Study of Ag transport in Cr2N0.61-7Ag nanocomposite thin film due to thermal exposition

•Cr2N0.61 matrix together with Ag nanoparticles are the constituents of grown films.•Silver diffuses to the free surface during annealing in the range 300–500°C.•Compact oxide layer is formed on the surface as a result of annealing.•Oxide layer on the surface hinders the Ag-transport onto the surface.•Surface Ag-content results from competition between intergranular diffusion of Ag and growth of oxide layer. Cr2N0.61-7Ag nanocomposite coatings were deposited on substrates made of Cr-V ledeburitic tool steel Vanadis 6 using reactive magnetron sputtering at a deposition temperature of 500°C. Investigations of as-deposited films and annealing experiments in closed-air atmosphere at temperatures of 300, 400 and 500°C and the durations up to 24h, followed by quantitative scanning electron microscopy, transmission electron microscopy, Auger electron spectroscopy and X-ray diffraction revealed that the films were composed of Cr2N0.61 matrix and individual silver agglomerates located along columnar crystals of the matrix. The maximal size of Ag-agglomerates was 80nm. The surface population density of silver agglomerates increased with prolonging the annealing time up to 2h and then decreased. The increase was more pronounced at lower annealing temperatures. This behaviour was referred to the competition between three phenomena, namely the transport of detached Ag atoms to the free surface, formation of oxide layer on the surface and sublimation of silver from the surface. At lower temperatures and/or shorter annealing times, the Ag-transport to the free surface was determined to be prevalent, thus, an increase in population density of silver agglomerates was determined. On the other hand, for higher temperatures and/or longer annealing times the population density of Ag-agglomerates rather decreased due to retarding effect of thicker oxide layer and sublimation of silver.