Domain wall conduction in insulating Pb(Zr(0.2) Ti(0.8))O(3) thin films is demonstrated. The observed electrical conduction currents can be clearly differentiated from displacement currents associated with ferroelectric polarization switching. The domain wall conduction, nonlinear and highly asymmetric due to the specific local probe measurement geometry, shows thermal activation at high temperatures, and high stability over time.

The properties of ferroelectric domain walls can significantly differ from those of their parent material. Elucidating their internal structure is essential for the design of advanced devices exploiting nanoscale ferroicity and such localized functional properties. Here, we probe the internal structure of 180° ferroelectric domain walls in lead zirconate titanate (PZT) thin films and lithium tantalate bulk crystals by means of second-harmonic generation microscopy. In both systems, we detect a pronounced second-harmonic signal at the walls. Local polarimetry analysis of this signal combined with numerical modelling reveals the existence of a planar polarization within the walls, with Néel and Bloch-like configurations in PZT and lithium tantalate, respectively. Moreover, we find domain wall chirality reversal at line defects crossing lithium tantalate crystals. Our results demonstrate a clear deviation from the ideal Ising configuration that is traditionally expected in uniaxial ferroelectrics, corroborating recent theoretical predictions of a more complex, often chiral structure.

Fibrous peptide networks, such as the structural framework of self-assembled fluorenylmethyloxycarbonyl diphenylalanine (Fmoc-FF) nanofibrils, have mechanical properties that could successfully mimic natural tissues, making them promising materials for tissue engineering scaffolds. These nanomaterials have been determined to exhibit shear piezoelectricity using piezoresponse force microscopy, as previously reported for FF nanotubes. Structural analyses of Fmoc-FF nanofibrils suggest that the observed piezoelectric response may result from the noncentrosymmetric nature of an underlying β-sheet topology. The observed piezoelectricity of Fmoc-FF fibrous networks is advantageous for a range of biomedical applications where electrical or mechanical stimuli are required.

Piezoresponse force microscopy (PFM) probes the mechanical deformation of a sample in response to an electric field applied with the tip of an atomic force microscope. Originally developed more than two decades ago to study ferroelectric materials, this technique has since been used to probe electromechanical functionality in a wide range of piezoelectric materials including organic and biological systems. PFM has also been demonstrated as a useful tool to detect mechanical strain originating from electrical phenomena in nonpiezoelectric materials. Paralleling advances in analytical and numerical modelling, many technical improvements have been made in the last decade: switching spectroscopy PFM allows the polarisation switching properties of ferroelectrics to be resolved in real space with nanometric resolution, while dual ac resonance tracking and band excitation PFM have been used to improve the signal-to-noise ratio. In turn, these advances have led to increasingly large multidimensional data sets containing more complete information on the properties of the sample studied. In this review, PFM operation and calibration are described, and recent advances in the characterisation of electromechanical coupling using PFM are presented. The breadth of the systems covered highlights the versatility and wide applicability of PFM in fields as diverse as materials engineering and nanomedicine. In each of these fields, combining PFM with complementary techniques is key to develop future insight into the intrinsic properties of the materials as well as for device applications.

Using multiscaling analysis, we compare the characteristic roughening of ferroelectric domain walls in PbðZr 0:2 Ti 0:8 ÞO 3 thin films with numerical simulations of weakly pinned one-dimensional interfaces. Although at length scales up to L MA ! 5 m the ferroelectric domain walls behave similarly to the numerical interfaces, showing a simple monoaffine scaling (with a well-defined roughness exponent ), we demonstrate more complex scaling at higher length scales, making the walls globally multiaffine (varying at different observation length scales). The dominant contributions to this multiaffine scaling appear to be very localized variations in the disorder potential, possibly related to dislocation defects present in the substrate. From a practical viewpoint, understanding the behavior of the domain walls as elastic disordered systems allows a more accurate description of domain switching, growth, and stability, all key parameters for the successful implementation of (multi)ferroic devices based on domains [9,10] or domain walls [11,12]. More broadly, ferroic epitaxial thin films provide an excellent model system for testing theoretical predictions, since parameters such as field, temperature, and defect density can be controlled over a wide range.Previous experimental roughening studies considered ferroic domain walls as equilibrated monoaffine interfaces collectively pinned by weak, randomly distributed disorder [13][14][15], for which particularly simple Gaussian scaling is expected. Whereas monoaffine interfaces present scaling properties (self-similarity) which can be described by a single scaling exponent at all length scales, in multiaffine systems, the scaling properties vary with the observation length scale, leading to a hierarchy of local scaling exponents [16]. Distinguishing between both cases through a multiscaling approach has proven useful in fracture studies, where multiaffine behavior was initially reported [17,18], but subsequently attributed to finite size artifacts [19]. However, recent atomic force microscopy (AFM) measurements have shown that the disorder potential landscape in ferroelectric thin films can in fact be very complex, with strong individual pinning centers [20,21], and local variations in the disorder strength and universality class [22]. Potentially, these systems could therefore provide the sought-after experimental realization of more complex multiaffine scaling of interfacial roughening predicted by theory [8], in which a rich and diverse disorder landscape-and possibly other interesting features-could be accessed. The multiaffine nature of such a system could be established by multiscaling analysis [19] of individual domain walls or even different portions of a single domain wall, and directly compared with an ideal monoaffine model of weak collective pinning, in which the scaling behavior is exactly known.In this Letter, we report on such a study of the roughening of ferroelectric domain walls in PbðZr 0:2 Ti 0:8 ÞO 3 (PZT) thin films, compared to numerically simulated ...