Functional nanostructured tungsten oxides films by RFsputtering

Polymorph tungsten oxide and its sub-stoichiometric phases (WO3-x) have an extraordinarily broad range of possible photonic applications, from electrochromic layers in smart windows, to UV optical detectors, full-optical chemical sensors and photo-electro-catalytic membranes.We focus on Radio-Frequency (RF) magnetron sputtering deposition as a broadly versatile method to synthesize WO3-xin different stoichiometries and nanostructures, easily up-scalable to industrial processes. We report on WO3-xfilms fabricated under different recipes, which deeply differ in terms of possible applications. Optical-grade compact WO3- x films can be fabricated by non-reactive magnetron RF-sputtering deposition from a WO3 target at room temperature, followed by thermal annealing to tailor stoichiometry and structure. Films transparent in the NIR and electrically conductive can be obtained, that perform well as transparent contacts [1], but also insulating films, with the possibility to embed them into multi-layered IR resonant photonic structures for opto-chemical sensing [2]. Nanoporous WO3-xphotoelectrodes for green H2production are obtained from metallic W target, by RF-plasma sputtering process in a diode configuration in a reactive 40% O2 /Ar atmosphere. By changing the total gas pressure in the growth chamber, at same partial O2pressure, a bilayered diode-like structure is formed, which improves photoelectron transfer and decreases the interfacial resistance (Rct), leading up to about a 30% increase in photo-electro-catalytic (PEC) performance compared to monolayers coatings and to a 93% faradaic efficiency, which is among the highest reported so far for WO3 photoanodes [3].