In organic materials, the initial charge separation occurs between molecules and the photo-generated electron-hole pairs are bound by a Coulombic interaction. After charge separation, the separated electron-hole pairs will recombine or ultimately separate by diffusion. An important length scale is the Onsager length where the thermal energy of diffusion becomes comparable to the Coulombic interaction. We present recent theoretical attempts to reveal charge generation and charge recombination processes in organic materials. The results could be helpful to quantify loss processes in organic electronic devices.
The increasing use of supercritical fluids in a wide range of practical applications has motivated us to understand the fundamental aspects of these fluids. In this article, supercritical fluid structures, probed by three spectroscopic methods, i.e. dynamic light scattering, terahertz absorption, and vibrational Raman spectroscopies, are reported. As another topic, nanomaterials, synthesized by pulsed-laser ablation of solid materials in a supercritical fluid, are described. Furthermore, applications of the synthesized nanomaterials to optoelectrical devices are briefly summarized, i.e., a Si quantum dot LED and solar cell materials.
Reports of superconductivity at temperatures above 200 K in high-pressure hydrogen sulfide (H2S) had generated considerable interest in metal hydrides and their physical properties. For the progress in both fundamental understanding and device application of metal hydrides, studies using single crystals or epitaxial thin films are essential. However, to date, a few metal hydride single crystals and epitaxial thin films have been fabricated, and both fundamental and applied research on these materials remain elusive compared with oxides and nitrides. Thus, we have started our research to establish a metal-hydride epitaxial thin film synthesis technology, and to search for new functionalities. This article reviews the recent progress, and we wish this article attracts much interest to a broad readership.
In the operation process of an organic semiconductor device represented by an organic LED (OLED), it is generally assumed that electron-hole pairs are generated as an intermediate state between carriers and excitons, which play a major role in current and light emission, respectively. However, since probing techniques for electron-hole pairs have not been established, the behavior of the pair during the semiconductor operation has not been clarified. In this paper, we show that electron spin resonance (ESR) measurements via recording current and emission intensity are effective for selection probes of electron-hole pairs. These techniques are expected to provide new information on the operation process of devices through non-destructive measurement of the operating state.
In addition to the static structures of proteins, information on dynamic structural changes in the time-domain is essential to understand the molecular mechanism of biological functions of proteins. Recently, we have developed novel methods based on transient grating (TG) spectroscopy to measure the time-dependent diffusion coefficient and thermodynamical properties, both of which are closely related to conformation change. In this article, the principle of the TG method for revealing the protein reaction is described. As an example, our recent study of the light-induced DNA binding reaction of the photo-sensor protein EL222 is presented. The dynamics of light-induced protein dimerization and DNA binding were determined by time-dependent diffusion detection. The reaction scheme and a mechanism for a specific DNA binding process were proposed based on the results.
The first-principles phonon calculation is a powerful tool for understanding and predicting phonon dynamics in solids. However, the widely used harmonic approximation breaks down when the thermal or zero-point amplitude of atomic vibrations becomes significant. Also, it is unable to handle phonon physics relevant to the lattice anharmonicity, including lattice thermal conductivity and the structural phase transition. To overcome this limitation, in recent years, new ab initio phonon calculation methods, which can treat anharmonic effects beyond the quasiharmonic level, have been developed. In this article, we introduce self-consistent phonon theory that can compute finite-temperature phonon dispersion as well as many-body perturbation theory for calculating phonon lifetimes. We demonstrate the validity and versatility of these methods through their applications to SrTiO3 and Ba8Ga16Ge30.
A Resistive Analog Neuromorphic Device (RAND) is a device that can store electrical resistance values in a non-volatile manner by utilizing the resistive switch effect in insulating oxides. By using this RAND, it is possible to realize small-sized and low-power consumption brain-inspired information processing. This article describes the overview of RAND, the mechanism of the analog resistance change, and an architecture using RAND. An example of the RAND circuit performance evaluation is also shown. We hope you will feel the necessity and inevitability of developing software and hardware synchronously for AI research.