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Circular cavity structures are fabricated on GaAs/ AlGaAs-based epi-wafer using SiO x hard mask to realize a proposed photonic crystal (PhC) structure with GaAs core layer having embedded InAs quantum dots (QDs) towards PhC laser fabrication. We investigate the evaluations of selective dry etching of the core layer for an epi-wafer using optical measurements. Photoluminescence (PL) intensity at 1285 nm, which is related to ground-state emission of QDs, monotonously decreases with increasing the etching depth of the core layer with QDs. The change of PL intensity for epi-wafer is good agreement with the behavior of the increased etching depth of the core layer which is evaluated by the measurements of scanning electron micrograph. We demonstrate a possibility of etching end-point detection and evaluation of etching rate during the dry etching of the core layer with QDs using in-situ optical emission spectroscopy.

For longitudinal spin Seebeck effect (LSSE) devices, a multilayer structure comprising ferromagnetic and nonmagnetic layers is expected to improve their thermoelectric power. In this study, we developed the fabrication method for alternately stacked yttrium-iron-garnet (YIG)/Pt multilayer films on a gadolinium gallium garnet (GGG) (110) substrate, GGG/[YIG(49 nm)/Pt(4 nm)]$_n$ ($n =$ 1 - 5) based on room-temperature sputtering and $ex$-$situ$ post-annealing method and we evaluated their structural and LSSE properties. The fabricated [YIG/Pt]$_n$ samples show flat YIG/Pt interfaces and almost identical saturation magnetization $M_{\rm s}$, although they contain polycrystalline YIG layers on Pt layers as well as single-crystalline YIG layers on GGG. In the samples, we observed clear LSSE signals and found that the LSSE thermoelectric power factor (PF) increases monotonically with increasing $n$; the PF of the [YIG/Pt]$_5$ sample is enhanced by a factor of $\sim 28$ compared to that of [YIG/Pt]$_1$. This work may provide a guideline for developing future multilayerbased LSSE devices., 21 pages, 4 figures

Diamond-like carbon (DLC) and carbon nitride (C-N) films have the superior properties of hardness and wear-resistance. They have been investigated extensively for several applications. In this present study, DLC and C-N films were prepared on silicon wafers, stainless steel sheets, high speed steel blocks and WC-Co tips by the hollow cathode discharge method at the high deposition rate of 0.3μm/min. Silicon or tungsten carbide-cobalt was deposited as an interlayer in order to improve the adhesion of DLC and C-N films. Raman spectra of the DLC and C-N films showed distinct D and G bands. The indenting hardness of the C-N films was found to be larger than that of the DLC films. The intensity ratio of the D band to G band in the DLC films related linearly to the indenting hardnesses. On the other hand, the intensity ratios in the C-N films were almost constant in spite of the different conditions of deposition. The indenting hardness in the C-N films depended on the amount of contained nitrogen. The DLC films exhibited a lower friction coefficient compared with the C-N films.

The de Haas-van Alphen (dHvA) effect has been investigated on high-quality single crystals of FeP in a double helical magnetic state with a 5 c period in the magnetic fields up to 14 T and at tempe...

We have measured the de Haas–van Alphen effect at 0.55 K in the field up to 9.5 T for the single crystal of Pauli paramagnetic NiAs. Six dHvA branches have been observed and they show complicated behavior as a function of the field direction which is applied in the symmetry planes (11\bar20), (10\bar10) and (0001). The corresponding cyclotron masses have been also determined from the temperature dependence of the dHvA amplitude. To discuss the experimental results we have performed the electronic band calculation of NiAs for the non-magnetic state by using the full potential LAPW method. The total energy calculated as a function of the lattice parameter a , keeping the ratio c / a as the observed value, becomes minimum at 3.60 A, which agrees very well with the observed one. The Fermi surface is found to consist of two kinds of hole surface around the ΓA axis and one electron surface with six fold symmetry. For each Fermi surface we have calculated dHvA oscillation frequencies and succeeded to explain the...

In recent years, the lithium-sulfur (Li-S) secondary battery has been energetically researched worldwide as a good candidate for next-generation secondary batteries. The sulfur active material has a theoretical capacity of 1675 mAh g-1and is abundant and highly inexpensive. However, several issues are associated with the use of Li-S secondary batteries, such as low utilization due to the insulating property of sulfur and the redox shuttle phenomenon caused by the dissolution of polysulfides generated during the discharge process. In the present work, we have developed a Li-S secondary battery using the carbon nanotube (CNT) technoloy. Multiwalled-CNTs were directly grown on a nickel current collector by using the thermal chemical vapor deposition (CVD) method. The CNT films were used as the electrode for the Li-S battery. The S-CNT cathode was fabricated by impregnating it with molten sulfur. Then, sulfur powder was uniformly placed on the CNT film and heated at more than the melting point of 113°C. Our CNT has a diameter of 10-15 nm and a length of 200-600 µm. Therefore, the CNT electrode has a wide reaction area owing to its large specific surface area. In addition, the active materials can react rapidly because the electrons quickly access through the CNTs that connect directly with the current collector. At IMLB 2014, we reported that coin-cell-type Li-S batteries with a sulfur loading of up to 10 mg cm-2 operate at a current density of 0.5 mA cm-2 [1]. However, more sulfur loading is required, in order to achieve the electrode capacity of 300 Wh kg-1 for practical usage. As sulfur loading increased to more than 10 mg cm-2, the discharge capacity decreased dramatically, probably owing to be attributed to inhomogeneous sulfur distribution in the CNT film. Moreover, the CNT films fell off the nickel current collector because of the shrinkage of the CNT bundles owing to the absorption of sulfur. Therefore, we attempted to synthesize harder CNT films with homogeneously impregnated sulfur. A thick amorphous carbon layer was coated on the CNTs by optimizing the thermal CVD process, thus making the CNT films harder. Moreover, the adhesiveness between the CNTs and the nickel current collector was enhanced, which improved CNT exfoliation. For homogeneous distribution, sulfur impregnation was performed in vacuum. The sulfur was considered to spread over the CNT films more uniformly. We could obtain the stable coin-cell-battery performance with sulfur loading of up to 20 mg cm-2, and the capacity was estimated to be more than 300 Wh kg-1 [2]. We manufactured 1 Ah-class pouch cell, with electrode surface area of 50 cm2. Reference [1] N.Tsukahara, presented at The 17thInternational Meeting on Lithium Batteries, Como, 2014 (unpublished) [2] T. Yamada, presented at The 56th Battery Symposium, Nagoya, 2015 (unpublished) Figure 1

Carbon nanotubes (CNTs) are attractive as nanosize structural elements from which devices can be constructed by bottom-up fabrication. A CNT is a macromolecule of carbon and is made by rolling a sheet of graphite into a cylindrical shape. CNTs exhibit excellent electrical properties that include current densities exceeding 109 A/cm2 and ballistic transport along the tube. Because of these factors, with their large electro-migration tolerance and low electrical resistance, CNTs can be used as nano-size wiring materials, and are thus becoming potential candidates for future LSI interconnects. Much effort has been made to produce CNT vias, which use bundles of MWNTs (multi-walled carbon nanotubes), as vertical wiring materials as shown in Figure 1. Sato et al. demonstrated low-resistance CNT vias employing a novel metallization technology, which used preformed catalyst metal particles, to grow dense MWNT-bundles by thermal chemical vapor deposition (CVD).

We have improved the high-current reliability of carbon nanotube (CNT) via interconnects by chemical mechanical polishing (CMP) and vacuum in situ metal deposition processes. These processes enable us to decrease the contact resistance of a CNT via to the upper and lower Cu lines, and also increase the number of CNTs contributing to current flow. Consequently, the current density per CNT was decreased, and current tolerance properties were improved. As a result, the CNTs via interconnects were able to withstand a high current density of 4×107 A/cm2 per via, i.e., 1.7×108 A/cm2 per CNT. In addition, we found that the failure mode of Cu-line/CNT-via/Cu-line interconnects with a CNT density of 3×1011 tubes/cm2 was the slit void formation at the Cu line under the via, which is similar to that of Cu via interconnects. Furthermore, we discussed how to further increase the tolerance of electromigration (EM), taking advantage of their high thermal conductivity.

The de Haas-van Alphen (dHvA) effect was measured for the paramagnetic compound CrP with an orthorhombic MnP-type structure using a high quality single crystal. Ten branches of dHvA frequency below 9200T are obtained in the (010) plane at 0.6K. Four frequencies in a field along the symmetry axes agree qualitatively with the theoretical results calculated with an all-electron relativistic LAPW method. The cyclotron mass ratios in two branches along the [100] axis are 4.6 and 3.1, respectively.

We fabricated a carbon nanotube (CNT) via interconnect and evaluated its electrical properties. We found that the CNT via resistance was independent of temperatures, which suggests that the carrier transport is ballistic. From the via height dependence of the resistance, the electron mean free path was estimated to be about 80 nm, which is similar to the via height predicted for hp32-nm technology node. This indicates that it will be possible to realize CNT vias with ballistic transport for hp32-nm technology node and below. It was also found that a CNT via was able to sustain a current density as high as 5.0 × 106 A/cm2 at 105 °C for 100 hours without any deterioration.

We fabricated a carbon nanotube (CNT) via interconnect and evaluated its robustness over a high-density current. CNTs were synthesized at temperatures as low as 365 °C, which is probably the lowest for this application, without degrading the ultra low-k interlayer dielectrics (k = 2.6). We measured the electrical properties of CNT vias as small as 160 nm in diameter and found that a CNT via was able to sustain a current density as high as 5.0×106 A/cm2 at 105 °C for 100 hours without any deterioration in its properties.

We studied the electrical properties of a carbon nanotube (CNT) via interconnect fabricated by a novel damascene process which is mostly compatible with conventional Cu interconnects. It was found that the resistance of 60-nm-height vias was independent of temperatures as high as 423 K, which suggests that the carrier transport is ballistic. The obtained resistance of 0.05 Omega for 2.8-mum-diameter vias is the lowest value ever reported. From the via height dependence of the resistance, the electron mean free path was estimated to be about 80 nm, which is similar to the via height predicted for 32-nm technology node (year 2013). This indicates that it will be possible to realize CNT vias with ballistic transport for 32-nm technology node and below.

The low-temperature specific heat and the X-ray diffraction have been measured for Ti1+xS2 (0 < x < 0.1) with the well-defined composition. The obtained lattice and internal parameters increase linearly with the Ti content. The observed electronic specific heat increases linearly with x13. This linear relation changes its slope at x13 = 0.26 and the value goes to zero at x = 0. It is concluded that the electronic structure of stoichiometric TiS2 has a band gap and two Ti-based conduction bands with a small energy difference.

The specific heat at the temperature range from 1.7 to 30 K and the dHvA effect at 0.55 K in the field up to 9.5 T have been measured for Pauli paramagnetic NiAs. The electronic specific heat coefficient is 3.0 mJ/(K2 mol) which is in good agreement with the value estimated from the calculated density of states. It is found that the dHvA oscillation in the field along [0001] consists of four frequencies which correspond to the extremal areas in the k-space of 0.06, 0.11, 0.16 and o.18 A−2.

Carbon nanotubes (CNTs) are good electronic conductors and have a high chemical stability. We have synthesized vertically aligned CNTs directly on nickel foils and applied them to a cathode of a lithium-sulfur (Li-S) rechargeable battery [1, 2]. The CNTs grown by our thermal CVD process have characteristically a spiral structure. CNT/S composite cathodes were fabricated by impregnating the CNT films with molten S. Figure 1 shows cycle performance and Columbic efficiency of the CNT/S composite cathode containing 8 mg cm-2 with S content of 86 wt% in a 2032 type cell. LiTFSI (0.86 M) dissolved in DME/DOL (9:1 vol %) with LiNO3 (3 wt%) additives was used as electrolyte. The high S loading cell retained a specific capacity of 1000 mAh g-1 even after 50 cycles. This good performance is considered to be attributed by the spiral CNT structure which can hold the electrolyte containing the dissolved polysulfides with a little loss. Reference [1] T. Nozue, presented at the 2012 MRS Spring Meeting, San Francisco, 2012 (unpublished) [2] T. Nozue, presented at The 54th Battery Symposium, Osaka, 2013 (unpublished)

We have improved the high-current reliability of carbon nanotube (CNT) via interconnects by chemical mechanical polishing (CMP) and vacuum in situ metal deposition processes. These processes enable us to decrease the contact resistance of a CNT via to the upper and lower Cu lines, and also increase the number of CNTs contributing to current flow. Consequently, the current density per CNT was decreased, and current tolerance properties were improved. As a result, the CNTs via interconnects were able to withstand a high current density of 4×107 A/cm2 per via, i.e., 1.7×108 A/cm2 per CNT. In addition, we found that the failure mode of Cu-line/CNT-via/Cu-line interconnects with a CNT density of 3×1011 tubes/cm2 was the slit void formation at the Cu line under the via, which is similar to that of Cu via interconnects. Furthermore, we discussed how to further increase the tolerance of electromigration (EM), taking advantage of their high thermal conductivity.

The 3d transition metal monopnictides show various interesting electric and magnetic properties. In this study, we have measured the dHvA effect and the transverse magnetoresistance in FeP which has the MnP-type structure and is antiferromagnetic below 125 K with the double helical spin structure. Ten dHvA branches were observed in the (0 0 1) and (1 0 0) planes and their cyclotron mass ratios at the [0 1 0] direction are 0.6–2.2.

We have performed electronic band calculations for the paramagnetic NiAs and NiSb using the full potential LAPW method. The Fermi surface of each compound consists of two kinds of cylindrical-like hole surface around the ΓA -axis and one electron surface. For NiSb one more Fermi surface is obtained. The dHvA oscillation frequencies expected from each Fermi surface are calculated. Recently, we have measured dHvA oscillation for the single crystal of NiAs at 0.55 K in a field of up to 9.5 T and observed six branches. The observed results are discussed in comparison with the calculated results.