Alkanethiol self-assembled monolayers on Au(111) surfaces investigated by non-contact AFM

Self-assembled monolayers (SAMs) of alkanethiol molecules(CH(3)-(CH(2))(n-1)-SH, C(n)) deposited on Au(111) surfaces were investigated by ultrahigh vacuum non-contact atomic force microscopy (UHV-NC-AFM). Octanethiol SAMs (C(8)) and hexadecanethiol (C(16)) SAMs self-assembled from ethanol solutions were used. Molecularly resolved NCAFM images of longer-chain alkanethiol (C(16)) SAMs, which are difficult to be observed by STM, are presented for the first time. The results show that the molecules in this film are hexagonally packed, making (root 3x root 3) R30 degrees structures. Imaging conditions were more stable in the case of SAMs with longer-chain molecules. This is probably because the rigidity depends on the chain length of the molecules. In addition, the high-resolution images of the stripe structures in lower-density region of C(8) SAMs were obtained by NC-AFM.