Epitaxial cobalt films in the thickness range of 3.9 to 8.6 nm were deposited on Al2O3[112¯0] substrates by dc magnetron sputtering at a substrate temperature of 315 °C. In situ annealing was performed in a vacuum after which the samples were rapidly quenched to room temperature in order to preserve the high temperature structure. Ex situ atomic-force microscopy revealed that surface roughening takes place during annealing and reaches a maximum when the annealing temperature TA is equal to a critical temperature TC~500 °C. We discovered that if TA>TC the surface becomes smooth again, although large rectangular pits that go down to the substrate also appear. X-ray-diffraction data show that unannealed samples are oriented along the hcp direction. Upon annealing samples transform to a preferentially fcc orientation for TATC. We show that surface or interface oxidation cannot be the sole cause of this effect. We speculate that an increasing interface strain at higher temperatures or a surface reconstruction of the substrate are possible mechanisms.
Digital Commons Citation
Shi, H. T. and Lederman, D., "Surface smoothing and crystalline reorientation in thin cobalt films" (1998). Faculty Scholarship. 360.
Shi, H. T., &Lederman, D. (1998). Surface Smoothing And Crystalline Reorientation In Thin Cobalt Films. Physical Review B - Condensed Matter and Materials Physics, 58(4), R1778-R1781. http://doi.org/10.1103/PhysRevB.58.R1778