of nucleation and growth stages of II-VI (CdSe and CdTe) and III-V (InP) QDs via monitoring the absorption spectra evolution of the prepared QDs over a wide range of temperatures (160 °C-220 °C ) and reaction times (3 s-900 s), while using only 10 mu;L of the QD precursors. A real-time absorption spectra evolution of QDs with a time delay of 3-15 s was obtained at each reaction temperature from the same 10 mL droplet containing the QDs while moving back and forth within the Teflon reactor with an average velocity of 1-2 cm/s. The developed droplet-based platform is the first small-scale strategy for automated in-situ spectral characterization of II-VI and III-V QDs, and provides further insights on the kinetics and mechanisms of intermediate growth stages of colloidal nanocrystals.

Understanding the evolution of composition and atomic structure of nanoalloy catalysts operated under realistic oxygen reduction reaction (ORR) conditions is essential for making commercially viable proton exchange membrane fuel cells (PEMFCs). This report describes findings of a study of palladium-alloyed electrocatalysts (PdNi) with different bimetallic compositions, aiming at establishing the relationship between catalyst&’s composition, atomic structure and activity for operando ORR at the cathode of an operating PEMFC. An intriguing composition-activity synergy was revealed by the strong dependance of catalytic activity upon the leaching process during the fuel cell operation. A maximal activity at ~50:50 in terms of atomic composition were also discovered where reflects a persistent fluctuation pattern of the interatomic distances along with an atomic-level reconstruction under the ORR and fuel cell operation conditions by in-situ High Energy X-ray Diffraction coupled with Pair Distribution Function Analysis (HE-XRD/PDFs). This finding on the structure-activity correlation extracted under PEMFC operating conditions has important implications to the design and preparation of catalysts with controlled activity and stability.

A well-known phenomenon occurs in face centered cubic thin films in which films deposited with initial (111) texture undergo a thickness-dependent texture transformation on annealing: thin films retain their (111) texture, while thick films transform to (100). This is commonly attributed to a competition between strain and interface energy, but several experiments have shown that that neither of these plays an important role in the transformation. The standard model is also unable to explain several unusual morphological features in the transformed films, such as abnormal giant (100) grains (many orders of magnitude larger than the film thickness) and grain boundaries with very high local curvature. To study the development of these features, we designed a custom heating stage for use inside a scanning electron microscope, allowing us to perform an in-situ analysis of the evolution of grain size and orientation in thin Ag films using electron backscatter diffraction (EBSD). Statistical analyses of the film structure throughout the transformation reveal many unexpected findings, including non-columnar grain growth, and indicate that in fact all grain populations grow abnormally.

Most surface sensitive characterization techniques such as X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) usually require high or ultra-high vacuum (UHV) environments for operation. This limits their applications to characterize the surface or interface of sample in liquid and gas environments. Graphene is famous for its high strength and transparency to electromagnetic radiation in a wide energy range. Recent theoretical and experimental research showed that graphene also is highly transparent to moderate (>100 eV) and high energy (above few keV) electrons and can be used therefore as electron transparent but molecularly impermeable windows separating high pressure sample compartment from UHV [1,2]. Due to its atomic thickness and reduced electron scattering at very low energies (less than few eV), the transparency of graphene in this energy range is expected to be very high. This however has not been proved yet experimentally. Therefore, the fabrication and study of electron transparent membranes at electron energies, below tens eV, will be valuable to fundamental science as well as to their practical applications in electron microscopy and spectroscopy.
In this presentation, we report on transfer-free wafer scale fabrication protocols of such graphene membrane arrays for these applications. Supported by Si₃N₄ or SiO₂ primary membrane, the CVD grown graphene membrane demonstrated high yield and high transparency to low energy electrons.The electron transparency of the graphene membrane was characterized using electron current attenuation tests in a wide electron energy range. The practical aspects of application of the graphene micro-window arrays for ambient pressure electron microscopy and spectroscopy are considered.
1. J. Kraus, R. Reichelt, S. Guenther, L. Gregoratti, M. Amati, M. Kiskinova, A. Yulaev, I. Vlassiokiv and A. Kolmakov, Nanoscale, 2014.
2. J. D. Stoll and A. Kolmakov, Nanotechnology, 2012, 23.

In the last decades both the scientific and the industrial interest on the production of monodisperse nanoparticles of various materials increased tremendously. Although many synthesis routes are already well developed and applied, for many systems a fundamental understanding of the underlying physical and chemical processes is still missing. Therefore time-resolved SAXS is a well-developed method to get an insight into the evolution of the morphology of nanoparticles. Thus, many setups have already been developed to access the particle nucleation and growth under various conditions via SAXS. A stopped-flow cell is well suited to access reaction times starting from 10 ms up to the continuum by injecting the reactants into a capillary, were they are accessible for scattering and spectroscopic measurements. However, there are systems were the use of this device is not possible (e.g. the CdS nucleation and Growth) due to a significant background signal from a time dependent coating of the containment walls. In the case of CdS nanoparticle nucleation we observed a change of the capillary background, which gives a significant contribution to the data modeling. To access those reactions, there is a need for a containment free in-situ setup with a time resolution in the ms regime with a dead time down to about 100 ms. Here we present a novel setup for containment-free scattering experiments on a free liquid drop. The chemicals are brought together in a Y-shaped micro mixer driven by syringe pumps. Once the volume of one drop is mixed, the injection is stopped, and a stable drop is adhered to a special shaped nozzle of the mixer due to adhesion forces. A stroboscopic operation mode of the setup allows a constant repetition of the drop generation in order to make this kind of experiment suitable for laboratory based experiments as well. In recent synchrotron based experiments at the APS in Chicago we realized a time resolution of 200 ms after a dead time of 100 ms to get for the first time an insight into the nanoparticle formation and growth of EDTA stabilized CdS via SAXS.

This study aims at investigating the catalytic hydrogenation of nitrogen dioxide NO₂ on Pt, Rh and Pt-Rh alloy catalysts. Nitrogen oxides are produced during the combustion of gasoline in the lean-burn regime, and PGM (Platinum-Group-Metals) are used as active components of the catalytic converter in order to reduce their emissions. In most studies of heterogeneous catalysis, very little information is available about the local morphological/structural changes that might occur during the reaction. Moreover, from a dynamical point of view, the kinetic parameters only reflect the global kinetics of the reaction taking place on the surface a large ensemble of nanoparticles with specific size and shape distribution. Thus, ensemble-averaging takes place eventually hiding more complex dynamics, such as periodic oscillations.
A better understanding of the ongoing catalytic reaction would lead to a better reproducibility, predictability and control of this reaction. In this view, a study of the hydrogenation of NO₂ gas over Pt, Rh and Pt-Rh nanocrystals is undertaken at the molecular level by means of Field Ion Microscopy (FIM) and Field Emission Microscopy (FEM).
The catalytic hydrogenation of NO₂ was monitored in real time. On Pt at 390K, amongst several non-linear behaviors, self-sustained periodic oscillations were observed. Fourier transform analyses and temporal autocorrelation functions were used to characterize the dynamics and to quantify the robustness of the kinetic oscillations. NO₂ hydrogenation was also studied on Rh at 450K and found to present many similarities by with platinum. However, the details of the dynamics reveal significant differences, such as the emergence of oscillations via a different bifurcation, the robustness of the system, as well as the pressure range for the occurrence of non-linear behaviors. Finally, the NO₂+H₂ reaction was studied on a Pt-17.4at.%Rh alloy catalyst of similar composition -that is used in catalytic converters. Surface explosions were observed in the temperature range of 390-515K. At 425K, periodic oscillations are observed with features lying between those observed on pure Pt and pure Rh samples. This observation implies the existence of synergistic effects between the metals.
Field ion microscopy and field emission microscopy are powerful techniques in materials science and chemistry. By exploiting the nanoscale resolution of the techniques, the results obtained allow for a better understanding of catalytic systems at the molecular level. The experiments also prove that robust nonlinear behaviors can be observed down to the nanoscale, without a significant loss of correlation due to fluctuations inherent to small chemical systems.

One dimensional nanostructures have the prospect to change the properties of materials used in contemporary devices. Physical properties change with dimension and size. Ceramics, semiconductor and carbon materials are easily synthesized as one dimensional structures with typical diameters of several nanometers and length-diameter ratios of 1000:1. However, only the metals as one of the oldest are difficult to fabricate in similar geometries. In contrast, micrometer diameter, millimeter length macroscopic metallic nanowires were grown and reported decades ago via the reduction of metal halides, based on a process described already in 1574. Recently we adopted the original process to grow perfect defect and flaw free nanostructures with diameters of several ten nanometers under UHV conditions. Several fcc , bcc and hcp metals can be synthesized by this method as nanowires. Typical diameters of the nanowhiskers are 100 nm and lengths of up to 50 µm are observed. The physical properties of the structures have been shown to be extraordinary. However several interesting aspects related to nanowhiskers remain open for investigations. In the presentation we will address two of them via in situ transmission electron microscopy: the growth of Cu nanowhiskers and the onset of the fcc-hcp phase transformation in Co.
In contrast to old believes the growth of whiskers is not determined by screw-dislocation embedded in the whisker parallel to its axis but by local variations on the atomic level on the substrate surface. In situ growth observations inside a TEM confirmed sequential ex situ growth experiments that the lengthening of the nanowires occurs by root growth. Adatom incorporation occurs at the interface between substrate and nanostructure. The microstructure of the nanowires was revealed to be perfect and defect-free. No dislocations, stacking faults, or grain boundaries were detected. The growth direction is, for fcc metals (Cu, Ag, Au, Pd), generally along the <110> crystallographic direction.
Compared to the perfect crystal structure of fcc nanowhiskers, those grown for Co exhibit stacking faults parallel to its axis when observed at room temperature. The overall crystal structure is fcc. In situ heating and cooling experiments performed in a high resolution TEM were carried out to reach the stable hcp crystal structure in Co nanowhiskers. During thermal cycling partial dislocations are nucleated and propagate parallel to the nanowire axis, forming only a local hcp structure, the overall fcc crystal structure however remains.

Magnetic shape memory alloys undergo a symmetry-breaking transformation with a change in structure and magnetism that are induced by changing the temperature, mechanical stress or magnetic field. In the low-temperature, low-symmetry martensite phase, macroscopic shape changes can be achieved by a field-induced twin boundary motion. Both effects make this class of materials very interesting for applications in magnetocaloric regenerators of solid-state cooling devices and as large-strain actuator materials. The energy efficiency in applications depends strongly on the microstructure developing during a martensitic transformation: A microstructure that forms with as low elastic energy as possible leads to a highly reversible transformation and is therefore beneficial for magnetocaloric applications. For efficient actuation by magnetic fields, mesoscopic low-symmetry twin boundaries are favorable since they can be moved by fields as low as 0.1 T. The significant influence of the microstructure on the functional properties highlights the importance to analyze how the microstructure forms and how the formation can be manipulated.
We use sputter-deposited epitaxial Ni-Mn-Ga films as a model system for the class of Ni-Mn-based magnetic shape memory alloys [1]. These films can also be prepared in a freestanding form which may lead to applications in microsystems.
The nucleation and growth of martensite is studied in dependence of temperature in situ by scanning electron microscopy and by X-ray diffraction. The final microstructure is additionally studied by means of transmission electron microscopy and electron backscatter diffraction. We identify the martensitic nucleus and its growth modes and follow the coalescence of differently oriented nuclei into macro-twins. We explain the shape of the nucleus and the growth process using a model derived from the phenomenological theory of martensite crystallography and finite element calculations. This allows us to describe the entire hierarchical microstructure present in all magnetic shape memory alloys step-by-step.
In an attempt to decrease hysteresis, we also analyze the development of the microstructure in situ in vicinity of a nanoindentation and show that the martensitic phase preferably tends to nucleate near the indent.
We conclude that the transformation hysteresis is on the one hand strongly influenced by nucleation and discuss its influence on the magnetocaloric effect [2]; on the other hand, a big share of energy is dissipated during interaction of large martensitic variants [3].
We acknowledge funding by DFG via FA 453/8 and SPP 1599.
[1] A. Backen, S. R. Yeduru, M. Kohl, S. Baunack, A. Diestel, B. Holzapfel, L. Schultz, S. Fähler, Acta Mat. 59, 3415 (2010)
[2] A. Diestel, R. Niemann, B. Schleicher, S. Schwabe, L. Schultz, S. Fähler, J. Appl. Phys. accepted (2015)
[3] R. Niemann, J. Kopecek, O. Heczko, J. Romberg, L. Schultz, S. Fähler, E. Vives, L. Manosa, A. Planes, Phys. Rev. B 89, 214118 (2014)

The in-situ visualization of nanoscale processes in liquids has recently been achieved in a transmission electron microscope (TEM) using microfabricated cells that seal a thin, ~100-nm liquid layer between electron-transparent membranes. Various chemical, electrochemical, and biological processes have been observed in these liquid cells, induced by either electron-beam exposure or external application of electrical bias, but to date all experiments in liquids have been conducted at room temperature. Here we present a design that can provide localized heating in a custom TEM liquid cell, enabling studies of temperature-activated processes (e.g., nanoparticle growth from solution or protein unfolding) or materials with temperature-dependent kinetics (e.g., lithium transport in battery materials). The heater design consisted of a series of thin-film Pt resistive temperature devices patterned to act as either heaters or thermometers contained within the liquid cell&’s 30-micron diameter silicon nitride membrane. The localized heating minimized sample drift caused by thermal expansion, and temperatures of a few hundred degrees Celsius could be achieved. In addition, to directly measure the liquid temperature, the cell was filled with liquid gallium and heated while collecting electron energy-loss spectra (EELS). The thermal expansion of the gallium caused a measurable shift in the gallium bulk plasmon energy, and therefore a heat map of the viewable area was obtained. Because our cell contains eight individually addressable electrodes, both heating and electrochemical experiments can be performed simultaneously. The custom heater design can be easily adapted to accommodate the geometry of the electrochemical, biological, or chemical system under study, opening a wide new parameter space of in-situ experiments in the TEM.

Understanding how bulk properties emerge from quantum states and low-energy fluctuations in materials is critical for developing a comprehensive understanding of collective and correlated phenomena. In addition to the wide range of spatial and temporal scales that must be accessed, the role of ever-present defects (e.g., grain boundaries, dislocations, impurities, etc.) must be elucidated, ideally with methods not solely reliant on ensemble averaging. Here, we describe our study of the nanoscale, localized structural dynamics of crystalline silicon via ultrafast electron microscopy (UEM). Real-space nanoscale dynamics were visualized with UEM bright-field imaging and correlated with atomic-scale motion obtained via both selected-area and convergent-beam diffraction (SAED and CBED, respectively) - all on the same pre-selected specimen region. Real-space frequency maps spanning one to 20 MHz revealed spatial variations in bend-contour oscillation frequencies covering tens of nanometers suggesting features of initially-excited vibrational modes are strongly-influenced by local defects. In momentum space, variation in excitation error due to oscillation of the reciprocal lattice relative to a fixed Ewald sphere manifests as Bragg-spot and ZOLZ-disk intensity modulation, independent of (and often obscuring) Debye-Waller effects. By correlating the spatially-dependent bend-contour motion in real space with the observed momentum-space response, a comprehensive understanding of the evolution of the overall dynamics - as well as the role of defects on those dynamics - can be obtained. Further, the results described here illustrate the practical importance of thorough characterization of the specimen region of interest in order to properly ascribe experimental observations to true structure-function relationships.

Assembly of molecular clusters and nanoparticles in solution is now recognized as an important mechanism of crystal growth in many materials, yet the assembly process and attachment mechanisms are poorly understood. To achieve this understanding we are investigating nucleation and assembly of iron and titanium oxides, phase transformation followed by the attachment using in situ and ex-situ TEM, and the forces that drive oriented attachment between nanocrystals and the factors that control them via AFM-based dynamic force spectroscopy (DFS). Our hypothesis is that attachment is due to reduction of surface energy and the driving forces that bring the particles together are a mix dipole-dipole interactions, van der Waals forces, and Coulombic interactions. Therefore they can be controlled via pH, ionic strength (IS), and ionic speciation. In-situ TEM shows that, in the iron oxide system, primary particles interact with one another through translational and rotational diffusion until a near-perfect lattice match is obtained either with true crystallographic alignment or across a twin plane. Oriented attachment then occurs through a sudden jump-to-contact. Analysis of the acceleration during attachment indicates it is driven by electrostatic attraction. Ex-situ TEM analysis shows that the TiO₂ nanowire branching occurs through attachment of anatase nanoparticles to rutile wires on a specific crystallographic plane for which the anatase-to-rutile transformation leads to creation of a (101) twin plane. In situ TEM heating experiments show that during the phase transformation from anatase into rutile the (103) plane of anatase becomes the (101) plane of rutile. This result is consistent with our ex situ experiment. Initial DFS measurements of the forces between (001) crystal basal planes of mica and (001) planes of ZnO show that the forces have strong relationship to pH, IS, and crystal orientation.

Electrochemical device attracts lots of interests due to its broad applications in energy storage and conversions. In situ characterization is crucially important to understand the electrode-electrolyte interfaces of electrochemical devices for improving the performance of devices. However, this is a complex problem that spans orders of magnitude in length and time scale which needs multimodal microscopy and spectroscopy platforms. Thus, we developed a novel multimodal approach to examine the same sample region cross different platforms. The electrochemical liquid cell plays an important role as a cross platform for the study of the same sample region without exposure to air. Thus the original nature of the sample can be preserved without future sample preparation and processing.
Here, we show an example of using this novel multimodal approach to study the Mg electrochemical deposition by examining the same sample area in-situ using liquid cell transmission electron microscopy (TEM), scanning transmission X-ray microscopy (STXM) and X-ray absorption spectroscopy (XAS). Magnesium Aluminum Chloride Complex (MACC) was synthesized and utilized as the electrolyte, where non-reversible features during discharge-charge cycles were observed. During discharge, a uniform Mg film was deposited on the electrode, which is consistent with the intrinsic non-dendritic nature of Mg deposition in Mg ion batteries. The Mg thin film was not dissolvable during the following charge process. We found that such Mg thin film from electrochemical deposition is organometallic Mg compounds as identified by in-situ STXM and XAS. This study provides insights on the non-reversibility issue of Mg ion batteries.

The recent discovery of hexagonal-close-packed (hcp) Au nanoparticles, crystallized at the tips of Ge nanowires following vapor-liquid-solid (VLS) growth, prompts interest in the mechanism of metastable phase formation in the Au catalyst. The equilibrium structure of Au is face-centered cubic, and observation of hexagonal close-packing in Au is very rare. Here we report on eutectic melting of Au nanocatalysts in the transmission electron microscope (TEM), followed by rapid quenching, and subsequent in situ annealing at intermediate temperatures. A metastable hexagonal Au-Ge alloy phase solidifies during quenching of the Au-Ge liquid in the TEM, and it is a likely precursor to formation of metastable hcp Au during nanowire post-VLS cooling. A novel aspect of the hcp Au phase formation is the rejection of quenched-in Ge from the alloy during low-temperature in situ TEM annealing, while maintaining the metastable hcp crystal structure, indicating that this is the likely pathway for hcp Au formation following nanowire growth. The kinetics of metastable phase formation are discussed in relation to the unique characteristics of VLS nanowire growth: Ge supersaturation during growth, and undercooling of the nanoscale Au-Ge liquid catalyst prior to its crystallization at the end of growth.

Nanostructured carbon materials are predicted to play a major role in future electronic applications. Cheaper and smaller components with improved or new functionality and lower power consumption are necessary, where conventional materials reach their limitations. Devices based on layered carbon materials, such as graphene or multilayer graphene, open for a giant technological leap in electro and optical performance. A cheap way to synthesize such materials on a large scale is chemical vapor deposition (CVD) growth on catalyst films like copper or nickel. However, the growth processes and the control of these is still not completely understood.
We present in situ transmission electron microscopy (TEM) experiments in a FEI Titan 80-300 Environmental TEM (ETEM) for studying the growth of layered carbon materials on these catalysts. The ETEM allows imaging with controlled gas environments around the sample up to a few mbar. In combination with a MEMS-based heating holder, growth of layered carbon materials is systematically studied at the atomic level.
NiO particles in the size range up to a few hundred nm are used as model material for the large-scale growth, as they provide a small surface curvature and mimic the native oxidized Ni surface found in conventional Ni thin films. The particles are reduced in the microscope under H₂ at 500-600°C in order to form a catalytically active Ni surface. Introducing carbon precursor gas at elevated temperature leads to growth of layered carbon. By following the appearance of carbon layers, the layer growth rate as well as the growth rate of individual graphene layers on the Ni surface can be determined directly from the ETEM observations.
These results add to a better understand the growth mechanism and help to control and optimize the formation process.

In this study we investigate how subtle changes in medium-range order (MRO) in diffraction-amorphous Cu_xZr_1-x alloys alter their crystallization kinetics. CuZr metallic glasses (MG) have gathered much attention due to their unique mechanical properties. It is known that although lacking long-range order, CuZr MG possesses ordered regions in the 1 - 3 nm length scale, or MRO, which correspond to the near-critical nuclei size as predicted by classic nucleation theory. We will explore and correlate changes in MRO to dynamic TEM (DTEM) measurements of crystallization kinetics. It provides insights to the fundamentals of the crystallization process, which serves a broader interest beyond this particular material system.
We sputter deposit ~30 nm of Cu_xZr_1-x thin film MG (x = 32% - 80 %) in a high vacuum chamber by varying the sputtering power during co-deposition. We then measure the crystallization speed in-situ during pulsed laser annealing using the DTEM at Lawrence Livermore National Laboratory. The DTEM provides a 9-frame movie during the crystallization process with both nanosecond temporal and nanometer spatial resolution. The crystallization pathways of this family of MG materials have been shown to change significantly across the compositional range. We hypothesize that the changes are due to a composition-induced variation of MRO, which we measure using fluctuation electron microscopy (FEM) on a Zeiss Libra TEM at the National Center for Electron Microscopy. FEM is a statistical microscopy technique with the ability to measure nanoscale order in amorphous materials.
This work performed under the auspices of the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under FWP SCW0974 by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344

The power of in situ transmission electron microscopy (TEM) arises from its ability to see directly the changes in a sample when a stimulus is applied. For example, in situ TEM studies of growth often involve flowing a reactive gas over a heated substrate, measuring the kinetics and structure of the growing material as a function of temperature or gas composition and flow. But a key frontier of in situ TEM is the simultaneous application of multiple stimuli to provide a unique probe of complex processes. In the case of growth experiments, the aim would be to apply stimuli such as electric fields, current flow or light illumination, to see how these stimuli alter growth and evaluate whether useful structures are produced. Here we discuss an in situ approach for modifying the environment during growth to examine the effects of an additional stimulus. Growth takes place on microfabricated substrates containing arrays of cantilevers. The cantilevers are made of silicon, with independent control of current flow through each to create local hotspots via resistive heating. Growth is therefore constrained within a well-defined environment on or between the cantilevers, and the local heater geometry has the additional benefit of low sample drift, even compared to membrane heaters. We illustrate the possibilities by modifying silicon nanowire growth using an electric field. By applying a voltage between adjacent cantilevers while flowing disilane gas, we can distort the AuSi catalytic liquid droplets that catalyze growth, somewhat analogous to the initial stages of formation of a Taylor cone, changing the nanowire growth direction and diameter. We show related growth and phase transformation phenomena that are also modified by field or current flow applied via the cantilever geometry, and discuss the possibilities of exploring more diverse stimuli during growth.

Graphene and other related 2D materials have recently attracted substantial research interest from academia and industry.[1] While, chemical vapour deposition (CVD) using transition metal catalysts has emerged as a preferred route for scalable and cost effective synthesis, the mechanisms underlying the growth continue to remain unclear. This has led to speculative claims in literature based on limited conclusions that post growth data allows and in-situ observations remain critically lacking.
Here, using a combination of complementary in-situ techniques such as high-pressure time and depth resolved x-ray photoelectron spectroscopy (XPS) and in-situ x-ray diffraction (XRD) at realistic CVD conditions of pressure (~0.001 - 1 mbar) and temperatures (700-1000^oC) we study the fundamental mechanisms underlying the growth of 2D materials on polycrystalline metallic catalysts during exposure to precursors (both gaseous and liquid precursors).
These techniques allow for continuous monitoring of the catalyst surface morphology, surface chemistry and bulk crystallography during the entire CVD process and allow for a detailed understanding of each stage in the CVD process. Coupled with ex-situ experiments [3,4] they allow for the development of a comprehensive growth mechanisms. [1,2].
Kidambi et al. Chem. Mat. (2014).
Kidambi et al. Nano Letters 13 (10), 4769-4778 (2013).
Kidambi et al. J. Phys.Chem. C. 116, 42, 22492-22501 (2012).

Catalytic techniques for producing atomically thin, two-dimensional (2D) materials, such as chemical vapor deposition (CVD), are widely seen as most promising for achieving the requisite level of control over structure and quality demanded by applications. Key to growth control is a detailed understanding of the underlying growth mechanisms, specifically the interactions of the precursors and growing 2D structure with the catalyst.[1] Here we investigate the formation of graphene and hexagonal boron nitride (hBN) on the surface of transition metal catalysts during CVD, using complementary in situ techniques under realistic reaction conditions. Time- and depth-resolved ambient pressure X-ray photoelectron spectroscopy provides a detailed account of the chemical evolution close to the catalyst&’s surface,[1-4] whilst in situ X-ray diffractometry/reflectometry gives complementary information on the catalyst&’s bulk structure.[3-6] Environmental scanning electron microscopy further allows 2D material formation to be spatially resolved providing information on kinetic processes. We thereby reveal key atomistic mechanisms involved in the catalytic formation of 2D materials.
For graphene, our data highlights an interdependency between the distribution of carbon close to the catalyst surface and the strength of the graphene-catalyst interaction. A strong interaction between graphene and the catalyst, as in the case of epitaxial graphene on Ni(111), causes a depletion of dissolved carbon close to the catalyst surface and prevents additional layer formation leading to a self-limiting graphene growth behavior for low exposure pressures (10^-6-10^-3 mbar). Increasing the hydrocarbon pressure further (to ~10^-1 mbar) increases the concentration of dissolved carbon near the catalyst surface leading to a weakening of the graphene-catalyst interaction accompanied by additional graphene layer formation[1]. For hBN, the situation is inherently more complex as two elements are now supplied to feed the growth. By developing a detailed understanding of element-specific feeding mechanisms for various catalyst systems, we demonstrate the growth of continuous, monolayer hBN films as well as large hBN single crystals with lateral dimensions of 0.3 mm.[6] We relate our results for both graphene and hBN to a general kinetic growth model that we have established,[7] and use them to consistently explain previous results in the literature. We discuss the implications of these observations in the context of controlled growth of 2D materials and the CVD of 2D heterostructures.
(1) Weatherup et al. J. Am. Chem. Soc. 2014, 136, 13698-13708
(2) Kidambi et al. Chem. Mater. 2014, 26, 6380-6392
(3) Weatherup et al. Nano Lett. 2013, 13, 4624-4631
(4) Weatherup et al. ChemPhysChem 2012, 13, 2544-2549
(5) Weatherup et al. Nano Lett. 2011, 11, 4154-4160
(6) Caneva et al. Nano Lett. 2015, 15, 1867-1875
(7) Weatherup et al. ACS Nano 2012, 6, 9996-10003

Metallic glasses serve as a model system to study nucleation and crystallization of solids owing to their simple metallic bonds and easily accessible slow crystallization kinetics. We have recently extended the remarkable thermoplastic formability of metallic glasses to fabricate nanoscale features [1,2]. By in situ heating size-controlled metallic glass nanorods down to ~ 5 nm in diameter inside a transmission electron microscope, we have directly investigated unusual nanoscale size effects in crystallization of metallic glasses.
We reveal that the crystallization kinetics is dramatically affected by the nanoscale dimension. We observe that the crystallization temperature exhibits interesting size-dependent crossover where it first decreases with the decreasing nanorod diameter, goes through a minimum, and rapidly increases afterward. We unveil that the underlying physics is governed by size-dependent, competing factors such as viscosity and surface-to-volume ratio. Viscosity increases with decreasing diameter of metallic glass nanorods below ~ 30 nm, supported by direct observation of slowed grain growth for small nanorods. The enhanced viscosity marks a departure from the conventional continuous description of glassy materials and points to a nanoscale confinement effect when the sample size approaches the size scale of intrinsic flow units.
Technologically, our finding provides insight into the crystallization of supercooled metallic glasses at relevant length scales. Our finding provides the necessary crystallization information to optimize processing conditions for thermoplastic forming of nanoscale metallic glasses for their stable and predictable manufacturing.
[1] G. Kumar, H. X. Tang, J. Schroers, Nanomoulding with amorphous metals, Nature 457, 868-872 (2009)
[2] Y. Liu, J. Liu, S. Sohn, Y. Li, J. J. Cha, J. Schroers, Metallic glass nanostructures of tunable shape and composition, Nature Communications 6:7043 (2015)

Complex oxides exhibit a wide range of desirable intrinsic properties and have been shown to display emergent phenomena at thin film heterointerfaces. Charge compensation, a requirement for stable heterointerfaces in polar materials, is a potential origin of novel interfacial properties. Understanding the effects of interfacial charge on growth behavior and physical properties requires the ability to synthesize materials with sub-monolayer control while characterizing them using techniques that provide atomic-level structural information in real time. This talk will describe recent in-situ X-ray studies at the Advanced Photon Source investigating the growth behavior of epitaxial polar LaGaO₃ thin films. Films were grown by 90 degree off-axis rf magnetron sputtering on the nominally charge-neutral TiO₂-terminated (001) surface of SrTiO₃. Growth by alternating deposition from two separate cation sources (La₂O₃ and Ga₂O₃) enabled precise control of film composition and termination. Both the out-of-plane lattice parameter and the oxygen octahedral tilting behavior were found to depend on film thickness and whether the film was terminated with a LaO or GaO₂ layer. The possibilities of modifying the behavior of polar oxide thin film heterostructures through precise control of film thickness and termination will be discussed.

Solids self-assembled from nanoparticles form a highly versatile class of hybrid inorganic-organic materials with organic ligand molecules interlock as spacers and provide tensile strength between inorganic cores. The ultrathin limit of such solids, nanoparticle membranes comprised of just a single layer of nanoparticles, is particularly interesting, because it exemplifies the special electronic and mechanical properties of these materials and because it can be viewed as a basic unit for building up more complex structures in a controlled layer-by-layer fashion. In this talk, I will focus on our work on understanding the self-assembly process of nanoparticle at air-water interface, and describe techniques used to form free-standing nanoparticle membranes. We show that these membranes are extremely strong, with Young&’s modulus on the order of Gigapascal, and even with only nanometer in thickness, they can vibrate like a macroscopic drumhead. In particular, we have recently discovered that molecular distribution asymmetry in these membranes ultimately influence the mechanical properties of the membrane, allowing more complex 3D superstructures to be formed.

Upon solvent evaporation, monodisperse colloidal nanocrystals undergo a phase change in which the isolated, disordered, non-interacting particles self-assemble into a highly-ordered, close-packed superlattice. While the initial and final states can be readily characterized using existing techniques, little is known about the pathway and dynamics between these two diverse states. We have chosen to study the self-assembly of lead sulfide (PbS) nanocrystals, which have a size-dependent tunable semiconductor band gap in the near-infrared region of the spectrum, making them interesting for photovoltaic and light-emitting diode applications. We used real-time in situ grazing-incidence X-ray scattering measurements to track the self-assembly of the 5.6 nm diameter, faceted PbS nanocrystals as they progress from colloid to superlattice. Our experimental apparatus consisted of a sealed chamber with X-ray transparent windows into which we flowed dry inert gas to controllably evaporate the colloidal solvent over the course of 30 minutes. During this period, we continuously monitored both the grazing-incidence small-angle X-ray scattering (GISAXS) and grazing-incidence wide-angle X-ray scattering (GIWAXS) to provide us with information about the superlattice and nanocrystal atomic lattice properties, respectively.
The nanocrystals initially assembled into a face-centered cubic (FCC) superlattice before uniaxially contracting with an exponential time decay into their final body-centered cubic (BCC) superlattice configuration. At early times in the self-assembly process, while still in the FCC phase, the nanocrystals facets became orientationally aligned relative to one another and maintained this alignment throughout the densification of the superlattice. We therefore observe two relevant time scales during the self-assembly: a fast orientational alignment of the nanocrystal facets and a slow contraction of the FCC superlattice into a BCC superlattice. As a result of the FCC to BCC transformation, the nanocrystals exhibited a transient collective tilting relative to the substrate, starting at 9.7° in the FCC and reducing to 0° in the BCC. The tilting of the nanocrystals with the superlattice contraction indicates that the interaction of the nanocrystals within the superlattice unit cell, rather than nanocrystal-substrate interactions, is the dominant driver of self-assembly. We demonstrate that this synchrotron-based X-ray scattering technique provides ample time resolution to characterize and extract the kinetic rates for the many processes occurring to form the complex final superlattice arrangement. This type information will enable more accurate modelling of self-assembly and the ability to better direct self-assembly in colloids, proteins, and polymers.

The assembly process of nanostructures from nanoparticles in solution is fundamental for “bottom-up” fabrication of functional materials and devices. The collective behaviour of these nanoparticle assemblies can give rise to new optoelectronic (1), electrochemical (2) and magnetic properties (3) different from the bulk or individual nanoparticles.
Using dynamic in situ TEM imaging (3-6) in liquids, we describe the nanoparticle-nanoparticle interaction in thin fluid layer. We extend on our recent study (7) of nanoparticle bonding to show the effect of attractive hydration and depletion forces (in the case of small molecules in solution) which arise due to a single to double layers of water molecules separating these interacting nanoparticles. Using a statistical method, we probe the strength of both short-range and long-range inter-particle interactions and empirically derive the nanoparticle-nanoparticle interaction potential.
Furthermore, we will show that interaction of nanoparticles with liquid-liquid interfaces in the case of phase separated surfactant in solution can be used for self-assembly. Our observation of the assembly dynamics of nanoparticles at fluid-fluid interface around the dispersed fluid-like surfactant (ethylenediaminetetraacetic acid (EDTA)) nanodroplets in solution reveal that particles bind to interface irreversibly until the interface is fully populated. We find that nanoparticles assemble into rings around phase separated dispersed nanodroplets via capillary force in solution through: (i) direct attachment to the fluid-fluid interface, (ii) insertion of new nanoparticles between interface-bound nanoparticles, and (iii) coalescence of assemblies.
Our findings show that the effect of intermolecular, hydration and capillary forces on assembly is few of many interactions that need to be understood for assembly of hierarchical nanostructures from nanoparticles serving as individual building blocks.
References
[1] K. L. Kelly, E. Coronado, L. L. Zhao, G. C. Schatz, The Journal of Physical Chemistry B 107 (2002), p. 668.
[2] Y. Yamada et al., Nature Chemistry 3 (2011), p. 372.
[3] G. Singh et al., Self-assembly of magnetite nanocubes into helical superstructures. Science 345 (2014), p. 1149.
[4] M. J. Williamson, R. M. Tromp, P. M. Vereecken, R. Hull, F. M. Ross, Nature Materials 2 (2003), p. 532.
[5] H. Zheng, R. Smith, Y. Jun, C. Kisielowski, U. Dahmen, A. P. Alavisatos, Science 324 (2009), p. 1309.
[6] U. Mirsaidov, H. Zheng, D. Bhattacharya, Y. Casana, P. Matsudaira, Proc. Natl. Acad. Sci. U.S.A. 109 (2012), p. 7187.
[7] Z. Aabdin, J. Lu, X. Zhu, U. Anand, D. Loh, H. Su, U. Mirsaidov, Nano Letters 14 (2014), p. 6639.

Directed assembly of nanoparticles using flow driven assembly techniques such as convective and capillary based assembly has been shown to be an effective approach to create functional structures with unique properties. However, in these assembly approaches, the processes are largely governed by the evaporation of water at the three-phase contact line and the assembly takes places only at the localized regions on surfaces. Therefore, scalability of these processes over large areas in a very short time is a major challenge. Here, we developed an entirely new assembly technique called interfacial convective assembly, which is driven by the displacement of a low surface tension solvent with water based colloidal solution. The assembly simultanaously takes place everywhere on the surface rather than the localized regions at the three-phase contact line. Therefore, this method enables assembly of various types of nanoparticles over centimeter square area in a few minutes, which is at least 10 times faster than convective assembly techniques. In order to understand the assembly mechanism, we examined the trajectory of particles in-situ under an inverted fluorescence microscope. During the assembly, we observed a turnover between the solvent and the water due to i) the surface tension difference between the solvent and water ii) faster evaporation rate of the solvent than water and iii) the difference in specific gravities. We observed that the evaporation of the solvent in the patterned surface is much slower than the evaporation outside the patterns. When the solvent inside the patterned surfaces completely evaporates, the particles migrate into the patterns. In-situ studies also revealed that Brownian force becomes very effective for the assembly of smaller size particles, which results in longer assembly times. This can be overcome by increasing temperature of the solvent to enhance the evaporation. Control of process parameters led to the well-organized nanoparticles in remarkably complex shapes.

Colloidal nanocrystals (NCs) can self-assemble at a liquid/air interface into new 2-dimensional materials of which the properties depend on the building block material as well as on the geometry into which they self-assemble [1]. Of particular interest is the challenge of using the shape of the NC building blocks to program the final geometry of the superstructure. The precise geometry can be important for the electrical transport properties of the material, or the directionality and polarization of emitted light.
We have recently found that the geometry of the superstructure formed by ZnS NCs with a bipyramidal shape can be tuned by the extent to which the tips are truncated [2]. Both the supercrystal symmetry and the orientation of the atomic lattice planes can be influenced, thus enabling full control over the geometry of the superstructure. Monte Carlo simulations have predicted that a two-step mechanism underlies this self-assembly process: (1) The NCs adsorb at the liquid/air interface in an orientation that depends on the extent of truncation. (2) When the surface density of NCs becomes sufficiently high, they form a close-packed superstructure of which the symmetry depends again on the degree of truncation.
We used a combination of in-situ time-resolved grazing incidence small angle X-ray scattering (GISAXS) and grazing incidence diffraction (GID) to selectively probe the liquid/air interface at nanometer and atomic scales. We found that the nanocrystals already at early stages form a hexagonal packed structure, which becomes close-packed over time. Furthermore, we have been able to probe to atomic orientation at the liquid/air interface and find that the addition of ligands induces atomic orientation. Our results give valuable insights in the driving forces and dynamics behind anisotropic nanocrystal close-packing at liquid/air interfaces.
[1] Vanmaekelbergh, D. Nano Today, 2011, 6, 419-437.
[2] van der Stam, W.; Gantapara, A. P.; Akkerman, Q. A.; Soligno, G.; Meeldijk, J. D.; van Roij, R.; Dijkstra, M.; de Mello Donega, C. Nano Lett., 2014, 14, 1032-1037.

The solution-phase assembly of nanocrystals (NCs) into ordered superstructures has attracted significant interest since the resulting mesoscale objects promise access to a wide range of tunable photonic, plasmonic, electronic, magnetic, and catalytic functionalities. Liquid environments that allow unrestricted diffusion and interaction of NCs are key to such assembly processes, but they also complicate the experimental investigation of the mechanisms by which ordered structures are formed. Liquid-cell transmission electron microscopy is the only technique that allows direct imaging of nanometer-scale processes in liquids, and has successfully been applied to imaging colloidal synthesis (nanoparticles, nanorods, core-shell structures^{1, 2}), electrochemistry (galvanic replacement reactions,³ electrodeposition, fuel cells), biological systems, etc.
Here we use liquid cell scanning TEM (STEM) to observe branched, octapod-shaped CdS/CdSe NCs in toluene, and to follow their self-assembly into interlocked linear chains in solution. By analyzing real-time image series we establish key characteristics of the assembly process such as the nucleation of the interlocked segments and their further growth into long 1D octapod chains. We find that that the smallest stable unit of interlocked octapods is the trimer. Surprisingly, long-chain growth does not involve the incorporation of individual octapods, even though monomers are abundant in the liquid cell and show extensive Brownian motion. Instead, the stable nucleus grows primarily by attachment to other supercritical units, all of which are mobile in solution. We propose a model for the physical origin of the striking suppression of dimers and the prevalence of trimers as the shortest chain of interlocked octapods in solution observed in our experiments. We also find relatively loose stacking of the octapods in solution, which explains several characteristics important to the growth of the octapod assemblies, such as the observed facile addition and removal of chain segments and the bending of chains in tight radii, which we find crucial to capturing and incorporating segments in the later growth stages of the 1D assemblies. We expect that by providing similar insight into the self-assembly of a wide range of nanoscale objects, liquid-cell electron microscopy can substantially advance our understanding of a broad range of self-assembly processes in solution.
1. Jungjohann, K. L.; Bliznakov, S.; Sutter, P. W.; Stach, E. A.; Sutter, E. A. Nano Letters 2013, 13, (6), 2964-2970.
2. Sutter, E. A.; Sutter, P. W. Journal of the American Chemical Society 2014, 136, 16865-16870.
3. Sutter, E.; Jungjohann, K.; Bliznakov, S.; Courty, A.; Maisonhaute, E.; Tenney, S.; Sutter, P. Nature Communications 2014, 5, 4946-4954.

Nanostructure fabrication via block copolymer (BCP) phase separation has demonstrated huge potential for electronics and data storage applications. Several studies focus on domain size control and generating long-range order over the size of several microns scale. However, from an industrial point of view, process robustness and processing time are also important. Recently, solvent immersion annealing^[1] has been demonstrated to be a promising process for ordering BCP films. Immersion annealing bypasses several barriers involved in conventional solvent vapor annealing and thermal annealing such as complicated setups and longer annealing-time duration. The solvent mixture used in immersion annealing is composed of a non-solvent which prevents dissolution of films and a good-solvent which plasticizes the films. Using appropriate solvent mixture, we can fine tune domain spacing and reduce annealing time from several hours to few minutes. Ex-situ neutron reflectivity (NR) studies on symmetric dPS-PMMA have suggested that the solvent mixture combinations we developed for BCP immersion annealing, cause a significant reduction (~ 50%) in domain size, compared to thermal annealing process. This highlights an obvious advantage since we can tune BCP domain spacing via proper solvent mixture combination without altering polymer chemistry. In-situ NR kinetic studies of immersion induced ordering of as-cast dPS-b-PMMA films demonstrated that phase separation via immersion annealing is significantly faster than thermal annealing. Also, in-situ kinetic studies on immersion annealing of (thermally) pre-ordered polymer film demonstrated that a longer time is required to achieve swollen ordered state compared to film swollen from quench-disordered state. However, irrespective of initial state of BCP films, final morphology obtained via immersion annealing remains the same. Further, above mentioned studies also unveil the mechanism of ordering and re-ordering of BCP films subjected to immersion annealing.
[1] Park, W. I.; Kim, J. M.; Jeong, J. W.; Jung, Y. S. ACS Nano2014, 8, 10009-10018

The formation and assembly of ultrasmall nanoparticles (UNPs, ~ 3 nm) are investigated as key “building blocks” in the formation of 2D and 3D-nanostructures by pulsed laser deposition (PLD). Pulsed laser ablation of targets into low-pressure background gases is first studied to understand the production of stoichiometric, metastable, amorphous UNPs that can crystallize and transform as tunable building blocks for the catalyst-free formation of larger nanostructures and films with metastable phases, depending on their size and arrival rate - addressing a longstanding mystery in PLD. Using in situ time-resolved optical imaging and spectroscopic diagnostics (ICCD imaging, ion probe, LIF) and ex situ advanced electron microscopy (SEM, TEM, atomic-resolution Z-contrast scanning TEM, nano-beam electron diffraction (NBED), EELS) we characterize both the plume conditions and “amorphous” UNPs produced and collected on room-temperature substrates, and their transformations to crystalline phases upon post annealing. We concentrate on TiO_2, a workhorse wide-bandgap semiconductor, and the conditions for the deposition of pure UNPs that form hyperbranched 3D mesoporous architectures at room temperature. First, phase transformations induced by annealing the loosely-assembled UNPs are studied using in situ Raman microscopy and in situ annealing within a TEM. Evidence for oriented attachment and templating of UNPs to grow crystals along preferred growth orientations is examined. Next, the dynamic integration of the UNPs during PLD at high substrate temperatures is studied. With increasing substrate temperature the UNPs become integrated into nanowires, nanosheets, or vertically-oriented crystalline nanorods, sometimes with unusual metastable phases (e.g., TiO₂(B), and “black TiO₂”). Theory and simulation, along with NBED and EELS data indicate that the evolution of a particular crystalline phase and preferred growth orientation is linked to the elimination of defects and ordering of TiO₆ octahedral units made possible by the metastable nature of the “amorphous” nanoparticle “building blocks”.
We also show that the conversion of stoichiometric, amorphous ultrasmall nanoparticles into crystalline nanostructures during PLD is not restricted to oxides, and has been demonstrated for the growth of two-dimensional metal chalcogenides (e.g., GaSe, MoSe₂).
Research sponsored by the U.S. Dept. of Energy, Office of Science, Basic Energy Sciences, Materials Science and Engineering Div. (synthesis science) and Scientific User Facilities Div. (characterization science).

Controlled self-assembly of Block Copolymer (BCP) thin films along with large-scale macroscopic alignment is essential to realize the potential of BCP systems in next-generation applications such as nanoelectronics. Particularly, fabrication of long-range ordered, high aspect ratio vertically oriented nanodomains of cylinder forming BCPs are attractive for photonics, membranes and nano-arrays. Towards these ends, we have recently developed a dynamic thermal-gradient based directed self-assembly method termed Cold Zone Annealing-Sharp (CZA-S) for processing BCP films on rigid as well as flexible substrates. In this technique, BCP films (up to 1 mm thick) are linearly translated over a sharp thermal gradient produced by a cold block-hot wire-cold block setup. The thermal gradient induces a strain gradient over the hot zone which leads to large-scale re-organization of the chains, giving >95% of vertical cylinder orientation with optimum processing conditions. To advance the understanding and exploit the full potential of this CZA-S process towards BCP-based device fabrication, it is imperative to understand the molecular-scale mechanism and kinetics of ordering during the process. To achieve that, we use Grazing Incidence Small Angle X-ray Scattering (GISAXS) at synchrotron source and probe the BCP film in-situ as it undergoes the CZA-S process. An X-ray beam is impinged on the sample while it is translated over a custom-built CZA-S set-up, such that the X-ray footprint probes the moving sample across the gradient. The GISAXS images are analyzed to obtain a time-temperature based grid of morphology versus processing parameters and a mechanism of BCP ordering is proposed. This work provides insights in to the molecular level ordering of BCP thin films under a dynamic thermal gradient field using in-situ GISAXS.

Magnetotactic bacteria biomineralize ordered chains of nearly perfect magnetic crystals (magnetosomes) and serve as an inspiration and source of a number of proteins used for the biomimetic synthesis of magnetic nanomaterials ¹. Using in situ fluid cell Scanning Transmission Electron Microscopy (STEM), we have imaged the process at nanometer resolution as it occurs in liquid ². Bacterial protein Mms6 first self-assembles into micelles, which become visible after binding iron from FeCl₃ in the solution. Upon addition of NaOH, a dense liquid precursor forms on the micelle. When more NaOH is added, the goo-like layer condenses to give birth to tiny iron oxide nanoparticles. In confining the nucleation to its surface, Mms6 suppresses undesired random particle formation elsewhere in the solution ². Recently, we extended the in situ analysis to probing the mechanism of bacterial magnetosome biomineralization. We used a correlative scanning transmission electron microscopy (STEM) and fluorescence microscopy to image viable magnetotactic bacteria in their native environment and worked to determine radiation damage thresholds and bacterial cell damage mechanisms in the fluid cell STEM ³. The post-STEM fluorescence imaging confirms presence of viable bacterial cells ³. This is the first step toward in vivo studies of magnetite biomineralization in magnetotactic bacteria. Understanding the steps of the crystal formation , both in vivo and in vitro, will allow mimicking Nature&’s own technology and develop better synthetic nanomaterials.
(1) Prozorov, T.; Bazylinski, D. A.; Mallapragada, S. K.; Prozorov, R. Mater. Sci. Eng. R 2013, 74, 133.
(2) Kashyap, S.; Woehl, T. J.; Liu, X.; Mallapragada, S. K.; Prozorov, T. ACS Nano2014, 8, 9097.
(3) Woehl, T. J.; Kashyap, S.; Firlar, E.; Perez-Gonzalez, T.; Faivre, D.; Trubitsyn, D.; Bazylinski, D. A.;
Prozorov, T. Sci. Rep.2014, 4, 6854.

The electronic properties of nanocrystals depend not only on their chemical composition, but also on their size and shape. By choosing the reaction conditions and chemicals used in the synthesis, different sizes and shapes are obtained, ranging from 0-dimensional quantum dots to 1-dimensional nanorods and 2-dimensional (2D) nanosheets. Ultrathin 2D nanosheets (NSs) possess extraordinary properties that are attractive for both fundamental studies and technological devices. Colloidal 2D nanosheets have been successfully prepared in a variety of compositions, but the understanding of their growth mechanism is, however, underdeveloped.
Recently, we have demonstrated that the shape of Cu_2-xS nanoparticles formed when dodecanethiol decomposes in the presence of a Cu-salt, changes from spherical nanocrystals to ultrathin 2D nanosheets when halides are added [1]. The tentative model proposed in ref [1] assumed that halides stabilize lamellar Cu-thiolate complexes at temperatures sufficiently high to allow the formation of monomers for nucleation and growth by thermolysis of the C-S bond. Therefore, nucleation and growth is only allowed within the 2D constraints of the halide stabilized template. Although plausible, this mechanism has not yet been supported by direct experimental evidence, which can only be obtained with in-situ X-ray measurements. In this work, Small-Angle X-ray Scattering (SAXS) was used to probe the structure of the Cu-thiolate precursor with and without halides, while Wide-Angle X-ray Scattering (WAXS) yielded information on the crystallinity of the product Cu_2-xS NCs.
We found that Cu_2-xS is a very robust system to study with in-situ x-ray scattering. The desired nanocrystal geometries are obtained in a capillary, despite the difficulties to exactly reproduce the reaction conditions of the lab. By following the precursors and the formation of the NCs simultaneously, we have been able to verify the mechanism proposed in ref [1] with temporal-resolution. Therefore, our results give meaningful insights in the formation of 2-dimensional nanosheets of binary semiconductors.
[1] van der Stam, W. et al.,Chem. Mater.27, 283minus;291 (2015)

Developing advanced materials for rechargeable batteries is one of the most pressing tasks in energy storage research. In order to reach desired high performance and long life time of batteries, together with high safety standard, researchers have paid much effort to optimize and balance various competing factors of the active materials at the electronic, atomic and molecular level, even extended to engineering scale. Fundamental materials exploration is critical to achieve the next generation battery technology. We have combined the synchrotron x-ray diffraction and absorption spectroscopy techniques to in-situ probe the electronic state evolution and crystal structure transformation of active cathode materials during synthesis as well as electrochemical performance. We have also developed model-free methodologies to computationally analyze large volume in-situ experimental data. In this talk, we will present our recent results in this area.

In contrast to synchrotron X-ray powder diffraction techniques, neutron powder diffraction methods have been rarely utilized for in situ studies due to the larger samples volumes and longer counting times that are traditionally required to obtain good counting statistics. Neutron diffraction measurements have the benefit of enhanced sensitivity to many key light elements (such as lithium and oxygen), as well as more favorable atomic form factors that allow useful diffraction data to be collected out to very low d-spacing values, aiding in accurate structure determination. We have taken advantage of improvements in both neutron sources and experimental design in order to for the first time follow in situ the process of Li/Na ion exchange in a solid state electrolyte, allowing us to study the reaction by which a novel metastable Li-ion solid state electrolyte is prepared. Excellent data sets suitable for full Rietveld refinement could be collected with 15 minute time steps for modest samples sizes (~500 mg), even at elevated reaction temperatures (~300 Celsius). Although the smooth evolution of lattice parameters during Na/Li ion exchange suggests that phase formation occurs through a continuous solid solution pathway, a close inspection of site occupancies and bond lengths obtained through full structural refinements indicates that the transformation occurs in two distinct steps. Furthermore, it can be seen that the replacement of Na by Li results in a local volume reduction at one cation site but in an unexpected volume expansion at another cation site. These results clearly demonstrate the value of neutron experiments in mechanistic studies of energy storage materials.

For the large-scale application of lithium-ion batteries in electric vehicles and grid-scale storage, it is desirable to develop cost-efficient methods for synthesizing electrode materials. The low temperature, soft chemistry method, such as solvothermal, is inexpensive and flexible for synthesizing battery materials. However there are a variety of synthesis parameters (temperature, pressure, reaction time, precursor concentration, pH value) that can have a strong influence on the material properties (structure, morphology, and stoichiometry) and electrochemical performance. As synthesis is generally carried out in a sealed reactor, like a black box where the inputs and outputs are known, little is known about the intermediate phases and the overall reaction pathway. Very often the synthesis condition is far from thermodynamic equilibrium, implying that the reactions and induced phase transformations very often proceed along a kinetics-controlled pathway, which excludes the feasibility of following synthesis reactions using ex-situ methods. In-situ, real time probing of structural and chemical evolution under real conditions provides direct information of the reactions during synthesis, elucidating intermediates, and detailing how temperature, pressure, time, and precursor concentration affect the kinetic reaction pathway. The results of such studies will enable strategies to optimize synthesis, opening a new avenue for synthetic control of the phases and material properties. The study will also deepen our understandings on the synthetic reaction mechanism and helps in rational design of new materials. In this presentation, we will show the development and application of in situ techniques for solvothermal synthesis of phosphates-based high-energy cathodes; specific examples will also be given on design and synthesis of new battery materials through in-situ studies[1,2].
[1] “Solvothermal Synthesis of LiMn_1-xFe_xPO₄ Cathode Materials: A Study of Reaction Mechanisms by Time-Resolved in Situ Synchrotron X-ray Diffraction” J Bai, J Hong, H Chen, J Graetz, F Wang, J Phys. Chem. C 119 (2015) 2266;
[2] “Structure Tracking Aided Design and Synthesis of Li₃V₂(PO₄)₃ Nanocrystals as High-Power Cathodes for Lithium Ion Batteries”, L. Wang, J. Bai. P. Gao, X. Wang, J.P. Looney, F. Wang (submitted).
The work was supported by DOE-EERE under the Advanced Battery Materials Research (BMR) program, under Contract No. DE-SC0012704.

Fe and Fe-oxide nanoparticles have a series of promising potential applications in physical and medical sciences. These include magnetic storage devices, catalysis, sensing, contrast enhancement in magnetic resonance imaging and magnetic hyperthermia [1-3].
Understanding of the Fe-Oxide NPs reduction to metal and the oxidation processes down to atomic scale is paramount for the control of the quality and the optimization of their applications.
A recently modified double aberration corrected JEOL 2200FS (S)TEM [4] has demonstrated the possibility of the analysis of metallic nanoparticles in gas environment at temperature allowing single atom visualisation by HAADF STEM in controlled gas reaction environment [5].
In this study, thin films of were deposited by sputtering on C films supported by standard TEM Cu grids. Nanoparticles were produced by annealing in-vacuum within the microscope column pre-sputtered iron thin films.
Nanoparticle formation and size distribution was monitored in-situ as a function of time and temperature by HAADF STEM imaging. After annealing nanoparticles were shown to consist of single crystal metallic Fe, composition confirmed by EDX analysis.
The Fe nanoparticle samples interaction with Hydrogen and Oxygen gases were studied in-situ at 300 °C with a differential pressure at the specimen in the range of 2.5-3.0 Pa. The interaction of the nanoparticles with the gases, as well as the substrate, will be discussed in terms of the changes in nanoparticle geometry, composition, size distribution, crystallinity and microstructural defects.
References:
[1] B D Terris and T Thomson, J. Phys. D 38, R199-R222 (2005)
[2] H. Galvis et al. Science 335, 835-838 (2012)
[3] Q A Pankhurst, N T K Thanh, S K Jones, and J Dobson, J. Phys. D 42, 224001 (2009)
[4] P L Gai and E D Boyes, Microscopy Research and Technique 72, 153 (2009)
[5] E D Boyes, M R Ward, L Lari, and P L Gai, Annalen der Physik 525, 423 (2013)
Acknowledgement: We thank the EPSRC (UK) for research grant EP/J018058/1

The overview presents two case studies - physical vapour deposited nanocrystalline CuCr alloys and severely wire drawn pearlitic steel - involving in situ TEM/STEM, x-ray diffraction methods, and atom probe tomography. Both materials exhibit very high strength, but are far from thermodynamic equilibrium. The CuCr alloy films were investigated with respect to their crystal structure, grain size, chemical supersaturation of the phases, their thermal stability and mechanical properties. The studies revealed that a body-centered cubic crystal structure can be achieved for upto ~70at%Cu, although the equilibrium solubility is significantly less than 1at%Cu. The nanocrystalline grain size helps to accommodate the supersaturation as revealed by in situ TEM/STEM studies and retards grain growth. Even more complex is the microstructure evolution of severely deformed pearlitic steel, which consists initially of a lamellar α-Fe (ferrite) / Fe₃C (cementite) microstructure. Wire drawing of pearlitic steel leads to fragmentation and decomposition of the Fe₃C phase during severe deformation. We were recently able to show for the first time that the carbon supersaturation of α-Fe due to the decomposition of cementite is indeed a body centred tetragonal (bct) martensite. This is surprising, as martensite is believed to form only by rapid quenching of steel from the high temperature austenite field. Therefore, we propose that cold drawing can induce a martensitic transformation.

Strain-engineering offers attractive possibilities for understanding and tuning the properties of semiconductors. If the band structure is changed due to strain, many material properties will be altered, including bandgap, effective mass, carrier mobility and dopant diffusivity. Recently, strain-dependent properties of semiconductor nanostructures have attracted research interest because these materials may be used as building blocks in next generation electronic devices. Especially, semiconductor nanowires (NWs) are found to be more flexible than their bulk counterparts because of their large surface-volume ratio. Thus, strain-engineering may play a significant role in tuning the material properties of these nanostructures and will lead to the discovery of some novel properties of these materials.
In this work, we have studied the electric transport property of individual InAs NWs under externally applied mechanical strain in transmission electron microscope (TEM) using an in situ TEM holder. The NWs were grown on Si substrates by molecular beam epitaxy and catalyzed by Au nanoparticles. The diameter of the NWs is around 50 nm and the length of them is around 10 µm.
In situ TEM study shows that the resistance of the InAs NW increases gradually when the NW is bent while the I-V curves remain linear at different strain levels. As the strain is released, the NWs recover their original shape and the I-V curves coincide with the ones obtained without any force applied on the NW in the initial state. The mechanism of this phenomenon can be related to the modification of the band structure of the InAs NWs due to a change in lattice structure resulting from the mechanical strain. The effect of defect generation on the transport properties will also be discussed based on measurements carried out after plastic deformation of NWs.

The recent developments in in situ Transmission Electron Microscopy (TEM) such as nano-indentation holders offer the possibility to perform quantitative measurements (load, displacement) on nanometer or sub-micron scale specimen. This is also the scale at which specific mechanisms are supposed to occur. Before these expensive options, other ways existed to gain insight about such deformation mechanisms. Here, we will show that dynamic observations of various processes such as dislocation multiplication, grain boundary rotation and grain boundary migration may directly provide quantitative information such as activation energy, activation volume, coupling factor,hellip;. about the mechanism at play, without the help of sensors. In the case of shear coupling grain boundary migration, the outcome of in situ TEM experiments can be related to atomic simulations performed under the Nudge-Elastic Band method.

Through in situ atomic scale mechanical microscopy, the long-standing uncertainties of atomic-scale plastic deformation mechanisms in NC materials (grain size G larger and less than 10 nm) were studied and clarified. The crossover plasticity transition from full dislocations to partial dislocations and twins was discovered as the diameter of the grain size of polycrystalline Pt decreased. For larger grains with G > ~ 10 nm, the movements and interactions of cross-grain full dislocations were frequently observed. For G between 6 and 10 nm, stacking faults resulting from partial dislocations become more frequent. For G< ~6 nm, the plasticity mechanism transforms from a mode of cross-grain dislocation to a collective grain rotation mechanism. This grain rotation process is mediated by grain boundary (GB) dislocations with the assistance of GB diffusion and shuffling. These in situ atomic-scale images provide a direct demonstration that grain rotation through the evolution of the misorientation angle between neighbouring grains, can be quantitatively assessed by the dislocation content within the grain boundaries. In combination with the Cs-corrected sub-angstrom imaging technologies, the opportunities for experimental mechanics at the atomic scale are emerging.
X.D. Han et al., Ultramicroscopy, http://dx.doi.org/10.1016/j.ultramic.2014.11.035i
L.H. Wang et al., In situ experimental mechanics of nanomaterials at the atomic scale. NPG Asia Mater. 5 (2013) e40.
L.H. Wang et al., Grain rotation mediated by grain boundary dislocations in nanocrystalline platinum. Nat. Commun. 5, 4402 (2014).
P. Liu et al., Direct dynamic atomic mechanisms of strain-induced grain rotation in nanocrystalline, textured, columnarstructured thin gold films, Scripta Mater.64, 343(2011).
L.H. Wang et al., In situ observation of dislocation behavior in nanometer grains. Phys. Rev. Lett. 105, 135501(2010).
P. Liu et al., Screw-rotation twinning through helical movement of triple-partials. Appl. Phys. Lett. 101, 121901(2012)
L.H. Wang et al., Transmission electron microscopy observations of dislocation annihilation and storage in nanograins. Appl. Phys. Lett. 98, 051905 (2011)