AVS 46th International Symposium
    Surface Science Division Friday Sessions
       Session SS1+AS+BI-FrM

Paper SS1+AS+BI-FrM3
Properties of Self-Assembled Monolayers of Biphenyl-Based Thiols

Friday, October 29, 1999, 9:00 am, Room 606

Session: Organic Films/Self-Assembled Monolayers
Presenter: T. Felgenhauer, University of Heidelberg, Germany
Authors: T. Felgenhauer, University of Heidelberg, Germany
H.-T. Rong, University of Heidelberg, Germany
M. Buck, University of Heidelberg, Germany
M. Grunze, University of Heidelberg, Germany
Correspondent: Click to Email
Despite their versatility to modify surface properties, self-assembled monolayers (SAM) based on alkane thiols have limitations concerning conformational stability or structural perfection. In search for more rigid molecules, thiols based on aromatic moieties offer an alternative. However, in contrast to SAMs consisting of alkane thiols experiments on aromatic thiols are relatively scarce. Our experiments focus on thiol SAMs consisting of 4,4'-substituted biphenyls (BP). To allow systematic investigations the number of methylene units between the biphenyl moiety and the thiol group was varied between zero and six. The electrochemical behavior of BP-SAMs turns out to be very different from alkane thiols. In general, the charge permeability of BP-SAMs is higher by orders of magnitude even though the electrochemical stability of BP-SAMs is dependent on the methylene spacer. Exposure to an etching solution reveals a stability significantly higher compared to alkane thiols and suggests an improved structural perfection of BP-SAMs. Spectroscopic characterization of the BP-SAMs yields an orientation of the biphenyl units alternating with the methylene chain length. Comparison of BP-SAMs on Au with those on Ag shows a reversal of the odd-even effect and demonstrates that the sulphur-substrate bond is crucial for the molecular orientation of the biphenyl-SAMs.