Amine species on self-assembled monolayers of ω-aminothiolates on gold as identified by XPS and NEXAFS spectroscopy

Functionalised surfaces are of interest in many fields, e. g. in biomedicine, materials science and molecular electronics. In this study a series of self-assembled aliphatic and aromatic monolayers on gold substrates with terminal amino groups was investigated. Four different thiol molecules were used: aliphatic 11-aminoundecane-1-thiol (AUDT), aromatic 4-aminobenzenethiol (ABT) and aromatic omega-amino thiols with an alkyl spacer as 4-aminophenylbutane-1-thiol (APBT) and 3-(4 ''-amino-1,1':4',1 ''-terphenyl-4-yl)propane-1-thiol (ATPT). Evaluation of N 1s XPS data revealed that on the aromatic self-assembled monolayers (SAMs) amino groups exist preferentially as primary amines, whereas on the aliphatic SAM protonated and/or hydrogen-bonded amines are the major species. This result is crosschecked by N K edge near edge X-ray absorption fine structure (NEXAFS) spectroscopy and can be rationalised by the different basicity of aliphatic and aromatic amines. Copyright (C) 2010 John Wiley & Sons, Ltd.