Microscopy (Oxford, England)最新文献

Low-dimensional materials, such as fullerenes, carbon nanotubes, graphene, hexagonal boron nitride, and transition metal dichalcogenides have garnered significant attention as candidates for next-generation device components. Their distinctive properties stem from reduced dimensionality and are significantly influenced by the behavior of quasiparticles, including excitons and phonons, particularly in non-periodic structures like vacancies and edges. Correlating local atomic structures with spectral features is crucial for elucidating their physical properties. Scanning transmission electron microscopy coupled with electron energy loss spectroscopy (EELS) offers localized spectral information at the single-atom level, providing valuable insights for materials characterization. Recent advances in monochromators for transmission electron microscopy have enhanced the energy resolution of EELS, enabling the measurement of optical and vibrational absorption properties at the nanoscale and atomic level. Additionally, phenomena like optically forbidden excitations and modulation of the local phonon density of states, previously inaccessible via conventional spectroscopic methods, are now observable. This review summarizes recent advancements in employing monochromated transmission electron microscopy to characterize low-dimensional materials.

Momentum-resolved EELS (q-EELS) offers unique insights into the electronic excitations governing material performance. We analyzed anisotropic plasmons in NIR-shielding WO3 and LaB6, and correlated exciton size with photocatalytic activity in TiO2, demonstrating the technique's power to elucidate the origins of key photo-functional properties. Momentum transfer (q)-resolved electron energy-loss spectroscopy (q-EELS) is a powerful tool for analyzing photo-functional materials. The technique's application has demonstrated in several recent studies. This study first investigated the anisotropic plasmon oscillations in Cs-doped hexagonal WO3, a near-infrared (NIR) shielding material, to understand the origin of its highly efficient light-scattering properties. This revealed how plasmon energies differ along different crystallographic directions, contributing to the broad NIR absorption capabilities of the material. Second, the study measured the q dispersion of carrier plasmons and thus quantified interactions (exchange-correlation effect) between carrier electrons in LaB6 crystals, another NIR shielding filter. This analysis provides critical insights into many-body effects not captured by the ideal free-electron gas model. Finally, the spatial spread sizes of excitons in anatase TiO2 were determined, establishing a correlation between the exciton size and the anisotropic photocatalytic activity of anatase TiO2. Collectively, this research demonstrates that q-EELS provides unique, q-dependent information on electronic excitations, deepening our understanding of the properties governing the performance of advanced materials.

Nanopipettes have emerged as versatile tools for diverse applications, ranging from single-molecule sensing and nanoparticle detection to scanning probe microscopies such as scanning electrochemical microscopy and scanning ion conductance microscopy (SICM). In all these fields, precise geometrical characterization is a prerequisite for quantitative analysis. However, conventional "post-experimental" characterization cannot guarantee that the tip maintained its critical geometry during the experiment. While membrane-free transmission electron microscopy enables the non-destructive observation required for "pre- and post-experimental" validation, it introduces a risk of beam-induced deformation. In this study, we systematically investigated the deformation dynamics of quartz and borosilicate glass nanopipettes. Our analysis revealed distinct mechanisms: quartz exhibited continuous spheroidization enabled by structural homogeneity, whereas borosilicate glass showed fracture due to heterogeneity. Crucially, we identified a stable regime where deformation is negligible. By adhering to these conditions, we successfully demonstrated the rigorous tracking of a single quartz nanopipette's geometry both before and after live-cell SICM imaging. This workflow provides the first direct evidence of structural stability throughout the functional process, establishing a quantitative framework for reliable nanopipette metrology.

In Monte Carlo simulations of electron sources, random initial conditions of the particles' velocity components at the cathode need to be generated: these velocities are governed by the initial energy and angular distribution of the source. To generate the distributions numerically, the probability densities must be integrated so that the distribution can be inverted. Unlike for thermionic sources, where these integrals can be performed using simple trigonometric functions, for field emission or thermal field emission sources it is not so straightforward to integrate the probability distributions analytically. In this paper, we will show how we have derived analytic formulæ for the integrals of the energy probability distributions for cold and thermal field emission sources. These formulæ involve the Gaussian hypergeometric function, which can be evaluated numerically using established computational techniques. Hence, the random energy, and therefore velocity components, can be generated efficiently for the many thousands of particles typically needed for a Monte Carlo analysis of field emission sources. We have implemented these integrals in a computer program and give results of the energy distribution for field emission sources generated by these techniques.

Detecting spin states of electrons at the atomic scale has been at the heart of progress in condensed matter physics. Spin-polarized scanning tunneling microscopy and spectroscopy (SP-STM/STS) has provided important insights into understanding the nature of various spin-dependent phenomena, owing to its capability to visualize energy- and spin-resolved local density-of-states with atomic resolution. This review provides an overview of recent progress in SP-STS using functionalized superconducting tips, focusing on two approaches: conventional superconducting tips and Yu-Shiba-Rusinov (YSR) tips, which are formed by placing a single magnetic atom at the apex of a superconducting tip. Due to their nearly full spin polarization, both types allow for precise detection of the sample's spin polarization. These advanced techniques will be powerful probes for pursuing emergent quantum phenomena that demand ultra-high spin sensitivity, such as the spin polarization of Majorana zero modes around vortex cores in topological superconductors.

Controlling electromagnetic modes in nanostructures is vital for developing advanced optical devices. Metal surfaces with periodic structures, so-called plasmonic crystals (PlCs) form band structures of surface plasmon polaritons (SPPs), providing highly controllable confinement of SPPs and conversion to far-field light. Angle-resolved cathodoluminescence (CL) spectroscopy, where emitted light upon electron beam irradiation is analyzed with angle selection, can be combined with electron microscopy to visualize eigenmodes at specific wavenumbers. This method allows not only identifying the optical properties of Bloch modes appearing in PlCs, but also accessing functions emerging by local defects introduced into the lattice. This paper reviews applications of angle-resolved CL spectroscopy to mode analysis in one-dimensional and two-dimensional PlCs, and modified structures such as cavities and waveguides. Furthermore, this paper introduces an application of this method to the analysis of enhanced light emission from a phosphor film integrated in a PlC, where emitter-resonator coupling is visualized at the nanoscale.

Electron-beam irradiation often induces unintended structural and chemical changes in materials. Here, we show that damage and reduction in tungsten trioxide (WO3) nanowires are primarily driven by a carrier-mediated ionization process. In situ electron microscopy and electron energy-loss spectroscopy reveal structural degradation accompanied by the reduction of W6+ to W5+, while carrier dynamics simulations identify persistent, high-density electron-hole populations. Quantitative analyses and control experiments indicate that knock-on displacement and heating contribute minimally. This study establishes a microscopy-based quantitative framework for understanding electron-beam-induced damage and redox processes, highlighting the potential of electron microscopy for mechanistic insights and nanoscale chemical patterning in oxides.

Si-photodiode is commonly used for the backscattered electron (BSE) detector in scanning electron microscope (SEM). However, it is difficult to detect low-energy electrons below 3 kV. We have developed a thin microchannel plate (MCP) chip with an energy filter grid as an alternative BSE detector for low-energy SEM observations. The MCP can get enough signals even at 1 keV electron beam operation. The energy filtering operation revealed that the MCP image is composed of SE and BSE signals. By filtering SE component, the low-energy BSE images are easily obtained, which will open-up the new observation method of SEM using low-BSE image.