Thermal conductivity of a 300-nm-thick VO 2 thin film and its temperature dependence across the metal-insulator phase transition (T MIT ) were studied using a pulsed light heating thermoreflectance technique. The VO 2 and Mo/VO 2 /Mo films with a VO 2 thickness of 300 nm were prepared on quartz glass substrates: the former was used for the characterization of electrical properties, and the latter was used for the thermal conductivity measurement. The VO 2 films were deposited by reactive rf magnetron sputtering using a V 2 O 3 target and an Ar-O 2 mixture gas at 645 K. The VO 2 films consisted of single phase VO 2 as confirmed by X-ray diffraction and electron beam diffraction. With increased temperature, the electrical resistivity of the VO 2 film decreased abruptly from 6.3 ' 10 %1 to 5.3 ' 10 %4 Ω cm across the T MIT of around 325-340 K. The thermal conductivity of the VO 2 film increased from 3.6 to 5.4 W m %1 K %1 across the T MIT . This discontinuity and temperature dependence of thermal conductivity can be explained by the phonon heat conduction and the Wiedemann-Franz law.

We investigated the thermal conductivity of 200-nm-thick amorphous indium–gallium–zinc-oxide (a-IGZO) films. Films with a chemical composition of In:Ga:Zn= 1:1:0.6 were prepared by dc magnetron sputtering using an IGZO ceramic target and an Ar–O2 sputtering gas. The carrier density of the films was systematically controlled from 1014 to >1019 cm-3 by varying the O2 flow ratio. Their Hall mobility was slightly higher than 10 cm2·V-1·s-1. Those films were sandwiched between 100-nm-thick Mo layers; their thermal diffusivity, measured by a pulsed light heating thermoreflectance technique, was ∼5.4×10-7 m2·s-1 and was almost independent of the carrier density. The average thermal conductivity was 1.4 W·m-1·K-1.

The simultaneous realization of low thermal conductivity and high thermoelectric power factor in materials has long been the goal for the social use of high-performance thermoelectric modules. Nanostructuring approaches have drawn considerable attention because of the success in reducing thermal conductivity. On the contrary, enhancement of the thermoelectric power factor, namely, the simultaneous increase of the Seebeck coefficient and electrical conductivity, has been difficult. We propose a method for the power factor enhancement by introducing coherent homoepitaxial interfaces with controlled dopant concentration, which enables the quasiballistic transmission of high-energy carriers. The wavenumber of the high-energy carriers is nearly conserved through the interfaces, resulting in simultaneous realization of a high Seebeck coefficient and relatively high electrical mobility. Here, we experimentally demonstrate the dopant-controlled epitaxial interface effect for the thermoelectric power factor enhancement using our "embedded-ZnO nanowire structure" having high-quality nanowire interfaces. This presents the methodology for substantial power factor enhancement by interface carrier scattering.

The thermal conductivities of c- and a-axis-oriented zinc oxide (ZnO) thin films with nominal thicknesses of 100, 200, and 300 nm are investigated. The c- and a-axis-oriented ZnO thin films were synthesized by radio frequency magnetron sputtering on the c- and r-plane sapphire substrates, respectively. The epitaxial relationship between the ZnO thin film and the c-plane sapphire substrate is (0001)[11¯00] || (0001)[112¯0], and that between the ZnO thin film and the r-plane sapphire substrate is (112¯0)[11¯00] || (011¯2)[112¯0]. The c-axis-oriented ZnO thin film has a columnar structure, whereas the a-axis-oriented ZnO thin film has a single domain-like structure and a significantly flat surface. The thermal conductivity of the c-axis-oriented ZnO thin film is in the range of 18–24 W m−1 K−1, whereas for the a-axis-oriented ZnO thin film, it is in the range of 24–29 W m−1 K−1. For the c-axis-oriented ZnO thin films, the phonon scattering on both the out-of-plane and in-plane grain boundaries affects the thermal conductivity. In contrast, the thermal conductivity of the a-axis-oriented ZnO thin films decreases with the decrease of the film thickness. The distribution of the normalized cumulative thermal conductivity of the a-axis-oriented ZnO thin films suggests that the heat transport carrier mostly consists of phonons with the mean free paths between 100 nm and 1 μm.

A global color impression from a multicolored textured pattern can be identified. It is not clear, however, how such a single color impression can be determined from the elemental colors of the multicolored textured pattern. To investigate this question, two hypotheses were evaluated. The first hypothesis is that a single color impression is determined by the colorimetric average of the elemental colors in the textured pattern (colorimetric average hypothesis). The second hypothesis is that the impression is influenced by the color appearances of the elemental colors in the textured pattern (color appearance hypothesis). Using an asymmetrical color matching method, the authors obtained single color impressions for random-dot textured patterns consisting of two colors with the same unique hue and brightness but each with a different saturation. Our results showed that the matched colors were not located on the line connecting the two elemental colors of the pattern, but rather were on the curved unique hue loci line. Furthermore, the chromaticities of the matches shifted toward a higher saturation than the colorimetric averages. These results support the color appearance hypothesis and suggest that a single color impression from a multicolored textured pattern is determined by a mechanism that integrates the color appearances, i.e., hue, saturation, and brightness (or lightness), of the elemental colors in the pattern. In addition, it seems that the integration of the color appearances is not a simple process, because the apparent saturation of the color impression was higher than that of the colorimetric average and the average of the chromaticities of the colors in the pattern.