Uncovering Molecular Morphologies of C60 and Ptcda on Insulators: Dewetting in Two Prototypical Organic Semiconductors

There has been considerable interest in recent years in the use of organic molecules as active electronic and optoelectronic materials for devices. As such, research into the properties and structures of molecular films, crystallites and isolated molecules on surfaces has become an active field, both for the promise of single molecule devices and the prospect of thin film organic electronics. However, despite the importance of insulating materials in typical device structures, there has been minimal study of molecular deposits on insulating surfaces due to difficulties with the use of many traditional surface science tools on such systems. Over the past decade, non-contact atomic force microscopy (nc-AFM) has proven to be a powerful surface science tool on insulators as well as other surfaces, and more recently on heterogeneous samples. Here, we have used UHV nc-AFM as a high resolution tool to study the growth and morphology of two commonly used prototypical molecular semiconductors: C60 and PTCDA, on alkali halides. The alkali halides used, KBr and NaCl, cleave well in situ with large atomically flat terraces (up to 1 micron) making them ideal for growth studies.