Measurement of Young's modulus variation with layer pair and interplanar spacing in gold–nickel nanolaminates using nanoindentation and the tapping mode

Abstract

The features of grain size and interface separation strengthen the mechanical behavior of metallic nanolaminates. In addition, the presence of interlayer lattice strains can lead to a superlattice structure within the nanolaminate. The superlattice affects intrinsic properties of technological interest including electronic, magnetic, and elastic. The complex elastic and plastic behaviors of gold–nickel nanolaminate superlattice coatings as studied using nanoindentation are revisited with the tapping mode of a force microscope. Young's modulus is determined with nanoindentation during the initial elastic unloading after plastic deformation at depths up to one-fifth the coating thickness. The tapping mode provides a measurement during the initial elastic deformation at depths of only a few nanometers. The tapping mode utilizes the shift in the resonant frequency of the probe-cantilever system as contact is made with the sample surface. Both of these nanoprobe test methods produce results for measurements conducted with loading normal to the surface plane. A softening in the Young's modulus of gold–nickel nanolaminate coatings occurs for samples with layer pair spacing between 1 and 9 nm. The magnitude of softening corresponds with a progressive increase in the tensile state as measured with the change of interplanar spacing along the growth direction.