Search

Abstract: Positron annihilation spectroscopy was applied to study relaxed P-doped n-type layers with Ge concentrations up to 30%. As-grown SiGe layers were defect-free and annihilations are superpositions from bulk Si and Ge. Proton irradiation at 2MeV energy with a fluence was used to produce saturated positron trapping in monovacancy related defects. The defects were identified as V–P pairs, the E-center. The distribution of Si and Ge atoms surrounding the E-center is the same as in the host lattice. The vacancy migration process leading to the formation of V–P pairs therefore does not seem to have a preference for either Si or Ge atoms. [Copyright &y& Elsevier]

The increasing global demand for food will be met chiefly by increased intensification of production. For crops, this will be achieved largely by increased yields per area with a smaller contribution from an increased number of crops grown in a seasonal cycle. Production systems show a spectrum of intensification practices characterised by varying methods of site preparation and pest control, and inputs of germplasm, nutrients and water. This paper highlights three main types of intensification (based largely on the quantity and efficiency of use of external inputs) and examines both the on- and off-site environmental consequences of each for soils, water quantity and quality, and climate forcing and regional climate change. The use of low amounts of external inputs is generally regarded as being the most environmentally-benign although this advantage over systems with higher inputs may disappear if the consequences are expressed per unit of product rather than per unit area. The adverse effects of production systems with high external inputs, especially losses of nutrients from fertilisers and manures to water courses and contributions of gases to climate forcing, have been quantified. Future intensification, including the use of improved germplasm via genetic modification, will seek to increase the efficiency of use of added inputs while minimising adverse effects on the environment. However, reducing the loss of nutrients from fertilisers and manures, and increasing the efficiency of water utilisation in crop production, remain considerable challenges. [Copyright &y& Elsevier]