Stranski–Krastanow growth of copper overlayers on the Ni(110) surface

Cu overlayer formation on the Ni(110) surface was studied using scanning tunneling microscopy (STM) in an ultrahigh vacuum. Room-temperature deposition of Cu onto a Ni(110) surface exhibited layer-by-layer growth up to 6 monolayers (MLs), followed by three-dimensional island formation, i.e., the Cu overlayer growth on the Ni(110) surface is classified as Stranski–Krastanow growth. At the initial growth stage, anisotropic two-dimensional islands were elongated in the close-packed [ 1 1 ¯ 0 ] direction. The nucleation of the second layer was strongly affected by the morphology of the first layer, and the second-layer islands also extended in the [ 1 1 ¯ 0 ] direction. The third and further layers grew two-dimensionally. Detailed STM images showed mosaic features due to Cu and Ni alloying. Three-dimensional islands were observed for Cu deposition beyond 6 ML. The (110)-oriented top surface of the islands had stripes along the [001] direction. In addition, bumps extending in the [ 1 1 ¯ 0 ] direction were formed on these island surfaces, indicating threading dislocation through the island to relieve the compressive stress of the overlayers. An atomic model of the bump compatible with the STM image was proposed.