Nanometer scale chemistry and microstructure of CrN/AlN multilayer films

Abstract

Nanometerscale multilayer CrN/AlN thin films were deposited by pulsed DC magnetron sputtering. Nanoscale resolution chemistry and microstructure of CrN/AlN films with modulation periods (Λ) of 4nm and 18nm were studied using advanced microscopy and diffraction. At the nanometer level, the interface between the CrN and AlN nanolayers contains a concentration gradient of Al and Cr. Inter-diffusion of Cr and Al atoms into the AlN and CrN layers was identified. Microstructural characterization revealed the CrN nanolayers epitaxially stabilize the AlN layers (2nm) to a cubic structure for the Λ=4nm film. The rapid repetition of the interfacial energy across the AlN nanolayers is critical for the coherent epitaxial growth. The film at Λ=4nm exhibited a superhardness of 42GPa. In contrast, the AlN layers (12.5nm) exhibited a hexagonal structure in the Λ=18nm film as the bulk energy becomes dominating, in which misorientated and incoherent interfaces were found. The hardness of the film dropped down to 23GPa.