It was experimentally demonstrated that, after ion irradiating 60nm thick Au films on Si substrates with 230keV Ar+ ions, annealing conditions could be found leading to strong diffusional contrasts between bombarded and unbombarded areas. While Au readily diffused into the bombarded part of the sample at 310C, its diffusion was still completely blocked under identical conditions in the unbombarded parts. Clear evidence was provided that this diffusional contrast was due to bombardment induced amorphization of the underlying Si substrate. The amorphous Si (a-Si), however, has to extend right to the Au/Si interface, since any intermediate crystalline layer will suppress the diffusional contrast. An example for this latter situation was realized by performing the ion bombardment prior to the evaporation of the top Au layer leading to a still crystalline Si surface layer, which was found to act as a barrier against Au diffusion at 310C. In accordance with the idea that a-Si, independent of its specific preparation, caused the observed Au diffusion enhancement, the effect was also found for a-Si prepared by evaporation at ambient temperature. In that case an even higher Au diffusion coefficient was obtained than for Si amorphized by ion bombardment pointing to subtle structural differences between both types of amorphous Si.

Influence of Ion-Induced Amorphicity on the Diffusion of Gold into Silicon. P.Erhart, K.Clémer, J.Eisenmenger, T.Müller, H.G.Boyen, P.Ziemann, J.Biskupek, U.Kaiser: Journal of Applied Physics, 2006, 100[6], 063534 (6pp)