Effect of molecular symmetry and packing efficiency on the epitaxial growth modes of monomolecular film on graphite studied by STM: the case of 2,4,6-tris (4,5-dimethyl-1,3-dithiol-2-ylidene)-1,3,5-cyclohexanetrione

The monomolecular film of 2,4,6-tris(4,5-dimethyl-1,3-dithiol-2-ylidene)-1, 3,5-cyclohexanetrione (HMTDTCHTO) vacuum-deposited on a (0 0 0 1) surface o f graphite was observed by scanning tunneling microscopy, in order to revea l its growth mode and structure. The unit lattice of the HMTDTCHTO monomole cular layer is incommensurate to the substrate lattice. The flat lying mole cules form an ordered close-packed arrangement in the film on the graphite. The results are compared with those of 2,4,6-tris(1,3-dithiol-2-ylidene)-1 ,3,5-cyclohexanetrione (TDTCHTO). The growth modes of some monomolecular fi lms are examined from a viewpoint of two-dimensional packing efficiency and molecular symmetry. (C) 2001 Elsevier Science B.V. All rights reserved.