Study of the structure of porous silicon via positron annihilation experiments

We performed two-dimensional angular correlation of the electron-positron annihilation radiation (2D-ACAR) and positron lifetime measurements on a porous Si sample. From the width of the narrow 2D-ACAR components, attributed to positronium atom, we estimated the average size of the pores to be approx. 2.4 nm and did not find evidence of a preferential propagation of the pores. Moreover, by comparing the 2D-ACAR spectrum with that observed in a pure Si crystal we isolated a further isotropic component to be attributed to crystal defects of unknown origin.