A novel flux coating method for the fabrication of layers of visible-light-responsive Ta3N5 crystals on tantalum substrates

Abstract

Layers of well-developed crystals of Ta₃N₅ were successfully fabricated on Ta substrates by using a novel flux coating method in a flow of NH₃. The flux coating method is a simple one: the Ta substrates were coated with aqueous solutions of sodium compounds (= fluxes) and subsequently heated in a flow of NH₃, whereupon the surfaces of the Ta substrates were dissolved in the flux, resulting in Ta₃N₅ crystal layers. The Ta in Ta₃N₅ was provided by the substrate. Therefore, crystal layers with good adhesion could be grown directly on the substrates. The shape of the individual crystals as well as the surface morphology of the layers formed was determined by the flux used. The crystals fabricated using NaCl–Na₂CO₃ as the flux were prismatic and had relatively smooth faces, covering the surface of the Ta substrate uniformly. The crystal growth field resulting from the use of this method yielded well-formed crystals, which presumably grew from a solution. Finally, it was confirmed that a thus-synthesized Ta₃N₅ crystal layer modified using Co-Pi as the co-catalyst generated a photoanodic current under visible-light irradiation.