The reaction of oxygen with titanium deposited on Si (1 0 0) surfaces has been studied at room temperature and low oxygen pressures, using XPS and ARXPS. The experimental results for Ti growth on Si can be explained using a model involving a two stage mechanism. The first stage is characterized by the formation of a uniform TiSix layer similar to 4 ML thick and the second one by the formation of metallic titanium that grows following a Stranki-Krastanov mechanism, that is, the formation of a Ti monolayer followed by the growth of Ti islands (7 ML thick) over the TiSix layer previously formed. The oxidation of Ti/Si interfaces strongly depends on the interface that is oxidized. For an interface corresponding to the first stage of deposition a Ti-O-Si mixed oxide layer is formed on the near surface. This layer is on top of a multilayer structure which is composed of TiO2 (Ti4+), titanium suboxides along with Ti-si(Ti-si + Ti1+ + Ti2+ + Ti3+), and substrate when going from the outer surface to the substrate whereas for an interface corresponding to the second stage no Ti-O-Si mixed oxide is detected and a Ti-0 rich layer is observed between the titanium suboxides and the Si substrate. (C) 2014 Elsevier B.V. All rights reserved.