We prepared patterned self-assembled monolayers (SAMs) consisting of hexadecanethiol (16AT) and ferrocenyldodecanethiol (12FAT). The samples were characterized by scanning force microscopy (SFM), X-ray photoelectron spectroscopy (XPS), electrochemistry and contact angle measurements. Lateral force mode (LFM) of SFM shows image contrast even between surface regions of quite similar hydrophobicity. The 12FAT regions undergo irreversible chemical changes and become electrochemically inactive upon long exposure to the laboratory atmosphere. These chemical changes can be monitored by LFM, XPS, contact angle and electrochemistry. The LFM images of the exposed and contaminated samples show a reversed frictional contrast relative to the LFM images of the fresh samples and to the LFM images of the exposed but ethanol-rinsed sample. XPS and SFM data show that the 12FAT regions show more contamination than the 16AT regions. Based on these observations, the mechanism of the LFM image contrast is discussed and other driving forces, arising not only from differences in hydrophobicity but also from basic material properties such as elasticity, packing and contamination, are suggested.