Whiskers growth in thin passivated Au films

We studied the process of Au whiskers formation from Au thin films deposited on the glass substrate and covered with a conform passivating alumina layer. We demonstrated that the film thickness and morphology play an important role in whiskers formation. Annealing of 10 nm thick Au film exhibiting the discontinuous, maze-like morphology resulted in the formation of Au whiskers. Straight gold whiskers of up to 25 μm in length with a constant diameter were obtained after annealing at the temperatures above 800 °C. The grown whiskers exhibited dislocation-free microstructure. Annealing of 20 nm thick passivated Au film exhibiting continuous morphology resulted in the constrained dewetting of the Au film underneath the alumina layer, and did not lead to the growth of whiskers. We proposed that the main driving force for the whiskers growth is the replacement of the Au/alumina and Au/glass interfaces by one alumina/glass interface of lower energy. We have developed a kinetic model of whiskers growth controlled by the diffusion of gold atoms along the Au/glass and Au/alumina interfaces. The estimated diffusivity was close to the self-diffusion coefficient on the surface of Au. We demonstrated that Au nanoparticles attached to the alumina layer could be easily stripped off from the glass substrate using ethanol.