| AVS 55th International Symposium & Exhibition | |
| Biological, Organic, and Soft Materials Focus Topic | Friday Sessions |
| Session BO+SS+AS-FrM |
| Session: | Self Assembled Ultrathin Organic Interfaces |
| Presenter: | G. Nenchev, University of New Hampshire |
| Authors: | G. Nenchev, University of New Hampshire B. Diaconescu, University of New Hampshire F. Hagelberg, East Tennessee State University K. Pohl, University of New Hampshire |
| Correspondent: | Click to Email |
The molecular self-assembly of alkanethiols (CH3(CH2)n-1SH) on Au(111) surface has been studied extensively in the last 20 years. Despite the abundance of experimental and theoretical data, the true nature of the processes involved in the monolayer formation is still not fully established. We will present a combined UHV VT-STM and DFT study of the adsorption of the simplest alkanethiol, methanethiol (CH3SH), on the reconstructed Au(111) surface. Our findings challenge the established notion that methanethiol is too short to form ordered structures even at low temperature. At sub-monolayer coverage, dimer chains are resolved on the FCC areas of the reconstruction pattern. At higher coverage the monolayer evolves into two continuous self-assembled phases: a rectangular c(4√3 x 2) phase, which coexists with the substrate reconstruction network, and a close-packed p(√3 x √3)R30° hexagonal phase. Our DFT calculation, which takes the reconstruction of the surface into account, confirms the non-dissociative character of the methanethiol adsorption and derives the bonding geometry of the molecular dimers - a sequence of shifted hollow-top and hollow-bridge bonding positions. The numerical calculation reveals that, in stark contrast to longer alkanethiols, at low temperature the self-assembly process of methanethiol is not driven by Van der Waals forces, but by a surface-mediated interaction. These novel results clearly demonstrate the unique nature of the methanethiol adsorption and self-assembly.
This work is supported by the National Science Foundation under Award #0425826 for the Center for High-Rate Nanomanufacturing and under Grant No. DMR-0134933. The computations are performed on the CRAY XT3 machine Sapphire at US Army/Engineer Research and Development Center (ERDC, Vicksburg, MS) in collaboration with Jackson State University, and supported by the DoD through Contract #W912HZ-06-C-005.