Redox reaction at buried ZnO/Ti thin film interface as seen by hard x-ray photoemission and thermal desorption spectroscopy

In the context of low-emissivity glazing, the redox reaction at a buried ZnO/Ti interface is studied in model nanometer-thick film stacks synthesized by magnetron sputtering deposition. For a given amount of Ti, the roles of annealing temperature up to 550 degrees C, of ZnO layer thickness, and of its crystalline quality are explored. The main originality of the approach is the use of hard x-ray photoemission spectroscopy to probe in situ chemical reactions at a buried interface in a non-destructive way. The detailed analysis of relevant core levels reveals the formation of a ZnxTiyOz x Ti y O z ternary compound and the nearly complete oxidation of Ti into TiO2. 2 . Thanks to complementary measurements of thermal desorption spectroscopy and electron probe microanalysis, unexpected diffusion of the Zn redox reaction by-product through the upper part of the stack and its desorption in vacuum are clearly evidenced. The reaction and mass transport pathways are rationalized through thermodynamic simulations.