Sequential nature of damage annealing and activation in implanted GaAs

Rapid thermal processing of implanted GaAs reveals a definitive sequence in the damage annealing and the electrical activation of ions. Removal of implantation-induced damage and restoration of GaAs crystallinity occurs first. Irrespective of implanted species, at this stage the GaAs is n-type and highly resistive with almost ideal values of electron mobility. Electrical activation is achieved next when, in a narrow anneal temperature window, the material becomes n- or p-type, or remains semi-insulating, commensurate to the chemical nature of the implanted ion. Such a two-step sequence in the electrical doping of GaAs by ion implantation may be unique of GaAs and other compound semiconductors

Forms, properties and dissolution of controlled-release nitrogenous fertilisers

The forms, properties and dissolution rates of controlled-release nitrogenous fertilizers are reviewed. These materials belong to one of the categories: coated materials, uncoated sparingly-water-soluble inorganic and organic compounds. Physical and chemical properties of the fertilizer materials are described along with their dissolution characteristics. Information on indigenous materials proposed as controlled-release N sources is scarce and is required to evaluate their comparative efficacy

Modeling the Growth and Development of Sorghum and Pearl Millet

The 1980s have witnessed substantial increases in food production. This has raised expectations that improved systems of farming will be rapidly adopted by small farmers in developing countries. The agroecological environment of such farms is fragile and the farmers are resource-poor. Therefore, strategies recommended for increasing food production must be ecologically sound and should result in sustainable agriculture. System modeling can greatly expedite the search for improved development strategies. Recent advances in crop modeling have made it possible to simulate yields and growth of several crops under varied soil and weather conditions with different management practices. This bulletin describes the framework of CERES (Crop Estimation Through Resource and Environment Synthesis) models developed by the International Benchmark Sites Network for Agrotechnology Transfer ( IBSNAT) and The International Crops Research Institute for the Semi- Ar i d Tropics ( ICRISAT) . Recent wor k on the simulation of nitrogen transformation in soils at the International Fertilizer Development Center ( IFDC) is discussed. A section on risk analyzes the cost-benefit implications of various inputs for increased crop production. RESCAP—a resource capture model developed at ICRISAT Center is presented. This publication is a cogent source book on the current status of development of CERES and RESCAP models, their data needs, outputs, and applications

Combined use of ion backscattering and x-ray rocking curves in the analyses of superlattices

Detailed compositional and structural analyses of superlattices have been carried out by mega-electron-volt He+ backscattering with channeling and with x-ray rocking curves. Through the combined use of the two techniques, depth profiles of strain, composition, and crystalline quality have been determined. An example of an AlxGa1-xAs/GaAs strained-layer-superlattice (SLS) is considered. The thicknesses of the individual periods in these SLS structures were accurately measured by backscattering spectrometry. The values so obtained were used in the detailed calculations of x-ray rocking curves. Excellent agreement between measured and calculated curves was achieved. Transition regions at the interfaces of the various layers in the SLS were also detected and measured by both techniques. The two techniques complement each other and together provide powerful quantitative tools to characterize SLS structures

Far infrared mapping of three Galactic star forming regions : W3(OH), S 209 & S 187

Three Galactic star forming regions associated with W3(OH), S209 and S187 have been simultaneously mapped in two trans-IRAS far infrared (FIR) bands centered at ~ 140 and 200 micron using the TIFR 100 cm balloon borne FIR telescope. These maps show extended FIR emission with structures. The HIRES processed IRAS maps of these regions at 12, 25, 60 & 100 micron have also been presented for comparison. Point-like sources have been extracted from the longest waveband TIFR maps and searched for associations in the other five bands. The diffuse emission from these regions have been quantified, which turns out to be a significant fraction of the total emission. The spatial distribution of cold dust (T < 30 K) for two of these sources (W3(OH) & S209), has been determined reliably from the maps in TIFR bands. The dust temperature and optical depth maps show complex morphology. In general the dust around S209 has been found to be warmer than that in W3(OH) region.Comment: Accepted for publication in Journal of Astrophysics and Astronomy (20 pages including 8 figures & 3 tables