EPITAXY AT NON-60-DEGREES ANGLES - AN STM STUDY OF 7CB ON HOPG

Studies of homologues are often useful for correlating material proper ties to molecular structure. The liquid crystal 4-heptyl-4'-cyanobiphe nyl (7CB) has received very little study, although the homologous 8CB has been studied extensively by STM. Here we report several unusual pr operties of 7CB monolayers on graphite, particularly the fact that ang les between contacting domains of this liquid crystal were observed to favor angles of 17 degrees rather than the expected 60 degrees angles . This and other observations, coupled with an experimentally determin ed unit cell of A = 3.85 +/- 0.37 nm, B = 1.10 +/- 0.10 nm, and Theta( AB) = 92 +/- 6 degrees, lead us to propose an unusual monolayer struct ure for 7CB, where only half of the molecules make the expected alkyl- graphite contact in any domain. The 7CB monolayer shows great complexi ty, including chirality effects and domain-domain interactions.