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J. Phys. Chem. C 2010, 114, 5400–5409
Electron Beam-Induced Damage of Alkanethiolate Self-Assembled Monolayers Adsorbed on GaAs (001): A Static SIMS Investigation† Chuanzhen Zhou,‡ Jason C. Jones,§ Aaron Trionfi,§ Julia W. P. Hsu,§ and Amy V. Walker*,‡,| Department of Chemistry and Center for Materials InnoVation, Washington UniVersity in St. Louis, Campus Box 1134, One Brookings DriVe, St. Louis, Missouri 63130, and Center for Integrated Nanotechnologies, Sandia National Laboratories, P.O. Box 5800 MS-1415, Albuquerque, New Mexico 87185-1415 ReceiVed: June 15, 2009; ReVised Manuscript ReceiVed: October 4, 2009
We have investigated the reaction pathways involved in the electron-beam-induced damage of -CH3, -OH, and -COOH terminated alkanethiolate self-assembled monolayers (SAMs) adsorbed on GaAs (001) using time-of-flight secondary ion mass spectrometry. Upon electron beam exposure, the monolayers dehydrogenate, leading to the formation of CdC bonds, cross-links, and polycyclic aromatic hydrocarbons (PAHs). We also observe C-S bond scission. The data suggest that the electron beam damage is not uniform along the alkanethiol backbone. Upon electron beam exposure, we observe the loss of CO2 and H2O from the -COOH and -OH terminated SAMs, respectively, indicating that the terminal groups decompose. Although the SAM degradation mechanism is similar to that previously reported for alkanethiolate SAMs adsorbed on metals, there are some important differences. First, the electron dose required to form CdC bonds and PAHs is much smaller than for SAMs adsorbed on metals. Second, although we observe C-S bond scission, we do not observe As-S or Ga-S bond scission and there is no desorption of S, or S-containing, fragments from the surface. We discuss the implications of these studies on the optimization of the experimental conditions for electron beam lithography using SAM resists on semiconductors. 1. Introduction Self-assembled monolayers (SAMs) form dense well-ordered films (1-2 nm thick) on a wide range of substrates including GaAs, Cu, Ag, Au, Pt, stainless steel, SiO2, and Al2O3.1,2 The thickness, as well as the molecular diameter (
