Substituent effect on epitaxy of mono-molecular layer on HOPG

The monolayer of tetramcthyl-bis[1,23,5]thiadiazolo-p-quinobis(1,3-dithiole ) (TMBTQBT) on graphite was examined by scanning tunneling microscopy. The monolayer crystal lattice of TMBTQDT was found to exhibit point-on-line coi ncidence epitaxy with respect to the (0001) graphite. and expands a little compared with the corresponding layer in the bulk crystal. This result indi cates that the S . . .S intermolecular interaction or bond in the TMBTQBT m onolayer is not strong or doesn't exist in contrast to the ease of pristine BTQBT. The high contrast positions in the STM image were found to correspo nd to the sulfur atoms of the TMBTQBT molecule.