The Need

Atomic Force Microscopy (AFM) was first used to characterize properties of a sample, including physical, material, electromechanical and chemical properties. For most of these multi-physical characterization schemes, an AFM tip scans over a sample while the tip is in contact with the surface. At the same time, a certain type of stimulus at a fixed frequency is applied either through the cantilever tip or to the sample directly, and the resulting response of the sample is eventually measured by sensing the corresponding cantilever deflection at the excitation (stimulus) frequency. As expected, the resulting mechanical response confined under the nanometer scale AFM tip is often very small, being comparable to or even less than the noise level. Currently, variable contact resonant frequency due to local mechanical contact conditions within AFM systems causes complicated artifacts.

The Technology

Researchers at The Ohio State University and in collaboration with the University of Illinois, led by Ohio State's Dr. Hanna Cho, , have designed a cantilever for AFM with an inner silicon paddle used to measure the piezoelectric properties of a material. The silicon inner paddle oscillates independently of the outer paddle at the first fundamental frequency and the cantilever outputs a signal above the background noise, using contact resonance as amplification. The first contact resonance frequency of this new cantilever system does not vary with respect to the tip-sample stiffness as long as the contact is stronger than a critical value, which is confirmed to be true in actual AFM measurements.

Commercial Applications

• Biochemistry and Chemistry: imaging molecules, cells, and tissues

• Materials Science and Nanotechnology: imaging polymers, nanostructures, and other materials

• Physics and Biophysics: measuring forces

Benefits/Advantages

• Provides unambiguous and reliable measurements of multi-physical properties, with much-reduced topographic and material crosstalk