Microstructure evolution of thin nickel films with embedded chromium oxide nanoparticles

We developed a fabrication method of thin metal matrix composite films reinforced with ceramic nanoparticles. To this end, we deposited a 20 nm Ni / ultrathin Cr-oxide layer / 20 nm Ni tri-layer on a sapphire substrate, and annealed the sample at the temperature of 700°C. We found that after annealing for 10 min the Cr-oxide layer agglomerates into single- or bi-crystalline faceted Cr₂O₃ nanoparticles, with the orientation relationship of (111¯)_Ni∥(0006)_Cr2O3and [112]_Ni∥[12¯10]_Cr2O3to the Ni matrix. We encountered a surprising vertical spread of the centers of mass of the Cr-oxide particles with respect to the initial position of the Cr-oxide layer. We developed a kinetic model of the evolution of particles shape and of their vertical drift, which enabled an estimate of the effective diffusion coefficient of the Ni-Cr₂O₃ interface ([Formula presented]). Though much slower than grain boundary diffusion in Ni, this interface diffusion enables fast transformation of ultra-thin Cr-oxide layer into an array of isolated Cr₂O₃nanoparticles embedded in the Ni film. The insight into the kinetics of the system obtained in the present work paves the way for the design of particle reinforcement of thin metal films with a precise control over the spatial positions of the particles.