Solvent Effect on Formation of Cysteamine Self-Assembled Monolayers on Au(111)

Abstract

Cysteamine (CA) self-assembled monolayers (SAMs) formed in various solutions on Au(111) were examined by scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) to understand the solvent effect on the SAM structure. The STM study revealed that the surface structure of CA SAMs prepared in polar protic solutions was strongly influenced by immersion time, while there were no significant structural changes in the SAMs prepared in nonpolar and polar aprotic solutions. This result implies that the proticity of the solvent and the immersion time play important roles in determining the surface structures of the amino-terminated CA SAMs due to the coadsorptoin of solvent molecules onto the clean monolayers, which are stabilized by hydrogen bonding between polar protic solvents and the clean monolayers. In addition, our STM and XPS results for CA SAMs on Au(111) suggest the existence of two different structural conformations, i.e., trans and gauche conformers.