Epitaxial growth of tungsten layers on MgO(001)

Smooth single crystal W(001) layers were grown on MgO(001) substrates by magnetron sputtering at 900 degrees C. X-ray diffraction omega-2 theta scans, x-rocking curves, pole figures, and reciprocal space maps indicate a 45 degrees-rotated epitaxial relationship: (001)(w)parallel to(001)(MgO) and [010](w)parallel to[110](MgO), and a relaxed lattice constant of 3.167 +/- 0.001 nm. A residual in-plane biaxial compressive strain is primarily attributed to differential thermal contraction after growth and decreases from -0.012 +/- 0.001 to -0.001 +/- 0.001 with increasing layer thickness d = 4.8-390 nm, suggesting relaxation during cooling by misfit dislocation growth through threading dislocation glide. The in-plane x-ray coherence length increases from 3.4 to 33.6 nm for d = 4.8-390 nm, while the out-of-plane x-ray coherence length is identical to the layer thickness for d <= 20 nm, but is smaller than d for d >= 49.7 nm, indicating local strain variations along the film growth direction. X-ray reflectivity analyses indicate that the root-mean-square surface roughness increases from 0.50 +/- 0.05 to 0.95 +/- 0.05 nm for d = 4.8-19.9 nm, suggesting a roughness exponent of 0.38, but remains relatively constant for d> 20 nm with a roughness of 1.00 +/- 0.05 nm at d = 47.9 nm. (C) 2015 American Vacuum Society.