Table of contents

The formation of multiple stationary striations between a nozzle exit and a conductive target plate was clearly observed at regular intervals using a digital camera along an atmospheric pressure plasma jet of dielectric barrier discharge using a neon gas into ambient air. From the results of measuring using a high-speed camera during the positive current phase, the emission initially started in the middle between the nozzle and the target, and striations progressed in both upward and downward directions. During the negative current phase, the emission initially started in a region near the target, and the striations rapidly progressed to the nozzle.

Effective light trapping is essential for improving the efficiency and reducing the cost of thin-film silicon solar cells. Here, we numerically study the optical characteristics of periodic three-dimensional (3D) silicon nanocavity arrays. We found that the 3D silicon nanocavity array shows low sensitivity to geometric structural parameters for photon capture and achieves an outstanding efficiency superior to those of previously reported silicon nanostructures such as a nanowire and a nanohole with the same thickness. This excellence is attributed to a better antireflection capability and more resonant modes. The 3D silicon nanocavity array provides a new light-trapping strategy for thin-film photovoltaic devices.

Previously, we reported a growth method by metalorganic vapor phase epitaxy using a single two-dimensional growth step, resulting in 1.2-µm crack-free GaN directly grown on 6H-SiC substrate. The introduction of Al-treatment prior to the standard GaN growth step resulted in improved surface wetting of gallium on the SiC substrate. Transmission electron microscope and energy dispersive spectrometer analysis of the epitaxial interface to the SiC determined that an ultra-thin AlGaN interlayer had formed measuring around 2–3 nm. We expect our growth technique can be applied to the fabrication of GaN/SiC high frequency and high power devices.

We introduce an easy process for the fabrication of solution-processed indium oxide (InO) thin film transistors (TFTs) by heating a precursor solution. InO TFTs fabricated from solutions of an InO precursor heated at 90 °C had the highest mobility of 4.61 cm² V⁻¹ s⁻¹ after being annealed at 200 °C. When the InO precursor solution is heated, HNO₃ may be thermally evaporated in the InO precursor solution. Nitrogen atoms can disrupt hydrolysis and condensation reactions. An InO thin film deposited from a solution of the heated InO precursor is advantageous for hydrolysis and condensation reactions due to the absence of nitrogen atoms.

Tetragonal ultrathin (1–5 nm) ordered MnGa films on a CsCl-type CoGa buffer layer were fabricated by a sputtering method. The (001)-CoGa layer was first deposited on a Cr-buffered MgO substrate and then annealed in-situ at 500 °C. The ultrathin MnGa film deposited on the CoGa buffer layer formed the L1₀ structure with very small roughness even when grown at room temperature. In addition, the films showed well-squared perpendicular magnetization hysteresis curves even when the film thickness was as little as 1 nm. The obtained results are important for the development of the MnGa-based spin-transfer torque devices for Gbit class magnetic random access memory and high frequency applications.

The energy band gaps of the alloy InAs_xSb_yP_1−x−y are calculated using the correlated function expansion (CFE) technique over the entire composition space x and y, for which the CFE band gap composition contour for the mid-infrared (MIR) spectral region of 2 (0.62)–5 µm (0.25 eV) is presented. The composition dependence of the valence-band maximum (VBM) is obtained using the universal tight binding (UTB) method, and the corresponding conduction-band minimum (CBM) can be computed from the difference between the band gap and the VBM. By organizing the relative positions of the VBM and CBM between the quaternary alloy InAsSbP and the binary compound InAs, the band alignments and band types of InAsSbP/InAs heterojunctions (HJs) along the lattice-matching conditions x and y [i.e., y = 0.311(1 − x)] are determined. It is found that the VBMs of the alloy InAs_xSb_yP_1−x−y are located within the band gap of InAs, whereas the CBMs of the alloy lie outside the band gap of InAs over the entire composition range. This implies that the InAs_xSb_yP_1−x−y/InAs HJs exhibit composition-tunable, type-II (staggered) band alignments. In addition, the conduction-band offset (CBO) and valence-band offset (VBO) of InAsSbP/InAs HJs both present the upward bowing trend, with the CBO curves appearing sharp and the VBO curves appearing smooth.

We carry out density-functional-theory calculations to study the stability of germanium multivacancies. We use supercells containing 216 atomic sites and simulate two configurations called the "part of hexagonal ring" (PHR) and fourfold configurations of the tri-, tetra-, and pentavacancies. We find that the fourfold configurations of the tetra- and pentavacancies are the most stable and these configurations are also the most stable in the case of silicon. However, we find that the PHR and fourfold configurations have similar energies in the case of the germanium trivacancy. These results are in contrast to those of the silicon trivacancy; the fourfold configuration has substantially lower energy than the PHR configuration. This difference between germanium and silicon is expected to originate from the fact that the four bonds in the fourfold configurations in the germanium trivacancy are weaker than those in the silicon one. By calculating dissociation energies, we find that the silicon tetravacancy is not easy to dissociate, whereas the germanium tetravacancy is not very stable compared with the silicon one.

The concentration changes of nickel-related species after thermal annealing in Schottky electrode-formed (EL-formed) and electrode-free (EL-free) p-type silicon samples diffused with nickel were measured by deep-level transient spectroscopy. The nickel donor center began to decay at approximately 100 °C with the activation energies of 1.06 and 0.26 eV for the EL-formed and EL-free samples, respectively, which were analyzed as the required energies for the center to form complexes with interstitial nickel (Ni_i) and hydrogen, respectively. These complexes evolved into extended complexes by further bonding of Ni_i at higher annealing temperatures. All the complexes above disappeared by evolving into precipitates within temperatures lower than 400 °C without recovering the nickel donor center. The transformation reactions of the complexes progressed at lower temperatures and shorter times in the EL-formed samples than in the EL-free samples because of the electric neutralization of the nickel-related species in the space-charge region of the electrode.

The electron paramagnetic resonance (EPR) technique was employed to detect oxygen vacancy defects in the tetragonal Ba_1−xCa_xTiO₃ (x = 0.03) ceramics (BCa3T) prepared via the mixed oxide route at 1300–1500 °C. In the rhombohedral phase below −100 °C, an EPR signal at g = 1.955 appeared in the insulating BCa3T with an electrical resistivity of 10⁸ Ω cm and was assigned to ionized oxygen vacancy defects. BCa3T prepared at 1300 °C showed a temperature-stable X6S dielectric specification (ε' = 1750). Three types of vacancy defect, namely, Ba, Ti, and O vacances, could coexist in BCa3T owing to the partial Ti-site occupation by Ca²⁺.

In order to understand the ferroelectric and ferroelastic phases in Ba_1−xSr_xAl₂O₄ for 0.7 ≤ x ≤ 1.0, we have investigated the crystal structures and their associated microstructures of the ferroelectric and ferroelastic phases mainly by transmission electron microscopy (TEM) and scanning transmission electron microscopy–high-angle angular dark-field (STEM–HAADF) experiments, combined with powder X-ray diffraction experiments. Electron diffraction experiments showed that the ferroelectric and ferroelastic phases of Ba_1−xSr_xAl₂O₄ for 0.7 ≤ x ≤ 1.0 should be characterized as a modulated structure with the modulation vector of $\boldsymbol{{q}} = 0,1/2,0$, whose space group should be monoclinic P2₁. High-resolution TEM experiments revealed that the microstructures in the monoclinic phase can be characterized as twin structures and nanometer-sized planar defects due to the monoclinic structure with the modulated structures, which are responsible for anomalous elastic behaviors and mechanoelectro-optical properties. In addition, subatomic-resolution STEM–HAADF images clearly indicated that the displacement of Al³⁺ ions involved in the AlO₄ tetrahedra should play a crucial role in the formation of the modulated structures and twin structures.

We have improved the properties of ambipolar organic field-effect transistors by chemically treating the source and drain electrodes with a vacuum-deposited biradicaloid film. Biradicaloid was a diphenyl derivative of s-indacenodiphenalene (Ph₂-IDPL). An alkane thiol self-assembled monolayer (SAM) was used as an insulator buffer layer at the Ph₂-IDPL/electrode interface to prevent off-current. We confirmed the transport level alignment at the Ph₂-IDPL/SAM/electrode interface by ultraviolet photoemission spectroscopy and inverse photoemission spectroscopy. Although Ph₂-IDPL transistors containing the SAM showed a higher on/off ratio or mobility than a previously reported device without the buffer layer, there was a trade-off between on/off ratio and mobility. Our results suggest that biradical molecules are promising candidates for use in low-power inverters.

The improvement of the contrast ratio of flexible liquid crystal displays (LCDs) fabricated using plastic substrates in a curved state is an important problem to achieve high-quality flexible LCDs. In this study, we evaluated the distributions of in-plane phase retardation and slow axis direction of polycarbonate substrates and the effects of curvature on the electro-optical properties of flexible LCDs. As a result, we clarified that the polycarbonate substrates have high uniformity in the in-plane phase retardation and slow axis direction, and that the change in the phase retardation of the polycarbonate substrate caused by the curvature deformation has a small effect on the electro-optical characteristics of flexible LCDs. We successfully achieved a high contrast ratio of $1042:1$ by fabricating the device using polycarbonate substrates. This result indicates that it is possible to realize high-quality images in flexible LCDs fabricated using polycarbonate substrates even in the curved state.

Liquid crystal (LC) cells with periodic alignment distributions were fabricated using chiral nematic LCs (N*LCs), which were prepared using mixtures of a nematic LC and a chiral dopant, along with photoreactive liquid crystalline polymer (PLCP) films. Periodic structures were formed by polarization holographic recording in the PLCP films. The director distribution in each cell depended on the ratio of chiral dopant present, i.e., the inherent helical pitch of the N*LCs. These periodic alignment structures with line defects in the LC grating cells were well explained on the basis of the elastic continuum theory of the N*LCs and the photoalignment effect of the PLCP films. The diffraction properties of the grating LC cells were also investigated using a polarized visible laser. The observed intensity and polarization states of the diffracted beams were consistent with theoretical ones calculated using the director distribution models. Our results clarify that the diffraction properties of the grating LC cells can be controlled by the helical pitch of the N*LCs.

We have designed and fabricated a contact grating device to increase diffraction efficiency on the basis of the principle of the Fabry–Perot resonator. The grating structure and layer thicknesses were carefully determined by considering the electric field strength in the device and the fabrication accuracy of the grating. The prototype device had a peak diffraction efficiency of 71% at an incident angle of 42°; these values were slightly different from the design values of 78% and 44.5°, respectively. Numerical calculations revealed that this deviation was caused by the fabricated grating structure. A higher terahertz power will be expected with a device as per the design.

We demonstrate a polarization conversion system by utilizing the polarization-splitting function of a liquid-crystal (LC) geometric-phase-based cylindrical lens. The system was constructed by combining the LC lens with a partially rubbed cell. The operation principle includes the following two steps. (i) The incident light is first decomposed into right- and left-handed circularly polarized light (RCP and LCP, respectively) as an attribute of geometric-phase-based optical elements. (ii) Then, only the RCP light is transformed into LCP light by passing it through the partially rubbed cell; as a result, the incident unpolarized light is converted into LCP light. We experimentally reveal the feasibility of the system by evaluating the effects, on the polarization conversion capability, of the diffraction efficiency, focal length, and partially rubbed cell's retardation. The polarization conversion efficiency was obtained to be 65% on average for 400–700 nm and a maximum of 79% at 610 nm.

We investigate the defect activation energy around the pn interface of Cu(In,Ga)Se₂ (CIGS)-based solar cells using a simple electrochemical impedance spectroscopy. By applying AC and DC voltages to the solar cells, we observed an "inductive" element around the pn interface, which is ignored in conventional deep-level transient spectroscopy or admittance spectroscopy. A defect model is evaluated by proposing an equivalent circuit that includes a positive/negative constant phase element (CPE) to represent the area around the CdS/CIGS interface. By fitting the impedance data, the CPE index and CPE constant show a relationship with the defect activation energy or defect concentration. This result is significant because it may help reveal the defect properties of CIGS solar cells or any other semiconductor devices.

In this paper, the Er³⁺ and Yb³⁺ co-doped ZnO films deposited by a novel thermal decomposition method under different annealing temperature process have been reported. The effects of annealing temperature on the morphology and properties of the films are systematically studied. The resulting spectra demonstrate that the Er³⁺ and Yb³⁺ co-doped ZnO films possessed the property of up-conversion, converting IR light into visible light that can be absorbed by amorphous silicon solar cell. After all, inner photoelectric effect of the Er³⁺ and Yb³⁺ co-doped ZnO films in the amorphous as a light scattering layer are also found with an infrared 980 nm laser as excitation source.

The influence of the Zn/Sn atomic ratio on the properties of the Cu–Zn–Sn–S-based film microstructure and solar cells was investigated. In addition to a small amount of SnS, Cu₂SnS₃, and ZnS coexisted in Zn-poor (Zn/Sn < 1) films, while Cu₂ZnSnS₄ (CZTS) was not formed. In contrast, the direct growth of a highly crystalline kesterite CZTS phase was evident in Zn-rich (Zn/Sn > 1) films, in which a ZnS phase was inevitably formed as a secondary phase. Despite its coexistence with CZTS in highly Zn-rich films, excess ZnS had a negligible influence on the crystalline quality of CZTS. Solar cells fabricated with more highly Zn-rich films exhibited better device properties, indicating that the ZnS inevitably present in these films positively impacted cell performance, especially the open-circuit voltage and fill factor. The best cell (Zn/Sn = 1.6) yielded an efficiency of 4.61%. The possible ZnS passivation of microstructural defects in CZTS cells is also discussed.

Ultra-thin Co₂MnSi Heusler alloy improves perpendicular magnetic anisotropy of FePd in an MgO-based magnetic tunnel junction after annealing it just once at a temperature of as low as 400 °C. Co₂MnSi as thin as 1.0 nm inserted between MgO and FePd facilitated phase-transformation of 3-nm-thick FePd to ordered L1₀ and led a change in magnetic anisotropy to perpendicular-to-the-plane. To make it even better, FePd also helped the phase-transformation of Co₂MnSi to ordered B2 known to have high spin polarization, which makes the L1₀ FePd/B2 Co₂MnSi bilayer promising for perpendicular-magnetic tunnel junction and improving both thermal stability and tunnel magnetoresistance.

We report solution-processed organic trilayer solar cells consisting of a bottom poly(3-hexylthiophene) (P3HT) layer, a conjugated polyelectrolyte (CPE) interlayer and [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM) top layer, wherein the CPE exists as an interlayer within the donor–acceptor junction. The influence of interlayer thickness on device properties was investigated, as well as the behavior of molecular dipoles in the trilayer solar cells when influenced by external electrical stimuli. We found that incorporation of an interlayer which is too thick results in decreased performance due to reduced short-circuit current (J_SC), open-circuit voltage (V_OC), and fill factor (FF). However the V_OC is found to increase significantly when a thin CPE layer is used in conjunction with an external electric field. These results provide an experimental approach to probe the influence of interfacial dipoles on the solar cell parameters and behavior of charge separating organic donor/acceptor junctions, yielding fundamental information about the influence of electrical dipoles on the donor/acceptor interface in organic solar cells.

We validate a model which is a combination of multiple trapping and release and percolation model for describing the conduction mechanism in amorphous indium gallium zinc oxide (a-IGZO) thin film transistors (TFT). We show that using just multiple trapping and release or percolation model is insufficient to explain TFT behavior as a function of temperature. We also show the intrinsic mobility is dependent on temperature due to scattering by ionic impurities or lattice. In solving the Poisson equation to find the surface potential and back potential as a function of gate voltage, we explicitly allow for the back surface to be floating, as is the case for a-IGZO transistors. The parameters for gap states, percolation barriers and intrinsic mobility at room temperature that we extract with this comprehensive model are in good agreement with those extracted in literature with partially-complete models.

In this study, a two-dimensional physically based semi-analytical model of source/drain series resistance in MOSFETs is developed, in which only one parameter needs to be extracted by measurement and the extracted parameter can be repeatedly used when the structure size of the source or drain is changed. The model at the first time separates the resistance into two independent parameters that multiply each other. One is the extracted parameter that is only related to the resistivity. The other one is calculated by the expressions obtained by using the semi-analytical method and Eigen function expansion method, and is only related to the structure size of the source or drain area. The model provides a new approach to solve the resistance problem and matches well with simulation results. It can be used easily to estimate the resistance when the device structure changes in device design.

We investigate numerically the rectification phenomena of bulk acoustic waves in an acoustic-wave rectifier composed of an elastically anisotropic material containing a periodic array of triangular holes. Paying special attention to the effects of elastic anisotropy on phonon mode coupling, we elucidate the rectification performance for quasi-longitudinal and slow transverse waves. We find that elastic anisotropy markedly improves acoustic-wave rectification in comparison with the system composed of isotropic materials, particularly for longitudinal acoustic waves.

In order to improve the rectification efficiency and current–voltage characteristics of self-switching diodes (SSD) the DC response is analyzed using technology computer aided design (TCAD). It is demonstrated that by varying geometrical parameters of L- and V-shaped SSDs or changing the dielectric permittivity of the trenches, a near zero threshold voltage can obtained, which is essential for energy harvesting applications. The carrier distribution inside the nanochannel is successfully simulated in two-dimensional mode for zero-, reverse-, and forward-bias conditions. This process allows for the evaluation of the effect of the lateral surface-charge on the formation and spatial distribution of the depletion region, in addition to, obtaining information on the physics of the SSD through the propose optimized geometries that were designed for tailoring and matching the desired frequencies of operation. The numerical results showed some insights for the improvement of the rectification efficiency and integration density using parallel SSD arrays.

We have developed an apparatus that allows the observation of the transient rotational motion of fine particles under a high magnetic field in order to determine anisotropic magnetic susceptibility. The anisotropic susceptibilities of spherical nanoparticles of bismuth and commercially available carbon nanofibers were determined. The estimated Δχ = 3.9 × 10⁻⁵ of spherical bismuth nanoparticles with a diameter of 370 nm was fairly consistent with the value determined previously by the magnetic field dependence of diffraction peak intensity in the X-ray diffraction (XRD) pattern, but was slightly smaller than the value for the bulk crystal. In contrast, the transient behavior of carbon nanofibers did not obey the theoretical motion of a single crystal. The wide distribution of fiber lengths, the irregularity of the structure in the fiber, and the connections between the fibers are suggested for the anomalous behavior.

The major role of the chemical reaction between a silica substrate and deposited carbon in the activation process for the formation of a surface-conduction electron emitter (SCE) is investigated. The SCE emits electrons by the tunneling effect when an electric field is applied across a nanoscale gap. The nanogap is spontaneously formed by the activation process, wherein a pulse voltage is applied between a pair of electrodes, which are separated by a narrow gap inside a vacuum chamber in the presence of hydrocarbons. At the gap, two elemental processes compete; the deposition of carbon by the electron-induced decomposition of hydrocarbons and the consumption of carbon by reaction with the silica substrate. The balance of the dynamics of the two processes, which simply depends on the temperature at the gap, is responsible for the spontaneous determination of the width of the nanogap. The calculation based on the model that involves the two competitive processes agrees with the experimental results on the activation process.

CuInS₂ thin films were prepared by sulfurization using a less hazardous liquid, metal–organic ditertiarybutylsulfide, on soda-lime glass substrates. Single-phase chalcopyrite CuInS₂ films were obtained after 15 min at 515 °C. The obtained CuInS₂ films were repeatedly sulfurized under different sulfurization conditions. The characteristics of these CuInS₂ films were determined by X-ray diffraction (XRD) and photoluminescence (PL) spectra analyses. The secondary impurity phase such as CuS was confirmed from XRD patterns. The growth mechanism of intrinsic defects related to the secondary phase is discussed in this paper.

We have performed transmission electron microscopy (TEM) observation of antiphase structures in a periodically inverted GaAs/Al_0.1Ga_0.9As waveguide fabricated on a (100) GaAs substrate intentionally misoriented toward $[0\bar{1}1]$ by 2°. We have unambiguously confirmed that the artificial (011) boundaries between the inverted and noninverted domains are of antiphase nature by TEM observations including conventional dark-field imaging and a two-beam technique. We also investigated unintentionally formed self-annihilating non-inverted GaAs domains grown on a Ge interlayer introduced for growing inverted GaAs epilayers using the sublattice-reversal epitaxy technique.

Noise analysis of the forward current of LEDs was performed to identify the rate-limiting process of a recently developed Eu-doped GaN (GaN:Eu) red LED. Although the noise power spectrum of conventional InGaN blue and AlGaInP amber LEDs followed Poisson distributions, that of the GaN:Eu red LED indicated a 1/f noise. The Poisson distribution that represents electron–hole (e–h) recombination was consistent with the light emitting process of the conventional LED. On the other hand, the 1/f noise revealed that the rate-limiting process of the GaN:Eu LED was trapping of injection charges rather than following e–h recombination to excite Eu. From the detailed analysis of the 1/f noise, several emission centers with different trapping time constants (>3.5 ns) were discovered. These results demonstrated the applicability of the noise analysis to characterization of charge dynamics in the new LEDs.

A plasma-induced shift in the resonance frequency of a curling probe measured by using a network analyzer (NWA) yields the electron density. This technique was applied here for measuring time-varying electron density in pulsed DC glow discharges. Using the NWA in an on-sweep synchronization mode with the discharge pulse allows measuring at pulse frequencies below 0.5 kHz. For higher pulse frequencies, an on-point mode was introduced which enabled time-resolved measurements of electron density at pulse frequencies reaching 25 kHz, with the minimal time interval of 2 µs, typically for nitrogen discharge at 10 Pa. In the afterglow regime, the decay time constant of electron density was measured for nitrogen and argon discharges at 40 Pa. In the case of argon, the electron density was observed to decrease in three steps. This characteristic behavior was tentatively attributed to a bi-Maxwellian electron energy distribution and Ramsauer effect, supported by Langmuir probe measurements.

The objective of this work is to understand the mechanism of plasma-assisted combustion in a steady-state premixed burner flame. We examined the spatiotemporal variation of the density of atomic oxygen in a premixed burner flame with the superposition of dielectric barrier discharge (DBD). We also measured the spatiotemporal variations of the optical emission intensities of Ar and OH. The experimental results reveal that atomic oxygen produced in the preheating zone by electron impact plays a key role in the activation of combustion reactions. This understanding is consistent with that described in our previous paper indicating that the production of "cold OH(A²Σ⁺)" via CHO + O → OH(A²Σ⁺) + CO has the sensitive response to the pulsed current of DBD [K. Zaima and K. Sasaki, Jpn. J. Appl. Phys. 53, 110309 (2014)].

A reversely-induced azimuthal current has been found in two-dimensional particle simulations with moderately screened rotating electric field (REF) though an ideally penetrating REF drives a "positive" azimuthal current following rotating E × B drifts. This brings us an alternative acceleration concept, called a negative-moving response (NMR) acceleration, of the helicon plasma under practical conditions using a converging magnetic field because the internal electric potential, formed by the plasma response against the external field, drives the "negative" azimuthal current. Under realistic experimental conditions, e.g., a magnetic field of 0.2 T, AC frequency of <100 MHz, and AC voltage of <1000 V, the resultant thrust can be estimated at an observable level of >0.1 mN with the NMR acceleration. Moreover, the reverse REF is more favorable to the NMR acceleration than the conventional forward one because the reverse field produces a Lissajous acceleration in the converging magnetic field.

Sustainment of long-scale surface-wave plasma (SWP) at pressures below 1 Pa is investigated for the application of the SWP as an assisting plasma source for roll-to-roll sputter deposition. A modified microwave coupler (MMC) for easier surface-wave propagation is proposed, on the basis of the concept of the power direction alignment of the slot antenna and surface-wave propagation. The superiority of the MMC-SWP over conventional SWPs is shown at a sustainment pressure as low as 0.6 Pa and an electron density as high as 3 × 10¹⁷ m⁻³. A polymer film is treated with the MMC-SWP at a low pressure of 0.6 Pa, and surface modification at a low pressure is proved using Ar plasma. These results show the availability of the MMC-SWP as the surface treatment plasma source that is compatible with sputter deposition in the same processing chamber.

In this work, we study the properties of tin oxide films, which were annealed in oxygen ambient for various periods. The as-deposited tin oxides are tin-dominant and, from the Hall measurements, they are of the n-type with high electron concentrations (>10¹⁹ cm⁻³) and would change to the p-type when the oxygen annealing is sufficiently long. We have also found that changes in the structure and crystallinity of the channel layer can be clearly observed by X-ray diffraction analysis and optical microscopy. On the basis of the observations, a physical scheme is proposed to describe the evolution of the electrical performance of oxygen-annealed devices. A hole mobility of 3.24 cm² V⁻¹ s⁻¹, a subthreshold swing of 0.43 V/dec, a threshold voltage of 1.4 V, and an on/off current ratio larger than 10³ are obtained as the channel is transformed into SnO.

The electrical characteristics and step coverage of ZrO₂ films deposited by atomic layer deposition were investigated for through-silicon via (TSV) and metal–insulator–metal applications at temperatures below 300 °C. ZrO₂ films were able to be conformally deposited on the scallops of 50-µm-diameter, 100-µm-deep TSV holes. The mean breakdown field of 30-nm-thick ZrO₂ films on 30-nm-thick Ta(N) increased about 41% (from 2.7 to 3.8 MV/cm) upon H₂ plasma treatment. With the plasma treatment, the breakdown field of the film increased and the temperature coefficient of capacitance decreased significantly, probably as a result of the decreased carbon concentration in the film.

Our original hybrid method combining tight-binding quantum chemical and classical molecular dynamics was first applied to the low-energy doping process of boron into a silicon substrate, which has a depth of more than 10 nm that is needed to evaluate an ultrashallow junction position. Tight-binding quantum chemical molecular dynamics calculation was used for an injected boron atom and surrounding silicon atoms within a sphere with a radius of 0.5 nm centered at the boron atom. This method is advantageous in treating the many-body collision effect and electron–electron interaction, which are more important in low-energy doping, compared with the Monte Carlo method with binary collision approximation. A comparison with a plasma doping experiment was also carried out. The junction positions were 6.2 nm for boron doping at an initial kinetic energy of 200 eV in the simulation results and 6.4 nm for 200 eV in the experimental results. Good agreement between simulation and experimental results indicates that our hybrid molecular dynamics method is applicable to doping profile prediction in a silicon structure with a depth of more than 10 nm that is needed to evaluate ultrashallow junction formation.

We evaluated room-temperature bonding characteristics of electroplated Au surfaces smoothed by the lift-off and imprint methods. As a result, we found that smoothed surfaces enable strong bonding; on the other hand, electroplated rough surfaces result in very weak bonding. In transmission electron microscopy observations, no delamination was observed at the bonding interface bonded at room temperature using a smooth surface prepared by the lift-off method. Moreover, the hermeticity of the bonding interface prepared using smoothed surfaces was evaluated using diaphragm structures. As a result, we confirmed that good hermetic sealing was achieved using the electroplated Au surface smoothed by the lift-off method.

The aim of this study is the electrical detection of pathogenic viruses, namely, adenovirus and rotavirus, using dielectrophoretic impedance measurement (DEPIM). DEPIM consists of two simultaneous processes: dielectrophoretic trapping of the target and measurement of the impedance change and increase in conductance with the number of trapped targets. This is the first study of applying DEPIM, which was originally developed to detect bacteria suspended in aqueous solutions, to virus detection. The dielectric properties of the viruses were also investigated in terms of their dielectrophoretic behavior. Although their estimated dielectric properties were different from those of bacteria, the trapped viruses increased the conductance of the microelectrode in a manner similar to that in bacteria detection. We demonstrated the electrical detection of viruses within 60 s at concentrations as low as 70 ng/ml for adenovirus and 50 ng/ml for rotavirus.

A method of suppressing sound radiation to the far field of a near-field acoustic communication system using an evanescent sound field is proposed. The amplitude of the evanescent sound field generated from an infinite vibrating plate attenuates exponentially with increasing a distance from the surface of the vibrating plate. However, a discontinuity of the sound field exists at the edge of the finite vibrating plate in practice, which broadens the wavenumber spectrum. A sound wave radiates over the evanescent sound field because of broadening of the wavenumber spectrum. Therefore, we calculated the optimum distribution of the particle velocity on the vibrating plate to reduce the broadening of the wavenumber spectrum. We focused on a window function that is utilized in the field of signal analysis for reducing the broadening of the frequency spectrum. The optimization calculation is necessary for the design of window function suitable for suppressing sound radiation and securing a spatial area for data communication. In addition, a wide frequency bandwidth is required to increase the data transmission speed. Therefore, we investigated a suitable method for calculating the sound pressure level at the far field to confirm the variation of the distribution of sound pressure level determined on the basis of the window shape and frequency. The distribution of the sound pressure level at a finite distance was in good agreement with that obtained at an infinite far field under the condition generating the evanescent sound field. Consequently, the window function was optimized by the method used to calculate the distribution of the sound pressure level at an infinite far field using the wavenumber spectrum on the vibrating plate. According to the result of comparing the distributions of the sound pressure level in the cases with and without the window function, it was confirmed that the area whose sound pressure level was reduced from the maximum level to −50 dB was extended. Additionally, we designed a sound insulator so as to realize a similar distribution of the particle velocity to that obtained using the optimized window function. Sound radiation was suppressed using a sound insulator put above the vibrating surface in the simulation using the three-dimensional finite element method. On the basis of this finding, it was suggested that near-field acoustic communication which suppressed sound radiation can be realized by applying the optimized window function to the particle velocity field.

We theoretically study the phonons propagating through a superlattice consisting of alternating layers of an elastic solid and a fluid. In this structure, there exist phononic bandgaps not originating from Bragg reflections. We examine the origin of these non-Bragg gaps and show that they are peculiar to the solid–fluid superlattices, where the number of allowed modes varies periodically. Even a single solid layer immersed in fluid contains discrete frequencies at which incident waves are perfectly reflected. We demonstrate the resonant reflection process at these frequencies. In the multilayered structure, these transmission zeros are gathered and form a bandgap. This is similar to the relation between atomic levels and an electronic energy band, though the allowed and forbidden states are interchanged. This non-Bragg gap introduces novel degrees of freedom to the design of phononic bandgap structures.

With the characteristics of low density, low elastic modulus, and low mechanical loss, poly(phenylene sulfide) (PPS) is a promising material for fabricating lightweight ultrasonic motors (USMs). For the first time, we used PPS to fabricate an annular elastomer with teeth and glued a piece of piezoelectric-ceramic annular disk to the bottom of the elastomer to form a vibrator. To explore for a material suitable for the rotor surface coming in contact with the PPS-based vibrator, several disk-shaped rotors made of different materials were fabricated to form traveling wave USMs. The polymer-based USM rotates successfully as the conventional metal-based USMs. The experimental results show that the USM with the aluminum rotor has the largest torque, which indicates that aluminum is the most suitable for the rotor surface among the tested materials.

We propose a simple method to generate low-frequency drift pulse trains by direct modulation of a laser diode system consisting of a distributed-feedback laser array and a semiconductor optical amplifier. We measure the temporal profiles, beat signals and spectra of pulses generated under three different sets of conditions. We found that low-frequency drift pulse trains are generated by application of a DC voltage to one of the laser diodes and a pulse voltage to the semiconductor optical amplifier.

This study calculated the ideal conversion efficiency of a photon-enhanced thermionic emission (PETE) energy converter driven by blackbody radiation. The results indicate that a PETE energy converter can provide high-efficiency conversion of 500–2000 K blackbody radiation using approximately 0.3–0.8 eV bandgap semiconductors as emitters. This optimal bandgap is much smaller than that for sunlight of approximately 1.4 eV. Because high-efficiency operation requires a high temperature in the emitter, the melting point of a material is the main factor limiting the maximum efficiency.