TlInS2 single crystals were grown by using Bridgman-Stockbauer technique. Measurements of DC conductivity were carried out in parallel (σ//) and perpendicular (σ⊥) directions to the c-axis over a temperature range from 303 to 463 K. The anisotropic behaviour of the electrical conductivity was also detected. AC conductivity and dielectric measurements were studied as a function of both frequency (102–106 Hz) and temperature (297–375 K). The frequency dependence of the AC conductivity revealed that σac(ω) obeys the universal law: σac(ω) = Aωs. The mechanism of the ac charge transport across the layers of TlInS2 single crystals was referred to the hopping over localized states near the Fermi level in the frequency range >3.5 × 103 Hz. The temperature dependence of σac(ω) for TlInS2 showed that σac is thermally activated process. Both of ϵ1 and ϵ2 decrease by increasing frequency and increase by increasing temperature. Some parameters were calculated as: the density of localized states near the Fermi level NF = 1.5 × 1020 eV-1 cm-3, the average time of charge carrier hoping between localized states τ = 3.79 μs and the average hopping distance R = 6.07 nm.

This is a theoretical study of the InGaN back-barrier on the properties of the Al03Ga0.7N/AlN/GaN/InGaN/GaN HEMT structure by self-consistently solving coupled Schrödinger and Poisson equations. Our calculation shows that by increasing the indium composition, the conduction band of the GaN buffer layer is raised and the confinement of 2DEG is improved. However, the additional quantum well formed by InGaN becomes deeper, inducing and confining more electrons in it. Another conductive channel is formed which may impair the device performance. With the increasing InGaN thickness, the well depth remains the same and the conduction band of GaN buffer layer rises, enhancing the confinement of the 2DEG without inducing more electrons in the well. The 2DEG sheet density decreases slightly with the indium composition and the physical mechanism is discussed. Low indium composition and thick InGaN back-barrier layer are beneficial to mitigate the short-channel effects, especially for high-frequency devices.

This paper introduces theoretic and experimental analyses of short-duration pulse propagation through a negative group delay (NGD) circuit. The basic analysis method of this electronic circuit operating in baseband and microwave frequencies is investigated. Then, its electrical fundamental characteristics vis-à-vis transient signals are developed. To validate the theoretic concept, planar hybrid devices with one- and two-stage NGD cells were designed, simulated, fabricated and tested. Transient analyses with ultra-wide band (UWB) pulse signals with different widths are realized. Then, experimental results in good agreement with the theoretical predictions were observed. Consequently, group delay going down under −2.5 ns is evidenced in baseband frequency up to 63 MHz with one-stage NGD cell. In time-domain, a Gaussian pulse in advance of about t0 = −1.5 ns or 20% of its half-height time-width was measured. This corresponds to a negative group velocity of about vg = L/t0 = −0.13c (L is the physical length of the tested device and c is light speed in the vacuum). More significant NGD value over 100-MHz bandwidth is stated with two-stage NGD cells. This results in a Gaussian pulse peak advance of about −5 ns (raising a group velocity of about vg = −0.12c) or 31% of its half-height time-width. Finally, some potential applications based on the NGD function are discussed.

We have experimentally investigated the unwinding process of the ferroelectric Sm-C* phase of a chiral AFLC smectic liquid crystal compound 12OF1M7 using the electro-optic properties, microscopic observations and constant current method. We found that this process occurs via two steps through an intermediate phase. Furthermore, we have established the (E-T) phase diagram of the studied compound by combining the experimental results.

Polycrystalline Cd thin films were evaporated in a vacuum onto glass substrates at Cd source temperature of 770 K. The as-deposited Cd films were subjected to a gradual heating at the rate of 5 K/min, up to a temperature of 650 K and were then maintained at this temperature for 5 min. Then, the respective samples were cooled down to room temperature at the same rate. The obtained CdO thin films were UV irradiated for 2 h (150 W mercury lamp, 3.18–3.65 eV). By means of XRD, AFM and XPS techniques, the structural characteristics of the typical obtained CdO samples before and after UV treatment were investigated. The obtained results indicate that the UV treatment induces a recrystallization process: changes in sample morphology, surface roughness and crystallite size and orientation. XRD and XPS studies evidenced an improvement in crystalline structure and stoichiometry. UV irradiated sample shows photo-catalytic properties.

Magnetic Resonance Imaging (MRI) that provides superior soft tissue contrast is commonly used for diagnosis of many diseases. However specificity of MRI cancer diagnosis can be further increased by application of target contrast agents comprising superparamagnetic nanoparticles (NPs) synthesised with biological objects, which deliver the contrast to the specific cancer cells. These superparamagnetic NPs shorten T2 relaxation time thus change contrast to noise ratio for tumor tissues. Therefore the impact of Fe3O4 size and silica coating for Fe3O4/silica core/shell superparamagnetic nanoparticles (NPs) on T2 relaxation time was studied at 9.4 T. The magnetic resonance imaging (MRI) studies were performed using homogenous agar solution of NPs. Naked Fe3O4NPs with a mean core diameter of 10.0 ± 1.3 (mean ± SD), 15.0 ± 2.5 and 20.0 ± 0.9 nm were analyzed. Silica coated Fe3O4 NPs with core size of 10.0 ± 1.3 nm and the shell thickness of 16.7 ± 1.8, 25.3 ± 2.7 and 33.9 ± 4.0 nm were also investigated. The T2 values of agar solutions with different NPs were calculated using a single slice multi echo method and single exponential fitting of the echo train. The measurements showed linear correlation between T2 and Fe3O4 core diameter as well as shell thickness. Silica coating, while improving functionalization and potentially reducing toxicity of NPs, decreases the impact of the magnetic core on T2, thus decreasing MRI contrast efficacy.

We report the effect of nitrogen and boron incorporation in the structure of spherical nanodiamond particles using ab initio density-functional theory. We changed the site of boron and nitrogen impurity from the center to the surface of the particles and calculated structural, electronic, cohesive and surface charge properties of each configuration. By moving the impurity from the center toward the surface, the internal strain of N and B doped nanodiamond drops. Unlike nitrogen, doping of boron causes lower broken bonds around impurity in the central region and also replacement of boron in the surface releases the strain of nanoparticle. We explain this observation by calculating the variation of the surface charge or polarity of the doped particles versus the site of dopant during the movement of impurities toward the surface which reduces the polarity in contrast to behavior of nitrogen doped particle. By moving the boron atom from the center toward the surface of the particle, p-type conduction occurs whereas nitrogen impurity does not create an n-type conduction. Results suggest that boron is a more effective dopant than nitrogen provided that it has not been placed in the central region of nanoparticle.

Plasma enhanced chemical vapor deposition was used to grow vertically aligned carbon nanotubes (CNTs) on silicon substrate. Field emission from these nanotubes was realized and used to fabricate a field emission-based sensor. Titanium dioxide was used as spacing layer between the emitters and a flexible anode made of silicon membrane. The variation of the emission current during mechanical vibration of the silicon membrane was measured and compared with a theoretical prediction. Experimental results show that field emission from CNTs is a good candidate for high frequency vibration sensing, measurement of resonance frequency, fabrication of accelerometer and other types of mechanical sensors. The fabricated device, due to a low distance between its electron emitters and the anode, works at low voltages with high emission current.

The cobalt/polyacrylonitrile (Co/PAN)-based carbon fibrous composites were prepared. The PAN incorporated with cobalt ions was in situ polymerized by initiating the complex solution of acrylonitrile (AN)/cobalt (II) chloride (CoCl2) in which the contents of cobalt ions were 0 wt.%, 0.29 wt.%, 0.56 wt.% and 1.14 wt.%, respectively. The ultrathin blue fibers were formed from the cobalt/PAN composites by the electrospinning method. The electrospun cobalt-incorporated PAN fibers were successfully stabilized in air and subsequently carbonized to form the carbon fibrous composites in a nitrogen (N2) atmosphere. Based on the scanning electron microscopy (SEM), we noticed that beads and beaded fibers were produced during the electrospinning process. When the content of cobalt ions in the complex solution was as high as 1.14 wt.%, there were many honeycomb-like structures and nanopores formed in both stabilized and carbonized fibers. The X-ray photoelectron spectra (XPS) were used to characterize the structure of the composite fibers.

ZnO/Si heterojunctions were prepared by the sol-gel method and hexagonal polycrystalline wurtzite structures with pores were observed by a field emission scanning electron microscope. The steady photovoltage properties of ZnO/Si heterojunctions were obtained under the illumination of a 532 nm continuum solid state laser with a 50 Hz chopper. In addition ns photoresponse signals were found when the samples were excited by a ps pulsed laser at room temperature. A possible mechanism was proposed to describe the photovoltaic process in the ZnO/Si heterojunction.

We present a numerical modeling of the effect of optical pulse position on the impulse response of a GaAs back-gated Metal-Semiconductor-Metal (MSM) photodetector at low bias voltages. The backside contact of the photodetector is set to the floating condition (disconnected from the external circuit). Experimentally the device response to the optical pulse is strong only when the position of the optical pulse is around the anode contact. We have used a one-dimensional time-dependent nonlinear ambipolar transport equation to model this behavior. Our numerical modeling results agree well with the reported experimental findings.

Synthesis of ZnO microprisms was achieved on Si substrates coated with Ce(NO3)3 thin films by a simple carbon-thermal evaporation method. The pre-deposited Ce(NO3)3 films may decompose at about 200 °C to be CeO2 microparticles, which can provide growing sites for the ZnO microstructures. The structural and optical properties of the as-obtained ZnO microstructures were characterized by a number of techniques, including X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, Fourier transform infrared spectrum and photoluminescence. The results indicate that the as-prepared ZnO microprisms exhibit hexagonal prism-like platforms showing well-defined crystallographic facets and hexagonal pyramid-like tops. Room temperature photoluminescence spectrum of the microstructures shows a strong ultraviolet emission band accompanied by a broad weak green emission band. Finally, the growth mechanism was discussed based on the experimental conditions and the ZnO crystal growth habits.

In this paper an original experimental device is presented. It allowed to obtain, for the first time, the total amount of liquid and vapour of metal created on the electrode surface by a non stationary electric arc (600 A/20 ms) burning in air at atmospheric pressure. The results are presented for two different materials Ag and AgSnO2 and for electrode gap values in the range 1–10 mm. The amount of liquid and vapour created under the arc action is compared with usual erosion rate in the same experimental conditions. In the case of Ag electrodes the amount of liquid metal created on the anode may be 3 to 5 times higher than on the cathode although the usual erosion rates are more important at the cathode. For the anode, the usual erosion may represent a very low percentage (<10%) of the total amount of metal liquid created showing then that a very small part of the liquid created during the arc is ejected. In the case of AgSnO2 electrodes the amount of liquid metal is smaller. The usual erosion rates at the cathode are higher than for the anode and the usual erosion represent 10 to 50% of the amount of liquid and vapour created.

The general method of diagnostics of the transient radiation of ribbon-shaped and axially-symmetric electron beams of small section (0.1 mm) and high-power density (1–100 kW/sm2) is described. Selective analysis of various types of transient radiation detectors of type photo-camera, video-camera and digital photo-camera is carried out at first. Advantages and disadvantages of radiation detectors are pointed out to be taken into account at analysis of the object under investigation.

The magnetohydrodynamic stability criterion of self-gravitating streaming fluid cylinder under the combined effect of capillary, inertia, pressure gradient and electromagnetic forces has been derived. The results are discussed analytically and some data are verified numerically for different parameters of the problem. The magnetic field is stabilizing, but the streaming is destabilizing while the self-gravitating and capillary forces are stabilizing or destabilizing according to restrictions. The stable and unstable domains are identified and moreover the influences of the magnetic field and capillary forces on the self-gravitating instability of the model have been examined. The including of the electromagnetic force together with both the capillary and self-gravitating forces improve the instability of the model. However, the self-gravitating instability will never be suppressed whatever are the effects of the capillary and MHD forces stabilizing effects.

Computational fluid dynamics solutions of the Reynolds Averaged Navier-Stokes equations have been used to numerically predict the thrust of a thermally choked ram accelerator in subdetonative velocity regime. Studies were focused on a projectile operating in a 38-mm-diameter ram accelerator tube loaded with premixed propellant gas; methane/oxygen/nitrogen at 5.15 MPa fill pressure. Simulations were carried out for a series of incoming velocities. The shear stress transport turbulence model (SST) and the eddy dissipation combustion model (EDM) with five-step reaction mechanism were used to simulate the fully turbulent reactive flow field around the projectile. The predicted projectile thrust-velocity agreed well with the experimental measurements, in addition, the CFD predicted pressure variation and magnitude along projectile axial direction also agreed well with the test data. The present investigation reveals some key features of the shock-wave system around the projectile, which are important in determining the characteristics of the thermally choked propulsive mode. These findings are useful in understanding the characteristics of high speed turbulent combustion process in the ram accelerator.

Knowledge of endothermic and exothermic heat capacities of optoelectrics materials is important to define their energy/data storage capability. Heat capacities of Se98-xZn2Inx (0 ≤ x ≤ 10) chalcogenide glasses at glass transitions (Tg) and crystallisations temperatures (Tc) have been reported in this work. The evaluated endothermic (ΔCpg) and exothermic (ΔCpc) heat capacities of Se98-xZn2Inx system varies with alloying concentrations obtained minimum and maximum respectively at threshold composition (6 at wt.% of In). The up and down trend in ΔCpc and ΔCpg at Tg, Tc could be explained on the basis of structural units/avarage coordination number 〈r〉 of the glassy materials.

The dynamics of MinD proteins have been acknowledged as playing a central role in accurate cell division. In our study, a spot tracking technique (STT) was applied to track motion and quantitatively characterize the dynamic behavior of MinD proteins on the level of particle cluster in Escherichia coli. We focused on the time and spatial distribution of MinD proteins. With the STT technique, the main quantitative results are twofold: (i) dynamic local and global pattern formations and (ii) energy landscape. The overall MinD cluster motion is governed by two dynamical time scales, namely the (slow) trapping time (~26 s) that appears at the cell poles, and the (fast) switching time (~1–2 s) which emerges between the cell poles. MinD cluster motion at the polar zones performs subdiffusion. The energy landscape is found to be two wells and one barrier. These energy landscape results are to relate with the memory effect of GFP-MinD cluster motion, measuring the PSD exponent approximately 1.57 (α ~ 0.57) corresponding to the estimated potential depth U0 ~ 1.75kBT.

In this study, we propose new approach to study on hydrogen implantation into SiC crystalline structure and its effect on thermal oxidation. This paper has investigated on effects of hydrogen implantation into the surface structure of 6H-SiC crystal before and after thermal oxidation in oxygen ambient. H ions were implanted in SiC with dose of 1×1016 atoms/cm2 and energy of 15 keV. AFM results of implanted and non-implanted areas show that roughness in the implanted area is more than the non-implanted but, we could not observe any evidence of implanting effect in the nano scrapes which were created during polish process. Also, crystal quality, effect of H implantation and depth of maximum concentration were determined by RBS- Channeling. Moreover, it shows that the collision of H ions has affected on the SiC atoms. Distribution and dose of H ions were estimated by ERD technique. Furthermore, bonding between SiC atoms was investigated in implanted and non-implanted areas by FTIR technique. In addition, FTIR results in two areas show a significant difference between both areas before and after oxidation in oxygen ambient.

We report a modified deep reactive ion etching method to realize high aspect ratio features and nano-grasses on silicon substrates. This etching technique uses sequential etching and passivation sub-cycles and it is based on three gases of H2, O2 and SF6 in the presence of rf-plasma. By adjusting the etching parameters such as the flows of various gases, the plasma power and duration of each cycle, the process can be controlled to obtain high aspect ratio vertical structures on silicon substrates. Features with aspect ratios of the order of 30–50 and heights of the order of 25–30 μm are obtained. On the other hand, one can program the etching parameters to achieve grass-full structures in desired places and with pre-designed patterns. The formation of nano-grass on silicon surface, improves its wetability with water and oil spills. This property has been used to entrap carbon nanotubes onto nano-structured surfaces in desired places.