Reduction of thermal conductivity κ while preserving high electrical conductivity σ in materials continues to be a vital goal in thermoelectric study for the reuse of exhaust heat energy. In the use of an eco-friendly and ubiquitous element, Si as thermoelectric material, high κ value in bulk Si is the essential bottleneck to achieve high dimensionless figure of merit. This is a motivation for many recent studies on reducing κ in Si, by nanostructuring, e.g., using grains/wires with size smaller than the phonon mean free path. However, κ reduction that can be achieved tends to be saturated presumably due to an amorphous limit. Here, we present a nanoarchitecture for defeating the κ amorphous limit while preserving bulk-like σ. This new nanoarchitecture is an assembly of Si nanocrystals with oriented crystals separated by a 1-monolayer amorphous layer with well-controlled nanoscale shaped interfaces. At these interfaces, novel phonon scattering occurs resulting in κ reduction below the amorphous limit. Preservation of bulk-like σ results from the coherency of the carrier wavefunctions among the oriented nanocrystals separated by the ultrathin amorphous layer.

The detail of electronic structures near the Fermi level in URu 2 Si 2 has been investigated employing stateof-art laser angle-resolved photoemission spectroscopy. The observation of a narrow dispersive band near the Fermi level in the ordered state as well as its absence in a Rh-substituted sample strongly suggest that the emergence of the narrow band is a clear signature of the hidden-order transition. The temperature dependence of the narrow band, which appears at the onset of the hidden-order transition, invokes the occurrence of periodicity modification in the ordered state, which is shown for the first time by any spectroscopic probe. We compare our data to other previous studies and discuss possible implications.

Scanning tunneling spectroscopic studies revealed the quantum-confinement effects in Ge nanocrystals formed with ultrahigh density (>1012cm−2) by Ge deposition on ultrathin Si oxide films. With decreasing crystal size, the conduction band maximum upshifted and the valence band minimum downshifted. The energy shift in both cases was about 0.7 eV with the size change from 7 to 2 nm. This shows that the energy band gaps of Ge nanocrystals increased to ∼1.4eV with decreasing size. This size dependence can be explained by the quantum-confinement effect in Ge nanocrystals.

In hypersonic flow computations, it is a key issue to predict surface heating accurately, though this is still challenging because there always are possibilities of resulting in anomalous solutions. In this paper, three properties for flux functions are proposed: 1) shock stability/robustness, 2) conservation of total enthalpy, and 3) resolving boundary layer. Then, numerical experiments are performed for widely used or recently developed flux functions, and these fluxes are categorized into five major groups based on how they satisfy the three properties. These tests reveal that no flux function investigated here possesses all the three properties. In particular, the first one is not satisfied by any flux functions, including flux-vector-splittings. Finally, contributions of those properties are compared in a two-dimensional, viscous, hypersonic blunt-body problem. Results showed that the first and the third properties are crucial, and the second one is preferred to predict hypersonic heating. A group of flux functions that best satisfies these properties is suggested, and they are recommended either to be used or designed for hypersonic heating computations.

Phonon transport in Si films was controlled using epitaxially-grown ultrasmall Ge nanodots (NDs) with ultrahigh density for the purpose of developing Si-based thermoelectric materials. The Si/Ge ND stacked structures, which were formed by the ultrathin SiO2 film technique, exhibited lower thermal conductivities than those of the conventional nanostructured SiGe bulk alloys, despite the stacked structures having a smaller Ge fraction. This came from the large thermal resistance caused by phonon scattering at the Si/Ge ND interfaces. The phonon scattering can be controlled by the Ge ND structure, which was independent of Si layer structure for carrier transport. These results demonstrate the effectiveness of ultrasmall epitaxial Ge NDs as phonon scattering sources, opening up a route for the realisation of Si-based thermoelectric materials.

The electronic properties of gold–silver binary cluster anions (AunAgm−; 2⩽n+m⩽4) were studied by using photoelectron spectroscopy (PES) with a magnetic-bottle-type electron spectrometer. The AunAgm− cluster anions were generated by a laser vaporization of a gold–silver alloy rod. For triatomic AunAg3−n clusters, monotonous increases of electron affinity (EA) were observed by the replacement of Ag atom by Au atom. In contrast, the change in EA of tetratomic AunAg4−n clusters was irregular; for n=0–2 their EAs are almost the same around 1.5 eV, whereas for n=3,4 they increase to around 2.7 eV. This irregularity in EA of AunAg4−n can be attributed to the contribution of an ionic bonding. For Au1Ag3− and Au2Ag2−, moreover, the PES spectra show two components whose intensity ratio depends on cluster source conditions, showing that two isomers should coexist at these two compositions.

We have developed a fully self-consistent method which is suitable to examine field emission currents, on the basis of the density functional theory. In our method, the nearby counterelectrode is not necessary. By using this method, we have investigated field emission currents from a biased metallic surface represented by the jellium model. We have found that the energy barrier between the jellium and vacuum becomes lower than the Fermi energy under strong electric fields (e.g., 10 V/nm for r(s) = 4 bohr). In this situation, the slope of the Fowler-Nordheim plot becomes flatter than that under a weaker field.

The authors observed a quantum-confinement effect in individual Ge1−xSnx quantum dots (QDs) on Si (111) substrates covered with ultrathin SiO2 films using scanning tunneling spectroscopy at room temperature. The quantum-confinement effect was featured by an increase in the energy band gap of ∼1.5eV with a decrease in QD diameter from 35to4nm. The peaks for quantum levels of QDs became broader with a decrease in the height-diameter aspect ratio of QDs, demonstrating the gradual emergence of two dimensionality in density of states of quasi zero-dimensional QDs with the QD flattening.