In this paper we report the success in fabricating FTO/Si surface-barrier photodiodes produced by spray pyrolysis deposition technique, under ambient conditions. Three types of photodetectors for low-voltage-bias operation were developed based on high-resistivity silicon: 1. X-Ray detectors with energy resolution of 16.5% at 661.5 keV (137Cs source), consisting of surface-barrier PIN photodiode with an active area of 50 mm2 operating at 5 V reverse bias, scintillator based on monocrystalline Bi4Ge3O12 and preamplifier (noise of 250 e- RMS.); 2. Fast-response surface-barrier FTO/n–n+ silicon epitaxial photodiodes, operating at 10 V bias with rise times of 2 ns at λ = 0.85 μm; 3. Radiation-resistant drift epitaxial surface-barrier PIN photodiodes for unbiased operating conditions, with an exponential impurity distribution in a 8 μm thick epitaxial layer. A built-in electrical field due to the carrier concentration distribution in the epitaxial layer provides a considerable improvement in the `critical fluence' value (3×1014 cm-2) for neutron irradiation.

We report the properties and optoelectronic applications of transparent and conductive indium and tin oxide films prepared by the spray pyrolysis method and doped with Sn or F, respectively. The film properties have been measured using X-ray diffraction, optical and electrical absorption. As examples of applications we produced a set of selective optical detectors for different spectral regions, covering the wavelength range from 0.25 to 1.1 μm, based on metal oxide-semiconductor heterostructures and using different substrates such as: GaP, GaSe, AlxGa1-xAs, GaAs and Si. The fabricated devices exhibit several features such as: production simplicity, high quantum efficiency, uniform sensitivity over the entire active area and a high response speed. Finally, we present a high quantum efficiency and solar blind monocrystalline zinc sulphide optical sensor fabricated by spray deposition as an alternative to the ultraviolet-enhanced SiC and GaN photodetectors and the performances of a solar cell. © 1998 Elsevier Science B.V. All rights reserved.

Structure and QED effects for 2s1/2 and 2p3/2 levels are calculated for lithiumlike U89+ trough neonlike U82+, lithiumlike Th87+ trough neonlike Th80+ and lithiumlike Bi80+ trough neonlike Bi73+. The results of the first two sets are compared with recent measurements of the 2s1/2-2p3/2 transition energy in 3 to 10-electron ions. Good agreement with experiment is found for most of the observed lines. Forty-one possible transitions are calculated for each ion in the eight ionization states, in the experimental energy range. Twenty-eight of these transitions have not been observed, nor calculated previously. We also calculate transition rates, branching ratios, excitation and ionization cross sections and confirm that the thirteen experimental observed transitions correspond to the ones with highest relative intensities. However, we find nineteen more transitions that could be measured in a more sensitive experiment.X

A new high quantum efficiency gallium phosphide Schottky photodiode has been developed by spray deposition of heavily doped tin oxide films on n-type epitaxial structures, as an alternative to the conventional Schottky photodiodes using a semitransparent gold electrode. It is shown that fluorine-doped tin oxide films are more effective as transparent electrodes than tin-doped indium oxide films. The proposed photodiodes have a typical responsivity near 0.33 A W-1 at 440 nm and an unbiased internal quantum efficiency close to 100%, in the range from 250 to 450 nm. The model used to calculate the internal quantum efficiency (based on the optical constants of tin oxide films and gallium phosphide epitaxial layers) is found to be in good agreement with the experimental results. The data show that the quantum efficiency is strongly dependent on the thickness of the transparent electrode, owing to optical interference effects. The noise equivalent power for 440 nm is 2.7 × 10-15 W Hz-1/2, which indicates that these photodiodes can be used for accurate measurements in the short-wavelength range, even in the presence of stronger infrared background radiation.

UV-enhanced monocrystalline zinc sulphide optical sensors with high quantum efficiency have been developed by spray deposition of heavy fluorine-doped tin oxide (FTO) thin films onto the surface of zinc sulphide monocrystals as an alternative to the UV-enhanced high-efficiency silicon photodetectors commonly used in precise radiometric and spectroscopic measurements as well as to new sensors based on SiC and GaN. The fabricated sensors have an unbiased internal quantum efficiency that is nearly 100% from 250 to 320 nm, and the typical sensitivity at 250 nm is 0.15 A W-1. The sensors are insensitive to solar radiation in conditions on the earth and can be used as solar blind photodetectors for precision UV measurements under direct solar illumination for both terrestrial and space applications. © 1998 Elsevier Science S.A. All rights reserved.

UV-enhanced monocrystalline zinc sulphide optical sensors with high quantum efficiency have been developed by spray deposition of heavy fluorine-doped tin oxide (FTO) thin films onto the surface of zinc sulphide monocrystals as an alternative to the UV-enhanced high-efficiency silicon photodetectors commonly used in precise radiometric and spectroscopic measurements as well as to new sensors based on SiC and GaN. The fabricated sensors have an unbiased internal quantum efficiency that is nearly 100% from 250 to 320 nm, and the typical sensitivity at 250 nm is 0.15 A W-1. The sensors are insensitive to solar radiation in conditions on the earth and can be used as solar blind photodetectors for precision UV measurements under direct solar illumination for both terrestrial and space applications.

The aim of this work is to study the role of hydrogen dilution and filament temperature on the properties of nanocrystalline silicon thin films (undoped and doped) produced by the hot wire technique. These deposition parameters are correlated to the film's structure, composition and electro-optical properties with special emphasis on boron doped nanocrystalline silicon carbide reported here. © 1998 Elsevier Science B.V. All rights reserved.

We present a set of high-efficiency optical sensors for the spectral range from 0.25 to 1.1 μm based on metal oxide-semiconductor heterostructures using different substrates: GaP, GaSe, AlxGa1 - xAs, GaAs and Si. A set of several transparent conductive metal oxide films such as indium, tin and zinc oxides fabricated by the spray pyrolysis method and its doping procedure has been investigated. The results show that heavily doped indium and tin oxide films are preferable as the active transparent conductive electrode in heterojunction surface-barrier structures. The fabricated sensors exhibit several features such as process simplicity, high quantum efficiency, uniformity of sensitivity over the active area and a high response speed. Such sensors can be used for precision measurements in different scientific and technical applications. © 1998 Elsevier Science S.A. All rights reserved.

We present a set of high-efficiency optical sensors for the spectral range from 0.25 to 1.1 μm based on metal oxide-semiconductor heterostructures using different substrates: GaP, GaSe, AlxGa1-xAs, GaAs and Si. A set of several transparent conductive metal oxide films such as indium, tin and zinc oxides fabricated by the spray pyrolysis method and its doping procedure has been investigated. The results show that heavily doped indium and tin oxide films are preferable as the active transparent conductive electrode in heterojunction surface-barrier structures. The fabricated sensors exhibit several features such as process simplicity, high quantum efficiency, uniformity of sensitivity over the active area and a high response speed. Such sensors can be used for precision measurements in different scientific and technical applications.

We have developed new types of functional and smart optical silicon sensors, based on ITO/multichannel insulator/silicon structures, which are able to execute electronic functions such as amplifying the photocurrent (without avalanche multiplication), transforming the input optical signal into a radio frequency output signal and transforming the analogue input optical signal to a digital output form, without external active electronic components. These new functional optical sensors allow a substantial simplification of the registration of optical signals as well as of the electronic scheme to be used. © 1998 Elsevier Science S.A. All rights reserved.

We have developed new types of functional and smart optical silicon sensors, based on ITO/multichannel insulator/silicon structures, which are able to execute electronic functions such as amplifying the photocurrent (without avalanche multiplication), transforming the input optical signal into a radio frequency output signal and transforming the analogue input optical signal to a digital output form, without external active electronic components. These new functional optical sensors allow as substantial simplification of the registration of optical signals as well as of the electronic scheme to be used.

Mossbauer and EPR spectroscopies were used to characterize the Fe clusters in an Fe-S protein isolated from Desulfovibrio desulfuricans (ATCC 27774). This protein was previously thought to contain hexanuclear Fe clusters, but a recent X-ray crystallographic measurement on a similar protein isolated from Desulfovibrio vulgaris showed that the protein contains two tetranuclear clusters, a cubane-type [4Fe-4S] cluster and a mixed-ligand cluster of novel structure [Lindley et al. (1997) Abstract, Chemistry of Metals in Biological Systems, European Research Conference, Tomar, Portugal]. Three protein samples poised at different redox potentials (as-purified, 40 and 320 mV) were investigated. In all three samples, the [4Fe-4S] cluster was found to be present in the diamagnetic 2+ oxidation state and exhibited typical Mossbauer spectra. The novel-structure cluster was found to be redox active. In the 320-mV and as-purified samples, the cluster is at a redox equilibrium between its fully oxidized and one-electron reduced states. In the 40-mV sample, the cluster is in a two-electron reduced state. Distinct spectral components associated with the four Fe sites of cluster 2 in the three oxidation states were identified. The spectroscopic parameters obtained for the Fe sites reflect different ligand environments, making it possible to assign the spectral components to individual Fe sites. In the fully oxidized state, all four iron ions are high-spin ferric and antiferromagnetically coupled to form a diamagnetic S = 0 state. In the one-electron and two-electron reduced states, the reducing electrons were found to localize, consecutively, onto two Fe sites that are rich in oxygen/nitrogen ligands. Based on the X-ray structure and the Mossbauer parameters, attempts could be made to identify the reduced Fe sites. For the two-electron reduced cluster, EPR and Mossbauer data indicate that the cluster is paramagnetic with a nonzero interger spin. For the one-electron reduced cluster, the data suggest a half-integer spin of 9/2 Characteristic fine and hyperfine parameters for all four Fe sites were obtained. Structural implications and the nature of the spin-coupling interactions are discussed.