Investigation of a contact resonance atomic force microscopy scan speed phenomenon
AuthorGlover, Christopher Cash
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There are many unexplained phenomena that have been observed via atomic force microscopy (AFM) experiments. Understanding the cause of these phenomena is important to perform more accurate quantitative imaging using contact-resonance AFM and other contact-mode AFM techniques at higher scan speeds. This thesis presents evidence to confirm the existence of a scan speed dependent contact-mode AFM phenomenon and applies a squeeze film hydrodynamic lubrication model to explain it. Contact-resonance spectroscopy is used to investigate the phenomenon in which, above a critical scan speed, there is a monotonic decrease in the measured contact-resonance frequency with increasing scan speed. The observed phenomenon was replicated on a mica sample in a randomized set of AFM experiments performed at the National Institute for Standards and Technology (NIST). A literature review revealed that there is a thin water film that exists on mica under certain relative humidity (RH) conditions that has dynamic properties. The squeeze film hydrodynamic lubrication model predicts the general trend observed in the experimental data. However, there exists a higher order model that can be used to investigate the scan speed phenomenon more completely.