The effects of beam dynamics on Atomic Force Microscopy measurements

R. Wagner
Purdue University,
United States

Keywords: AFM, beam thoery, PFM, contact reonance, bimodal


The microcantilever beam is central to static and dynamic measurements with the atomic force microscope (AFM). Its order unity stiffness, high resonance frequencies, and high optical lever sensitivity have enabled many advances in AFM metrology. However, the microcantilever simultaneously complicates the interpretation of many experiments due to non-rectilinear tip motion, frequency-dependent optical lever calibration, and non-linear processes that contribute to microcantilever dynamics. Analysis of the microcantilever motion that only interprets it as a lumped element mass-spring-damper model can miss important details of the cantilever response. In this talk, several studies that aim to better understand the influence of cantilever dynamics on different AFM measurements will be reviewed. Specifically, I will discuss the implementation and interpretation of direct measurements of the microcantilever’s operating deflection shape, the different rolls cantilever dynamics can play in both improving and complicating piezoresponse force microscopy, and the influence of nonlinear dynamics in both bimodal and contact resonance AFM. In each of these studies, complications from beam dynamics conspire to make analysis of AFM data more complicated than we might otherwise hope. However, by understanding how the AFM microcantilever vibrates we can account for the effects of cantilever dynamics in existing measurements. Additionally, a deeper understanding of cantilever vibrations can help devise new measurements that extract additional information about the sample. For example, the point where contact between the tip and sample is lost in contact resonance AFM with increasing drive amplitude, or the distribution of a force acting on the body of the cantilever can be extracted via analysis of the cantilever dynamics. It is likely that such detailed analysis and interpretation is often not needed for many commonly used AFM modes. However, when pushing the limits of instrument sensitivity or when developing new AFM modalities it is often important to keep in mind that the microcantilever is a continuous vibrating structure subject to a variety of both linear and nonlinear forces.