Nano Science and Technology Institute

Mechanical Nonlinear Generation with Coupled Torsional Harmonic Cantilevers for Sensitive and Quantitative Atomic Force Microscopy of Material Characteristics

Topography (top) and higher harmonic amplitude (bottom) image of a polymer surface on a silicon substrate.
Tapping-mode has been the most widely used mode of operation in atomic force microscopy. Recent studies have shown that higher harmonics of the cantilever vibrations carries information about material properties such as stiffness, viscoelasticity or capillary forces.

A major problem with higher harmonic imaging is the low signal to noise ratio. Here we present a micromachined cantilever that enhances the signal levels at a particular higher harmonic by 40 dB. We demonstrate that the higher harmonic signal is sensitive to the thickness of an oxide film thermally grown on silicon, and enable mapping of chemical composition variations across a polymer surface.

The enhanced higher harmonic generation achieved with the coupled torsional harmonic cantilever presented in this paper enables sensitive measurement of mechanical properties with nanoscale lateral resolution. The applications of harmonic imaging demonstrated here show the potential of nanomechanical measurements for the study and design of materials engineered at the nanoscale.

Nanotech 2005 Conference Proceedings

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