Acoustic emission during grain boundary diffusion induced grain boundary migrations and reactions in thin films

Grain boundary, GB, diffusion induced boundary migrations or solid state reactions, at low temperatures – where the bulk diffusion is frozen out – are, at least partly, the result of relaxation of stresses, induced by the inequality of GB atomic fluxes. It was also observed [1] that the GB/interface motions have a jerky character. Thus we made an attempt, first time in the literature to our knowledge, to detect acoustic emission noises in binary Au(15nm)/Ag(15nm) as well as in Au/Cu thin films with different thickness ratios (keeping the thickness of Au constant, to be 25nm), having DIGM as well as GB diffusion induced solid state reactions, respectively [2,3]. Isotherm heat treatments were carried out in Perkin Elmer-7 DSC modified in a manner to be able to connect the needle of a piezoelectric sensor to the surface of the thin film deposited on the (001) oriented single crystal of Si with native oxide layer. At the selected temperatures (between 170 and 240C) considerable alloying in the whole volume of the films took place, leading to formation of solid solution as well as compounds according to the phase diagrams [2,3]. Although – due to the small emitted peaks - the signal to noise ratio is low, the acoustic activity versus time curves showed a clear maximum followed by a decay in the time interval corresponding to the changes in the depth profiles. Attempts to increase the signal/noise ratio are in progress.

[1] C.R.M. Grovenor, Acta Metall., 33 (1983) 579

[2] G. Y. Molnar et al. Belstein J. of Nanotechnology, 7 (2016) 474

[3] A. Tynkova et al. Belstein J. of Nanotechnology, 5 (2014) 1491