Low-Temperature Chemical Approaches for Synthesizing Sulfides and Nitrides of Reactive Transition Metals

The advent of the sol–gel technique over the past several decades and the recognition of its excellent flexibility for synthesizing a large variety of oxide ceramics and glasses in both bulk and thin-film forms has generated considerable interest in using solution-based processes to prepare ceramic materials. Because of the success of the sol–gel technique, a number of other chemical processes have been developed utilizing metalorganic/organometallic starting materials to create molecularly architectured precursors, which have proven effective in synthesizing both oxide and non-oxide materials. In the present study, two different chemical approaches have been implemented to synthesize non-oxides (sulfides and nitrides) of reactive transition-metal elements. Accordingly, a novel thio-sol–gel process for preparing TiS₂ and NbS₂ powders has been studied. In the case of TiS₂ synthesis, the chemical reaction has been examined in detail using Fourier-transform infrared spectroscopy (FTIR) and gas chromatography (GC). The effects of modification of the titanium precursor on the morphology of the final sulfide have also been investigated and are discussed. A second, more generalized process has been developed for synthesizing homogeneous precursors in multicomponent systems. Its utilization in preparing ternary nitrides has been demonstrated, and is also presented. © 1997 by John Wiley & Sons, Ltd.     

Feedforward Neural Network Trained by BFGS Algorithm for Modeling Plasma Etching of Silicon Carbide

Electron cyclotron resonance (ECR) plasma etching of silicon carbide is numerically modeled by a feedforward neural network (FNN), which is trained by the Broyden, Fletcher, Goldfarb, and Shanno (BFGS) optimization algorithm and the conventional backpropagation (BP) algorithm. The training samples are obtained from our experimental results, which meet the requirement of Box–Wilson central-composite-designed experimental test design. By using the samples, the BFGS algorithm is compared with the conventional BP algorithm with different hidden neuron numbers, different number of iterations and various learning rates. It is shown that the BFGS algorithm requires less hidden neurons and less iteration to obtain the same training results, and it also provides much smaller cross-validation errors. Therefore, the FNN trained by the BFGS algorithm possesses much better approximation and generalization ability. The silicon carbide ECR process modeling results demonstrate that the FNN trained by the BFGS algorithm are fast, reliable, and accurate.      

SYNERGISTIC KILLING EFFECT IN PRE-UV-IRRADIATED MICROCOCCUS RADIOPHILUS

Abstract— Both the UV- and y-radiation survival curves of Micrococcus radiophilus are distinguished by large shoulders. However, a combination radiation treatment results in an enhanced killing effect. Pre-UV treatment is found to give a synergistic kill as compared to an additive kill when the sequence of radiation treatments is reversed.     

Ab-initio study of fluorine-doped tin dioxide: A prospective catalyst support for water electrolysis

In an attempt to identify new electrochemically stable catalyst supports for electrolysis of water, the electronic structure of SnO₂ doped with different fluorine concentrations has been calculated using the Vienna ab-initio simulation package (VASP) in the projector-augmented wave (PAW) method with the general gradient approximation (GGA) for conducting the exchange-correlation corrections. The role of fluorine in improving the electronic conductivity is discussed. An increase in the density of electronic states at the Fermi level with increase in the concentration of fluorine incorporated into the main SnO₂ matrix agrees well with published experimental observations. Despite a gradual decrease in the cohesive energies for the fluorine-doped tin oxide with increase in fluorine concentration, the doped material still remains an appropriate candidate for use as catalyst supports in water electrolysis warranting further experimental validation.     

Effects of Antimony Doping on Electronic Structure of SnO2

Within the framework of the density functional, an investigation is carried out of the electronic structure of stannic oxide and its variations due to antimony doping. It is shown that doping gives rise to formation of an impurity-induced half-filled band below the bottom of the oxide conduction band ensuring the material conduction properties. The changes in the valence band caused by the introduced impurity are in a good agreement with the photoemission data.     

In situ Raman microscopy during discharge of a high capacity silicon–carbon composite Li-ion battery negative electrode

In situ Raman microscopy study has been performed in order to characterize the surface of the Si/C composite anode and also to monitor the alloying/dealloying behavior of Si/C with Li ion during electrochemical discharging/charging processes at a microscopic level. This study shows that the Si particles are covered by graphite and hard carbon, with demonstration of further evidence of amorphisation of silicon and presence of mixed phases of Li–Si.     

Chemical processing of rare earth chalcogenides

Chalcogenides are compounds containing sulfur, selenium and tellurium and are well known for their semiconducting and optical properties. Their characteristic absorption at low frequencies render these materials excellent for long wavelength transmission. In the past few years, the need for far infrared transmitting materials to be used in target acquisition equipment formed the basis for identifying several new crystalline sulfide materials which transmit into the extended far infrared (IR) spectral region. Rare earth sulfides exhibiting excellent transmission into the far infrared (8-14 μm) emerged as a new group of infrared window materials. This paper reviews the status of binary and ternary rare earth sulfide compounds for optical window application. Conventional and non-conventional techniques used for processing these materials will be discussed in complete detail. The use of metallorganic precursors and modification of the precursor chemistry to tailor the composition of the final ceramic will be described. The potential of these emergent low temperature chemical processing techniques such as sol-gel, precipitation and co-precipitation for synthesis of non-oxide ceramics will also be addressed, particularly in light of their successful application in processing of novel electronic oxide ceramics, glasses and composites.