CONTACT GEOMETRY IMPLICATIONS FOR NANOSCALE MECHANICAL PROPERTY MEASUREMENTS WITH ATOMIC FORCE MICROSCOPY

Gheorghe Stan, Robert Cook, and Prahalad Parthangal

National Institute of Standards and Technology

Gaithersburg, Maryland 20899

Nanomechanical property measurements constitute a challenge to accurately characterize materials and devices at the nanoscale. From the perspective of their use in optical and electronic nanodevices, ZnO nanowires have received a great attention in the last few years. However, their measured mechanical properties (e.g. elastic moduli) exhibit large variations, smaller and larger than their bulk counterparts. If an increase in the elastic moduli is expected at the nanoscale due to the surface predominance, a reduction, sometimes reported as low as 80 percent of the bulk value, can not be reasonably supported. One reason for these variations could come from inappropriate consideration of the real contact geometry in the measurements based on contact mechanics. By using atomic force microscopy we have measured the radial elastic modulus and the shear modulus of ZnO nanowires with diameter around 50 nm. A proper and accurate consideration of the contact geometry has revealed an increase in both investigated elastic moduli. The observed increase in the shear modulus shows that, indeed, the stiffening of the nanowires comes primarily from the surface tension. An easy method of using well-known materials as references for the measurements is proposed to eliminate the unknown parameters which otherwise would require elaborate calibrations with the atomic force microscope.

Author Informations:

Name:                           Gheorghe Stan

Mentor’s name:            Robert F. Cook

Division:                       Ceramics, 852

Laboratory:                   MSEL

Room/Building:               B107/217

Mail Stop:                     8526

Telephone #:                 301-975-3675

Fax #:                             301-975-5995

Email:                           gheorghe.stan@nist.gov

Sigma Xi:                      not a member

Category:                       Materials