METAL DIFFUSION ALONG THE FILM-SUBSTRATE INTERFACE IN PARTIALLY DEWETTED THIN FILMS

In a recent work [1], an indirect evidence for fast self-diffusion of Ni along the Ni-sapphire interface has been obtained. Polycrystalline Ni films of 40 nm in thickness were deposited on sapphire substrates. Solid state dewetting and grain boundary grooving in the films were studied at 700°C. An unusual flat topography of the grain boundary grooves and homogeneous thickening of the film were interpreted in terms of fast Ni self-diffusion along the film-substrate interface [1].

Based on these results, we propose a new method of measuring the metal heterodiffusion along the Ni-sapphire interface. We deposited a 4 nm thick Au film on partially dewetted Ni film which consists of holes (dewetted areas) surrounded by a bi-crystalline film. Afterwards, a diffusion annealing was performed at the temperature of 600°C, at which the morphology of the Ni film is highly stable. Gold atoms diffused from the edge of the holes along the Ni-sapphire interface, and the concentration decay in the direction from the hole edge to the unperturbed film was quantitatively characterized by high resolution transmission electron microscopy. Based on the suggested method, diffusion coefficient of Au along a film-substrate interface was determined.

[1] D. Amram, L. Klinger, N. Gazit, H. Gluska, E. Rabkin. ”Grain boundary grooving in thin films

revisited: the role of interface diffusion”, Acta mater. 2014; 69:386.