Small-angle Electron Diffraction Research Articles

Recent advances in small-angle electron diffraction and Lorentz microscopy.

We describe small-angle electron diffraction (SmAED) and Lorentz microscopy using a conventional transmission electron microscope. In SmAED, electron diffraction patterns with a wide-angular range on the order of 1 × 10-2 rad to 1 × 10-7 rad can be obtained. It is demonstrated that magnetic information of nanoscale magnetic microstructures can be obtained by Fresnel imaging, Foucault imaging and SmAED. In particular, we report magnetic microstructures associated with magnetic stripes and magnetic skyrmions revealed by Lorentz microscopy with SmAED. SmAED can be applied to the analysis of microstructures in functional materials such as dielectric, ferromagnetic and multiferroic materials.

Magnetic bubbles in an M-type hexagonal ferrite observed by hollow-cone Foucault imaging and small-angle electron diffraction

We report hollow-cone imaging and small-angle electron diffraction (SmAED) of nanoscale magnetic textures such as magnetic-striped domains and magnetic bubbles of M-type hexagonal ferrite BaFe10.35Sc1.6Mg0.05O19. The advantage of the hollow-cone Foucault (HCF) method is that magnetic domains with various directions of magnetization can be visualized under an infocus condition. Moreover, the contrast of magnetic domain walls in magnetic bubbles depends on the inclination angle of the illumination beam. The combination of SmAED and HCF imaging proves that magnetization at domain walls exhibits in-plane directions in the magnetic-striped domains and magnetic bubbles.

Observation of magnetic domains in uniaxial magnets via small-angle electron diffraction and Foucault imaging

Observation of magnetic domains is important in understanding the magnetic properties of magnetic materials and devices. In this paper, we report that the magnetic domains of M-type hexaferrites with uniaxial anisotropy can be visualized via small-angle electron diffraction and Foucault imaging. The position of the diffraction spots has the same period as that of magnetic domains in a Sc-substituted hexaferrite (BaFe12-x-δScxMgδO19). Conversely, the spots were observed four times longer than the period of magnetic domains in hexaferrite without substitution (BaFe12O19), demonstrating the long-range order of the Bloch walls. When the specimen was tilted, the magnetic deflection effect, as well as the periodic spots of magnetic domains, occurred. Thus, we were able to visualize the magnetic domains with different magnetization directions and domain orientations by selecting deflection spots. The results indicate that the technique utilized in this study is useful in observing the magnetic materials with uniaxial anisotropy.

Local photo-mechanical stiffness revealed in gold nanoparticles supracrystals by ultrafast small-angle electron diffraction.

We demonstrate that highly ordered two-dimensional crystals of ligand-capped gold nanoparticles display a local photo-mechanical stiffness as high as that of solids such as graphite. In out-of-equilibrium electron diffraction experiments, a strong temperature jump is induced in a thin film with a femtosecond laser pulse. The initial electronic excitation transfers energy to the underlying structural degrees of freedom, with a rate generally proportional to the stiffness of the material. Using femtosecond small-angle electron diffraction, we observe the temporal evolution of the diffraction feature associated with the nearest-neighbor nanoparticle distance. The Debye-Waller decay for the octanethiol-capped nanoparticle supracrystal, in particular, is found to be unexpectedly fast, almost as fast as the stiffest solid known and observed by the same technique, i.e., graphite. Our observations unravel that local stiffness in a dense supramolecular assembly can be created by van der Waals interactions up to a level comparable to crystalline systems characterized by covalent bonding.

Direct observation of photo-mechanical stiffness in alkanethiol-capped gold nanoparticles supracrystals by ultrafast small-angle electron diffraction

We demonstrate that ultrastiff bonding between nanoparticles can be engineered by ad hoc assemblies of ligands, reaching strengths comparable to that of strong covalent bonds. Our observation relies on femtosecond small-angle electron diffraction.

Facile photochemical synthesis of ZnO nanoparticles in aqueous solution without capping agents

Photochemical synthesis of nanoparticles is a promising alternative to harsh chemical methods. In this report, synthesis of ZnO nanoparticles by photochemical route in an aqueous solvent mixture without capping agents is reported. Formation of ZnO nanoparticles is confirmed using absorption-fluorescence, photoluminescence, X-ray diffraction and small angle electron diffraction studies. Size and shape of nanoparticles is confirmed using dynamic light scattering, scanning and transmission electron microscopy. Reusability of the solvent mixture and photochemical route makes this a promising method for synthesis of ZnO nanoparticles.

Electron diffraction covering a wide angular range from Bragg diffraction to small-angle diffraction.

We construct an electron optical system to investigate Bragg diffraction (the crystal lattice plane, 10-2 to 10-3 rad) with the objective lens turned off by adjusting the current in the intermediate lenses. A crossover was located on the selected-area aperture plane. Thus, the dark-field imaging can be performed by using a selected-area aperture to select Bragg diffraction spots. The camera length can be controlled in the range of 0.8-4 m without exciting the objective lens. Furthermore, we can observe the magnetic-field dependence of electron diffraction using the objective lens under weak excitation conditions. The diffraction mode for Bragg diffraction can be easily switched to a small-angle electron diffraction mode having a camera length of more than 100 m. We propose this experimental method to acquire electron diffraction patterns that depict an extensive angular range from 10-2 to 10-7 rad. This method is applied to analyze the magnetic microstructures in three distinct magnetic materials, i.e. a uniaxial magnetic structure of BaFe10.35Sc1.6Mg0.05O19, a martensite of a Ni-Mn-Ga alloy, and a helical magnetic structure of Ba0.5Sr1.5Zn2Fe12O22.

Formation process of skyrmion lattice domain boundaries: The role of grain boundaries

We report on the formation process of skyrmion lattice (SkL) domain boundaries in FeGe using Lorentz transmission electron microscopy and small-angle electron diffraction. We observed that grain boundaries and edges play an important role in the formation of SkL domain boundaries; The SkL domain boundary is stabilized at the intersection of two grains. A micromagnetic simulation using the Landau−Lifshitz−Gilbert equation revealed that the SkL domains separated by a boundary represent the lowest energy configuration. Conversely, in a wide area, SkL domain boundaries were not formed and SkL domains with different orientations rotated to form a single SkL domain.

PM-17Magnetic Microstructures Observation of Functional Materials by Small Angle Electron Diffraction and Lorentz Microscopy

PM-17Magnetic Microstructures Observation of Functional Materials by Small Angle Electron Diffraction and Lorentz Microscopy

Convenient Optics for High Dispersion Small Angle Electron Diffraction with Highly Coherent Low Dose Illumination

Convenient Optics for High Dispersion Small Angle Electron Diffraction with Highly Coherent Low Dose Illumination

Foucault imaging and small-angle electron diffraction in controlled external magnetic fields.

We report a method for acquiring Foucault images and small-angle electron diffraction patterns in external magnetic fields using a conventional transmission electron microscope without any modification. In the electron optical system that we have constructed, external magnetic fields parallel to the optical axis can be controlled using the objective lens pole piece under weak excitation conditions in the Foucault mode and the diffraction mode. We observe two ferromagnetic perovskite-type manganese oxides, La0.7Sr0.3MnO3 (LSMO) and Nd0.5Sr0.5MnO3, in order to visualize magnetic domains and their magnetic responses to external magnetic fields. In rhombohedral-structured LSMO, pinning of magnetic domain walls at crystallographic twin boundaries was found to have a strong influence on the generation of new magnetic domains in external applied magnetic fields.

Foucault optical system by using a nondedicated conventional TEM

We have constructed an electron optical system for both Foucault imaging and small‐angle electron diffraction (SmAED) modes by using a nondedicated conventional transmission electron microscope. The objective lens is switched off as for Lorentz microscopy. An objective mini‐lens is utilized in order to make a crossover on the plane where a selected area aperture is located. The aperture works for an angular selection in the Foucault mode. The present electron optical system has two advantages: one is the independent control of the illumination and the imaging optics, and the other is the application of external magnetic fields to the specimen parallel to the optical axis with the objective lens. In SmAED mode, the maximum camera length is estimated to be approximately 1300 m. We succeeded in the observation of magnetic domain structures and SmAED patterns of the rhombohedral phase of La0.7Sr0.3MnO3 by using the present electron optical system. Copyright © 2016 John Wiley & Sons, Ltd.

Lorentz microscopy and small-angle electron diffraction study of magnetic textures inLa1−xSrxMnO3(0.15<x<0.30): The role of magnetic anisotropy

Magnetic textures in the ferromagnetic phases of La$_{1-x}$Sr$_x$MnO$_3$ for 0.15 $< x <$ 0.30 have been investigated by Lorentz microscopy combined with small-angle electron diffraction experiments. Various types of magnetic textures characterized by stripe, plate-shaped, and cylindrical (magnetic bubble) domains were found. Two distinct types of magnetic stripe domains appeared in the orthorhombic structure with an inversion symmetry of La$_{0.825}$Sr$_{0.175}$MnO$_3$, depending significantly on magnetocrystalline anisotropy. Based on in-situ observations as functions of temperature and the strength of the external magnetic field, a magnetic field-temperature phase diagram was constructed, showing the stabilization of magnetic bubbles in the ferromagnetic phase of La$_{0.825}$Sr$_{0.175}$MnO$_3$.

Order/Disorder Dynamics in a Dodecanethiol-Capped Gold Nanoparticles Supracrystal by Small-Angle Ultrafast Electron Diffraction.

The design and the characterization of functionalized gold nanoparticles supracrystals require atomically resolved information on both the metallic core and the external organic ligand shell. At present, there is no known approach to characterize simultaneously the static local order of the ligands and of the nanoparticles, nor their dynamical evolution. In this work, we apply femtosecond small-angle electron diffraction combined with angular cross-correlation analysis, to retrieve the local arrangement from nanometer to interatomic scales in glassy aggregates. With this technique we study a two-dimensional distribution of functionalized gold nanoparticles deposited on amorphous carbon. We show that the dodecanethiol ligand chains, coating the gold cores, order in a preferential orientation on the nanoparticle surface and throughout the supracrystal. Furthermore, we retrieve the dynamics of the supracrystal upon excitation with light and show that the positional disorder is induced by light pulses, while its overall homogeneity is surprisingly found to transiently increase. This new technique will enable the systematic investigation of the static and dynamical structural properties of nanoassembled materials containing light elements, relevant for several applications including signal processing and biology.

Observation of spin textures in La1−xSrxMnO3 (x = 0.175)

We have investigated topological spin textures in the ferromagnetic metallic phase of La0.825Sr0.175MnO3 with the centrosymmetric crystal structure by small-angle electron diffraction (SmAED) and low-temperature Lorentz transmission electron microscopy (TEM) experiments. In-situ Lorentz TEM and SmAED experiments revealed that type-I and type-II magnetic bubbles evolved from magnetic stripe domains with the Bloch-type domain wall by applying vertical magnetic field. Type-I magnetic bubbles with left-handed and right-handed spin helicity were randomly distributed and simultaneously type-II magnetic bubbles are formed locally. The important point about type-I and type-II magnetic bubbles is that their emergence depends strongly on whether perpendicular magnetic field is applied parallel to the magnetic easy axis along the [001] direction. Our experimental results suggested that the stabilization of magnetic bubbles should originate from the long-range dipole-dipole interactions, as opposed to the Dzyaloshinskii-Moriya interaction in helical magnets.

B11-O-15Simultaneous realization of Foucault imaging and small angle electron diffraction by conventional TEM

B11-O-15Simultaneous realization of Foucault imaging and small angle electron diffraction by conventional TEM

Oxygen reduction to hydrogen peroxide on Fe3O4 nanoparticles supported on Printex carbon and Graphene

Fe3O4 nanoparticles supported on graphene (Fe3O4/graphene) and Printex carbon (Fe3O4/Printex) are reported as promising catalysts for oxygen reduction reaction (ORR) to H2O2 in alkaline medium. The catalysts were synthesized by a simple precipitation method using NaBH4 as reducing agent to favor the formation of the magnetite phase. The structure and morphology of the catalysts was evaluated by x-ray diffraction, transmission electron microscopy and small angle electron diffraction. The electrocatalytic activity towards ORR was investigated by means of cyclic and linear voltammetries in 1molL−1 KOH. The linear polarization curves highlighted the synergetic effect between the oxide and the carbon supports. Analysis of the polarization curves showed that electro-catalytic activity of the materials towards oxygen reduction expressed by the current density at −0.3V vs SCE increases from Printex (0.29mAcm−2)<Fe3O4/Printex (0.38mAcm−2)<graphene (0.85mAcm−2)<Fe3O4/graphene (1.12mAcm−2). The number of exchanged electrons was close to 2.7 for both catalysts, and the % H2O2 electro-generated above 60% in the −0.2 to −0.7V (vs SCE) potential range. Furthermore, both Fe3O4/graphene and Fe3O4/Printex catalysts show excellent durability.

Synthesis of mullite-based coatings from alumina and zircon powder mixtures by plasma spraying and laser remelting

A mechanical mixture of alumina and pulverized zircon sand in 3:2 M ratio has been plasma sprayed to obtain mullite coating. Thereafter, the top layer of the coating has been remelted using laser. The presence of a mullite phase in the as-sprayed and laser remelted coatings has been confirmed qualitatively using X-ray diffraction. Both as-sprayed and laser remelted coatings have been characterized for their microstructure, hardness and porosity. The ultrafine grain structure of the coating produced by rapid quenching has been analyzed using transmission electron microscope. Presence of a mullite phase in the coatings has also been confirmed using small angle electron diffraction. Laser remelting has resulted in an appreciable reduction in porosity and increase in hardness in the coatings.

Controlled Morphology of Electrochemically Deposited CuSCN by Variation of Applied Bias Voltage

CuSCN is a p-type semiconductor essentially used in semiconductor sensitized solar cells for scavenging the photogenerated holes. Here we report, cathodic electrodeposition of CuSCN using NaSCN and Cu2+. Control over the film morphology is found to be highly dependent on the applied potential. One-dimensional rod like morphology with a strong (003) orientation is obtained under lower applied potential. Under higher applied potential the morphology changes to a more granular type. Films are structurally characterized by x-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM) with small angle electron diffraction (SAED).

Structural order in ultrathin films of the monolayer protected clusters based upon 4 nm gold nanocrystals: an experimental and theoretical study.

The structural order in ultrathin films of monolayer protected clusters (MPCs) is important in a number of application areas but can be difficult to demonstrate by conventional methods, particularly when the metallic core dimension, d, is in the intermediate size-range, 1.5 < d < 5.0 nm. Here, improved techniques for the synthesis of monodisperse thiolate-protected gold nanoparticles have made possible the production of dodecane-thiolate saturated ∼4 ± 0.5 nm Au clusters with single-crystal core structure and morphology. An ultrathin ordered film or superlattice of these nanocrystal-core MPCs is prepared and investigated using aberration corrected scanning/transmission electron microscopy (STEM) which allowed imaging of long-range hexagonally ordered superlattices of the nanocrystals, separated by the thiolate groups. The lattice constants determined by direct imaging are in good agreement with those determined by small-angle electron diffraction. The STEM image revealed the characteristic grain boundary (GB) with sigma (Σ) 13 in the interface between two crystals. The formation and structures found are interpreted on the basis of theoretical calculations employing molecular dynamics (MD) simulations and coarse-grained (CG) approach.