In the far-ultraviolet region (< 200 nm), many materials have strong absorbance due to electronic excitations and electron transfers intra- and inter-materials. Recently, a new far-ultraviolet spectroscopy based on the attenuated total reflectance method has been developed, and systematic spectral measurements of various liquid and solid samples have been reported. In this tutorial, recent far-ultraviolet studies focusing on functional materials such as titanium dioxide and ionic liquid are summarized. By introducing the original system into the instrument, spectral measurements under light irradiations and electrochemical environments were achieved. The obtained data were related to the material properties such as the photocatalytic activity and molecular behavior near the electrode surface. High applicability and flexibility for various objectives are important advantages of the present spectroscopic technique.
Combining the conventional concept of “congruent” with the essentially new concept of “stoichiometry”; a material with the activities of its constituent elements being unity is stoichiometric, we have developed cs-MgO:LiNbO3 and cs-MgO:LiTaO3 by introducing Mg and a vacancy, both of which are simultaneously congruent and stoichiometric. They yield no segregation of ionic species during growth so that there is no compositional change in the growing crystals even if they experience an unexpected perturbation, which is not possible with the conventional congruent LiNbO3 (c-LiNbO3). They are easy to grow with an extremely homogeneous composition and are effective at achieving excellent nonlinear optical properties. The growth fundamentals are thermodynamically and experimentally explained.
In recent years, “hot electrons”, with kinetic energy that is higher than the surrounding electrons, are attracting attention. Hot electrons are studied for their use in photochemistry and the enhancement of the efficiency of photo-electron conversion although hot electrons are not preferred during measurement. It is necessary to irradiate light with a sufficiently short wavelength beyond the band gap to excite electrons to a high energy state. However, hot electrons can be generated by using localized surface plasmon resonance. Here, we will outline the processes from the method of generating hot electrons to the transfer of the hot electrons generated in metals to semiconductors or adsorbed molecules through an interface, and the induced chemical reaction for the application to energy generation.
Deep-ultraviolet (DUV) light-emitting diodes (LEDs) with UV-C emission wavelengths shorter than 280 nm have huge potential for a wide range of applications, including surface disinfection, air/water purification, medical diagnostics, lithographic microfabrication, and ICT. Rapid progress has been made recently in the development of AlGaN-based DUV-LEDs. However, DUV-LEDs continue to have much lower output power than the more widely used blue LEDs and traditional mercury lamps. We have studied DUV-LEDs with nanophotonic structures to significantly reduce the internal optical absorption and efficiency droop. In this paper, we show high-power single-chip 265 nm DUV-LEDs with output power in excess of 500 mW, bringing substantial advantages over conventional mercury vapor lamps.
Our group has recently found improper ferroelectric materials in aluminate-sodalite-type compounds that belong to a zeolite-family. The aluminate-sodalite-type compounds are mainly composed of eco-friendly elements, which are ubiquitous in the earth’s crust. A conventional strategy for the development of ferroelectric materials is based on perovskite-type compounds, leading to many practical applications for device elements such as capacitors and frequency filters. Aluminate-sodalite-type ferroelectrics, on the other hand, show excellent performance for pyroelectric energy harvesting, which exceeds that of lead-based perovskite-type compounds, indicating the potential of non-perovskite-type ferroelectrics for functional materials. Here we give an overview of the improper ferroelectricity in aluminate-sodalite-type compounds and discuss their performance for pyroelectric energy harvesting in connection with their improper ferroelectricity.
Inverted organic photovoltaic cells (OPV) reveal high durability and efficient performance by introducing a uniform, air-stable, and low-temperature chemical bath deposited amorphous compact titanium oxide (TiOx) as the electron collection layer. For the last several decades, Kanazawa University had been developing fabrication processes for the inverted OPVs and has investigated mechanisms for the improvement of durability. Herein, in the first half, we introduce the fabrication process of inverted OPVs and demonstrate our developed TiOx layer by chemical bath deposition. In the second half, we also investigate the inner structure in a bulk heterojunction by a solvent treatment and the molecular orientation control method for highly efficient OPVs.
This article deals with recent achievements and challenges in materials informatics, especially material data accumulation and the effective description of materials. Along with the introduction of the case studies of this research field, the technologies expected for future development are also discussed.