Study of positronium in low-k dielectric films by means of 2D-angular correlation experiments at a high-intensity slow-positron beam

Depth-resolved measurements of two-dimensional angular correlation of annihilation radiation (2D-ACAR) were performed at the intense slow-positron beam at Lawrence Livermore National Laboratory. The formation of positronium was studied in thin films of methyl-silsesquioxane (MSSQ) spin-on glass containing large open-volume defects (voids). Two samples with different average void sizes were investigated and positronium formation could be found in both cases. The width of the angular correlation related to annihilation of para-positronium (p-Ps) increased with the void size consistent with the annihilation of nonthermalized p-Ps.