Ultrahigh-vacuum quasiepitaxial growth of model van der Waals thin films. II. Experiment

Abstract

We study the growth of the archetypal planar molecular compounds; 3,4,9,10 perylenetetracarboxylic dianhydride 3,4,7,9 naphthalenetetracarboxylic dianhydride, and copper phthalocyanine on a variety of substrates by the ultrahigh-vacuum process of organic molecular-beam deposition. The thin-film structures are grown as monolayers, multilayers, alternating thin-film stacks (or multiple quantum wells), and bulk thin films with thicknesses extending to 4000 Å. Techniques used to investigate these structures include scanning tunneling microscopy, in situ reflection high-energy electron diffraction, electron mi- croscopy, x-ray diffraction, and optical and electronic characterization. We find that highly ordered crystalline thin-film growth (i.e., quasiepitaxy) can often be achieved independent of the commensurability of the grown layer and the substrate. Such structural ordering is shown to strongly influence both the optical and electronic properties of the films. The structures experimentally determined for these film systems are consistent with the theoretical predictions made in paper I, where we analyze films consisting of large planar organic molecules bonded by van der Waals forces. These results provide evidence for the generality of quasiepitaxial growth of such molecular thin-film systems.