Growth of single-crystal CrN on MgO(001) : Effects of low-energy ion-irradiation on surface morphological evolution and physical properties

• CrN layers, 0.5 ╡m thick, were grown on MgO(001) at Ts=570-775░C by ultrahigh vacuum magnetically unbalanced magnetron sputter deposition in pure N2 discharges at 20 mTorr. Layers grown at Ts=700░C are stoichiometric single crystals exhibiting cube-on-cube epitaxy: (001)CrN(001)MgO with [100]CrN[100]MgO. At higher temperatures, N2 desorption during deposition results in understoichiometric polycrystalline films with N fractions decreasing to 0.35, 0.28, and 0.07 with Ts=730, 760, and 775░C, respectively. The surface morphologies of epitaxial CrN(001) layers were found to depend strongly on the incident ion-to-metal flux ratio JN2+/JCr which was varied between 1.7 and 14 with the ion energy maintained constant at 12 eV. The surfaces of layers grown with JN2+/JCr=1.7 consist of self-organized square-shaped mounds, due to kinetic roughening, with edges aligned along orthogonal <100> directions. The mounds have an average peak-to-valley height =5.1 nm and an in-plane correlation length of =0.21 ╡m. The combination of atomic shadowing by the mounds with low adatom mobility results in the formation of nanopipes extending along the growth direction. Increasing JN2+/JCr to 14 leads, due to increased adatom mobilities, to much smoother surfaces with =2.5 nm and =0.52 ╡m. Correspondingly, the nanopipe density decreases from 870 to 270 ╡m-2 to <20 ╡m-2 as JN2+/JCr is increased from 1.7 to 6 to 10. The hardness of dense CrN(001) is 28.5▒1 GPa, but decreases to 22.5▒1 GPa for layers containing significant nanopipe densities. The CrN(001) elastic modulus, 405▒15 GPa, room-temperature resistivity, 7.7╫10-2 cm, and relaxed lattice constant, 0.4162▒0.0008 nm, are independent of JN2+/JCr. ⌐ 2002 American Institute of Physics.

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