Tunnel diode oscillator-based technique has been usedfor quantum oscillations spectra determination of a quasi-twodimensional organic metal in pulsed high magnetic fields of up to55 T. It is demonstrated that reliable field-dependentquantitative data can be obtained in the case of complexoscillatory spectra provided adequate data processing isconducted.

In this work, we present experimental evidence and analytical studies of the XRD patterns and optical characterizations of ZnS films with different optical thicknesses. Thin films of ZnS were deposited on glass substrates by thermal evaporation. The crystallite size increased as the optical thicknesses. The overall absorbance has been increased with the film thickness and the direct band gap was obtained. It decreases with the increasing in the thickness of the films.

This paper focuses on the modelling of a SiC-JFET. The novelty aspect is the dependence on temperature. An accurate model has been used in a previous work and an identification procedure for the main model parameters has been demonstrated. Readers have asked for a more advanced SiC JFET temperature-dependent model. A limitation of the current model versus temperature is verified and explained in order to introduce the necessity of a new temperature dependence model. A more advanced model is then considered and a comparative study between experiment and simulation of the device is established. The characteristics of three SiC JFETs devices are considered from experimental and simulation point-of-view. Simulations results clearly replicate the experimental data at different temperatures and a new validity approach, namely validity maps, is proposed. Validity domains are discussed.

The characteristics of heterojunction diode pSe-nMoSe2 fabricated from thermally evaporated p-Se films on n-type Molybdenum diselenide (MoSe2) grown by direct vapour transport (DVT) technique have been examined by using current-voltage measurements. To investigate the dark current transport mechanism in pSe-nMoSe2 heterojunctions the current-voltage characteristics were measured in the temperature range 100–300 K. The prepared diode shows a rectification ratio of the order of 103 within the range –2 to 2 V. A multi-step tunnelling model was used to analyze the I-V-T characteristics of the prepared device. The activation energy determined from the saturation current was about 1.16 eV.

The process of multiwavelengh detection by a single system is possible when considering multilevel structures. Indeed, in a quantum structure with specific profile, levels can be confined in a single band leading to Infrared intersubband transitions which may be responsible of strong enough absorption. In this work we present the theoretical determination of the absorption spectra in a specific GaAs/AlGaAs superlattice containing four confined minibands. For this, we have calculated the electronic states, the dipole matrix elements and the Fermi level's position versus temperature and doping. We analyze the importance of the different transitions absorption peaks and their behavior when varying either the temperature or the free electrons density, both in the parabolic and the non parabolic cases.

Electrical and gas sensing properties polyaniline-chloroaluminium phthalocyanine (PAni-ClAlPc) composite thin films were investigated to study the gas sensing behavior of composites. Devices (chemiresistor gas sensors) were prepared by spin coating method from PAni as the base of composites and ClAlPc (with different concentrations) as the second component onto interdigitated electrodes. The sensitivity, reversibility, response and recovery time of these thin films on exposure to different concentrations (0–2000 ppm) of CO2 gas and the suitability of different composites as materials to be used in practical gas sensors at different temperatures were investigated. The sensitivity factor of composites was obtained in a range between 0.05–7.20. PAni + 10% ClAlPc was the perfect candidate composite to fabricate gas sensor at 300 K and PAni + 15% ClAlPc at 350 K. Thus, (PAni-ClAlPc) composites have better response than pure PAni. After that, devices were exposed to humidity, an unexpected behavior was absorbed. Conductivity of thin films were increased on exposure lower RH% and decreased on higher RH%. Finally, 1000 ppm CO2 was mixed to humidity and introduced to chamber, obtained results showed the CO2 mixtures decreased the sensitivity of thin films in compare with pure CO2.

Iron (III) chloride tetraphenylporphyrin (FeTPPCl) thin films are prepared on quartz and glass substrates at room temperature by thermal evaporation technique. The X-ray diffraction showed the amorphous nature for both the as-deposited and the annealed films at 423 K in air for 2 h, whereas the powder has the tetragonal form with lattice constants of a = 13.53  $\acute\AA$ and c = 9.82  $\acute\AA$ . The optical properties of FeTPPCl films are investigated using a spectrophotometric measurement of transmittance and reflectance at normal incidence of light in the wavelength range 190–2500 nm for the as-deposited and the annealed films. Absorption spectra of the films showed B, N and C absorption bands in the UV region followed by a Q-band in the visible region. The onset optical gap is determined from the analysis of the absorption coefficient values and found to be 1.53 eV for both the as-deposited and annealed films. The dispersion of the refractive index, n, is discussed in terms of Cauchy relation and the single oscillator model. The polarizability, the dispersion parameters, the ratio of free carrier concentration to the free carrier effective mass are also estimated.

The present paper reports the preparation of (Se80Te20)100-xAgx (0 ≤ x ≤ 4) chalcogenide glasses in bulk by using melt quenching technique. DSC runs of these samples have been taken at four different heating rates (5, 10, 15, 20 K/min). The variation in crystallization temperature Tc with Ag concentration at different heating rates has been studied. A strong co-relation between the pre-exponential factor K0 of rate constant K of crystallization and activation energy of crystallization Ec has been observed. The variation of rate constant K with composition and the dependence of Ec with Ag concentration have been studied.

Black coatings are widely used in numerous applications e.g., decorative coatings, solar panels, optical instruments. The films are mostly prepared by liquid phase deposition or vapor phase deposition. In this paper we review the techniques of deposition and the properties of the most important black coatings. Optical properties are particularly presented and discussed.

We studied capacitance-voltage characteristics of ZnO thin-film transistors (TFT's), grown by metalorganic chemical vapor deposition (MOCVD). We compared two ZnO TFT's: one grown at 450 °C and the other at 350 °C. ZnO grown at 450 °C showed smooth capacitance profile with electron density of 1.5×1020 cm-3. In contrast, ZnO grown at 350 °C showed a capacitance jump when gate voltage was changed to negative voltages. Current-voltage characteristics measured in the two samples did not show much difference. We explain that the capacitance jump is related to p-type ZnO layer formed at the SiO2 interface. Current-voltage and capacitance-voltage data support that our ZnO films have anisotropic conductivity.

It has been observed in many cases that the effective dielectric constant of some general composite media can reach as high as thousands at low frequency side. In this paper, a numerical method is used to simulate this phenomenon and study the parameters which could affect the dielectric spectrum. In order to obtain the effective dielectric constant and conductivity of the composite and understand the dominant factors of large dielectric enhancement of low frequency side, a three-dimensional finite difference method (3D-FDM) is used to simulate general mixtures and mixtures with membrane structure. A special FDM grid is introduced to handle the membrane that coats the inclusions of the composite medium. We analyze the influence of the membrane thickness, membrane conductivity, inclusion insertion ratio, and inclusion shape on the effective dielectric constant and conductivity of the composite. The results show that: (1) the low-conductivity membrane may be the cause of the dielectric enhancement of low frequency side; (2) the membrane thickness, membrane conductivity, and inclusion insertion ratio can affect the dielectric enhancement level significantly; and (3) the physics of the dielectric enhancement is probably related to the frequency dependence of the effective plate separation of the capacitor model.

The electronic structure of γ-Al2O3 and α-Al2O3 has been investigated by means of the density functional theory. A comparison of the calculation results with experimental data for amorphous alumina films is also presented. The electronic structure is described in terms of band structure and density of states. It has been found that γ-Al2O3 have similar electronic structure withα-Al2O3 and amorphous Al2O3. Effective electron masses in γ-Al2O3 as well as in α-Al2O3 equal to $m_e^\ast$ ≈ 0.4 m 0 that is in a good agreement with the experimentally found tunnel electron mass in amorphous Al2O3. The heavy holes in both alumina crystals are explained by the valence band top forming by O 2p π nonbonding orbitals.

Nano structure films of cadmium thiogallate CdGa2S4 have been prepared by a conventional thermal evaporation technique (at substrate temperature = 303 K). These films were deposited on both glass and quartz substrates. X-ray diffraction measurements showed that CdGa2S4 compound in the powder form has a polycrystalline nature with a tetragonal structure. The as-deposited film was annealed at 673 K for 2 h under vacuum 10-3 Pa and was irradiated by 10 kGy γ co rays. This resulted in a transformation to nanostructure grains of CdGa2S4 thin films. Transmission electron microscopy was carried out for all of the investigated films, which also confirmed that those films could be transformed to nanostructure grains. Optical properties of the CdGa2S4 films under investigation were examined using spectrophotometric measurements of transmittance and reflectance at normal incidence in the wavelength range 400–2500 nm. It was found that both refractive index n and absorption index k changed with the heat and irradiation treatments. The dispersion of refractive index in CdGa2S4 was analyzed according to the single oscillator model. Some dispersion parameters were determined for all investigated films. The calculated values of β (which is defined as the parameter used to determine the type of crystal) indicate that CdGa2S4 belongs to the covalent class for all films investigated. The ratio of the free carrier concentration to the effective mass N/m* was also determined. The analysis of the absorption coefficient indicated that this ternary defect chalcopyrite compound has both direct and indirect transitions in relevance to the energy gaps E g1 dir, E g2 dir and E g ind, respectively. These energy values decreased by irradiation, while they increased by annealing.

Strontium-substituted barium vanadates, Ba5-x Srx DyTi3V7O30 (x = 0–5), were prepared by a high-temperature sold-state reaction method. The formation of the materials was checked by X-ray diffraction technique. Preliminary structural analyses of the materials exhibit the formation of new compounds in orthorhombic structure. Surface morphology of the compounds was studied by scanning electron microscopy. The effect of Sr on microstructure of the materials has resulted in a modification of the electrical properties. Study of electrical properties using impedance analysis technique exhibit (i) the presence of negative temperature coefficient of resistance behavior, (ii) presence of temperature dependent electrical relaxation phenomena, (iii) evidences of single electrical relaxation attributed to the presence of bulk contribution to the electrical properties, (iv) an enhancement in the barrier to the mobility of charge carriers on Sr-substitution. The effects of Sr in the electrical conductivity as a function of temperature at different frequency are explained in impedance spectrum analyses.

Gallium arsenide (GaAs) thin films have been deposited on ITO-coated glass substrates from acid aqueous solution by electrodeposition technique. The structure and the morphology of the samples were analyzed by X-ray diffraction (XRD) and atomic force microscope (AFM). The optical characteristics were investigated at room temperature using a UV-Vis spectrometer. At lower deposition time, the XRD patterns exhibit a mixture of both cubic and orthorhombic GaAs phases. With further increase of the film thickness, only orthorhombic structure was observed with a preferred (100) orientation. By applying the Debye-Scherrer method, the estimated crystallite size for the (200) orientation ranged from 30 to 50 nm, whereas for the (022) orientation was found to be 13–22 nm. From the AFM measurements, the rms surface roughness ranged between 11.4 and 18.4 nm. The analysis of the optical absorption data of the annealed GaAs film deposited at different times revealed direct band gap energy in the range of 1.60–1.85 eV. The large blueshifts observed in this study can be fully explained by the Burstein-Moss effect.

In this work, we demonstrated a simple route to pattern nanostructures on the 3-aminopropyltriethoxysilane (APTES) film adsorbed on mica using nanolithography technology. Various nanopatterns (linear, foursquare and triangular) could be achieved by controlling and designing the scanning direction of AFM tip. Also, it was found that the adsorbed APTES film could be induced to rearrange into a bilayer structure. The parameters for the formation of nanostructures were investigated by contact mode atomic force microscopy (AFM). The results indicated that the height of the nanopatterns built on the adsorbed film increased with the decrease of the depth of a tip pushed in. The driving force for the formation of nanopatterns is the combination of the capillarity and inducement action of a tip to APTES molecules. The results presented in this work will improve our understanding to the formation process of short-chain alkoxysilane molecular bilayer and multilayer on mica in a position-selective way.

We analytically formulate electromagnetic fields of circular loop-coilsplaced around double-structured axisymmetrical cylinders with differentelectrical conductivities and magnetic permeabilities. Formulae are given interms of conductivity, permeability and frequency in a vector potentialformalism subject to the appropriate boundary conditions on the cylindricalsurface. The impedance of the coil is numerically computed for real andimaginary parts, whose behavior is investigated in detail on the Gauss planefor various electromagnetic properties. Our model will make it clear how theimpedance of the coil depends on the conductivity and permeability insubregion of the base material, and also on the excitation frequency.

Branched treelike carbon nanotubes were grown by plasma enhanced chemical vapor deposition method on a silicon wafer. Patterned structures of as grown nanostructures were used for the fabrication of a gas sensor, which operates based on the field ionization of various gases. The variations in the electrical resistivity and the emission current of the fabricated device are related to the chemisorption and field ionization mechanisms, respectively. The sensor is capable of gas detection at room temperature and at low pressures with working at low voltages. Different gases such as H2, O2, C2H2 and Ar have been used to examine the gas sensitivity characteristics of the fabricated sensors.

A novel embedded cylindrical-array magnetic actuator (ECAMA) is proposed and verified by experiments to provide sufficient magnetic force for spindle deviation regulation of high-speed milling process. Four I-shape silicon steel columns enclosing the spindle constitute the backbone of the ECAMA. The shape of modified concave-type yokes is designed to reduce the average air gap between magnetic poles and the spindle. In contrast to the conventional AMB (active magnetic bearing) design for which coils are usually wound on the yokes, the copper wire is wound on the I-shape silicon steel columns. As a result, the overall wound coil turns can be much increased. In other words, stronger magnetic force can be induced by ECAMA. On the other hand, to reduce the cost of ECAMA, two pairs of self-sensing modules are employed to replace the gap sensors for measurement of spindle position deviation. In order to verify the efficacy of the proposed ECAMA and the self-sensing module, high-speed milling tests are undertaken. By inspection on the precision and quality of the finish surface of workpiece, the superiority of ECAMA and the self-sensing module are assured.

The tight-binding model is used to inquire the uniaxial strain effect on the electronic structure of 2D graphene sheet and quasi-1D armchair graphene nanoribbons. The dependence of Dirac points and gap on the uniaxial strain is investigated. The band edges deviate from the corners of the first Brillouin Zone (BZ) gradually with the strain applied. The gap can be opened only when graphene sheet is highly strained. The threshold of the gap induced by strain along armchair directions distinguishes from that by strain along zigzag direction. A controlled strain can be applied to achieve the semiconductor-metal transition in armchair graphene ribbons.