Positron annihilation investigation of porous silicon heat treated to 1000degrees C

Positron lifetime and Doppler broadening spectroscopies were applied to inv estigate a porous silicon film subjected to heat treatment in an argon atmo sphere. Heating between 300 and 500 degrees C increased the mass of the fil m by 17% due to oxygen uptake and the concentration of open volume defects associated with the formation of an oxide layer on the silicon nanocrystall ites increased by a factor of 3. Between 600 and 1000 degrees C their conce ntration decreased gradually to 1/2 the original concentration. Doppler bro adening results indicate two distinct electron momentum distributions, one arising from open volume defects and one from pickoff annihilation of posit ronium at the pore walls caused by electrons with an unexpectedly narrow mo mentum distribution. (C) 1998 American Institute of Physics. [S0021-8979(98 )00624-0].