SCANNING TUNNELING MICROSCOPE OBSERVATION OF A POLAR LIQUID-CRYSTAL AND ITS COMPUTER-SIMULATION

The scanning tunneling microscope (STM) constructed in the laboratory was utilized to observe the molecular arrangement of a new type of liq uid crystalline molecule, 5-(p-dodecyloxyphenyl)pyrazine-2-carbonitril e (DOPPC), which has large dipole moments along the molecular axis. Th e DOPPC molecules adsorbed on a graphite substrate showed several diff erent STM images with regular two-dimensional molecular arrays. They r evealed a novel inter-digitated double-row structure, differing from t he single-row and the double-row structures proposed for the STM image s of cyanobiphenyl liquid crystals. Moreover, a computer calculation w as conducted based on electrostatic multipole-multipole interaction an d simulated the most energetically preferable molecular arrangement, w hich agreed well with the observed STM image.