Table of contents

Polar anchoring energy coefficient is one of the important parameters to improve the performance of liquid crystal displays (LCDs). To determine the polar anchoring energy coefficient with high accuracy, the symmetric oblique incident transmission ellipsometry (SOITE) method with voltage correction is proposed. As a result, the polar anchoring energy coefficients are found to be little affected by the voltage diminution at the alignment film and can be determined by the SOITE method. However, the reduced elastic anisotropy κ was not fixed by changing the thickness of the alignment film. These results indicate a possibility that the SOITE method with voltage correction can be used to determine the device parameters with high accuracy. Consequently, it may contribute to the technological development of high-performance LCDs.

An ultraviolet crosslinking glucose-based resist material in nanoimprint lithography was studied for environmental applicability and 65 nm dense line patterning. In this study, the applyication of a glucose derivative as an ecofriendlier compound to the resist material in an advanced nanopatterning process was demonstrated. It was found that the developed glucose-based resist material with an epoxy group in cationic polymerization had the properties of high-crosslinked polymer networks for step and flash nanoimprint lithography and created 65 nm rectangular dense line patterns. In addition, an elemental analysis was carried out to evaluate resist material shrinkage in ultraviolet irradiation and the resistance of a crosslinked film. This desirable concept using a glucose derivative with an epoxy group in the resist material is one of the most promising processes ready to be incorporated into the mass production of advanced electronic device applications.

As a convenient method for modifying the hole-transport property of fullerene materials, hydrogenation of fullerene C₇₀ is considered theoretically. Firstly, for the analysis of the carrier-transfer mechanism between C₇₀H₂ molecules, the geometrical difference between C₇₀H₂ and C₇₀H₂⁺, the natural population analysis (NPA) charge, and the electron spin resonance (ESR) parameters (spin density) of C₇₀H₂⁺ are calculated by density functional theory [B3LYP/6-311G(d,p)]. Secondly, the reorganization energies (λ) and electronic coupling elements (H_AB) of eight isomers of C₇₀H₂ with a small heat of formation are calculated and compared with that of C₇₀. It is shown that four isomers of C₇₀H₂ have a smaller λ than C₇₀ (120 meV) and that the magnitude of λ of C₇₀H₂ isomers is closely related to the geometrical difference between C₇₀H₂ and C₇₀H₂⁺. Four isomers of C₇₀H₂ have larger H_AB than C₇₀ (24 meV). Isomers with delocalized highest occupied molecular orbital (HOMO) tend to have small λ and large H_AB. At 300 K, the best isomer has hole-transfer rate constant (k_ht) which is over six times as large as that of C₇₀.

As a hole injection layer for organic devices, a tungsten oxide (WO_x) thin film was vapor-deposited on an indium–tin oxide (ITO) substrate, on which a self-assembled monolayer (SAM) of either 3-aminopropyltrimethoxysilane (APS), phenyltrimethoxysilane (PTMS), or octadecyltrimethoxysilane (ODS) was prepared to modify the surface characteristics. The deposition of WO_x substantially increased the ionization potential (I_p) of the substrate surface, which was effective in enhancing hole injection. The formation of SAM on WO_x reduced I_p, but enabled the control of the surface free energy so as to modify the growth morphology of an organic film deposited on its surface. A hole-only device was prepared using a hole transport material of N,N '-diphenyl-N,N '-bis(3-methylphenyl)-(1,1'-biphenyl)-4,4'-diamine (TPD). In the space-charge-limited region, a high current was drawn by using an anode that has a high I_p. At low driving voltages, however, the current flow was considerably influenced by the surface free energy. It was found that the PTMS-SAM on WO_x gives a satisfactory accommodation of both the work function and the surface energy.

Generally, macroscopic molecular orientation state in liquid crystal layer can be described by Ossen and Frank's continuum theory. However, the validity of applying the continuum theory to nematic liquid crystal thin film (NLCF) has not been confirmed yet. In this study, we experimentally examined NLCF by employing spectroscopic ellipsometer. As a result, theoretical and experimental result represent a good agreement when NLCF thickness is from 60 to 250 nm. Furthermore, the influence of surface roughness on alignment film surface and glass substrate was also examined.

The current-gain cutoff frequencies for bottom contact n-channel C₆₀ and p-channel pentacene thin-film transistors (TFTs) with channel lengths of 2–10 µm have been investigated. The cutoff frequency was estimated by direct measurement of the gate and drain modulation currents. The measured cutoff frequencies for both C₆₀ and pentacene TFTs increase consistently with reducing channel length. Cutoff frequencies of 27.7 and 11.4 MHz were obtained from C₆₀ and pentacene TFTs with a channel length of 2 µm, respectively.

The characteristics of organic thin-film transistors (OTFTs) with tailored liquid sources of HfO₂ as a high-κ insulator were investigated using excimer laser irradiation. We have demonstrated that the OTFT characteristics were improved more by short wavelength light source irradiation than UV irradiation to cleave chemical bonds of organic residues in the alkoxy-derived HfO₂ films. The field-effect mobilities and on–off ratios obtained for one shot of excimer laser irradiation were 0.18 cm² V^-1 s^-1 and 750, respectively.

The effects of gate dielectrics material in organic thin film transistors (OTFTs) were investigated. The gate dielectrics were deposited by plasma enhanced chemical vapor deposition (PECVD) with cyclohexane and tetraethylorthosilane (TEOS) respectively used as organic and inorganic precursors. The gate dielectrics (gate insulators) were deposited as either organic plasma-polymer or organic–inorganic hybrid plasma-polymer thin film by using cyclohexane or cyclohexane with TEOS, respectively. Additionally, hydrogen and argon were used as precursor bubbler gases. A polyimide (PI) substrate was used in the fabrication of pentacene OTFTs with a plasma-polymer gate insulator, an Au source–drain (S/D), and Cu gate electrodes. Different gate dielectrics were investigated. The as-grown plasma-polymer thin films were first analyzed using Fourier-transform infrared (FT-IR) spectroscopy. Also, they were analyzed by nano-indentation and capacitance measurements. The electrical properties, such as mobility and threshold voltage of the pentacene field-effect transistors with the plasma-polymer gate-dielectrics were investigated. Transistor with cyclohexane gate dielectric had a higher field-effect mobility, µ_FET = 0.84 cm² V^-1 s^-1, and a smaller threshold voltage, V_T= -6.8 V, than the transistor with the hybrid gate-dielectric.

An investigation of threshold voltage shifts in organic thin-film transistors (TFTs) based on pentacene with an additional soluble fullerene derivatives of [6,6]-phenyl C₆₁-butyric acid methyl ester (PCBM) on gate dielectric. With an additional soluble fullerene layer, the threshold voltage (V_th) is optimized from -3.9 to -1.1 V without affect the mode operation of the devices, while retaining the carrier mobility (0.02–0.03 cm² V^-1 s^-1) and on/off current ratio (∼10⁴). Furthermore, the existence of PCBM agglomerates as electron acceptor-like traps resulted in a shift of V_th in the positive and reversible directions depending on the magnitude of gate bias (V_bias) as well as duration of time bias (T_bias). The device operation changed into normally-on (depletion–accumulation) mode upon positive V_bias as the duration of T_bias was increased, which attributes to the formation of a conductive layer at the pentacene–fullerene interface. Moreover, the recovery of V_th was further enhanced by a high negative V_bias for a short duration. In addition, the mobility was minimally affected by both V_bias conditions.

Strontium titanate (SrTiO₃) thin film with a dielectric constant of ε_r = 12.1 prepared on a heavily doped n-type silicon wafer by sputtering. Both pentacene and C₆₀ field-effect transistors fabricated using the self-assembled monolayer (SAM)-free SrTiO₃ as an insulator showed well-saturated output characteristics at a driving voltage as low as -3 or 3 V. Hole mobility of the pentacene-FET was 0.28 cm² V^-1 s^-1, while electron mobility of the C₆₀-FET was 0.09 cm² V^-1 s^-1.

We investigated the characteristics of solution-processed mixed-single-layer organic light-emitting devices (OLEDs) by mixing an electron injection material, a hole transport material, and a dopant material based on 5,6,11,12-tetraphenylnaphthacene (rubrene). The mixed-single-layer OLEDs showed better performance by optimizing the solution concentration and mixing ratio of organic materials. The performance was further improved by mixing chloroform (95 wt %) and toluene (5 wt %) as a solvent. The maximum luminance and power efficiency obtained were 12,400 cd/m² and 1.1 lm/W, respectively. The mixed-single-layer OLEDs by solution process can be expected as an alternative route to the fabrication of small-molecular OLEDs with reduced cost of devices and avoiding the complexities of the co-evaporation of multiple organic materials in the vacuum deposition process.

We demonstrated highly efficient green organic light-emitting diodes (OLEDs) by inserting a mixed hole blocking layer (HBL) between the emitting layer (EML) and electron transporting layer (ETL). We compared 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), N-arylbenzimidazoles trimer (TPBi), and 4,7-diphenyl-1,10-phenanthroline (Bphen) as the hole blocking layer. Thereafter, we mixed BCP with TPBi and Bphen. We obtained improved efficiency from the mixed HBL devices and the TPBi mixed with BCP device showed the best efficiency.

We fabricated organic light-emitting diodes (OLEDs) containing chlorophylls in the active region, which were extracted from spinach using a chemical method. Photoluminescence (PL) cannot be observed in the thin film of the extracted chlorophylls owing to concentration quenching. To overcome the concentration quenching, a host material, poly[(m-phenylenevinylene)-alt-(2,5-dihexyloxy-p-phenylenevinylene)] (PPV) was added in the active region. This leads to the observaton of electroluminescence (EL) signals originating from chlorophyll a. We also evaluated the lifetime of the PL and EL. Consequently, the OLEDs containing carotenoids in the active region exhibit the light-emission much longer time than that without carotenoidos. This is assigned to the antioxidant activities of carotenoids. OLEDs containing a large amount of carotenoids are resistant to the oxidation damage.

The self-aligned color-changeing organic light-emitting diodes with the ink-jet printing (IJP) dots have been investigated, and we have studied a device structure of a micro-area color-changeing method involving the IJP emission of dots and their periphery, where a side-coupling emission mode and double-area emission mode were used. The distance of the side-coupling emission from emission dot was estimated to be 10 µm. The brightnesses of the dots and their periphery at 100 mA/cm² were 1,300 and 380 cd/m², respectively.

The purpose of this study is to apply anthracene needle-like crystals (NLCs) to an organic electroluminescence (EL) device. The NLCs growth depended on dipping speed. The slower the dipping speed, the wider NLCs grew. It was confirmed that the NLCs were anthracene by the Raman spectrum and X-ray diffraction (XRD) pattern. The lattice spacing determined from XRD corresponded to the step height obtained from surface images taken using atomic force microscopy. The anthracene NLCs bridged between Au and Al electrodes with a drawing speed of 2 µm/s.

We describe the enhancement of electron injection by external light irradiation in organic light-emitting diodes (OLEDs) with a charge generation layer (CGL). Under He–Ne laser irradiation, photon-induced charge generation under electric field occurred in the CGL. Electrons and holes were generated in the CGL and the electrons were directly injected into adjacent electron transport layers. As a result, the enhancement of current density under light irradiation was observed. A thousand fold enhancement of current density was obtained for light irradiation under forward biased condition. Current density was determined by the intensity of light irradiation and was saturated under the higher voltage regions. Up-converted light emission was also observed under the light irradiation.

We proposed a laminate method, which demonstrates a double-faced organic light emitting device. This device can display different images at both sides. To carry out a simple fabrication process, a lamination process was carried out at the interface between a refection cathode on a poly(ethylene naphthalate) (PEN) film and on organic emission layer on a glass substrate. This device yields the ultimate low-cost product and does not require a high vacuum pressure.

The carrier mobility (µ) and lifetime (τ) of polymer solar cells based on the active layer with various compositions of regioregular poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM) have been investigated through photoinduced charge carrier extraction by linearly increasing voltage measurement. Increase in the PCBM content resulted in the increase in the mobility up to one order of magnitude and the highest performance was attained at the composition of P3HT:PCBM (3:2), which corresponds to the bending point of mobility and lifetime. Furthermore, the mobility-lifetime product µτ was almost constant with various weight ratios of P3HT and PCBM. This result implies that the composition does not affect the charge correction efficiency before recombination. A semiconducting thin-film optics simulator was applied for prediction of the photovoltaic performance. Theoretical and experimental cell performance results were in good agreement with each other.

We investigated the photovoltaic properties of organic multilayered photovoltaic devices consisting of Indium–tin-oxide (ITO)/oxide/tetraphenyl porphyrin (H₂TPP, ZnTPP)/fullerene (C₆₀)/bathocuproine (BCP)/Al structures. The open-circuit voltage V_OC increases with the thickness of porphyrin layers between 10 and 30 nm. The upper limit of V_OC is attributed to the built-in potential and the energy difference between the highest occupied molecular orbital (HOMO) of H₂TPP and the lowest unoccupied molecular orbital (LUMO) of the C₆₀ layer ΔE. The use of oxide hole collection layers, such as NiO and MoO₃, is effective for increasing the built-in potential across the organic layers resulting in the improved V_OC. The "kink" in the J–V curve observed at approximately V_OC for the device with a thick H₂TPP layer and the device with and without a MoO_x layer is analyzed on the basis of the Poole–Frenkel and Schottky models assuming the amorphous porphyrin layers as dielectrics. The resistance of the organic layers is dominated by the field-dependent bulk resistance of H₂TPP films for V<V_OC, whereas the kink above V_OC was attributed to the relatively high Schottky barrier for holes at the ITO/H₂TPP and ITO/MoO₃ interfaces.

Multiple surface plasmon resonance (SPR) sensors were prepared on a waveguide, and vapor sensing was carried out. A BK-7 slide glass was used as a waveguide core, and three pairs of Ag films (50 nm)/polymer films with various thicknesses were prepared separately on the waveguide. White light was input from the substrate edge, and the spectrum of the output light was observed. Discrete SPR dips can be observed in the output light spectra by selecting the dielectric constant and the thickness of the polymer film, which govern the SPR condition. The sensors with poly(vinyl alcohol) as sensing material were prepared and the water vapor sorption properties were investigated. Furthermore, polyisoprene, poly(vinyl carbazole), poly(methyl methacrylate), and perfluorinated polymer were used as sensing materials, and the detection of various vapors was carried out.

Liquid-crystal (LC)-coated substrates with a planar LC alignment can be fabricated by UV irradiation during LC coating using a slit coater. The alignment transition from a planar alignment to a vertical alignment was caused by UV irradiation after LC coating when a certain UV-curable additive was doped with the nematic LC. These results are applicable to the development of a novel fabrication technology for printable LC devices.

In this paper we show near-edge X-ray absorption fine structure (NEXAFS) analysis of monolayers that are formed by thermal hydrosilylation from 1-alkene diluted in mesitylene. The monolayers are not purely aliphatic as originally proposed. Instead the bound molecules have an alkenyl structure that is promoted by the presence of mesitylene. The double bonds are more prevalent than in our previous report for monolayers formed without mesitylene. Simulated NEXAFS spectra suggest that the double bonds are present in the form of 2-alkenyl moieties. The presence of double bonds impairs the use of these monolayers as dielectrics and enables their use for conductive interfaces.

Au ion implantation in Fe ion-implanted Al₂O₃ (Fe/Al₂O₃) has been performed in order to tailor the structural, magnetic and optical properties of Fe granules in Al₂O₃ matrix. After Au ion implantation, Rutherford backscattering (RBS) measurements indicate the decrease and the redistribution of retained Fe atoms with the inclusion of Au atoms, and the patterns of X-ray diffraction (XRD) show the formation of Au granules in the Fe/Al₂O₃. Besides, the magnetization curves of the Fe/Al₂O₃ after Au ion implantation show still the superparamagnetic characteristics and the decrease of saturation magnetization, and the optical absorption measurements indicate the formation of Au granules in the Fe/Al₂O₃ in accordance with the XRD result. In addition, we investigated a behavior of Fe granules in Al₂O₃ matrix by conversion electron Mössbauer spectroscopy (CEMS), which indicates the decrease of superparamagnetic state as a function of Au ion dose. As a result, it is suggested that Au ion implantation has potentialities to tailor the physical properties of Fe granules in Al₂O₃ matrix.

Surface treatment effect on TiO₂ thin films with the anatase phase by dielectric barrier discharge (DBD) air plasmas has been investigated for a variety of gas pressures and treatment times. At a low gas pressure (100 hPa) at which a glow-like discharge plasma occurs, hydrophilicities of TiO₂ thin films treated at 5 and 30 min are enhanced compared with that of the as-grown thin film. For the 5 min treatment, this trend is more pronounced probably due to oxygen absorbed on the surface from the air plasma. For the 30 min treatment, the enhanced hydrophilicity is probably due to oxygen vacancy created on the surface by a high fluence of the plasma. When the gas pressure increases to 400 hPa at which a streamer discharge plasma occurs, the hydrophilicity is more weakened than that of the as-grown thin film: the plasma-induced damage occurs regardless of the treatment time. This result would probably result from the higher discharge current and UV light intensity caused by the higher breakdown voltage based on Paschen's law.

Chromium nitride thin films were deposited by RF reactive unbalanced magnetron sputtering on (100) Si single-crystal or glassy carbon substrates. The characteristics of the thin films were measured by Rutherford backscattering spectroscopy, X-ray diffractometry, and scanning electron microscopy. From the results of the above measurements, it was found that our samples were stoichiometric chromium nitride thin films. The chemical bonding state was estimated using the results of the Fourier-transform infrared spectroscopy. A peak attributed to the Cr–N bond was observed at around 380 cm^-1, and it could be obtained with any beam splitter and atmosphere. Furthermore, the influence of residual stress was also investigated. Residual stresses of CrN thin films, which were calculated from their strains, were quite low.

V_1-xTi_xO₂ films were prepared on glass substrates by excimer-laser-assisted metal organic deposition (ELAMOD) and thermal MOD processes. The VO₂ phase was successfully formed in the range of x = 0–0.35 at 300 °C in air using the ELAMOD process. This is a big advantage in terms of fabrication process for glass or organic substrates. It was also confirmed that dense films were obtained by preparing TiO₂ buffer layers on glass substrates. Furthermore, the detailed effect of Ti content in VO₂ films on metal–insulator (MI) transition properties was examined. As Ti content increased, the broadening of MI transition and the decreasing of the hysteresis width occurred. At x = 0.14, the hysteresis disappeared. The temperature coefficient of electrical resistance (TCR) value of the film (x = 0.14) remained at approximately -3%/K from 300 to 340 K and was more than -4%/K from 340 to 350 K.

We studied the vacancy-induced ferromagnetism in bulk and at the (1010) surface of wurtzite ZnO using density functional theory calculations. It is found out that surface vacancies are energetically favored to bulk vacancies and that the ferromagnetism is induced by Zn vacancies but not by O vacancies. Moreover, local magnetic moments induced at O atoms adjacent to the Zn vacancy are calculated to be larger on the surface than in bulk. These findings indicate that Zn vacancies at surfaces are responsible for the experimentally observed room-temperature ferromagnetism in undoped ZnO thin films and nanoparticles.

Mechanical alloying is a viable technique to produce coatings of limited thickness on a solid substrate. Elemental copper powder was mechanically alloyed with nickel balls in a planetary ball mill under various milling times and rotation speeds. The mutual diffusion of the elements during milling which led to the formation of a Ni–Cu solid solution and the creation of Ni–Cu coating on the surface of Ni balls was studied. The maximum hardness of the coating increased to threefold (HV_0.01594) that of the substrate. Micro-structural characterization of the coating surface using optical microscope, scanning electron microscope (SEM), and electron probe micro-analyzer (EPMA) indicates that, by using appropriate processing conditions, a thick, fully-dense coating can be metallurgically bonded to the nickel balls. X-ray diffraction (XRD) results revealed the formation of nanocrystalline solid solutions.

The structure dependent magnetism and intermixing characteristics of Ti/Fe(001) thin films were investigated using molecular dynamics simulations and ab initio calculations. Through density functional theory based ab initio calculations, sharply decreased demagnetization energy of Fe(001) substrate by the interface intermixing was observed. The intermixing at the Ti/Fe(001) interface was limited within only the topmost layer of the Fe(001) substrate at temperatures ranging from 300 to 600 K with incident energies of a Ti atom from 0.1 to 5 eV. Both the high deposition temperature and the high incident energy of the Ti adatom inproved the surface smoothness of the deposited Ti films. The elevated temperature significantly increased the amount of Ti/Fe interface intermixing, while the incident energy dependency was negligible. The extremely low atomic intermixing ratio and short diffusion length of Ti/Fe system compared to other transition metal thin films could be explained by comparing the local acceleration and incorporation energy barrier effects.

This paper explored the change in the surface resistance of the discontinuous palladium (Pd) films during hydrogen exposure. In our experiments, we observed a remarkable rise in the electrical resistance of the discontinuous film which consists of nano-sized particles, when it was exposed to thin hydrogen. By studying the resistance change ratio before and after hydrogen exposure, we have found that it demonstrates an inverse exponential relationship with the ratio of on-film particle radius to the inter island separation. This suggests that the change in the film resistance under hydrogen exposure is primarily associated with the variation of surface work function which is caused by the hydrogen absorption on the Pd surface.

Thin films of scandia-stabilized zirconia (ScSZ) for a solid oxide fuel cell (SOFC) electrolyte were prepared using electron beam vapor deposition. The effects of annealing temperature, substrate temperature, and e-beam gun power on the structure and surface morphology of the thin films were examined. It was found that the ScSZ thin film samples annealed at approximately 1000 °C consisted of a single cubic phase. The crystal orientation of the ScSZ films increased with substrate temperature and with e-beam gun power. A good adhesion to the substrate and a columnar structure were observed from the fractured cross-sectional view of the ScSZ films on a NiO-YSZ anode substrate. The ionic conductivity of the ScSZ film with 2.5 µm thickness was observed to be 9.46×10^-3 S cm^-1 at 700 °C with the conduction activation energy of 0.82 eV. The results in this study showed that the crystallite size of the ScSZ thin films and thus the electrochemical properties can be improved by optimizing e-beam deposition conditions and annealing temperature.

Cu₂ZnSnS₄ (CZTS) thin films were fabricated using a rapid thermal process in 5% H₂S+ N₂ atmosphere from precursors prepared by the sol–gel method. The precursors were preheated at 250 °C for 10 min and then sulfurized at different temperatures from 300 to 600 °C for 10 min. XRD studies showed that the samples sulfurized at 500–600 °C had a CZTS structure. With increasing sulfurization temperature, the chemical composition ratio of sulfur/metal and the grains size of CZTS increased. From the (αh ν)²–hν plot, the CZTS films had a band gap of ∼1.5 eV.

The change in magnetic characteristics of NiFe₂O₄ nanoparticles upon the absorption of oleic acid and their desorption by heat treatment was examined in this research. With a heat treatment at 600 °C, the median diameter increased from 5.4 to 16.2 nm. However, the saturation magnetization varied by only 0.3%. On the other hand, with the coating of oleic acid, the saturation magnetization of NiFe₂O₄ nanoparticles decreased from 31.7 to 30.0 emu/g. After desorption by heat treatment at 600 °C, the saturation magnetization was increased. From these results, it was clear that coating NiFe₂O₄ nanoparticles with oleic acid decreased the saturation magnetization. This phenomenon may enable us to control the magnetization characteristics of nanoparticles.

We present for the first time the temperature dependence of resistivity, anomalous Hall effect, and extraordinary magnetoresistance (MR) in 6.5% Mn-doped ZnSnAs₂ epitaxial film prepared by molecular beam epitaxy (MBE) on InP(001) substrates. The magnetic field dependence of magnetization (M–H curve) show clear hysteresis loops at 300 K for magnetic fields applied both perpendicular and parallel to the sample surface. The Curie temperature was evaluated to be 350 K. Near-zero-field hysteresis loops in the anomalous Hall resistance were also observed at various temperatures corresponding to the hysteretic out-of-plane magnetization of the sample. Negative and positive values of MR were observed in the low-field region. The behavior of the MR can be properly described by the Khosla–Fischer semi-empirical model for spin scattering of carriers in an impurity band. These characteristics strongly indicate a carrier-spin interaction in Mn-doped ZnSnAs₂.

The ordered double perovskite oxide, Sr₂FeMoO₆, has a half-metallic property and is considered as one of the best materials for creating spin-polarized current for next-generation spintronics devices. In order to optimize the fabrication conditions for (001)-oriented single-crystalline Sr₂FeMoO₆ thin films, a combinatorial pulsed laser deposition (PLD) technique, together with combinatorial (high-throughput) characterization, were carried out. It is found that atmospheric pressure during the deposition affects the formation of secondary phases, thus careful control of this parameter is necessary. On the other hand, substrate temperature affects the electric transport property and surface flatness; better results are obtained at a higher substrate temperature.

Composite nickel sheets with nanosized nickel–zinc ferrite particles were prepared as electromagnetic shielding materials by electroforming in a modified nickel–sulfate bath with nickel–zinc ferrite particles. The nanosized nickel–zinc ferrites were prepared by combustion synthesis and mechanical milling. The combustion temperature and propagation rate were about 1150 °C and 8.9 mm/s, respectively. Neutron diffractometry revealed that the final nickel–zinc ferrites formed by combustion synthesis followed by mechanical milling were Ni_0.42Zn_0.58Fe₂O₄ with the crystal structure and lattice parameter of Fd3m and 0.84124 nm, respectively. Microstructure observation and chemical analysis by transmission electron microscopy and energy-dispersive spectroscopy respectively showed that nanosized nickel–zinc ferrite particles with a diameter of about 20 nm exist in the thin composite nickel sheet. Maximum magnetization (M_s), residual magnetization (M_r), and coercive force (_iH_c) were 7.75 Wb/m²/kg, 0.88 m³/kg, and 1297 A/m, respectively. The complex permeability decreases with an increase in frequency, and its real value (µ_r') has an maximum at about 0.65 GHz.

Samples of a CuBa₂Ca₃Cu₄O_10+δ superconductor were synthesized under a high pressure of 5 GPa at 1100–1200 °C for 30 min using precursors produced by solid-state reaction and polymerized complex methods. Compared with the precursors prepared by the solid-state reaction method, the precursors produced by the polymerized complex method have low grain sizes. The superconductive transition temperature of the samples prepared using precursors made by the polymerized complex method was found to be 113 K. The volume fractions of the superconducting phase in the samples prepared using precursors made by the solid-state reaction and polymerized complex methods were 49 and 36%, respectively. From these results, precursors made by the polymerized complex method can be used in the high-pressure synthesis of superconductors similarly to those made by the solid-state reaction method.

CaGa₂S₄:Ce crystallites were synthesized by the mechanochemical reaction of CaS, Ga₂S₃, and Ce₂S₃ source powders. The growth process was studied by observing X-ray diffraction (XRD) patterns and Raman scattering spectra of the synthesized powder as a parameter of reaction time. Ce doping of CaGa₂S₄ was studied in terms of its photoluminescence (PL). The approximate crystallite size calculated by a Williamson–Hall plot was 59 (+5, -3) nm.

We report the influences of the sodium dodecyl-benzenesulfonate (SDBS), hydrothermal reaction temperature and time on the size of potassium sodium niobate (K,Na)NbO₃ (KNN) template particles to determine the regularities of these changes. In the reaction with a small autoclave, when the quantity of SDBS reached 1.5 wt %, the width of the obtained platelike KNN-hydrate particles reached a maximum of 1.5 µm and the thickness was 0.15 µm, meaning that the aspect ratio was 10/1. To accommodate practical applications, a large autoclave was used in the following hydrothermal reaction. We found that the size of the platelike particles increased with improved reaction temperature and time. Particles 1.5 to 5 µm wide and 0.15 to 0.4 µm thick were prepared. After calcining these particles at 450 °C, platelike KNN template particles were obtained. Finally, tape-casting results showed that the platelike KNN templates have the (100) orientation.

Cr–N–O, Cr–Zn–N–O, and Zn–O thin films were prepared by pulsed laser deposition. The compositional analysis of the Cr–Zn–N–O thin films by Rutherford backscattering spectroscopy revealed that they are ternary compounds of the Cr–Zn–N–O system. Their Vickers hardness was about 4200 kgf/mm². X-ray diffraction indicated that the Cr–N–O and Cr–Zn–N–O thin films have the NaCl-type structure (B1), the same as CrN. Transition electron microscopy observation indicated that a grain of the (Cr,Zn)(N,O) phase existed, on the basis of which it could be considered as a solid solution of B1-CrN and a high-pressure phase of ZnO with the B1 structure.

Bi₂Me_xV_1-xO_5.5-3x/2 (Me = Cu; 0≤x≤0.2) powders were prepared by the ammonium carbonate coprecipitation method. The starting salts were bismuth nitrate, copper nitrate, cobalt nitrate, and vanadium sulphate. The thermal decomposition of Bi₂Me_xV_1-xO_5.5-3x/2 precursors was completed at about 500 °C. The crystallite structure, surface morphology, and ionic conductivity of the prepared powders and pellets were examined using X-ray diffractometry, field emission scanning electron microscopy, and an impedance analyzer, respectively. The average particle sizes of the Bi₂Cu_0.1V_0.9O_5.35 and Bi₂Co_0.1V_0.9O_5.35 powders were 10–50 nm. The tetragonal structure (γ-phase) appeared at sintering temperatures higher than 700 °C and the peak intensity increased at higher sintering temperatures. The ionic conductivities of the Bi₂Cu_0.1V_0.9O_5.35 and Bi₂Co_0.1V_0.9O_5.35 pellets sintered at 800 °C showed the highest values of 6.8×10^-2 S cm^-1 at 700 °C and 9.1×10^-2 S cm^-1 at 700 °C, respectively. The optimum concentration of the Cu and Co dopants in Bi₂Me_xV_1-xO_5.5-3x/2 was determined to be 0.1. The results of this study demonstrated that the ammonium carbonate coprecipitation process could be used as an economical method for the preparation of Bi₂Me_xV_1-xO_5.5-3x/2 electrolytes for intermediate-temperature solid oxide fuel cells.

We investigated the in-depth profile of electrical properties of InSb films grown on Si(111) substrates using various InSb bilayers. The InSb bilayers were prepared using three types of initial In-induced surface reconstructions on Si(111) substrates such as √3×√3-In, 2×2-In, and √7×√3-In. The InSb films were grown using a two-step growth procedure. In the growth procedure, the 1st layer was deposited using at a low growth rate of about 1 Å/min. The in-depth profile of the electrical properties of the InSb films was obtained by reciprocally repeated chemical etching and Hall measurement. The electron mobility of the films was gradually decreased with decreasing thickness. The electron mobility at room temperature of the InSb film grown via √7×√3-In surface reconstruction was estimated to be about 61,000 cm²/(V·s) in the region near the surface and about 20,000 cm²/(V·s) in the region approximately 0.2 µm from the InSb/Si interface. These indicate that the high electron mobility of the samples grown on the InSb bilayer using at a low growth rate during the first layer deposition originated from the reduction of the regions with low electron mobility near the InSb/Si interface.

The instability of Eu complexes against ultraviolet (UV) light irradiation is an important problem to solve before they can be practically applied in white light-emitting diodes. A novel technique of encapsulating tris(2-thenoyltrifluoroacetonato)(1,10-phenanthroline)europium(III) [Eu(TTA)₃phen] was investigated using high-pressure annealing (solvothermal process) as a final process in the sol–gel synthesis. The photoluminescence and excitation spectra of encapsulated Eu(TTA)₃phen samples synthesized by solvothermal and conventional annealing processes were almost the same. A half brightness time of 589 min was achieved while irradiating with UV light of 360 nm and 5 mW/cm² by optimization of ammonia concentration and annealing temperature. The longest half brightness time was longer than that of encapsulated Eu(TTA)₃phen synthesized by conventional thermal treatment. One possible reason for this result is that the chemical reaction of the sol–gel based glass network occurs more efficiently with high-pressure annealing. As a result, a high encapsulating efficiency was achieved owing to the small amount of organic component in the sol–gel derived glass network.

Using the first-principles calculations, the changes in the magnetic moment and the electronic structure of Al/Fe(001) thin film systems were investigated with varying Al thickness and the interface intermixing amount. When Al overlayer was 1 ML thick, the interface intermixing was not favorable, which is consistent with experimental observations. However, when the Al layers were 2 ML and 3 ML, the interface intermixing was exothermic and the Fe atoms intermixed in the Al layer lattices had reduced magnetic moments. As the intermixing amount was increased, the magnetic moments were decreased. The origins of enhancement and reduction in the Fe magnetic moments could be found from the projected 3d-electron density of states analysis.

The effects of high-temperature thermal annealing on cathodoluminescence (CL) spectra in SiO_x (0.9 ≤x ≤1.87) films prepared by radio-frequency sputtering are investigated. The CL intensities for the as-deposited films are weak but they increase after thermal annealing at 900 and 1100 °C. One of features in the CL spectra for the films annealed at 1100 °C is a peak at a photon energy of ∼2.7 eV with an asymmetric tail on the lower energy side. In order to analyze the spectral features, optical transition energies are calculated for Si_n clusters with n = 2–5, embedded in a SiO_x matrix, by ab initio molecular orbital calculation. In addition, the probabilities of formation are statistically estimated for those Si clusters under the assumption of a chemically ordered random network for the SiO_x network. The comparison of the experimental results with the calculated transition energies and the statistics of the Si clusters suggests that a contribution of the Si₂ clusters to the CL spectra are dominant, whereas those of the Si_n clusters with n > 3 are considerably small.

X-ray fluorescence holographic study on a room-temperature ferromagnetic semiconductor film of ZnSnAs₂:Mn was performed using a strong X-ray beam of third generation synchrotron radiation of SPring-8. The real space reconstructions of the environments around Mn atoms were successfully visualized from the observed holograms despite the very small amount of Mn atoms. The reconstructions revealed that the Mn atoms occupy the cation (Zn or Sn) site.

(Ba_0.5Sr_0.5)_1-xCa_xCo_0.8Fe_0.2O_3-δ (BSCCF), (Ba_0.5Sr_0.5)_0.8La_0.2Co_0.8Fe_0.2O_3-δ (BSLCF), and (Ba_0.5Sr_0.5)_0.8La_0.2-xCa_xCo_0.8Fe_0.2O_3-δ (BSLCCF) perovskite oxides were synthesized by the modified citrate method and characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). These oxides showed primarily a cubic phase with their dense bodies after sintering. The lattice parameter was decreased with increasing Ca²⁺-ion content in BSCCF. Conversely, the substitution of Ca²⁺ ions for La³⁺ ions in BSLCCF increased the lattice parameter. The maximum electrical conductivities were 96 S·cm^-1 at 650 °C for the 30 mol % Ca²⁺-substituted BSCCF and 353 S·cm^-1 at 350 °C for BSLCF. The thermal expansion coefficient (TEC) of BSCCF was almost constant regardless of the Ca²⁺-ion contents, whereas that of BSLCCF decreased with decreasing Ca²⁺-ion content.

The effects of Pr³⁺ substitution on electrical properties of Bi(Fe_0.95Mn_0.05)O₃ (BFMO) thin films are investigated. The leakage current densities of BFMO films can be significantly suppressed by Pr³⁺ substitution. Dielectric analysis reveals that dielectric constants of the films increase with increasing Pr³⁺ content. Reduced loss tangents are obtained in Pr³⁺-substituted BFMO films. Ferroelectric measurements demonstrate that Pr³⁺ substitution is helpful for lowering the coercive fields of films. In addition, a double hysteresis loop is observed in the BFMO film with 25% Bi³⁺ substituted by Pr³⁺. This may be ascribed to the existence of the defect-complexes.

The luminescent properties of Eu³⁺ doped CaMoSiO₄ red phosphor were investigated. The aim of this work is to investigate the effect of an activator on the luminescent properties of red-emitting CaMoSiO₄:Eu³⁺ phosphor. CaMoSiO₄:Eu³⁺ phosphors were synthesized using a combustion method to obtain small spherical particles that have smooth and round surfaces. Using urea as a fuel and ammonium nitrate as an oxidizer, CaMoSiO₄:Eu³⁺ was successfully synthesized using this combustion method. The Eu³⁺ influenced the photoluminescence (PL) spectra of the produced CaMoSiO₄:Eu³⁺ phosphors. The experiment results showed that the strongest emissions occurred with an optimal concentration of the Eu³⁺; it exhibited a red emission spectrum for near-ultraviolet (UV) excitation. The material would be suited for the fluorescent material used in UV light-emitting diodes (UV-LEDs). The characteristics of the synthesized CaMoSiO₄:Eu³⁺ phosphor were investigated by means of X-ray diffraction (XRD), a scanning electron microscope (SEM), and PL detection.

Towards an application for terahertz detector, a monolithic integrated device structure of a triple-barrier resonant tunneling diodes (TBRTDs) with a bow-tie antenna is proposed and its terahertz rectification properties are investigated on the basis of a physics-based equivalent circuit model. A possibility of zero-bias detection is examined owing to nonlinear asymmetric current–voltage characteristics. A possibility of broadband zero-bias detection in terahertz range is suggested for a tentatively designed device structure. A method to analyze rectified signal is established taking the self-bias effect into account.

A nitride layer was formed on a SiC surface by direct nitridation in NH₃ or N₂. The surface was characterized by X-ray photoelectron spectroscopy (XPS). The thickness of the nitride layer was estimated to be less than 2 nm. The metal–insulator–semiconductor (MIS) Schottky diode was formed on SiC using the nitride layer as the interface layer to estimate the interface state density between the nitride layer and the SiC substrate from the diode factor n. The interface state density was on the order of 10¹¹–10¹² eV^-1·cm^-2 at 0.3 eV below the conduction band edge. A SiO₂ film was deposited on the nitridation layer to form an MIS diode. The interface state density of the SiO₂/nitride/SiC sample was lower than that of the MIS Schottoky diode.

We have studied the bias stress and environment stability effects of transparent bottom-gate, bottom contact spin-coated zinc–tin oxide (ZTO) thin-film transistors (TFT). Various ratios of zinc to tin (Zn:Sn= 2:1, 1:1, and 1:2) were used for TFT fabrication. The linear mobilities of the TFTs with Zn:Sn= 2:1, 1:1, and 1:2 are 2.27, 6.77, and 0.44 cm² V^-1 s^-1 respectively. The on/off drain current ratio is 10⁸ for Zn:Sn= 2:1. However, the off-current increases by more than 5 orders in 7 days, which appears to be due to the adsorption of oxygen and water molecules. The TFTs are stable under negative bias stress for more than 10,000 s, but they show a large threshold shift under positive bias stress.

The present study describes the first detailed evaluation of the rise and the decay time of scintillation phenomenon in In³⁺- and Ga³⁺-doped ZnO thin films with different dopant concentrations. In³⁺-(25, 55, and 141 ppm) and Ga³⁺-(33, 67, 333, and 1374 ppm) doped ZnO films were grown by the Liquid Phase Epitaxy (LPE) method. The characterization was performed using the pulse X-ray equipped streak camera system. Both the rise and the decay times were shortened considerably with increasing content of In³⁺ and Ga³⁺ in the films. However, the scintillation light yield under ²⁴¹Am α-ray excitation reduced when concentration of In³⁺ and Ga³⁺ in the ZnO films was high.

Zinc oxide (ZnO) thin-film transistors (TFTs) were fabricated by thermal chemical vapor deposition (CVD) using aqueous solutions of zinc acetate (ZnAc₂) dihydrate as a source. The precursor was supplied to the substrate by the nitrogen bubbling method through a plate with numerous orifices in the ZnAc₂ solution. The ZnO thin films were grown on silicon substrates in the growth temperature (T_G) range from 280 to 700 °C. The growth rate of ZnO thin films were linearly proportional to the growth temperature, which suggested that the growth rate is limited by the decomposition of ZnAc₂. Depletion-mode TFTs with the ZnO film grown at T_G = 350 °C was found to exhibit a relatively low saturation mobility (µ_sat). However, µ_sat increased from 1 to 14 cm²·V^-1·s^-1 and the operational mode was changed from the depletion mode to the enhancement mode by annealing treatment at 200 °C for 2 h under N₂ ambient.

In the present paper, we describe the development of an α-ray imaging detector based on a ZnO single crystalline scintillator and a position-sensitive photomultiplier tube (PSPMT). The ZnO crystal was grown by the hydrothermal synthesis method with 2-in.-φ in diameter. The ZnO specimen was polished out to be 0.5 mm in thickness. After optically coupling with PSPMT, the crystal was irradiated with ²⁴¹Am α-ray for evaluation of both spatial resolution and pulse height spectrum. Using the charge center of the gravity method, two-dimensional α-ray images were successfully obtained. The efficiency of the energy window in terms of imaging quality was also examined.

The electroplating method was improved using double anodes and a penetrated jig to fill high-aspect-ratio through silicon vias (TSVs) with copper. In this study, the double anodes were used to limit the formation of voids that degrade the electrical properties when the device is working. In addition, in this study we examined how the V-shaped electroplated copper is formed in the first electroplating step to seal openings. After establishing the conditions for electroplating using the double anodes and current wave, a void-free interconnection was fabricated, which consisted of TSVs with a diameter of 40 µm and an aspect ratios of 6.25:1 and 10:1 for silicon interposers.

A copper-doped silica (Cu-SiO₂) film of 50 nm thickness was prepared by cosputter deposition of Cu and SiO₂ targets. A metal–oxide–metal (MOM) cell comprising a Cu-SiO₂ layer sandwiched between a Cu top electrode and a Pt or Al bottom electrode was utilized to characterize resistive switching behavior. Both cells exhibited bipolar switching behavior. Electric conduction of the cell in the high-resistance state prepared using the Pt bottom electrode followed the space-charge-limited-current mechanism, whereas the cell prepared using the Al bottom electrode exhibited Schottky emission. An intermediate oxide layer was observed and attributed to the Schottky emission in the cell prepared using Al bottom electrode.

Cu₂ZnSnS₄ (CZTS) thin films were prepared by simultaneous sputtering of metallic targets and sulfurizing a metallic precursor under elemental sulfur atmosphere in a sealed tube. Subsequently, they were applied to the fabrication of thin film solar cells. The precursors with desired compositional ratio and thickness were obtained by controlling the area ratio of sputtering targets and also sputtering parameters. We have succeeded in obtaining high-quality polycrystalline CZTS thin films by sulfurization under a sulfur vapor pressure higher than atmospheric pressure. A CZTS-based solar cell with 3.7% conversion efficiency was obtained from CZTS films sulfurized at 590 °C for 7 min.

Organic soft linear actuators made of conducting polymers such as polypyrrole (PPy) films are of special interest for application in microelectromechanical systems (MEMS) because they generate large electrochemomechanical stress and strain. In this work, a PPy actuator was fabricated by galvanostatic electropolymerization. The electrochemical deformation behaviors of the PPy actuator were investigated in aqueous solutions of an electrolyte, lithium bis(trifluoromethanesulphonyl)imide (LiTFSI), containing different concentrations of 2-propanol. Marked improvement of the electrochemical strain from 3 to 12% was achieved when the actuator was driven by a potential between -1 and 1 V in the LiTFSI electrolyte containing 20 to 40% of 2-propanol under a load stress of 0.3 MPa. Possible mechanisms for these behaviors were discussed.

Micrometer-sized three-dimensional superlattices were fabricated by assembling Au nanocrystals modified with mercaptosuccinic acid in aqueous suspensions. Each superlattice formed a single crystal arrangement with a hexagonal close-packed structure where a=5.1 nm. The superlattices were densely deposited on a glass substrate and their electrical properties were investigated. The superlattice-assembled film showed ohmic behavior in the temperature range from 20 to 285 K. The absolute value of the resistivity was in the semiconductor region, but the resistivity slightly decreased as the temperature decreased. The temperature coefficient of the film was one order of magnitude smaller than that of bulk Au.

In this study, we array n-type silicon nanowires (SiNWs) on a flexible plastic substrate and investigate the effects of tensile strain on the optoelectronic characteristics of the laterally arrayed SiNWs under the illumination of 633-nm-wavelength light in air at room temperature. The unstrained SiNW array has an efficiency of approximately 5.3 µA/W at a bias voltage of 5 V. When the plastic substrate suffers from a tensile strain of up to 2.2% in parallel to the channels of SiNWs, dark current and photocurrent increase markedly owing to the change in their band structure caused by the tensile strain.

The interaction of magnesium atom (Mg) and ionic species (Mg⁺ and Mg²⁺) with graphene chip (finite sized graphene) have been investigated by means of density functional theory (DFT) method. The B3LYP/6-31G(d) calculation showed that the Mg atom does not make a chemical bind to the graphene chip. On the other hand, the ionic species can bind srongly to a hexagonal site of graphene chip. Time-dependent (TD)-DFT calculation of Mg⁺ doped graphene showed that the first excitation band is assigned to a charge transfer band from a π-orbital of graphene chip (HOMO: highest occupied molecular orbital) to a singly occupied molecular orbital (SOMO) composed of Mg⁺(3s) orbital, whereas the second excitation band is composed of a π–π^* transition corresponding to the HOMO–lowest unoccupied molecular orbital (LUMO) excitation of free graphene chip. The nature of the interaction between the Mg ions and the graphene chip was discussed on the basis of theoretical results.

The structures and electronic states of graphene–water interaction systems have been investigated by means of density functional theory (DFT) method to elucidate the effects of water clusters on the electronic states of graphene chip. Solvation caused by five to eight water molecules (n = 5–8) was examined as the interaction systems. A graphene chip composed of 14 benzene rings was used as a model of finite-sized graphene (C₄₂H₁₆). The water clusters interact with the graphene chip with hydrogen bonds. The band gap of graphene was slightly red-shifted by the solvation and the first excitation energy was saturated around n = 5. The electronic states of graphene–water systems were discussed on the basis of theoretical results.

The structures and electronic states of boron- and nitrogen-substituted graphene chips (B-, N-, and BN-doped graphene chips) have been investigated by means of the density functional theory (DFT) method in order to shed light on the mechanism of change in the electronic properties of graphene chips caused by heteroatoms. The atomic charge of nitrogen atoms in N-graphene was a negative value, whereas that of boron atoms in B-graphene was positive. In the case of the BN-doped graphene chip, a charge polarization such as B^δ+–N^δ- was found. It was also found that the B–N bond pair is preferentially formed because of the large heat of formation of the B–N bond. The BN-doped graphene chips showed a large red shift of the band gap compared with that of normal graphene. The electric states of BN-graphenes were discussed on the basis of theoretical results.

When a nanoindentation is carried out on a coating–substrate system, the resulting deformation can be influenced by not only the coating but also the substrate. In order to measure the coating-only contact properties, many works have been done to extract the critical indentation depth. In this study, we proposed a morphological parameter to determine the critical indentation depth by materializing interfacial constraints. From nanoindents were formed on 1.2-µm-thick Cu and Au coatings, several morphological parameters were analyzed such as remnant indentation volume, impression apex angle and apex bluntness. The critical relative depths of the Cu and Au coatings were, respectively, as 0.25 and 0.16 consistent with the results from the hardness and volumetric approach. In addition, the apex angle approach can explain the discrepancy between both hardness and volumetric approach because the new approach traces the ratio of superficial edge recovery and depth-directional shrinkage inside of an impression.

The anisotropic alignment of boron nitride (BN) nanosheets was performed in polysiloxane/BN nanosheet composite film under a DC electric field with a change in polarity. The hexagonal BN nanosheets were dispersed by sonication in a prepolymer mixture of polysiloxane followed by high-speed mixing. The homogeneous suspension was cast onto a spacer of microscale thickness and applied to a high DC electric field while changing polarity before the mixture became cross-linked. Analysis revealed that linearly aligned BN nanosheet (LABN) bridges were fabricated in the composite film while connecting the film planes as bridges. This is for first report on the fabrication of linearly aligned nanosheet bridges inside organic–inorganic hybrid films. The fabricated LABN bridges were attributed to the enhancement in the thermal conductivity of the composite film, and the mechanisms underlying the formation of LABN bridges and heat conduction were discussed.

Ti–Fe nanoparticles were prepared by pulsed wire discharge (PWD) using iron (Fe) and titanium (Ti) twisted wire in Ar gas at a pressure of 100 kPa. The content of Fe (C_Fe), which was changed from 0 to 100 wt %, was controlled by adjusting the number of Ti and Fe wires in the twisted wire. From the X-ray diffraction, the phase of the prepared nanoparticles changed from α-Ti to β-Ti, FeTi, Fe₂Ti, Fe(Ti), and Fe with increasing C_Fe. FeTi nanoparticles were obtained at approximately C_Fe = 30 wt %. From these results, the phases of the prepared Ti–Fe nanoparticles were controlled by adjusting the content of Fe in the twisted wire.

In this study, the substrate shape effect on the Cu substrates for Sn whisker growth has been investigated. A Cu foil, as a substrate, was bent to 90° by a universal testing machine. The matte Sn layers were electroplated on the Cu substrate under various current densities. Then, the samples were given heat treatment under various temperatures for 250 h. The results indicate that Sn whisker growth was promoted by the compression stress on the concave side and was restrained by the tension stress on the convex side. The increase of plating thickness in electroplating process offered the extensive residual stress to mitigate the Sn whisker growth. Increasing the aging temperatures also enhanced the thickness of the oxide layer. Thick oxide layers can prevent Sn whisker growth.

The synthesis of triangular silver nanoplates on various substrates was studied in this work. A silver nanocolloid/solution was prepared by a pulsed wire discharged (PWD) method in deionized water with various wire diameters and relative energies (K), where K is defined as the ratio of the charged energy of the capacitor to the vaporization energy of the wire. The effect of the substrate dipping time in the silver colloid/solution on silver nanoplate growth was investigated. The formation of the silver nanoplate has been analyzed using X-ray diffraction (XRD) with Cu Kα radiation and scanning electron microscopy (SEM). The results indicated that silver nanoplates were formed on Cu, W, Ni, and Si substrates but not on SiO₂ substrates with increasing K. The size or number of silver nanoplates increased rapidly on Si(100) substrates. With increasing substrate dipping time, the size or the number of triangular silver nanoplates linearly increased. It was concluded that the ionization of silver atoms in the discharge and the reduction of silver ions on the substrates are possible mechanisms behind the formation of silver nanoplates on substrates.

The surface mounting technology of electronic devices using pick-and-place machines is commonly used to fabricate functional electronic appliances, such as motherboards, flat panel displays, and mobile phones. However, the pick-and-place method begins to encounter difficulties in mounting electronic devices when devices shrink to a few hundreds of micrometers or less. We propose a new blade-coating method of placing microstructures smaller than several hundreds of micrometers on a substrate. The method comprises three steps: (1) preparing a microstructure dispersion consisting of chemically modified microstructures and a water-insoluble organic solvent, (2) continuous blade-coating of water and the dispersion on a chemically patterned substrate on which hydrophilic areas are surrounded by a hydrophobic self-assembled monolayer, and (3) spontaneous placing of the microstructures on the hydrophilic areas by a water/solvent interfacial force that acts on the microstructures. Using this method, we have been able to place microstructures ranging in length from submicrometer to one hundred micrometers, including silicon nanowires and SiO₂ microstructures of various sizes. However, our blade-coating method for placing microstructures can be realized with successful combinations of chemical modifiers for the microstructures and water-insoluble solvents. We present a simple method of assessing dispersion using a chemically modified glass test tube filled with water and a solvent for the dispersion.

Thermoacoustic carbon nanotube (CNT) speakers were fabricated using CNT webs spun from a multiwalled carbon nanotube (MWNT) array of 0.8–1.6 mm height. The generated sound pressure level (SPL) showed a linear relationship with frequency over a wide range from 10 Hz to 40 kHz with a slope of 6 dB/octave. In addition to this, significantly broad and flat SPLs were obtained in the ultrasonic region, ranging from 40 to 100 kHz. The distance from the speaker to the microphone was 0.5 m. The high SPL is due to the good heat radiation property of the MWNT web. Herein, we showed an acoustical property for the MWNT web thermoacoustic speaker from the viewpoint of the structural web morphology. The role of heat radiation behavior and the effects of the length of individual MWNTs are discussed.

This paper describes a simple, low cost one-step liquid-phase process for the synthesis of highly aligned carbon nanotube (CNT) arrays (HACNTAs). Highly pure HACNTAs were grown on a stainless steel substrate by resistance-heating in methanol solution containing one of the organometallic complex catalyst precursors, ferrocene Fe(C₅H₅)₂ and iron pentacarbonyl Fe(CO)₅. Effects of the catalyst precursors on the formation and morphologies of HACNTAs were examined. A small amount of non-aligned multi-walled CNTs (MWCNTs) were grown from 1 mM Fe(C₅H₅)₂ methanol solution. Highly pure HACNTAs composed of MWCNTs were readily grown from 10 and 40 mM Fe(C₅H₅)₂ methanol solutions by this one-step liquid-phase process. From the Fe(CO)₅ methanol solution, HACNTAs were prepared even at a very low Fe(CO)₅ concentration of 0.01 mM, which was about 1/1000 lower than that of Fe(C₅H₅)₂. The optimal low concentration is attributed to the low decomposition temperature of Fe(CO)₅.

Composites of carboxylated multiwalled carbon nanotubes (c-MWNTs) and CdSe nanoparticles were prepared by the electrostatic interaction. CdSe nanoparticles were stabilized by 2-(dimethylamino)ethanethiol hydrochloride to develop positive charges on their surfaces in aqueous solution. The structural characteristics of these composites were analyzed using X-ray diffraction (XRD), and transmission electron microscopy (TEM). Ultraviolet/visible (UV/vis) spectra of c-MWNT–CdSe composites showed the characteristic bands at ∼250 nm. These results indicate that the energy state of c-MWNTs is significantly modified, which was caused by the homogeneous distribution of CdSe nanoparticles in c-MWNTs, and the bond formation between c-MWNTs and CdSe nanoparticles. The photoluminescence (PL) of CdSe nanoparticles in the composites was characterized in comparison with that of CdSe nanoparticles. PL of CdSe in c-MWNT–CdSe composites was collected at ∼568 nm in solution, but disappeared in powder state.

Single-walled carbon nanotubes (SWNTs) were fabricated by chemical vapor deposition using alcohol as a feeding gas of carbon. From the results of Raman spectroscopy with four kinds of exciting laser and consideration of chirality using the Kataura plot and chirality map, we found that the SWNTs grew with sizes from 0.92 to 1.41 nm in diameter, the possible chirality of which was 30. Metallic and semiconducting SWNTs grew. However, when irradiating 800 nm free-electron laser (FEL) during growth, the SWNTs of 1.1 nm diameter grew with a reduced possible chirality of 5, the electric property of which could be semiconducting. We revealed that the irradiation of FEL was effective to control the chirality of SWNTs to achieve ultrahigh-dense field effect devices.

Tetrapod-shaped ZnO crystals were synthesized via a simple oxidation process of Zn–C mixture in air at atmospheric pressure. The influence of carbon on the morphology and optical properties of the ZnO crystals was investigated. The ZnO crystals were characterized with an X-ray diffractometer (XRD), a scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and a cathodoluminescence (CL) spectroscopy. With increasing the carbon content in Zn source material, the size of ZnO tetrapods increased significantly. However, tetrapod-shaped ZnO crystals were not found from Zn–C mixture with a weight ratio of 1:1, indicating that carbon had an effect on the morphology of ZnO crystals as well as the size of tetrapods. CL spectra of the ZnO crystals exhibited a strong ultraviolet (UV) emission peak at 380 nm and a weak green emission peak at 510 nm. As the carbon content increased, the intensity of UV emission decreased and the green emission increased.

Various shapes of ZnO and CdO nanostructures were successfully grown on a- and c-plane sapphire substrates coated with Au nanocolloidal solution by atmospheric-pressure chemical vapor deposition methods under a simultaneous source supply of metal powder (Zn or Cd) and H₂O. The ZnO and CdO nanorods (NRs) grown at higher substrate temperatures (T_Ss) exhibited tapered shapes, resulting from the competition between the axial growth due to the vapor–liquid–solid (VLS) mechanism and the radial growth due to the vapor–solid (VS) mechanism. The alternate source supply of Zn and H₂O was found to be effective for suppressing the tapering of ZnO NRs. The appearance of the Y- and T-shaped nanotrees of CdO may be due to the splitting and migration of catalytic particles during the growth process. These results suggest that both the source supply sequence and the substrate temperature are important factors for the shape design of oxide nanostructures.

TiO₂ nanofibers were synthesized from natural leucoxene mineral via a hydrothermal process. The shapes, crystalline structure, shape transformation, phase transformation, and specific surface area of the resulting nanostructured materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Brunauer–Emmett–Teller (BET) surface area measurements. The size of prepared nanofibers was about 12–58 nm in width and about 3–22 µm in length. The BET surface area of the prepared sample was about 55 m²/g. Obtained nanofibers were preliminarily applied as photocatalysts for hydrogen evolution and electrodes for dye-sensitized solar cells (DSSCs).

Various types of calcium fluoride nanocrystals were prepared by the reactions between calcium metal and ammonium fluoride in liquid ammonia. The obtained nanocrystals were observed by X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM), absorption spectroscopy, and fluorescent spectroscopy. The particle size of pure CaF₂ nanocrystals was about 14 nm. The addition of pyridine and the selection of the period of pyridine removal gave two particle size ranges, which were 8–10 and 13–15 nm. The nanocrystals were successfully doped with Mn²⁺ and Eu²⁺. The optical properties of the nanocrystals were investigated. The results implied that Eu²⁺ was stable in the CaF₂ nanocrystals.

Using (Bi_0.5Na_0.5)_0.83Ba_0.17TiO₃ nanopowders synthesized by an oxalate precursor route, 0.2-wt %-CuO-doped ceramics can be sintered at a low temperature of 880 °C. The shrinkage rate is 16.5%, the relative density D_r is 98%, the relative dielectric constant ε^T₃₃/ε₀ (1 kHz) is 705, the loss tan δ (1 kHz) is 2.50%, the electromechanical coupling factor k_p is 13.6%, and the piezoelectric charge coefficient d₃₃ is 105 pC/N.

Charge carrier transport in donor–acceptor (D–A) composites based on either poly(N-vinyl carbazole) or polyimide derivative incorporating either carbon single-walled nanotubes or nanocrystals of J-aggregated cyanine dyes is shown to exhibit a similar behavior. In the composite films, polymer/nanomaterial interface provides pathways of the high conductivity. Charge–transfer states (CTS) formed at the D–A interface are involved in the transport. The charge transport along the interface is suggested to arise due to the D–A integer charge transfer and strong interaction between adjacent opposite charges located on the donor and acceptor molecules. The approach based on the concept of sequence of charge carrier transfers through charge transfer states describes the increased electron and hole mobility in the composites. The approach predicts enhanced conductivity with reduced activation energy. Moreover, once the density of electron–hole pairs at the interface is rather high, significant part of the charge carriers can avoid hopping transport resulting in conductivity of metal type. The value of two-dimensional conductivity is estimated by numerical modeling.

A biosensor structure comprising silicon nitride (Si₃N₄) micrograting arrays coated with a spin-on-glass (SOG) material was investigated. This grating structure was located on a silicon groove, which was etched by a deep reactive ion etching (DRIE) process. The biosensor was used as a specific detector of DNA molecules and antibody–antigen interactions. In our DNA sensing experiments, the first step was the activation of the grating surface with amine functional groups, followed by attachment of a 23-base oligonucleotide probe layer for hybridization with a complementary target DNA. The sensing device was tested for detecting specific antigen/antibody interactions for human serum albumin (HSA) and antigen bovine serum albumin (BSA). The readout system consisted of a white light lamp that illuminated a small spot on the grating surface at normal incidence through a fiber optic probe with a spectrometer used to collect the reflected light through a second fiber. We show that these sensing devices have the capability to detect DNA as well as antigen–antibody binding for HSA. The detection sensitivity for HSA was better than that for DNA mainly owing to the larger size and concomitant refractive index changes upon binding to the sensor. We show that it is possible to quantify the amount of biomolecules bound to the grating surface by measuring the wavelength shift of the reflectance spectra upon exposure to the samples.

An electrochemically controlled surface plasmon resonance (SPR) immunosensor for the detection of human immunoglobulin G (IgG) has been developed using poly(pyrrole-3-carboxylic acid) (PP3C) film. In this work, a pyrrole-3-carboxylic acid monomer was used for electropolymerization of a PP3C film on a gold-coated high-refractive-index glass slide. In situ electrochemical (EC)-SPR spectroscopy was performed to study the kinetic property and electroactivity property of the PP3C film. Moreover, ultraviolet–visible (UV–vis) spectroscopy was performed to characterize the PP3C film. Finally, the immunosensor-based PP3C film was constructed. The carboxylic acid surface of the PP3C film was activated for the immobilization of anti-human IgG. The immunosensor electrode was used for probing the binding reaction of anti-human IgG/human IgG with several concentrations of human IgG at different constant applied potentials. The probe immobilization and immunosensing process were in situ monitored by EC-SPR technique. The sensitivity of the sensor was improved by controlling the morphology of the PP3C film by applying the potential.

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