A. Agronin

Submicron ferroelectric domain structures tailored by high-voltage scanning probe microscopy

We have developed a high voltage atomic force microscope that allowed us to tailor submicrometer ferroelectric domains in bulk ferroelectrics. One- and two-dimensional domain configurations have been fabricated in LiNbO3, RbTiOPO4, and RbTiOAsO4 ferroelectric crystals. It is found that the application of superhigh electric fields (reaching 5×107 V/cm) by the atomic force microscope tip leads to a unique polarization reversal mechanism, and open the way to a technology for photonic and acoustic devices.

Dynamics of ferroelectric domain growth in the field of atomic force microscope

Application of very high voltage to atomic force microscope tip leads to the growth of narrow, stringlike domains in some ferroelectrics, a phenomenon that was named “ferroelectric domain breakdown.” In this work the dynamics of domain breakdown have been studied experimentally and theoretically in stoichiometric lithium niobate (LN). The theory has been found to be in a good agreement with the measured domain radius temporal dependence. Dynamics of domain growth has also been studied in ultrathin LN crystals, where the domain breakdown phenomenon does not take place. It is also shown that domain formation processes occurring in bulk and ultrathin crystals are very different, and this is ascribed to the observed difference in depolarization energy dependence on the domain length.

Ferroelectric domain reversal in LiNbO3 crystals using high-voltage atomic force microscopy

High-voltage atomic force microscopy is used for nanoscale polarization reversal in LiNbO3 single crystals. The tailored domain patterns have been observed using piezoelectric force microscopy and etching techniques. A variety of domain shapes preserving the elementary crystallographic symmetry have been obtained. It has been found that the sidewise domain wall motion under the huge electric field near the apex of atomic force microscope tip occurs in isotropic manner. The dependence of the domain equilibrium size on the applied high voltage is analyzed and discussed.

Direct observation of pinning centers in ferroelectrics

We present a direct observation of nanoscale ferroelectric domain pinning centers in lithium niobate crystals. A high-voltage atomic force microscope has been used to tailor nanodomain structures in LiNbO3 crystal with high defect concentration. Domain pinning and depinning events have been captured following thermally induced domain decay process. The pinning centers’ influence on the domain wall dynamics has been analyzed by comparing domain growth in stoichiometric and congruent LiNbO3 crystals.

Nanoscale piezoelectric coefficient measurements in ionic conducting ferroelectrics

In this work the piezoresponse mode of the atomic force microscope has been applied for piezoelectric coefficient measurements in nanometer scale in high conductive RbTiOPO4 and KTiOPO4 ferroelectric crystals with specifically tailored domain configurations. A strong dependence of the amplitude and phase contrast between oppositely polarized domains on the frequency of the measuring alternate voltage was observed, and allowed the finding of the optimal conditions for piezoelectric coefficient measurements. A theoretical method, taking into account the inhomogeneity of the electric field under the atomic force microscope tip apex, the screening of the applied electric field, and the elastic clamping of the piezoelectrically excited region by the surrounding matrix has been developed for obtaining d33 in ferroelectrics with high ionic conductivity.

Noncollinear second-harmonic generation in sub-micrometer-poled RbTiOPO 4

We have generated noncollinear quasi-phase-matched second harmonic wave in an RbTiOPO(4) crystal that was poled using the high-voltage atomic force microscope (HV-AFM). To the best of our knowledge, this is the first systematic nonlinear frequency conversion study of samples produced by the HV-AFM method. The short poling period of 1.18 microm enabled us to observe second harmonic generation at very large angles with respect to the fundamental wave. The setup was used to optically explore the homogeneity of the poled area. The measurements are in a reasonable agreement with an analytic calculations.

High-voltage atomic force microscopy: a new technology for nanoscale optical devices

Reversal of the spontaneous polarization direction under an applied electric field is a basic property of ferroelectrics. However the traditional techniques used for fabrication of domain gratings have been able to produce domains not smaller then 2 micrometers. Sub-micron and nanometer scale domains may be fabricated using atomic force microscopy based techniques; however, to date there was no success in fabricating stable domains that elongate without widening throughout thick ferroelectrics. A breakthrough in the field emerged with the recent development of the high voltage atomic force microscope that enabled to obtain sub-micrometer stable domain configurations in bulk ferroelectrics. Diverse stable domain configurations were fabricated in several ferroelectric crystals like LiNbO3 and RbTiOPO4. Studying the influence of the applied high voltage, and the tip velocity on the domain strips has allowed fabricating domain gratings (with a domain width of 590 micron) useful for backward propagating quasi-phase-matched frequency conversion. It is found that string-like domains are formed due to the super-high electric field of the high voltage atomic force microscope tip. The domains, which resemble channels of an electrical breakdown, nucleate under an electric field of around 10 in a power of seven Volts per centimeter at the ferroelectric surface, and grow throughout the crystal bulk where the external electric field is practically zero. A theory explaining the shape of the formed domains shows that the driving force for the domain breakdown is the decrease of the total free energy of the system with increasing domain length.