Wie Xie
Fudan University

Recently, much attention has been devoted to the propagation behavior of photons in confining micro-structures at the concerned frequency region of strong light-matter interaction. Due to the strong coupling of photons and excitons, the waveguide of exciton–polariton wave shows an anomalously slow group velocity compared with the uncoupled light, which could be applied in information storage and processing. Here, we study the propagation of exciton–polaritons in real space and the population evolution in momentum space in a one-dimensional ZnO microwire at room temperature. Polaritons with nonzero momentum along the c-axis propagate as far as tens of micrometers along the microwire. The momentum distribution of the propagating polariton gas depends on the propagation distance; only the polaritons with large c-axis momenta survive after traveling a long distance owing to the propagation loss of polaritons in such a waveguide system.

Amir Reuveny
University of Tokyo

We fabricated extremely flexible short-channel (2 μm channel length) organic thin-film transistors in a bottom-contact architecture. The transistors demonstrated excellent mechanical stability under systematic bending tests at a bending radius as small as 600 μm and were durable against severe crumpling. Important device characteristics such as field-effect mobility and saturation current were maintained throughout the mechanical tests, providing evidence for the phenomenal flexibility. The mechanical stability benefited from the thinness of the base film (1-μm-thick parylene diX-SR) and encapsulation as well as the utilization of a self-assembled-layer contact-modified staggered structure with a polymeric gate dielectric. The proposed approach is an important step in realizing flexible large-area sensors and high-frequency ultra-flexible circuits.

Takuya Ozaki
Kyoto University

Most commercial GaN-based devices such as visible light-emitting diodes (LEDs) have been fabricated on sapphire (0001) substrates, but the large difference in the a-lattice parameters and the thermal expansion coefficients between GaN and sapphire cause high-density dislocations, large residual strain, and bowing in GaN/sapphire wafers. To circumvent these issues, we propose to use ScAlMgO4 (SCAM) (0001) substrates for InGaN-based LEDs. GaN grown on SCAM by metal-organic vapor phase epitaxy is nearly strain-free with an in-plane compressive strain of -1.26 × 10^-3, which is much smaller than that in conventional GaN/sapphire due to the smaller thermal expansion mismatch between GaN and SCAM. InGaN/GaN QW LEDs fabricated on the GaN/SCAM templates exhibit bright blue electroluminescence. The device performances of LEDs on SCAM are comparable to those on sapphire. Our achievements indicate that SCAM is a promising substrate for highly efficient InGaN-based light emitters.

Zhi Chen
South China University of Technology

Utilization of photons with sub-band-gap energy, mostly near-infrared (NIR) photons, is highly desirable for photovoltaic cells; which can be achieved by adding an up-conversion (UC) layer at the rear face of photovoltaic cells. Here, the NIR-to-visible up-conversion luminescence is markedly enhanced for BaCl₂:Er³⁺ phosphors when excited simultaneously at two wavelengths (808 and 980 nm) in contrast to the case of single-wavelength excitation. Furthermore, the photocurrent response results demonstrate that the multi-wavelength simultaneously excited UC strategy in BaCl₂:Er³⁺ phosphors allows for better and broader harvesting of NIR solar energy, which is expected to open the possibilities of the remarkable improvement of the power conversion efficiency of next-generation solar cells.

Prabhat Verma
Osaka University

The use of optical antennas in tip-enhanced Raman spectroscopy (TERS) makes it a powerful optical analysis and imaging technique at the nanoscale. Optical antennas can work as nano-light sources in the visible region. The plasmonic resonance of an antenna depends on its length; thus, by varying the length, one can tune the enhancement in TERS for a given excitation wavelength. This brings TERS to a new level, where both resonant Raman and plasmonic enhancement can be invoked simultaneously. In this study, we have demonstrated a fabrication method based on focused ion beam milling to realize optical antennas with desired lengths. We measured the resonances of these fabricated antennas and found them drastically dependent on the antenna length. We then performed TERS imaging of carbon nanotubes with our fabricated antennas to demonstrate the antenna length dependence on plasmonic resonance.

Sho Okubo
National Institute of Advanced Industrial Science and Technology

We have carried out dual-comb spectroscopy and observed in a simultaneous acquisition a 140-THz-wide spectrum from 1.0 to 1.9 μm using two fiber-based frequency combs phase-locked to each other. This ultrabroad-wavelength bandwidth is realized by setting the difference between the repetition rates of the two combs to 7.6 Hz using the sub-Hz-linewidth fiber combs. The recorded spectrum contains five vibration-rotation bands of C₂H₂, CH₄, and H₂O at different wavelengths across the whole spectrum. The determined transition frequencies of C₂H₂ agree with those from the previous sub-Doppler resolution measurement of individual lines using CW lasers within 2 MHz.

Takuo Hiratani
Tokyo Institute of Technology

In this paper, we report the first-ever demonstration of a room-temperature continuous-wave operation of a current injection-type membrane distributed-reflector (DR) laser on Si-substrate consisting of an active DFB and a passive DBR regions to obtain higher output power at one side. A threshold current of 250 μA was obtained with the stripe width of 0.7 μm, the DFB region length of 30 μm, and the DBR region length of 90 μm. An external differential quantum efficiency of 11% with a light output ratio between the front and the rear of 6.7 was obtained. Further, the single-mode operation at 1545 nm with a side-mode suppression-ratio of 22 dB was obtained at the bias current of 2 times the threshold. These results indicate that membrane DR lasers on Si can be good candidate toward applications to light sources for on-chip optical interconnects.

Jon Øyvind Kjellman
University of Tokyo

A compact, novel photonic crystal cavity aimed at applications with strict area limitations is presented. Optimization shows that the gentle confinement method previously used for line-defect cavities can be applied to more limited geometries. It also shows that it is paramount to consider the boundary region to minimize in-plane losses. The investigation show that a near optimum boundary thickness can be found by considering the boundary region as a Fabry-Pérot resonator. This optimization strategy is shown to be deterministic in terms of resonance wavelength. For an optimized air-clad, silicon cavity, finite-difference time-domain simulations give Q-values as high as 75,000 which is comparable to other photonic crystal cavities of similar size.

Hiroyuki Narisawa
Tohoku University

The current perpendicular to film plane type giant magnetoresistance (CPP-GMR) effect in Co₂Fe_0.4Mn_0.6Si/Ag₈₃Mg₁₇/Co₂Fe_0.4Mn_0.6Si junctions was investigated. An epitaxially grown 5-nm-thick Ag₈₃Mg₁₇ film having partially ordered L1₂ structure was fabricated on the Co₂Fe_0.4Mn_0.6Si layer by magnetron sputtering. CPP-GMR effects were observed in the submicrometer-sized junctions, and the maximum value of the observed (intrinsic) MR ratio was 40% (48%) at room temperature. The average change in the resistance-area product was 23 mΩ·μm² for the Ag-Mg junctions, which was higher than those of conventional CPP-GMR junctions using a Ag spacer layer. The experimental results suggest that CPP-GMR junctions using a Ag-Mg spacer layer would be advantageous for use in the reading head of hard disc drives.

Yuki Hibino
University of Tokyo

Electric field control of magnetism has been proposed as a new information writing method for a magnetic recordings. We investigated the electric field effect on magnetic anisotropy in a perpendicularly magnetized Pt/Co system with a top ultrathin Pd layer (Pt/Co/Pd structure). Although Pd is usually a non-magnetic material, we observed a clear modulation of the magnetic anisotropy of the system by applying an electric field to the surface of the Pd layer. This result shows that the magnetic anisotropy can be modulated by electric field even when non-magnetic Pd was inserted at the interface formed by the magnetic layer and the insulator. This founding showed the possibility that the electron state of non-magnetic material contributes to the magnetic anisotropy of the system and can be controlled by electric field.

Takayuki Tahara
Kyoto University

Si spintronics attracts strong attention in a decade. Since the first success of room temperature (RT) spin transport in n-type degenerate Si in 2011, much effort has been paid for realization of Si spin MOSFET in order to construct spin-based logic systems, such as a reconfigurable logic circuit using the Sugahara-Tanaka type spin transistors. In this paper, we report on a RT operation of Si spin MOSFET made of non-degenerate n-type Si. Spin signals are efficiently modulated by a gate voltage application, and an on/off ratio is ca. 10³. This success paved a way for the practical use of Si spin MOSFETs.

Akihiro Nakamura
University of Tokyo

The highest efficiency of 24.4% for the solar-to-hydrogen (STH) energy conversion was obtained in an outdoor field test by combining concentrator photovoltaic (CPV) modules with InGaP/GaAs/Ge three-junction cells and polymer-electrolyte electrochemical (EC) cells. The high efficiency was obtained by using the high-efficiency CPV modules (>31% under the present operation conditions) and the direct connection between the CPV modules and the EC cells with an almost optimized number of elements in series. The STH efficiency bottleneck was clarified to be the efficiency of the CPV modules, the over-potential of the EC cells, and matching of the operation point to the maximal-power point of the CPV modules.

Tohru Oka
Toyoda Gosei Co. Ltd

This report describes 1.2-kV-class vertical GaN-based trench MOSFETs on a free-standing GaN substrate with a low specific on-resistance. A redesigned epitaxial layer structure following our previous work with a regular hexagonal trench gate layout enables us to reduce the specific on-resistance to as low as 1.8 mΩ·cm² while obtaining a sufficient blocking voltage for 1.2-kV-class operation. Normally-off operation with a threshold voltage of 3.5 V is also demonstrated. To our knowledge, this is the first report for vertical GaN-based MOSFETs with a specific on-resistance of less than 2 mΩ·cm².

Rai Moriya
University of Tokyo

The van der Waals (vdW) heterostructure based on two-dimensional materials reveal various exotic phenomena in the field of condensed matter science. Among two-dimensional materials, graphene presents unique property as a gate-tunable electrode material due to its low density of states and gapless band structure. We fabricate a graphene/MoS₂/metal vertical heterostructure by using mechanical exfoliation and dry transfer of graphene and MoS₂2 layers. The vdW interface between graphene and MoS₂ exhibits Schottky barrier. The application of gate voltage to the graphene layer enables us to modulate the Schottky barrier height; thus gives rise to the control of the current flow across the vdW interface. The device exhibits large current modulation of ~105 simultaneously with a large current density of ~10₄ A/cm², thereby demonstrating the potential high performance of the exfoliated-graphene/MoS₂/metal vertical field effect transistor for electronics applications.

Pierre-Alix Carles
NTT Basic Research Laboratories

A small dynamic-random-access memory (DRAM) coupled with a high charge sensitivity electrometer based on a silicon field-effect transistor allows study of the law of equipartition of energy through statistical analysis of the movement of single electrons at various conditions in thermal equilibrium. We are able to observe a behavior that differs from what is predicted by the law of equipartition energy: when the charging energy of the capacitor of the DRAM is comparable to or smaller than the thermal energy k_BT/2, random electron motion is ruled perfectly by thermal energy; on the other hand, when the charging energy becomes higher in relation to the thermal energy k_BT/2, random electron motion is suppressed which indicates a deviation from the law of equipartition of energy. We believe that our results are perfectly universal among all electronic devices.

Kenji Hamada
Mitsubishi Electric Corporation

We have successfully developed 4H-SiC devices including metal-oxide-semiconductor field-effect transistors (MOSFETs) and Schottky barrier diodes (SBDs) with a rated voltage of 3.3 kV. The conduction loss of the SiC-MOSFET was reduced to as low as that of the Si-insulated gate bipolar transistor (IGBT) by the n-type doping of the junction field-effect transistor region (JFET doping). The JFET doping technique is effective in reducing the temperature coefficient of resistance in the JFET region, leading to the decreased on-resistance of the SiC-MOSFET at high temperatures. These devices have been applied to 3.3 kV/1500 A modules for the world's first all-SiC traction inverter. The switching loss of the new traction inverter system is approximately 55% less than that of a conventional inverter system incorporating Si modules.

Tomo-o Terasawa
University of Tokyo

Using radiation-mode optical microscopy we developed [Nat. Commun. 6, 6834 (2015)], the effect of oxygen on the graphene growth was investigated. Real-time observation during the CVD process of graphene revealed that the growth feature quickly responded to the concentration of the oxygen in the growth atmosphere. The saturated nucleation density of graphene monotonically increased as the oxygen concentration, while the growth rate showed a maximum at a certain oxygen concentration. The graphene changed from the compact shape to the dendritic one with the increase in the oxygen concentration. The oxygen adsorbed on Cu consumed the growth precursors of graphene, while it simultaneously enhanced the detachment of H atoms from the graphene edge. Our results emphasized that real time observation is essential to elucidate the growth mechanism and to optimize the parameters for fabrication of a large-area and single-crystal graphene.

M Shoufie Ukhtary
Tohoku University

Single layer of graphene can absorb nearly 100% of electromagnetic (EM) wave coming directly to it, provided that we have total reflection geometry and EM wave frequency of GHz. Instead of being reflected, the EM wave is absorbed totally at certain angle of incident. This can be understood by the excitation of surface plasmon on graphene with small wave vector and frequency. We also found out that the absorption probability depends on graphene's Fermi energy. These results open up possibilities for the development of simple electromagnetic wave-switching devices operated by gate voltage.

Takashi Ikuno
Toyota Central R&D Labs.

We have found that light-weight bimorph strips consisting of multi-walled carbon nanotube freestanding films (MWNT-FSFs) and Ni thin films exhibit a continuous bending-stretching motion on a hot plate even below the temperature of 100°C. The Ni/MWNT-FSFs exhibited this motion at a difference between the hotplate temperature and room temperature as small as 5°C. The requirements of this motion have been qualitatively elucidated by a simulation based on a relaxation time approximation. We believe that the MWNT-FSFs developed in this study could be one of the building blocks for energy conversion nanodevices.

Tomoya Koshi
Waseda University

We proposed a self-healing metal wire using electric field trapping of gold nanoparticles by a dielectrophoresis force. A cracked gold wire can retrieve its conductivity through the self-healing function. In this paper, we examined the healing voltage causing the electric field trapping and determined the healing time. First, the forces acting on a nanoparticle were analyzed and a theoretical healing voltage curve was calculated. Then, gold wires with 200- to 1,600-nm-wide cracks were fabricated on glass substrate and the self-healing function was verified. As a result, gold wires with cracks of up to 1,200 nm in width were successfully healed by applying less than ~2.5 V. The healing times were 10 to 285 s for 200- to 1,200-nm-wide cracks. Through scanning electron microscope analysis after the healing experiments, we confirmed that the cracks were healed by assembled nanoparticles.

Ikumi Yamada
Kyoto University

Silicon nanowires (SiNWs) have been grown on Si(100) substrates with and without a thermal oxide layer by rf magnetron sputtering of Si in Ar/H₂. Experiments employed thin Au layers as catalysts, demonstrating a significant and substantial growth of randomly oriented, plolycrystalline SiNWs, typically 20 μm long and 350 nm in diameter after 60 min of growth on both Si and SiO2 substrates at 700 °C. The growth rate was at least two times higher than those by conventional vapor-liquid-solid methods such as thermal evaporation and chemical vapor deposition, and the SiNW growth on SiO₂ was achieved without an additional layer of Si thereon in this study. These indicate the possibility of providing an alternative method for SiNW growth that is free from toxic feed gases and high-temperature tube furnaces, and hence is suitable for growth on large-diameter substrates in industry.

Muneki Akazawa
Hiroshima University

We attempted to transfer a phosphorus ion (P⁺)-implanted oxidized silicon-on-insulator (SOI) layer with a midair cavity to a glass substrate using meniscus force at a low temperature. The SiO₂ column size was controlled by etching time and the minimum column size was 104 nm. The transfer yield of the implanted sample was significantly improved by decreasing the column size, and the maximum transfer yield was 95% when the implantation dose was 1 × 10¹⁵ cm^-2. The causes of increasing transfer yield are considered to be the tapered SiO2 column shape and the hydrophilicity of the surface of oxidized samples with implantation. N-channel thin-film transistors (TFTs) fabricated using the films on glass at 300 °C showed a field-effect mobility of 505 cm² V^-1 s^-1, a threshold voltage of 2.47 V and a subthreshold swing of 324 mV/dec on average.

Hiroshi Hashizume
Meijo University

In this study, we elucidated the oxidative inactivation process of Penicillium digitatum spores treated with neutral oxygen radicals on the basis of the doses using fluorescent confocal-laser microscopy and transmission electron microscopy. We previously showed that ground-state atomic oxygen [O(³P_j)] was crucial species responsible for inactivating P. digitatum spores with an atmospheric-pressure oxygen radical source, and that the radicals, in particular O(³P_j), inhibited the function of cell membranes without major morphological changes and oxidize the intracellular organelles. Moreover, in this study, we clarified the correspondence of the oxidation degree in the spore with the inactivation on the basis of O(³P_j) dose under the specific flux. Thus, we have quantitatively demonstrated the oxidative inactivation process; the inhibition of cell membranes, the oxidation of intracellular organelles, and finally the intracellular nanostructural degradation with an increase of the dose.

Kenji Ikeda
Osaka University

We describe a new method for the selective crystallization of the metastable phase (α-form) of indomethacin. To obtain the α-form, we prepared a highly supersaturated solution and then introduced forcible nucleation techniques, namely, laser irradiation and magnetic stirring. When the laser irradiated near the side wall, the α-form crystallized within 24 h. The α-form crystals showed temporal stability for at least 8 months in air ambient at room temperature. We conclude that control of the laser irradiation focal point is an effective way of selectively crystallizing the metastable phase of indomethacin with temporal stability.