Table of contents

We have investigated high-temperature electron transport in metamorphic InGaAs/InAlAs modulation-doped heterostructures with several indium contents. The electron mobility characterizing the low-field transport properties was obtained from the Hall measurements. From room temperature to 400 K, ∼26% decrease in the mobility was observed, which is well-explained by the polar-optical-phonon scattering theory. The indium content dependence of the mobility is explained by the theory with the Γ-valley electron mass. On the other hand, the electron saturation velocity characterizing the high-field transport properties was studied by means of the delay-time analysis of the transistors with gate length of 0.12–1.0 μm. We observed ∼12% decrease in the saturation velocity from room temperature to 400 K, which is smaller than that in the mobility and roughly consistent with the energy relaxation theory. In the indium content dependence of the saturation velocity, the effect of decrease in the electron density in the L- and X-valley is important. The high-frequency performance of the transistors at high temperatures shows a deterioration according to the decrease in the saturation velocity.

Research results of spintronics based on spin-orbit (SO) interaction in non-magnetic semiconductor hetero-junctions obtained recently have been described. Works are based on the two-dimensional electron gases (2DEGs) confined at compound semiconductor narrow band-gap hetero-interface. Due to the electric field originated from the confining potential asymmetry, the 2DEG often yields strong SO interaction which could reveal under no magnetic field. This type of SO interaction (Rashba interaction) can be controlled by the applied gate voltage and hence the field effect transistor (FET) utilizing this principle has so far been proposed and discussed extensively. We describe two recent results in this paper: First is molecular beam epitaxy (MBE) growth of novel narrow-gap modulation-doped heterojunction, InGaSb/InAlSb material system which possibly reveals high quality electronic properties as well as very strong Rashba SO coupling. Recently we indeed obtained the sample with a very large SO coupling constant of ~40×10⁻¹² eVm which is almost comparable to the best value obtained in the former InGaAs/InAlAs systems. Second is relating to the control of Rashba SO interaction in long wires with side gates. As a result of careful analysis about the dependencies of the SO coupling constant on the gate voltage, we confirmed the side-gate control of the Rashba effect for the first time, which could be a promising result to develop the spin-FET based quantum-bit devices.

Co@Ag nanoparticles have been prepared in microemulsions by the successive reaction technique. It was observed that, under the experimental conditions of this study, the size of the Co nuclei is limited by the reactant concentration (approx. 0.7 nm), whereas the Ag covering is templated by the microemulsion droplet size (approx. 7 nm). The as-prepared particles mainly contain clusters in the form of Co₃O₄, which evolves to Co as the samples are annealed in a reducing atmosphere at high temperatures. At temperatures >300 °C the pasivating surfactant layer decomposes with the subsequent growth of the nanoparticles, converging their properties to Co and Ag bulk.

The synthesis of carbon nanotubes (CNTs) and carbon nanofilaments (CNFs) was investigated using the catalytic decomposition of acetylene over alumina-supported palladium catalysts prepared with the impregnation of palladium acetylacetonate (Pd/Al₂O₃) and deposition of dodecanethiol-protected palladium nanoparticles (DT-Pd/Al₂O₃). The synthesized carbon products consisted of multi-walled carbon nanotubes together with a significant number of CNFs. At 700 °C over Pd/Al₂O₃, the carbon products were mainly made up of CNFs in the range of 9–26 nm in diameter, while CNTs with well-defined layer structures were synthesized at 800 °C. When Pd loading was 0.5 wt.%, carbon tubules showed better crystallinity than those of 2.5 wt.% at 700 °C. DT-Pd/Al₂O₃, showing better dispersion of DT-Pd nanoparticles, showed narrower size-distribution of CNTs than that of Pd/Al₂O₃. Over several supports (Al₂O₃, SiO₂–Al₂O₃, SiO₂, and Y) with DT-Pd nanoparticles, we obtained amorphous carbon-free CNTs showing a narrower diameter range of 6–21 nm at 700 °C.

We report the transport properties of C₆₀ thin film field-effect transistors (FETs) with a channel of several-hundred nanometers. Asymmetrical drain current I_D versus source-drain voltage V_DS characteristics were observed. This phenomenon could be explained in terms of the high contact-resistance between the C₆₀ thin film and the source/drain electrodes. This device showed a current on/off ratio >10⁵.

Mn²⁺-doped GeO₂–B₂O₃–ZnO (GBZ) glasses were investigated and developed as long-lasting phosphorescence host materials. Transparent glass-ceramics were obtained after heat-treated at the first crystallization temperature for 20 min. By X-ray diffraction measurement and SEM observation, it is clarified that Zn₂GeO₄ crystallites with a diameter of about 1 μm precipitate on the sample's surface after heat-treatment. An orange long-lasting phosphorescence from Mn²⁺ was observed in the 25GeO₂–25B₂O₃–50ZnO glass matrix, however, a stronger long-lasting green phosphorescence was observed in the phase of Zn₂GeO₄ crystallites. This phenomenon is considered to be due to the different ligand field environment surrounding Mn²⁺ ions in the glass and the glass-ceramics. A possible mechanism for the long-lasting phosphorescence in the Mn²⁺-doped glass was discussed.

Performance of holographic gratings, prepared by using epoxy-functionalized siloxane compound as a reactive diluent, was compared with that using N-vinylpyrrolidinone as a diluent in the presence of various contents of liquid crystal under different exposure beam intensity. Siloxane component strongly influenced the kinetics of polymerization, diffusion, and phase separation of the liquid crystalline compound, and high diffraction efficiency was obtained when 3-acryloxypropyltrimethoxysilane or 2-[(3,4-epoxycyclohexyl)ethyl]trimethoxysilane was used as a reactive diluent even at a very low concentration (10–25 wt%) of commercial liquid crystal mixture, E7 (Merk), in contrast to the case with N-vinylpyrrolidinone or benzyl glycidyl ether as the diluent without siloxane component.

The phase-separated morphologies of gratings, such as spacing and surface topology, observed by SEM and AFM, were well controlled, and very regular and smooth morphologies were observed for the holographic gratings prepared with 3-acryloxypropyltrimethoxysilane and various contents of the liquid crystal.

Thermal, optical and electrochemical properties of phenyl-substituted disilanes have been investigated. Phase-transition temperature increased with increasing the number of phenyl substitutents. σ–π Conjugation effect by the introduction of phenyl-substitutents also strongly affected LUMO levels of disilanes with slight change of their HOMO levels.

Biodegradable hydrogels for temperature-controlled erosion were prepared by co-crosslinking N-isopropylacrylamide (NIPAAm) and methacrylate (MA)-introduced polyrotaxane (PRX) in which many α-cyclodextrins (α-CDs) are threaded onto a poly(ethylene glycol) chain capped with bulky end-groups via ester linkages. The amount of MA attached to hydroxyl group of α-CDs in PRX could be varied by the feed ratio of GMA and PRX. The prepared hydrogels were transparent below lower critical solution temperature (LCST) of PNIPAAm matrix (32 °C). By elevating temperature above the LCST, water contents were slightly decreased, and the hydrogels became opaque. Elevating temperature in an aqueous condition above the LCST led to dehydration of the PNIPAAm matrix, which accompanies α-CD sliding to expose the ester linkage to the medium and enhances erosion of the hydrogels.

A hydrotropic dendrimer, made of polyglycerol dendrimer of generation 4 (PGD-G4), was conjugated with cholesterol. The self-assembled structure of the conjugate in water was characterized by ¹H-NMR, dynamic light scattering (DLS) and atomic force microscopy (AFM). One cholesterol molecule was conjugated to PGD-G4, which was confirmed by MALDI-TOF mass spectroscopy. The DLS analysis showed that the conjugate formed self-assembly with a diameter of 49.9–59.9 nm. The AFM image suggests that the self-assembly is a micelle-like sphere. The level of paclitaxel solubilization by the conjugate in water was similar to that of PGD-G4 itself, and this suggests that the PGD-G4 is located on the outer part of the self-assembly to function as a hydrotrope.

A polyethylene/montmorillonite(MMT) nanocomposite was prepared by in situ polymerization method using MMT-supported methylaluminoxane(MAO) cocatalyst and/or Cp₂ZrCl₂ catalyst. The catalyst components had been supported on the unmodified MMT-Na and modified commercial product, Cloisite 25A. With XRD it was found that the layered silicate gallery of Cloisite 25A was exfoliated by incorporating MAO cocatalyst and zirconocene catalyst while the d-spacing of MMT-Na was less changed. The in situ polymerization of ethylene was carried out to prepare the nanocomposite by using the supported MMT, and the fully exfoliated product was obtained with Cloisite 25A. The decomposition temperature of the obtained nanocomposite increased up to 25 °C, but the melting temperature was not improved much.

Direct docking of nanomolecules, such as proteins, is responsible for biological signal transduction in cells. This physiological interaction is mimicked by various biosensors in nanotechnology. In many cases phosphorylation of protein is involved in protein–protein interaction, and understanding phosphorylation-dependent interaction is necessary to design novel biosensors. Here, we developed and tested a specific method for studying on interaction of phospho-proteins in silico. The algorithm, named phospho-pivot modeling, consists of two parts: first is to generate a library of virtual complexes by pivoting phospho-ligand at the docking site on the receptor, and second is to grade them according to probability in atomic proximity between two molecules. After a 90-min computation by a personal computer, the phospho-pivot modeling yielded an in silico model for the complex of Ser/Thr phosphatase-1 (PP1) and calyculin A, an inhibitory compound of PP1, which was superimposed on the crystal structure in database with r.m.s.d. of 0.23 Å. The phospho-pivot modeling was applied on the prediction for the complex of PP1 and phospho-CPI-17, an inhibitory protein, whose complex structure is unknown. A 1285-min computation selected one converged structure of the PP1·CPI-17 complex out of 186,624 models. The computation time was reduced to 400 min by adding a prescreening process, where virtual complexes with conflicts between main chains were dismissed from the grading process. Thus, phospho-pivot modeling algorithm is sufficient to predict complex structure of proteins, whose monomeric structures have been solved.

A novel preparation method for core/shell nanoparticles with hydrophilic polymeric shell was designed and characterized. The core is composed of poly(lactide-co-glycolide) and polymeric shell is composed of pluronics (poly (ethylene oxide)-poly (propylene oxide)-poly(ethylene oxide) triblock copolymer, F-127) and hyaluronic acid (HA). The role of core is to provide the nucleus for the stable formation of hydrophilic polymeric shell by physical adsorption and that of polymeric shell is to provide the hydrophilic network for protein loading. Lysozyme, which was used as a model drug and protonated in the physiological pH, was successfully loaded into polymeric shell up to 7 wt% via ionic interaction between HA and lysozyme and the sustained release pattern was observed, which was due to the stable immobilization of lysozyme in the polymeric shell.

RNAs possess potentials to become excellent bio-material because of their biochemical and biological activities. For instance, most RNA splicings are catalyzed by machinery including their own RNAs or other RNAs. The eukaryote machineries for splicing of pre-mRNA, which are called spliceosomes, are flexible and accurate for separating substrates. Although RNAs themselves catalyze the splicing, spliceosomes are supported by many proteins. Furthermore, a great accuracy is required for the alternative splicing because there are choices available, which must be regulated in tissue-specific and developmental manners. Neural-salient serine/arginine-rich (NSSR) proteins 1 and 2 are candidates for supporting the accuracy of the splicing. The features of their amino acid sequences suggest that NSSRs are SR proteins, which bind to pre-mRNA and determine the splicing site. Since SR proteins have a RNA recognition motif or motives (RRM or RRMs), which binds to RNA, we predicted the secondary and tertiary structures of NSSRs' RRM by comparing them to RRMs of other proteins. The predicted structure suggested that the RNA binding activity of NSSRs' RRM is similar to the poly A binding protein (PABP). Moreover, to detect the targets for NSSR, mRNAs were obtained by screening them from murine brains with bacterial recombinant NSSRs' RRM and microarray experiments were conducted using these mRNAs. The results suggested that NSSRs bind specifically to particular pre-mRNAs and regulate the alternative splicing of the binding pre-mRNA.

Polyrotaxanes with both sulfonyl and carboxyl groups were synthesized and characterized for mimicking the anticoagulant activity of heparin. A polyrotaxane consisting of α-cyclodextrins (α-CDs) and poly(ethylene glycol) (PEG) was synthesized, and carboxyethylester (CEE) groups and taurine were successively conjugated with the polyrotaxane to obtain taurine-conjugated carboxyethylester-polyrotaxanes (TAU-CEE-PRxs). The number of α-CDs and the anionic groups could be varied by synthetic conditions. The structural factors of TAU-CEE-PRxs affecting anticoagulant activity were suggested as following: (i) relatively lower threading percentage of α-CDs, (ii) the ratio of anionic groups similar to heparin, and (iii) lower molecular weight of PEG. The TAU-CEE-PRx that sufficiently meet the mentioned requirements showed enhanced antithrombin III (AT III) activity, indicating that the TAU-CEE-PRx interacts with AT III and/or thrombin. From these results, it is suggested that the sliding and rotation of free α-CDs with anionic groups are related with enhancing anticoagulant activity.

In recent years, label-free biosensors not requiring external modifications have been receiving intense attention. A label-free optical biosensor, which retains many of the desirable features of conventional surface plasmon resonance (SPR) reflectometry, namely, the ability to monitor the kinetics of biomolecular interactions in real-time without a label has been developed with several important advantages: the biosensor device is easy to fabricate, and simple to implement, requiring only an UV–Vis spectrophotometer or flatbed scanner. Importantly, the label-free optical biosensor can be easily multiplexed to enable high-throughput monitoring of biomolecular interactions in an array-based format. In this research, the development of a localized surface plasmon resonance (LSPR)-based label-free optical biosensor using a surface modified nanoparticle layer is aimed. This optical detection method promises to offer a massively parallel detection capability in a highly miniaturized package. The two-dimensional nanoparticle layer was formed by the surface modified silica nanoparticles. The optical properties and surface analysis of nanoparticle layer substrate were characterized through transmission measurements and atomic force microscopy (AFM). Simultaneously, the nanoparticle layer substrate was applied to the optical LSPR-based biosensor for label-free monitoring of the antigen–antibody reaction. The anti-fibrinogen antibody was immobilized onto the nanoparticle layer substrate surface. Different concentrations of fibrinogen were introduced to the anti-fibrinogen antibody immobilized nanoparticle layer substrate surface, and the change in the absorption spectrum, caused by the antigen–antibody reaction, was observed. By using this anti-fibrinogen antibody immobilized nanoparticle layer substrate; the detection limit of this optical LSPR-based biosensor was 10 ng/ml.

A bilayered electrode bearing the configuration SnO₂|TiO₂ over a substrate like transparent conducting Indium Tin Oxide coated glass was found to store the charge accumulated during ultraviolet illumination. Photogenerated electrons from TiO₂ are transferred to SnO₂ that store the excess charge via cation intercalation. A red shift in the absorbance of the coating was observed due to the reduction of the valence state of Sn during charging and a high capacitance in the bilayer electrode was detected by ac impedance measurements. The charge storage property of SnO₂|TiO₂ electrode makes it a candidate material to be used as an anode for improved photocathodic protection of metals and/or steels.

Synthesis, crystal structure and solubility of a new non-linear optical material L-arginine maleate dihydrate have been reported here. From the solubility studies with different solvents, water was found to be the most suitable one. Title compound crystallized in the triclinic space group P1 with Z=1 and unit cell dimensions a=5.264(3) Å, b=8.039(3) Å, c=9.784(3) Å, α=106.19(3)°, β=97.24(3)°, γ=101.66(2)°. The present complex of L-arginine contains a positively charged zwitterionic arginine molecule and a negatively charged semi-maleate ion. The molecules are held together by a three-dimensional network of hydrogen bonds.

With the increasing of electromagnetic pollution and the widely use of commercial and military products, there is an increasing interest in electromagnetic interference (EMI) shielding. This paper mainly aims at electrical conductivity and EMI shielding effectiveness (SE) of the conducting composites made from silicone rubber (SR) with different loading levels of HCl-doped polyaniline (PAN-HCl) in the low frequency range from 3 to 1500 MHz. The result indicates that SE of the composites increase and the volume resistivity decrease with increasing mass ratio loading of PAN-HCl in the SR. The measured SE of the composites are from 16 to 19.3 dB at 100 mass ratio loading of the PAN-HCl and the volume resistivity decrease nine orders of magnitude compared with that of the emeraldine base form of PAN (PAN-EB) composites.

Conversion coating modified by alumina has been studied as a way for improving the resistance to thermal oxidation of an austenitic stainless steel. Conversion coating, characterized by a particular morphology and strong interfacial adhesion with the substrate, facilitate the electrochemical deposition of ceramic layers and enhance their adhesion to the substrate. The influence of the current density and treatment time on alumina deposit was studied using statistical experimental designs like Doehlert uniform shell design. After heating, coatings present a continuous composition gradient with refractory compounds at the surface. The behavior at high temperature (1000 °C) of the alumina coating was investigated. The presence of alumina increases the oxidation resistance of an austenitic stainless steel at 1000 °C. The morphology and the chemical composition of the deposit are analyzed. Results on the thermal stability of coating on austenitic stainless steel are presented.

The effect of sintering temperature on the transport properties of Ag-sheathed-(Bi_1.6Pb_0.4)Sr₂Ca₂Cu₃O₁₀–(γ-Fe₂O₃)_0.01 superconductor tapes prepared by the powder-in-tube technique with sintering time fixed at 50 h has been investigated. The maximum transport critical current density, J_c of 6490 A/cm² at 77 K, was observed at sintering temperature of 845 °C. A further single intermediate rolling step increases J_c to 9560 A/cm². Sintering temperature from 830 to 845 °C increases the 2223 phase content and resulted in improved J_c. At 850 °C, the content of 2223 phase decreased resulting in a corresponding decrease in J_c. X-ray diffraction patterns suggest that the 2212 phase reacts with non-superconducting phase such as CaCuO₂, (SrCa)₂CuO₃, CaO, and CuO to form the 2223 phase. Samples without γ-Fe₂O₃ prepared under the same condition showed a lower J_c with maximum at 1560 A/cm². Our results show that nanomagnetic γ-Fe₂O₃ addition improved J_c which supports previous calculations on the possibility of frozen flux superconductor with nanomagnetic addition in this class of materials.

A needle-like probe is the simplest tool to manipulate fine spheres. It catches fine spheres by adhesion forces without any holding device. Metallic spheres of 10–100 μm are difficult to manipulate with the needle-like probe, because the gravity rivals the adhesion forces in the dynamics of the spheres. Large and heavy spheres arranged on a substrate are easily disturbed because of the same reason. Here, a manipulator equipped with a direct power source, which applies voltage to the probe, is fabricated. Large and heavy spheres are adhered by the controllable electrostatic force. Besides the manipulation, the apparatus is designed to weld the spheres by using the probe as electrode for spot/arc welding. Experiments on the manipulation showed that the probe caught gold spheres of 40–80 μm by applying 20–50 V and released by putting them down after cutting the power off. Following to manipulation, welding experiments were carried out at various conditions. Two power sources, a high-voltage and low-current power source and a low-voltage and high-current power source, and two welding methods, arc welding and spot welding, are examined. The experiments showed that the gold spheres of 40–80 μm can be welded by the spot welding using the high-voltage and low-current power source, of which maximum power rating is 10 kV×1 mA. The probe is kept to touch the sphere and 4 kV or more is applied. Electric sparks are generated at the interface of the probe and the substrate, and the sphere is welded to the substrate. In both the manipulation and welding, the contact pressure must be very low. A tower of gold spheres is fabricated as an example of three-dimensional microstructures composed of fine spheres.

To develop a new way to produce the molybdenum disulfide (MoS₂) solid lubrication film, the following two-step chemical reaction technique was attempted. Firstly, a Mo film was prepared by multi-arc ion plating technique, and secondly the Mo film was sulfurized by a low temperature ion sulfuration technique to obtain the MoS₂ solid lubrication film. This MoS₂ film was a composite film consisted of MoS₂ and Mo. The lubricant MoS₂ is dominant in the surface and metal Mo is dominant in the deep layer. It is an ideal frictional surface. The tribological properties showed that the solid lubrication MoS₂ film possessed an excellent anti-friction property.

A coupled thermo-mechanical model of plane-strain orthogonal turning of hardened steel was presented. In general, the flow stress models used in computer simulation of machining processes are a function of effective strain, effective strain rate and temperature developed during the cutting process. However, these models do not adequately describe the material behavior in hard machining, where the workpiece material is machined in its hardened condition. This hardness modifies the strength and work hardening characteristics of the material being cut. So, the flow stress of the work-material was taken with literature [H. Yan, J. Hua, R. Shivpuri, Development of flow stress model for hard machining of AISI H13 work tool steel. The Fourth International Conference on Physical and Numerical Simulation of Materials Processing, Shanghui in China, 2004, p. 5] in order to take into account the effect of the large strain, strain-rate, temperature and initial workpiece hardness. Then a series of numerical simulations had been done to investigate the effect of machining parameters on the machinability of hardened steel AISI H13 in finish turning process. The results obtained are helpful for optimizing process parameters and improving the design of cutting inserts in finish turning of hardened steel AISI H13.