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Notes: An inhomogeneous laminar conductor model developed earlier has been applied to glasses in the system Na2O-GeO2. Detailed modulus spectra have been measured for glasses containing 10–20 mol % Na2O. The experimental data are in satisfactory agreement with the theoretical values as obtained by this model.

Notes: Highly conductive phosphorus-doped n-type hydrogenated microcrystalline silicon (μc-Si:H) films have been prepared by the usual (13.56 MHz) radio-frequency glow discharge of silane (SiH4), phosphine (PH3), and hydrogen (H2) in an ultrahigh-vacuum deposition system. The highest conductivity of the films obtained in this study is 100 S cm−1 after optimizing the hydrogen dilution ratio, chamber pressure, substrate temperature, and doping concentration of phosphorus. The formation of microcrystallinity in the material has been studied by transmission electron microscopy, x-ray-diffraction studies, and Raman spectroscopy. The volume fraction of microcrystallinity in these amorphous-microcrystalline mixed-phase materials has been estimated from Raman spectra. Sizes of the crystallites and volume fraction of microcrystallinity vary with hydrogen dilution, chamber pressure, and substrate temperature. The variations in the properties with deposition parameters have been explained in terms of the growth kinetics. The n-type μc-Si:H thin film, thus developed, has been applied in the first cell of a double-junction amorphous silicon solar cell. The prepared p-i-n–p-i-n stacked cell employing the n-type μc-Si:H film has exhibited appreciable improvement in open-circuit voltage, fill factor, and efficiency compared to the one with amorphous n layer in the inner n–p contact. Degradation of the cells prepared with and without μc-n layer has been studied. © 1995 American Institute of Physics.

Notes: Composite materials containing conducting polypyrrole and insulating poly (vinyl methyl ether) (PVME) have been synthesized by oxidative polymerization of pyrrole in ethanol using FeCl3 oxidant in the presence of PVME. The ac conductivity measurements have been carried out in the frequency range of 100 Hz to 10 MHz and in the temperature range of 110 to 350 K. The frequency dependent conductivity has been explained on the basis of a small polaron tunnelling mechanism. © 1997 American Institute of Physics.

Notes: Temperature-dependent quantum efficiency in the device structure indium-tinoxide/[(2-methoxy-5(2′-ethylhexyloxy-)-p-phenylenevinylene)]/Ca/Al has been investigated over the temperature range from 20 to 296 K. A blueshift is observed in the electroluminescence spectra with an increasing temperature or voltage. From Fourier transform infrared spectra and UV-visible analyses have been observed that the conjugated length of the polymer chain decreases due to photo oxidation under UV component of sun light. The change in band gap resulting from the change in the conjugated length causes the observed blueshift. Quantum efficiency increases with decreasing temperature partly because of the enhancement of photoluminescence efficiency and partly because of the improved balance of holes and electrons. At a fixed temperature, an optimum voltage is required to obtain the maximum efficiency, and with increasing temperature, this voltage increases. © 2001 American Institute of Physics.

Notes: The microstructural dependence of electrical properties of (Ba, Sr)TiO3(BST) thin films were studied from the viewpoint of dc and ac electrical properties. The films were grown using a pulsed laser deposition technique in a temperature range of 300 to 600 °C, inducing changes in grain size, structure, and morphology. Consequently, two different types of films were realized, of which type I, was polycrystalline, multigrained, while type II was [100] oriented possessing a densely packed fibrous microstructure. Leakage current measurements were done at elevated temperatures to provide evidence of the conduction mechanism present in these films. The results revealed a contribution from both electronic and ionic conduction. In the case of type I films, two trapping levels were identified with energies around 0.5 and 2.73 eV, which possibly originate from oxygen vacancies VO¨ and Ti3+ centers, respectively. These levels act as shallow and deep traps and are reflected in the current–voltage characteristics of the BST thin films. The activation energy associated with oxygen vacancy motion in this case was obtained as 1.28 eV. On the contrary, type II films showed no evidence of deep trap energy levels, while the identified activation energy associated with shallow traps was obtained as 0.38 eV. The activation energy obtained for oxygen vacancy motion in type II films was around 1.02 eV. The dc measurement results were further elucidated through ac impedance analysis, which revealed a grain boundary dominated response in type I in comparison to type II films where grain response is highlighted. A comparison of the mean relaxation time of the two films revealed three orders of magnitude higher relaxation time in the case of type I films. Due to smaller grain size in type I films the grains were considered to be completely depleted giving rise to only grain boundary response for the bulk of the film. The activation energy obtained from conductivity plots agree very well with that of dc measurements giving values 1.3 and 1.07 eV for type I and type II films, respectively. Since oxygen vacancy transport have been identified as the origin of resistance degradation in BST thin films, type I films with their higher value of activation energy for oxygen ion mobility explains the improvement in breakdown characteristics under constant high dc field stress. The role of microstructure in controlling the rate of degradation is found useful in this instance to enhance the film properties under high electric field stresses. © 2000 American Institute of Physics.

Notes: Fractal growth of metallic silver within a polymer matrix has been induced by chemical reduction of a suitable sol. A fractal dimension of 1.73±0.01 over a length scale 100–10 000 nm has been estimated. The fractal structure consists of an aggregation of nanosized silver particles having diameters of the order of 15 nm. Electrical conductivity of these nanoparticles shows a lowering of the effective Debye temperature as the particle size is reduced.

Notes: Silver nanowires of diameter ∼40 nm and length ∼0.3 mm have been grown by electrodeposition within the pores of silica gels which were heat treated in the temperature range 523 to 823 K and, subsequently, soaked in a silver nitrate solution. A staircase current–voltage characteristic was observed in the direction of electrodeposition after nanowires were disrupted by the application of a dc voltage pulse. Such gels containing interrupted nanowires of silver showed a dielectric constant value ∼104 both in directions parallel and perpendicular to that of electrodeposition. © 2000 American Institute of Physics.

Notes: Silver nanowires of diameter ∼2 nm and length ∼2 mm have been grown by an electrodeposition method within a polyvinyl alcohol film subjected to a two-stage treatment, viz., in ammonium persulphate and pyrrole solutions, respectively. A staircase current–voltage characteristic has been measured in this composite. Also, the material shows a dielectric constant ∼104. Both these effects are observed when the applied electric field is in a direction perpendicular to that of the electrodeposition process. © 2000 American Institute of Physics.

Notes: A large reduction in the leakage current behavior in (Ba, Sr)TiO3 (BST) thin films was observed by graded-layer donor doping. The graded doping was achieved by introducing La-doped BST layers in the grown BST films. The films showed a large decrease (about six orders of magnitude) in the leakage current in comparison to undoped films at an electric field of 100 kV/cm. The large decrease in leakage current was attributed to the formation of highly resistive layers, originating from compensating defect chemistry involved for La-doped films grown in oxidizing environment. Temperature-dependent leakage-current behavior was studied to investigate the conduction mechanism and explanations of the results were sought from Poole–Frenkel conduction mechanism. © 2001 American Institute of Physics.