M. A. Dolbilov

Formation of Self-Similar Surface Nano-Domain Structures in Lithium Niobate Under Highly Nonequilibrium Conditions

Formation of the nanoscale domain structure in the surface layer as a result of pulsed UV laser irradiation has been studied experimentally in congruent single crystalline lithium niobate LiNbO3. The self-assembled structures have been classified and statistically analyzed. The structure is formed by growth, turning, and branching of domain rays strictly oriented along three Y+ directions. High-resolution microscopy shows that the rays represent the chains of individual needle-like nano-domains. The results of computer simulation of the domain structure formation using experimentally revealed rules are in good agreement with the experimental ones.

Field induced evolution of regular and random 2D domain structures and shape of isolated domains in LiNbO3 and LiTaO3

The shapes of isolated domains produced by application of the uniform external electric field in different experimental conditions were investigated experimentally in single crystalline lithium niobate LiNbO 3 and lithium tantalate LiTaO 3 . The study of the domain kinetics by computer simulation and experimentally by polarization reversal of the model structure using two-dimensional regular electrode pattern confirms applicability of the kinetic approach to explanation of the experimentally observed evolution of the domain shape and geometry of the domain structure. It has been shown that the fast domain walls strictly oriented along X directions appear after domain merging.

Influence of Surface Layers Modified by Proton Exchange on Domain Kinetics of Lithium Niobate

The abnormal domain kinetics in congruent lithium niobate single crystals caused by surface modification using proton exchange was studied experimentally. The dependence of domain kinetics on polarity of the growing domains at the surface with proton exchange was revealed. The abnormal smooth motion of irregularly shaped domain walls with finger-like features and correlated nucleation was observed for growth of domains with Z + at surface with proton exchange. Such behavior drastically differs from jump-like motion of plane domain walls oriented along Y directions observed both in conventional lithium niobate and for growth of domains with Z – at surface with proton exchange.

Abnormal Domain Growth in Lithium Niobate with Surface Layer Modified by Proton Exchange

Formation of abnormal domain shapes was studied in single crystalline LiNbO3 with surface layer modified by proton exchange. It has been shown that the isolated domain shape is very sensitive to the electric field: 1) three-rayed stars and concave polygons appear in low field, 2) hexagonal domains form in moderate field, 3) oriented domain rays grow in high field. The transformation from concave to convex polygon and the fast growth of narrow domain rays in front of the growing domain wall were investigated. The obtained abnormal behavior was attributed to non-effective external screening of depolarization field caused by artificial dielectric layer.

Nanoscale Domain Effects in Ferroelectrics. Formation and Evolution of Self-Assembled Structures in LiNbO3 and LiTaO3

We discuss the most interesting nanoscale domain effects resulting in formation and evolution of self-assembled domain structures in various representatives of LiNbO 3 and LiTaO 3 family. Several exotic domain kinetic scenarios for complete suppression of the classical wall motion have been revealed. It has been shown that the modification of the surface layer allows to obtain: (1) the wall motion controlled by merging with nanoscale domains generated in front of the moving wall and (2) the discrete switching by enlargement of the web-like self-assembled ensemble of isolated domains. The formation of nanoscale quasi-periodic and self-similar structures during cooling after pulse heating without any application of external electric field was studied. It has been shown that all experimental results can be explained, if the retardation of the bulk screening of the depolarization field is taken into account.

Complex study of bulk screening processes in single crystals of lithium niobate and lithium tantalate family

Comprehensive study of depolarization field bulk screening was carried out in lithium niobate and lithium tantalate single crystals with various stoichiometry. Three used complementary methods are based on: 1) dependence of coercive field on delay time; 2) decrease of optical contrast of domain wall trace; 3) relaxation of light diffraction intensity on domain walls. The following parameters of bulk screening process were obtained: relaxation time constants, type of relaxation law, maximal value of bias field and “true” value of coercive field. Advantages and disadvantages of used experimental methods were analyzed.

Study of Nanoscale Domain Structure Formation Using Raman Confocal Microscopy

The original technique based on the laser confocal microscopy and Raman spectroscopy was applied for the domain visualization in the bulk of lithium niobate LiNbO3 (LN) single crystal. The change of the Raman spectrum in the vicinity of the domain walls of LN was used. The technique capabilities were inspected in LN with different types of domain geometry. The estimation of the spatial resolution at different depth was carried out for periodically poled LN. The proposed analysis of the three-dimensional nanodomain image allows us to characterize the evolution of the self-assembled nanodomain structures produced in LN with surface layer modification.

Characterization of Bulk Screening in Single Crystals of Lithium Niobate and Lithium Tantalate Family

Kinetics of bulk screening of depolarization field was studied in single crystalline lithium niobate and lithium tantalate of various compositions by analysis of the switching current, birefringence contrast, and diffraction of coherent light on the domain walls. The bulk screening process was quantitatively characterized by several essential parameters, such as a type of relaxation law, relaxation time constants, and maximum value of bulk screening field. Advantages and disadvantages of used experimental methods were discussed. The comparison of the obtained and previously published results was carried out.

Formation of nanodomain structures during polarization reversal in congruent lithium niobate implanted with ar ions

We present the experimental study of the formation of self-similar nanodomain structures during polarization reversal in single-crystalline congruent lithium niobate (CLN) implanted by Ar ions. The formed dense surface nanodomain structure with charged domain walls differs drastically from the growth of the hexagonal domains in unimplanted CLN. The lack of wall shape stability during sideways domain wall motion was revealed. The analysis of the domain structure images in the bulk, obtained by Raman confocal microscopy, revealed the main stages of the domain structure evolution starting at unimplanted polar surface and consisting of nanodomain chain elongation, merging of isolated domains, and domain widening. The switching current data has been fitted by modification of Kolmogorov-Avrami formula for switching in a linearly increasing field. The observed experimental facts have been attributed to formation of an amorphous thin surface layer and increase of the bulk conductivity resulting from oxygen out-diffusion under radiation heating in vacuum during ion implantation. The formation of the experimentally obtained abnormal domain shapes has been explained while taking into account the step generation at the domain wall in the bulk during switching in a low electric field.

Abnormal Domain Evolution in Lithium Niobate with Surface Layer Modified by Cu Ion Implantation

Anomalies of domain structure evolution in congruent lithium niobate with surface layers modified by implantation of Cu ions were investigated. Formation of residual domains and growth of areas occupied by domain patterns with high density of charged domain walls were studied during cyclic polarization reversal. Growth of unusual three-rayed star domains was observed during polarization reversal in low external field much less than the threshold field for conventional congruent lithium niobate. The complicated geometry of these domains in the bulk was revealed using scanning laser confocal microscopy combined with Raman spectroscopy.