Hydrogen is an eco-friendly energy resource because of the absence of greenhouse gas emission at the point of use, and the infrastructure for hydrogen has now been put in place. However, with our present technologies, greenhouse gases are emitted during hydrogen production. Water splitting using solar energy is one of the emerging technologies to produce hydrogen without greenhouse gases. Among several techniques for the water splitting, photoelectrochemistry using semiconductor photocatalysts is the most viable. This article describes recent developments with semiconductor photocatalysts for photoelectrochemistry and introduces our photocatalyst material: cubic silicon carbide.

A quantum key distribution enables us to share a secure random bit sequence between two parties. Its security is supposed to be based on the property that any attempt to distinguish encoded quantum states causes a disturbance in the signal. In this article, we introduce a Round-Robin Differential Phase-Shift (RRDPS) quantum key distribution protocol as a new protocol that can guarantee security without monitoring for a disturbance. It makes a noisy channel available for quantum key distribution.

Transparent conducting films with a low resistance, high transparency, high flexibility, light weight and low cost are required for optical device applications. Graphene and silver nanowires have been expected to replace conventional indium-tin oxide films. Graphenes, however, have the disadvantage of high electric resistance, and silver nanowires have the issues of roughness, chemical instability and difficulty with energy-level control. The authors have found that graphene/silver nanowire/polymer stacked layers overcome these disadvantages.

GaAs_1-xBi_x and its related alloys open up a new path to exploit metastable alloys exhibiting a particular property such as luminescence with a temperature-insensitive wavelength. The surfactant-like effect of Bi atoms contributes to an improvement in quality of GaAs_1-xBi_x under extreme growth conditions outside the conventional one for high-quality III-V semiconductors. GaAs_0.905Bi_0.095 emits a bright photoluminescence at a wavelength of 1.3µm without an intensity degradation compared to GaAs_1-xBi_x (x < 9.5%). A lasing emission of up to 1.2 and 1.05µm was demonstrated in photo- and electrically-pumped GaAs_1-xBi_x lasers, respectively at room temperature. Laser-quality GaAs_1-xBi_x alloys can be grown by molecular beam epitaxy under low temperature conditions.

New computing functionality emerging from spatial correlations due to the near-field interaction between local processing and memory elements is discussed. In particular, we investigate the possibility of solving a problem analogous to the spin-glass problem by using a coupled oscillator (dipole) system, in which the individual coupling strengths can be modified to optimize the system so that the exact solution can be easily obtained. For this algorithm, we propose an implementation based on a coupled plasmon-particle system interacting with a phase-change material, which exhibits a threshold behavior and plasticity to provide processing and memory functions, respectively.

Real-time measurement of the absolute frequency of continuous-wave terahertz (CW-THz) radiation is required for the characterization and frequency calibration of practical CW-THz sources. We proposed a method for real-time monitoring of the absolute frequency of CW-THz radiation based on dual THz frequency combs of photocarriers (PC-THz combs) with different frequency spacings. Regardless of the absence of frequency controls in the PC-THz combs, a frequency precision of 10^-11 was achieved at a measurement rate of 100 Hz. Furthermore, large fluctuations of the CW-THz frequencies, crossing a few modes of the PC-THz combs, was correctly monitored in real time. The proposed method will be a powerful tool for the research and development of practical CW-THz sources, and other applications.

Single-walled carbon nanotubes have unique optical properties as a result of their one-dimensional structure. Not only do they exhibit strong polarization for both absorption and emission, large exciton binding energies allow for room-temperature excitonic luminescence. Furthermore, their emission is in the telecom-wavelength range and they can be directly synthesized on silicon substrates, providing new opportunities for nanoscale photonics and optoelectronics. Here we discuss the use of individual single-walled carbon nanotubes for the generation, manipulation, and detection of light on a chip.

‘Pore engineering’, which is a method for controlling the memory performance of conducting-bridge random access memory (CBRAM) by considering the polycrystalline oxide memory layer as a nano-porous body, is proposed. This method enables the control of important memory parameters by providing appropriate solvents to the pores, and by controlling the pore size and physical and chemical properties of the pore surface. In this paper, it was confirmed that forming and set voltages were achieved, and their dispersions were reduced by supplying solvents with a high solubility of Cu to the HfO₂ layer of the Cu/HfO₂/Pt structures. Not only was there a reduction of the switching voltages and their dispersion but also an improvement in both the immunity against external disturbances and cycling endurance was achieved by supplying an ionic liquid.