Formation of self-assembled epitaxial nickel nanostructures

Highly orientated nickel magnetic nanoparticles were obtained by pulsed laser deposition technique on silicon (100) substrate using epitaxial titanium nitride film as the template. These nanoparticles have been characterized by conventional and high-resolution transmission electron microscopy, scanning transmission electron microscopy Z-contrast imaging, and x-ray diffraction techniques. The results have shown that the growth of nickel on epitaxially grown titanium nitride follows a three-dimensional island growth mechanism. The predominant orientation of nickel islands observed is Ni(100)llTiN(100)llSi(100), the so-called ‘‘cube-on-cube'' orientation relation. The islands are faceted with a truncated pyramidal shape and bounded by (111) planes at sides and (100) plane at the top. Islands with nontruncated pyramidal shape were also found in some samples, but with rotational orientation relations, where the nickel crystal rotates with an approximate angle of 90° with respect to one of TiN (110) directions parallel to the interface. The appearance of this rotational epitaxial growth did not show any obvious deposition temperature dependence in the range of 400- 650 °C, rather it seemed to be closely related to the crystalline quality of TiN template. The actual size of islands varies from a few nanometers to tens of nanometers, depending on the deposition time and temperature. The three-dimensional growth of nickel islands and the island faceting could be explained by the surface energy anisotropy of both nickel and titanium nitride.