The present paper reports the measurements on space charge limited conduction in amorphous thin films of Ge20Se $_{80-x}$ Agx (x = 0, 10, 15, 20). I−V characteristics have been measured at various fixed temperatures. These characteristics show that, at low electric fields, an ohmic behaviour is observed. However, at high electric fields (E ~ 104 V/cm), the current becomes superohmic. At high fields (104 V/cm), current could be fitted to the theory of space charge limited conduction (SCLC) in case of uniform distribution of localized states in the mobility gap of these materials. Using the theory of SCLC for the uniform distribution of the traps, the density of localized states near Fermi level is calculated. It is observed that, on addition of Ag in Ge20Se80 alloy, density of localized states first increases till 10 at% of Ag and then decreases.

The intersubband absorption in symmetric double quantum wells under the laser field is theoretically calculated within the framework of the effective mass approximation. Results obtained show that intersubbband optical transition and energy levels in double quantum well can significantly be modified and controlled by intense laser field. This statement gives a new degree of freedom in various device applications based on the intersubband transition of electrons.

Thin films of AgInTe2 were prepared on quartz substrates by a flash evaporation technique at substrate temperature ~303 K. The compositions of both the bulk and thin films, with thickness (~208–350 nm), were checked using energy dispersive X-ray spectroscopy (EDX). X-ray diffraction (XRD) measurements showed that AgInTe2 compound is characterized by a tetragonal structure while the as deposited films have amorphous nature. On annealing at 423 and 573 K (for two hours and under vacuum ~10−3 Pa), the films were identified to be single-phase, polycrystalline with a preferred (112) orientation. The optical properties of the films were investigated using spectrophotometric measurements of transmittance and reflectance at normal incidence in the wavelength range (~500–2500 nm). The refractive index (n) and the absorption index (k) of AgInTe2 were determined from the absolute values of the measured transmittance and reflectance. It was found that both (n) and (k) depend markedly on the temperature of heat treatment. The dispersion of refractive index in AgInTe2 was analyzed using the concept of the single oscillator model. Within this concept some dispersion parameters were determined for as deposited and annealed flash evaporated AgInTe2 films at 423 K for 2 h. The calculated values of β indicated that AgInTe2 films belong to ionic class. The ratio of the free carrier concentration to the effective mass (N/m*) were, also determined. The analysis of the absorption coefficient indicated that, this ternary chalcopyrite compound has three allowed direct transitions corresponding to three energies gaps Eg 1, Eg 2 and Eg 3. The crystal field (Δcf), the spin orbit (Δso) and the deformation potential (b) were calculated for both as deposited and annealed flash InAgTe2 films at ~423 K for 2 h.

In our previous work we investigated numerically the influence of the steric properties of conducting particles in a non-conducting host matrix on the electrical conductivity threshold of the material, especially in regard to the shape and orientational order of the particles. In the present work we consider theoretically some additional geometrical aspects of the percolation problem. As regards the percolation threshold itself, we consider three aspects: the probability of inter-penetration of half-soft conducting particles for different penetration depths (penetration probability function), different kinds of inhomogeneous distribution of particles in non-conducting host, size effects, and the agglomeration of conducting particles. We also analyze the size of the conducting-particles' clusters below and above the percolation threshold and compare some characteristic critical exponents with the results in the literature.

Anisotropic etching of silicon is achieved in the presence of ultra-violet exposure in a solution containing hydrofluoric/nitric/acetic acids (HNA). The HNA solution is typically used for polishing silicon and etching polysilicon due to its isotropic etching property. In the technique proposed in this paper which is called UV-HNA, the etching of silicon is enhanced in the direction determined by UV exposure. A mixture of HF/HNO3/CH3COOH with a relative composition of 1:15:5 seems suitable for revealing 〈111〉 planes with an etch rate of 10 μm/h at 35 °C. The bottom of the etched craters is hillock-free and etch rates as high as 60 μm/h can be achieved using higher concentration of HF acid in HNA solution. In the latter case the etching is more isotropic and mask undercut is observed. Also membranes with a depth of 400 μm are fabricated on n-type Si 〈100〉 with a thickness of 500 μm by means of standard 34 wt% solution of KOH at temperature of 60 °C. Problems encountered during the experiment, and their solutions are discussed and results of these experiments are reported.

We have study the effect of Tin impurity and Swift heavy ion irradiation on the optical properties of the chalcogenide thin films. Thin films are prepared by thermal evaporation technique and irradiated by swift heavy ion beam of 60 MeV Si5+ ion with influence of 5 × 1012 ions/cm2. The SHI induced structural and optical changes in the thin films due to which optical band gap decrease. Reduction of the optical band gap is may be due to increase the defect states near to the band tails in the band gap on irradiation.

We present results concerning the carrier transfer between In(Ga)As quantum rings in a stacked multilayer structure, which is characterised by a bimodal size distribution. This transfer of carriers explains the observed temperature behaviour of diode lasers based on that kind of stacked layer structures. The inter-ring carrier transfer can be possible by phonon assisted tunnelling from the ground state of the small-ring family towards the big-ring family of the bimodal size distribution. This process is thermally activated in the range 40–80 K.

Indium oxide (In2O3) violet photodiodes were fabricated. The In2O3 layers were from oxidation of InN deposited by magnetron reactive sputtering. It was found the photocurrent approximately 5.06 × 10−4 A at a bias of 2 V and a photocurrent to dark current contrast ratio higher than around two orders of magnitude. The reverse leakage current prior to breakdown is around 10−5 A. The photodiodes exhibited a narrow responsive region at wavelength from 400 nm to 440 nm. The values of responsivity and quantum efficiency (QE) at 420 nm at biases of 2 V were 0.1985 A/W and 58.62%, respectively.

Modification of the non-assisted gas flow-line across the target surface in a Grimm-type glow discharge source is described. The new flow–line permits the gas to flow through a cylindrical annular space ending with a disc-space annular gap, facing the target surface. This configuration would cause directed jet assisted gas flow rays to impinge on infinite points across the cathode surface. Improvement has been achieved in the V-I characteristics where $\DeltaV$ / $\Delta I$ increases from 1.8 to 3.5 V/mA. The sputtering as well as simultaneous deposition rates, have been increased by a factor of 16 and 17 respectively. These roll over with increasing sputtering time, their maximum values at a characteristic time, t oc of 21 min. The t oc value was constant for different operating parameters provided that the source geometry assembly is kept fixed. The presence of a glass substrate in the anode cavity has, apparently, no effect on the obtained data. Improvements have also been achieved in the crater profile, characterized by an approximately flat crater bottom with nearly vertical walls, and less re-deposited particles on the crater depth and edge. Fixing the distance Z of the substrate from target surface, along the cell axis, and varying the deposition time from 1 to 30 min, a sequence of changes in the deposited film were observed by X-ray diffraction and energy dispersion X-ray (EDX). These changes start with an amorphous structure, followed by the appearance of Cu and Zn crystallites and a probable deposition of Cu5Zn8 clusters. The profile of the number of sputtered particles at different Z values is characterized by a number of peaks and troughs. This behavior has been explained by the occurrence of local cluster-dissociation and formation, by different collision processes. The improvements achieved by the application of the present jet assisted gas flow can be of value in the analytical application of this type of glow discharge.

The thermal conductivity and the interface thermal contact resistance of four different in thickness CuO films, obtained by PVD on a tungsten carbide substrate were investigated with a developed modulated photothermal method based on infrared measurement. According to the knowledge of the substrate thermophysical properties, the gain between the thermal perturbation and the response of the sample was used as the experimental data. The results show the dependence of the effective longitudinal thermal conductivity on the film thickness. Scanning electron microscopy observations reveal the strong anisotropy and columnar structure of the deposits. Moreover, the chemical composition of films was tested. A similar composition for each film was also verified.

Hydrogen diffusion is monitored during plasma conditions corresponding to the growth of polymorphous and microcrystalline silicon thin films in the temperature range from 50 to 300 °C. Structural changes of the films were monitored in situ by Spectroscopic Ellipsometry measurements and interpreted with the Bruggemann Effective Medium Approximation along with the Tetrahedron Model. For both materials, diffusion of hydrogen leading to the formation of a hydrogen-rich subsurface layer during the first minute of exposure to the hydrogen plasma is observed. This initial phase was followed by a steady-sate regime during which the thickness of the subsurface layer stayed relatively constant and the total film thickness decreased as a function of time. This steady-state is explained as the result of the equilibrium between hydrogen diffusion and etching. The hydrogen diffusion coefficient and etching rate were calculated from these measurements and found to be higher in amorphous than in polymorphous silicon. This result is consistent with the growth dynamics of polymorphous silicon. It also provides information concerning the nucleation of micro-crystallites in amorphous silicon under very large atomic hydrogen flow conditions. Moreover, it also explains why polymorphous silicon films do not undergo the phase transition to microcrystalline, even if deposited under relatively similar large atomic hydrogen flow conditions.

In spite of the extensive experimental investigations reported in the literature on porous alumina templates, the theoretical mechanisms, and their dependence on process parameters such as potential difference, current density and electrolytes, are not well understood. A theoretical model developed and published for porous structure formation under constant current electrochemical anodization of aluminum is adopted for constant voltage anodization. The model is based on the rate equation approach in which both the alumina formation and etching are considered. The model employs a minimal number of parameters and yet captures the essence of the experimental observations. The model yields an analytical solution relating the model parameters, process parameters and thickness of the film, which is easy to interpret and use. The results of normalized current versus time obtained from the model are in good agreement with the experimental results reported for a range of voltages, 20–40 V. It is also observed that the thickness of the Al2O3 pore follows V 1/2 behavior for anytime during the anodization.

Manganese-doped cadmium sulfide nanoparticles are synthesized in a flexible polymer matrix (synthetic rubber) by a chemical route. They are bombarded with 80-MeV oxygen ions having electronic energy loss (S e ) dominant over nuclear energy loss (S n ) and with fluence variation 1011–1013 ions/cm2. Piling up of nanoparticles along certain direction was observed in atomic force microscopy (AFM) images of irradiated samples. Such elongated nanostructures are as a result of nanoparticle growth during ion passage through the samples. Specifically, elongated structures in the form of nanoneedles, nanochannels and nanorods have been observed. The fluence dependent photoluminescence spectra (PL) show significant luminescent peaks at 445 nm and 706 nm, respectively which are tunable with ion fluence. Such a tunability could be promising as lasing materials in nano-luminescent devices and laser diodes. Further, detection of efficient third harmonic generation (THG) in these samples (by using irradiation of a Cr:fosterite laser) could be promising in nanoscopy and nonlinear optics.

We examine numerically the effect of quasiperiodicity in the nature of the states in Fibonacci semiconductor superlattices by means of the transfer matrix formalism. We are interested in the GaAs/Alx Ga1 − x As layers, having identical thickness, where the aluminium concentration x takes, two different values. We have found that each miniband of the periodic superlattice splits in several sub-minibands, that is small minigaps appear. We demonstrate that the origin of these small inner minigaps is due to the loss of long-range quantum coherent of the electrons wave. The corresponding electronic spectrum shows a high fragment. The states having transmission coefficient close to zero in the minibands can be viewed as consisting of singular localised states.

Transient laser-induced anomalous photovoltaic effect hasbeen studied in La0.8Sr0.2MnO3 films grown on theSrTiO3 (001) substrates by laser molecular beam epitaxy. It isdemonstrated that the signal polarity is reversed when the films areirradiated through the substrate rather than at the air/filminterface. The microstructures in these films are clarified in termsof the oriented microdomains with their (101) plane parallel to thesubstrate surface, suggesting off-diagonal Seebeck effect plays animportant role for our observation. From the results, we obtain theanisotropy of the thermoelectric power $\Delta S=S_{ab}-S_{c}=0.3~\mu$ V/K, where S ab and S c are the ab-plane and c-axis Seebeck coefficients.

Reactively evaporated TiO2 thin films were deposited on the glass substrate by electron beam heating technique. In the first stage evaporation rates are varied keeping substrate temperature fixed at 200 °C and oxygen flow rate at 9.0 sccm for all the samples. The deposition rates were varied from 0.12–0.20 nm/s with a step of 0.02 to optimize the optical constants for the film in the wavelength band of 380–850 nm as a high index material for multilayer optical coatings and filters. The films prepared at higher deposition rates have shown low refractive index values and comparatively higher extinction coefficients for the given substrate temperature in the desired spectral range. The best optical constants were observed for the sample prepared at 0.12 nm/s (at λ = 550 nm: n: 2.39 and k: of the order of 10−9). However, the variation in refractive index for all the samples was found to be in the range of 2.39–2.21 at 550 nm. In the second stage, films were prepared at a fixed deposition rate of 0.12 nm/s at different substrate temperature (50 °C, 100 °C, 150 °C and 200 °C) to study the optical properties of the films as a function of substrate temperature in order to investigate the potential of TiO2 film application as medium index layer. It was observed that refractive index decreases with decreasing substrate temperature. However, it was not found true for absorption. Instead, at Ts = 50 °C extremely low absorption (of the order of 10−5) has been observed with refractive index of 1.83, which increased sharply for next higher substrate temperature. Variation in absorption characteristics is found with varying substrate temperatures. The result shows that TiO2 films can be used as high and medium index layer in optical coating by varying the deposition parameters during growth. Effectively, one can achieve performance of two materials with only one. This effect could be utilized to produce variable index layers and coatings. Two samples with best high and medium optical constant values, were further investigated using Atomic force microscopy (AFM), X-ray diffraction (XRD) and scanning electron microscopy (SEM) for surface and structure analysis. The results show that the particle size for the film is very small (10–20 nm), and the surface appears to be very compact, smooth and free of pinholes with roughness in angstrom range, extremely suitable for optical applications in single and multilayer structures.

In this paper an analysis of optical fiber chromatic dispersion in noisy interferometric system is introduced. The interferometric relative intensity noise (IRIN) is derived in interferometric systems, by considering all effects such as the optical fiber chromatic dispersion and white noise applied to light from a laser diode. The direct relative intensity noise (RIN) is compared with the RIN caused by phase-to-intensity noise conversion. Numerical calculations reveal that the optical fiber chromatic dispersion can enhance significantly the IRIN magnitude and lead to a shift of the IRIN dips. The results can be employed to estimate the influence of the chromatic dispersion in phase-to-intensity noise conversion, which use either self-delayed interferences or interferometers.

Developing the ability to characterize photon statistics of light sources has been one of the important driving forces of Quantum Optics. Photon statistics is also a crucial parameter to evaluate of quantum key distribution security. As practical quantum cryptographic systems encode information on faint laser pulses, we present a simple method to measure and calibrate their intensity noise with respect to shotnoise reference. The technique is based on the record of photodetection timetags in the photon counting regime. Two different methods are considered to produce light pulse: first, direct pulsing of a laser diode driving current, second, chopping the CW laser beam emitted by a laser diode with an acousto-optical modulator. As predicted by basic Quantum Optics theory, levels of attenuation used in practical quantum key distribution systems lead in both cases to Poissonian photon number distribution in the generated light pulses.

Ba doped PLZT ceramic compositions with formula Pb0.982−z La0.012Δ0.006Baz (Zr0.55Ti0.45)O3 for z = 0 to 6 mole% are synthesized by mixed-oxide method. Powder XRD studies indicate the coexistence of rhombohedral and tetragonal phase in 5 mole% Ba doped PLZT composition. SEM pictures show grain size control as Ba concentration increases in PLZT system. $\varepsilon_{rt}$ and tan δ are increased up to 4 mole% and 5 mole% Ba doped PLZT composition respectively. Dielectric maximum ( $\varepsilon_{T_C}$ ) is decreased to 4 mole% Ba doped PLZT and Curie temperature (T C ) is decreased with increase of Ba concentration in PLZT system. Coercive field (E c ) has shown gradual enhancement over series. Remanent (P r ) and spontaneous (P s ) polarizations are decreased to 5 mole% Ba doped PLZT composition.

Collective effects in the radiation emission via Thomson back-scattering of an intense optical laser pulse by high brightness electron beams are analyzed. The micro-bunching of the electron beam on the scale of the wavelength of the emitted radiation and the consequent free-electron-laser instability may significantly enhance the number of photons emitted. Scaling-laws of the radiation properties, both in the collective and incoherent spontaneous regimes versus laser and electron beam parameters are discussed in the framework of the one-dimensional model.