On the characteristics of helium filled nano-pores in amorphous silicon thin films

Abstract

A joint theory–experimental study is presented of irregularly shaped nano-pores in amorphous silicon. STEM– ELLS spectra were measured for each pore. The observed helium $1s^2\to 1s2p$(¹P) excitation energies were found to be shifted from that of a free atom. The relation between the helium density in the pore and these energy shifts is explored and shown to be completely consistent with earlier studies of helium in its bulk condensed phases as well as encapsulated as bubbles in solid silicon. The density, pressure and depth of the pores, all key properties for applications, were determined. An alternative and novel method for determining the depth of the pores more accurately is presented.