Nanoscale polarization manipulation and imaging in ferroelectric Langmuir-Blodgett polymer films

TL;DR

This study demonstrates nanoscale imaging and manipulation of ferroelectric polarization in ultrathin Langmuir-Blodgett polymer films using advanced microscopy techniques, revealing domain structures and switching behavior at the nanometer scale.

Contribution

It introduces the application of PFM and SSPFM to image and control ferroelectric domains in ultrathin polymer films, with high spatial resolution and reversible polarization patterning.

Findings

Ferroelectric domains of 25-50 nm size were imaged.

Imaging resolution was below 5 nm.

Polarization patterns could be written and erased repeatedly.

Abstract

The behavior of ferroelectricity at the nanoscale is the focus of increasing research activity because of intense interest in the fundamental nature of spontaneous order in condensed-matter systems and because of the many practical applications of ferroelectric thin films to, for example, electromechanical transducers, infrared imaging sensors, and nonvolatile random-access memories. Ferroelectricity, in analogy with its namesake ferromagnetism, is the property of some crystalline systems to maintain a permanent, but reversible, electrical polarization in the absence of an external electric field. The imaging and dynamics of the piezoelectric response at the nanoscale is perhaps the most direct means of probing polarization, as has been demonstrated in a number of thin films and nanostructures . Here we report the use of piezoresponse force microscopy (PFM) and switching spectroscopy PFM (SSPFM) to image the ferroelectric properties, domain structure, and polarization switching of ultrathin ferroelectric Langmuir-Blodgett films of poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) copolymers. PFM imaging of P(VDF-TrFE) thin films reveals ferroelectric domain sizes on the order of 25-50 nm and an imaging resolution below 5 nm. The feature sizes in topography and PFM images are comparable and the boundaries of uniformly polarized regions coincide with topographic features. Arbitrary polarization patterns could be repeatedly written and erased, with writing resolution limited by the grain size. Hysteresis loops from individual domains show clear coercive voltage, but are not well saturated at +/-10 V amplitude.