GROWTH OF THE ORGANIC MOLECULAR SEMICONDUCTOR PTCDA ON SE-PASSIVATED GAAS(100) - AN STM STUDY

We investigate the monolayer and multilayer growth of the organic mole cular semiconductor (OMS) 3, 4, 9, 10-perylenetetracarboxylic dianhydr ide (PTCDA) on the Se-passivated GaAs(100) (2 x 1) surface using STM. Deposition of similar to 2 ML PTCDA at room temperature results in the formation of clusters, implying good chemical passivation of the subs trate. However, we also find a significant number of molecules pinned at high energy defect sites, some of which induce molecular ordering. At higher PTCDA coverage we find that the film invariably orients to t he substrate revealing a critical, though weak, molecule-substrate int eraction. We present the first molecularly resolved STM images obtaine d from a thick PTCDA film (similar to 60 Angstrom) and show unit cell dimensions and orientation in excellent agreement with our previous LE ED study.