Combined analysis employing in-situ X-ray photoelectron spectroscopy. Auger electron spectroscopy, and ex-situ X-ray diffraction has demonstrated the feasibility to deposit single-phase barium oxide overlayers by a direct sublimation of BaO material from an effusion cell. Furthermore, in situ scanning tunneling microscopy has confirmed that the BaO grows as nanoclusters with dimensions down to similar to 2 nm. (C) 2011 Elsevier B.V. All rights reserved.