Table of contents

Waveguide quasi-phase-matching (QPM) twin photon generation (TPG) devices are the key device for future quantum communication. We examined the temperature dependences of the twin photon wavelengths of a MgO:LiNbO₃ waveguide Type-I QPM TPG device to clarify the possibility of twin photon wavelength tuning. It turned out that, in a typical device of 19 µm QPM grating period for TPG in the 1.55 µm band, twin photon wavelength tuning ranges of ≃16 and 300 nm can be obtained for degenerate and nondegenerate TPG, respectively, with temperature control in 25–150 °C.

We demonstrate a polarization imaging screen using vector gratings by ultraviolet laser direct writing of polarized-light-induced optical anisotropy in photocrosslinkable polymer liquid crystals. For realizing a polarization-sensitive diffraction in the image screen, spatial distribution of the optical anisotropy has been designed, and the right- and left-hand side circularly polarized optical image are clearly reconstructed as the +1st- and -1st-ordered diffraction according to the theoretical expectation.

Wavelength dependence of ex-vivo ultrahigh-resolution optical coherence tomography (UHR-OCT) imaging of thyroid gland using supercontinuum at wavelength from 800 to 1700 nm was demonstrated. The wavelength dependence of the thickness of follicular epithelium and fine structures such as round or oval follicles were observed from the UHR-OCT cross sectional images. The reconstructed en-face OCT images at all wavelength regions were obtained and the images of follicles with several different signal intensities were observed in 1060 and 1700 nm UHR-OCT images. To our knowledge, this is the first observation of wavelength dependence of OCT images of thyroid gland structure.

We fabricated fine electrodes conventionally by nanoimprint lithography (NIL) to measure the electric properties of nanofibers and showed the performance of fine electrodes by the field-effect transistor (FET) measurement of a semiconducting polymer nanofiber. Furthermore, we performed the FET measurement of regioregular poly(3-hexylthiophene-2,5-diyl) (rr-P3HT) nanofibers using fabricated fine electrodes. As a result, the mobility was estimated to be 1.32×10^-3 cm² V^-1 s^-1, which was on the same order as that reported previously. The fabrication method was clarified to be effective for molecular electronics.

In terms of environmental friendliness, halogenated compounds including 1,2-dichlorobenzene (ODCB), which is a solvent frequently used in the preparation of polymer/fullerene bulk heterojunction composites for photocells, are not desirable. As a result of exploration in this context, 1,2,4-trimethylbenzene (TMB) has been found as a useful solvent for the preparation of poly(3-hexylthiophene) (P3HT)/C₇₀ composite. A preliminary experiment has shown that the power conversion efficiency of a device with a P3HT/C₇₀ composite film prepared from TMB solution reaches 0.45%, which is higher than the previously reported value for P3HT/C₇₀-based devices prepared from ODCB solution by one order of magnitude.

Positioning of two different types of cells in contact with each other is of particular importance to analyze interactions between the cells. However, previous methods require sequential injection of two different cell suspensions and flow switching during the operation. Here, we present a novel method to pair two different types of cells on microfluidic devices. Single-step pairing was achieved by introducing each cell suspension from different inlets into the microchannel which has a microslit arranged with a hydrodynamic weir. As an application of the pairing, cell fusion through the microslit was studied.

The impact of polarization fields in multiple quantum well (MQW) structures is revealed by photoluminescence measurements and band diagram calculations. We observe a blue shift of luminous energy of 33 meV and an increased light emission of 19% for In_xGa_1-xN/In_yGa_1-yN MQWs with respect to In_xGa_1-xN/GaN MQWs. Band diagram calculations show a lowering of the polarization fields and an increase in wave function overlap of 22% by adding indium into the barriers. We therefore attribute the observed blue shift and increased emission to an improved electron and hole wave function overlap due to lower electric fields in In_xGa_1-xN/In_yGa_1-yN structures.

The magnetic properties of bulk Cr tips have been investigated by spin-polarized scanning tunneling spectroscopy (SP-STS). To extract the properties of the Cr tips, we performed low-temperature SP-STS measurements on a well-known model system: nanometric Co islands on Cu(111). Our experiments indicate the existence of uncompensated magnetic moments at the apex of the Cr tips, which rotate in the direction of the applied vertical magnetic field and become aligned with it at approximately 2 T. We extracted a tip spin polarization of 45% at the Fermi energy. We showed that the tip spin polarization can change with a modification of the tip apex.

We investigate the electronic contribution to local dielectric property in terms of the local polarizability density and dielectric constant density, for the cubic, tetragonal, and monoclinic structure of HfO₂ and compare their dielectric properties with those of SiO₂. We show appropriate termination conditions of our cluster models to realize the condensed property of dielectric; point charge conditions for HfO₂ whose bond is ionic, while hydrogen termination conditions for SiO₂ whose bond has covalent property. We show that local parts of materials have complicated responses to external electric fields, in particular, rotational ones. Hence, nanosize materials should be studied in the local and tensor quantity analysis to describe rotational responses correctly. It is clarified that the electronic contribution to local polarizability and dielectric constant densities is almost independent of the structures of HfO₂ crystals. We show that the electronic contribution to dielectric response of HfO₂ is significantly large compared to those of SiO₂. In addition, it is found that the average value of dielectric constant around O atoms is larger than other regions in both HfO₂ and SiO₂.

In-situ X-ray photoemission spectroscopy (XPS) has been used to investigate the initial stages of TiO₂ growth on a Si(001) substrate by atomic layer deposition (ALD). The core level spectra of Si 2p, C 1s, O 1s, and Ti 2p were measured at every half reaction in the titanium tetra-isopropoxide (TTIP)–H₂O ALD process. The ligand exchange reactions were verified using the periodic oscillation of the C 1s concentration, as well as changes in the hydroxyl concentration. XPS analysis revealed that Ti₂O₃ and Si oxide were formed at the initial stages of TiO₂ growth. A stoichiometric TiO₂ layer was dominantly formed after two cycles and was chemically saturated after four cycles.

The optical properties of (0001) ZnO layers grown at 1000 °C on (0001) sapphire substrates by halide vapor phase epitaxy (HVPE) were investigated by various photoluminescence (PL) measurements. A layer grown with a H₂O/ZnCl₂ (VI/II) ratio of 20 on a 0.4-µm-thick buffer layer exhibited a significant near-band-edge (NBE) peak blueshift and degraded internal quantum efficiency (η_int) due to residual compressive stress. Growth with a VI/II ratio of 600 diminished the NBE peak blueshift; however, deep level emission and a reduction of PL decay time (τ_PL) were caused by point defects generated by excess O source supply. A layer without the NBE peak blueshift and deep level emission was realized by growth with a VI/II ratio of 20 and a buffer layer of 0.8 µm. The η_int and τ_PL for HVPE-grown layers could be improved to 4.1% and 122.8 ps by using the thick buffer layer and appropriate VI/II ratio.

An indium-incorporated germanium–antimony–telluride material, In₂₀Ge₁₅Sb₁₀Te₅₅ (IGST), was investigated as a recording material for phase change memory. The crystallization temperature of IGST was 226 °C, which is 75 °C higher than that of conventional GST. The reset current of the device using IGST was about 10 mA for a plug 180 nm in diameter, which enabled a low-power operation, compared with the GST-based device. A cycle endurance of up to 1.5×10⁴ was achieved. The data retention was estimated to be 10 years at 145 °C. These data clearly show that IGST exhibits promising characteristics as a recording material for phase change memory.

The defect-related photoluminescence (PL) levels of CuInS₂ thin films prepared by sulfurization using ditertiarybutylsulfide [(t-C₄H₉)₂S: DTBS] have been investigated. The PL spectra exhibit three low-energy peaks at 1.37, 1.34, and 1.24 eV. On the basis of these PL spectra observed at different excitation intensities, the emissions are attributed to donor–acceptor pair transitions. The ionization energies of donors in CuInS₂ thin films are determined to be 125, 150, and 280 meV, which are, respectively, due to indium atom-occupied copper vacancies (In_Cu), sulfur vacancies (V_S), and sulfur atom-occupied copper vacancies (S_Cu); whereas that of the acceptor is determined to be 100 meV and has been reported to the copper vacancy (V_Cu). Using these data, a band diagram for the defect levels of CuInS₂ thin films prepared by sulfurization is proposed.

A new low-dielectric-constant spin-on glass (SOG) with a k value of 2.4 has been developed for a gap-filling process in advanced memory devices. The low-shrinkage characteristic of the SOG during thermal curing provides capabilities of gap filling and planarizing as high as those of conventional reflowable SOGs. The low-shrinkage SOG has thermal stability up to 800 °C and chemical stability against diluted hydrofluoric acid, sulfuric acid–hydrogen peroxide, and amine-based solutions, which makes it possible to be used as an interlevel dielectric of memory devices. Tungsten and aluminum interconnects fabricated using the low-shrinkage SOG showed a parasitic capacitance 30% lower than those fabricated using silicon dioxide and a sufficiently long line-to-line dielectric breakdown lifetime. Taking advantage of the high chemical stability of the SOG, an all-wet damageless via-formation process using an amine-based photoresist stripper has been developed. By using the process, the low-shrinkage SOG can be applied to multilevel metallization.

We simulated and compared the material properties of barium titanate for five states, namely, (1) the orthorhombic state, (2) the orthorhombic state near the orthorhombic–tetragonal phase boundary, (3) the tetragonal state near the orthorhombic–tetragonal phase boundary, (4) the tetragonal state, and (5) the tetragonal state near the tetragonal–cubic phase boundary by using a modified time-dependent Devonshire–Ginzburg–Landau model. We reproduced reasonable variations in piezoelectric coefficients, dielectric susceptibilities, and elastic compliance constants for the above-mentioned five states, especially for the phase boundary states. Moreover, we simulated the hysteresis curves of the dependence of electric polarization and strain on electric field and the dependence of the hysteresis curves on compressive stress. The obtained simulation results are well explained by the polarization rotation or extension, which is made easy by the free energy flattening induced by temperature or electric field.

We demonstrate blue organic light-emitting devices (OLEDs) with high luminance based on DNA biopolymer. We incorporated aromatic surfactant in the synthesis of DNA biopolymer, which results in lower operation voltage of biopolymer-based OLEDs and a turn-on voltage of 3.77 V was achieved. Maximum luminance of 12277 cd/m² and a 46.4% enhancement in luminous efficacy of blue OLED based on DNA biopolymer was demonstrated compared to the reference device. This demonstrates a viable and facile route to adjust the conductivity of DNA biopolymer and paves the way towards multifunctional biomaterial-based optoelectronic devices and applications.

Dielectric spectroscopy is used to clarify the ion adsorption on a 5° SiO_x alignment film. The results show that both ion concentration and dc conductivity decrease after ion adsorption. The decrease in ions concentration mainly comes from large ionic impurities, possibly corresponding to the colloids formed by ions associated with water. Also, it is found by simulating the voltage holding ratio (VHR) that the long-term voltage decay is determined by the dc conductivity of liquid crystal (LC), which corresponds to ions whose concentration is kept constant. This is interpreted as evidence for the assumption that ion concentration is determined by the solubility of LCs, which is determined by the water concentration in LCs.

This study describes a novel method for manufacturing a hole injection layer of an organic light-emitting diode (OLED), comprising an ultraviolet (UV) reactive Br–fluorocarbon precursor (Br–CF₂–C₆F₄–CF₂–Br). The proposed method can be used to form a fluorizated polyxylylene film, demonstrating high repeatability on the anode as the hole injection layer of organic electroluminescent devices to enhance the hole injection, reduce the operating voltage of 1.2 V, and extend the operational lifetime by more than 150 times under a high current density of 125 mA/cm². Using a spin-coating process, the remaining precursor can be recycled to prevent wasting materials. UV curing without the solvent-removing process shortens manufacturing time. Hence, fabricating a high performance OLED using a simple, low-cost process is the aim of this study.

We demonstrate that power recycling is feasible by using a semitransparent strip of Al electrode as an interconnecting layer to merge a white organic light-emitting device (WOLED) and an organic photovoltaic (OPV) cell. The device is called a photovoltaic organic light-emitting device (PVOLED). It has a glass/indium tin oxide (ITO)/copper phthalocyanine (CuPc)/4,4,4-tris(3-methyl-phenylphenylamino) triphenylamine (m-MTDATA):V₂O₅/2-N',N-bis(1-naphthyl)-N,N'-diphenyl-1'-biphenyl-4,4'-diamine (NPB)/4,4'-bis(carbazol-9-yl)biphenyl (CBP):bis[3,5-difluoro-2-(2-pyridyl) phenyl-(2-carboxypyridyl)] iridium(II) (FIrpic):4-(dicyanomethylene)-2-t-butyl-6 (1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB)/4,7-diphenyl-1,10-phenanthroline (BPhen)/LiF/Al/poly(3-hexylthiophene) (P3HT):[6,6]-phenyl-C₆₁ butyric acid methyl ester (PCBM)/V₂O₅/Al structure. A power recycling efficiency of 10.133% is achieved using the WOLED of the PVOLED operated at 9 V and a brightness of 2110 cd/m² when the conversion efficiency of the OPV cell is 2.3%. We found that the power recycling efficiency decreases at a high brightness and a high applied voltage owing to an increase in the input power of the WOLED. A high efficiency (18.3 cd/A) and a high contrast ratio (9.3) are obtained in the device operated at 2500 cd/m² under an ambient illumination of 24000 lx. Reasonable white light emission with Commission Internationale De L'Eclairage (CIE) color coordinates of (0.32, 0.44) at 20 mA/cm² and a slight color shift occur in spite of the high current density of 50 mA/cm².

We modeled the effects of surface roughness (SR) on a near-infrared guided-mode resonance (GMR) biosensor. A power spectral density function was used to describe the SR with spatial autocorrelation integration through a rigorous coupled-wave analysis (RCWA), and a peak wavelength value (PWV) shift in reflectance was observed under transverse electric (TE) and transverse magnetic (TM) polarization. Sub-nanometer SR caused significant PWV shifts, leading to invalid spectral recognition. In addition to random roughness, we studied the PWV reflectance shift for SR models such as sinusoidal, rectangular, and effective medium types. All SR models showed a larger PWV shift for TM polarization than for TE polarization. Owing to SR, PWV reflectance decreased abruptly for TM polarization at small angular deviations from normal incidence. However, the symmetrically splitting of the reflectance spectra for TE polarization implied a high angular tolerance to fabrication errors. Compared to vertical sidewall roughness in our prior work, the SR is much more deleterious for GMR biosensing and should be appropriately controlled.

Electrooptic (EO) properties were studied for a polydiacetylene (PDA) nanoparticle (NP) submonolayer film on a thin gold film at a surface coverage of σ∼0.084, using the attenuated total reflection geometry at the surface plasmon resonance condition. Both linear and second-order EO effects (Pockels and Kerr effects) were observed from the PDA NP submonolayer, although the Pockels effect will be absent in the PDA NP film under the electric dipole approximation. The second- and third-order nonlinear susceptibilities of the PDA NPs are determined to be χ⁽²⁾ ∼10² pm/V and χ⁽³⁾ ∼10^-9 esu, respectively. The susceptibilities are almost compatible with those in general nonlinear optical materials. The origin of the Pockels effect in the PDA NP film is also discussed.

We have developed a micro multipoint laser Doppler velocimeter (µ-MLDV) that enables selective collection of Doppler interference photons. In previous report [H. Ishida et al.: Rev. Sci. Instrum. 82 (2011) 076104], developed the reflection-type µ-MLDV, and showed the results of demonstrations performed on transparent artificial flow channels. In this study, we attempted to perform in-vivo experiments using animals. It can measure absolute velocity and generate tomographs of blood vessels courses. The present system can perform noninvasive in-vivo measurements with a detection limit of about 0.5 mm/s and a spatial resolution in the x–y plane of 125 µm. It is thus able to image venulae. It was used to image venulae in a mouse ear and a subcutaneous blood vessel in a mouse abdomen at a depth of about 1.0 mm below the skin.

Micromagnetic modeling has been performed to study responses of giant magnetoresistance (GMR)-type differential readers (GDRs). Our results show that the pulse shape in GDRs is Gaussian-like, which is consistent with the counterpart in conventional heads. The key finding is that GDR signals increase with decreasing gap length. Magnetostatic interactions among the free layers, hard biases and transition bits are responsible for the signal enhancement at small gap length. Signal enhancement at small gap length is very useful in linear scaling for differential readers since media vertical fields approach zero towards a transition.

An exchange-biased spin valve with Conetic-based free layers of Co₉₀Fe₁₀, Co₉₀Fe₁₀/Conetic and Conetic was investigated. The spin valve with the Co₉₀Fe₁₀ free layer showed the highest giant magnetoresistance (GMR) ratio of 4% but showed the lowest normalized sensitivity of 0.02 Oe^-1. The GMR ratio of 3% and the normalized sensitivity of 0.07 Oe^-1 were obtained for the spin valve with the Co₉₀Fe₁₀/Conetic free layer after annealing. The spin valve having the Conetic free layer showed softer magnetic properties and well-defined smaller anisotropy than the other spin valves. Though the spin valve showed the lowest GMR of 0.4% after annealing, it showed the highest normalized sensitivity of 0.14 Oe^-1. Our study shows that further improvement in MR response of spin valves with Conetic-based free layers can make a spin valve sensor promising for detecting extremely low fields.

The recessed-gate AlGaN/GaN metal–oxide–semiconductor heterostructure field-effect transistors (MOSHFETs) with a p-GaN back-barrier studied in this work exhibited much lower buffer leakage current than those without the back-barrier. The threshold voltage of the device with the p-GaN back-barrier was controlled by varying the depth of gate recess etching, and a value as high as 2.9 V was obtained with deep gate-recess etching into the channel layer. The device structure has the advantage of both low leakage current and high threshold voltage, which is important for power-switching applications. In contrast, the performance parameters of the device, such as subthreshold slope and field-effect mobility, can be degraded owing to increased plasma damage with increasing recess depth.

We propose a technique for continuously controlling the full range of pretilt angles with a high process margin. The proposed method is characterized by tuning the thickness of a heterogeneous polyimide layer that consists of homeotropic and planar polyimides. The thickness of the mixture can be controlled by varying the concentration of the solvent. The liquid crystal (LC) pretilt generated at the very thin mixture film is insensitive to some incorrect mixing ratio, since the segregation of the depth direction of the mixture including the van der Waals effect in interactions with LCs decreases ultimately. Consequently, we can obtain continuous LC pretilt angles with a high process margin by controlling mixing ratio in a very thin heterogeneous polyimide film. Furthermore, it is possible to achieve excellent reliability, uniformity, and productivity using this technique. A simple mathematical model based on van der Waals interaction provides a good description of the experimental results.

We demonstrated an organic near-infrared (NIR) photodiode on the basis of the bulk heterojunction (BHJ) structure by using tin phthalocyanine (SnPc) and C₆₀ fullerene with a high incident photon–electron conversion efficiency (IPCE) of 50% at a wavelength of 750 nm. The cell showed optical responses to about 1000 nm and had a specific detectivity D^* of 1.59 ×10¹¹ cm Hz^1/2/W. The SnPc:C₆₀ ratio in the BHJ layer influenced the optical response. Higher ratios enhanced NIR sensitivity but reduced the peak IPCE; the optimal ratio was 3:1. The optical interference of directly incident light and light reflected from an Al electrode was also examined to enhance the IPCE at longer wavelengths. With a 90-nm-thick C₆₀ layer, the first antinode of the standing wave at a wavelength of 750 nm was located at the BHJ layer; this layer enhanced the IPCE at 700 and 800 nm but reduced it at 400 nm.

A low-insertion-loss V-band complementary metal–oxide–semiconductor (CMOS) band-pass filter is demonstrated. The proposed filter architecture has the following features: the low-frequency transmission-zero (ω_z1) and the high-frequency transmission-zero (ω_z2) can be tuned individually by adjusting the value of the series capacitor (C_s) and the size of the built-in inductor–capacitor (LC) resonator, respectively. The folded short-stub technique is used to reduce the chip size of the filter. To reduce the silicon substrate loss, the CMOS-process-compatible backside inductively-coupled-plasma (ICP) deep trench technology is used to selectively remove the silicon underneath the filter. After the ICP etching, the filter achieves insertion-loss (1/S₂₁) lower than 3 dB over the frequency range of 46.5–85.5 GHz. The minimum insertion-loss is -1.8 dB at 60 GHz.

The drain current vs gate voltage (I_D–V_G) and drain current vs drain voltage (I_D–V_D) characteristics of ferroelectric gate-all-around Si nanowire transistors are derived using the drift/diffusion transport theory. It is pointed out that the nonsaturated polarization in the ferroelectric film, which occurs near the drain region in the channel owing to the influence of the applied drain voltage, plays an important role in the calculation of the drain current as well as the polarization near the source region, and a graphical method using analytical expressions for the minor polarization hysteresis loops is presented to calculate the mobile charge density in the nanowire. By numerical analysis, the gate voltage range suitable for memory operation is determined in Si nanowire transistors with ferroelectric poly(vinylidene fluoride–trifluoroethylene) [P(VDF–TrFE)] gate films.

We report a near infrared (NIR) single photon detector (SPD) using an InGaAs/InP avalanche photodiode (APD) operated with a bipolar rectangular gating signal. The use of the bipolar gating pulse enabled us to operate the APD well below the breakdown voltage during the gate-off time. As a result, it permits to decrease the lifetime of the trapped carriers, and then reduces the after-pulse noise of the detector. At a repetition rate of 200 MHz, the after-pulse probability is 8.2% less comparing to that of conventional gating signal SPD.

This study demonstrates a simple and fast method of the operation mode control for ZnO nanowire field effect transistors (FETs) with hydrogen peroxide (H₂O₂, 10%) solution treatment for 5–10 s. With this H₂O₂ treatment, the surface of ZnO nanowires was roughened as confirmed by transmission electron microscopy images and the defect level-related emission was increased from photoluminescence (PL) data. Correspondingly, the threshold voltage of H₂O₂-treated ZnO nanowire FETs shifted to the positive gate bias direction, leading a transition of the operation mode from depletion-mode to enhancement-mode. This H₂O₂ solution treatment can be a useful method for controlling the operation mode of ZnO nanowire FETs with a wide threshold voltage shift in a few second solution treatment.

We present the results of density functional theory calculation in oxygen dissociative adsorption process on two types of isolated platinum (Pt) clusters: Pt₄ and Pt₁₀, by taking into account the effect of cluster reconstruction. The strength of Pt–Pt bonds in the clusters is mainly defined by d–d hybridization and interstitial bonding orbitals (IBO). Oxygen that adsorbed on the clusters is weakening the IBO and thus inducing geometry reconstruction as occurred in Pt₁₀ cluster. However, cluster that could undergo structural deformation is found to promote oxygen dissociation with no energy barrier. The details show that maintaining well-balanced of attractive and repulsive (Hellmann–Feynman) forces between atoms is considered to be the main key to avoid any considerable rise of energy barrier. Furthermore, a modest energy barrier that gained in Pt₄ cluster is presumed to be originate from inequality of intramolecular forces between atoms.

In this paper, we present a computational study on the electronic and charge transport properties of armchair boron nitride-confined graphene nanoribbon structures. We compare the electronic bandstructure of hydrogen passivated armchair graphene nanoribbons (AGNRs) with the bandstructure of boron nitride-confined AGNRs. Our study reveals that due to the energy gap opening in (3p+2) AGNRs in these novel hybrid structures and the possibility of realizing parallel arrays of semiconducting and isolating nanoribbons in them, they can be considered as better candidates for electronic applications than hydrogen passivated AGNRs. We also calculate the charge transmission probability and density of states in these nanostructures and investigate their behavior under different biases. In doing so, we have used the non-equilibrium Green's function formalism to solve the Schrödinger equation and have coupled it to a two-dimensional Poisson-solver for treating the electrostatics of the system.

A new atomic force microscopy (AFM) force mapping technique has been used to investigate insulating thin (100) films of NaCl on conducting Cu(111) substrate at 78 K. This technique was able to map the interaction forces between the AFM tip and the surface ions of the sample. The site-specific force curves of the (100) surface of the NaCl thin films are presented. We observed only an attractive short-range interaction force at the Na⁺ and Cl^- sites. We propose simple models to explain the behavior of the force curves at the different ion sites.

The sensitivity of flexural vibration for an atomic force microscope (AFM) cantilever with a crack has been studied. An explicit expression for the sensitivity of vibration modes of the cracked cantilever has been obtained using the relationship between the resonant frequency and contact stiffness of the cantilever and sample. Results show that the sensitivities of the three modes of the cracked cantilever are higher than those of the cantilever without crack when the contact stiffness is low. When the contact stiffness is high, however, the situation is reverse. Therefore, a cracked AFM cantilever can be used for imaging soft samples such as biological molecules and polymers. In addition, the crack near the free end of cantilever that leads to a higher sensitivity. This is useful for the design of a highly sensitive cantilever.

Nonpolar GaN substrates are necessary for the improvement of GaN device performance. The growth of high-quality nonpolar GaN crystals, however, has not yet been achieved. In this study, we grew a-plane GaN crystals using the Na flux method and investigated the effects of the substrate surface treatment on the crystallinity of grown GaN crystals. A-plane GaN substrates with chemical mechanical polishing (CMP) and with chemical etching using pyrophosphoric acid were used as the seed substrates. We found that full width at the half-maximum (FWHM) of the X-ray rocking curve (XRC) of GaN crystals grown on the substrate with chemical etching was smaller than that on the substrate with CMP. The results show that chemical etching is more effective than CMP for improving the crystallinity of a-plane GaN crystals.

ZnO thin films were grown on porous silicon by plasma-assisted molecular beam epitaxy. Thermal annealing was then carried out at various temperatures in the range from 500 to 700 °C for 10 min. Atomic force microscopy, scanning electron microscopy, X-ray diffraction, and photoluminescence were carried out to investigate the effects of the annealing temperature on the properties of the ZnO thin films. The ZnO thin films exhibit a mountain-range-like surface. With increasing annealing temperature, the grain size increased and the residual stress decreased. The activation energy of the free exciton (FX) emission from the ZnO thin films was found to be about 32 meV and the fitting parameters in Varshni's empirical equation were α= 2×10^-3 eV/K and β= 1200 K. The photoluminescence (PL) intensity ratio of near-band-edge emission to deep-level emission of the ZnO thin films increased with increasing annealing temperature.

P-type CuGaO₂ films have been fabricated on silicon substrates by the sol–gel method. The stable sol solutions for CuGaO₂ growth were developed by the mixing of Cu–O and Ga–O sol solutions using copper(II) acetate monohydrate and tris(acetylacetonato) gallium(III), respectively. Phase separation in CuGaO₂ films depends on the sol solution temperature and postbake temperature and duration. CuGaO₂ films without a CuO phase were fabricated by postbaking at temperatures of approximately 800 °C for 1 h in N₂ atmosphere. The sol–gel-derived CuGaO₂ films show high transparency of more than 80% in the visible range, and the energy gap is approximately 3.6 eV.

Nanocomposite thin films consisting of spinel-type magnetic semiconductor (Fe,Zn)₃O₄ and perovskite-type ferroelectric BiFeO₃ were prepared by a self-assembled growth method from a composition-adjusted Fe–Zn–Bi–O single target using a pulsed laser deposition technique. It is found that BiFeO₃ square patterns reflecting the in-plane lattice shape of the SrTiO₃ substrate are grown directly from the substrate interface with inverse pyramid shapes embedded in a (Fe,Zn)₃O₄ matrix in the absence of other phases. This self-assembled growth should be a convenient method to fabricate a lot of nano-heterojunctions with complicated oxide structures, which is applicable to spintronic oxide materials.

Mn²⁺-doped Ba_0.5Sr_0.5TiO₃ (BST) thin films were prepared on Pt-coated sapphire substrates by RF magnetron sputtering. By analyzing the energy state of particles during the sputtering, deposition parameters (substrate temperature, sputtering power, and atmosphere) were optimized for superior dielectric properties. Our results indicated that a compromise of relatively high tunability and low loss could be achieved. Resultant BST thin films has a tunability of 50% and dielectric loss of 0.64% at an applied field of 1.2 MV/cm, under optimized sputtering conditions of substrate temperature at 750 °C, pressure at 4 Pa with an O₂/(O₂+ Ar) mixing ratio of 50%, and sputter RF power density at 6.8 W/cm².

To clarify the growth mechanism of the lateral growth of Ge in the rapid-melting-growth process, two types of molecular-dynamics simulation were investigated in this study. One was the nucleation of Si_1-xGe_x (0 ≤x ≤1) from supercooled melts, and the other is the growth rate of supercooled Si_1-xGe_x melts using a crystalline Si_1-xGe_x seed. The incubation time is found to be minimum at approximately 0.70 T_m (T_m: melting temperature for Si_1-xGe_x). No nucleation was found when the temperature was higher than 0.75 T_m. The crystal growth rates of Si_1-xGe_x peaked between 0.90 T_m and 0.94 T_m for both the [100] and [111] orientations. These results suggest that 0.90 T_m to 0.94 T_m of Si_1-xGe_x (x = 1) is an optimum temperature range to grow crystalline Ge in the rapid-melting-growth process.

The microstructures in Na_0.5K_0.5NbO₃ (NKN) ceramics sintered at 960 °C with CuO additives were investigated with transmission electron microscopy (TEM). As a new microstructural constituent, CuO pockets have been observed at the grain boundaries of NKN and also inside the NKN matrix. The melting of CuO is caused by the element Na from the matrix, which forms Na–Cu–O eutectoid compounds whose melting point is lower than the sintering temperature. The kinetics of melting reaction largely depends on the size of the pocket. The interaction starts at the interfaces between the pocket and the matrix and advances into the interior of the pocket. The smaller pocket would melt earlier during the sintering process, flow into triple junctions between matrix grains, and participate in sintering via liquid phase sintering. In the larger pockets, the melting starts at the interfaces. Thus the outer areas are melted, but the CuO particles in the center remained unmelted. The NKN matrix then grows further into the pocket through liquid phase sintering, leaving low-angle grain boundaries behind that interface with the remaining CuO particles. The unmelted CuO particles in the pocket remain as the second-phase particles.

The propagation of crystal defects from a 3C-SiC intermediate layer (3C-SiC IL) to hexagonal III–nitride epilayers formed by a metalorganic vapor phased epitaxy (MOVPE) has been investigated by observing the interface between the 3C-SiC IL and the hexagonal III–nitride epilayers. The 3C-SiC(111) IL grown on a Si(111) substrate has many stacking faults (SFs) that form along the 3C-SiC111 planes. The density of the SFs decreases with separation from the Si substrate. The initial III–nitride epilayers have V-shaped trenches due to the SFs of the 3C-SiC IL. However, there are some SFs, that do not generate V-shaped trenches. On the basis of high-resolution cross-sectional observations by transmission electron microscopy and X-ray pole-figure analysis, an atomic model for the SFs is considered in terms of twin bands of 3C-SiC. V-shaped trenches were determined to be formed on protrusions consisting of the twin bands in the 3C-SiC IL.

We systematically studied spatial inhomogeneity of aluminum content in air-bridged lateral epitaxially grown (ABLEG) AlGaN ternary alloy films by high-resolution photoluminescence mapping probed with cross-sectional scanning near-field optical microscopy (SNOM). We observed the content changes along the vertical <0001> and the horizontal <110> growth directions in AlGaN films with four different mask widths. The spatial inhomogeneity was determined by considering the following factors: the different growth rates of the lateral and vertical directions, the aluminum and gallium adatom supplies from a gas that depend on mask width, and the aluminum and gallium adatom diffusions on the (0001) and (110) facets.

The electronic structure and chemical properties of the interface between indium tin oxide (ITO) modified by a fluorinated self-assembled monolayer (F-SAM) and a N,N '-bis(1-naphthyl)-N,N '-diphenyl-1,1'-diphenyl-1,4'-diamine (α-NPD) layer were investigated in order to clarify the effects of the F-SAM modification of ITO anodes on the driving voltage and lifetime of organic light-emitting diodes (OLEDs). Ultraviolet and X-ray photoelectron spectroscopy revealed that the F-SAM modification of ITO led to a shallower highest occupied molecular orbital level in the α-NPD layer near the interface than in conventionally treated ITO, a chemical reaction between F-SAM and α-NPD, and the migration of adsorbed fluorine into the α-NPD layer. These results indicate that high conductance, the suppression of crystallization, and the inhibition of oxidation in the hole-transporting layer along with a small hole-injection barrier height at the anode/HTL interface contribute to the excellent properties of OLEDs having ITO anodes modified by F-SAM.

The influence of lithium and potassium doping on the structural and electrical characteristics of Li_x(K_yNa_1-y)_1-x(Nb_0.9Ta_0.06Sb_0.04)O₃ lead-free piezoelectric ceramic prepared by the conventional solid-state reaction method was investigated and discussed. X-ray diffraction (XRD) and the scanning electron microscopy (SEM) were carried out to analyze the phases and microstructures of the ceramic specimens, respectively. An impedance analyzer (HP4294A) was used to measure the relative dielectric constant and loss tangent. The electromechanical coupling factor (k_P) and the relative dielectric constant (ε_r) of Li_x(K_yNa_1-y)_1-x(Nb_0.9Ta_0.06Sb_0.04)O₃ piezoelectric ceramic for x = 0.06 and y = 0.485 were 1280 and 42.8%, respectively. Finally, the Curie temperature (T_c) of the piezoelectric ceramic was about 340 °C and the orthogonal-to-tetragonal phase transition temperature (T_o–t) was about 110 °C.

The thermophysical properties of Nb-doped TiO₂ (Nb:TiO₂) films were studied in terms of electrical conductivity and Nb concentration. The thermal diffusivity of Nb:TiO₂ films with various Nb concentrations was investigated and found to range from (1.2–2.1)×10^-6 m² s^-1. The thermal conductivity of Nb:TiO₂ films with 8.5 at. % Nb concentration is proportional to the electrical conductivity in conformity with the Wiedemann–Franz law. The thermal conductivity carried by phonons, λ_ph, of Nb:TiO₂ films decreased with increasing Nb concentration. The mean free path of phonons, l_ph, in Nb:TiO₂ films was estimated to be almost the same as the average distance between Nb impurities. The grain size was much larger than l_ph. Thus, phonon scattering by Nb impurities should be the dominant factor for the change in λ_ph.

Low-temperature atmospheric-pressure plasma (APP) jets and a metal stencil mask have been used for the patterning of fibronectins deposited on a silicon (Si) wafer. Fibronectins typically constitute the extracellular matrix (ECM) and a micro-patterned ECM may be used for arranging living cells in a desired pattern on the substrate surface. Such a technique can be used for the fabrication of cell chips. In this study, patterning of 100-µm-wide lines of fibronectin layers has been demonstrated. Desorption of fibronectins from the surface by plasma application has been confirmed by atomic force microscopy (AFM) and Fourier transform infrared spectroscopy (FT-IR).

Fluidic self-assembly (FSA) is a promising technique for fabricating devices that are composed of large numbers of small electronic components. We have previously proposed a printing method that utilizes the FSA principle. In our method, by simply blade-coating first water and then a dispersion liquid of microstructures on a substrate, the microstructures are automatically placed on pre-patterned hydrophilic areas by means of water/solvent interfacial force. To improve the placement probability of microstructures on the intended hydrophilic areas, in the present study we investigate the influence of the volume of water droplets on the probability of microstructure placement. We prepared various sizes of hydrophilic patterns on a glass substrate to vary the volume of water droplets in hydrophilic areas, and placed square SiO₂ plates, measuring 50 ×50 ×0.3 µm³, using FSA. The probability and accuracy of placement was evaluated using a high-speed microscope, and the results were interpreted using a simple model based on capture coefficients and the collision cross section of the water droplets. We verified that the model closely fitted the experimentally obtained probability of placement as observed using the high-speed microscope. We found that the capture coefficient increased with increasing area of the water droplet. These results indicate that the size of the hydrophilic area is one key to improving the probability and accuracy of our placement technique.

New chemical mechanical polishing processes using nanocolloidal ceria slurry are proposed for high-precision and low-damage planarization of silicon-dioxide-based dielectric films. In the polishing process of a shallow trench isolation structure, a hard pad and a cationic polymer additive are used in combination with the slurry. The new process is effective in improving the planarity and reducing the microscratch count in comparison with a conventional polishing process with calcined ceria slurry and a standard pad. In the polishing process of an interconnect structure with ultralow-k interlayer dielectrics (ULK-ILDs), the standard pad should be used since the ULK-ILDs are easily damaged. By employing a spin-on-type ULK-ILD having a self-planarizing effect, a high planarity is obtained when using the nanocolloidal ceria slurry with the standard pad. The electrical measurement of the interconnect structure indicates that dielectric damage due to the process is successfully suppressed.

A novel etching process with etchant mist was developed and applied to oxide thin films such as zinc oxide (ZnO), zinc magnesium oxide (ZnMgO), and indium tin oxide (ITO). By using this process, it was shown that precise control of the etching characteristics is possible with a reasonable etching rate, for example, in the range of 10–100 nm/min, and a fine pattern of high accuracy can also be realized, even though this is usually very difficult by conventional wet etching processes, for ZnO and ZnMgO. The mist etching process was found to be similarly and successfully applied to ITO. The mechanism of mist etching has been studied by examining the etching temperature dependence of pattern accuracy, and it was shown that the mechanism was different from that of conventional liquid-phase spray etching. It was ascertained that fine pattern etching was attained using mist droplets completely (or partly) gasified by the heat applied to the substrate. This technique was applied to the fabrication of a ZnO thin-film transistor (TFT) with a ZnO active channel length of 4 µm. The electrical properties of the TFT were found to be excellent with fine uniformity over the entire 4-in. wafer.

In this study, the dependence of Cu electrochemical mechanical planarization (ECMP) rate on electric potential and mechanical force in electrolyte is investigated using potentiodynamic analysis, electrochemical impedance spectroscopy (EIS), and X-ray photoelectron spectroscopy (XPS). In chemical etching, CMP, electropolishing, and ECMP processes, the Cu removal rate is mainly affected by the interplay between electric potential and mechanical force. An equivalent circuit is built by fitting the EIS results to explain the behavior of Cu dissolution and Cu passive film. The Cu dissolution rate increased with decreasing charge-transfer time-delay. The resistance of the Cu passive film (R_p) is proportional to the intensity ratio of Cu₂O/[Cu(OH)₂+ CuO].

To develop a vacuum-electrospray beam source for secondary ion mass spectrometry (SIMS), beam characteristics of charged droplets electrosprayed in vacuum were investigated in the negative-ion mode as well as the positive-ion mode. A quaternary ammonium ionic liquid was tested. Experimental results showed that there are differences as well as similarities between the positive-ion mode and the negative-ion mode. Beam current changed greatly with capillary voltage and the flow rate of the ionic liquid. Transient response analysis showed that the vacuum electrospray generated a mixed beam consisting of charged particles of smaller m/z values (m/z∼10³) and charged droplets of larger m/z values (m/z∼10⁵ to 10⁶). It turned out that the m/z values of the charged droplets diminished with increasing capillary voltage. Using a three-dimensional positioning stage, the capillary position dependence on the beam characteristics was measured. It proved to be of great importance to align the central axis of a capillary with those of apertures in order to maximize the current component of the charged droplets of the larger m/z values and minimize the ratio of the current component of the smaller m/z values. A high alignment accuracy proved to be required at small gap lengths between a capillary tip and a counter electrode.

In this work, a simple method for fabricating gold nanoparticle (AuNP) layer on a poly(dimethylsiloxane) (PDMS) substrate based on electrostatic deposition of AuNP colloid onto a chemically-modified PDMS surface using 3-aminopropyltriethoxysilane (γ-APTES) was developed. AuNPs of 100 nm diameter were successfully dispersed and deposited onto the chemically-modified PDMS surface. The morphology and optical property of the AuNP layer were examined by atomic force microscopy (AFM) and UV–visible absorption spectroscopy, respectively. It was found that the prepared AuNP layer on PDMS could work as a localized surface plasma resonance (LSPR) sensor. The sensing characteristics were examined by changing the refractive index of solution surrounding the AuNP and antigen-antibody events on the AuNP surface. Changes in absorbance intensity and peak wavelength shift of the LSPR band were both clearly observed. The developed technique can hopefully expand the applications of PDMS for not only micro channel fabrication, but also sensing construction for easier and simpler preparation of microfluidic biosensors, which were then applied for immunoassays and other biochemical analyses.

To make the rapid separation of serum/blood cells possible in a whole bloodstream flow without centrifugation and Pasteur pipette suction, the first step is to use a microchannel to transport the whole bloodstream into a microdevice. Subsequently, the resulting serum/blood cell is separated from the whole bloodstream by applying other technologies. Creating the serum makes this subsequent separation possible. To perform the actual separation, a microchannel with multiple symmetric curvilinear microelectrodes has been designed on a glass substrate and fabricated with micro-electromechanical system technology. The blood cells can be observed clearly by black-field microscopy imaging. A local dielectrophoretic (DEP) force, obtained from nonuniform electric fields, was used for manipulating and separating the blood cells from a continuous whole bloodstream. The experimental studies show that the blood cells incur a local dielectrophoretic field when they are suspended in a continuous flow (v = 0.02–0.1 cm/s) and exposed to AC fields at a frequency of 200 kHz. Using this device, the symmetric curvilinear microelectrodes provide a local dielectrophoretic field that is sufficiently strong for separating nearby blood cells and purifying the serum in a continuous whole bloodstream flow.

In this research, the static behavior of torsional nano-/micro-actuators under van der Waals (vdW) force is studied. First, the equilibrium equation governing the static behavior of torsional nano-/micro-actuators under vdW force is obtained. Then the energy method is utilized to investigate the statical stability of nano-/micro-actuator equilibrium points and a useful equation is suggested for the successful and stable design of nano-/micro-actuators under vdW force. Then, the equilibrium angle of nano-/micro-actuators is calculated both numerically and analytically using the homotopy perturbation method (HPM). It is observed that, with increasing instability number, defined in this paper, the rotation angle of the actuator is increased and pull-in suddenly occurs. Since analytical results are in good agreement with the numerical ones, the analytical method presented in this paper can be used as a fast, precise, and stable design tool in nano-/micro-actuators under vdW force.

Inter-symbol interference (ISI) caused by multi-path propagation, especially in shallow water channel, degrades the performance of underwater acoustic (UWA) communication systems. In this paper, we combine soft minimum mean squared error (MMSE) equalization and the serially concatenated trellis coded modulation (SCTCM) decoding to develop an iterative receiver in time–frequency domain (TFD) for underwater acoustic point to point communications. Based on sound speed profile (SSP) measured in the lake and finite-element ray (FER) tracing method (Bellhop), the shallow water channel is constructed to evaluate the performance of the proposed iterative receiver. The results suggest that the proposed iterative receiver can reduce the calculation complexity of the equalizer and obtain better performance using less receiving elements.

Blocking oscillation (BO) is a unique operation mode of resistive superconducting quantum interference devices (RSQUIDs). The author presents experimental measurements of periodic BO by means of the average voltage method. Test circuits are fabricated using a Nb/AlO_x/Nb integration process. The input/output voltage ratio in an RSQUID, of which the output is connected to a Josephson transmission line (JTL), becomes 2 under appropriate operation conditions. Since the voltage ratio is exactly proportional to the input/output switching frequency ratio, the results demonstrate the periodic BO, in which the numbers of switching during one period are 2 and 1 in the input and output junction, respectively.