Quantitative Characterization by Transmission Electron Microscopy and Its Application to Interfacial Phenomena in Crystalline Materials

This paper reviews quantitative characterization via transmission electron microscopy (TEM) and its application to interfacial phenomena based on the results obtained through the studies. Several signals generated by the interaction between the specimen and the electron beam with a probe size of less than 1 nm are utilized for a quantitative analysis, which yields considerable chemical and physical information. This review describes several phenomena near the interfaces, e.g., clear solid-vapor interface (surface) segregation of yttria in the zirconia nanoparticles by an energy-dispersive X-ray spectroscopy analysis, the evaluation of the local magnetic moment at the grain boundary in terms of electron energy loss spectroscopy equipped with TEM, and grain boundary character dependence of the magnetism. The direct measurement of the stress to the dislocation transferred across the grain boundary and the microstructure evolution focused on the grain boundary formation caused by plastic deformation are discussed as examples of material dynamics associated with the grain boundary. Finally, the outlook for future investigations of interface studies, including the recent progress, is also discussed.

Machine Learning for Optical Scanning Probe Nanoscopy

The ability to perform nanometer-scale optical imaging and spectroscopy is key to deciphering the low-energy effects in quantum materials, as well as vibrational fingerprints in planetary and extraterrestrial particles, catalytic substances, and aqueous biological samples. These tasks can be accomplished by the scattering-type scanning near-field optical microscopy (s-SNOM) technique that has recently spread to many research fields and enabled notable discoveries. Herein, it is shown that the s-SNOM, together with scanning probe research in general, can benefit in many ways from artificial-intelligence (AI) and machine-learning (ML) algorithms. Augmented with AI- and ML-enhanced data acquisition and analysis, scanning probe optical nanoscopy is poised to become more efficient, accurate, and intelligent.

Accurate quantification of phosphorus intergranular segregation in iron by STEM-EDX

This study describes a method to quantify phosphorus grain boundary segregation by Energy Dispersive X-ray Spectroscopy in Scanning Transmission Electron Microscope (STEM-EDX). A "box-type method" is employed, removing the long-discussed problems of interaction volume and the beam broadening effect. The proposed methodology also introduces a novel way of subtracting the spectrum background to remove the influence of coherent Bremsstrahlung and spurious peaks. A Fe-P model alloy was used to compare the box method to the quantification results previously obtained by atom probe tomography on two high angle grain boundaries. The results are specifically reported in surface concentration (atom/nm²) to avoid additional hypotheses and allow the results between the two techniques to be directly compared. The measurements show that the box-type method can accurately measure phosphorus intergranular segregation in iron.

Anisotropic Angstrom-Wide Conductive Channels in Black Phosphorus by Top-down Cu Intercalation

Intercalation in black phosphorus (BP) can induce and modulate a variety of the properties including superconductivity like other two-dimensional (2D) materials. In this perspective, spatially controlled intercalation has the possibility to incorporate different properties into a single crystal of BP. We demonstrate anisotropic angstrom-wide (∼4.3 Å) Cu intercalation in BP, where Cu atoms are intercalated along a zigzag direction of BP because of its inherent anisotropy. With atomic structure, its microstructural effects, arising from the angstrom-wide Cu intercalation, were investigated and extended to relation with macrostructure. As the intercalation mechanism, it was revealed by in situ transmission electron microscopy and theoretical calculation that Cu atoms are intercalated through top-down direction of BP. The Cu intercalation anisotropically induces transition of angstrom-wide electronic channels from semiconductor to semimetal in BP. Our findings throw light on the fundamental relationship between microstructure changes and properties in intercalated BP, and tailoring anisotropic 2D materials at angstrom scale.

Evolution in X-ray Analysis from Micro to Atomic Scales in Aberration- Corrected Scanning Transmission Electron Microscopes

X-ray analysis is one of the most robust approaches to extract quantitative information from various materials, and is widely used in various fields ever since Raimond Castaing established procedures to analyze electron-induced X-ray signals for materials characterization 70 years ago. The recent development of aberration-correction technology in a (scanning) transmission electron microscopes (S/TEM) offers refined electron probes below the Å level, making atomic-resolution X-ray analysis possible. In addition, the latest silicon drift detectors (SDDs) allow complex detector arrangements and new configurational designs to maximize the collection efficiency of X-ray signals, which make it feasible to acquire X-ray signals from single atoms. In this review paper, recent progress and advantages related to S/TEM-based X-ray analysis will be discussed: (1) progress in quantification for materials characterization including the recent applications to light element analysis, (2) progress in analytical spatial resolution for atomic-resolution analysis and (3) progress in analytical sensitivity toward single atom detection and analysis in materials. Both atomic resolution analysis and single atom analysis are evaluated theoretically through multislice-based calculation for electron propagation in oriented crystalline specimen in combination with X-ray spectrum simulation.

Energy-dispersive X-ray spectroscopy for an atomic-scale quantitative analysis of Pd-Pt core-shell nanoparticles

The properties of core-shell nanoparticles, which are used for many catalytic processes as an alternative to platinum, depend on the size of both the particle and the shell. It is thus necessary to develop a quantitative method to determine the shell thickness. Pd-Pt core-shell particles were analyzed using scanning transmission electron microscopy (STEM) and energy-dispersive X-ray spectroscopy (EDX). Quantitative EDX line profiles acquired from the core-shell particle were compared to four core-shell models. The results indicate that the thickness of the Pt shell corresponds to two atomic layers. Meanwhile, high-angle annular dark-field STEM images from the same particle were analyzed and compared to simulated images. Again, this experiment demonstrates that the shell thickness was of two atomic layers. Our results indicate that, in small particles, it is possible to use EDX for a precise atomic-scale quantitative analysis.

Evaluating the stoichiometric trait distributions of cultured bacterial populations and uncultured microbial communities

We measured the stoichiometric trait distribution of cultured freshwater bacterial populations under different resource conditions and compared them to natural microbial communities sampled from three lakes. Trait distributions showed population differences among growth phases and community differences among lakes that would have been masked by only reporting the mean biomass value. The stoichiometric trait distribution of the environmental isolates changed with P availability, growth phase and genotype, with P availability having the strongest effect. The distribution of biomass ratios within each isolate growth experiment were the most constrained during the stages of rapid growth and commonly had unimodal distributions. In contrast to the population distributions, the distribution of N:P and C:P for a similar number of cells from each of the lake communities had narrower stoichiometric distributions and more commonly exhibited multiple modes. © 2019 Society for Applied Microbiology and John Wiley & Sons Ltd.

Structure and local chemical properties of boron-terminated tetravacancies in hexagonal boron nitride

Imaging and spectroscopy performed in a low-voltage scanning transmission electron microscope are used to characterize the structure and chemical properties of boron-terminated tetravacancies in hexagonal boron nitride. We confirm earlier theoretical predictions about the structure of these defects and identify new features in the electron energy-loss spectra of B atoms using high resolution chemical maps, highlighting differences between these areas and pristine sample regions. We correlate our experimental data with calculations which help explain our observations.