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Proof of Concept for seeking collaboration to derive the speed of light 𝑐, an be derived from first principles using only directly measurable quantities, without assuming its value anywhere in the calculation chain. The methodology involves accelerating electrons in a High Voltage Electron Microscope (HVEM) across a wide energy range, measuring their velocity using an integrated time-of-flight (TOF) system, and comparing the de Broglie wavelength inferred from relativistic momentum to the wavelength derived from Bragg diffraction patterns in a gold target. The goal is to assess whether these independently obtained wavelengths agree across the relativistic regime, thereby enabling an empirical derivation of 𝑐.

An electron beam traversing a structured plasmonic field is shown to undergo diffraction with characteristic angular patterns of both elastic and inelastic outgoing electron components. In particular, a plasmonic {\it grating} (e.g., a standing wave formed by two counter-propagating plasmons in a thin film) produces diffraction orders of the same parity as the net number of exchanged plasmons. Large diffracted beam fractions are predicted to occur for realistic plasmon intensities in attainable geometries due to a combination of phase and amplitude changes locally imprinted on the passing electron wave. Our study opens new vistas in the study of multiphoton exchanges between electron beams and evanescent optical fields with unexplored effects related to the transversal component of the electron wave function.

Valence-band ultraviolet photoemission spectroscopy (UPS) at 173K and 6p core-level X-ray photoemission spectroscopy (XPS) at room temperature were performed on a high quality uranium single crystal. Significant agreement is found with first-principles electronic band-structure calculations, using a generalized gradient approximation (GGA). In addition, using Low Energy Electron Diffraction (LEED) for the (001) surface, we find a well-ordered orthorhombic crystallographic structure representative of the bulk material.

MATERIALS & STRESSES M&S BUILDING SETUPS AND EXPERIMENTS - ELECTRON DIFFRACTION APPARATUS WITH DR F COFFIN

This report describes the progress that has been made over the last years toward the generation of ultrashort electron pulses, and their application to time resolved electron diffraction. We have generated electron pulses of picosecond duration using an ultrafast laser system, tested a number of photocathode materials, built an apparatus to measure electron pulse durations in the femtosecond domain, and designed and built an electron diffractometer for time resolved electron diffraction. We demonstrated that the diffractometer, which uses a novel one dimensional detection scheme, is well capable of determining atomic distances in molecules to better than on hundredth of an Angstrom. A sophisticated noise suppression system maintains a signal to noise ratio sufficient for pump probe experiments. Further developments include the design of a reflectron electron gun for femtosecond electron pulses, and a two dimensional electron diffraction detector. Finally, significant progress has been made in the interfacing of adaptive optics to a learning algorithm, and the generation of spectrally tunable ultrashort laser pulses at 200 nm.

The award W911NF-14-1-0071 made to Delaware State University enabled the acquisition of a benchtop low-voltage Transmission Electron Microscope (TEM) with Scanning Electron Microscope (SEM) Capability: LV EM 5. The instrument acquisition supports Analysis of Inorganic Solution-Processed Flexible Solar Cells and has been used to accomplished the project objectives: 1. Support the project Novel Thin-Film Photovoltaic Technologies Using Solution Nano-Precursors to Cu2ZnSnS4, Fe2SiS4, andFe2GeS4-Based Absorber Layers, research ongoing in Dr. Daniela Radus (PI) laboratory. 2. Build strength in nanotechnology-related research and education at DSU. The project resulted in two presentations at the National American Chemical Society Meeting, March 20-24, 2015 in Denver, CO. The instrument was critical to achieve high throughput analysis of nanoparticles used in solution processed thin-films. The LV EM 5 has been used in TEM mode for nanoparticles size screening. SEM mode has been used to identify silica nanostructure morphologies and packing on a analysis stub. Three students and two faculty members have been trained and are using the instrument since installation and training sessions in November2014.

A method for automatically aligning consecutive datasets of large, two-dimensional multi-tile electron backscatter diffraction (EBSD) scans with high accuracy was developed. The method involves first locating grain and phase boundaries within search regions containing overlapping data in adjacent scan tiles, and subsequently using cross-correlation algorithms to determine the relative position of the individual scan tiles which maximizes the fraction of overlapping boundaries. Savitzky-Golay filtering in two dimensions was used to estimate the background, which was then subtracted from the cross-correlation to enhance the peak signal in samples with a high density of interfaces. The technique was demonstrated on datasets with a range of grain boundary densities. The equations were implemented as enhancements to a recently published open source code for automated stitching of multi-tile datasets.

A method for automatically aligning consecutive datasets of large, two-dimensional multi-tile electron backscatter diffraction (EBSD) scans with high accuracy was developed. The method involves first locating grain and phase boundaries within search regions containing overlapping data in adjacent scan tiles, and subsequently using cross-correlation algorithms to determine the relative position of the individual scan tiles which maximizes the fraction of overlapping boundaries. Savitzky-Golay filtering in two dimensions was used to estimate the background, which was then subtracted from the cross-correlation to enhance the peak signal in samples with a high density of interfaces. The technique was demonstrated on datasets with a range of grain boundary densities. The equations were implemented as enhancements to a recently published open source code for automated stitching of multi-tile datasets.

Surface Patterson Functions have been derived by direct inversion of experimental Low-Energy Electron Diffraction I-V spectra measured at multiple incident angles. The direct inversion is computationally simple and can be used to discriminate between different structural models. 1x1 YSi_2 epitaxial layers grown on Si(111) have been used to illustrate the analysis. We introduce a suitable R-factor for the Patterson Function to make the structural discrimination as objective as possible. From six competing models needed to complete the geometrical search, four could easily be discarded, achieving a very significant and useful reduction in the parameter space to be explored by standard dynamical LEED methods. The amount and quality of data needed for this analysis is discussed.

Surface Patterson Functions have been derived by direct inversion of experimental Low-Energy Electron Diffraction I-V spectra measured at multiple incident angles. The direct inversion is computationally simple and can be used to discriminate between different structural models. 1x1 YSi_2 epitaxial layers grown on Si(111) have been used to illustrate the analysis. We introduce a suitable R-factor for the Patterson Function to make the structural discrimination as objective as possible. From six competing models needed to complete the geometrical search, four could easily be discarded, achieving a very significant and useful reduction in the parameter space to be explored by standard dynamical LEED methods. The amount and quality of data needed for this analysis is discussed.

A Space Shuttle Reaction Control System (RCS) thruster failed during a firing test at the NASA White Sands Test Facility (WSTF), Las Cruces, New Mexico. The firing test was being conducted to investigate a previous electrical malfunction. A number of cracks were found associated with the fuel closure plate/injector assembly (Fig 1). The firing test failure generated a flight constraint to the launch of STS-133. A team comprised of several NASA centers and other research institutes was assembled to investigate and determine the root cause of the failure. The JSC Materials Evaluation Laboratory was asked to compare and characterize the outboard circumferential electron beam (EB) weld between the fuel closure plate (Titanium 6Al-4V) and the injector (Niobium C-103 alloy) of four different RCS thrusters, including the failed RCS thruster. Several metallographic challenges in grinding/polishing, and particularly in etching were encountered because of the differences in hardness, ductility, and chemical resistance between the two alloys and the bimetallic weld. Segments from each thruster were sectioned from the outboard weld. The segments were hot-compression mounted using a conductive, carbon-filled epoxy. A grinding/polishing procedure for titanium alloys was used [1]. This procedure worked well on the titanium; but a thin, disturbed layer was visible on the niobium surface by means of polarized light. Once polished, each sample was micrographed using bright field, differential interference contrast optical microscopy, and scanning electron microscopy (SEM) using a backscatter electron (BSE) detector. No typical weld anomalies were observed in any of the cross sections. However, areas of large atomic contrast were clearly visible in the weld nugget, particularly along fusion line interfaces between the titanium and the niobium. This prompted the need to better understand the chemistry and microstructure of the weld (Fig 2). Energy Dispersive X-Ray Spectroscopy (EDS) was used to confirm the chemical composition of the variations in contrast in these areas. Niobium alloys generally require exposure to more aggressive chemical reagents than titanium alloys for etching because of niobium s chemical resistance; therefore, the titanium portion of the sample was etched first. A five second immersion in Kroll s reagent revealed a general microstructure on the titanium portion of the sample; however, the titanium heat affected zone closest to the weld, was over-etched due to higher concentrations of refined grains and an increase in eta-phase. The Kroll s etchant also revealed some microstructure in the weld nugget itself; the niobium portion of the sample remained unetched.

We have been analyzing Itokawa samples in order to definitively establish the degree of shock experienced by the regolith of asteroid Itokawa, and to devise a bridge between shock determinations by standard light optical petrography, crystal structures as determined by electron and X-ray diffraction techniques. We are making measurements of olivine crystal structures and using these to elucidate critical regolith impact processes. We use electron back-scattered diffraction (EBSD) and synchrotron X-ray diffraction (SXRD). We are comparing the Itokawa samples to L and LL chondrite meteorites chosen to span the shock scale experienced by Itokawa, specifically Chainpur (LL3.4, Shock Stage 1), Semarkona (LL3.00, S2), Kilabo (LL6, S3), NWA100 (L6, S4) and Chelyabinsk (LL5, S4). In SXRD we measure the line broadening of olivine reflections as a measure of shock stage. In this presentation we concentrate on the EBSD work. We employed JSC's Supra 55 variable pressure FEG-SEM and Bruker EBSD system. We are not seeking actual strain values, but rather indirect strain-related measurements such as extent of intra-grain lattice rotation, and determining whether shock state \"standards\" (meteorite samples of accepted shock state, and appropriate small grain size) show strain measurements that may be statistically differentiated, using a sampling of particles (number and size range) typical of asteroid regoliths. Using our system we determined that a column pressure of 9 Pa and no C-coating on the sample was optimal. We varied camera exposure time and gain to optimize mapping performance, concluding that 320x240 pattern pixilation, frame averaging of 3, 15 kV, and low extractor voltage yielded an acceptable balance of hit rate (>90%), speed (11 fps) and map quality using an exposure time of 30 ms (gain 650). We found that there was no strong effect of step size on Grain Orientation Spread (GOS) and Grain Reference Orientation Deviation angle (GROD-a) distribution; there was some effect on grain average Kernel Average Misorientation (KAM) (reduced with smaller step size for the same grain), as expected. We monitored GOS, Maximum Orientation Spread (MOS) and GROD-a differences between whole olivine grains and sub-sampled areas, and found that there were significant differences between the whole grain dataset and subsets, as well as between subsets, likely due to sampling-related \"noise\". Also, in general (and logically) whole grains exhibit greater degrees of cumulative lattice rotation. Sampling size affects the apparent strain character of the grain, at least as measured by GOS, MOS and GROD-a. There were differences in the distribution frequencies of GOS and MOS between shock stages, and in plots of MOS and GOS vs. grain diameter. These results are generally consistent with those reported this year. However, it is unknown whether the differences between samples of different shock states exceeds the clustering of these values to the extent that shock stage determinations can still be made with confidence. We are investigating this by examination of meteorites with higher shock stage 4 to 5. Our research will improve our understanding of how small, primitive solar system bodies formed and evolved, and improve understanding of the processes that determine the history and future of habitability of environments on other solar system bodies. The results will directly enrich the ongoing asteroid and comet exploration missions by NASA and JAXA, and broaden our understanding of the origin and evolution of small bodies in the early solar system, and elucidate the nature of asteroid and comet regolith.

The detection and size analysis of small metal particles supported on amorphous substrates becomes increasingly difficult when the particle size approaches that of the phase contrast background structures of the support. An approach of digital image analysis, involving Fourier transformation of the original image, filtering, and image reconstruction was studied with respect to the likelihood of unambiguously detecting particles of less than 1 nm diameter on amorphous substrates from a single electron micrograph.

This volume was digitized and made accessible online due to deterioration of the original print copy.

This volume was digitized and made accessible online due to deterioration of the original print copy.

A coherent exposition of the theory of scattering from a dynamic lattice, which applies to the scattering of Bloch wave electrons as well as the scattering of plane waves, is presented. This is achieved by developing a generalized diffraction model, along the lines conceived by Van Hove, appropriate for the scattering of Bloch waves. The resulting diffraction model provides a basis for treating processes controlled by electron-phonon interaction in general and subsumes the standard diffraction model results. The diffraction model origins of the standard approximate expressions used to describe electron-phonon interaction controlled processors are also revealed. Keywords: Electron scattering in crystalline and disordered metals, Electrical and thermal transport in metals, Sham-Ziman approximation, Structure factors, Diffraction models, Electron phonon interaction, X ray and neutron scattering from metals.

Book Source: Digital Library of India Item 2015.192599 dc.contributor.author: Vibhakar Vasantrao Bhokare dc.date.accessioned: 2015-07-08T01:29:57Z dc.date.available: 2015-07-08T01:29:57Z dc.date.digitalpublicationdate: 2005-08-31 dc.identifier.barcode: 1990010091007 dc.identifier.origpath: /rawdataupload/upload/0091/007 dc.identifier.copyno: 1 dc.identifier.uri: http://www.new.dli.ernet.in/handle/2015/192599 dc.description.scannerno: 12 dc.description.scanningcentre: IIIT, Allahabad dc.description.main: 1 dc.description.tagged: 0 dc.description.totalpages: 82 dc.format.mimetype: application/pdf dc.language.iso: English dc.publisher: Indian Institute Of Technology Kanpur dc.rights: Out_of_copyright dc.source.library: Indian Institute Of Technology Kanpur dc.subject.classification: Technology dc.subject.classification: Engineering. Technology In General dc.subject.classification: Mechanical Engineering In General. Nuclear Technology. Electrical Engineering. Machinery dc.title: Greens Function Method For Electron Diffraction And Band Structure Problems

Book Source: Digital Library of India Item 2015.192599 dc.contributor.author: Vibhakar Vasantrao Bhokare dc.date.accessioned: 2015-07-08T01:29:57Z dc.date.available: 2015-07-08T01:29:57Z dc.date.digitalpublicationdate: 2005-08-31 dc.identifier.barcode: 1990010091007 dc.identifier.origpath: /rawdataupload/upload/0091/007 dc.identifier.copyno: 1 dc.identifier.uri: http://www.new.dli.ernet.in/handle/2015/192599 dc.description.scannerno: 12 dc.description.scanningcentre: IIIT, Allahabad dc.description.main: 1 dc.description.tagged: 0 dc.description.totalpages: 82 dc.format.mimetype: application/pdf dc.language.iso: English dc.publisher: Indian Institute Of Technology Kanpur dc.rights: Out_of_copyright dc.source.library: Indian Institute Of Technology Kanpur dc.subject.classification: Technology dc.subject.classification: Engineering. Technology In General dc.subject.classification: Mechanical Engineering In General. Nuclear Technology. Electrical Engineering. Machinery dc.title: Greens Function Method For Electron Diffraction And Band Structure Problems

Book Source: Digital Library of India Item 2015.192599 dc.contributor.author: Vibhakar Vasantrao Bhokare dc.date.accessioned: 2015-07-08T01:29:57Z dc.date.available: 2015-07-08T01:29:57Z dc.date.digitalpublicationdate: 2005-08-31 dc.identifier.barcode: 1990010091007 dc.identifier.origpath: /rawdataupload/upload/0091/007 dc.identifier.copyno: 1 dc.identifier.uri: http://www.new.dli.ernet.in/handle/2015/192599 dc.description.scannerno: 12 dc.description.scanningcentre: IIIT, Allahabad dc.description.main: 1 dc.description.tagged: 0 dc.description.totalpages: 82 dc.format.mimetype: application/pdf dc.language.iso: English dc.publisher: Indian Institute Of Technology Kanpur dc.rights: Out_of_copyright dc.source.library: Indian Institute Of Technology Kanpur dc.subject.classification: Technology dc.subject.classification: Engineering. Technology In General dc.subject.classification: Mechanical Engineering In General. Nuclear Technology. Electrical Engineering. Machinery dc.title: Greens Function Method For Electron Diffraction And Band Structure Problems

Spot Profile Analysis is an efficient process used to evaluate both qualitatively and quantitatively the defect structure of crystal surfaces. The process consists of analyzing the angular distribution of a Low Energy Electron Diffraction (LEED) spot. This paper describes the design, construction, and testing of a new LEED detection system which uses a position sensitive detector. The electron optics built for this system incorporate several unique design features. These features include unipotential lenses, and the use of an easily removable electron source. Preliminary testing of the system shows transfer widths in the 300 angstrom range for electron energies from 80 to 250 eV.

Intensities of LEED and PED are analyzed from a statistical point of view. The probability distribution is compared with a Porter-Thomas law, characteristic of a chaotic quantum system. The agreement obtained is understood in terms of analogies between simple models and Berry's conjecture for a typical wavefunction of a chaotic system. The consequences of this behaviour on surface structural analysis are qualitatively discussed by looking at the behaviour of standard correlation factors.

Book Source: Digital Library of India Item 2015.191622 dc.contributor.author: Vibhakar Vasantrao Bhokare dc.date.accessioned: 2015-07-08T01:06:58Z dc.date.available: 2015-07-08T01:06:58Z dc.date.digitalpublicationdate: 2005-08-31 dc.identifier.barcode: 1990010090123 dc.identifier.origpath: /rawdataupload/upload/0090/123 dc.identifier.copyno: 1 dc.identifier.uri: http://www.new.dli.ernet.in/handle/2015/191622 dc.description.scannerno: 12 dc.description.scanningcentre: IIIT, Allahabad dc.description.main: 1 dc.description.tagged: 0 dc.description.totalpages: 81 dc.format.mimetype: application/pdf dc.language.iso: English dc.publisher: Indian Institute Of Technology Kanpur dc.rights: Out_of_copyright dc.source.library: Indian Institute Of Technology Kanpur dc.subject.classification: Technology dc.subject.classification: Engineering. Technology In General dc.subject.classification: Mechanical Engineering In General. Nuclear Technology. Electrical Engineering. Machinery dc.title: Greens Function Method For Electron Diffraction And Band Structure Problems

A technique for the measurement of electron diffraction patterns of polycrystalline materials is described. The image of the diffraction pattern is projected by a photographic en larger at a predetermined magnification onto a chart that is calibrated directly in d spacings. This technique is rapid, as no calculations are involved. Accuracy is equal to, or better than, that achieved with the classical method.

A technique for the measurement of electron diffraction patterns of polycrystalline materials is described. The image of the diffraction pattern is projected by a photographic en larger at a predetermined magnification onto a chart that is calibrated directly in d spacings. This technique is rapid, as no calculations are involved. Accuracy is equal to, or better than, that achieved with the classical method.

A technique for the measurement of electron diffraction patterns of polycrystalline materials is described. The image of the diffraction pattern is projected by a photographic en larger at a predetermined magnification onto a chart that is calibrated directly in d spacings. This technique is rapid, as no calculations are involved. Accuracy is equal to, or better than, that achieved with the classical method.

We present a method for producing sub-100 fs electron bunches that are suitable for single-shot ultrafast electron diffraction experiments in the 100 keV energy range. A combination of analytical results and state-of-the-art numerical simulations show that it is possible to create 100 keV, 0.1 pC, 20 fs electron bunches with a spotsize smaller than 500 micron and a transverse coherence length of 3 nm, using established technologies in a table-top set-up. The system operates in the space-charge dominated regime to produce energy-correlated bunches that are recompressed by established radio-frequency techniques. With this approach we overcome the Coulomb expansion of the bunch, providing an entirely new ultrafast electron diffraction source concept.

The paper considers the process of Thomson scattering of coherent diffraction radiation (CDR) produced by the preceding bunch of the accelerator on one of the following bunches. It is shown that the yield of scattered hard photons is proportional to N$_e^3$, where N$_e$ is the number of electrons per bunch. A geometry is chosen for the CDR generation and an expression is obtained for the scattered photon spectrum with regard to the geometry used, that depends in an explicit form on the bunch size. A technique is proposed for measuring the bunch length using scattered radiation characteristics.

This abstract summarizes initial results of an investigation of the surface defects in Ge films grown epitaxially on cleaved GaAs(110). Most of the effort has centered on characterizing the electronic properties of the interface, i.e., band gap discontinuities, localized bonding, work function changes, and abruptness of the interface. X-ray and ultraviolet photoelectron spectroscopy have been used as the main analytical techniques in these investigations. In summary, we have demonstrated that it is possible to extract quantitative information on structural defects even for (1x1) overlayers using LEED. For epitaxial growth of Ge on GaAs(110) under the present experimental conditions, the overlayers appear to have a higher concentration of extended defects than the substrates on which they are grown. At low growth temperatures, this may be due to a mechanism that inhibits layer-by-layer growth, causing the surface to be highly stepped. For annealed layers, dislocations grown into the film may propagate to the surface and cause the Ge layer to be polycrystalline but sill oriented. The symmetry of the patterns differs from that observed by Moench and Gant. It is possible that the appearance of superlattices is related to growth mode.

The molecular structures of cis- aand trans-1,2-dichloroethene were studied in the gas phase by electron diffraction, using our new real-time data acquisition technique. For cis-dichloroethene the structural parameters are (r sub a distances (Angstroms) and angles (deg), with 3sigma in parentheses): C-C1:1.717(2); C=C:1.337(4); C1-C=C: 124.0(2); and H-C=C:120.3(3). For trans-dichloroethene: C-C1:1.725(2); C=C:1.332(8); C1-C=C:120.8(6); and H-C=C:124.0(3). The experimental work was augmented by ab initio gradient geometry refinements of the two compounds and of cis- and trans-difluorothene. The 4-21G, 5-31G**, and 3-3-21G basis sets were used in various series of calculations. Without any exception, the calculated structural trends for the cis- and trans-configurations are in excellent agreement with the experiments.

Analysis of biaxial texture of MgO films grown by ion-beam-assisted deposition (IBAD) has been performed using a quantitative reflection high-energy electron diffraction (RHEED) based method. MgO biaxial texture is determined by analysis of diffraction spot shapes from single RHEED images, and by measuring the width of RHEED in-plane rocking curves for MgO films grown on amorphous Si3N4 by IBAD using 750 eV Ar+ ions, at 45 incidence angle, and MgO e-beam evaporation. RHEED-based biaxial texture measurement accuracy is verified by comparison with in-plane and out-of-plane orientation distribution measurements made using transmission electron microscopy and x-ray rocking curves. In situ RHEED measurements also enable the analysis of the evolution of the biaxial texture which narrows with increasing film thickness. RHEED-based measurements of IBAD MgO biaxial texture show that the minimum in-plane orientation distribution depends on the out-of-plane orientation distribution, and indicates that the minimum obtainable in-plane orientation on distribution is 2 .

Analysis of biaxial texture of MgO films grown by ion-beam-assisted deposition (IBAD) has been performed using a quantitative reflection high-energy electron diffraction (RHEED) based method. MgO biaxial texture is determined by analysis of diffraction spot shapes from single RHEED images, and by measuring the width of RHEED in-plane rocking curves for MgO films grown on amorphous Si3N4 by IBAD using 750 eV Ar+ ions, at 45 incidence angle, and MgO e-beam evaporation. RHEED-based biaxial texture measurement accuracy is verified by comparison with in-plane and out-of-plane orientation distribution measurements made using transmission electron microscopy and x-ray rocking curves. In situ RHEED measurements also enable the analysis of the evolution of the biaxial texture which narrows with increasing film thickness. RHEED-based measurements of IBAD MgO biaxial texture show that the minimum in-plane orientation distribution depends on the out-of-plane orientation distribution, and indicates that the minimum obtainable in-plane orientation on distribution is 2 .

Measurements of the first lobe of diffraction transition radiation from a hole in a thin aluminum foil for electron-beam energies of 32.9 MeV and 63.3 MeV has been made. The effect of the hole size was investigated using radii of 3 cm, 5 cm, and 7 cm. Although the measured peak angle and intensity are not well matched to the theoretical values, these experiments attempt to isolate the diffraction transition radiation from Cerenkov radiation and transition radiation. The normalization of the detected signal to the beam current was tried for compensation of the beam fluctuation. Conclusive results have not yet been obtained, but this investigation provides directions for future experiments.

Transmission electron microscopy and diffraction have been used to study the packing arrangements of docosyl thiol (RSH), didocosyl sulfide (RSR), and didocosyl disulfide (RSSR) on gold single crystal foils. The specimens include gold films in (100) and (111) orientations. Docosyl thiol and didocosyl disulfide adsorbed on (111) faces assemble in coincidence lattice structures yielding hexagonal overlayers c(7 x 7) in which the short interchain distance indicates freely rotating methylene chains. On a (100) surface both alkyl groups exhibit an in-plane structure consisting of a base-centered square array in which the interchain distance implies a hindered chain movement. We have presented evidence that substrate crystallography does control the packing of monolayer alkyl sulfides adsorbed from the solution phase.

Transmission electron microscopy and diffraction have been used to study the packing arrangements of docosyl thiol (RSH), didocosyl sulfide (RSR), and didocosyl disulfide (RSSR) on gold single crystal foils. The specimens include gold films in (100) and (111) orientations. Docosyl thiol and didocosyl disulfide adsorbed on (111) faces assemble in coincidence lattice structures yielding hexagonal overlayers c(7 x 7) in which the short interchain distance indicates freely rotating methylene chains. On a (100) surface both alkyl groups exhibit an in-plane structure consisting of a base-centered square array in which the interchain distance implies a hindered chain movement. We have presented evidence that substrate crystallography does control the packing of monolayer alkyl sulfides adsorbed from the solution phase.

While a perfect hcp (0001) surface has three-fold symmetry, the diffraction patterns commonly obtained are six-fold symmetric. This apparent change in symmetry occurs because on a stepped surface, the atomic layers on adjacent terraces are rotated by 180 degrees. Here we use a Low-Energy Electron Microscope to acquire the three-fold diffraction pattern from a single hcp Ru terrace and measure the intensity-vs-energy curves for several diffracted beams. By means of multiple scattering calculations fitted to the experimental data with a Pendry R-factor of 0.077, we find that the surface is contracted by 3.5(+-0.9) at 456 K.

The metal microclusters are formed in the gas phase by an isobaric cooling due to argon carrier gas, followed by adiabatic expansions through nozzle apertures. Electron diffraction patterns of these condensates show the typical Debye-Scherrer rings for the f.c.c. Pb metal. The average size of clusters obtained, depending on the experimental conditions, ranges from 30 to 100 angstrom in diameter, and the cubic lattice parameters for these clusters are essentially the same, within an experimental error of 0.3%, as that for the bulk crystal. The analysis of the Bragg-peak intensities is carried out based on the usual kinematical theory and the dynamical (two-beam approximation) theory by Blackman. The former theory fails completely in accounting for small angle reflections (s less than 5 1/angstrom), whereas the latter explains successfully the whole observed intensities, except for the 2nd and 3rd order reflections (400), (440), (333), and (600). From the damping of peak intensities the temperatures of these clusters are estimated to be of the order of 150 K.

Equal-channel angular (ECA) pressing is a promising method to achieve refinement of grain size to 1.0 micrometer or less for aluminum and its alloys. Computer-aided electron backscatter diffraction (EBSD) analysis of high purity aluminum (99.99%) which had been subjected to one pass, four passes, and twelve passes through an ECA die was performed. Grain and subgrain size and boundary misorientation distributions during such large-strain deformation processing were of particular interest. A texture was present after one pressing and the boundary misorientation distribution had a peak at 5 deg - 10 deg although boundaries were present in all misorientation ranges. Fine equaixed grains were achieved after twelve passes through the ECA die, accompanied by random orientation and misorientation distributions.

Thesis (Ph. D.)--University of California, 1967

Understanding Fivefold Symmetry in Electron-Diffraction Patterns 作者： Min Lequan 1 作者单位： 1. University of Science and Technology Beijing 通讯作者： Min Lequan Email:[email protected] 提交时间： 2024-03-27 11:29:49 摘要: Electron-diffraction patterns with 5-fold rotational symmetry of experimental alloy phases are assumed to be produced by periodic structures. Two three-dimensional periodic structures are presented based on  regular pentagonal dodecahedrons. These structures can be used as atomic models to describe the alloy phases. The Fourier-transform patterns of the models are found to be similar to the corresponding electron-diffraction patterns of these alloy phases. Details of the motivations and approaches that lead to these models are also discussed. Condensed matter physics Electron-diffraction 5-fold symmetry Quasicrystal Regular pentagonal dodecahedrons Periodic models Fourier-transform patterns. 来自： 闵乐泉 分类： 物理学 >> 凝聚态:结构、力学和热性能 说明： 本文是新完成的一篇研究论文，尚未向杂志和会议投稿 投稿状态： 未投稿 引用： ChinaXiv:202403.00361 (或此版本 ChinaXiv:202403.00361V1 ) DOI:10.12074/202403.00361V1 CSTR:32003.36.ChinaXiv.202403.00361.V1 推荐引用方式： Min Lequan.(2024).Understanding Fivefold Symmetry in Electron-Diffraction Patterns.中国科学院科技论文预发布平台.[ChinaXiv:202403.00361] 版本历史 [V3] 2024-05-24 12:20:17 ChinaXiv:202403.00361v3 查看此版本 下载全文 [V2] 2024-04-22 10:25:39 ChinaXiv:202403.00361v2 查看此版本 下载全文 [V1] 2024-03-27 11:29:49 ChinaXiv:202403.00361V1 下载全文

This article is from Journal of Applied Crystallography , volume 46 . Abstract Corresponding two-dimensional grain maps from the diffraction contrast tomography and electron backscatter diffraction characterization methods were aligned and compared, focusing on the spatial resolution at the internal interfaces. The compared grain boundary networks show a remarkably good agreement both morphologically and in crystallographic orientation.

Note this registration has been withdrawn: Proof of Concept for seeking collaboration to derive the speed of light 𝑐, an be derived from first principles using only directly measurable quantities, without assuming its value anywhere in the calculation chain. The methodology involves accelerating electrons in a High Voltage Electron Microscope (HVEM) across a wide energy range, measuring their velocity using an integrated time-of-flight (TOF) system, and comparing the de Broglie wavelength inferred from relativistic momentum to the wavelength derived from Bragg diffraction patterns in a gold target. The goal is to assess whether these independently obtained wavelengths agree across the relativistic regime, thereby enabling an empirical derivation of 𝑐.

Very-low-energy electron diffraction with a support of full-potential band calculations is used to achieve the energy positions, K// dispersions, lifetimes and Fourier compositions of the photoemission final states in Bi2Sr2CaCu2O8 at low excitation energies. Highly structured final states explain the dramatic matrix element effects in photoemission. Intense c(2x2) diffraction reveals a significant extrinsic contribution to the shadow Fermi surface. The final-state diffraction effects can be utilized to tune the photoemission experiment on specific valence states or Fermi surface replicas.

Using high-quality gas phase electron scattering calculations and multiple scattering theory, we attempt to gain insights on the radiation damage to DNA induced by secondary low-energy electrons in the condensed phase, and to bridge the existing gap with the gas phase theory and experiments. The origin of different resonant features (arising from single molecules or diffraction) is discussed and the calculations are compared to existing experiments in thin films.

The epitaxial growth of complex oxide thin films provide three avenues to generate unique properties: the ability to influence the 3-dimensional structure of the film, the presence of a surface, and the generation of an interface. In all three cases, a clear understanding of the resulting atomic structure is desirable. However, determining the full structure of an epitaxial thin film (lattice parameters, space group, atomic positions, surface reconstructions) on a routine basis is a serious challenge. In this paper we highlight the remarkable information that can be extracted from both the Bragg scattering and inelastic multiple scattering events that occur during Reflection High Energy Electron Diffraction. We review some methods to extract structural information and show how mature techniques used in other fields can be directly applied to the {\em in-situ} and real-time diffraction images of a growing film. These collection of techniques give access to both the epitaxially influenced 3 dimensional bulk structure of the film, and any reconstructions that may happen at the surface.

Bell System Technical Journal, 19: 1. January 1940 pp 152-155. Technical Digests: An Interesting Application of Electron Diffraction. (Germer, L.H.; Storks, K.H.)

Double-slit diffraction is a corner stone of quantum mechanics. It illustrates key features of quantum mechanics: interference and the particle-wave duality of matter. In 1965, Richard Feynman presented a thought experiment to show these features. Here we demonstrate the full realization of his famous thought experiment. By placing a movable mask in front of a double-slit to control the transmission through the individual slits, probability distributions for single- and double-slit arrangements were observed. Also, by recording single electron detection events diffracting through a double-slit, a diffraction pattern was built up from individual events.

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The geometric structure of azidotrifluoromethane has been obtained by a combined analysis of electron diffraction intensities and ground state rotational constants derived from the microwave spectrum. Structural data on covalent azides are rare due to the explosive nature and handling difficulties encountered with these compounds. One of the more stable covalent azides is CF3N3.

We review briefly the motivation for the characterization of materials in three dimensions. Most materials of practical value are polycrystalline, and the arrangement of the crystals or grains in space is usually sufficiently complicated that plane sections do not suffice to describe microstructure quantitatively. Furthermore, most properties, even in materials with cubic crystal symmetry, are anisotropic, which means that even small deviations from uniform (random) texture lead to anisotropic behavior of the polycrystal. Elastic response is mildly anisotropic in most cases, and the plastic response of a material can be strongly anisotropic. A further complication is that many processing routes lead to heterogeneous microstructures, so it is often necessary to characterize the gradients in microstructure and accept that there is not a single representative microstructure. Although it is an accepted axiom of materials science that properties depend on microstructure, it is worth pointing out the great variety of important problems that are known to be sensitive to microstructure, such as surface roughening, intergranular corrosion, fatigue crack initiation and initiation, fracture toughness, hot ductility dip cracking, electromigration, and hillock formation.

We review briefly the motivation for the characterization of materials in three dimensions. Most materials of practical value are polycrystalline, and the arrangement of the crystals or grains in space is usually sufficiently complicated that plane sections do not suffice to describe microstructure quantitatively. Furthermore, most properties, even in materials with cubic crystal symmetry, are anisotropic, which means that even small deviations from uniform (random) texture lead to anisotropic behavior of the polycrystal. Elastic response is mildly anisotropic in most cases, and the plastic response of a material can be strongly anisotropic. A further complication is that many processing routes lead to heterogeneous microstructures, so it is often necessary to characterize the gradients in microstructure and accept that there is not a single representative microstructure. Although it is an accepted axiom of materials science that properties depend on microstructure, it is worth pointing out the great variety of important problems that are known to be sensitive to microstructure, such as surface roughening, intergranular corrosion, fatigue crack initiation and initiation, fracture toughness, hot ductility dip cracking, electromigration, and hillock formation.