Alkanethiol adsorption on the Au(100) surfaces is studied by using scanning tunneling microscopy, x-ray photoelectron spectroscopy and electrochemical techniques. Adsorption of hexanethiol (HT) on the Au(100)-hex surface results in the formation of elongated Au islands following the typical stripes of the reconstruction. Ordered molecular arrays forming hexagonally distorted square patterns cover the stripes with surface coverage ≈ 0.33. On the other hand, HT adsorption on the Au(100)-(1x1) surface shows the absence of the elongated island and the formation of square molecular patterns with a surface coverage ≈ 0.44. The core level shift of thiolates adsorbed on the Au(100)-(1x1) and Au(111) is only 0.15 eV suggesting that chemistry rather than surface sites determines the binding energy of the S 2p core level. These results are also important to complete our knowledge of the chemistry and surface structure for small thiolated AuNPs where the Au(100) together with the Au(111) are the dominant faces.

The surface structure of self-assembled monolayers of hexanethiolate (HT) on the Au(100)-(1 × 1) surface has been studied by density functional theory (DFT) calculations and their results compared to scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) data. We have found two novel surface structure models consisting of adsorbed thiolates on the Au(100)-(1 × 1) surface that fairly account for experimental STM and XPS observations. Surprisingly, these models exhibit better thermodynamic stability than those consisting of thiolate–Auad–thiolate moieties on a reconstructed Au(100)-(1 × 1) surface. Also these proposed models are more stable than the thiolate–Auad–thiolate containing c(4 × 2) lattice on the reconstructed Au(111) suggesting a surface dependent chemistry for thiolates on Au. However, the possible existence of other models with similar or better stability than those proposed in this work and also the possible coexistence of different surface structures and chemistry on the substrate surface cannot be excluded.