  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.
