Structural and electrical properties of nanocolumnar W-Mo thin films with a Janus-like structure

A Janus-like structure is obtained in W-Mo thin films with a clear separation between both metals. Thin films are deposited on glass and silicon substrates by magnetron co-sputtering using glancing angle deposition technique with two tilted targets (oblique angle α = 80°). Films (two thickness series of 300 nm and 1 μm) are prepared with the same pressure (0.33 Pa) and tungsten target current (IW = 140 mA) but with various molybdenum target currents (from 10 to 200 mA). The effect of Mo target current and thickness on the films microstructure and electrical response is investigated using scanning and transmission electron microscopy, X-ray diffraction and van der Pauw method. Porous and columnar W-Mo thin films with inclined columns are obtained due to the shadowing effect. Playing on the Mo target current allows controlling the architecture of the films until obtaining columns perpendicular to the substrate surface and equivalent W and Mo atomic concentrations. X-ray diffraction shows a significant thickness effect on the films microstructure with dominance of α or β phases of W for 1 μm or 300 nm, respectively. From transmission electron microscopy, W and Mo are pointed out in distinct sides of the columns and a finer structural analysis supports the clear separation between W and Mo. This two components design is repeated for all columns in the film proving that W-Mo thin films exhibit a Janus-like structure.