Papers by Author: Charles Dauwe

Abstract: Positron transmission experiments were performed on free-standing poly(methyl-methacrylate) (PMMA) and polystyrene (PS) films of nanometric thicknesses made by spin coating. The power_law equation z1/2(E) )=(α/ρ)En was determined from the measurements of the S-parameter as a function of the positron implantation energy. These transmission experiments indicate that n = 1.90(±0.08) and α = 1.33(±0.10) μg cm-2 which deviates from the values found by Algers et al. (n = 1.71(±0.05) and α = 2.8(±0.2) μg cm-2) and the commonly used parameters (n = 1.6 and α = 4.0 μg cm-2).

Abstract: Positron annihilation lifetime measurements on polymethylmethacrylate (PMMA) at low temperature were performed. Different discrete fitting procedures have been used to analyze the experimental data. It shows that the extracted parameters depend strongly on the fitting procedure. The physical meaning of the results is discussed. The blob model seems to give the best annihilation parameters.