Growth behaviour and electronic properties of organic semiconductors on metal surfaces
The focus of this paper is to review our recent achievements in understanding the growth mechanism of organic semiconductors on metal surfaces and the electronic structures at the organic semiconductor/metal interface with scanning tunnelling microscopy (STM) and photoemission spectroscopy (PES) measurements. By choosing model systems of high-symmetrical organic molecules growth on metal surfaces, especially at the initial growth stage, the driving forces for the formation of organic ordered layers are addressed, for example, perylene growth on Ru(0001) in monolayer regime is mainly controlled by the laterally repulsive molecule-molecule interaction. Concerning whether band bending occurs within organic semiconductor layer on metal surfaces, growth of N,N'-bis-(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine (NPB) overlayer on the well-defined Ag(111) surface and PES measurements are performed. The results showed band bending occurring within the organic overlayer, and the decrease of the work function with NPB thickness results from contributions from both the band bending and the dipole layer formed due to surface polarisation at the NPB/Ag(111) interface.
Keywords: organic semiconductors, metal surfaces, growth mechanisms, electronic structures, nanotechnology