Interface controlled microstructure evolution in nanolayered thin films

X-ray nano-diffraction and transmission electron microscopy were conducted along the thickness of a ~ 4 μm thick CrN/AlN multilayer with continuously increasing AlN layer thicknesses from ~ 1 to 15 nm on ~ 7 nm thick CrN template layers. The experiments reveal coherent growth, large columnar grains extending over several (bi-)layers for thin AlN layer thicknesses below ~ 4 nm. Above ~ 4 nm, the nucleation of the thermodynamically stable wurtzite structured AlN is favored, leading to coherency breakdown and reduction of the overall strains, disrupting the columnar microstructure and limiting the maximum grain size in film growth direction to the layer thickness.