The focus of this research is the X-ray photoelectron spectroscopy (XPS) analysis of thin films consisting of Au metal clusters embedded in a dielectric matrix of Al-O coatings. The coatings were deposited by co-sputtering an Al + Au target in a reactive atmosphere with Au contents up to 8 at.%. The Al-O matrix was kept amorphous even after annealing at 1000 degrees C. In the as-deposited films the presence of Au clusters with sizes smaller than 1-2 nm (not detected by XRD) was demonstrated by XPS. With increasing annealing temperature, Au clustering in the dielectric matrix was also confirmed by XPS, in agreement with XRD results. (C) 2011 Elsevier B.V. All rights reserved.