EPITAXIAL-GROWTH OF ORGANIC-CRYSTALS ON ORGANIC SUBSTRATES POLYNUCLEAR AROMATIC-HYDROCARBONS

The epitaxial growth of organic crystals on some organic substrates was studied in various combinations of the deposit and the substrate, especially in the case of polynuclear aromatic hydrocarbons. Crystals of polynuclear aromatic hydrocarbons are known to be classified into the following four types on the basis of molecular packing mode in the crystal: herringbone (HB)-, sandwich herringbone (SHB)-, gamma- and beta-types [Desiraju and Gavezotti, Acta Cryst. B 45 (1989) 473]. The HB- or SHB-type crystal was found to grow epitaxially on an organic substrate having the same packing type. The a- and b-axes of the deposit are parallel to the a- (or b-) and b- (or a-) axes of the organic substrates, respectively. In the combination of different packing types, e.g. the HB-type on the SHB-type substrate (HB/SHB) and the gamma-type on the SHB-type (gamma/SHB), the deposit does not always exhibit well-defined epitaxy, but in some cases, the deposit grows epitaxially as polymorphs. This suggests the possibility of controlling the stacking of organic thin films by careful selection of organic substrates.