Unexpected Dynamics of the Tip-induced Polarization Reversal in Lithium Niobate Single Crystals
Ferroelectric single crystals with tailored domain structure nowadays are widely used in acoustic, nonlinear optical and data storage devices. As such, the investigation of the polarization reversal mechanisms on the level of a single domain is of immense scientific importance. Scanning probe microscopy (SPM) provides perfect set of the tools for nanometer-scale investigations of the ferroelectrics. Tip-induced polarization reversal is one of the most prominent of them. Polarization switching by inhomogeneous electric field of the tip allows to create isolated nanodomains and complex domain structures. However this complex process still needs systematic investigations. Here we report a number of unexpected phenomena in the thin lithium niobate single crystal caused by the action of electric field produced by biased SPM tip.
The first one is the long-range domaindomain interaction which changes switching process and can lead to wide range of the domain dynamics in the chain, including intermittency, quasiperiodicity and chaos. The second phenomenon was observed after switching by sequences of the bipolar triangular pulses and gave rise to a surprisingly broad range of domain morphologies. Detailed studies showed that domain growth is multi-stage process with "abnormal" polarization reversal against applied electric field on the one of the stages. Humidity measurement showed that all diversity of observed phenomena is dependent on the sample surface state and can be controlled by the value of relative humidity in the SPM chamber.
This fact allowed us to conclude that polarization reversal process in ferroelectrics is controlled by surface screening charge dynamics. From the point of view of potential applications, observed set of phenomena is very interesting in connection to the emergent computing paradigm known as memcomputing. It enables a new generation of devices and potentially leads to new forms of information processing.
The research was conducted at the Center for Nanophase Materials Sciences, which is sponsored at Oak Ridge National Laboratory by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy.