New Multi-Harmonic Techniques for Sensing Tip-Sample Interactions and Nanomechanical Material Property Mapping in Dynamic Atomic Force Microscopy

The Atomic Force Microscope (AFM) is a versatile tool for studying and characterizing materials at the micro-and nano-scales. The microcantilever designs used in AFM, as well as the experimental and theoretical approaches for quantitative material characterization, are now well developed and understood. However, there are still certain experimental conditions where the conventional design of these probes and the existing material characterization methods limit the applicability of the tool. The challenges associated with the probe design are addressed by integrating additional degrees of freedom into these probes that enabled modification of the eigen-structure of the probes as desired. Designing, fabricating and experimentally demonstrating the performance of probes with embedded accelerometers for direct measurement of tip accelerations and integrated low frequency paddles for improving signal-to-noise ratio have been the most significant contributions in this direction. In terms of material characterization using AFM, the use of higher harmonics of resonant cantilever vibration were proposed 20 years ago. Yet due to challenges in acquiring several higher harmonics in regular tapping mode AFM, higher harmonic AFM has been bypassed by other multi-frequency methods. We reconsider higher harmonic AFM with a focus on utilizing a small number of measurable higher harmonics of the resonant mode. We develop a mathematical background for the frugal use of higher harmonics, and test the effectiveness of the method by estimating the properties of some polymer blends