Ferroelectrics and multiferroics have recently emerged as perspective materials for information technology and data storage applications. The combination of extremely narrow domain wall width and the capability to manipulate polarization by electric field opens the pathway toward ultrahigh (>10 TBit inch−2) storage densities and small (sub-10 nm) feature sizes. The coupling between polarization and chemical and transport properties enables applications in ferroelectric lithography and electroresistive devices. The progress in these applications, as well as fundamental studies of polarization dynamics and the role of defects and disorder on domain nucleation and wall motion, requires the capability to probe these effects on the nanometer scale. In this review, we summarize the recent progress in applications of piezoresponse force microscopy (PFM) for imaging, manipulation and spectroscopy of ferroelectric switching processes. We briefly introduce the principles and relevant instrumental aspects of PFM, with special emphasis on resolution and information limits. The local imaging studies of domain dynamics, including local switching and relaxation accessed through imaging experiments and spectroscopic studies of polarization switching, are discussed in detail. Finally, we review the recent progress on understanding and exploiting photochemical processes on ferroelectric surfaces, the role of surface adsorbates, and imaging and switching in liquids. Beyond classical applications, probing local bias-induced transition dynamics by PFM opens the pathway to studies of the influence of a single defect on electrochemical and solid state processes, thus providing model systems for batteries, fuel cells and supercapacitor applications.

https://iopscience.iop.org/article/10.1088/0034-4885/73/5/056502/pdf

Local polarization dynamics in ferroelectric materials

Piezoresponse force microscopy (PFM) detects the local piezoelectric deformation of a sample caused by an applied electric field from the tip of a scanning force microscope. PFM is able to measure deformations in the sub-picometre regime and can map ferroelectric domain patterns with a lateral resolution of a few nanometres. These two properties have made PFM the preferred technique for recording and investigating ferroelectric domain patterns. In this review we shall describe the technical aspects of PFM for domain imaging. Particular attention will be paid to the quantitative analysis of PFM images.

https://iopscience.iop.org/article/10.1088/0022-3727/44/46/464003/pdf

Piezoresponse force microscopy (PFM)

In this paper, we review recent advances in piezoresponse force microscopy (PFM) with respect to nanoscale ferroelectric research, summarize the basic principles of PFM, illustrate what information can be obtained from PFM experiments and delineate the limitations of PFM signal interpretation relevant to quantitative imaging of a broad range of piezoelectrically active materials. Particular attention is given to orientational PFM imaging and data interpretation as well as to electromechanics and kinetics of nanoscale ferroelectric switching in PFM.

Piezoresponse force microscopy and recent advances in nanoscale studies of ferroelectrics

Quantitative determination of contact stiffness using atomic force acoustic microscopy

Ferroic materials play an increasingly important role in novel (nano)electronic devices. Recently, research on domain walls (DWs) receives a big boost by the discovery of DW conductivity (DWC) in BiFeO3 and Pb(ZrxTi1-x)O3 ferroic thin films. Here, it is demonstrated that DWC is not restricted to thin films, but equally applies to millimeter-thick wide-bandgap, ferroic single crystals, such as LiNbO3. In this material transport along DWs can be switched by super-bandgap illumination and tuned by engineering the tilting angle of DWs with respect to the polar axis. The results are consistently obtained using conductive atomic force microscopy to locally map the DWC and macroscopic contacts, thereby in addition investigating the temperature dependence, DW transport activation energies, and relaxation behavior.

Conducting Domain Walls in Lithium Niobate Single Crystals

The three-dimensional orientation of polarization vectors at the surface of ferroelectric barium–titanate (BaTiO3) ceramics is evaluated using voltage-modulated scanning force microscopy (SFM). By applying an ac voltage to the conductive SFM tip, we measure the relative amount of the three orthogonal components Px, Py, and Pz, of the polarization vector at any surface point. The measured polarization orientation together with the actual domain-wall orientation allows a precise reconstruction of the crystallographic orientation of the investigated grains down to a 40 nm resolution. Excellent agreement is obtained when comparing this orientation with the crystallographic reconstruction revealed by etch patterns from the sample surface topography. We show that the surface topography manifests a domain structure, which was present in the past, while the actual ferroelectric domain configuration is revealed by the modulation technique.

H.-J. Güntherodt

Papers

Nanoscale reconstruction of surface crystallography from three-dimensional polarization distribution in ferroelectric barium-titanate ceramics