Electron Diffraction Studies Research Articles

Order-disorder phase transitions in Fe81Ga19-RE ALLOYS (RE = Dy, Er, Tb, Yb) according to neutron diffraction data

New data on the phase compositions and structural transformations in a number of Fe81Ga19 alloys doped with trace amount (≤ 0.2 at.%) of rare earth elements are presented. The data are obtained in neutron diffraction experiments performed with high resolution and in continuous temperature scanning mode when heated to 900 °C and subsequent cooling. It has been established that structural rearrangements proceed in a generally identical manner both in the original Fe81Ga19 alloy and in its doped analogues. Slow heating and subsequent cooling of the alloys (rate ±2 °C/min) leads to the formation of clusters of the D03 phase with sizes in the range (200–300) Å in the matrix of the disordered A2 phase. The sizes and volume fraction of clusters (~0.3 of the sample volume) weakly depend on the specific composition. The degree of ordering of the clusters atomic structure changes with temperature according to a second-order phase transition and is close to unity at room temperature. The search for structural ordering corresponding to the modified D03 phase, discovered in a number of electron diffraction studies, did not lead to a positive result.

Very high-T hydration in the lower gabbro section of Semail ophiolite, Hydrous components of the lower crust at fast-spreading ridge

Totally fresh black gabbros are observed locally at the very base of the gabbro section in southern Semail ophiolite. Devoid of medium to low-temperature diffuse alteration, the black gabbros are characterized by cloudy plagioclase marked by a high density of hydrothermal inclusions below the optical microscope resolution, evolving into diopside and pargasite crystals ∼10 μm sized. They record hydration at temperature over 900 °C as shown by their major elements composition. Focused Electron Backscattered Electron Diffraction (EBSD) study of the crystalline inclusions, suggests a phase transition from diopside to amphibole, and traces consistent crystallographic relationships of diopside inclusions with their host plagioclase. The detailed geometry of the microcrack system traces a complete fluid path from inter-grain cracking, to plagioclase intra-grain network, possibly thermally-induced. The evidence of solid-state deformation overprinting the magmatic textures suggests that twinning mechanism in plagioclase controls the intra-grain diffusion of hydrous fluids. Located at the interface of the Moho Transition Zone (MTZ) and semi-brittle lithosphere, the ‘black gabbros’ record a narrow domain where focused fluid flow induces rapid cooling below the gabbro solidus at the lowest limit of the magma chamber.

3D electron diffraction studies of synthetic rhabdophane (DyPO4·nH2O).

In this study, we report the results of continuous rotation electron diffraction studies of single DyPO4·nH2O (rhabdophane) nanocrystals. The diffraction patterns can be fit to a trigonal lattice (P3121) with lattice parameters a= 7.019 (5) and c= 6.417 (5) Å. However, there is also a set of diffuse background scattering features present that are associated with a disordered superstructure that is double these lattice parameters and fits with an arrangement of water molecules present in the structure pore. Pair distribution function (PDF) maps based on the diffuse background allowed the extent of the water correlation to be estimated, with 2-3 nm correlation along the c axis and ∼5 nm along the a/b axis.

Simultaneous Real and Momentum Space Electron Diffraction from a Fullerene Molecule.

Plane-wave electrons undergo momentum transfer as they scatter off a target in overlapping spherical waves. The transferred momentum leads to target structural information to be encoded in angle and energy differential scattering. For symmetric, periodic, or structured targets this can engender diffraction in the electron intensity both in real and momentum space. With the example of elastic scattering from a C_{60} molecule we show these simultaneous diffraction signatures. Simulated angle-momentum diffractograms can be imaged in experiments with a two-dimensional detector and an energy-tunable electron gun. The result may inspire the invention of technology to extend scopes of electron diffraction studies, open a track of electron crystallography using the momentum-differential diffraction, and motivate research about controlling the time delay between the pump laser pulse and probe electron pulse by tuning the electron impact speed in ultrafast electron diffraction experiments.

Polymorphism of an Nα-Aroyl-N-Aryl-Phenylalanine Amide: An X-ray and Electron Diffraction Study

Polymorphism of an Nα-Aroyl-N-Aryl-Phenylalanine Amide: An X-ray and Electron Diffraction Study

Facile fabrication of functional poly (para-phenylenediamine) nanotubes using self-degraded methyl orange template

Polyaniline (PANI) derivatives, such as poly(phenylenediamine) (para, ortho and meta derivatives) and their nanostructures are attracting immense interest in wide potential applications due to their unique multifunctionality. Here, we report synthesis of polymer nanotubes from poly (para-phenylenediamine) (PpPD) by a simple self-degrading template method using methyl orange (MO) as the structure-directing template and potassium persulfate (KPS) as the oxidant. Two experiment schemes with reversed additions of monomer and oxidant are tested and they demonstrate influence on morphology of the as-produced materials. Electron microscopy and diffraction studies show that the nanotubes with 80 −100 nm outer diameter and more than 1 μm in length, exhibit rectangular cross-section and partial crystallinity. The chemical structures of the material are characterized by EDX, FTIR and UV-Visible spectroscopy. Results show that PpPD nanotubes could be successfully prepared by the facile solution route and demonstrate that the MO template is versatile for preparing nanotubes for not only of conducting polymer but also for its derivative.

Study of quantum electron diffraction for the LISA test-mass charging

The future Laser Interferometer Space Antenna (LISA) for gravitational wave detection in space and the precursor LISA Pathfinder missions rely on metal test masses (TMs) playing the role of free-falling geodesic-reference and interferometer end mirrors. Charge deposited on the TMs by high-energy particles of galactic and solar origin couples with stray electric fields thus perturbing the free-falling geodesic motion. In previous works it has been shown that sub-keV electrons play a relevant role for TM charging. In particular, electrons with energies below 100 eV show a wave-like behavior when impacting on the gold coatings of the TMs and electrode-housing (EH), the capacitive position sensor/actuator that surrounds the TMs. We aim at studying the effects of quantum diffraction of electrons on LISA Pathfinder and LISA TMs and EH gold lattice. We calculate the quantum diffraction probability of electrons with energies < 100 eV impinging on gold lattice from different directions by using the methods of quantum mechanics. The effects of electron quantum diffraction on LISA TM charging are reported here for the first time. This work is also of interest for the second-generation LISA-like space interferometers and for all space missions whose performance relies on free-falling metal test masses.

Structural and Optical Properties of Aluminium Nitride Thin Films Fabricated Using Pulsed Laser Deposition and DC Magnetron Sputtering on Various Substrates

Abstract Aluminium nitride thin films were fabricated using pulsed laser deposition and DC magnetron sputtering. Different technological parameters and the effects of different substrates on the optical and structural parameters of AlN samples were studied. An X-ray diffraction study was performed for the layer deposited on the Si3N4 substrate. A high-energy electron diffraction study was also carried out for the layer deposited on a KCl substrate. Transmission spectra of layers on quartz, sapphire, and glass substrates were obtained. An evaluation of the optical band gap of the obtained layers was carried out (Eg form 3.81 to 5.81 eV) and the refractive index was calculated (2.58). The relative density of the film (N1TN-AlN sample) is 1.26 and was calculated using the Lorentz-Lorentz relationship. Layers of aluminium nitride show an amorphous character with a polycrystalline region. It was shown that the properties of AlN films strongly depend on the method, growth conditions, and substrate used.

High bunch charge low-energy electron streak diffraction

For time-resolved diffraction studies of irreversible structural dynamics upon photoexcitation, there are constraints on the number of perturbation cycles due to thermal effects and accumulated strain, which impact the degree of crystal order and spatial resolution. This problem is exasperated for surface studies that are more prone to disordering and defect formation. Ultrafast electron diffraction studies of these systems, with the conventional stroboscopic pump–probe protocol, require repetitive measurements on well-prepared diffraction samples to acquire and average signals above background in the dynamic range of interest from few tens to hundreds of picoseconds. Here, we present ultrafast streaked low-energy electron diffraction (LEED) that demands, in principle, only a single excitation per nominal data acquisition timeframe. By exploiting the space–time correlation characteristics of the streaking method and high-charge 2 keV electron bunches in the transmission geometry, we demonstrate about one order of magnitude reduction in the accumulated number of the excitation cycles and total electron dose, and 48% decrease in the root mean square error of the model fit residual compared to the conventional time-scanning measurement. We believe that our results demonstrate a viable alternative method with higher sensitivity to that of nanotip-based ultrafast LEED studies relying on a few electrons per a single excitation, to access to all classes of structural dynamics to provide an atomic level view of surface processes.

Local Heating Induced Single-Crystalline Phase Control in Electrochemical Synthesis of Nanomaterials.

Development of synthetic strategies selectively yielding single crystals is desired owing to the facet-dependent chemical reactivities. Recent advances in electrochemical materials synthesis yielded nanomaterials that are surfactant-free, however, typically in polycrystalline forms. In this work, an electrochemical synthetic strategy selectively yielding single-crystalline nanoparticles by implementation of surface-selective heating of the working electrode is developed. Single crystals of copper, silver, gold, and platinum are afforded, and the crystallinity verified by electron diffraction and chemical reactivity studies. Notably, Cu (100) surface prepared by electrochemical synthesis yielded high single product selectivity when applied to electrochemical CO2 reduction catalysis.

Fe-carbide/Fe-oxide-based nanocomposites synthesized as magnetic nanomaterials via laser ablation synthesis in solution (LASiS)

Magnetic nanostructured materials (MNMs) have gained prominence in materials technology developments owing to their potential biomedical applications for hyperthermia cancer treatment, and transplant organ cryopreservation. Herein, we report the facile and cost-effective synthesis of Fe-based composite MNMs, comprising both Fe@Fe2O3 and Fe3C@C core-shell nanoparticles (NPs), via Laser Ablation Synthesis in Solution (LASiS) using Fe targets ablated under acetone and toluene. Detailed materials characterizations using electron microscopy-based imaging, diffraction studies, and spectroscopic analyses - including Raman and Mössbauer spectroscopy - relate the structure-composition properties for different Fe-oxide/carbide phases in the aforesaid MNMs to their respective magnetic responses. Specifically, we confirm the presence of ultra-small (2–10 nm) amorphous Fe-oxide NPs, as well as Fe@Fe2O3 core-shell NPs (20–40 nm) in the samples synthesized by ablating Fe under acetone. In contrast, samples synthesized under toluene indicate a higher concentration of Fe3C@C core-shell NPs (20–40 nm) with a relatively low concentration of Fe2O3 NPs (2–10 nm). Furthermore, the crystallinity of the metallic phases and carbonaceous shell coatings are systematically increased by carrying out LASiS under heated toluene (up to ∼95 °C). Mössbauer spectroscopy results indicate that the elevation in toluene temperature leads to an increase in the concentrations of Fe3C@C NPs from ∼40 % to ∼53 % (at.).

In-Plane Anisotropy in the Layered Topological Insulator Ta2Ni3Te5 Investigated via TEM and Polarized Raman Spectroscopy.

Layered Ta2M3Te5 (M = Pd, Ni) has emerged as a platform to study 2D topological insulators, which have exotic properties such as spin-momentum locking and the presence of Dirac fermions for use in conventional and quantum-based electronics. In particular, Ta2Ni3Te5 has been shown to have superconductivity under pressure and is predicted to have second-order topology. Despite being an interesting material with fascinating physics, the detailed crystalline and phononic properties of this material are still unknown. In this study, we use transmission electron microscopy (TEM) and polarized Raman spectroscopy (PRS) to reveal the anisotropic properties of exfoliated few-layer Ta2Ni3Te5. An electron diffraction and TEM study reveals structural anisotropy in the material, with a preferential crystal orientation along the [010] direction. Through Raman spectroscopy, we discovered 15 vibrational modes, 3 of which are ultralow-frequency modes, which show anisotropic response with sample orientation varying with the polarization of the incident beam. Using angle-resolved PRS, we assigned the vibrational symmetries of 11 modes to Ag and two modes to B3g. We also found that linear dichroism plays a role in understanding the Raman signature of this material, which requires the use of complex elements in the Raman tensors. The anisotropy of the Raman scattering also depends on the excitation energies. Our observations reveal the anisotropic nature of Ta2Ni3Te5, establish a quick and nondestructive Raman fingerprint for determining sample orientation, and represent a significant advance in the fundamental understanding of the two-dimensional topological insulator (2DTI) Ta2Ni3Te5 material.

Synthesis technique and electron beam damage study of nanometer-thin single-crystalline thymine.

Samples suitable for electron diffraction studies must satisfy certain characteristics such as having a thickness in the range of 10-100 nm. We report, to our knowledge, the first successful synthesis technique of nanometer-thin sheets of single-crystalline thymine suitable for electron diffraction and spectroscopy studies. This development provides a well-defined system to explore issues related to UV photochemistry of DNA and high intrinsic stability essential to maintaining integrity of genetic information. The crystals are grown using the evaporation technique, and the nanometer-thin sheets are obtained via microtoming. The sample is characterized via x-ray diffraction and is subsequently studied using electron diffraction via a transmission electron microscope. Thymine is found to be more radiation resistant than similar molecular moieties (e.g., carbamazepine) by a factor of 5. This raises interesting questions about the role of the fast relaxation processes of electron scattering-induced excited states, extending the concept of radiation hardening beyond photoexcited states. The high stability of thymine in particular opens the door for further studies of these ultrafast relaxation processes giving rise to the high stability of DNA to UV radiation.

Synthesis of copper-reduced graphene oxide nanomaterials using glucose and study of its antibacterial and anticancer activities.

In this work, glucose-capped copper nanoparticles decorated reduced graphene oxide nanomaterial are synthesized at 100°C and 200°C via chemical reduction method and studied for their antibacterial and anticancer activities. Synthesized nanomaterials were characterized using X-ray Diffraction, Fourier-transform infrared, Transmission Electron Microscope, and RAMAN. It is observed in Transmission electron microscopy and Selected area electron diffraction studies that copper nanoparticles deposited onto reduced graphene oxide are smaller than nanoparticles generated in the absence of reduced graphene oxide. Also, the size of copper nanoparticles synthesized at 200°C is smaller than at 100°C. Results suggest that Cu/Glu/rGO synthesized at both temperatures showed significant antibacterial activity against Escherichia coli and Bacillus anthracis, similarly, showed significant cell death in cancer cell lines [Cal33 and HCT-116 p53 (+/+)]. Interestingly, the nanomaterials were seen to be more effective against the cancer cell lines harboring aggregating mutant p53. Tumors with aggregating mutants of p53 are difficult to treat hence, Cu/Glu/rGO can be promising therapeutic agents against these difficult cancers. However, the antibacterial and anticancer activity of Cu/Glu/rGO synthesized at 100°C where Cu2O form is obtained was found to be more effective compared to Cu/Glu/rGO synthesized at 200°C where Cu form is obtained. Though fine-tuning of the material may be required for its commercial applications.

The influence of temperature on structural and third order nonlinear properties of cadmium sulfide nanoparticle films prepared by chemical reaction method

In this work Cadmium sulfide nanoparticles)CdS-NPs(was deposited on glass substrates using a polymerassisted chemical reaction method (CRM) and annealed at different temperatures, 300∘C, 400∘Cand 500∘C. The structural and optical characteristics of CdS-NPs films were investigated using X-ray diffraction (XRD), FTIR analysis, UV–Vis absorption spectroscopy and scanning electron microscopy (SEM). X-ray diffraction (XRD) and selected area electron diffraction studies confirmed the formation of nanocrystalline cubic phase of CdS in the films. The calculation shows that the CdS crystallized in cubic phase and formed NPs with average crystallite sizes of 17.2, 20.1 and 23.3 nm and the microstrain is about 0.034, 0.030 and 0.026 for CdS films annealed at 300∘C, 400∘C and 500∘C. The UV–Vis spectrophotometer measurements showed that the films were highly transparent value of 97 % at annealing temperature of 300∘Cand 400∘C. The direct allowed bandgaps have been determined and they lie in the range 2.49 -205 eV for CdS-NPs film annealed at temperatures of 300 ∘C–500∘C. The thermal non-linear refractive indices (n2) of the CdS-NPs are determined using open and closed aperture Z-scan techniques. The optical limiting (OL) behaviours have been studied. It was shown that the OL efficiency depended on the CdS-NPs temperature. Under laser irradiation, self-diffraction rings were seen in CdS-NPs-300∘C, CdS-NPs-400∘C and CdS-NPs-500∘C. With increased input power, each pattern is created by a rise in the number of rings and the diameter of the outermost ring. The aim of the current project studies is to investigate the linear and nonlinear optical characteristics to find fresh applications for CdS-NPs in the world of optical modulators.

Electron Diffraction Study of the Structural Changes in a Thin GeTe Crystal Exposed to High-Power Femtosecond Laser Radiation

Electron Diffraction Study of the Structural Changes in a Thin GeTe Crystal Exposed to High-Power Femtosecond Laser Radiation

Exploring the labyrinth of light: multiple Bragg Diffraction phenomena in face-centered cubic photonic crystals

This work presents the outcomes of an experimental study aimed at exploring electron diffraction phenomena within a controlled environment. The experiment involved measuring the radii of diffraction rings produced under varying acceleration voltages, with a focus on the first-order ring. Unexpectedly, the observed values were half of the anticipated results, raising questions about the accuracy of the measurements. The analysis revealed that the measured value of d1 closely resembled the theoretical value of d2, suggesting a potential oversight of the first diffraction ring, possibly due to its diminutive size. The high brightness of the incident light further complicated the measurement process. Accounting for the possibility of overlooking the first diffraction ring, the derived values for d2 (128.24±33.26 pm) and d3 (70.00±5.21 pm) were compared to theoretical values (123 pm and 80 pm, respectively). Despite the challenges, the experimental results fell within an acceptable range, considering the inherent uncertainties. To mitigate errors in radii measurement, the article suggests the implementation of an automated system and recommends a thorough reassessment of experimental setup configurations to optimize conditions for more accurate measurements. The findings highlight the importance of methodological refinement to enhance precision and reliability in electron diffraction studies. This work contributes valuable insights to the field and underscores the continuous need for advancements in experimental techniques.

Deformation and failure behavior of nanocrystalline WCu

The technical potential of WCu alloys is limited by the modest fracture characteristics of the material system in its coarse-grained condition. To provide a nanocrystalline microstructure and improve mechanical properties, a W-50 at.% Cu composite was processed using high-pressure torsion deformation at a temperature of 200 °C. Therefore, two specimens were subjected to 100% and 1000% shear strains, respectively. Scanning electron and scanning transmission electron microscopy, including nanoscale energy dispersive X-ray spectroscopy mappings, were used to quantify the resulting microstructures. The average grain sizes for the 100% and 1000% deformed specimens were determined to be 14.7 ± 6.6 nm and 10.5 ± 5.6 nm, with the amount of mechanically intermixed W in the Cu grains increasing from 15.4 at.% to 15.9 at.%. X-ray diffraction and selected area electron diffraction studies both revealed strained lattice parameters of the W and Cu phases, respectively. Mechanical properties were investigated using in-situ notched microcantilever tests. The mean conditional fracture toughness and J-integral values were comparable for both conditions, at 3.7 ± 0.4 MPa√m and 245 ± 58 J/m2, respectively. The related behavior could be attributed to the low fault tolerance of the highly deformed states and was substantiated by cleaved globular W grains along the fractured surfaces. In addition, the detailed relationship between the altered grain boundary conditions, the degree of mechanical intermixing and the influence of the different microstructures on the fracture properties were carefully evaluated and discussed to pave the way for future application of these high-strength nanocomposites.

Interplay of Kinetic Limitations and Disintegration: Selective Growth of Hexagonal Boron Nitride and Borophene Monolayers on Metal Substrates.

The CVD growth of bielemental 2D-materials by using molecular precursors involves complex formation kinetics taking place at the surface and sometimes also subsurface regions of the substrate. Competing microscopic processes fundamentally limit the parameter space for optimal growth of the desired material. Kinetic limitations for diffusion and nucleation cause a high density of small domains and grain boundaries. These are usually overcome by increasing the growth temperature and decreasing the growth rate. In contrast, the nature of molecular precursors with limited thermal stability can result in dissociation and preferential desorption, leading to an undesired or ill-defined composition of the 2D-material. Here we demonstrate these constraints in a combined low-energy electron diffraction and low-energy electron microscopy study by examining the selective formation of single-layer hexagonal boron nitride (hBN) and borophene on Ir(111) using a borazine precursor. We derive a temperature-pressure phase diagram and apply classical nucleation theory to describe our results. By considering the competing processes, we find an optimum growth temperature for hBN of 950 °C. At lower temperatures, the hBN island density is increased, while at higher temperatures the precursor disintegrates and borophene is formed. Our results introduce an additional aspect that must be considered in any high-temperature growth of bielemental 2D-materials from single molecular precursors.

Nanobeam electron diffraction studies of functional metal/semiconductor junctions

Nanobeam electron diffraction studies of functional metal/semiconductor junctions