Electron Diffraction Experiments Research Articles

If the wave function collapse absolutely in the interaction, how can the weird nature of particles are born in the interaction? �A discussion on quantum entanglement experiments

Objectives: Particles can re-exhibit volatility after their wave function (or wave packet) collapses (proven by experiments such as secondary electron diffraction experiments). Is the volatility recovered or does the collapse process not destroy the volatility or is the collapse process not there at all? After the wave function (or wave packet) of a particle collapses, the superposition state should not exist. Methods: If the wave function can be collapsed by measurement and the quantum characteristics cannot be recovered after the collapse, then the microscopic particles that reach the free motion state through interaction can no longer have the quantum characteristics of quantum parallelism, Quantum Entanglement (QEM) or quantum state superposition. Findings: Restricted by the conditions in this conditional adverbial clause, logically, it is impossible to find Quantum Entanglement State (QEMS) by experiment (recognizing that the quantum superposition state is a non-real state, it is recognized that the state is unobservable). Under the assumption that entangled states (or superposition states) exist and that measurement can destroy entangled states, the related experimental phenomena are interpreted as QEMS. Application: This is clearly a logical cycle. Experiments show that the non-projective measurement cannot eliminate the diffraction effect of electron rays. Keywords: Logical Cycle, Quantum Entanglement, Quantum Mechanics, Quantum Non-Locality, Wave Function Collapse

Performance of an Indium-sealed S-band RF Photoelectron Gun for Time-resolved Electron Diffraction Experiments

We have developed a one-and-half -cell S-band radio-frequency (RF) photoelectron gun (photogun) fed by a coaxial coupler. The RF photogun is dedicated to ultrafast-electron-diffraction experiments by generating electron bunches of 3-MeV energy and a-few-pC charge, which is not strict condition compared to those for X-ray free-electron lasers. Brazing of RF cavities is welldeveloped process for making RF guns or RF accelerators. Sometimes, however, a failure occurs in the brazing process, causing the entire electron gun or accelerating cavity to spoil. Axial-symmetric design of the RF photogun permits indium sealing for cavity cells, a photocathode plate, and a coupling RF part. We firstly report that the indium-sealed RF photogun successfully meets the required performance and long-term stability for ultrafast electron diffraction experiments. We have stably operated the RF photogun for more than three years with the electron beam conditions of ~ 3-MeV energy, up-to-10-pC charge, and a repetition rate of 50 Hz. The quantum efficiency of the copper photocathode had improved from 10−6 to 10−5 depending on vacuum condition from 10−8 to 5 × 10−10 Torr, respectively. Measured emittance and energy spread of the generated electron beam showed 0.3 mm-mrad and less than 0.25%, respectively, for a bunch charge of ~ 2 pC, which agree well with those obtained by ASTRA simulation.

Optical fiber-driven low-energy electron gun for time-resolved streak diffraction

The wave guiding feature of the optical fibre optical fibres is specifically exploited to construct a novel type of electron gun to realize single-shot low-energy electron diffraction experiments with the sub-picosecond resolution for studying irreversible samples.

Chemically Accurate Adsorption Energies: CO and H2O on the MgO(001) Surface.

Hybrid MP2:DFT-D structure optimizations are performed at BSSE-free CBS-extrapolated potential energy surfaces for molecule-oxide surface interactions (BSSE, basis set superposition error; CBS, complete basis set limit). Subsequently single point MP2 calculations are performed to estimate the effects of increasing the basis set size in the CBS extrapolation and increasing the cluster model size. The resulting estimates of the periodic MP2 limit agree within 1 kJ/mol with Local MP2 calculations using periodic boundary conditions. Single point CCSD(T) calculations are performed to determine ΔCC = CCSD(T) - MP2 energy differences. The final hybrid MP2:DFT-D+ΔCC estimate for CO on the MgO(001) surface at low coverage, -21.2 ± 0.5 kJ/mol, is in close agreement with the reference energy derived from temperature-programmed desorption experiments, -20.6 ± 2.4 kJ/mol. For H2O on MgO(001), at limiting zero coverage, we predict an adsorption energy of -53.7 ± 4.2 kJ/mol which falls in the range of values, -55.8 ± 12.2 kJ/mol, derived from a high coverage low energy electron diffraction experiments and estimated lateral interactions.

A New and Unexpected Spatial Relationship Between Interaction Volume and Diffraction Pattern in Electron Microscopy in Transmission.

The finding of this study is that the interaction volume in electron microscopy in transmission is well ordered laterally, with a remarkable and unexpected consequence being that lateral subsections of the interaction volume produce subsections of the Kikuchi diffraction pattern. It makes the microstructure of samples directly visible in Kikuchi patterns. This is first illustrated with polycrystalline Ti-10Al-25Nb with an on-axis transmission Kikuchi diffraction set-up in a scanning electron microscope. It is then shown via a Monte Carlo simulation and a large-angle convergent-beam electron diffraction experiment that this phenomenon finds its origin in the nature of the differential elastic and quasi-elastic cross sections. This phenomenon is then quantified by a careful image analysis of Kikuchi patterns recorded across a vertical interface in a silicon sample specifically designed and fabricated. A Monte Carlo simulation reproducing all the geometric parameters is conducted. Experiments and simulations match very well qualitatively, but with a slight quantitativity gap. The specificity of the thermal diffuse scattering cross-section, not available in the simulation, is thought to be responsible for this gap. Beside Kikuchi diffraction, the case of diffraction spots and diffuse background present in the pattern is also discussed.

Extracting dislocation microstructures by deep learning

The microstructure of dislocations can be accessed by the total density of dislocations or the density of geometrically necessary dislocations (GND). The total dislocation density determines the flow strength of a crystal, which, in the case of high dislocation contents, is a quantity very difficult to measure accurately. On the other hand, related to crystal rotations, the GND densities are conveniently measured from electron diffraction experiments or calculated via simulations. Here, a novel and modern approach is proposed to understand the microstructures of dislocations based on deep learning, which estimates the total density of dislocations from a given density of GND distributions. In this method, the convolutional neural networks (ConvNets) are applied to extract the hidden information in the GND distribution maps to understand the microstructures of dislocations. It is demonstrated that the pre-trained ConvNets can be used to predict the distribution of total dislocation density from a small GND density map. Moreover, this technique is further developed to post-process real EBSD images for α-Fe to estimate the average total dislocation density, which corresponds to stress increments from a Taylor hardening assumption that is in good agreement with experimental values. Compared with previous methods involving much effort to track individual dislocations or other quantities, the present machine learning method is quick and convenient to use.

Quantitative determination of polarization from 4D scanning electron diffraction experiments

Quantitative determination of polarization from 4D scanning electron diffraction experiments

Transmission low-energy electron diffraction using double-gated single nanotip field emitter

We explore the spatial coherence of double-gate single nanotip field emitters by low-energy electron diffraction experiments in transmission mode. By producing collimated field emission pulses from the single nanotip cathode and irradiating a suspended monolayer graphene film without additional optics, we observed sharper and higher resolution Bragg diffraction spots than a previous experiment using a nanotip array cathode. In particular, we found complete conservation of the size and the shape of the diffraction spots with those of the incident beam on the sample. The result indicates that the transverse coherence of a nanofabricated double-gate single-tip emitter is much larger than a few nanometers as determined by the apparent diffraction spot size and overall spatial resolution of the observed diffraction pattern.

Golden ultrafast melting

Condensed Matter Understanding fast melting of metals is important for applications such as welding and micromachining. However, fast melting leaves simulation as the only option for probing the process. Mo et al. performed ultrafast electron diffraction experiments on laser-pulsed gold films. This

Phase Diagram of near Equiatomic Zr-Pd Alloy

The exact eutectoid and peritectoid temperatures in near equiatomic Zr-Pd compositions have been determined by using the diffusion couple method and microstructure analysis. The crystal structure of Zr13Pd12 compound were estimated to be orthorhombic with a = 1.78 nm, b = 0.80 nm and c = 1.00 nm from the electron diffraction experiments. The Zr13Pd12 compound is formed at 1100 ± 2 K with a peritectoid reaction between Zr2Pd and ZrPd compounds. The ZrPd compound transforms to Zr13Pd12 and Zr9Pd11 compounds by a eutectoid reaction at 1028 ± 4 K. Based on these results, the phase diagram of near equiatomic Zr-Pd binary system is reconstructed.

Electron diffraction and imaging for atom probe tomography.

Previous work has shown that pre- and post-experiment quantification of atom probe tomography (APT) specimen geometry using electron microscopy can constrain otherwise unknown parameters, leading to an improvement in data fidelity. To that end, an electron microscopy and diffraction system has been developed for in situ compatibility with modern APT hardware. The system is capable of secondary and backscattered scanning electron imaging, bright field and dark field scanning transmission electron imaging, and scanning transmission electron diffraction. Additionally, the system is also capable of in situ dynamic electron diffraction experiments using laser pulsed heating of the APT specimen.

TEM study on a new Zr-(Fe, Cu) phase in furnace-cooled Zr-1.0Sn-0.3Nb-0.3Fe-0.1Cu alloy

A new Zr-(Fe, Cu) phase was found in furnace-cooled Zr-1.0Sn-0.3Nb-0.3Fe- 0.1Cu alloy and alloys aged at 580 °C for 10min, 2 h and 10 h. Electron diffraction experiment shows the crystal structure of this phase to be body-centered tetragonal with unit cell dimensions determined to be a = b = 6.49 Å, c = 5.37 Å. Its possible space groups have been discussed and the reason accounting for its formation is believed to be the addition of Cu according to the atom-level images. In addition, no crystal structural or chemical composition changes were observed throughout the aging process.

Single Crystal Organic Nanoflowers

Nano-flowers reported so far were mostly constituted of inorganic or hybrid materials. We have synthesized and crystallized a new organic compound, 1, 2-bis(tritylthio)ethane forming an organic nano-flower consisting of single crystalline petals. Crystal structure at nano and micro level indicates that π-π stacking interactions between aromatic systems is the principal factor governing molecular recognition and assembly. Single crystal X-ray Diffraction (S-XRD) supported by Selective Area Electron Diffraction (SAED) experiments indicate the single crystalline nature of the flower-like assembly even at the nanoscale. In order to fabricate the nanoflower as a potential stimulus responsive material; the ‘petals’ were coated with magnetite nanoparticles, verified by Energy-dispersive X-ray spectroscopic (EDX) analysis. Herein, we have further tested the potential utility of the hybrid material in water remediation as a nano-based adsorbent for removal of heavy metals like chromium.

Cs-corrected HAADF-STEM observations on the structural modulations caused by charge density wave and Te-vacancy ordering in LaTe<sub>2</sub><sub>−</sub><sub><italic>δ</italic></sub>

Microstructural features play a critical role for the understanding of the essential properties of novel functional materials and new devices. Atomic-resolution scanning transmission electron microscopy (STEM) is invaluable for determining the average atomic structure and local structural defects. For strongly correlated electron materials, STEM can be applied to distinguish the structural modulation caused by charge density wave (CDW), chemical ordering (vacancy or impurity atoms). RTe2− δ (R=La, Ce) compounds have attracted recent attention due to their effective low dimensionality. The materials play host to a CDW state above room temperature and can be described in terms of a modulated Cu2Sb-type structure (P4/ nmm ) based on alternating layers of square-planar Te sheets and a corrugated RTe slab. Furthermore, pressure-induced superconductivity in CeTe1.82 with T C of 2.7 K has been reported, suggesting that the nonstoichiometric Te defects are correlated to superconductivity in this material system. Here, we report the study of the structural modulations in LaTe2− δ using STEM. The LaTe2− δ single crystal was grown by self-flux technique. The TEM samples used in the present study were prepared by crushing the well- characterized single crystal, and then the resultant suspensions were dispersed on a holey carbon-covered Cu grid. Electron diffraction experiments were performed in the FEI Tecnai F20 microscope, and HRTEM and high angle annular dark field (HAADF) STEM were performed in the JEOL ARM200F equipped with double aberration correctors and cold field emission gun at room temperature. The experiment result revealing the charge density wave in LaTe2− δ can be tuned by the Te content; the structural modulation correlated with charge density wave can be characterized by a modulation wave vector of q CDW=(1/2− α ) a ∗, where α is the incommensurate parameter determined by the chemical composition. Our experiment data demonstrate that the Cs-corrected HAADF-STEM image can directly reveal the atomic displacements in the Te plane due to electron-phonon coupling. Detailed analysis suggests that the Te atomic displacements adopt an incommensurate wave-pocket structure along each Te-chain with a long periodicity determined by the CDW incommensurability. In addition to the q CDW=(1/2− α ) a ∗ CDW modulation, a superstructure with the vector q 2=1/5(3 a ∗+ b ∗) has been also observed in some regions. In previous study, this modulation was proposed to be correlated with CDW instability, however, recent experimental and theoretical analysis on the electronic structure (FS) shows that there is no such nesting wave vector could be identified. In this paper, our Cs-STEM observations directly demonstrated that the q 2 superstructure actually originates from an imperfect stoichiometry in this layered system. We proposed a 5 × 5 supercell associated with the Te vacancy ordering with the chemical composition of LaTe1.85 based on detailed STEM data analysis. From HRTEM images, it is also noted that the CDW modulation ( q CDW) totally disappears in the region with Te vacancy ordering, suggesting that the CDW can not coexist in the crystals with the Te vacancy ordering. The possible correlation between the ordering of the nonstoichiometric Te defects and the superconductivity in this material system needs to be further investigated.

Selective Catalytic Ammonia Oxidation to Nitrogen by Atomic Oxygen Species on Ag(111)

Ammonia-selective catalytic oxidation was studied on the planar Ag(111) single-crystal model catalyst surface under ultra-high-vacuum (UHV) conditions. A variety of oxygen species were prepared via ozone decomposition on pristine Ag(111). Surface coverages of oxygen species were quantified by temperature-programmed desorption (TPD) and X-ray photoemission spectroscopy techniques. Exposure of ozone on Ag(111) at 140 K led to a surface atomic oxygen (Oa) overlayer. Low-energy electron diffraction experiments revealed that annealing of this atomic oxygen-covered Ag(111) surface at 473 K in UHV resulted in the formation of ordered oxide surfaces (Oox) with p(5×1) or c(4×8) surface structures. Ammonia interactions with O/Ag(111) surfaces monitored by temperature-programmed reaction spectroscopy indicated that disordered surface atomic oxygen selectively catalyzed N–H bond cleavage, yielding mostly N2 along with minor amounts of NO and N2O. Higher coverage O/Ag(111) surfaces, whose structure was tentatively ass...

Fully Atomistic Understanding of the Electronic and Optical Properties of a Prototypical Doped Charge-Transfer Interface.

The current study generates profound atomistic insights into doping-induced changes of the optical and electronic properties of the prototypical PTCDA/Ag(111) interface. For doping K atoms are used, as KxPTCDA/Ag(111) has the distinct advantage of forming well-defined stoichiometric phases. To arrive at a conclusive, unambiguous, and fully atomistic understanding of the interface properties, we combine state-of-the-art density-functional theory calculations with optical differential reflectance data, photoelectron spectra, and X-ray standing wave measurements. In combination with the full structural characterization of the KxPTCDA/Ag(111) interface by low-energy electron diffraction and scanning tunneling microscopy experiments (ACS Nano2016, 10, 2365–2374), the present comprehensive study provides access to a fully characterized reference system for a well-defined metal–organic interface in the presence of dopant atoms, which can serve as an ideal benchmark for future research and applications. The combination of the employed complementary techniques allows us to understand the peculiarities of the optical spectra of K2PTCDA/Ag(111) and their counterintuitive similarity to those of neutral PTCDA layers. They also clearly describe the transition from a metallic character of the (pristine) adsorbed PTCDA layer on Ag(111) to a semiconducting state upon doping, which is the opposite of the effect (degenerate) doping usually has on semiconducting materials. All experimental and theoretical efforts also unanimously reveal a reduced electronic coupling between the adsorbate and the substrate, which goes hand in hand with an increasing adsorption distance of the PTCDA molecules caused by a bending of their carboxylic oxygens away from the substrate and toward the potassium atoms.

Intramolecular π-π Interactions in Flexibly Linked Partially Fluorinated Bisarenes in the Gas Phase.

Three compounds with phenyl and pentafluorophenyl rings bridged by (CH2 )3 and (CH2 )2 SiMe2 units were synthesized by hydrosilylation and C-C coupling reactions. Their solid-state structures are dominated by intermolecular π stacking interactions, primarily leading to dimeric or chain-type aggregates. Analysis of free molecules in the gas phase by electron diffraction revealed the most abundant conformer to be significantly stabilized by intramolecular π-π interactions. For the silicon compounds, structures characterized by σ-π interactions between methyl and pentafluorophenyl groups are second lowest in energy and cannot be excluded completely by the gas electron diffraction experiments. C6 H5 (CH2 )3 C6 F5 , in contrast, is present as a single conformer. The gas-phase structures served as a reference for the evaluation of a series of (dispersion-corrected) quantum-chemical calculations.

Phase-Field Study of Sodiation of Snsb Thin Film Electrodes

Sodium-metal and sodium-metal alloys (metal = Sn, Sb, In, Ge) are very promising active materials for the negative electrodes of thin-film batteries. Sodium intercalation into the grain-formed films is a complex electrochemical and mechanical phenomenon, which primarily determines the performance of a battery. Thus, the fundamental understanding of the Na-ions intercalation processes is essential to develop long lasting battery technology. In the present work we present a phase-field modeling (PFM) study of (electro-)chemical sodiation of SnSb thin-film electrodes. The PFM is developed and applied to explore the sodium diffusion/intercalation and its influence on the evolution of SnSb grain structure. The PFM was developed using the MOOSE Framework.1,2 The model was validated against our experimental measurements, where SnSb thin films are prepared using ball-milling techniques and are deposited onto a carbon film/copper mesh transmission electron microscopy (TEM) grid (EMS CF-400-Cu) using DC magnetron sputtering. In-situTEM and electron diffraction experiments are used to directly image sodium diffusion and to determine the local structures. Employong the PFM an electrochemical free energy function, considering sodium diffusion within the grains and the grain boundary (GB) along with the elastic stress field associated with Na intercalation, is established. The phase-field GB model is used to generate thin-film grain structures and subsequently to study their evolution under the sodium diffusion. Results show that Na diffusion first proceeds through the GB and then through the grains, and that the electrochemical sodiation is much faster than the chemical sodiation due to an applied electric potential, which drives more Na-ions towards the electrode. The elastic strain energy associated with the sodium intercalation slows down Na diffusion due to the stress build-up. At the first glance, the generated stress has the detrimental effect on the sodiation; however, by slowing down the diffusion process it provides a stabilization function, as less Na is available inside a grain, thus avoiding a potential for irreversible crystallization. In addition, to increase the fundamental understanding of sodium diffusion/intercalation and the GB evolution, sensitivity analysis was performed. Thus, the present modeling work (in conjunction with the experimental work) allows a mechanistic interpretation of the origin of different mechanical, electrochemical and transport phenomena occurring during the sodiation of thin films SnSb electrodes.

Formation of metastable phases in Zr-ion-irradiated Al2O3 upon thermal annealing.

Formation of metastable phases in Zr-ion-irradiated corundum alumina (Al2O3) upon thermal annealing was examined using transmission electron microscopy. A metastable cubic spinel phase was formed in the topmost layer of the as-irradiated microstructure. During thermal annealing at temperatures ranging from 1073 to 1273 K, this spinel layer grew in extent via an unusual corundum-to-spinel phase transformation. A normal spinel-to-corundum phase transformation was observed at post-irradiation annealing temperatures greater than 1473 K. In addition, ZrO2 nanocrystals embedded in α-Al2O3 were observed to form at these higher temperatures. High-resolution transmission electron microscopy observations and electron diffraction experiments revealed that the structure of the ZrO2 precipitates observed in this study are consistent with a high-pressure metastable orthorhombic phase of ZrO2 known as the Ortho-I phase.

Space charge effects and aberrations on electron pulse compression in a spherical electrostatic capacitor

The effects of space charge, aberrations and relativity on temporal compression are investigated for a compact spherical electrostatic capacitor (α-SDA). By employing the three-dimensional (3D) field simulation and the 3D space charge model based on numerical General Particle Tracer and SIMION, we map the compression efficiency for a wide range of initial beam size and single-pulse electron number and determine the optimum conditions of electron pulses for the most effective compression. The results demonstrate that both space charge effects and aberrations prevent the compression of electron pulses into the sub-ps region if the electron number and the beam size are not properly optimized. Our results suggest that α-SDA is an effective compression approach for electron pulses under the optimum conditions. It may serve as a potential key component in designing future time-resolved electron sources for electron diffraction and spectroscopy experiments.