Growth and morphology of SnPc films on the S-GaAs(001) surface: a combined XPS, AFM and NEXAFS study

The morphology and molecular ordering of the organic semiconductor tin phthalocyanine (SnPc) on the sulphur-terminated GaAs(001) surface have been monitored by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and near-edge X-ray absorption fine structure (NEXAFS). XPS measurements using synchrotron radiation reveal weak interfacial bonding between the organic molecules and the inorganic semiconductor substrate. The attenuation of XPS core-level peak intensities with increasing organic film thickness suggests a Stranski-Krastanov growth mode, and an island morphology is confirmed by AFM. Although the SnPc clusters do not have specific crystalline facets, NEXAFS spectra show an angle dependence consistent with a molecular orientation close to the surface plane, within the clusters. (C) 2004 Elsevier B.V. All rights reserved.