Authors: O. Sahin, C.F. Quate and O. Solgaard
Affilation: Stanford University, United States
Pages: 663 - 666
Keywords: atomic force microscope, tapping mode, cantilever, material characterization
Tapping-mode atomic force microscopy has been the most widely used mode of operation. Due to non-linear tip-sample forces, dynamics of the cantilever motion is an extremely rich problem. Recent studies have shown that higher harmonics of the cantilever vibrations has the potential to image material properties such as stiffness, viscoelasticity or capillary forces. A major problem with the higher harmonic imaging is the low signal to noise ratio. Here we present recent advancements we made in higher harmonic generation and imaging. These techniques have the potential to enable quantitative mechanical property measurements and chemical compositional mapping. We have designed, fabricated and experimentally demonstrated the use of a new class of micromachined cantilevers, called coupled torsional harmonic cantilevers. These cantilevers have an asymmetric shape with an offset tip. This couples the flexural vibrations to torsional modes through higher harmonic generation. Torsional modes have high mechanical bandwidth and high sensitivity that enhances particular harmonics by 40dB. This technique has the potential to provide quantitative measurements. We demonstrate measurement of the ratio of the stiffness of the two materials and map chemical composition across a surface.
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