Characterizing ferroelectric properties via SS-PFM: separating the instrument from the sample

B. Pittenger
Bruker Nano,
United States

Keywords: Characterization, ferroelectric properties, SS-PFM

Summary:

The behavior of a very wide range of samples from biomaterials to microelectromechanical systems is influenced by their electromechanical response.[1] Ferroelectric materials are of particular interest for their ability to switch polarization under an applied electric field and maintain their state when the field is removed. To develop a more complete understanding of the behavior of these materials it is important to characterize their response at the nanoscale. Piezoresponse force microscopy (PFM) is ideal for this since it combines imaging of the piezoelectric response with spectroscopy and domain manipulation, all localized to the nanoscale by an AFM probe tip. Unfortunately there are several challenges in doing PFM measurements well. For one, the many types of electromechanical response of the sample can be difficult to separate.[2] Additionally, the observed signal is often influenced by the measurement system (AFM and probe) as well as the sample. For example, electrostatic forces between cantilever and surface or background signals from within the AFM could result in a response similar to that of that of a piezoelectric material. [3] Finally, PFM scanning is usually done in contact mode, resulting in inconsistent results when tip or sample are damaged by lateral forces. Softer probes could partially mitigate this issue, but are more prone to electrostatic artifacts in the PFM measurements.[4] In this presentation we will discuss Bruker's new Switching Spectroscopy PFM (SS-PFM) mode and how it can help with many of these issues. SS-PFM allows contact resonance enhancement of the PFM signal and can be used without contact mode scanning to provide more repeatable results on delicate samples or on samples that can damage the probe tip. It provides detailed spectra at varying read and write voltages allowing construction of ferroelectric hysteresis loops. Arrays of these spectra can be used to assemble hyperspectral maps of electromechanical response.