A thermal and passivation study of self-assembled monolayers on thin gold films

Self-assembled monolayers (SAMS) are currently being evaluated as passivation coatings to prepare metallic surfaces for low temperature bonding applications such as nanoelectromechanical devices One of the requirements of this coating is its ability to thermally desorb just prior to bonding. In this paper, we used XPS to investigate the passivation properties of dodecanethiol (C-12) on 50 nm gold layers and the effects of heating the SAMs at different temperatures were investigated in situ using surface plasmon resonance spectroscopy in the Kretschmann configuration. As temperature increases, progressive shifts in the resonant dip of the angular spectra towards lower resonant angle were observed. Such shifts are most likely due to the physical and chemical changes from an ordered state to a more disordered structure. Supporting XPS evidence was also obtained by comparing the core level spectra of carbon and sulfur at different temperatures. With a layer of SAMs present on gold surface, XPS surface analysis also revealed significant reduction in the quantities of C and O as compared to blank gold surface. These findings facilitate the evaluation of the thermal stability and passivating characteristic of self-assembled monolayers in micro or nanodevices under operating environment. (C) 2007 Elsevier B.V. All rights reserved.