Electron Diffraction Imaging Research Articles

AFM, Nano − indentation and TEM characterization study of HFCVD diamond on tantalum and diamond seeded cemented carbide inserts

This research describes an enhanced characterization technique for studying diamond production by hot filament chemical vapor deposition (HFCVD) on cemented carbide (WC − Co) SPUN inserts. The characteristics of diamond (Dia.) and tantalum (Ta) seeded powders used as seeding materials were determined using a variety of microscopic characterizations. Topographic and cross-sectional pictures obtained using field emission scanning electron microscopy (FESEM), respectively, demonstrate that the Ta-seeded substrate had a higher nucleation density, whereas the Dia.-seeded substrate had thicker coatings. Findings from atomic force microscopy (AFM) show that Ta-seeded substrates' mechanical strength is expectedly higher due to the smaller grains and higher apparent density. According to the X-ray diffraction (XRD) results, the Dia. − seeded substrate displayed a lower dislocation density, strain, and Burgers' vector magnitude. The highly crystalline structure of the Ta-seeded sample appeared in the Transmission electron microscopy (TEM) selected area electron diffraction (SAED) images. However, the multi-gradient sample structure of the Dia.-seeded Sample obtained increased its ductility property. The nanoindentation results demonstrated that the Ta-seeded substrate had a higher hardness while the Dia.-seeded substrate had a higher Stiffness and Youngs' modulus value. The findings are crucial for present-day CVD applications since Ta powders offer an alternative option to diamond powders.

Fabrication of highly oriented Mn4N/Pt epitaxial bilayer structure on MgO(001) for spintronics applications

Magnetization control by electric current or spin current is an attractive technology with potential applications in memory and logic devices, and Mn4N has attracted much attention in recent years as a candidate material for current-induced magnetization switching and magnetic domain wall motion, as well as a skyrmion material. For these applications, a bilayer structure of Mn4N and heavy metals must be formed with high crystalline quality. In this study, we have achieved the epitaxial growth of Mn4N thin films on MgO(001) with a Pt underlayer. The reflection high-energy electron diffraction images and x-ray diffraction ω-rocking curves show that the Mn4N films fabricated on the Pt underlayers exhibit higher crystalline quality than the Mn4N films directly formed on the MgO. Furthermore, anomalous Hall effect loops with bump-like structures were observed. This is considered to be due to the topological spin texture. The Mn4N/Pt epitaxial bilayer structure has potential for use in spin–orbit torque applications and is a candidate configuration for topological spin textures.

Topochemical Fluorination of LaBaInO4 to LaBaInO3F2, Their Optical Characterization, and Photocatalytic Activities for Hydrogen Evolution.

We report on a nonoxidative topochemical route for the synthesis of a novel indate-based oxyfluoride, LaBaInO3F2, using a low-temperature reaction of Ruddlesden-Popper-type LaBaInO4 with polyvinylidene difluoride as a fluorinating agent. The reaction involves the replacement of oxide ions with fluoride ions as well as the insertion of fluoride ions into the interstitial sites. From the characterization via powder X-ray diffraction (PXRD) and Rietveld analysis as well as automated electron diffraction tomography (ADT), it is deduced that the fluorination results in a symmetry lowering from I4/mmm (139) to monoclinic C2/c (15) with an expansion perpendicular to the perovskite layers and a strong tilting of the octahedra in the ab plane. Disorder of the anions on the apical and interstitial sites seems to be favored. The most stable configuration for the anion ordering is estimated based on an evaluation of bond distances from the ADT measurements via bond valence sums (BVSs). The observed disordering of the anions in the oxyfluoride results in changes in the optical properties and thus shows that the topochemical anion modification can present a viable route to alter the optical properties. Partial densities of states (PDOSs) obtained from ab initio density functional theory (DFT) calculations reveal a bandgap modification upon fluoride-ion introduction which originates from the presence of the oxide anions on the interstitial sites. The photocatalytic performance of the oxide and oxyfluoride shows that both materials are photocatalytically active for hydrogen (H2) evolution.

Dose symmetric electron diffraction tomography (DS-EDT): Implementation of a dose-symmetric tomography scheme in 3D electron diffraction

Beam sensitive nanomaterials such as zeolites or metal-organic frameworks (MOF) represent a great challenge for crystallographic structure determination and refinement. The strong electron-matter interaction and the high spatial resolution achievable make electron diffraction the technique of choice for particles of sizes below a micrometer and many different 3-dimensional electron diffraction (3D ED) techniques have been developed in recent years. Nevertheless, beam sensitivity of the samples can lead to the crystal structure being damaged during the data acquisition impeding the determination of its structure. A simple way to reduce beam damage is to lower the dose during the experiment. However, this implies weaker diffraction intensities which can become problematic for the exploitation of the data.In order to obtain complete data sets with strong intensities without damaging the crystals, we developed the dose symmetric electron diffraction tomography (DS-EDT) method, combining the low-dose electron diffraction tomography (LD-EDT) technique with the dose-symmetric tomography scheme known from cryo-EM. In order to reduce the dose on an individual crystal and still obtain enough data for a structure solution and refinement, we partition the dose over several crystals. The individual datasets are then merged in order to achieve the necessary completeness. On two test structures we first show that merging of data from small domains of the reciprocal space is indeed sufficient to obtain reliable data for structure solution and refinement. Second, we show on the beam sensitive manganese formate that high-quality data can be obtained on a few frames while the frames that have suffered from beam damage can still be used to determine the orientation matrix and the unit cell of the crystals. The results from the dynamical refinement on the obtained data show a high accuracy of the atom positions. In this way, DS-EDT can reduce the total dose on an individual crystal by an order of magnitude with respect to the already very dose-efficient LD-EDT.

Precession electron diffraction tomography for structural analysis of nanoparticles: a study of minimal size and associated dynamical effects

Precession electron diffraction tomography for structural analysis of nanoparticles: a study of minimal size and associated dynamical effects

Using electron energy-loss spectroscopy to measure nanoscale electronic and vibrational dynamics in a TEM.

Electron energy-loss spectroscopy (EELS) can measure similar information to x-ray, UV-Vis, and IR spectroscopies but with atomic resolution and increased scattering cross-sections. Recent advances in electron monochromators have expanded EELS capabilities from chemical identification to the realms of synchrotron-level core-loss measurements and to low-loss, 10-100meV excitations, such as phonons, excitons, and valence structures. EELS measurements are easily correlated with electron diffraction and atomic-scale real-space imaging in a transmission electron microscope (TEM) to provide detailed local pictures of quasiparticle and bonding states. This perspective provides an overview of existing high-resolution EELS (HR-EELS) capabilities while also motivating the powerful next step in the field-ultrafast EELS in a TEM. Ultrafast EELS aims to combine atomic-level, element-specific, and correlated temporal measurements to better understand spatially specific excited-state phenomena. Ultrafast EELS measurements also add to the abilities of steady-state HR-EELS by being able to image the electromagnetic field and use electrons to excite photon-forbidden and momentum-specific transitions. We discuss the technical challenges ultrafast HR-EELS currently faces, as well as how integration with in situ and cryo measurements could expand the technique to new systems of interest, especially molecular and biological samples.

Type-II Red Phosphorus: Wavy Packing of Twisted Pentagonal Tubes.

Elemental phosphorus exhibits fascinating structural varieties and versatile properties. The unique nature of phosphorus bonds can lead to the formation of extremely complex structures, and detailed structural information on some phosphorus polymorphs is yet to be investigated. In this study, we investigated an unidentified crystalline phase of phosphorus, type-II red phosphorus (RP), by combining state-of-the-art structural characterization techniques. Electron diffraction tomography, atomic-resolution scanning transmission electron microscopy (STEM), powder X-ray diffraction, and Raman spectroscopy were concurrently used to elucidate the hidden structural motifs and their packing in type-II RP. Electron diffraction tomography, performed using individual crystalline nanowires, was used to identify a triclinic unit cell with volume of 5330 ų, the largest unit cell for elemental phosphorus crystals up to now, which contains approximately 250 phosphorus atoms. Atomic-resolution STEM imaging, which was performed along different crystal-zone axes, confirmed that the twisted wavy tubular motif is the basic building block of type-II RP. Our study discovered and presented a new variation of building blocks in phosphorus, and it provides insights to clarify the complexities observed in phosphorus as well as other relevant systems.

Type‐II Red Phosphorus: Wavy Packing of Twisted Pentagonal Tubes

AbstractElemental phosphorus exhibits fascinating structural varieties and versatile properties. The unique nature of phosphorus bonds can lead to the formation of extremely complex structures, and detailed structural information on some phosphorus polymorphs is yet to be investigated. In this study, we investigated an unidentified crystalline phase of phosphorus, type‐II red phosphorus (RP), by combining state‐of‐the‐art structural characterization techniques. Electron diffraction tomography, atomic‐resolution scanning transmission electron microscopy (STEM), powder X‐ray diffraction, and Raman spectroscopy were concurrently used to elucidate the hidden structural motifs and their packing in type‐II RP. Electron diffraction tomography, performed using individual crystalline nanowires, was used to identify a triclinic unit cell with volume of 5330 Å3, which is the largest unit cell for elemental phosphorus crystals up to now and contains approximately 250 phosphorus atoms. Atomic‐resolution STEM imaging, which was performed along different crystal‐zone axes, confirmed that the twisted wavy tubular motif is the basic building block of type‐II RP. Our study discovered and presented a new variation of building blocks in phosphorus, and it provides insights to clarify the complexities observed in phosphorus as well as other relevant systems.

Novel applications of generative adversarial networks (GANs) in the analysis of ultrafast electron diffraction (UED) images.

Inferring transient molecular structural dynamics from diffraction data is an ambiguous task that often requires different approximation methods. In this paper, we present an attempt to tackle this problem using machine learning. Although most recent applications of machine learning for the analysis of diffraction images apply only a single neural network to an experimental dataset and train it on the task of prediction, our approach utilizes an additional generator network trained on both synthetic and experimental data. Our network converts experimental data into idealized diffraction patterns from which information is extracted via a convolutional neural network trained on synthetic data only. We validate this approach on ultrafast electron diffraction data of bismuth samples undergoing thermalization upon excitation via 800nm laser pulses. The network was able to predict transient temperatures with a deviation of less than 6% from analytically estimated values. Notably, this performance was achieved on a dataset of 408 images only. We believe that employing this network in experimental settings where high volumes of visual data are collected, such as beam lines, could provide insights into the structural dynamics of different samples.

Scanning Precession Electron Tomography (SPET) for Structural Analysis of Thin Films along Their Thickness

Accurate structure analysis of epitaxial perovskite thin films is a fundamental step towards the ability to tune their physical properties as desired. Precession-assisted electron diffraction tomography (PEDT) has proven to be an effective technique for performing ab initio structure solutions and refinements for this class of materials. As the film thickness or the region of interest (ROI) decrease in size, the capacity to collect PEDT data with smaller electron beams is a key parameter and ROI tracking becomes a major issue. To circumvent this problem, we considered here an alternative approach to acquiring data by combining PEDT with a scan over an area, extracting the intensities collected at different positions and using them to perform accurate structure refinements. As a proof of concept, a Scanning Precession Electron Tomography (SPET) experiment is performed on a 35 nm thick perovskite PrVO3(PVO) film deposited on a SrTiO3 (STO) substrate. This way, it was possible to detect small changes in the PVO structure along the film thickness, from the variation in unit cell parameters to atomic positions. We believe that SPET has the potential to become the standard procedure for the accurate structure analysis of ROIs as small as 10 nm.

Hydrogen-induced phase with martensitic-like characteristics in Ti-Ni shape memory alloys

It has been reported that functional and mechanical properties of Ti-Ni shape memory alloys could be degraded by hydrogen absorption. Many studies have indicated the formation of a hardened layer on the surface in hydrogen-absorbed Ti-Ni alloys. However, the underlying microstructural features and their impact on the functional and mechanical properties remain unclear. In the present study, ex situ and in situ electron microscopy characterizations of the high-hardness layer in a hydrogen-charged Ti-Ni alloy were performed for the first time. Electron diffraction and atomic resolution imaging revealed that the hardened layers have an orthorhombic structure with a four-layer stacking sequence and a martensitic-like crystallographic nature such as lattice correspondence including 12 variants of the orthorhombic phase against each orientation of the parent cubic (B2) phase. In situ and ex situ observations in an electron microscope confirmed that the orthorhombic phase undergoes athermal transformation upon cooling and stress- and/or strain-induced transformation upon deformation, which further characterizes the martensitic-like nature of this phase. The effect of hydrogen on the original phase transformation from the cubic (B2) to the monoclinic (B19′) structure is also discussed.

Locating Hydrogen Positions for COF-300 by Cryo-3D Electron Diffraction.

Covalent organic frameworks (COFs) have wide-ranging applications, and their host-guest interactions play an essential role in the achievement of COF functions. To investigate these host-guest interactions, it is necessary to locate all atoms, especially hydrogen atoms. However, it is difficult to determine the hydrogen atomic positions in COFs because of the complexities in synthesizing high-quality large single crystals. Three-dimensional electron diffraction (3D ED) has unique advantages for the structural determination of nanocrystals and identification of light atoms. In this study, it was demonstrated for the first time that the hydrogen atoms of a COF, not only on the framework but also on the guest molecule, can be located by 3D ED using continuous precession electron diffraction tomography (cPEDT) under cryogenic conditions. The host-guest interactions were clarified with the location of the hydrogen atoms. These findings provide novel insights into the investigation of COFs.

Continuous electron diffraction tomography with Gatan electron counting cameras and Latitude D

Continuous electron diffraction tomography with Gatan electron counting cameras and <i>Latitude D</i>

Formation and structure of the Al–Mn–Pt “Robinson-type” phase

The stable “Robinson-type” phase (R-phase, Cmcm, a = 7.730 Å, b = 24.035 Å and c = 12.597 Å) was revealed at 700 °C in a small compositional region around Al79.5Mn16Pt4.5. Partial phase equilibria in its vicinity were determined at 700 °C. At this temperature, it is in equilibrium with the ternary extension of the Al–Mn T-phase, whose compositional region propagates up to that of the R-phase. An atomic model of the R-phase, containing 124 Al, 24 Mn and 8 Pt atoms, was deduced using direct methods applied to the 3D electron-diffraction tomography data and compared to those of the Al–Mn–Ni R-phase and Al–Mn–Pt(Pd) T-phase.

Locating Hydrogen Positions for COF‐300 by Cryo‐3D Electron Diffraction

Locating Hydrogen Positions for COF‐300 by Cryo‐3D Electron Diffraction

Structural, optical and giant dielectric constant properties of pure ktenasite and schulenbergite/CuO minerals

In this study, schulenbergite [(Cu,Zn)7(SO4)2(OH)10·3H2O)]/CuO and pure ktenasite [(Cu,Zn)5(SO4)2(OH)6·6H2O)] minerals were simply synthesized via addition of sodium sulfide (Na2S) to a mixture of nanosized CuO powder dispersed into Zn(NO3)2·6H2O solution. The X-ray diffraction patterns illustrate the formation of schulenbergite/CuO mineral with ratio of 69:31% and 87/13% owing to additions of 0.1 and 0.2 mol L−1 Na2S, respectively. The addition of 0.4 mol L−1 Na2S substance lead to formation of pure ktenasite [(Cu,Zn)5(SO4)2(OH)6·6H2O)] mineral. The absorption vibration modes based on Fourier-transform infrared (FTIR) analysis verified the formation of schulenbergite/CuO and pure ktenasite compositions. The scanning electron microscope micrographs of schulenbergite/CuO and pure ktenasite samples reveal the formation of mixed grains with needle, sheets, cotton and wool shapes. The selected area electron diffraction images of the synthesized powders show strong dot-rings, indicating polycrystalline nature. Optically, all samples possess a high absorption ability for infrared-visible light wavelengths. At lower frequencies, the pellet of pure ktenasite sample exhibits giant dielectric constant characteristics. Exactly, pure ktenasite sample reveals a dielectric constant value of ~ 1.3 × 106 at frequency of 42 Hz. For schulenbergite/CuO (87/13%) sample, a large dielectric constant value of ~ 5311 was measured at frequency of 42 Hz. The colossal and variable relative permittivity values make the pure ktenasite [(Cu,Zn)5(SO4)2(OH)6·6H2O)] mineral is a suggested material for energy storage applications.

Can NbO Keep nbo Topology under Electrons? -Unveiling Novel Aspects of Niobium Monoxide at the Atomic Scale.

A precise investigation of NbO has been carried out by advanced electron microscopy combined with powder and single crystal X-ray diffraction (XRD). The structure of pristine NbO has been determined as Pm-3 m space group (SG) with a = 4.211 Å and the positions of Nb and O at the 3c and 3d Wyckoff positions, respectively, which is consistent with previous report based on powder XRD data. Electron beams induced a structural transition, which was investigated and explained by combining electron diffraction and atomic-resolution imaging. The results revealed that the electron beam stimulated both Nb and O atom-migrations within each fcc sublattice, and that the final structure was SG Fm-3 m with a = 4.29 Å, Nb and O at the 4a and 4b with 75 % occupancy and same chemical composition. Antiphase planar defects were discovered in the pristine NbO and related to the structural transformation. Theoretical calculations performed by density functional theory (DFT) supported the experimental conclusions.

Protection of titanium alloys against high temperature oxidation during closed-die forging: Structural analysis of the boro-silicate glass coating/Ti-6Al-4V alloy interfacial region by correlative imaging

We analyse herein the interfacial region formed between a borosilicate glass coating and Ti-6Al-4V alloy after a transient of 8 h at 1150 °C. The correlation of two optical and electron microscopy methods (Raman and Backscatter Electron Diffraction imaging) enabled an accurate description of this particular interface. This interface is composed of five different phases, namely Ti2O3, TiB2, TiB, Ti5Si3 and Ti6Si2B, and it proves to be protective against oxygen permeation. Finally, this study also enabled the development of a Raman database for Ti borides, silicides, and borosilicides, in part from experimental and more completely from theoretical (DFT computations) data.

Effects of Heat Treatment in Air Atmosphere on Dip Coating Deposited CdS Thin Films for Photo Sensor Applications

Objective: In this report, photo sensitive materials with enhanced charge carriers have been prepared using dip coating technique. Methods: Cadmium sulphide (CdS) is N-type semiconductor compound belonging to II-VI group. CdS nanoparticles were synthesized using non-aqueous chemical method and characterized by ultraviolet-visible (UV-Vis) absorption spectroscopy, photoluminescence (PL) and transmission electron microscopy. CdS films were deposited on fluorine doped tin oxide (FTO) glass slides using dip coating method at different dip times and heat treated in air and analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive analysis by X-rays (EDAX), mapping and atomic force microscopy (AFM). Results: Quantum confinement effect was observed in UV-Vis absorption spectra of CdS nanoparticles. Quenching of luminescence intensity and blue shift at smaller wavelengths were observed in PL spectra. Presence of highly dense rectangular shaped grains in CdS films and increment in particle sizes with increase in dip time were shown by AFM images. Selected area electron diffraction images showed ring patterns indicating polycrystalline nature of CdS nanoparticles. Increase in crystallite size and decrease in crystal defects by heat treatment in air and increment in grain size with increase in dip time were shown by SEM images. XRD analysis of CdS films showed polycrystalline nature. Conclusion: In previous work, preparation of dip coating deposited CdS films on FTO glass substrates for optoelectronic device applications such as photo sensors has not been reported. In this study, I-V characteristics of heterojunctions under dark and illumination conditions were discussed. Experimental results obtained in our study and their comparison with previous reports were also discussed.

High Photosensitivity Nanocrystalline p-Cu2S/n-FTO Heterojunction Photodetectors Prepared by Dip Coating Method

Objective: The aim of present work is to fabricate nanocrystalline p-Cu2S/n-FTO heterojunction photo detectors with high photosensitivity. Methods: Copper sulphide (Cu2S) is semiconductor compound belonging to I-VI group. Cost effective chemical method was used to synthesize thioglycerol capped Cu2S nanoparticles with improved optoelectronic and physical properties. These nanoparticles were investigated by ultraviolet-visible (UV-Vis) absorption spectroscopy, photoluminescence (PL) and transmission electron microscopy (TEM). Cu2S films were deposited on fluorine doped tin oxide (FTO) glass slides using cost effective dip coating method at different dip times and heat treated in air atmosphere. Wide band gap fluorine doped tin oxide, n-type semiconductor was used as transparent window material together with narrow band gap Cu2S, p-type semiconductor used as absorber layer in case of Cu2S/FTO heterojunction photo detectors under reverse biased mode and illumination. Results: Cu2S films were characterized by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive Analysis by X-rays (EDAX), Mapping and Atomic Force Microscopy (AFM). Selected Area Electron Diffraction (SAED) images showed ring patterns indicating that Cu2S nanoparticles are polycrystalline in nature and spot patterns indicating that Cu2S nanoparticles are monocrystalline in nature. Conclusion: Previously, preparation of optoelectronic devices such as photo detectors using Cu2S films has not been reported. In this study, photo detectors having enhanced photosensitivity were prepared using Cu2S films. I-V characteristics of p-Cu2S/n-FTO heterojunctions under dark and illumination conditions were examined. It was observed that film conductivity decreases under dark condition and increases under illumination condition with increase in dip time in case of Cu2S/FTO heterojunction photo detectors.