Elastic-property measurements of ultrathin films using atomic force acoustic microscopy

Abstract

Atomic force acoustic microscopy (AFAM), an emerging technique thataffords nanoscale lateral and depth resolution, was employed to measure theelastic properties of ultrathin films. We measured the indentation modulusM of three nickel films approximately 50, 200, and 800 nm thick. In contrastto conventional methods such as nanoindentation, the AFAM results remainedfree of any influence of the silicon substrate, even for the 50 nm film. X-raydiffraction and scanning electron microscopy results indicated that the filmswere nanocrystalline with a strong preferred (111) orientation. Values ofM ranged from 210 to 223 GPa, lower than expected from values for bulk nickel. The reducedvalues of the elastic modulus may be attributed to grain-size effects in the nanocrystallinefilms.