Formation of defect structures in Au-polysilane interfaces probed by low energy positron beams

Formation and accumulation of defect structures at interfaces between polysilanes and vacuum-evaporated gold (Au) electrodes are discussed quantitatively by low energy positron annihilation spectroscopy. The size distribution of the defects at the interface is analyzed based on the values of ortho-positronium (o-Ps) lifetime (τ₃), and no effect of the evaporation process is observed in the polymer films. The intensity of o-Ps (I₃) indicates no considerable change before and after Au evaporation on dialkyl-substituted polysilanes, however, the values of I₃ is increased ∼20% in phenyl-substituted polysilane (PMPS) by the evaporation. The I₃ dependence on incident positron energy suggests the formation of the defects not only at an Au-PMPS interface but also in PMPS bulk phase as deep as 400 nm from the interface. Phenyl ring dissociation from the polymer backbone will play a significant role in the selective formation of the defects in PMPS. This is the first report on the direct measurement of defect structures at conjugated polymer-metal interface with non-destructive way, implying that electrode fabrication by vacuum evaporation affects the solid state structure of polymers.