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Spatial variations of oxygen precipitation have been studied in silicon wafers submitted to rapid thermal annealing (RTA) in nitrogen ambients at a temperature above 1150 °C prior to a two-step precipitation treatment. The samples submitted to high temperature preannealing show a consistent enhancement of oxygen precipitation, which is dependent on the RTA time and temperature. Oxygen precipitate density measurements show that oxygen precipitation is not homogeneous inside the wafer, but peaks near the surfaces, with a minimum in the bulk. The high treatment in N2 results in the formation of defects which act as precursors for the subsequent nucleation and growth of oxygen precipitates. There is strong evidence that these precursors are generated by the thermal nitridation of the silicon surface and subsequent vacancy injection into the bulk of the wafer.

Abstract:The energy intensity of modern food systems represents a major issue in a scenario of decreasing oil resources and increasing population. Beside the use of renewable energy, an increased efficiency in food systems could contribute to reduce fossil fuels dependence. In this sense, food losses and waste (FLW) have crucial consequences on the energy balance. Based on the concept of "embodied energy", food wastage can be framed as a double waste of energy, both in terms of non-consumed food energy and the inputs used for production. Secondary data regarding direct and indirect energy inputs and FLW have been collected for the Italian food chain to estimate the embodied energy of food waste. Since in 2011 the production and distribution of food implied the use of 822 PJ and 18 Mt of food was discarded, 67 PJ of food energy and 100 PJ of embodied energy were wasted. These figures are equivalent to 12.2% of the total nutritional energy output and to 1.3% of the final energy use in Italy, respectively. The concept of double energy waste sheds new light on the intertwined relationship between energy and food security, suggesting that appropriate food waste reduction policies could result in a higher food production level and relevant energy savings.