Monolayer epitaxy of a triangular molecule on grpahite

摘要

2,4,6-Tris(1,3-dithiol-2-ylidene)-1,3,5-cyclohexanetrione (C_15H_6O_3S_6 abbreviated TDTCHTO) has a shape fo triangular propeller-like strucutre, and is knwon to crystallizes an orthoghombic structure (orthorhombic-I) by solutiongroth process. In his study, monolayer of TDTCHTO was gronw on a graphite (0 0 1) surface by vacuum-depostion, and was studie don its structure and eptiaxy by STEM. The obsered two-dimensional lattice of TDTCHTO monolayer is hexagonal with α=1.77 nm, in which the two molecules stack with their triangular moleculr planes paralel onto the graphite surface. As a result, the monolayer of TDTCHTO forms a different laeyr structure from the known orthorhomic structur, and therefreo the moleuclar packign with hexagonal symmetry may be promoed by the symmetry of grphite surface. From the STM observation, the epitaxy is concluded as commensurate, not point-on-line coincidence, which means that an interaction between TDTCHTO and graphtie is sronger comaring with side-by-side intermolecular interaction in the monolayer. The α-axis of he monolayer TDTCHTO makes an angle of 14 deg with the αβ=-axis of graphite, and every molecule is coordinated on equivalent lattice point of grahite. This monolayer strucutre is discussed in relation with the orthorhombic-II observed with TEM for a thickeer film grown on grahite.