[en] The optical properties of conductive transparent thin films of undoped SnO², prepared by using magnetron sputtering, were studied by measuring the transmittance and the reflectance between lambda=0.25 μm and lambda=3 μm. The extracted optical constants are interpreted to give values of a direct band gap of the order of 4 eV and of an indirect band gap of the order of 3 eV. Typical SnO₂ films transmit approx. 85% of visible light, have sheet resistance R-sheet (100-800) Ω-sheet and resistivities of (2.4 10^-3-1.8 10^-2) Ω cm

[en] In recent years, the scientific community has considered with interest the possibility to integrate YBCO-based devices with silicon-based electronics. In fact, the proved YBCO radiation hardness makes this integration appealing from the point of view of space and telecommunication applications. In this paper we report on the influence of buffered substrate properties on the superconducting performances of YBCO films. In this framework we here consider the Si/CeO₂/YBCO multilayer. The non-satisfying quality of the YBCO film in this multilayer is attributed to an unavoidable interlayer of SiO₂ between Si and CeO₂. On the other hand, we prove, by means of quantitative magneto-optical analysis, the excellent properties of the bi-layer CeO₂/YBCO on YSZ substrate. Thus, these measurements indicate YSZ as the best candidate to be deposited between Si and CeO₂ for optimal YBCO performances on silicon

[en] Two sets of a-SiC: H films were deposited by glow discharge in an Ar-SiH₄-CH₄ atmosphere to investigate the effect of a variable CH₄/SiH₄ ratio on the physical properties. The composition of the films was determined by resonant nuclear reaction and by Rutherford backscattering measurements, the optical gap and the index of refraction by transmissivity measurements in the visible-UV-NIR range, the bonding configuration by IR transmissivity measurements and the resistivity and the photoconductivity by electrical measurements in the dark and under a 500W/m² illumination. Results indicate that with increasing carbon content the refractive index decreases systematically over all wavelengths, the energy gap increases, the dark resistivity increases, the bonding configuration becomes dominated by carbon-containing chains and the structure more disordered

[en] In this work a hybrid graphene-based flexible micro-supercapacitor (MSC) exploiting a novel composite material was fabricated and extensively characterized. The MSC electrodes have been obtained from a synthesized composite aerogel of reduced graphene oxide and polycrystalline nanoparticles of molybdenum (IV) oxide (MoO₂) and then dispersed in a solution containing poly(3,4-ethylenedioxythiophene) (PEDOT). Usually in MSCs the electrons have to percolate through the nanostructured Three-dimensional (3D) matrix in order to reach the collectors, made by metal thin films that provide electrical contacts only on the surface of active material. In the attempt to enable a more efficient charge transfer and to allow direct electrical contact without metal deposition, in this study a highly doped PEDOT acting both as current collector and as binder for the nanocomposite material has been employed. 3D MSCs were fabricated through a Lithographie, Galvanoformung, Abformung (LIGA)-like process to obtain high aspect ratio microstructures in polydimethylsiloxane replicas. Capacitance values of 94 F g⁻¹ for the nanocomposite and of 14 mF cm⁻² for the device were achieved. Moreover, bending test has demonstrated good performance preservation in a U shape conformation of the device. (paper)

[en] Dye-sensitized solar cells (DSSCs) are getting increasing attention as low-cost, easy-to-prepare and colored photovoltaic devices. In the current work, in view of optimizing the fabrication procedures and understanding the mechanisms of dye attachment to the semiconductor photoanode, absorbance measurements have been performed at different dye impregnation times ranging from few minutes to 24 hours using UV-Vis spectroscopy. In addition to the traditional absorbance experiments, based on diffuse and specular reflectance on dye impregnated thin films and on the desorption of dye molecules from the photoanodes by means of a basic solution, an alternative in-situ solution depletion measurement, which enables fast and continuous evaluation of dye uptake, is presented. Photoanodes have been prepared with two different nanostructured semiconducting films: mesoporous TiO₂, using a commercially available paste from Solaronix, and sponge-like ZnO obtained in our laboratory from sputtering and thermal annealing. Two different dyes have been analyzed: Ruthenizer 535-bisTBA (N719), which is widely used because it gives optimal photovoltaic performances, and a new metal-free organic dye based on a hemisquaraine molecule (CT1). Dye sensitized cells were fabricated using a customized microfluidic architecture. The results of absorbance measurements are presented and discussed in relation to the obtained solar energy conversion efficiencies and the incident photon-to-electron conversion efficiencies (IPCE).

[en] Two series of amorphous carbon alloys were deposited by reactive sputtering using a graphite target and argon as a sputtering gas. The effect of hydrogen or nitrogen on the structure of amorphous carbon was investigated using photothermal deflection spectroscopy (PDS), UV-Vis-near infrared spectroscopy, Fourier Transform Infrared (FT-IR), Raman and Photoluminescence (PL) techniques. The change in the structure of hydrogenated amorphous carbon (a-C:H) is due to the fact that H incorporation favours the formation of sp³ sites. In fact, the hydrogen incorporation relaxes the structure enough to improve electronic properties by increasing the number of terminal bonds. In the amorphous carbon nitride (a-CN) films, the lone pairs belonging to the nitrogen atoms are important in determining the optical properties of the films. The nitrogen alters the structure of carbon and creates cavities to be responsible for hydroxyl (OH) inclusions

[en] MoO_x/n-CdTe photosensitive heterostructures were prepared by the deposition of molybdenum oxide thin films onto n-type single-crystal CdTe substrates by DC reactive magnetron sputtering. The obtained heterojunctions possessed sharply defined rectifying properties with the rectification ration RR  ∼ 10⁶. The temperature dependences of the height of the potential barrier and series resistance of the MoO_x/CdTe heterojunctions were investigated. The dominating current transport mechanisms through the heterojunctions were determined at forward and reverse biases. The analysis of capacitance-voltage ( C – V ) characteristics, measured at different frequencies of the small amplitude AC signal and corrected by the effect of the series resistance, provided evidence of the presence of electrically charged interface states, which significantly affect the measured capacitance. (paper)

[en] One of the materials widely used in the fabrication of transition-edge sensor for photon counting is titanium. In the visible-near infrared spectral region the photon absorption occurs directly in the film and the quantum efficiency of the detector is limited by the reflection losses at the film surface, which are around 60%. For many applications like quantum cryptography these losses are too high. One way to reduce the reflection is to apply an antireflection coating on the films. In this work we present different solutions based on the deposition of few layers of amorphous silicon-nitrogen alloys, a material with a tunable refraction index. The design of multilayer is based on an optimisation program which adopts a genetic algorithm to find out the global minimum of the reflectivity among a wide range of thickness possibilities for the different layers. We present solutions that minimize the reflectivity simultaneously at different telecommunication wavelengths or in a continuum band. The simulations are compared with experimental results

[en] Most of power electronic circuits use power semiconductor switching devices which ideally present infinite resistance when off, zero resistance when on, and switch instantaneously between those two states. Switches and rectifiers are key components in power electronic systems, which cover a wide range of applications, from power transmission to control electronics and power supplies. Typical power switching devices such as diodes, thyristors, and transistors are based on a monocrystalline silicon semiconductor or silicon carbide. Silicon is less expensive, more widely used, and a more versatile processing material than silicon carbide. The silicon carbide (SiC) has properties that allow devices with high power voltage rating and high operating temperatures. The technology overcomes some crystal growth obstacles, by using the hydrogen in the fabrication of 4H-SiC wafers. The presence of structural defects on 4H-SiC wafers was shown by different techniques such as optical microscopy and scanning electron microscopy. The presence of different SiC polytypes inclusions was found by Raman spectroscopy. Schottky diodes were realized on investigated wafers in order to obtain information about the correlation between those defects and electrical properties of the devices. The diodes with voltage breakdown as 600 V and ideality factor as 1.05 were obtained and characterized after packaging

[en] A simple model to evaluate the impedance of a cell in the presence of the generation and recombination of charges is proposed. The analysis is performed by considering a typical asymmetric cell having one electrode perfectly blocking and the other electrode perfectly transparent. The dependence of the impedance of the cell, in the shape of a slab, on the recombination coefficient is investigated. We obtain approximated expressions for the impedance of the cell valid in the low and high frequency regions. The frequencies defining the regions where approximated expressions hold are deduced by means of the asymptotic expansions for the real and imaginary parts of the electrical impedance of the cell.