Growth and characterization of epitaxial Zr(0001) thin films on Al2O3(0001)

The authors report the growth of epitaxial Zr(0 0 0 1) thin films on Al2O3(0 0 0 1) substrates at a temperature of 700 degrees C via dc magnetron sputtering in an ultrahigh vacuum deposition system equipped with facilities for chemical vapor deposition, low-energy electron diffraction, and Auger electron spectroscopy. Zr layers with a nominal thickness of similar to 220 nm are deposited at a rate of similar to 0.06 nm/s in 10 mTorr Ar atmosphere. In situ Auger electron spectra of the as-deposited film surface reveal the presence of a Zr peak at 145 eV and Hf peak at 172 eV, the latter due to the presence of Hf impurities in the Zr sputter target. In situ low-energy electron diffraction patterns acquired from the Zr sample show sixfold symmetric spots with an in-plane lattice spacing of 0.3160.02nm, characteristic of Zr(0 0 0 1)-(1 x 1) surface. Cross-sectional transmission electron microscopy images reveal columnar growth and the formation of a crystalline, 22 +/- 8 nm thick, interfacial layer. Energy dispersive x-ray spectra obtained from this region reveal the presence of both Zr and Al. The authors attribute the formation of this interfacial layer to plasma-induced substrate decomposition during sputtering followed by interdiffusion of Al and Zr at the film-substrate interface. omega-2 theta x-ray diffraction data show that the Zr layers are single-phase with hexagonal close-packed structure. Using high-resolution symmetric as well as asymmetric reciprocal space maps, the authors determined that the film is fully relaxed with in-plane and out-of-plane orientation lattice parameters of 0.324 and 0.516 nm, respectively, and identified epitaxial orientation relationships as Zr(0 0 0 4) parallel to Al2O3(0 0 0 12) and Zr(10 (1) over bar0) parallel to Al2O3(11 (2) over bar0). (C) 2016 American Vacuum Society.