Reflection Electron Diffraction Research Articles

материаловЭволюция границ зерен алюминия в процессе изотермического отжига

Using an example of textured aluminum foils, the possibilities of using the reflected electron diffraction method for in situ studies of the behavior of grain boundaries during isothermal annealing have been experimentally demonstrated. It is shown that there is no homogeneity of the microstructure in space and no continuity of its change in time during grain growth. The experimentally discovered rotation of the crystal lattice near the grain boundary in the region of a thermal etching groove can have a retarding effect on the movement of the boundary.

How to induce superconductivity in epitaxial graphene via remote proximity effect through an intercalated gold layer

Graphene holds promises for exploring exotic superconductivity with Dirac-like fermions. Making graphene a superconductor at large scales is however a long-lasting challenge. A possible solution relies on epitaxially-grown graphene, using a superconducting substrate. Such substrates are scarce, and usually destroy the Dirac character of the electronic band structure. Using electron diffraction (reflection high-energy, and low-energy), scanning tunneling microscopy and spectroscopy, atomic force microscopy, angle-resolved photoemission spectroscopy, Raman spectroscopy, and density functional theory calculations, we introduce a strategy to induce superconductivity in epitaxial graphene via a remote proximity effect, from the rhenium substrate through an intercalated gold layer. Weak graphene–Au interaction, contrasting with the strong undesired graphene–Re interaction, is demonstrated by a reduced graphene corrugation, an increased distance between graphene and the underlying metal, a linear electronic dispersion and a characteristic vibrational signature, both latter features revealing also a slight p doping of graphene. We also reveal that the main shortcoming of the intercalation approach to proximity superconductivity is the creation of a high density of point defects in graphene (1014 cm−2). Finally, we demonstrate remote proximity superconductivity in graphene/Au/Re(0001), at low temperature.

Cross-Examination of Ultrafast Structural, Interfacial, and Carrier Dynamics of Supported Monolayer MoS2.

In this Letter, the ultrafast structural, interfacial, and carrier dynamics of monolayer MoS2 supported on sapphire are cross-examined by the combination of ultrafast electron diffraction (UED) and transient reflectivity techniques. The out-of-plane motions directly probed by reflection UED suggest a limited anisotropy in the atomic motions of monolayer MoS2, which is distinct from that of related materials such as graphene and WSe2. Besides thermal diffusion, the MoS2-sapphire interface exhibits structural dynamics trailing those of the overlaying MoS2 and are in stark contrast with the sapphire bulk, which is consistent with the limited thermal boundary conductance. These structural dynamics provide justification for the determination of carriers being trapped by defects in ∼600 fs and releasing energy within a few picoseconds. The rich findings attest to the strength of combining techniques with real-time optical and direct structure probes for a detailed understanding of dynamical processes in functional materials.

Electron Diffraction Study of Epitaxial Graphene Structure Grown upon SiC (0001) Thermal Destruction in Ar Atmosphere and in High Vacuum

We have studied the structure of epitaxial graphene obtained as a result of thermal desorption of the silicon carbide surface under conditions of vacuum synthesis and in Ar medium by reflection electron diffraction. As a result of the study, a significantly more uniform buffer layer coating of the SiC surface by epitaxial graphene has been found when forming in inert medium on the surface of 4H- and 6H-SiC(0001) polytypes compared with the synthesis of graphene in high vacuum. The quality of the coating has been shown to depend on the degree of perfection of the original single crystal.

Электронографическое изучение структуры эпитаксиального графена, сформированного путем термического разложения SiC(0001) в атмосфере Ar и в высоком вакууме

The structure of epitaxial graphene formed by thermal destruction of silicon carbide surface in the conditions of vacuum synthesis and in an Ar environment has been studied by reflection electron diffraction. As a result of the conducted study it is found the notably more homogeneous graphene coating of buffer layer on the SiC surface under the graphene formation on the polytypes 4H- и 6H- SiC(0001) surfaces in the inert environment as against the graphene synthesis in vacuum. The dependence of quality of the covering from degree of initial single crystal perfection is shown.

Reflected diffraction from linearly patterned surfaces

We discuss the optical analogy of reflected electron diffraction from a grating with non-uniform spacing at the nanoscale, and its relationship to another grating with uniform spacing. Two analytical approaches that offer a quantitative solution for the reflected diffraction from a grating are presented. A compact and low-cost experimental kit for demonstrating the physics behind the reflected diffraction from one-dimensional surface structures is described. As an example, the convolution theorem is used to explain the reflected diffraction from a sample consisting of two individual one-dimensional surface structures overlapping orthogonally. This study will broaden students' understanding of the physics behind diffraction.

Molecular beam epitaxy growth and optical properties of Mg3N2 films

Epitaxial Mg3N2 films with a (100) orientation have been grown by plasma-assisted molecular beam epitaxy on single crystal MgO substrates. The growth was monitored in situ by both reflection high-energy electron diffraction and optical reflectivity. The growth rate was determined from the optical reflectivity during growth. The index of refraction of Mg3N2 was measured by spectroscopic ellipsometry and found to be in good agreement with the in situ reflectivity. The optical bandgap was found to be ∼2.5 eV from transmission measurements.

Using of sonochemically prepared SbSI for electrospun nanofibers

A novel polymeric, polyacrylonitrile (PAN) nanofibers containing ferroelectric and semiconducting antimony sulfoiodide (SbSI) have been made by electrospinning. SbSI nanowires, used as the filler, have been prepared sonochemically from antimony sulphide (Sb2S3) and antimony tri-iodide (SbI3) for the first time. Nanocrystalline SbSI has been fabricated in ethanol under ultrasonic irradiation (20kHz, 565W/cm2) at 323K within 2h. The products have been characterized by using techniques such as powder X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, high-resolution transmission electron microscopy, selected area electron diffraction and optical diffuse reflection as well as transmission spectroscopy. The good quality of the nanocrystals and their dispersion in the nanofiber’s volume is important because this material is attractive for nanogenerators due to its ferroelectric and piezoelectric properties. The amplitude of the voltage pulse, generated under shock pressure of 3.0MPa, has reached 180V in the prototype PAN/SbSI piezoelectric nanogenerator. The peak output voltage of about 0.2V was measured in bending/releasing conditions with the deformation frequency of 1Hz.

Transformation of Cerium Oxide Nanoparticles from a Diesel Fuel Additive during Combustion in a Diesel Engine

Nanoscale cerium oxide is used as a diesel fuel additive to reduce particulate matter emissions and increase fuel economy, but its fate in the environment has not been established. Cerium oxide released as a result of the combustion of diesel fuel containing the additive Envirox, which utilizes suspended nanoscale cerium oxide to reduce particulate matter emissions and increase fuel economy, was captured from the exhaust stream of a diesel engine and was characterized using a combination of bulk analytical techniques and high resolution transmission electron microscopy. The combustion process induced significant changes in the size and morphology of the particles; ∼15 nm aggregates consisting of 5-7 nm faceted crystals in the fuel additive became 50-300 nm, near-spherical, single crystals in the exhaust. Electron diffraction identified the original cerium oxide particles as cerium(IV) oxide (CeO2, standard FCC structure) with no detectable quantities of Ce(III), whereas in the exhaust the ceria particles had additional electron diffraction reflections indicative of a CeO2 superstructure containing ordered oxygen vacancies. The surfactant coating present on the cerium oxide particles in the additive was lost during combustion, but in roughly 30% of the observed particles in the exhaust, a new surface coating formed, approximately 2-5 nm thick. The results of this study suggest that pristine, laboratory-produced, nanoscale cerium oxide is not a good substitute for the cerium oxide released from fuel-borne catalyst applications and that future toxicity experiments and modeling will require the use/consideration of more realistic materials.

ДЕФОРМАЦИОННЫЙ РЕЛЬЕФ – ОТРАЖЕНИЕ ВНУТРЕННИХ ПРОЦЕССОВ ПРИ ПЛАСТИЧЕСКОЙ ДЕФОРМАЦИИ МОНОКРИСТАЛЛОВ НИКЕЛЯ

In spite of the fact that the deformation relief is the case study of the scientists of physics of metals for several decades, there are a large number of issues associated with the mechanisms and the objective of its formation. Moreover, the development of the instrumental base allows carrying out the detailed experimental studies at the better than ever level. One of the most relevant issues during plastic deformation of metals is the destruction of a crystal that is caused by the formation of areas with the high allocation of deformation. Basing on the deformation relief, many researchers analyze the state of a material from the point of view of preserving the crystal integrity. This study is aimed to determine the methods of formation of structural elements of deformation relief of various types (slip traces, meso- and macrobands, and corrugated surface) and to identify the role of each type of relief in the increase and decrease of local deformation. The authors carried out the experimental study on the compressive deformation of FCC nickel single crystals of different crystallographic orientation and the further study of the deformation relief. To analyze the relief, the authors used optical microscopy, confocal laser scanning microscopy, and the reflection electron diffraction method; to process the results, the statistical and fractal analysis was used. The study determined the methods of formation of structural elements of the deformational relief (slip traces, meso- and macrobands, and corrugated surface), specified their common and distinctive features. The paper sets the objective of self-organization of traces of slip into the relief elements of a larger scale level (band of slip tracks, meso- and macrobands) and identifies the methods of self-organization of slip traces at the micro- and mesolevel.

Evolution of the structural and magnetotransport properties of magnetite films depending on the temperature of their synthesis on the SiO2/Si(001) surface

The methods of transmission and reflection electron diffraction have been used to investigate the structure of Fe3O4 films depending on the temperature of their synthesis on an Si substrate coated with an ultrathin layer of SiO2. The thus-grown polycrystalline films of magnetite had a texture, the axis of which was perpendicular to the surface of the SiO2 film. It has been revealed that, with an increase in the growth temperature, a structural rearrangement occurs which is characterized by an increase in the volume fraction of grains with the preferred (311) orientation. A study of the magnetotransport properties of the films has shown that the magnitude of their magnetoresistance increases with an increase in the temperature of their synthesis. It has been established that in the Fe3O4/SiO2/Si system with a tunneling-thin layer of SiO2 the magnetoresistance decreases as a result of the flow of an electric current through the silicon substrate.

Metallic interface in non-SrTiO3 based titanate superlattice

We report on the fabrication of all perovskite Mott insulator/band insulator YTiO3/CaTiO3 superlattices by pulsed laser deposition. The combination of in situ reflection high energy electron diffraction, X-ray diffraction, and X-ray reflectivity confirms the high quality of the films grown in a layer-by-layer mode. Electrical transport measurements reveal that a non-SrTiO3 based two-dimensional electron gas system has formed at the YTiO3/CaTiO3 interface. These studies offer another route in the pursuit of complex oxide two-dimensional electron gas systems, which allows to obtain greater insights into the exotic many-body phenomena at such interfaces.

Growth, structure, and electronic properties of nonpolar thin films on a polar substrate:Cr2O3on ZnO (0001) and ZnO (0001¯)

The growth and geometric and electronic structures of ${\mathrm{Cr}}_{2}{\mathrm{O}}_{3}$ layers on the polar ZnO surfaces were characterized to determine how polar substrates can influence the properties of nonpolar films. X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy (UPS), high resolution transmission electron microscopy (HRTEM), reflection high energy electron diffraction, low energy electron diffraction, x-ray diffraction (XRD), and x-ray reflectivity (XRR) were employed to characterize the growth mode, film quality, and interfacial electronic properties. Chromium oxide growth on ZnO $(000\overline{1})$ and $(0001)$ followed the same trends: two-dimensional growth with initial disorder followed by the formation of epitaxial ${\mathrm{Cr}}_{2}{\mathrm{O}}_{3} (0001)$. Despite the initial disorder, HRTEM and XRD/XRR measurements on thicker films revealed an abrupt interface with the ${\mathrm{Cr}}_{2}{\mathrm{O}}_{3}$ lattice extending all the way to the interface. This indicates that above a critical thickness of 10--15 $\mathrm{Cr}\ensuremath{-}{\mathrm{O}}_{3}\ensuremath{-}\mathrm{Cr}$ repeat units, the entire film reorganizes into an ordered structure. It is postulated that the oxygen remained ordered throughout the growth but that the chromium initially filled interstices randomly in the oxygen sublattice, which allowed the film to eventually grow with a well-defined epitaxial relationship with the substrate. The polar interfaces showed a small band offset that decayed with increasing film thickness, suggesting that the compensating charges at the interface may partially migrate to the film surface. No evidence of formal changes in the Cr oxidation state at the interfaces was seen. On the other hand, statistical analyses of UPS valence band spectra revealed an enhanced density of states near the valence band edge for ${\mathrm{Cr}}_{2}{\mathrm{O}}_{3}$ on ZnO $(0001)$, consistent with stabilization of the positive interface by filling surface electronic states. In contrast, no significant valence band differences were observed between bulk ${\mathrm{Cr}}_{2}{\mathrm{O}}_{3}$ and thin ${\mathrm{Cr}}_{2}{\mathrm{O}}_{3}$ layers on ZnO $(000\overline{1})$, suggesting a different charge compensation mechanism on the negative surface. The potential impact of these findings on the surface properties of chromium oxide thin films is discussed.

Расчет дифракции отраженных электронов на монокристалле

Расчет дифракции отраженных электронов на монокристалле

Complex oxide growth using simultaneous in situ reflection high-energy electron diffraction and x-ray reflectivity: When is one layer complete?

During layer-by-layer homoepitaxial growth, both the Reflection High-Energy Electron Diffraction (RHEED) intensity and the x-ray reflection intensity will oscillate, and each complete oscillation indicates the addition of one monolayer of material. However, it is well documented, but not well understood, that the phase of the RHEED oscillations varies from growth to growth and thus the maxima in the RHEED intensity oscillations do not necessarily occur at the completion of a layer. We demonstrate this by using simultaneous in situ x-ray reflectivity and RHEED to characterize layer-by-layer growth of SrTiO3. We show that we can control the RHEED oscillation phase by changing the pre-growth substrate annealing conditions, changing the RHEED oscillation phase by as much as 137°. In addition, during growth via pulsed laser deposition, the relaxation times between each laser pulse can be used to determine when a layer is complete, independent of the phase of the RHEED oscillation.

Heteroepitaxy of AIIIBV films on vicinal Si(001) substrates

GaAs films on Si substrates miscut from the (001) plane by 6° in the [110] direction are grown by molecular beam epitaxy (MBE). GaAs films are grown both on the Si surface terminated by arsenic atoms and on thin pseudomorphic GaP/Si layers. The condition of formation of the As sublayer and the first monolayer of GaP on the Si surface is defined as the GaAs film orientation (001) or \((00\bar 1)\). The processes of Si surface preparation and formation of the As sublayer and GaAs and GaP epitaxial layers are monitored by means of high-energy electron diffraction reflection (RHEED). The grown structures are investigated by methods of X-ray diffraction, atomic force microscopy (ATM), high-resolution transmission electron microscopy (HRTEM), and low-temperature luminescences. It is shown that the epitaxial film orientation affects both the surface morphology and its crystalline properties. Intense photoluminescence is obtained from the In0.17Ga0.83As quantum well structure grown on the GaAs/Si buffer layer.

Nanoscale Lamellar Monoclinic Li2MnO3 Phase with Stacking Disordering in Lithium-Rich and Oxygen-Deficient Li1.07Mn1.93O4−δ Cathode Materials

The powdered crystalline samples of nominal composition Li1.07Mn1.93O4-δ have been investigated by transmission electron microscopy (TEM) combined with X-ray powder diffraction (XRD) at room temperature. As suggested by the TEM observation, the dominant phase of the particles is a cubic spinel Li1+αMn2-αO4-δ with space group Fd3̅m. A monoclinic Li2MnO3 phase with C2/m space group was also identified. Furthermore, the occurrence of nanoscale rotational twinning domains in Li2MnO3 with 120° rotation angles, stacked along the [103]m/[111]c ("m" and "c" represent the monoclinic and cubic descriptions, respectively) axis was also observed. These nanoscale rotational twining domains are responsible for the pseudo-3-fold axis and their formation is supported by the superstructure reflections in selected-area electron-diffraction (SAED) patterns. Similar patterns were reported in the literature but may have been misinterpreted without the consideration of such domains. Consistent with the TEM observation, the XRD results reveal the increasing percentage of monoclinic Li2MnO3 with increasing annealing time, associated with more oxygen vacancies. In addition, the electron beam irradiation during TEM studies may cause the nucleation of nanoscale cubic spinel Li-Mn-O crystallites on the monoclinic Li2MnO3 grains. These results provide the detailed structural information about the Li1.07Mn1.93O4-δ samples and advance the understanding of corresponding electrochemical properties of this material as well as other layer structured cathode materials for lithium-ion batteries.

Structural-phase state of chromium-fullerite-chromium films subjected to heat treatment in vacuum

The patterns of change in the structure and the phase composition of chromium-fullerite-chromium films subjected to heat treatment in vacuum at different temperatures (470, 570, and 620 K) are studied via scanning electron and atomic force microscopies, X-ray diffraction, reflection-electron diffraction, and X-ray spectral microanalysis. It is found that sample annealing at 470 and 570 K leads to recrystallization of the fullerite and the emergence and growth of a new CrxC60 phase, accompanied by volumetric changes that generate internal mechanical stresses. During the process of stress relaxation, the film starts to crack, and lamellar crystallites of the fullerite phase start to grow. Film destruction and the growth of C60 crystallites on the surface are not observed in chromium-fullerite-chromium films annealed at 620 K.

Distribution of local deformations in diamond crystals according to the analysis of Kikuchi lines profile intensities

The histogram method has been proposed to determine strains in diamond crystals by the analysis of reflection electron diffraction bands in Kikuchi patterns. The anisotropy has been defined of the local strain distribution on the surface of two diamond samples produced by the temperature gradient method in the Fe-Al-C system and by growing on a surface of a statically synthesized diamond single crystal (Ni-Mn-C) in the Mg-C + Bor system.

Interpretation of “Anomalous” Electron Diffraction Reflections Observed in Human Tooth Enamel Grains: The Role of Shape Effect

Interpretation of “Anomalous” Electron Diffraction Reflections Observed in Human Tooth Enamel Grains: The Role of Shape Effect