Positron annihilation spectroscopy of voids in silicon

Reference:

Potter, N. R., 2007. Positron annihilation spectroscopy of voids in silicon. Thesis (Master of Philosophy (MPhil)). University of Bath.

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Abstract

An analysis of nanovoided Silicon is presented. The method of production was high dose implantation of Helium ions followed by annealing. This caused production of two species of defect. The first, large voids several micrometers in diameter, are extensively studied elsewhere in literature. The second, previously unknown defect, are shown to be 30-50 atom defects, some of which are decorated with oxygen. A new analysis technique was developed to characterise these defects. It is shown the previously published measurements of the defects are inaccurate and a superposition of clean and decorated defects. In addition, preliminary work on polarised (magnetised) samples is presented. This utilises the helicity of the polarised positron beam to target spin polarised electrons in iron. It is demonstrated that a clear difference is seen between magnetised and non-magnetised samples even with a weakly polarised beam.

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