Pulsed Laser Deposition of Epitaxial and Polycrystalline Bismuth Vanadate Thin Filmsby Alexander J.E. Rettie, Shirin Mozaffari, Martin D. McDaniel, Kristen N. Pearson, John G. Ekerdt, John T. Market, and C. Buddie Mullins
We report pulsed laser deposition (PLD) synthesis of monoclinic bismuth vanadate (BiVO4, BVO) thin films. X-ray diffraction (XRD), atomic force microscopy, x-ray photoelectron spectroscopy and scanning electron microscopy were used to characterize the samples. Epitaxial, c-axis oriented growth was achieved using single crystal yttria-stabilized zirconia (100), a substrate temperature of 575-600 °C and an oxygen pressure of 7.8 mTorr. The volatility of Bi necessitated a large excess (Bi:V = ~6:1) of this element in the ceramic targets to obtain stoichiometric films. XRD confirmed a BVO (001) || YSZ (001) and BVO  || YSZ  epitaxial relationship. Film growth was 3-D and the morphology was discontinuous, consisting of irregular, smooth grains. Attempts to use a lattice-matched conductive buffer layer (indium tin oxide) to facilitate photoelectrochemical (PEC) testing of the epitaxial films were unsuccessful. Additionally, dense, continuous polycrystalline films were deposited on fluorine-doped tin oxide (FTO) on glass substrates at room temperature with stoichiometric targets and post-deposition annealing in air. Photocurrents of ~0.15 and ~0.05 mA cm-2 were observed at 1.23 V vs. RHE under backside AM1.5G illumination with and without a hole scavenger (Na2SO3), respectively. We argue that the relatively low PEC performance is due to the high oxygen content inherent in the PLD process, and suggest that these continuous films may be well-suited to investigating oxygen-related defects in BVO.