We report the fabrication of AlGaN/GaN high electron mobility transistors (MIS-HEMTs) with a high breakdown voltage by employing a metal-insulator-semiconductor (MIS) gate structure using Si3N4 insulator. The Si3N4 films were deposited by plasma enhanced chemical vapor deposition (PECVD) as the surface passivation, interlayer films and the gate dielectric. In comparison with Schottky-gate HEMTs, the gate leakage currents of MIS-HEMTs exhibited three orders of magnitude reduction. With similar device structures, the off-state breakdown voltage of MIS-HEMTs was 1050 V with a specific on-resistance of 4.0 mΩ cm2, whereas the breakdown voltage and specific on-resistance of SG-HEMTs were 740 V and 4.4 mΩ cm2, respectively. In addition, the MIS-HEMTs exhibited little current slump in the pulsed measurements and possessed faster switch speed than Si MOSFET. We demonstrate that AlGaN/GaN MIS-HEMTs are promising not only for microwave applications but also for high power switching applications.

Local electrical conductivities were measured for plastically deformed n-GaN single crystals by scanning spreading resistance microscopy (SSRM). In the SSRM images, many spots with high conductivity were observed, which can be attributed to introduced edge dislocations whose line direction is along [0 0 0 1] and Burgers vector is b = (a/3)[1 2¯$\bar{2}$ 1 0]. This result is in contrast to the previous studies which showed that grown-in edge dislocations of the same type in GaN films exhibit virtually no conduction. This suggests that the dislocation conduction depends sensitively on the dislocation core structure. Current-voltage spectra indicated a Frenkel-Poole mechanism for the conduction.

We study the structural and electronic properties of Mg3Bi2 in both hexagonal and body center cubic (bcc) phases by using first-principles calculations based on the density functional theory (DFT). We solve the Kohn-Sham equations using the full potential linearized augmented plane wave (FP-LAPW) method. The generalized gradient approximations as proposed by Perdew-Burke-Ernzerhof (PBE sol GGA) and Engel-Vosko (EV-GGA) are employed to calculate the exchange correlation potential. Using GGA, we compute the optimized lattice parameters of the bcc. This is the first instance of such application of GGA. In close agreement with experimental results, our electronic calculations show that the hexagonal phase is a direct gap semiconductor with energy gap of 0.2520 eV. The bcc phase calculated band structure shows a direct gap semiconductor with band gap of 1.0306 eV. We further study the effects of applying pressure on the band structure of the system.

Dye-sensitized solar cells with thin film TiO2 electrodes were fabricated. The TiO2 films were prepared on conducting and non-conducting glass substrates. A high-intensity laser was shining on the dye/TiO2 electrodes to excite the dyes and inject electrons to the conduction band of the TiO2 electrode. The dye degradation rate showed much difference for the dyes adsorbed on the TiO2 films on conducting and non-conducting glass substrates. On non-conducting glass substrate the injected electrons gathered near where they were injected. This increased the local Fermi level of the TiO2 conduction band and consequently the electron injection efficiency was decreased, leading to a relatively high degradation rate for the dyes when they were radiated by a high-intensity laser. The experimental results showed that dye stability is sensitive to the local electro-chemical environment.

SnS nanoparticle has been synthesized initially using SnCl2 · 2H2O and Na2S · XH2O, in the presence of TEA by precipitation method and XRD and FTIR techniques have been used for characterization of the sample. Powder X-ray diffraction studies revealed the particle size to be 48 nm and the pattern represents polycrystalline herzenbergite orthorhombic crystal structure of SnS. The FTIR result also confirmed the SnS at 2354 cm−1. Secondly SnS:Se thin films have been deposited on glass substrates by electron beam evaporation technique and the films were annealed at 100 °C and 200 °C for 1 h. The unannealed films are amorphous in nature and the annealed film shows that a sharp crystalline peak is due to SnS. Also a peak is shown at 2θ = 14.39°, which is due to characteristic peak of SnSe2, established by their XRD patterns. The band gap energy (Eg) was determined from transmission spectra and an optical band gap of Eg varies from 1.6 eV to 1.79 eV.

This paper presents a low-temperature route for producing RFe0.6Ni0.4O3 (where R = Pr, Nd and Sm) thin films by an aqueous inorganic sol-gel process. The films produced were characterized by X-ray diffraction (XRD) for structural, four probes for electrical and UV-vis spectroscopy for optical properties. As-deposited films were amorphous and after annealing them at 650 °C, crystallinity appears and shows an orthorhombic structure. From UV-vis spectroscopy, variation in optical band gap and transmission is seen with change of rare-earth ions. From electrical resistivity measurement, semiconducting behavior is observed. The difference in activation energy is observed. This variation could be due to the orthorhombic distortion caused by size of rare-earth ion and which may impact the Fe-O-Fe or Fe-O-Ni or Ni-O-Ni bond angle, and hence affects the single particle band width in the present system.

Nitrogen-doped TiO2 nanothin films were synthesized by spray pyrolysis method using TiCl4 as a precursor. Five samples including 0.0, 0.1, 0.2, 0.3 and 0.4 molar urea (as a nitrogen source) were fabricated. XRD spectra of the samples confirm that increasing the nitrogen doping initiates anatase to rutile-phase transformation and narrows band gap from 3.60 to 3.46 eV. This means that doping nitrogen increases the rate of the anatase to rutile-phase transformation. UV-vis spectrophotometer of the thin films showed 85–90% transmission in the visible region. AFM images indicate the increase of roughness and the grain size of the samples by increasing nitrogen doping. Optical band gaps were calculated by Tauc plot with values larger than those reported for bulk samples. The larger band gap might be due to the strain from lattice distortion. High hydrophilicity and photocatalytic properties were observed in thin films during UV illumination that persists for 210 min. It was found that the sample with the largest amount of N doping shows the best hydrophilicity activity and photocatalytic property.

Neodymium-doped zinc oxide (NZO) thin films were deposited on glass substrates by spray pyrolysis technique. X-ray diffraction patterns have shown that both undoped and Nd-doped ZnO films exhibit the hexagonal wurtzite crystal structure with a preferential orientation along [0 0 2] direction.

The effective doping concentration has been determined by Rutherford backscattering measurements showing that the neodymium is not incorporated easily into ZnO host matrix. The surface roughness was shown to increase with Nd doping. NZO films are highly transparent in the visible region. The lowest electrical resistivity value of about 4.0 10−2 Ω cm was obtained for 1% Nd effective doping.

CoxTi1–xO2 films were deposited by spray pyrolysis technique on Si(1 0 0) substrates at 475 °C. A hydro-alcoholic solution containing titanium (iv) isopropoxide and Co(NO3)2 with various Co doping levels from x = 0–0.015 in solution was used as spray solution. Grazing incident angle of X-ray diffraction illustrates that the CoxTi1–xO2 films are single phase and polycrystal with mixed orientations. Study of surface morphology of the films by atomic force microscope reveals that the annealing atmosphere does not significantly affect the grain size and the microstructure of the films. This study provides further insight into the importance of annealing atmosphere on magnetization of the films. Room temperature magneto-optical Kerr measurement was employed in polar mode. A hysteresis loop and a paramagnetic behavior have been recorded for samples annealed in H2 ambient gas and air, respectively. Chemical composition analysis by X-ray photo-electron spectroscopy showed that Co atoms are bounded to oxygen and no metallic clusters are present. Moreover, it indicates the formation of high spin Co2+ for the sample x = 0.008 annealed in H2 ambient gas. The origin of magnetization can be attributed to the contribution of oxygen vacancies in the spin polarization of the structure.

In this paper a transient finite volume model for electrodynamic levitation devices analysis has been developed. Both electromagnetic and mechanical equations are time stepped and coupled to give the dynamic characteristic of the motion. Furthermore, the nonconforming mesh technique is introduced to take movement into account. To check the efficiency and accuracy of the transient finite volume method (FVM) model, the Team Workshop Problem 28 is used.

We report the magneto-optical Kerr signal enhancement due to the capping effect of SnO2 on the Co67Fe4B14.5Si14.5 amorphous ribbons. The amorphous melt spun ribbons are mounted on glass substrate and capped by SnO2 with different thicknesses by using electron-beam evaporation technique. The magnetic behavior of the ribbons is investigated by the magneto-optical Kerr effect. As the SnO2 layer thickness increases up to about 70 nm, the Kerr signal increases more than two times with respect to that for uncovered ribbon. The results were analyzed using a formalism based on a 4 × 4 matrix method. A good agreement of the experimental results with the theoretical results is observed.

In this study, we report a method to generate a reliable and homogeneous brush-shape air plasma plume at atmospheric pressure for surface modification of PET polymers and biomedical applications. The room-temperature air plasma plume consists of well-aligned and stable microplasma jets formed in the vicinity of the ends of hollow optical fibers at atmospheric pressure. This plasma plume may lead to the uniform and large-area surface modification of PET polymers. The plasma plume may efficiently prevent the heat-sensitive polymers from being damaged and significantly affect the surface properties of treated polymers, such as surface chemical compositions, hydrophobicity and biocompatibility. Compared to a high density of blood platelets adhering onto the untreated PET sample, no adhesion of blood platelets is observed on the plasma-activated PET sample due to the surface functionalization. The reaction processes of plasma-activated species at the surface of treated polymers are discussed based on the obtained experimental results.

Quantitative flow fields from the acoustic streaming were measured experimentally using the stereoscopic PIV. The acoustic streaming pattern between the ultrasonic transducer and stationary plate, maximum acoustic streaming velocity, velocity variation at resonance and non-resonance, variation of flow pattern and velocity with gap variation were experimentally verified. The maximum acoustic velocity between the gap in the open channel at resonance and non-resonance was located at the ultrasonic transducer center at radial direction and at the neighborhood of the ultrasonic transducer at axial direction. In the vicinity of the ultrasonic transducer surface, larger average acoustic velocity occurred at the edge of the transducer than at the transducer center at the resonant gap. At non-resonant gap, the maximum acoustic velocity exists toward the edge of the transducer. The turbulent intensity varied with gap size and maximum value existed at the transducer center with radial direction and at surface of the stationary plate or transducer with axial direction. At resonant gaps, there was almost zero radial acoustic streaming velocity at the ultrasonic transducer center and there existed only axial streaming velocity. For axial directions, maximum acoustic streaming velocity was located at z position of −16 mm.

A numerical study of a controlled flow evolving in a Taylor-Couette system is presented in this paper. The study is devoted to investigate the effect of the outer cylinder cross-section variation on the flow behavior. It is aimed to make assessment of the flow response in terms of the criticality of the early transitional flow regimes and the accompanying flow topology alterations. The numerical simulations are carried out on the Fluent software package for a three-dimensional incompressible flow. The basic system is characterized by a height H = 200 mm, a ratio of the inner to the outer cylinders radii η = 0.9, an aspect ratio corresponding to the cylinders height reported to the gap length Г = 40 and a ratio of the gap to the radius of the inner cylinder δ = 0.1. The numerical deformation of the outer cylinder is executed using the dynamic mesh program according to a predefined function implemented in a homemade program as an UDF (user defined function). It is established that the first instability mode of transition is retarded from Tac1 = 41.33, corresponding to the first Taylor number critical value, to Tac1 = 70 when the deforming amplitude is equal to 15% the external cylinder diameter value. This flow relaminarization process is accompanied by substantial modifications in the flow behavior and configuration.

The picosecond ultrasonics technique is used to investigate the viscoelastic properties of nucleus of fixed single osteoblast progenitor cells adhering on a titanium alloy substrate. A two-color probing picosecond ultrasonics and a fluorescence visualization setups were developed and combined to allow to distinguish subcomponents inside the cell under investigation. It opens the way for quantitative measurements of the viscoelastic properties of single cells and of their sub-micrometer thickness. It is shown that a blue probe, λ = 400 nm, is preferable to a red probe, λ = 800 nm, to perform these measurements with fixed sub-micrometer bone cells. 26 GHz acoustic frequencies are detected in cells as thin as 135 nm. A 1D analytical model of the acoustic generation and of the optical detection is used to describe the experimental results. The nucleus longitudinal elastic moduli (13–16 GPa) and dynamic viscosities (13–30 cP) are measured at high frequencies (GHz) from a time-frequency analysis of the experimental data of fixed single cells.