Numerical calculation of thermoreflectance coefficient of c-Si for wavelengths of 200-800 nm and temperatures of 300-500 K

In this paper, the thermoreflectance (TR) coefficient of c-Si is numerically calculated over the wavelength range of 200–800 nm and the temperature range of 300–500 K using a complex permittivity model that considers interband transitions and free carriers. The calculated results are in good agreement with literature values, and it is found that the temperature dependence of the TR coefficient is almost negligible at wavelengths above 500 nm. On the other hand, in the wavelength range of 200–500 nm, the TR coefficient depends strongly on the wavelength, and the temperature stability also changes significantly depending on the wavelength. This suggests that the wavelength of the probe light for TR measurement should be appropriately selected to realize high sensitivity and temperature stability, considering the constraints of the optical system and the temperature range of the sample

Effect of the Particle Size of Al/Ni Multilayer Powder on the Exothermic Characterization

In this study, the exothermic temperature performance of various Al/Ni multilayer powders with particle sizes ranging from under 75 to over 850 µm, which generate enormous heat during self-propagating exothermic reactions, was determined using a high-speed sampling pyrometer. The Al/Ni multilayer powders were prepared by a cold-rolling and pulverizing method. The multilayer constitution of the Al/Ni multilayer powders was examined by observing the cross-section of the powders using scanning electron microscopy; the results indicate that the powders had similar lamellar structures regardless of the particle size. Exothermic reactions were carried out to measure the temperature changes during the experiment using a pyrometer. We found that the maximum temperature and the duration of the exothermic reaction increased with an increase in the particle size caused by the heat dissipation of the surface area of the Al/Ni multilayer powder. This indicates that the thermal characteristics of the exothermic reaction of the Al/Ni multilayer powder can be controlled by adjusting the particle size of the Al/Ni multilayer powder. Finally, we concluded that this controllability of the exothermic phenomenon can be applied as a local heating source in a wide range of fields

Determination of Seebeck coefficient originating from phonon-drag effect using Si single crystals at different carrier densities

Abstract The phonon-drag effect is useful for improving the thermoelectric performance, especially the Seebeck coefficient. Therefore, the phonon and electron transport properties of Si single crystals at different carrier densities were investigated, and the relationship between these properties and the phonon-drag effect was clarified. Phonon transport properties were determined using nanoindentation and spot-periodic heating radiation thermometry. The electron transport properties were determined based on the electrical conductivity of Si. The diffusive Seebeck coefficient derived from the electron transport properties was in good agreement with previous reports. However, the value of the phonon-drag Seebeck coefficient derived from the phonon transport properties is very low. This phenomenon suggests that phonons with a normal mean free path (MFP) do not contribute to the increase in the Seebeck coefficient; however, phonons with a long MFP and low frequency increase the Seebeck coefficient via the phonon-drag effect. Moreover, the phonon-drag effect was sufficiently pronounced even at 300 K and in the heavily doped region. These features are key in designing thermoelectric materials with enhanced performance derived from the phonon-drag effect

Surface Modification of Bi₂Te₃ Nanoplates Deposited with Tin, Palladium, and Tin/Palladium Using Electroless Deposition

Surface-modified nanoplate-shaped thermoelectric materials can achieve good thermoelectric performance. Herein, single-crystalline Bi2Te3 nanoplates with regular hexagonal shapes were prepared via solvothermal techniques. Surface modification was performed to deposit different metals onto the nanoplates using electroless deposition. Nanoparticle-shaped tin (Sn) and layer-shaped palladium (Pd) formed on the Bi2Te3 nanoplates via electroless deposition. For the sequential deposition of Sn and Pd, the surface morphology was mostly the same as that of the Sn-Bi2Te3 nanoplates. To assess the thermoelectric properties of the nanoplates as closely as possible, they were compressed into thin bulk shapes at 300 K. The Sn-Bi2Te3 and Sn/Pd-Bi2Te3 nanoplates exhibited the lowest lattice thermal conductivity of 1.1 W/(m·K), indicating that nanoparticle-shaped Sn facilitated the scattering of phonons. By contrast, the Pd-Bi2Te3 nanoplates exhibited the highest electrical conductivity. Thus, the highest power factor (15 μW/(m∙K2)) and dimensionless ZT (32 × 10−3) were obtained for the Pd-Bi2Te3 nanoplates. These thermoelectric properties were not as high as those of the sintered Bi2Te3 samples; however, this study revealed the effect of different metal depositions on Bi2Te3 nanoplates for improving thermoelectric performance. These findings offer venues for improving thermoelectric performance by sintering nanoplates deposited with appropriate metals

Development of Novel Thermal Diffusivity Analysis by Spot Periodic Heating and Infrared Radiation Thermometer Method

A spot periodic heating method is a highly accurate, non-contact method for the evaluation of anisotropy and relative thermophysical property distribution. However, accurately evaluating thermal diffusivity is difficult due to the influence of temperature wave reflection from the whole surface of the sample. This study proposes a method to derive thermal diffusivity using a parameter table based on heat transfer equations using the concept of optimum distance between heating-point and measurement point. This method considers finite sample size, sensitivity distribution of infrared ray detector, intensity distribution of heating laser and sample thickness. In these results, the obtained thermal diffusivity of pure copper corresponded well with previous literature values. In conclusion, this method is considered highly effective in evaluating the thermal diffusivity in the horizontal direction

放射線安全管理年報 -1999年度-

National Institute for Fusion Science constructed Large Helical Device (LHD) which is the largest magnetic confinement plasma experimental device using super conductive magnet coils. It took eight years to construct and the first plasma shot had been carried out on March 1998. Since then good plasma confinement experiments have been performed. This is the report of administrative work at the radiation safety center considering radiation protection for workers at the LHD and related devices, and radiation monitoring in the site. Major scope is as follows. (1) Radiation measurement and dose monitoring in the radiation controlled area and in the site using particularly developed monitoring system named as Radiation Monitoring System Applicable to Fusion Experiments (RMSAFE). (2) Establishment of education and registration system for radiation workers and access control system for the LHD controlled area. I hope this report will be helpful for management of future radiation protection in the research institute