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 mm thick, were grown on MgO~001! at Ts5570– 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)CrNuu(001)MgO with @100#CrNuu@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 Ts5730, 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 JN 2 1 /JCr which was varied between 1.7 and 14 with the ion energy maintained constant at 12 eV. The surfaces of layers grown with JN 2 1 /JCr51.7 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 ^h&55.1 nm and an in-plane correlation length of ^d&50.21 mm. The combination of atomic shadowing by the mounds with low adatom mobility results in the formation of nanopipes extending along the growth direction. Increasing JN 2 1 /JCr to 14 leads, due to increased adatom mobilities, to much smoother surfaces with ^h&52.5 nm and ^d&50.52 mm. Correspondingly, the nanopipe density decreases from 870 to 270 mm to ,20 mm as JN 2 1 /JCr is increased from 1.7 to 6 to 10. The hardness of dense CrN~001! is 28.561 GPa, but decreases to 22.561 GPa for layers containing significant nanopipe densities. The CrN~001! elastic modulus, 405615 GPa, room-temperature resistivity, 7.7310 V cm, and relaxed lattice constant, 0.416260.0008 nm, are independent of JN 2 1 /JCr . © 2002 American Institute of Physics. @DOI: 10.1063/1.1446239#