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Fine powders composed of tellurium grains of average size <10 nm were produced by dry vibration milling combined with liquid-phase sedimentation techniques, starting from polycrystalline powders with average grain diameter of ca. 30 μm. Nanocomposite films were obtained by binding the nanosized tellurium grains with poly(methyl methacrylate). Raman spectroscopy revealed that the films were based on the coexistence of tellurium and tellurium oxide crystalline phases due to a partial oxidation in air of the grains. The optical measurements of the fabricated material showed that the absorbance was nearly constant in the 310–2200 nm range and that a typical UV absorption peak of the nanostructured tellurium was centered at around 260 nm. An extensive characterization of the photoconductivity properties was carried out by illuminating the tellurium-poly(methyl methacrylate) films with white light or radiations of different spectral composition selected from the UV–Vis-NIR region. Data analysis has allowed to demonstrate that the photoresponse is closely related to the optical absorption and is independent of the spectral composition of the incident radiation in the wavelength range from 310 to 2200 nm, while the photocurrent increases linearly as a function of the optical power density over about three orders of magnitude. [ABSTRACT FROM AUTHOR]

Hydrogenated amorphous silicon carbon films were grown by PECVD from silane/methane gas mixtures by fixing the methane ratio in the gas phase and by changing the rf power and pressure. The effects of the discharge parameters on the optical, electrical and structural properties were investigated. These effects were attributed to the variation of carbon content in the film. The analyses enabled us to determine the optimal growth conditions to produce a-SiC:H materials, suitable in solar cell applications, with a good photosensitivity and low defect density of states. [Copyright &y& Elsevier]

The time-resolved photoconductance of amorphous and crystalline LaAlO3/SrTiO3 interfaces, both hosting an interfacial 2-dimensional electron gas, is investigated under irradiation by variable-wavelengths, visible or ultraviolet photons. Unlike bare SrTiO3 single crystals, showing relatively small photoconductance effects, both kinds of interfaces exhibit an intense and highly persistent photoconductance with extraordinarily long characteristic times. The temporal behaviour of the extra photoinduced conductance persisting after light irradiation shows a complex dependence on interface type (whether amorphous or crystalline), sample history and irradiation wavelength. The experimental results indicate that different mechanisms of photoexcitation are responsible for the photoconductance of crystalline and amorphous LaAlO3/SrTiO3 interfaces under visible light. We propose that the response of crystalline samples is mainly due to the promotion of electrons from the valence bands of both SrTiO3 and LaAlO3. This second channel is less relevant in amorphous LaAlO3/SrTiO3, where the higher density of point defects plays instead a major role. [ABSTRACT FROM AUTHOR]

The dark conductivity and Hall mobility of hydrogenated silicon films deposited varying the silane concentration f=SiH4/(SiH4+H2) in a conventional plasma enhanced chemical vapor deposition system have been investigated as a function of temperature, taking into account their structural properties. The electrical properties have been studied in terms of a structural two-phase model. A clear transition from the electrical transport governed by a crystalline phase, in the range 1%<=f<=3%, to that controlled by an amorphous phase, for f>3%, has been evidenced. Some metastable effects of the dark conductivity have been noticed. [ABSTRACT FROM AUTHOR]

We performed an investigation of the variations of the IR absorption peaks as a function of the annealing temperature, Ta, in a-SiC:H alloys. The samples were grown by plasma enhanced chemical vapor deposition using a gas mixture of SiH4+C2H2. We followed the evolution of several peaks during the thermal cycle (i.e. heating from 25 to 250 °C followed by cooling under identical conditions). The analysis of some characteristic parameters of the IR peaks evidences the reversible behavior of the IR absorption as a function of Ta cycles. The link with similar reversible resistivity effects is studied. [Copyright &y& Elsevier]

The effects of rf power on the optical, electrical and structural properties of hydrogenated amorphous silicon-carbon (a-Si[sub 1-x] C[sub x] :H) films deposited by plasma-enhanced chemical vapour deposition from gas mixtures of silane (SiH[sub 4])+ methane (CH[sub 4]) and SiH[sub 4] + acetylene (C[sub 2]H[sub 2]) are reported. It was found that on increasing the rf power there is a marked increase in the carbon incorporation in CH4-based alloys grown in the low-power regime. a-Si[sub 1-x] C[sub x ] :H films with an opticalenergy gap from 1.9 to 2.2 eV were produced and the increasing C content did not affect the disorder and defect density. Furthermore these films can be obtained with a high deposition rate and good electronic properties. On the contrary, in C[sub 2]H[sub 2]-based alloys on increase in the rf power the optical gap and Urbach energy decrease while the photoconductivity increases. These behaviours can be attributed to decreases in both carbon and hydrogen incorporation. However, these alloys have, in the investigated range of the deposition parameters, inferior electrical properties with respect to the CH[sub 4]-based alloys. [ABSTRACT FROM AUTHOR]

Large-area graphitic films, produced by an advantageous technique based on spraying a graphite lacquer on glass and low-density polyethylene (LDPE) substrates were studied for their thermoresistive applications. The spray technique uniformly covered the surface of the substrate by graphite platelet (GP) unities, which have a tendency to align parallel to the interfacial plane. Transmission electron microscopy analysis showed that the deposited films were composed of overlapped graphite platelets of different thickness, ranging from a few tens to hundreds of graphene layers, and Raman measurements provided evidence for a good graphitic quality of the material. The GP films deposited on glass and LDPE substrates exhibited different thermoresistive properties during cooling–heating cycles in the −40 to +40 °C range. Indeed, negative values of the temperature coefficient of resistance, ranging from −4 × 10−4 to −7 × 10−4 °C−1 have been observed on glass substrates, while positive values varying between 4 × 10−3 and 8 × 10−3 °C−1 were measured when the films were supported by LDPE. These behaviors were attributed to the different thermal expansion coefficients of the substrates. The appreciable thermoresistive properties of the graphite platelet films on LDPE could be useful for plastic electronic applications. [ABSTRACT FROM AUTHOR]