Study of electronic properties of III-V semiconductors and semiconductor-superlattices

We have studied different methods for calculating band structures of solids and their density of states which can predict the electronic properties of solids accurately. Especially, computational methods like tight binding approximation and pseudo potential method have been studied and applied to find the band structures and density of states of semiconductors and its superlattices. The project work is divided into two parts. In first part, pseudo potential method has been used to solve computationally by MATLAB, the energy Eigen values of III-V semiconductors like GaAs and AlAs and IV semiconductor i.e. Ge and get a graphical representation of their band structures. In second part, TB-LMTO program which uses tight binding method has been applied to find the band structures and density of states of GaAs and AlAs semiconductors and their superlattices (GaAs/AlAs). A comparison of conducting behaviour of these materials is made finally

Characterization of Limestone Sample from Northeast India and its Implication on Beneficiation

Two limestone samples, from the same source (Assam, north-east India) have been petromineralogically characterized. In hand specimens, both samples are quite similar and are highly fossiliferous. Under optical microscope the fossils that are indentified belong mostly to two different Phy-llum, viz., Protozoa and Mollusca. The Protozoans are mainly Foraminifera and the Molluscans are Lamellibran-chia. Both categories have been petrified to calcium carbonate only and the fossils are embedded in a lime matrix. Due to the dominance of Nummulite fossils, the samples can be named as 'Nummulitic limestones'.The fossil records indicate that the limestones may be of Eocene age (< 65 million years)

Coal Mining in Meghalaya - a boon or bane?

Thin seams of coal occur assiciated with the Lakadong sandstones of Eocene age in the Jaintia Hills of Megha-laya. These Tertiary coals are low-ash coking coals but due to their high sulfur content they do not find proper market in the iron and steel industries. However, they are being mined rampantly for use as a fuel for other small and medium-scale industries such as power, cement, tea, fertilizer and bricks etc. Due to unscientific mining methods the environment is seriously affected destroying the land, soil, forest, water and the natural heritages. The law of the land is also a major bottleneck for persuading large-scale integrated mechanized mining by public and private sectors. Government efforts are yet to deliver a clear cut mineral and mining policy or any significant results towards protecting the environment. This is a serious issue which needs attention of the policy makers, planners, administrators, mining engineers, geo-enVironmentalists, scientists, technocrats, entre-preneurs and academicians to discuss, deliberate and suggest some solution for the benefit of the people of Meghalaya as well as for the protection of the environment

Petrology of Mn carbonate–silicate rocks from the Gangpur Group, India

Metamorphosed Mn carbonate–silicate rocks with or without oxides (assemblage I) and Mn silicate–oxide rocks with minor Mn carbonate (assemblage II) occur as conformable lenses within metapelites and metacherts of the Precambrian Gangpur Group, India. The petrology of the carbonate minerals: rhodochrosite, kutnahorite, and calcite that occur in these two assemblages is reported. Early stabilisation of spessartine, aegirine, quartz, and carbonates (in a wide solid solution range) was followed by pyroxmangite, tephroite, rhodonite through decarbonation reactions. Subsequently, jacobsite, hematite, braunite, hollandite and hausmannite have formed by decarbonation–oxidation processes during prograde metamorphism. Textural characteristics and chemical composition of constituent phases suggest that the mineral assemblages reflect a complex relationship between protolithic composition, variation of XCO2 (<0.2 to 0.3) and oxygen fugacity. A variation of XCO2 and fO2 would imply internal buffering of pore fluids through mineral reactions that produced diverse assemblages in the carbonate bearing manganiferous rocks. A minor change in temperature (from around 400 to 450 °C) does not appear to have had any major influence on the formation of different mineral associations