Morphological and mechanical properties study of [WO3/W]n nanoscale multilayers

Microstructure, morphology and hardness of W, WO3 single layers and WO3/W multilayers with various period thicknesses have been studied. Films have been deposited via RF sputtering at a working pressure of 0.5 Pa and with a power density of 1.18 W/cm2. W layers are crystallised. WO3 single layers were investigated with various oxygen partial pressure (PO2=10-30%). The roughness increases with PO2. This phenomenon is ascribed to active resputtering of the deposited layer by oxygen ions. For a PO2=10%, the layer possesses a stoichiometric composition WO3, an amorphous structure and a homogeneous surface morphology. PO2=10% was chosen to performed WO3/W multilayers, in order to elaborate amorphous/crystallised multilayers and to study their mechanical properties. Several period thicknesses (Λ) have been investigated and X-ray reflectivity patterns reveal a multilayered structure even for the lowest Λ of 2 nm. Nevertheless, no effects of the period thickness on the hardness were observed which is in disagreement with Hall Petch and Lehoczky theories.