Scanning tunneling microscopy investigation of tricycloquinazoline liquid crystals on gold

Abstract

Self-assembled monolayers (SAMs) of hexaalkylthioether derivatives of tricycloquinazoline (TCQ) on Au(111) and tungsten diselenide (WSe2) were investigated by scanning tunneling microscopy (STM). The Au(111) surfaces were found to be etched by the thioether containing solutions. Corroded surfaces which are similar to gold surfaces that were coated with SAMs of thiols or disul®des were revealed by STM. Atomic adsorption spectroscopy proved that an amount of gold that corresponds to ca. 30% of a monolayer was dissolved in 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 cases folded upwards and shielding the aromatic cores. Only after long immersion times were crystalline areas observed locally, in which the alkyl chains were lying ¯at on the gold surface. On WSe2 mono- and multilayers of TCQ molecules in face-on orientation could be imaged by STM. The observed columnar structures displayed long-range order.