Nonlinear dynamics of microcantilevers in liquid environment dynamic atomic force microscopy
Abstract
Dynamic atomic force microscopy (dAFM) uses a microcantilever probe with a sharp tip mounted on the free-end that is made to oscillate in close proximity to a sample where the presence of nonlinear, tip-sample interaction forces affect the oscillations of the probe. dAFM methods were originally designed to operate in ambient air or vacuum, where quality factors of microcantilever probe are typically high. It was in these high quality factor regimes where much of the theory and understanding of the cantilever dynamics in dAFM originally developed. Prompted by the motivation to image a number of biological samples in pseudo-native environments, the oscillating dAFM probe was introduced to a liquid medium in the mid-nineties. The move to liquid environments brought with it theory and underlying assumptions that were established for operation in air and vacuum but frequently break down in liquids. Due to the presence of significant hydrodynamic loading, the quality factors of microcantilever probes in liquids are typically moderate to low. These low quality factor regimes introduce a new class of nonlinear phenomena in addition to new channels for compositional mapping of material properties. This thesis focuses on aspects of the microcantilever dynamics unique to liquid environment dAFM. A high-fidelity model for the dynamics of microcantilevers interacting with substrates that is able to incorporate experimentally calibrated lumped parameters is developed. A study of the dynamics of microcantilevers with moderate quality factors based on a slow time description of the probe dynamics is presented. An investigation into the dynamics of microcantilevers with low quality factors through numerical simulations, experiments and continuation is provided. Finally, compositional mapping in low quality factor regimes is investigated.
Degree
Ph.D.
Advisors
Raman, Purdue University.
Subject Area
Mechanical engineering
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.