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The aim of this paper is to present data on the dependence of the electro-optical characteristics and structure of n-type microcrystalline silicon films on the r.f. power used during the deposition of films produced by the plasma-enhanced chemical vapour deposition technique. The interest of these films arise from the fact that they combine some electro-optical advantages of amorphous (wide optical gap) and crystalline materials (electronic behaviour), highly interesting in the production of a wide variety of optoelectronic devices such as solar cells and thin film transistors. In this paper, microcrystalline n-type films presenting simultaneously optical gaps of about 2.3 eV, dark conductivity of 6.5 S cm-1 and Hall mobility of about 0.86 cm2 V-1 s-1 will be reported, the highest combined values for n-type microcrystalline silicon films, as far as we know. © 1997 Elsevier Science S.A.

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The objective of this work is to present an analytical model able to interpret the experimental dependence of the uniformity of films produced by the plasma-enhanced chemical vapour deposition technique on the deposition parameters (discharge pressure, gas flow temperature and rf power density). The model proposed is based on the Navier-Stokes equations applied to a gas flow considered to be quasi-incompressible and quasi-inviscous, whenever the Mach number is below 0·3. This condition leads to the establishment of the proper quasisteady-state gas flow equations, and the corresponding equations of energy and momentum balance ascribed to the mass profile of the species formed, under the presence of a low-rf-power plasma density, are able to predict the uniformity distribution of the film over the entire deposited substrate area.

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The aim of this work is to present an analytical model able to interpret the experimental data of the dependence of film's uniformity on the discharge pressure, gas flow and temperature used during the production of thin films by the plasma enhancement chemical vapour deposition technique, under optimised electrode's geometry and electric field distribution. To do so, the gas flow is considered to be quasi-incompressible and inviscous leading to the establishment of the electro-fluid-mechanics equations able to interpret the film's uniformity over the substrate area, when the discharge process takes place in the low power regime.

The magnitude of the time autocorrelation function M between states excited by two Gaussian laser pulses is calculated for both hydrogen and rubidium atoms inparallel electric and magnetic fields. M is determined by a full quantum-mechanical calculation but the peaks are identified with the periods of the shortest periodicorbits of the corresponding classical system. Qualitative agreement is obtained with experimental results, however, discrepancies are found in the relative heights ofthe peaks.

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This work reports the structure and electro-optical characteristics of different metal oxide films obtained by spray pyrolysis on heated glass substrates, aiming their application in optoelectronic devices. The results show that this technique leads to thin films with properties ranging from dielectric to degenerate semiconductors, offering the following advantages: simplicity, low cost, high productivity and the possibility of covering large areas, highly important for large area device applications.

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This paper deals with the structure, composition and electro-optical characteristics of n-type amorphous and microcrystalline silicon thin films produced by plasma-enhanced chemical vapour deposition in a hydrogenhelium mixture. In addition, special emphasis is given to the role that hydrogen incorporation plays in the film's properties and in the characteristics of n-type microcrystalline films presenting simultaneously optical gaps of about 2·3 eV (controlled by the hydrogen content in the film), a dark conductivity of 6-5S cm-1 and a Hall mobility of about 0·86 cm2 V-1 s-1, the highest combined values for n-type microcrystalline silicon films, as far as we know.

High quantum efficiency, UV-enhanced monocrystalline zinc sulphide optical sensors for precise radiometric and spectroscopic measurements have been developed by spray deposition of heavy fluorinedoped tin oxide thin films with carrier concentration near 1021 cm-3 onto the surface of zinc sulphide monocrystals as an alternative to the UV-enhanced silicon photodetectors as well as to new detectors based on SiC and GaN. The fabricated sensors have an unbiased internal quantum efficiency that was nearly 100% from 250 to 320 nm, and the typical sensitivity at 290 nm is 0.15 A/W. The sensors were insensitive to solar radiation in earth's conditions and can be used as solar blind photodetectors for precision UV-measurements under direct solar illumination, both terrestrial and space applications.

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The structure of desulfoferrodoxin (DFX), a protein containing two mononuclear non-heme iron centres, has been solved by the MAD method using phases determined at 2.8 Angstrom resolution. The iron atoms in the native protein were used as the anomalous scatterers. The model was built from an electron density map obtained after density modification and refined against data collected at 1.9 Angstrom. Desulfoferrodoxin is a homodimer which can be described in terms of two domains, each with two crystallographically equivalent non-heme mononuclear iron centres. Domain I is similar to desulforedoxin with distorted rubredoxin-type centres, and domain II has iron centres with square pyramidal coordination to four nitrogens from histidines as the equatorial ligands and one sulfur from a cysteine as the axial ligand. Domain I in DFX shows a remarkable structural fit with the DX homodimer. Furthermore, three beta-sheets extending from one monomer to another in DFX, two in domain I and one in domain II, strongly support the assumption of DFX as a functional dimer. A calcium ion, indispensable in the crystallisation process, was assumed at the dimer interface and appears to contribute to dimer stabilisation. The C-terminal domain in the monomer has a topology fold similar to that of fibronectin III.

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{Dodecaheme cytochrome c has been purified from Desulfovibrio (D.) desulfuricans ATCC 27774 cells grown under both nitrate and sulfate-respiring conditions. Therefore, it is likely to play a role in the electron-transfer system of both respiratory chains. Its molecular mass (37 768 kDa) was determined by electrospray mass spectrometry. Its first 39 amino acids were sequenced and a motif was found between amino acids 32 and 37 that seems to exist in all the cytochromes of the c3 type from sulfate-reducing bacteria sequenced at present. The midpoint redox potentials of this cytochrome were estimated to be -68, -120, -248 and -310 mV. Electron paramagnetic resonance spectroscopy of the oxidized cytochrome shows several low-spin components with a g(max) spreading from 3.254 to 2.983. Two crystalline forms were obtained by vapour diffusion from a solution containing 2% PEG 6000 and 0.25-0.75 M acetate buffer pH = 5.5. Both crystals belong to monoclinic space groups: one is PZ,, with a = 61.00

The primary structure of desulfoferrodoxin from Desulfovibrio desulfuricans ATCC 27774, a redox protein with two mononuclear iron sites, was determined by automatic Edman degradation and mass spectrometry of the composing peptides, It contains 125 amino acid residues of which five are cysteines, The first four, Cys-9, Cys-12, Cys-28 and Cys-29, are responsible for the binding of Center I which has a distorted tetrahedral sulfur coordination similar to that found in desulforedoxin from D. gigas, The remaining Cys-115 is proposed to be involved in the coordination of Center II, which is probably octahedrally coordinated with predominantly nitrogen/oxygen containing ligands as previously suggested by Mossbauer and Raman spectroscopy.