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.

In physical systems, interactions between phenomena of different nature, generally coupled to each other, are often involved. Their comprehensive study requires the use of various physical models sharing a unique set of physical quantities. In an effort to correctly model these systems, numerical methods are frequently used. However, computational tools dedicated to such a specific scope of use are barely available. Furthermore, unsuited numerical discretization and high memory costs are two major drawbacks limiting the use of coupled numerical models. We present in this paper a global method which enables the independent use of existing computational tools, the numerical adaption to each physical model and the reduction of the memory use. This method has resorted to a unique discretization and topology for each physical model. The link between these independent models is ensured by the projection of quantities common to them. Thus computational tools, originally not intended to operate together, can be used again. After a theoretical description of the projection method, we will present successive application to discretizations of different nature. Thus, numerical efficiency of the projections in themselves will be tested. Because of the large range of combination of physical models, additional tests will be carried out in order to determine the most accurate coupling flowchart. A highly coupled problem, involving three different physical models, will be presented using the projection method. Results show a significant gain in flexibility and cuts in memory costs. Present test-cases reveal that accuracy is of same order as the one obtained using dedicated tools.

We propose in this work, contact Schottky Nickel/porous silicon (PSi) system, coupled to nanocrystallites size variation of material for a possible technique to reduce dark current. The device consists of metal- semiconductor-metal photodiode (MSM-PD). Higher barrier ΦΒ enhances the performance of MSM-PD through reduction in dark current (Is), and benefits to resolve noise from signal detection of the devices. In order to reduce much more Is, we proposed different anodization times (5–7–10 min) as method to tune the size of nanocrystallites. As result Is value was reduced to almost two orders of magnitude for 10 min etching time, and the value of Is ≈ 10–10 A. ΦΒ reached the value of 0.882 eV. Among the hypothesis suggested in the reduction of Is was the quantum confinement effects. According to Rhoderick model, the Schottky barrier height is explicitly linked to the band gap energy due to the presence of interface states. The existence of narrow nanocrystallites increased energy band gap of PSi and the Schottky barrier height, which in turn reduces Is. The photoluminescence measurements confirmed our hypothesis. Photosensitivity of the device was established by adopting the MSM configuration, and strong absorption was detected in visible range.

A theoretical analysis of the line broadening of localized atomic transitions in liquid helium is presented. It is shown that accurate information can be derived on the long-range part of the He*-He interaction as well as on the local structure near the He* emitters. The analysis confirms that in corona discharges in liquid helium the emitting He* atoms reside in cavities and that for known He*-He interaction the size of the cavities can be deduced from the line profile. The He*-He interaction was calculated using the full configuration interaction (CI) method as implemented in the Molpro package. The widths of atomic lines due to fluorescent transitions between different excited states of helium atoms were calculated as a function of external pressure in the range from 0.1 and 3.5 MPa using the static approximation method, and the input from the results of the CI calculation and cavity diameters calculated using the bubble model. The calculated widths showed excellent agreement with experimental data of liquid helium excited by corona discharges. A second, analytical analysis using a power function to represent the He*-He interaction showed qualitative agreement with the experimental data.

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.

Proton transfer reaction-mass spectrometry (PTR-MS) offers many advantages for trace gas analysis, including no sample preparation, real-time analysis, high selectivity and sensitivity, ultra-low detection limits and very short response times. These characteristic features have made it an ideal tool for many applications in science, technology and society. Here we will discuss recent developments, in particular advances concerning sensitivity, selectivity and general applicability.

Thin layers of nanoporous silicon PS were synthesized by anodic etching, in order to develop photovoltaic cells. We proposed a diluted concentration of hydrofluoric acid with different etching current densities (1, 3, 5 mA/cm2) on a fairly short time anodization. Observations by scanning electron microscope, electrical measurements and optical measurements revealed that the structural properties of PS layers depended on strong conditions of prints. The reverse and forward component of the I-V characteristics showed an appropriate method to explore and extract the parameters of the diode ideality factor n. The optimum conditions of formation of PS were: HF concentration of 1% and an etching current density of mA/cm2. Unlike silicon, which has a low absorption of short visible wavelengths, it was shown that the PS had wide energy gap of ≈ 2 eV, and a marked improvement in the absorption between 400 and 600 nm. This property has been used to optimize the response of the solar cell Ni/PS/c-Si. Efficiency performance close to 4.2% was obtained with a Voc of 400 mV, and fill factor of 46%. The solar cell exhibited better response than the reference cell Ni/c-Si. These results show that PS/c-Si heterojunction has a potential for photovoltaic applications.

This document gives an overview of a power supply construction suitable for dielectric barrier discharge (DBD) reactor excitation. The influence of temperature and voltage change on DBD reactor parameters is discussed. A power electronic supply system topology allowing for continuous resonant frequency tracking is proposed together with simulation and test stand results of operation. An additional feature of proposed topology is the output peak to peak voltage control.

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.

The aim of this work was to investigate a simple and effective method to produce porous silicon from a powder of silicon. The preparation of porous silicon (PS) was realized by exposing silicon powders to acid vapor attack issued from acid solutions containing a 48% of HF and 65% of HNO3. The bond configuration of powder silicon before and after attack with acid vapor was monitored by Fourier transmission infrared spectroscopy (FTIR) and it was found that the PS was produced due to the newly formed Si-H bond during acid vapor attack. From the photoluminescence spectroscopy, it was shown that powder silicon attacked with acid vapor can lead to an increase of photoluminescence (PL) intensity when they are excited by light compared to untreated powder silicon and can provide blue shifts in the PL spectrum by increasing exposing time. This behavior may be attributed to the reduction in the size of the silicon, indicating consequently the formation of PS powder. The experimental results suggest a possibility that the chemical attack with acid vapor of the powder silicon provides a relatively easy way to produce porous silicon.

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.

Organic complementary inverters were fabricated with low-voltage pentacene/SrTiO3 and C60/SrTiO3 field-effect transistors (FETs), without formation of self-assembled monolayer on surface of the dielectric SrTiO3. The inverters showed the highest gain of 18.4 at an operating voltage as low as 3 V, where the pentacene/SrTiO3 and C60/SrTiO3 FETs on the inverters showed hole and electron mobilities of 0.85 and 0.07 cm2/V s with threshold voltages (VT) of −1.1 and −0.2 V, respectively.

In the present study, Fe2O3 was used as catalyst for the removal of NO in a hybrid plasma- catalytic reactor. The catalyst was located either directly inside the hybrid plasma-catalytic reactor or in a separate catalytic reactor, which followed ozone producing and injecting plasma reactor. Ozone production in such a reactor was dependent on the state of the electrode surface. The fresh catalyst ensured an order of magnitude smaller ozone concentration in the outlet of the hybrid reactor. After a short treatment of the catalyst with NO2, its ability to destroy ozone diminished but was regained after heating of the reactor up to 100 °C. Similarly to earlier results obtained with TiO2, the removal of NO in the hybrid reactor with Fe2O3 was enhanced compared to that in an ordinary plasma reactor. In the ozone injection reactor, oxidation of NO to NO2 took place with considerably higher efficiency compared to the hybrid reactor. The use of catalyst in the ozonation stage further improved the oxidation of NO2 to N2O5. The time-dependence effects of NO removal during plasma and ozone oxidation were explained by reactions between NO2 adsorbed on surface, with surface-bound NO3 and gas phase NO as the reaction product.

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.

Thin films of furfurylidenemalononitrile (FMN) were deposited on different substrates at room temperature by thermal evaporation technique under a high vacuum. The structure of the powder was confirmed by Fourier transformation infrared (FTIR) technique. The unit cell dimensions were determined from X-ray diffraction (XRD) studies. The optical properties were investigated using spectrophotometric measurements of the transmittance and reflectance at normal incidence of light in the wavelength range from 200 to 2500 nm. The refractive index (n), the absorption index (k) and the absorption coefficient (α) were calculated. The analysis of the spectral behavior of the absorption coefficient in the absorption region revealed an indirect allowed transition. The refractive index dispersion was analyzed using the single oscillator model. Some dispersion parameters were estimated. Complex dielectric function and optical conductivity were determined. The influence of the irradiation with high-energy X-rays (6 MeV) on the studied properties was also investigated.

Cold air plasmas of DC and pulsed corona discharges: positive streamers and negative Trichel pulses were used for bio-decontamination of Streptococci biofilm and Bacillus cereus spores on polypropylene plastic surfaces. The reduction of bacterial population (evaluated as log10) in the biofilm on plastic surfaces treated by DC corona reached 2.4 logs with 10 min treatment time and 3.3 logs with 2 min treatment time with water spraying. The enhancement of plasma biocidal effects on the biofilm by electro-spraying of water through a hollow needle high-voltage electrode was investigated. No significant polarity effect was found with DC corona. Pulsed corona was demonstrated slightly more bactericidal for spores, especially in the negative polarity where the bacterial population reduction reached up to 2.2 logs at 10 min exposure time.

A dielectric barrier discharge was used for the oxidative coupling of methane (OCM) with oxygen at the pressure of 1.2 bar. A dielectric barrier discharge (DBD) reactor was powered at the frequency of about 6 kHz. Molar ratio CH4/O2 in the inlet gas containing 50% or 25% of argon was 3, 6 and 12. The effects of temperature (110, 150 and 340 ◦C), gas flow rate, molar ratio of methane to oxygen on the overall methane and oxygen conversion and methane conversion to methanol, ethanol, hydrocarbons, carbon oxides and water were studied. In the studied system the increase of the temperature decreases the conversion of methane to methanol. The increase of the molar ratio of methane to oxygen increased the methane conversion to hydrocarbons and strongly decreased the methane conversion to alcohols. The conversion of methane to hydrocarbons increased and the conversion of methane to methanol decreased with the decrease of the gas flow rate from 2 to 1 NL/h.

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.