STM-induced light emission of conjugated polymer thin film in different chain aggregations

The STM-induced luminescence (STML) of a conjugated polymer poly[2-methoxy-5-(2′-ethyl-hexyloxy)-p-phenylene vinylene] (MEHPPV) with or without annealing on substrate of Ag(1 1 1) were investigated in air at room temperature. The surface morphologies of pure Ag(1 1 1), MEHPPV thin film on Ag(1 1 1) with or without annealing were modified by STM scans under higher positive or negative sample biases. The experimental results show that for MEHPPV film without annealing, the STML intensity increases after aggregates formation induced by STM scans. However, for annealed MEHPPV film, the negative bias scans decrease the STML intensity. The chain aggregations among MEHPPV molecules are believed to be the key factor for the behavior.