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Positron annihilation spectroscopy applied to porous silicon films (1995)

Knights, A. P. ; Kowalski, G. ; Saleh, A. S. ; [et al.]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 78 (1995), S. 4411-4415

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ISSN: 1089-7550

Source: AIP Digital Archive

Topics: Physics

Notes: 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. © 1995 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.359848

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A vertical positron beam for low-temperature surface studies (1987)

Rice-Evans, P. C. ; Britton, D. T. ; Cowan, B. P.

Springer

Applied physics 43 (1987), S. 283-285

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ISSN: 1432-0630

Keywords: 78.70B

Source: Springer Online Journal Archives 1860-2000

Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics

Notes: Abstract A cryostat system incorporating a low-energy positron beam for surface measurements down to Temperatures below 2 K is currently under construction at the Royal Holloway and Bedford New College. The positron beam has recently been brought into operation and its operating characteristics have been evaluated. Positrons from a22Na source are converted with an efficiency of ε=2×10−4 and transported magnetically at 1.5 V above the work function to a target at the bottom of a cryostat. The transmission of a 7 mm diameter beam is found to be constant over a range of axial field strengths from 40 to 50 G.