Journal of Materials Research


Substrate effects on indentation plastic zone development in thin soft films

D. E. Kramera1, A. A. Volinskya2, N. R. Moodya3 and W. W. Gerbericha4

a1 Metallurgy Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899–8553

a2 Motorola, DigitalDNA Labs, Process and Materials Characterization Lab, Mesa, Arizona 85202

a3 Materials Reliability Division, Sandia National Labs, Livermore, California 94551–0969

a4 Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455


Plastic zone evolution in Al–2 wt% Si metal films on silicon and sapphire substrates was studied using nanoindentation and atomic force microscopy (AFM). AFM was used to measure the extent of plastic pileup, which is a measure of the plastic zone radius in the film. It was found that the plastic zone size develops in a self-similar fashion with increasing indenter penetration when normalized by the contact radius, regardless of film hardness or underlying substrate properties. This behavior was used to develop a hardness model that uses the extent of the plastic zone radius to calculate a core region within the indenter contact that is subject to an elevated contact pressure. AFM measurements also indicated that as film thickness decreases, constraint imposed by the indenter and substrate traps the film thereby reducing the pileup volume.

(Received January 05 2001)

(Accepted August 20 2001)