Dewetting of Ni and NiAg solid thin films and formation of nanowires on ripple patterned substrates

The solid state dewetting process of thin Ni films during thermal annealing on smooth and ripple patterned silicon dioxide was investigated. The ripple pattern was created by ion etching under oblique incidence and has a corrugation wavelength of about 40nm. Scanning electron microscopy images show a faster decrease of Ni surface coverage for the templated dewetting on the ripple pattern with increasing temperature indicating an additional driving force of curvature induced diffusion. The ridges act as diffusion barriers trapping Ni in the valleys. Finding adequate parameters for film thickness and annealing temperature leads to the formation of nanorods or nanowires. The kinetics of dewetting was analyzed by means of in situ electrical resistance measurements, whereas Ni surface diffusion on Ni(111) planes was determined to be the kinetically limiting process with an activation energy of 0.32±0.02eV. The addition of Ag to the Ni film switches the dewetting mechanism from the common capillarity driven growth mode of voids to the fractal-like growth mode and improves the nanowire formation by self-organization on the templates. Ag is immiscible in Ni and segregates to the surface acting as a kind of catalyst during the dewetting process.