Until now, characterizing piezoelectricity at the nanoscale was only possible through the use
of an Atomic Force Microscope using the mode Piezoresponse Force Microscopy (PFM).
However, a team of researchers have created a new AFM mode that is able to map
piezoelectricity in a direct manner. The new mode, called “Direct Piezoelectric Force
Microscopy (DPFM)” maps piezoelectricity by measuring tiny currents, in the order of
femtoAmpere, produced by the piezoelectric effect with a transimpedance amplifier, which
consists into a current-to- voltage converter.
The amplifier component consists of a Femtoampere Input Bias Current Electrometer
Amplifier populated with a 1 TeraOhm resistor as a feedback resistor in a transimpedance
configuration. An additional voltage amplifier, with the inverting amplifier topology, is located
at the output of the transimpedance, using an ADI AD8429. With such tandem of amplifiers,
researchers were capable of measuring the generated charge of several piezoelectric
materials directly. Such amplifier does not leak almost any of the generated charge, enabling
it is measuring using a standard solid platinum tip. The tip scans the surface to study, and
measured the charge generated by the material. Such simply concept was not completed by
any other research mainly to the particularity of the amplifier used, that released in 2016 by
Analog Devices Inc.
In this particular research, the material is stressed by a tiny needle, an AFM tip with
nanometric size. The tip applies a force in the range of hundreds of microNewton and
measures the generated charge that is created into the material. The new mode was proved
by characterizing several common ferroelectric materials: A Periodically Poled Lithium
Niobate, Bismuth Ferrite (BFO) and different Lead Zirconate Titanate (PZT). The mode is
employed in standard constant force contact mode AFM, by using a solid platinum tip with
part number RMN-25Pt200H. As the mapping is performed in constant mode, the amplifier
gives zero signal while scanning a single domain, however, where the tip crosses a domain,
a current is generated as a consequence of the inversion of the generated charge. The
researchers are able to integrate the current obtained in order to estimate the generated
charge by the material. Just few quantities are really quantitative in AFM, being one of them
the force applied by the tip. By known the force and integrating the current generated,
researchers are able to estimate the d33 piezoelectric constant of the materials scanned.
Force-vs- distance curves where the tip is placed in one spot and the force applied is
changed through a constant force rate applied. By performing such experiments,
researchers are able to distinguish between down and up domains, and it opens a window
into made spectroscopy experiments quantitative.
This new AFM mode enhances this microscopy technique as a standard characterization
technique available for material research specifically for the case of piezoelectricity and
This article has been republished from materials provided by Universitat Autonoma de Barcelona. Note: material may have been edited for length and content. For further information, please contact the cited source.
Piezo-generated charge mapping revealed through Direct Piezoelectric Force Microscopy, A. Gomez et al. , Nature Communications (2017), DOI: 10.1038/s41467-017- 01361-2.