Growth of heterolayered [cubic-TaC(111) + rhombohedral-Ta3C2(0001)] nanocomposite thin films on Al2O3(0001)

We report the formation of highly-oriented B1-TaC(111) and rhombohedral-Ta3C2(0001) phases on Al2O3(0001) substrate during ultrahigh vacuum dc magnetron sputtering a TaC target in 5 mTorr Ar/C2H4 gas mixtures with 0.1% 1% ethylene partial pressures pc at temperatures Ts = 1123 K 1273 K. determined as-deposited layer morphology, crystallinity, microstructure, spatial compositional variation using X-ray diffraction along scanning transmission electron microscopies energy dispersive spectroscopy. find that layers grown exhibit strongly facetted surfaces columnar grains while those higher are rough irregular features. Films deposited show primarily B1-TaC 111 reflections. Layers lower (= K) two-phase mixture twins, oriented respect to as: (111)TaC∥(0001)Ta3C2, [2¯11]TaC∥[112¯0]Ta3C2 [1¯1¯2]TaC∥[112¯0]Ta3C2 (0001)Ta3C2∥(0001)Al2O3, [101¯0]Ta3C2∥[112¯0]Al2O3. Interestingly, we observe Ta3C2 phase near film/substrate interfaces top layers. suggest stoichiometric is more stable than sub-stoichiometric as consequence which form over These results exciting possibility growth cubic-TaC and/or layered-Ta3C2 appropriate choice deposition parameters.