AVS 49th International Symposium
    Nanometer Structures Wednesday Sessions
       Session NS+EL-WeA

Paper NS+EL-WeA9
Modification of Self-assembled Monolayers by Free Radical-dominant Plasma: The Effect of the Chain Length and the Substrate

Wednesday, November 6, 2002, 4:40 pm, Room C-207

Session: Nanolithography & Self Assembly
Presenter: M. Grunze, Universität Heidelberg, Germany
Authors: M. Zharnikov, Universität Heidelberg, Germany
S. Frey, Universität Heidelberg, Germany
M. Grunze, Universität Heidelberg, Germany
M.-C. Wang, Chung Yuan Christian University, Taiwan (ROC)
J.-D. Liao, Chung Yuan Christian University, Taiwan (ROC)
C.-C. Weng, Chung Yuan Christian University, Taiwan (ROC)
R. Klauser, Synchrotron Radiation Research Center, Taiwan (ROC)
Correspondent: Click to Email
Synchrotron-based high-resolution photoelectron spectroscopy was applied to study the modification of aliphatic and aromatic thiol-derived self-assembled monolayers (SAMs) on (111) gold and silver substrates by a nitrogen-oxygen downstream microwave plasma. It was found that the plasma treatment does not result in a "soft" modification of SAMs, but in their massive damage and disordering. Contrary to the electron beam treatment, both the aliphatic and aromatic films became modified and damaged in a similar way, with the extent of the changes depending on the length of the molecular chains and, above all, on the substrate. For SAMs on Au a profound desorption of the entire SAM constituents and a complete fragmentation of the residual hydrocarbons is observed. For the SAMs on Ag only partial desorption and oxidation took place and, for short treatment times, the films remained practically intact. The desorption of molecular species was preceded by the oxidation of the pristine thiolates to weakly-bonded sulfones, which occurred after the penetration of chemically active oxygen species into the S/substrate interface via defect sites. Such a mechanism clearly explains the observed dependence of damage extent on the SAM thickness and emphasizes the importance of the strength of the thiolate-substrate bond. Thus, a stronger thiolate-substrate bond can be suggested for Ag as compared to the Au substrate. In addition, considering the similarity of the plasma-induced processes and UV-photooxidation, one can extend the major conclusions obtained for the plasma treatment to UV-photooxidation.