Metallic gallium was observed on the surfaces of GaN commercial samples following argon ion milling. SIMS measurements confirmed that the commercial GaN had approximately 0.02% bulk oxygen present. The SIMS signal was standardized using a specimen of known oxygen content, as determined by elastic recoil detection analysis using 200 MeV heavy ions of Au-197. Despite this 2-5% oxygen was observed by XPS in the bulk of the GaN after the argon ion milling. This oxygen is believed to be from the original surface oxide that re-cycles on the GaN surface during the ion milling. (C) 2004 Elsevier B.V. All rights reserved.