Clustering in a precipitate free GeMn magnetic semiconductor

We present the first study relating structural parameters of precipitate free Ge0.95Mn0.05 films to magnetisation data. Nanometer sized clusters - areas with increased Mn content on substitutional lattice sites compared to the host matrix - are detected in transmission electron microscopy (TEM) analysis. The films show no overall spontaneous magnetisation at all down to 2K. The TEM and magnetisation results are interpreted in terms of an assembly of superparamagnetic moments developing in the dense distribution of clusters. Each cluster individually turns ferromagnetic below an ordering temperature which depends on its volume and Mn content.Comment: accepted for publication in Phys. Rev. Lett. (2006). High resolution images ibide

Interplay between the electrical transport properties of GeMn thin films and Ge substrates

We present evidence that electrical transport studies of epitaxial p-type GeMn thin films fabricated on high resistivity Ge substrates are severely influenced by parallel conduction through the substrate, related to the large intrinsic conductivity of Ge due to its small bandgap. Anomalous Hall measurements and large magneto resistance effects are completely understood by taking a dominating substrate contribution as well as the measurement geometry into account. It is shown that substrate conduction persists also for well conducting, degenerate, p-type thin films, giving rise to an effective two-layer conduction scheme. Using n-type Ge substrates, parallel conduction through the substrate can be reduced for the p-type epi-layers, as a consequence of the emerging pn-interface junction. GeMn thin films fabricated on these substrates exhibit a negligible magneto resistance effect. Our study underlines the importance of a thorough characterization and understanding of possible substrate contributions for electrical transport studies of GeMn thin films.Comment: 9 pages, 9 figure

Design and simulation of thin-film silicon quantum well photovoltaic cell

A new thin-film silicon photovoltaic cell could be designed by inserting quantum well layers in the intrinsic region. Calculations show the improvement in spectral absorption due to the quantum well layer insertion. This article reports the design parameters and enhanced spectral absorption for a newly designed thin-film silicon quantum well photovoltaic cell. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/1057

Kinetics and Mechanism of Sulfation Reactions

Roasting of metallic sulfides have been studies by a large number of investigators in recent years. Wadsworth, McCabe in U.S.A. and Smirnov and his group have contrib-uted to our understanding of the roasting mechanism to a very considerable extent. On the basis of these works, two kinds of mechanisms have been proposed for the formation of metallic sulfate from metallic sulfide and oxygen. One of the theory suggests a direct formation of metallic sulfate, whereas the other theory assumes prior formation of metallic oxide of SO2 to SO3, which combines with metallic oxide to give sulfate. Present investigation is aimed at further clearing up the mechanism of sulfate formation and estabilishing the role of individuality of the system on a more generalised basis

Kinetics and Mechanism of Sulfation Reactions during roasting of Sulfides

ROASTING of sulphidic minerals is one of the very important steps in the extraction metallurgical practice of most of the non-ferrous metals from their concentrates. In recent times, the technique of roasting has undergone substantial changes leading to higher production and better products, more suitable for subsequent operations. Some of these processes have developed on the basis of our understanding of the kinetic limitations of the old proc-esses and elimination of such kinetic bottlenecks like diffusion in the roasting processes. These new processes like flash roasting or fluidized roasting are being increasingly utilised in production units. However, our present state of knowledge on the kinetics of roasting reaction lacks certain fundamental understanding of the process which is explained in the following paragraphs

Stress Corrosion Cracking of Copper-Manganese Alloys-Effect of Some Chemical Variables

Copper-manganese alloys, like a few other copper alloys, exhibit stress corrosion cracking in ammonia atmosphere, also they give cracking in Mattosson's solution which is a solution of copper sulphate, ammonium sulphate and ammo-nium hydroxide. Four compositions of copper-manganese alloys in their homogenous solid solution range, conta-ining 8 to 23 percent manganese, have been tested under varying conditions of Mattsson's solution in respect of PH and copper content for an assessment of the effect of these variables on the stress corrosion behaviour of these alloys

Stress corrosion cracking of copper-manganese alloys-effect of some chemical variables

OCCURRENCE of stress corrosion cracking in binary copper-manganese alloys in the presence of ammonia has been first reported by Lahiri1 where it has also been observed that Mattsson's solution2 comprising CuSO4, 5H2O and (NH4)2SO4 and ammonia, a very aggressive medium for stress corrosion cracking of brass, is very much effective in producing ready cracking in copper-manganese alloys. Coppermanganese system provides a wide range of solid solution; in this respect it is comparable to the copperzinc system, the stress corrosion studies of which have been carried out extensively. A few recent papers3'4'5 deal with the elect-rochemical aspects of stress corrosion cracking of alpha brass in Mattsson's solution. In this context it will be of interest to study the behaviour of homogeneous copper-manganese alloys under the variable conditions of Matt-sson's solution to get an insight into the mechanism of stress corrosion cracking