Low-temperature positron annihilation study of B+-ion implanted PMMA.

Temperature dependent positron annihilation lifetime spectroscopy (PALS) measurements in the range of 50-300 K are carried out to study positronium formation in 40 KeV B⁺-ion implanted polymethylmethacrylate (B:PMMA) with two ion doses of 3.13 × 10¹⁵ and 3.75 × 10¹⁶ ions/cm². The investigated samples show the various temperature trends of ortho-positronium (o-Ps) lifetime ז₃ and intensity I₃ in PMMA before and after ion implantation. Two transitions in the vicinity of ~150 and ~250 K, ascribed to γ and β transitions, respectively, are observed in the PMMA and B:PMMA samples in consistent with reference data for pristine sample. The obtained results are compared with room temperature PALS study of PMMA with different molecular weight (M_w) which known from literature. It is found that B⁺-ion implantation leads to decreasing M_w in PMMA at lower ion dose. At higher ion dose the local destruction of polymeric structure follows to broadening of lifetime distribution (hole size distribution). [ABSTRACT FROM AUTHOR]