The functionalities of materials are governed by their electronic states and it is significantly important to trace their temporal variations to understand their dynamics. This paper describes the principles of time-resolved measurements by photoelectron spectroscopy that directly probes the electronic states of matter. The paper introduces research examples of carrier dynamics in graphene layers, grown on SiC substrates, at the time scale from femtoseconds to nanoseconds. Temporal evolution of the Dirac Fermions in graphene indicates a significant role of the scattering process at the Dirac point. Selective chemical measurements at the overlayer/substrate interface revealed the distinguishing carrier dynamics between graphene and SiC crystals. These research projects demonstrate that measurements by time-resolved soft X-ray photoemission spectroscopy are significant for developing the next generation of ultrafast devices.
In recent years, the performance of organic solar cells for practical applications has been improved significantly. Of these, energy harvesting applications with indoor light are attracting interest due to the recent growth of IoT. Therefore, we have been working on a standardization of the evaluation method under indoor light mainly for organic solar cells, and JEITA JT 9101 was created by referring to the IEC 60904 standard. The standard defines three types of reference indoor light, and describes a method to evaluate the efficiency of a solar cell. We continue to develop the international standard.
Since the discovery of continuous, coherent THz radiation from a mesa structure of intrinsic Josephson junction fabricated on a single crystal of Bi2Sr2CaCu2O8+δ in 2007, intensive studies, not only of the basic physics but also of applications, have been performed. So far, the best performance has been achieved within the frequency range from 0.3 to 11 THz, with the maximum output power of 30 µW, and with a spectral width of the coherent and continuous emission of THz radiation that is generally less than 0.5 GHz. Furthermore, a synchronized operation of an array of three such emitters was reported to yield the greatly enhanced power of 610 µW. We describe a brief overview of the development of superconducting THz emitters.
X-ray diagnosis represented by radiographs and CTs provide only two-dimensional monochrome images and do not have color (or energy) information. SPECT and PET are commonly used for nuclear medicine diagnosis, but in recent years, gamma ray imaging in general has been more of a focus in the field of advanced clinical applications. For example, visualizations of nuclear reactions that occur in the body is an urgent task for both proton therapy and internal alpha therapy. Interestingly, the same nuclear reaction is anticipated to occur between cosmic rays and interstellar matter in the universe, and thus may be a major topic for MeV gamma-ray astronomy. In this paper, we review the forefront of gamma-ray imaging using Compton cameras and future prospects as a new bridge connecting space and medicine.
The infrared convergent heating floating zone (IR-FZ) method is a crucible-free zone melting method. The control of the dopant segregation is possible by using a solvent with a suitable composition. In the conventional IR-FZ, however, the molten zone, which is maintained between the feed and the grown crystal by the balance of the surface tension and the gravity of the melt, is so unstable that the typical diameter of the grown crystal is 6〜15 mm at most. Slight modifications of the convergent heating such as the convergent position and tilt of the ellipsoidal mirrors was found to be quite effective to improve the diameter of a grown crystal up to the inch level.
In the early stage of arteriosclerosis, lesions appear on the vascular endothelial functions. It is important to evaluate these functions as early as possible because the lesions are still reversible. We have evaluated the viscoelastic properties of the blood vessel wall by measuring the arterial pressure and change in arterial diameter. In the present paper, we introduce the ultrasonic probe we recently developed to measure both the radial arterial pressure and the change in arterial diameter at the same position and the measured hysteresis property between the change in diameter and instantaneous pressure during a heartbeat.
Owing to the recent trend of "Materials Informatics", we can easily access excellent databases that provide a variety of information on materials. In contrast, such databases provide only single crystal bulk information, and do not provide information on lattice defects. The group of the present authors succeeded in dramatically improving the process of determining the crystal interface structures using machine learning techniques such as virtual screening, Bayesian optimization, and transfer learning. This paper will introduce the results of our studies.