Nickel-Assisted Laser Oxidation of WSe ₂ Layered Films for Spatially Controlled WO ₃ Patterning Process toward Resistive Memory and Molecular Sensing

A novel approach to convert a 2D WSe₂ film into a WO_<i>x</i> film by the laser-induced oxidation process using a nickel (Ni) adsorption layer, namely Ni-assisted laser oxidation process, was demonstrated. A layer of Ni metal was deposited to absorb the heat of the laser and oxidize the top WSe₂ layer, for which an aluminum oxide (Al₂O₃) layer is then deposited as a barrier layer. A continuous wave laser with a wavelength of 808 nm is selected as the laser source, as it is not absorbed by the WSe₂ layer. By introducing a patterned Ni layer, the selective oxidation process on WSe₂ into WO₃ can be achieved owing to the photothermal effects caused by the Ni layer with O₂ gas. The successful oxidation parameters, including laser powers and irradiation durations with a fixed Al₂O₃ barrier layer thickness of 50 nm, were investigated. Resistive random-access memory (RRAM) devices fabricated using the Ni-assisted laser-oxidized WO₃ structure exhibit clear resistive switching behavior compared to the structure without the laser oxidation process. In addition, the Ni-assisted laser-oxidized WO₃ structure showed obvious surface enhanced Raman spectroscopy (SERS) signals of crystal violet (CV) and methylene blue (MB) with the lowest concentration of 10^-6 M.