Cinematographic study ofstochastic chemical events at atomic resolution.

Interface structure studies by atomic resolution electron microscopy, order–disorder phenomena and atomic diffusion in gas-phase synthesized nanocrystalline solids

Nanoscale materials show a variety of interesting physical and chemical properties. Since the properties are mostly determined by mesoscopic- and atomicscale areas of the materials, characterization of nanoscale materials at the atomic level is crucial for understanding the origin of their properties as well as for tailoring them to industrial needs. High-resolution electron microscopy (HREM) is an effective method to observe atomic structures in nanophase materials. The “structure-imaging technique,” originated by Ueda et al., and Cowley and Iijima, contributed much to the development of the method. Innovations are anticipated in (1) three-dimensional analysis of nanophase materials in real space, (2) observation of dynamic phenomena, and (3) extraction of compositional and physical information from nanometer-sized areas. Using the structure-imaging technique, one can observe directly nanometer-scale particles and defect structures such as voids and line and plane defects in crystals, including surfaces and interfaces. There were previously some limitations on the study of the dynamic process on the atomic level since images were captured on films. The recent development of high-sensitivity silicon-integrated-target-television (SIT-TV) cameras has initiated a new stage of HREM.Our time-resolved-high-resolution-electron-microscopy (TRHREM) system is composed of a 200-kV HREM (JEOL: JEM-2010) equipped with a high-sensitivity SIT-TV camera, various types of dedicated sample holders, an ultrahigh-vacuum (UHV) sample-preparation chamber, and a digital videotape recorder, as partly illustrated in Figure 5. The HREM images at 0.8–1.0-million magnification are recorded on the videotape recorder. In the U.S.-Japan TV system, one “frame image” of 1/30-s time resolution is composed of two interlaced “field images” of 1/60-s time resolution. The digital videotape recorder enables us to output the two “field images” separately from two frame memories.

Quantitative investigations of atomic processes on metal surfaces at atomic resolution

ABSTRACTIn this study, we provide a novel approach to the epitaxial integration of TiO2 with Si(100) and investigate the defect mediated ferromagnetism in TiO2 structure. Epitaxial TiO2 thin films were grown on a TiN/Si(100) epitaxial heterostructure through oxidation of TiN where a single crystalline rutile-TiO2 (r-TiO2) with a [110] out-of-plane orientation was obtained. The epitaxial relationship is determined to be TiO2(1$\bar 1$0)||TiN(100) and TiO2(110)||TiN(110). We rationalized this epitaxy using the domain matching epitaxy paradigm. First TiN is grown epitaxially on Si(100). Subsequently, TiN/Si(100) samples are oxidized to create r-TiO2/TiN/Si(100) epitaxial heterostructures. The details of the mechanism behind the oxidation of single crystalline TiN to TiO2 was investigated using atomic scale high resolution electron microscopy techniques. Defects introduced to the heterostructure during oxidation caused ferromagnetism in TiO2 thin film which is reversible and can be tuned by controlling oxygen partial pressure. The source of magnetization is correlated with the presence of oxygen vacancy leading to introduction of two localized states; hybrid and polaron among neighboring Ti atoms, and titanium vacancy providing four holes to form molecular oxygen. We present structure property correlations and its impact on the next generation solid state devices.

In principle the structure of matter at the atomic level can be revealed by utilizing the short wavelength of the high-energy beam of an electron microscope. In practice, a number of difficulties, mainly technical in nature, have previously prevented such atomic resolution bom being attained. Here we describe how atomic resolution has been realised in the electron microscope and review the potential impact of this achievement on our understanding of materials. We emphasize the role of the microscope in clarifying the nature of local irregularities in the structure, since it is these which point to an explanation of macroscopic behaviour. Specific examples are presented of the succes of this approach, drawn from a variety of disciplines. The prospects for further development of atomic resolution and its applications are also considered.

Undeniably, the characterization of solids at the atomic scale using electron beams has become a core aspect of materials sciences. In fact, current abilities of advanced electron microscopes read like a fairy tale: Why not visualize the atomic structure of nanocrystals, defects, and surfaces? No problem, it can be done at a single atom level except for the detection of hydrogen atoms. Are you interested in the chemical composition of nanomaterials at the atomic scale? Atomically resolved maps of elemental distributions can be acquired before lunch, but it takes a little longer if you want to have them in three dimensions. Interested in property–function relationships? In situ microscopy will provide the needed solutions. In any case, ‘‘seeing is believing,’’ and one can trust the recorded images of atomic structures since they provide an artifactfree view of nature’s secrets and largely make obsolete the old-fashioned art of acquiring and interpreting low magnification images that often exhibit complex diffraction contrast. Certainly, advertisements for electron microscopes read like such tales, but reality must surely be different. Not at all! It is mind-buckling that the reality of forefront electron microscopy nowadays resides in the vicinity of such dream-like capabilities because recent technological advancements have placed electron microscopy into this spot. Never before in its distinguished history was the prospect for further improvements so rich. In fact, its impact reaches beyond materials sciences and

Time-resolved FT-IR. difference spectroscopy has recently been established as a new biophysical tool for the investigation of molecular reaction mechanisms of proteins at the atomic level.1 Complementary to NMR spectroscopy and x-ray structure analysis, which provide the static protein ground state structure with atomic resolution, time-resolved FT-IR difference spectroscopy monitors the dynamics of proteins at the atomic level. Although infrared spectroscopy is a classical method of analytical and structural investigations 2, it can also provide valuable insight into the mechanisms of chemical reactions. Especially timeresolved Fourier-Transform-Infrared-difference-spectroscopy has recently proved itself as a powerful new method for studies of molecular reaction mechanisms of large proteins up to 120000 Dalton and time resolution up to nanoseconds.

A molecule is a quantum mechanical entity. "Watching motions and reactions of a molecule with our eyes" has therefore been a dream of chemists for a century. This dream has come true with the aid of the movies of atomic-resolution transmission electron microscopic (AR-TEM) molecular images through real-time observation of dynamic motions of single organic molecules (denoted hereafter as single-molecule atomic-resolution real-time (SMART) TEM imaging). Since 2007, we have reported movies of a variety of single organic molecules, organometallic molecules, and their assemblies, which are rotating, stretching, and reacting. Like movies in the theater, the atomic-resolution molecular movies provide us information on the 3-D structures of the molecules and also their time evolution. The success of the SMART-TEM imaging crucially depends on the development of "chemical fishhooks" with which fish (organic molecules) in solution can be captured on a single-walled carbon nanotube (CNT, serving as a "fishing rod"). The captured molecules are connected to a slowly vibrating CNT, and their motions are displayed on a monitor in real time. A "fishing line" connecting the fish and the rod may be a σ-bond, a van der Waals force, or other weak connections. Here, the molecule/CNT system behaves as a coupled oscillator, where the low-frequency anisotropic vibration of the CNT is transmitted to the molecules via the weak chemical connections that act as an energy filter. Interpretation of the observed motions of the molecules at atomic resolution needs us to consider the quantum mechanical nature of electrons as well as bond rotation, letting us deviate from the conventional statistical world of chemistry. What new horizons can we explore? We have so far carried out conformational studies of individual molecules, assigning anti or gauche conformations to each C-C bond in conformers that we saw. We can also determine the structures of van der Waals assemblies of organic molecules, thereby providing mechanistic insights into crystal formation-phenomena of general significance in science, engineering, and our daily life. Whereas many of the single organic molecules in a vacuum seen by SMART-TEM are sufficiently long-lived for detailed studies, molecules with low ionization potentials (<6 eV) were found to undergo chemical reactions, for example, [60]fullerene and organometallic compounds possibly via a hole catalysis mechanism, where a radical cation of CNT generated under electron irradiation catalyzes the transformation via an electron transfer mechanism. Common organic molecules whose ionization potentials are much higher (>8 eV) than that of CNT (5 eV) remain stable for a time long enough for observation at 60-120 kV acceleration voltage, as they are not oxidized by the CNT radical cation. Alternatively, the reaction may have taken place via an excited state of a molecule produced by energy transfer from CNT possessing excess energy provided by the electron beam. SMART-TEM imaging is a simple approach to the study of the structures and reactions of molecules and their assemblies and will serve as a gateway to the research and education of the science connecting the quantum mechanical world and the real world.

We review the time structure of synchrotron radiation and its use for fast time-resolved diffraction experiments in macromolecular photo-cycles using flash photolysis to initiate the reaction. The source parameters and optics for ID09 at ESRF are presented together with the phase-locked chopper and femtosecond laser. The chopper can set up a 900 Hz pulse train of 100 ps pulses from the hybrid bunch-mode and, in conjunction with a femtosecond laser, it can be used for stroboscopic data collection with both monochromatic and polychromatic beams. Single-pulse Laue data from Cutinase, a 22 kD lipolic enzyme, are presented which show that the quality of single-pulse Laue patterns is sufficient to refine the excited state(s) in a reaction pathway from a known ground state. The flash photolysis technique is discussed and an example is given for heme proteins. The radiation damage from a laser pulse in the femto and picosecond range can be reduced by triggering at a wavelength where the interaction is strong. We propose the use of microcrystals between 25–50 μm for efficient photolysis with femto and picosecond pulses. The performance of circular storage rings is compared with the predicted performance of an X-ray free electron laser (XFEL). The combination of micro beams, a gain of 105 photons per pulse and an ultrashort pulse length of 100 fs is likely to improve pulsed diffraction data very substantially. It may be used to image coherent nuclear motion at atomic resolution in ultrafast uni-molecular reactions.We review the time structure of synchrotron radiation and its use for fast time-resolved diffraction experiments in macromolecular photo-cycles using flash photolysis to initiate the reaction. The source parameters and optics for ID09 at ESRF are presented together with the phase-locked chopper and femtosecond laser. The chopper can set up a 900 Hz pulse train of 100 ps pulses from the hybrid bunch-mode and, in conjunction with a femtosecond laser, it can be used for stroboscopic data collection with both monochromatic and polychromatic beams. Single-pulse Laue data from Cutinase, a 22 kD lipolic enzyme, are presented which show that the quality of single-pulse Laue patterns is sufficient to refine the excited state(s) in a reaction pathway from a known ground state. The flash photolysis technique is discussed and an example is given for heme proteins. The radiation damage from a laser pulse in the femto and picosecond range can be reduced by triggering at a wavelength where the interaction is strong. We ...

Robust control over the carrier type is fundamental for the fabrication of nanocrystal‐based optoelectronic devices, such as the p–n homojunction, but effective incorporation of impurities in semiconductor nanocrystals and its characterization is highly challenging due to their small size. Herein, InAs nanocrystals (NCs), post‐synthetically doped with Cd, serve as a model system for successful p‐type doping of originally n‐type InAs nanocrystals, as demonstrated in field effect transistors (FETs). Advanced structural analysis, using atomic resolution electron microscopy and synchrotron X‐ray absorption fine structure spectroscopy reveal that Cd impurities reside near and on the nanocrystal surface acting as substitutional p‐dopants replacing Indium. Commensurately, Cd‐doped InAs FETs exhibit remarkable stability of their hole conduction, mobility, and hysteretic behavior over time when exposed to air, while intrinsic InAs NCs FETs are easily oxidized and their performance quickly declines. Therefore, Cd plays a dual role acting as a p‐type dopant, and also protects the nanocrystals from oxidation, as evidenced directly by X‐ray photoelectron spectroscopy measurements of air exposed samples of intrinsic and Cd‐doped InAs NCs films. This study demonstrates robust p‐type doping of InAs nanocrystals, setting the stage for implementation of such doped nanocrystal systems in printed electronic devices.

Heteroanionic materials exhibit great structural diversity with adjustable electronic, magnetic, and optical properties that provide immense opportunities for materials design. Within this material family, perovskite oxynitrides incorporate earth-abundant nitrogen with differing size, electronegativity, and charge into oxide, enabling a unique approach to tuning metal-anion covalency and energy of metal cation electronic states, thereby achieving functionality that may be inaccessible from their perovskite oxide counterparts, which have been widely studied as electrocatalysts. However, it is very challenging to directly obtain such materials due to the poor thermal stability of late transition metals coordinated with N and/or at high valence states. Herein, we introduce an effective strategy to prepare a perovskite oxynitride with a small fraction of sites substituted with Ir and adopt it as the first electrocatalyst in this material family, thereby enabling high activity and efficient utilization of precious metal content. From a series of characterization techniques, including X-ray absorption spectroscopy, atomic resolution electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction, we prove the successful incorporation of Ir into a strontium tungsten oxynitride perovskite structure and discover the formation of a unique Ir-N/O coordination structure. Benefitting from this, the material exhibits a high activity toward the hydrogen evolution reaction, which exhibits an ultralow overpotential of only 8 mV to reach 10 mA/cm2geo in 0.5 M H2SO4 and 4.5-fold enhanced mass activity compared to commercial Pt/C. This work opens a new avenue for oxynitride material synthesis as well as pursuit of a new class of high-performance electrocatalysts.

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Single crystals of the van der Waals layered $5d$ transition-metal compound ${\mathrm{Os}}_{0.55}{\mathrm{Cl}}_{2}$ were grown and characterized by x-ray diffraction, magnetization and heat-capacity measurements, and atomic resolution electron microscopy. The crystals are stable in air and easily cleaved. The structure is derived from the ${\mathrm{CdCl}}_{2}$ structure type, with triangular layers of transition metal sites coordinated by edge-sharing octahedra of Cl and separated by a van der Waals gap. On average, only 55% of the metal sites are occupied by Os, and evidence for short- and long-ranged vacancy orders is observed by diffraction and real-space imaging. Magnetization data indicate magnetocrystalline anisotropy due to spin-orbit coupling, antiferromagnetic correlations, and no sign of magnetic order or spin freezing down to 0.4 K. Heat-capacity measurements in applied magnetic fields show only a broad, field-dependent anomaly. The magnetic susceptibility and heat capacity obey power laws at low temperature and low field with exponents close to 0.5. The power law behaviors of the low-temperature heat capacity and magnetic susceptibility suggest gapless magnetic fluctuations prevent spin freezing or ordering in ${\mathrm{Os}}_{0.55}{\mathrm{Cl}}_{2}$. Divergence of the magnetic Gruneisen parameter indicates nearness to a magnetic quantum critical point. Similarities to behaviors of spin-liquid materials are noted, and in total the results suggest ${\mathrm{Os}}_{0.55}{\mathrm{Cl}}_{2}$ may be an example of a quantum spin liquid in the limit of strong chemical disorder.

Early-stage latent thermal failure of single-crystal Ni-rich layered cathode

Virtual reality (VR) viewing of experimentally determined macromolecular 3D structures, at the atomic level resolution, represents closest to reality and most accurate visualization of microscopic molecular world to date. We used NanoPro Life Science (Nanome Inc.) VR software as a currently developing platform to create graphical visualization for results of pairwise analyses of liganded and apo 3D X-ray structures of alpha/beta hydrolase fold and related proteins. Interactive, movable 3D graphs were created to identify interaction matrices between amino acid residues revealed only upon ligand binding. Analyses of both covalent and reversible, small ligand molecule binding relationships were facilitated when displayed alongside corresponding 3D X-ray structures of studied macromolecules at the atomic resolution. Owing to facile manipulation in the VR space and facilitated perception of complex graphical intermolecular relationships, revelation and understanding of intramolecular residue networks controlling macromolecular function was rapid. This was in spite of thousands of interacting points given in the each 3D graph. Application of this valuable tool to VR visualization of pairwise analysis of structurally diverse macromolecules will be discussed. 3D graphs were developed in the .pdb file format allowing for their display and investigation in practically any molecular visualization environment, as well as in the cutting edge, VR visualization of the macromolecular world. Support or Funding Information This work was supported by the CounterACT Program, National Institutes of Health Office of the Director, Grant R21 NS098998 from NINDS. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.