Voltage characteristics of polysilicon thin films transistors (Poly-Si TFTs) are related to basic material and device parameters. Understanding and modeling the electrical behavior of poly-Si TFT require knowledge of equivalent properties of polysilicon which are strongly affected by defects present in this material. A numerical analysis, which studies the electrical characteristics of small-grains poly-Si TFTs, has been investigated. The density of states (DOS) in the band gap is modeled by assuming an exponential distribution of deep and tail states. The proposed model evaluates the influence of both deep and tail states on the electrical conduction process and the dominant contribution of tail states on the threshold voltage values while the deep states in the middle of polysilicon gap controls the lower threshold regime. The surface potential and ON/OFF current ratio are also calculated. The comparison of the generated current-voltage characteristics obtained from numerical simulation TCAD-ATLAS with those reported in the literature show a good agreement.

The as-prepared samples of Sn10Sb20Se $_{70-X}$ TeX chalcogenide system were amorphous as evidenced by X-ray diffraction and Differential scanning calorimetry studies. The different crystalline phases emerged in annealed Sn10Sb20Se $_{70-X}$ TeX samples have been identified. Glass transition temperature T g of the as-prepared samples decreases sharply with tellurium substitution upto 2 at% and then it starts increasing upto 10 at% and decreases again on further substitution of tellurium. The change in glass transition temperature T g has been explained based on bond formation energy of different heteropolar bonds and crystalline phases obtained in the annealed samples with different tellurium contents.

A modified and improved low frequency model for polycrystalline silicon thin-film transistors (poly-Si TFTs) is developed in this paper. For small grain size poly-Si TFTs, based on carrier number fluctuations, an improvement of the standard low frequency noise model has been investigated to explain the noise characteristics of poly-Si TFTs. An exponential energy distribution for interface density of states is employed to model the interface trap capacitance. For large grain size devices, mobility fluctuations related to fluctuations of the grain boundary charges is used to describe the excess subthreshold noise. The anomalous noise increase behavior of poly-Si TFTs when operated in the kink regime is also studied and modeled. The proposed model and the experimental data agree well over a wide range of operation regimes.

Photoinduced reversible switching of charge carrier mobility in conjugated polymers was studied by theoretical and experimental methods. The quantum chemical calculations showed that the presence of dipolar species in the vicinity of a polymer chain modifies the on-chain site energies and consequently increases the width of the distribution of hopping transport states. The influence of photoswitchable charge carrier traps on charge transport was evaluated by current-voltage measurement and by impedance spectroscopy method. It was found that deep traps switchable by photochromic reaction may significantly control the transport of charge carriers, which is exemplified as a significant decrease of the current and increase of parallel resistance measured by impedance spectroscopy.

Plant fibers with nonzero microfibril angle show no plane reflection symmetries, the groups of spatial symmetry transformations consisting of rotations only. The spatial point symmetry group of any material made of such fibers is of order which is half of the order of the symmetry group of the corresponding orthotropic material. However, materials consisting of fibers show similar degeneracies of stiffness eigenvalues as the non-fibrous materials. Stiffness degeneracies appear to be controlled by the integer exponents of dicycle conditions applied on products of vectors generating symmetry groups. It is found that flat orthotropic sheets always retain their planar shape in eigen deformations, whereas those made of fibers with microfibrils do not. Features of the out-of-plane deformations are clarified. Orthotropic material elements experience normal on-axis eigen strains only, whereas fibrous bodies with orthotropic fiber alignment may experience on-axis shear strains as eigen strains.

Note to the reader:

On page 10402-p12, four mistakes have been corrected on September 7, 2009:

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The ZnSx Se $_{1-x}$ (0 ≤x≤ 1) films were deposited on soda lime glass substrates by thermal evaporation technique. Optical and structural properties of these films were compared with the ZnSx Se $_{1-x}$ films deposited by various other techniques. XRD measurement showed that ZnSx Se $_{1-x}$ films are polycrystalline in nature with the preferred orientation along [111]. It was observed that the lattice constant decreases and the optical energy band gap increases with the sulfur content of the film. These results are in good agreement with the properties of ZnSx Se $_{1-x}$ films deposited by various other methods. Additionally, it was observed that the refractive index of a ZnSx Se $_{1-x}$ film decreases with increasing sulfur content. The results reported in this paper suggest that the lattice constants, optical energy band gap and refractive index of ZnSx Se $_{1-x}$ film can be tailored for a specific application by selecting suitable value of x.

V2O5 thin films were prepared by the sol-gel spin coating process. The Li+ ions insertion effect on optical and electrochromic properties of those films was studied. The diffusion coefficient was calculated using both cyclic voltammograms and chronoamperometric curves. The amount x of Li+ ions in Lix V2O5 was also calculated. Finally, the electrochromic performance evolution characteristics such as the reversibility, coloration efficiency, coloration memory stability and response time were studied.

Phase diagram of a ferroelectric thin film with two surface layers is studied in frame of the effective field theory (EFT) of transverse Ising model (TIM). The surface of the system is formed from two layers characterized by the exchange interaction anisotropy $R_s =\frac{J_s }{J}$ and the transverse field $\Omega _{s}$ . The crossover from the ferroelectric phase (FP) to the paraelectric phase (PP) is discussed. The phase diagram of the system is studied in $\big( {\frac{K_B T_c }{J},\frac{\Omega _s }{J}} \big)$ coordinates as function of the thickness parameter L. The special attention is given to the effect of the transverse field $\Omega _{s}$ on the phase transitions.

Thin films of titanium, copper and silver with various roughnesses were prepared by physical vapour deposition technique: dc magnetron sputtering. By varying the deposition time from few minutes to one hour it was possible to obtain metallic films with surface roughness average ranging from 1 to 20 nm. The wettability of these films was studied by measuring the contact angle using the sessile drop method and surface forces were investigated using the atomic force microscopy (AFM) by measuring the pull-off force between the AFM tip and the surfaces. Experimental results have been mainly discussed in terms of metal surface reactivity, Young modulus of the materials and real surface of contact between the AFM tip and the film surfaces.

Thin films of head-tail (H-T) regio-regular poly[3-(4-octyloxyphenyl) thiophene] (POOPT) were grown using the MAPLE (Matrix Assisted Pulsed Laser Evaporation) technique in which the target is a frozen solution of the polymer in chloroform. Target evaporation was obtained by laser irradiation at 1064 nm and substrates were kept at different temperatures. Information concerning the preservation of the polymer local chemical structure following laser irradiation was obtained by FTIR (Fourier Transform InfraRed) spectroscopy. Based on FTIR data, the chemical structure of the deposited polymer seemed to undergo little or no damage. From UV-Visible spectroscopic analysis, it turned out that the degree of order of the film is strongly affected by the substrate temperature: the polymer was deposited in a disordered form on the substrate at room temperature whereas on the hot surface we locally obtained the π-stacked structure characteristic of polythiophenes. Atomic force microscopy (AFM) images showed that the polymer formed aggregates of different dimensions (<1 μm to 5 μm) with a columnar shape and showed micrometric domains with sharp and apparently regular edges for the film grown on a hot substrate.Electrical measurements performed by a standard two-probe technique confirm that the structural order degree strongly affects the film charge transport properties.

We have fabricated and characterised colloidal silver nanoparticles by the electrical arc discharge method in DI water. Size and optical properties of the silver nanoparticles were studied versus different arc currents. Optical absorption indicates a plasmonic peak at 392 nm for 10 A which increases to 398 nm for 20 A arc current. This reveals that by raising the arc current the size of the nanoparticles increases. Optical absorption of silver nanoparticles after 3 weeks shows precipitation of them in a water medium. The effect of different surfactant and stabilizer concentrations such as cethyl trimethylammonium bromide (CTAB), polyvinyl pyrrolidone (PVP), sodium citrate, sodium dodecyl sulfate (SDS), sodium di-2-ethylsulfosuccinate (AOT) and carboxymethyl cellulose (CMC) on the stability of silver nanoparticles was investigated. The colloidal silver nanoparticles with 100 μM concentration were stable for more than 3 months at 50 μM CTAB and 6 months at 10 μM sodium citrate concentration, respectively. SEM images of the sample prepared at 50 μM CTAB concentration reveal uniform and fine nanoparticles. The mean size from TEM images is about 14 nm. TEM images of the sample prepared at 10 μM sodium citrate concentration show a shell of citrate that covers the silver nanoparticles.

Using low molecular weight polyethylenimine (PEI), transparent thin films of TiO2 nanoparticles were prepared by layer-by-layer self assembly method. UV-visible spectrophotometry was employed in a quantitative manner to monitor the adsorbed mass of TiO2 and PEI after each dip cycle. The adsorption of both TiO2 and PEI showed a saturation dip time of 10 min. The effect of dip time on the growth mode and surface morphology was investigated by scanning electron microscopy (SEM) and non-contact atomic force microscopy (AFM). It was found that growth proceeds in the form of laterally broad islands in case of short dip times, and taller but laterally smaller islands in case of longer dip times. A model was proposed which describes the role of dip time on the lateral growth of TiO2 islands. Low molecular weight PEI resulted in around 25% less adsorption of PEI and TiO2 in comparison with high molecular weight PEI, but because of lower remaining ash, could be promising for dye-sensitized solar cell photoelectrode applications, in which removal of polyelectrolyte after the formation of thin film enhances the electrical properties and therefore the efficiency of solar cell.

One-dimensional (1D) SnO2 nanowires were synthesized from SnO powder by heat treatment of SnO powder under Ar gas flow at atmospheric pressure, with the next annealing on the air at 1000 °C. The morphology and microstructure of the single crystalline SnO2 nanowires are characterized by means of the X-ray diffraction (XRD) and scanning electron microscopy (SEM). The band gaps of the products are ~(3.42–3.78 eV) determined from UV/visible absorption spectral results. The SnO2 nanowires show stable photoluminescence (PL) with one emission peak centred at around ~2 eV.

A comparative study of the low temperature conductivity of an ensemble of multiwall carbon nanotubes and semiconductor nanowires is presented. The quasi one-dimensional samples are made in nanoporous templates by electrodeposition and CVD growth. Three different structures are studied in parallel: multiwall carbon nanotubes,tellurium nanowires, and silicon nanowires. It is shown that the Coulomb blockade regime dominates the electronic transport below 50 K, together with weak and strong localization effects. In the Coulomb blockade regime, a scaling law of the conductance measured as a function of the temperature and the voltage is systematically observed. This allows a single scaling parameter α to be defined. This parameter accounts for the specific realization of the “disorder”, and plays the role of a fingerprint for each sample. Correlations between α and the conductance measured as a function of temperature and voltage, as a function of the perpendicular magnetic field, and as a function of the temperature and voltage in the localized regime below 1 K have been performed. Three universal laws are reported. They relate the coefficient α (1) to the normalized Coulomb blockade conductance $G_{T}(\alpha)$ , (2) to the phase coherence length $l_{\phi}(\alpha)$ , and (3) to the activation energy $E_{a}(\alpha)$ . These observations suggest a description of the wires and tubes in terms of a chain of quantum dots; the wires and tubes break into a series of islands. The quantum dots are defined by conducting islands with a typical length on the order of the phase coherence length separated by poorly conducting regions (low density of carriers or potential barriers due to defects). A corresponding model is developed in order to put the three universal laws in a common frame.


The effect of structural disorder under bias voltage on the transmission properties of a non-interacting electron across multibarrier systems (GaAs/Alx Ga $_{1-x}$ As) is exhaustively studied by a computational model using exact Airy function formalism and the transfer-matrix technique. In ordered systems we study the effect of bias voltage on miniband structure. For disordered structures we investigate the transmission coefficient. Different types of eigenstates are obtained, those having a very low Lyapunov exponent close to the resonant energy and those with high slope in other region. Commuting resonance energy is theoretically demonstrated in this paper, the obtained values are in good agreement with the existing numerical results.

We report a novel technique to broaden and reshape the spectrum of picosecond laser pulse based on the seeder of gain switch laser diode and Yb3+-doped fiber amplifier (YDFA). From compensating the seed spectrum with the gain of YDFA, the seed pulse of 7 nm bandwidth is broadened to 20 nm, and the flat top spectral shape is obtained as well. A self-made fiber coupled tunable filter is used to realize the tunable output laser with the wavelength range from 1053 nm to 1073 nm and the line width of 1.4 nm.

This study reports our numerical simulation of light extraction efficiency enhancement for a single quantum well by Extraordinary Optical Transmission (EOT) induced by a silver plate with air slit array. Our numerical experiment indicates that the enhancing effect could depend on a series of factors, namely, the nature of EOT, the polarizations and the positions of the quantum wells. Only by using TM polarized source significant enhancement can be achieved, and the enhancement excited by Fabry-Perot resonance is greater than that by surface plasmon polaritons; yet moving the source off the Ag/GaN interface will have the enhancement weakened. Position of the source, to be specific, either below an air slit or a silver strip, can lead to quite different results; and the greatest enhancement occurs when the source is placed right below the air slit.

Angle-resolved reflection spectroscopy is used to study surface plasmon polariton modes of metallic gratings consisting of sub-wavelength grooves. The used optical set-up allows recording of zero and m = −1 order reflection spectra in the visible and near infra-red spectral region. The different modes and their mutual coupling was identified in the dispersion diagram by means of modal theory. Surface plasmon modes at the grating surface and cavity modes in the sub-wavelength grooves were evidenced.

Two simulation methods of the energy transmitted by the arc roots to the electrode material are described and their results are compared together and with these found by other authors. About a copper electrode the time phase evolutions are given when a constant energy flux is applied to the contact surface. The obtained results are better for vacuum and small current. The cathode and anode result discussions lead to propositions to improve arc root models.

Piezoelectric elements can be used to harvest electrical energy when impact forces are applied to their surfaces. Often, however, only the peak voltages, or peak power output is used as a measure of device performance, and the total energy harvested during an impact force is overlooked. For energy harvesting applications, such as small-scale piezoelectric batteries, the total energy generated over an impact cycle should be considered. In this paper the total energy efficiency of several commercially available piezoelectric materials are evaluated using impact testing. The results revealed that different materials have significantly different energy efficiencies due to factors such as material type and device construction. Further, it was found that peak power output is not always the most appropriate measure of device performance for energy conversion applications.