Scanning probe microscopy of self-assembled organic monolayers

STM/AFM and LFM microscopes were used for morphological analysis of uniform and patterned self-assembled monolayers (SAMs) formed from docosanethiol (HS-(CH₂)₁₁CH₃), dodecanethiol (HS-(CH₂)₁₁CH₃) and mercaptododecanoic acid (HS-(CH₂)₁₁COOH) molecules adsorbed at 200nm gold film deposited onto silicon wafer. All measurements were performed in air. The lateral distances between atoms were determined using HOPG sample for calibration. Images obtained on clen Au substrate revealed that the surface was not uniform but was composed from flat crystallites having {111} surfaces. For DCT/Au samples a (√3 x √3) R30° reconstruction of molecules was detected. In this case, electron tunneling was pesumed to occur between the microscope itp and gold-bound uslfur atom of DCT molecule. Depressions with a diameter of 40÷150 Å and a depth of approximately 2.4 Å were observed on otherwise flat surface of DCT monolayer. Our results support hypothesis that defects are formed by removal of Au atoms that takes place during monolayer formation when the substrate is immersed in ethanol solution.