Growth of Ni Films Observed by Scanning Tunneling Microscopy and X-ray

Scanning tunneling microscopy was used to measure the mean lateral dimensions D of grains at the surface of Ni films with thicknesses ranging from 15 to 200nm. The same films were analyzed by x-ray diffraction to obtain the average linear dimensions δ of coherent scattering regions in the direction normal to the film plane (coherence depths). For thin Ni films condensed on single sapphire substrate at room temperature, these two lengths D and δ are equal and increase with film thickness. But for films thicker than 130nm, these two lengths have different constant values and D > δ. This is because the coherent scattering depth is not only limited by the grain sizes but also by various defects in the grains. The difference between the constant values of D and δ disappears for films after annealing for 30min at 423K in the ultra-high vacuum system.