Investigation of Intermediate Steps in the Self-Assembly of n-Alkanethiols on Gold Surfaces by Soft X-ray Spectroscopy

Near-edge X-ray absorption fine structure (NEXAFS) spectroscopy was used to investigate the intermediate steps in the self-assembly of the long-chain thiol CH₃(CH₂)₂₁ on gold surfaces. After a first rapid adsorption process the alkyl chains are strongly entangled. The slow, second step observed previously by Bain et al. (J. Am. Chem. Soc. 1989, 111, 321) can be identified as an ordering process where the initially entangled alkyl chains are gradually straightened. The process of self-assembly thus resembles the grafting of end-functionalized polymers to a surface (“polymer brushes”).