AVS 46th International Symposium
    Surface Science Division Thursday Sessions
       Session SS1+AS+BI-ThM

Paper SS1+AS+BI-ThM2
Surface Phase Transitions of Asymmetric Dialkyl Disulfide Self-Assembled Monolayers

Thursday, October 28, 1999, 8:40 am, Room 606

Session: Self-Assembled Monolayers
Presenter: M. Hara, Frontier Research Program, RIKEN, Japan
Authors: M. Hara, Frontier Research Program, RIKEN, Japan
K. Kamei, Frontier Research Program, RIKEN, Japan
T. Araki, Frontier Research Program, RIKEN, Japan
K. Fujita, Frontier Research Program, RIKEN, Japan
W. Knoll, Frontier Research Program, RIKEN, Japan
Correspondent: Click to Email
Adsorption and desorption processes of asymmetric dialkyl disulfide (hexyl octadecyl disulfide: C6-SS-C18) self-assembled monolayers (SAMs) on Au(111) have been investigated by surface plasmon resonance (SPR), mass spectroscopy (MS), thermal desorption spectroscopy (TDS), and scanning tunneling microscopy (STM). Formation of C6-SS-C6 and C18-SS-C18 dimer species in the monolayer and also in the solution through dimerization and exchange processes has been confirmed during the monolayer growth. In the TDS spectra for shorter immersion SAMs, C6 monomer species showed the strong peaks, and gradually C6-SS-C6 dimer and C18 monomer peaks become stronger for longer immersion. Phase-separated domains of pure C6 and pure C18 striped phases have been visualized in the initial growth stage by STM and the area of the C6 domain was larger than that of C18 one. These results suggest that S-S bonds were cleaved when disulfides adsorbed on Au surface followed by the surface diffusion to form phase separation before standing-up SAM formation. After the C6-rich SAM growth, molecules are dimerized and then exchange process starts from the weakly bound C6-SS-C6 dimers toward C18-rich SAM. SPR kinetics studies also showed the double exponential growth which is different from usual Langmuir adsorption isotherm. Following those results, we propose more detailed surface phase transition model of alkanethiol SAM growth through the dimerization and the exchange processes.