A study of single injection space-charge-limited current flow in insulator with two sets of traps distributed in energy is presented for a particular situation in which the energy separation of the two sets of traps is too small to give rise a current-voltage characteristic with maximum structure. The current-voltage characteristic is obtained in a simplified way with the help of regional approximation method. The obtained J-V characteristic is compared with previously reported experimental work on p-type GaSe sample. The comparison shows very good agreement between theoretical and experimental result, confirming the correctness of the analysis.

Single crystalline wurzite GaN nanorods are successfully synthesized on the tantalum catalyzed Si substrate by RF magnetron sputtering. The products are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectra (FTIR), transmission electron microscopy (TEM), selected-area electron diffraction (SAED) and photoluminescence (PL). The results show that the nanorods have a hexagonal wurtzite structure with diameters ranging from 80 to 200 nm and lengths typically up to 10 µm. The PL spectrum exhibits a strong UV light emission at 364 nm. The growth mechanism of the crystalline GaN nanorods is discussed briefly.

Amorphous Se70Te30–x Cdx (x = 0, 10) are obtained by thermal evaporation under vacuum of bulk materials on pyrographite and glass substrates. The I – V characteristic curves for the two film compositions are typical for a memory switch. They exhibited a transition from an ohmic region in the lower field followed by non-ohmic region in the high field region in the preswitching region, which has been explained by the Poole-Frenkel effect. The temperature dependence of current in the ohmic region is found to be of thermally activated process. The mean value of the threshold voltage $\bar{V}_{th}$ increases linearly with increasing film thickness in the thickness range (100–491 nm), while it decreases exponentially with increasing temperature in the temperature range (293–343 K) for both compositions. The results are explained in accordance with the electrothermal model for the switching process. The effect of Cd on these parameters is also investigated.

The characteristics of organic light-emitting devices based on tris-(8-hydroxyquinoline) aluminum (Alq3) with NaCl thin films inserted at both anode/organic and organic/cathode interfaces are investigated. We optimize the thicknesses of NaCl at both interfaces, and we get the optimal device with the structure of ITO/NaCl(2.0 nm)/N,N'-bis(1-naphthyl)-N,N'-diphenyl-1,1' biphenyl-4,4'-dimaine(NPB)/Alq3/NaCl(2.0 nm)/Al. The device shows much better electroluminescent (EL) performance than that of the as-stated standard device with only LiF buffer layer. The maximal current efficiency and power efficiency is improved by 31% and 67%, the turn-on voltage is also reduced from 4.2 V for the standard device to 3.1 V for our target device. This is due to enhanced electron injection and blocked hole injection, which results in more balanced hole and electron currents.

The present paper reports on the fabrication of In2O3 layers by oxidation of InN thin films deposited on n-type silicon substrate by magnetron reactive sputtering. The subsequent solar cells using the resulting In2O3/Si heterojunctions exhibit an ideality factor, deduced from current-voltage (I – V) characteristics of around 2.52 at a forward bias of 0.5 V. Other measured parameters were the short-circuit current (I sc ), the open-circuit voltage (V oc ), the maximum output power (P m ), the fill factor (FF) and the efficiency (η ), which had values of were 3.17 mA, 0.75 V, 0.869 mW, 0.365 and 9.66 %, respectively, under AM 1.5 illumination. The value of series resistance was around 107 Ω. In2O3 films formed by the oxidation of InN have a higher open-circuit voltage than In2O3-based solar cells formed by the oxidation of indium.

In2S3 thin films were deposited by flash evaporation of In2S3 powder. The effect of annealing in vacuum and under sulphur and oxygen atmosphere on the structural, compositional and optical properties of these films was investigated. X-ray diffraction studies reveal that the as-deposited films are amorphous. The formation of β-In2S3 phase is obtained after annealing under vacuum at 693 K or under sulphur pressure at a lower annealing temperature (573 K). The EDAX analysis reveals that the sulphurized films are nearly stoichiometric and those annealed in vacuum are sulphur deficient. Optical transmission spectra showed a slight shift of the absorption edge towards lower wavelengths. The optical gap value varied between 2.4 and 3 eV as a function of the film thickness, the annealing temperature and the atmosphere ambient.

TiO2 thin films were synthesized by the sol-gel method and spin coating process. The calcination temperature was changed from 100 to 550 °C. XRD patterns show increasing the content of polycrystalline anatase phase with increasing the calcination temperature. The AFM results indicate granular morphology of the films, which particle size changes from 22 to 166 nm by increasing the calcination temperature. The RBS, EDX and Raman spectroscopy of the films show the ratio of Ti:O ~0.5, and diffusion of sodium ions from substrate into the layer, by increasing the calcination temperature. The UV-vis spectroscopy of the films indicates a red shift by increasing the calcination temperature. The contact angle meter experiment shows that superhydrophilicity of the films depends on the formation of anatase crystal structure and diffused sodium content from substrate to the layer. The best hydrophilicity property was observed at 450 °C calcination temperature, where the film is converted to a superhydrophilic surface after 10 min under 2 mW/cm2 UV irradiation. Water droplet on TiO2 thin film on Si(111), Si(100), and quartz substrates is spread to smaller angles rather than glass and polycrystalline Si substrates under UV irradiation.

We report the influence of an exciton-blocking layer and/or an Al2O3 thin layer at the interface “organic acceptor/aluminium” on the efficiency of CuPc/C60 based photovoltaic cells. The presence, or not, of a thin Al2O3 layer depends on the encapsulating process of the devices. In the case of glass/ITO/CuPc/C60/Al cells, the presence of an Al2O3 thin layer at the interface “organic acceptor/aluminium” increases strongly the open circuit voltage of the cells but decreases slightly their short circuit current and fill factor. In the case of glass/ITO/CuPc/C60/Alq3/Al cells, the open circuit voltage is systematically higher than without Alq3. However, in that case, the presence of Al2O3 does not improve significantly the cell performances. All these results are discussed in terms of series and shunt resistance values related to possible oxygen contamination and organic covalent action with the Al films. The effectiveness of these different phenomena depends on the presence, or not, of Alq3 and/or Al2O3 layers.

An attempt was made to widen the photosensitivity spectral range of poly(3-hexylthiophene)-fullerene blend by adding an extra electron donor — a newly synthesized soluble phthalocyanine derivative (SnClPc) having the electron absorption band at 708 nm. As the electron acceptor, home-synthesised di(ethoxycarbonyl) methano-fullerene carboxylate (C61(CO2Et)2) was used, and as the hole transporter — the regioregular poly 3-hexylthiophene (P3HT). The sandwich-type samples were prepared on an ITO glass substrate by coating it with a 30–50 nm thick PEDOT:PSS layer followed by a ~100 nm thick P3HT:C61(CO2Et)2:SnClPc blend. For the top electrodes In or Au were used. Spectral dependences of the PV effect and of the influence of external magnetic field (0–3000 Oe) on it were studied in the 370–1000 nm spectral range in vacuum of ~10-6 Torr. Significant photosensitivity of the blend was observed in the 370–800 nm spectral range. However, the short-circuit photocurrent quantum efficiency evaluated for absorbed light was found to be 4 times higher for illumination in the P3HT absorption band as compared with that in the SnClPc band. The observed magnetic field effect shows that the low IPCE values may be explained by the space charge formation in the samples, leading to a strong geminate recombination of CP states.

In this paper, a new type PCF with three different air-hole diameters in cladding region is proposed and investigated by using a compact 2-D finite difference frequency domain (FDFD) method with anisotropic perfectly matched layers (PML) absorbing boundary conditions. Through numerical simulation we found that by optimizing the geometrical parameters, our proposed structure with fewer of air-hole rings greatly meets the performance criteria such as ultraflattened dispersion and low confinement loss, which is highly instructive for designing photonic crystal fibers.

We present results on the realization of a multicolour microspherical glass light source fabricated from the erbium doped fluoride glass ZBLALiP. Whispering gallery mode lasing and upconversion processes give rise to laser and fluorescent emissions at multiple wavelengths from the ultraviolet to the infrared. Thirteen discrete emissions ranging from 320 to 849 nm have been observed in the upconversion spectrum. A Judd-Ofelt analysis was performed to calculate the radiative properties of Er3+:ZBLALiP microspheres, including the radiative transition probabilities, the electric dipole strengths, the branching ratios and the radiative lifetimes of the transitions involved. We have also identified the primary processes responsible for the generation of the observed wavelengths and have shown that this material has an improved range of emissions over other erbium doped fluoride glasses.

The purpose of this work is to study the formation of hydroxyapatite (Ca10 (PO4)6(OH)2) on the surface of glass 48S4 with chemical composition: SiO2: 48%, CaO: 30%, Na2O: 18% and P2O5: 4% in weight ratio. This selected composition presents phosphorus contributions lower than that in Bioglass® [Hench et al. J. Biomed. Mater. 36, 117 (1971)] developed by L. Hench. Comparison of the kinetic formation of hydroxyapatite on the glass surfaces of these two biomaterials was made.The Material was prepared by melting and rapid quenching. It shows a bioactive character. This phenomenon is confirmed by the “in vitro” formation of hydroxycarbonate apatite (HCA) layer on the surface of glassafter immersion in the Simulated Body Fluid (SBF). Before immersion in SBF, The proposed composition of glass was analyzed using several physicochemical methods like XRD, FTIR, SEM, and EDS confirming the composition and its amorphous state well. The pellets were soaked in SBF for 2 h, 1, 3, 7 and 15 days at 37 °C. The analyses of SBF after each immersion time were carried out using ICP-OES method. Results show important exchanges of ions between the surface of glass and the SBF. They revealed the formation of an amorphous CaO-P2O5- rich layer on the surface of the specimens after 1 day in the solution and a crystalline HCA layer after 3 days immersion time as will be shown by XRD, EDS and FTIR analysis. The cristallinity increases with immersion time. After 15 days immersion in SBF liquid, the specimens are still fully covered by hydroxycarbonate apatite (HCA) layer.

In Tip-Enhanced Raman Spectroscopy (TERS) a metal (or metallized) sharp tip is used to enhance the electromagnetic field by a localized surface-plasmon excitation. Two different modes – atomic force mode (AFM) and scanning tunneling mode (STM) – together with their respective types of probe tips are used in TERS experiments. We have compared the efficiency in enhancing the Raman signal on a thin dye layer for metal-coated AFM tips as well as for electrochemically etched metal STM tips. A much higher enhancement factor and better reproducibility were found when using STM tips. The very different performance is mainly attributed to the more efficient plasmonic excitation when using bulk-metal tips and possibly to the morphological differences in the tip and apex shapes existing between the two tip types.

Structure, wetting, mechanical and electrical transport properties of tin- (2.5, 3.5, 5 and 10) wt.% silver alloys have been investigated. The results showed that, addition of silver to pure tin causes more precipitations of the intermetallic compound Ag3Sn. A new intermetallic compound Ag4Sn has been formed with adding Ag more than 3.5 wt.%. This compound causes continuous increase in the Young's modulus and electrical resistivity. While for the wetting measurements, additions of silver to pure tin up to 5 wt.% reduces the contact angle. Above that, the contact angle increases due to more precipitations of Ag–Sn compounds, which may tend to reduce the adhesive forces between molten alloys and the substrate.

Both the reflection and transmission coefficients of oil palm fruits of various moisture contents have been measured using a rectangular dielectric waveguide (RDWG) technique in the frequency range between 8 GHz and 12 GHz. Good agreement between predicted and measured values of reflection coefficient suggests the potential of RDWG technique as a new, fast and accurate method for the determination of moisture content in oil palm fruits.

Literature shows a lack of works based on non-invasive methods for computing the propagation coefficient γ, a complex number related to dynamic vascular properties. Its imaginary part is inversely related to the wave speed C through the relationship $C=\omega/{\rm Im}(\gamma)$ , while its real part a, called attenuation, represents loss of pulse energy per unit of length. In this work an expression is derived giving the propagation coefficient when assuming a pulsatile flow through a viscoelastic vessel. The effects of physical and geometrical parameters of the tube are then studied. In particular, the effects of increasing the reflection coefficient, on the determination of the propagation coefficient are investigated in a first step. In a second step, we simulate a variation of tube length under physiological conditions. The method developed here is based on the knowledge of instantaneous velocity and radius values at only two sites. It takes into account the presence of a reflection site of unknown reflection coefficient, localised in the distal end of the vessel. The values of wave speed and attenuation obtained with this method are in a good agreement with the theory. This method has the advantage to be usable for small portions of the arterial tree.

A comprehensive integrated model of stochastic convective transport in a solidifying binary melt is presented in this work. The detailed transport phenomena in the particle and bulk phases are coupled together through a stochastic Eulerian-Lagrangian formalism, capturing the physical mechanisms and consequences of particle agglomeration, de-agglomeration, and the underlying hydrodynamic interactions. The interactions between random thermo-fluidic fluctuations in the continuum carrier phase and the associated growth/dissolution of particle phases are modeled by employing a Langevin formalism. Representative case studies highlighting the implications of the dynamics of the fragmented dendrites on the overall convective patterns in an electromagnetically-stirred semi-solid binary melt are subsequently presented, so as to emphasize on the comprehensive physical bases and to illustrate the fundamental approach of the present predictive methodology.