Publications

Thickness and surface effects on abnormal grain growth in nanocrystalline nickel films

Hattar, Khalid M.; Miller, Bryan; Robertson, Ian M.; Kacher, Josh

Nanostructured metal thin films have been shown to have unique thermal, mechanical, and electrical properties when the internal structure can be maintained. However, this far-from-equilibrium structure has been shown in many cases to be unstable at elevated temperatures. This work investigates the role of surface ledges, large nickel inclusions, electron beam exposure and film thickness on the evolution of high purity, pulsed-laser deposited, free-standing, nickel films via in situ transmission electron microscopy annealing. Grain growth appeared enhanced in a limited temperature range near surface ledges present in the film, but was not affected by large nickel inclusions. In addition, extended exposure to the electron beam resulted in abnormal grain growth. This was hypothesized to be a result of enhanced nickel oxide growth on the surfaces. Finally, increasing film thickness was observed to accelerate the onset of abnormal grain growth and increased the size and number of larger grains. These observations should provide warning that the initial and dynamic surface present in thin films should be taken under consideration during any annealing study, as it may significantly impact the final crystalline structure.