Elastic constants, Poisson ratios, and the elastic anisotropy of VN(001), (011), and (111) epitaxial layers grown by reactive magnetron sputter deposition

Elastic constants are determined for single-crystal stoichiometric NaCl-structure VN(001), VN(011), and VN(111) epitaxial layers grown by magnetically unbalanced reactive magnetron sputter deposition on 001-, 011-, and 111-oriented MgO substrates at 430 degrees C. The relaxed lattice parameter a(o) = 0.4134 +/- 0.0004 nm, obtained from high-resolution reciprocal space maps, and the mass density rho = 6.1 g/cm(3), determined from the combination of Rutherford backscattering spectroscopy and film thickness measurements, of the VN layers are both in good agreement with reported values for bulk crystals. Sub-picosecond ultrasonic optical pump/probe techniques are used to generate and detect VN longitudinal sound waves with measured velocities v(001) = 9.8 +/- 0.3, v(011) = 9.1 +/- 0.3, and v(111) = 9.1 +/- 0.3 km/s. The VN c(11) elastic constant is determined from the sound wave velocity measurements as 585 +/- 30 GPa; the c(44) elastic constant, 126 +/- 3 GPa, is obtained from surface acoustic wave measurements. From the combination of c(11), c(44), v(hkl), and rho we obtain the VN c(12) elastic constant 178 +/- 33 GPa, the VN elastic anisotropy A = 0.62, the isotropic Poisson ratio nu = 0.29, and the anisotropic Poisson ratios nu(001) = 0.23, nu(011) = 0.30, and nu(111) = 0.29.