Andreas Roelofs

Review of Ferroelectric Domain Imaging by Piezoresponse Force Microscopy

This chapter describes the principles, theoretical background, recent developments, and applications of a local probe-based technique for nondestructive high-resolution ferroelectric domain imaging and manipulation—piezoresponse force microscopy (PFM). This technique has proven to be a powerful tool for the characterization of ferroelectric thin films, ceramics, and single crystals. Recent advances in application of PFM for studying a mechanism of polarization reversal at the nanoscale, domain dynamics, degradation effects, and size-dependent phenomena in ferroelectrics are reviewed in detail. Examples of using PFM for the characterization of various polar materials such as ferroelectric films, piezoelectric semiconductors, and ferroelectric relaxors are given.

Charge-based scanning probe readback of nanometer-scale ferroelectric domain patterns at megahertz rates

We present a method for data storage in continuous ferroelectric (FE) media, applicable to storage systems based on one or more scanning probes. Written FE domains are read back in a destructive fashion by applying a constant voltage of magnitude greater than the coercive voltage, as is done in FE random access memory (FeRAM). The resulting flow of screening charges through the readback amplifier provides sufficient signal to allow readback of domains of minimum dimension of the order of 10 nm at MHz rates, orders of magnitude faster than previously demonstrated techniques for readback of domains in continuous FE media.

Correlating structural and resistive changes in Ti:NiO resistive memory elements

Structural and resistive changes in Ti-doped NiO resistive random access memory structures that occur upon electroforming have been investigated using hard x-ray microscopy. Electroforming leads to structural changes in regions of size up to about one micrometer, much larger than the grain size of the structure. Such changes are consistent with a migration of ionic species or defects during electroforming over regions containing many crystalline grains.