Role of molecular conformations in rubrene thin film growth.

A systematic analysis of the growth of rubrene (C42H28), an organic molecule that currently attracts considerable attention with regard to its application in molecular electronics, is carried out by using x-ray absorption spectroscopy and thermal desorption spectroscopy. The results allow us to unravel a fundamental mechanism that effectively limits organic epitaxy for a large class of organic molecules. If the structure of the free molecule differs substantially from that of the corresponding molecular structure in the bulk, the crystallization is severely hampered.