Characterisation of Self-Assembled Monolayers on Germanium Surfaces via NEXAFS

Abstract

The formation of self-assembled monolayers (SAMs) by suitable organic molecules with appropriate anchor groups on semiconductor surfaces may be used either to probe both the chemical state and the quality of the surface or to achieve surface passivation. Molecules with thiol anchor groups are able to bond to hydrogen-terminated germanium surfaces (Ge-S bond). We have prepared SAMs of alkylthiols with trifluoroacetate head groups on germanium. The germanium surface prior to and after SAMs formation has been characterised by Near-Edge X-Ray Absorption Fine Structure spectroscopy (NEXAFS) with synchrotron radiation in the PTB laboratory at BESSY II. We succeeded in assigning S-NEXAFS peaks to the Ge-S bond formed during self-assembly and were able to distinguish between different fluorine species via F-NEXAFS.