Scanning tunneling microscopy investigation of tricycloquinazoline liquid crystals on gold

Self-assembled monolayers (SAMs) of hexaalkylthioether derivatives of tricy cloquinazoline (TCQ) on Au(111) and tungsten diselenide (WSe2) were investi gated by scanning tunneling microscopy (STM). The Au(111) surfaces were fou nd to be etched by the thioether containing solutions. Corroded surfaces wh ich are similar to gold surfaces that were coated with SAMs of thiols or di sulfides were revealed by STM. Atomic adsorption spectroscopy proved that a n amount of gold that corresponds to ca. 30% of a monolayer was dissolved i n the assembly solutions. On gold, the aromatic cores of the molecules were found to be in face-on orientation. The alkyl substituents were in most ca ses folded upwards and shielding the aromatic cores. Only after long immers ion times were crystalline areas observed locally, in which the alkyl chain s were lying flat on the gold surface. On WSe2 mono- and multilayers of TCQ molecules in face-on orientation could be imaged by STM. The observed colu mnar structures displayed long-range order. (C) 2000 Elsevier Science S.A. All rights reserved.