Strain is induced when an electric field is applied to a ferroelectric, piezoelectric, dielectric, or ion conducting material (inverse piezoelectric effect, electrostriction, electrochemical strain). The strain-related sample surface displacement can be detected in the piezoresponse force microscopy (PFM) mode of an atomic force microscope (AFM). Contact resonance PFM (CR-PFM), where the drive frequency matches a resonance of the coupled tip-sample system, offers higher sensitivity to surface displacement (noise floor of ~ 0.1 pm) than quasi-static PFM (~ 10 pm). However, conversion of the experimental results to quantitative displacement data is more complex for CR-PFM than quasi-static PFM.
Our project is aimed at establishing CR-PFM as a technique for quantitative imaging of bias-induced strain, and for measuring frequency dependent responses within an extended range (~ 10 kHz to 10 MHz). We have implemented several new approaches to solving key measurement issues. Both laser interferometry and PFM-based procedures for quantifying the “shape factor” that relates the AFM deflection amplitude to surface displacement were demonstrated (Ref. 1). Isomorphic CR-PFM, a new imaging technique in which the CR frequency is held constant for all pixels while force is varied, was shown to produce image contrast more directly related to material properties than competing techniques (Ref. 3). Excitation at higher eigenmodes, beyond the commonly used first flexural mode, was shown to provide increased sensitivity as well as reduction or elimination of electrostatic artifacts (Ref. 2). We welcome new ideas for advancing the measurement science, or for applying quantitative CR-PFM to novel materials and device structures, such as piezoelectric devices for energy harvesting and nano-generation, or lithium ion battery materials for improved power generation and charging rate. An Asylum Research Cypher S and other AFM platforms are available for this research.
Killgore, J. P., Deolia, A., Robins, L. H., & Murray, T. W. (2019). Experimental reconstruction of the contact resonance shape factor for quantification and amplification of bias-induced strain in atomic force microscopy. Applied Physics Letters, 114, 133108.
MacDonald, G. A., DelRio, F. W., and Killgore, J. P. (2018). Higher-eigenmode piezoresponse force microscopy: a path towards increased sensitivity and the elimination of electrostatic artifacts. Nano Futures 2, 015005.
Robins L H, Brubaker M D, Tung R C, and Killgore J P (2020). Isomorphic contact resonance force microscopy and piezoresponse force microscopy of an AlN thin film: demonstration of a new contact resonance technique. Nano Futures, in press.
Atomic force microscopy; Contact resonance force microscopy; Electrochemical strain microscopy; Piezoresponse force microscopy; Scanning probe microscopy; Anode materials; Cathode materials; Electrical energy storage; Electrostriction; Energy harvesting; Ferroelectric; Lithium ion battery; Multiferroic; Piezoelectric.