Searching New Crystalline Substrates for OMBE : Topological and Energetic Aspects of Cleavable Organic Crystals

Thin films of organic semiconductors are intensively studied in view of their exploitation in modern electronic devices. Until now, few crystalline substrates have been used as clean surfaces for organic molecular beam epitaxy (OMBE). Among them, β-alanine crystals recently proved to be valuable substrates because of their cleavage along (010) surfaces. To increase the set of available substrates, we searched layered structures through the Cambridge Structural Database by means of the ToposPro program package. Also, we propose here an energy partitioning scheme with a new descriptor that allows one to determine the feasibility of cleaving a crystal along a given crystallographic plane. This procedure is based on the partition of cohesive energy among molecules in a given layer in the crystal structure and molecules found in adjacent layers. The experimental validation on 12 selected amino acid structures, selected among potentially suitable compounds for the OMBE trials, showed the reliability of the method proposed here.