Positron annihilation spectroscopy applied to porous silicon films

Abstract

A monoenergetic slow positron beam has been used for the first time to profile porous silicon films. High values of the Doppler-broadened line shape parameters are observed, which correspond to positron annihilation within the porous layers and these are attributed to the decay of para-positronium. After allowing for the reduced density of the porous film, fitted values of thickness were deduced which were in reasonable agreement with values obtained from ellipsometry measurements. Low values of the Doppler parameters observed for the two samples with the thinnest films are attributed to oxide residing at the interface of the porous and bulk silicon regions. Etching the samples in a solution of 48% hydrogen fluoride reduced the porous film thickness significantly, suggesting that a considerable amount of the film consists of SiO2. A four-component convolution analysis routine is used to analyze the individual 511 keV annihilation peaks, the result of which confirms the formation of positronium within the porous layer. Positron annihilation is shown to be a promising method for the nondestructive investigation of thin porous films.

Investigation of magnetron-sputtered titanium nitride films using positron annihilation spectroscopy

“…For samples a, b and c the positrons probe only the TiN film itself and have no interaction with the Si substrate. In the cases of the thinner samples d, e and f, however, a steady increase in the value of S at incident energies above 15 keV is consistent with positrons annihilating in the Si which is known to have a value of 0.493 in this experimental system [14]. This conclusion is confirmed by the estimated values of film thickness given in table 1.…”

A positron annihilation investigation of porous silicon

“…Others [11][12][13] have observed a very long positron lifetime ͑up to 20 ns͒ indicative of positronium formation in the pores. Most recently, Knight et al, 14 through investigations with a slow positron beam, again found evidence of positronium formation within the porous layer. These investigations show that positrons are sensitive to the near-surface, and surface of porous silicon, and that formation of positronium occurs.…”

Polypropylene Films Studied with Variable Positron Beams

“…A rise in S implies a narrowing of the line. Such narrowing occurs when for instance vacancies [40], large open volume defects (voids) [41,42] or pores are present in a sample [43].…”