Kinetic pathways of diffusion and solid-state reactions in nanostructured thin films

Abstract

Kinetic pathways of diffusion and solid state reactions in nanostructured thin film systemsMass transport and solid state reactions in nanocrystalline thin films is reviewed.It is illustrated that diffusion along different grain boundaries, GB, can have important effects on the overall intermixing process between two pure films.These processes can be well characterized by a bimodal GB network, with different (fast and slow) diffusivities. First the atoms migrate along fast GBs (triple junctions) and accumulate at the film surface. These accumulated atoms form a secondary diffusion source for back diffusion along slow boundaries.Thus the GBs of the thin films can be gradually filled up with the diffusing atoms and composition depth profiles reflect the result of these processes. Similar process can be observed in binary systems with intermetallic layers: instead of nucleation and growth of the reaction layer at the initial interface, the reaction takes place in the GBs and the amount of the product phase growths by the motion of its interfaces perpendicular to the GBs. Thus, the entire layer of the pure parent films can be consumed by this GB diffusion induced solid state reaction (GBDIREAC), and a fully homogeneous product layer can be obtained.

Formation of Cu6Sn5 phase by cold homogenization in nanocrystalline Cu–Sn bilayers at room temperature

“…Even the entire layer of the pure parent films can be consumed and a complete intermixing of components in the binary nanocrystalline couple can be achieved by grain boundary migrations through the volume [29]. Competition and/or simultaneous kinetics of the growth of the planar layer and the DIGM in the form of GBDIREAC can be also achieved.…”

“…The planar growth of this layer can be the result of nucleation of the phase at the interface/GBs and a subsequent lateral growth of these nuclei by GB diffusion. If the product layer is not a solid solution but intermetallic compound then one can speak about GB diffusion-induced solid-state reaction (GBDIREAC) [29].…”

Low temperature homogenization in nanocrystalline PdCu thin film system

“…It is known that in thin layered systems homogenization can occur even at low temperatures where the volume diffusion can be neglected [1][2][3][4]. During these processes the interdiffusion takes place along grain-boundaries, GBs.…”

“…In DIGM the grain boundaries move perpendicular to the original boundary plane and leave an alloyed zone behind. Furthermore it was also illustrated [5][6][7][8][9][10][11][12] that complete homogenization of bilayered films can also happen by formations of reaction products along the grain boundaries, (grain boundary diffusion induced reaction, GBDIREAC [4]). The most important difference, as compared to the well-investigated cases of DIGM/DIR in systems forming solid solutions, lies in the formation of new phases.…”

Growth and thermal oxidation of Ru and ZrO2 thin films as oxidation protective layers

“…169 The kinetic mechanisms of compound formation during growth by magnetron sputtering, are based on the basic thin film kinetics of reaction, combined with surface and in-depth diffusion, which can be found in refs. 170,171,172 . However, each system exhibits its own reaction and inter-diffusion kinetics, and, it should be studied separately.…”