Growth and characterisation of zirconia surfaces on Cu(111)

Abstract

Ultra-thin films of zirconia have been prepared on a Cu(111) substrate using two different growth methods and characterised by a range of surface analytical techniques. The first method employed zirconium tetra-tert-butoxide [Zr(OC(CH₃)₃)₄] as a precursor which was contacted with the heated substrate surface under high vacuum conditions to produce the oxide in a CVD-type process. TPD, MBS and XPS studies reveal that the precursor is readily adsorbed and decomposes rapidly at substrate temperatures above ca. 550 K to give stoichiometric ZrO₂, and predominantly methylpropene and water vapour as gas phase by-products. The second method for oxide film growth involved the vacuum evaporation and oxidation of zirconium metal. Conversion to ZrO₂ was achieved using high oxygen exposures and annealing at elevated temperatures to ensure complete oxidation of the base metal. Both methods produce zirconia films on the Cu(111) substrate which are thermally stable in vacuum up to ca. 923 K, and only start to degrade rapidly for temperatures in excess of 1073 K. After annealing at 923 K, LEED showed the zirconia to exhibit long-range ordering with a unit cell indicative of the growth of (111)-oriented cubic zirconia.