The results of investigation of the single domain growth in electric field applied by conductive tip of the scanning probe microscope in thin plates of lithium niobate (LiNbO3) crystals doped with MgO after various surface preparations and at various ambient conditions are presented. It has been shown that the sizes of the produced domain can exceed by several orders of magnitude the value of the tip curvature radius. The observed effect has been explained taking into account the existence of the conductive adsorbed surface layer in all experimental conditions. We have demonstrated that the domain growth decelerates with decreasing of the layer conductivity. The existence of the conductive adsorbed surface layers drastically changes the spatial distribution of electric field. In addition to strongly localized electric field, just in the vicinity of the tip there exists the field component remaining homogeneous over the distance exceeding the radius of any experimentally produced domain. The crucial role of the conductive properties of the adsorbed surface layers on the screening of the depolarization field has been revealed. Within proposed approach the domain growth is controlled by the current in the external circuit including the surface layer with low conductivity. The proposed model allows us to explain time and field dependences of the domain size for various types of surface treatment.

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.

Organic-inorganic hybrid films are prepared via the hydrolysis and polycondensation of tetraethoxysilane in chitosan solutions. It is shown that the composition of reagents, the time of synthesis, the crosslinking of chitosan macromolecules via amino groups by glutaric aldehyde, and the conditions of drying affect structurization of the resulting films. With the use of optical polarization microscopy and atomic force microscopy, it is found that the films contain silica particles with a wide size distribution. The crosslinking of the chitosan matrix by glutaric aldehyde results in the predominant formation of inorganic nanoparticles in the films. A good sorption capacity of the films for copper ions in solutions is found. It increases by a factor of 1.7 as the content of the silica in the films increases to 30 wt %.

Shape of local hysteresis loops was studied by scanning probe microscopy using pulsed and in-field modes. Intermediate states on the loops measured in pulsed mode were revealed and explained by partial backswitching in the area under SPM tip. The obtained slope of the loops measured in the in-field mode was explained taking into account the interaction between two types of charges: induced in sample by switching voltage and in cantilever by modulation voltage. Dependence of loops slope on the position of the laser spot on the cantilever was found. Computer simulation was used for explanation of the observed data.

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.

Self-assembled formation of dense structures of oriented domain rays under application of uniform electric field was studied in single crystalline lithium niobate wafers with surface layers modified by Ar ion implantation. Two types of domain structures were observed: strictly oriented straight domain rays and cogged ones appeared due to the fingering effect. The piezoresponse force microscopy was used for high-resolution domain imaging. Geometrical characteristics of the domain patterns obtained for different strength of applied field were extracted by statistical analysis. The correlated nucleation mechanism was claimed to be responsible for the formation of observed self-assembled domain structures.

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.

ФЦП «Исследования и разработки по приоритетным направлениям развития научно-технологического комплекса России на 2007-2013 годы»

In the paper we adopt the analytical Landau-Ginzburg-Devonshire theory to describe the ferroelectric domain structure formation using Scanning Probe Microscopy. We calculate the effective local piezoresponse of the domain structure within the decoupling approximation using the conventional relation between piezoelectric tensor components and the spontaneous polarization vector. The depth profile of the polarization distribution was derived from the nonlinear Landau-Ginzburg-Devonshire equation. We demonstrate that depending on the material parameters such as the intrinsic domain wall width and probe apex geometry, the shape of the nucleating nanodomains induced by the probe can be either oblate or prolate. The derived analytical expressions for the polarization redistribution caused by the biased probe are valid for both first and second order ferroelectrics.

Hybrid nanocomposite membrane films with different silicon contents (4.5–12.3%) are acquired by the hydrolytic polycondensation of tetraethoxysilan (TEOS) in 4% solution of cellulose diacetate (CDA) and ethylcellulose (ECel) in organic solvents (acetone and tetrahydrofuran (THF)). Fourier IR spectroscopy is used to confirm the formation of a Si-network with Si-O-Si bonds that are linked with the cellulose derivatives by H-bonds. Hybrid films are insoluble in aqueous solutions containing 5–20 vol % of an organic component. Atomic force microscopy is used to confirm the presence of nanosized structures on the surfaces of the obtained films. The sizes of these structures depend on the polymer nature ratio of polymer and TEOS in synthesis, and they reduce as the Si content in the film increases. The equilibrium degree of swelling of hybrid films and a coefficient of diffusion of an organic substance from organic-water solutions (acetone water or THF water) are highest for the films obtained at the equimolar ratio polymer-TEOS in synthesis. The thermodynamic parameters of the interaction between hybrid films (Flory-Huggins parameter) with the liquid medium, as well as the factor of the relation THF from the THF-water solutions in Ecel/TEOS films, are calculated. Correlations of the structure and composition of hybrid films and their behavior in organic-water solutions are shown and discussed.

The effect of the domain wall intrinsic width, relaxation time of the screening charges, and the dead layer thickness on the velocity of the planar 180 degrees-domain wall moving under homogeneous external electric field in ferroelectric capacitor is analyzed. The limiting cases of domain wall motion, including (i) the motion induced by the external and local internal field originated at the wall-surface junction for nonzero dead layer thickness and (ii) the motion induced by the effective electric field averaged over the domain wall surface, are considered. We demonstrate the crossover between two screening regimes: the first one corresponds to the low domain wall velocity, when the wall drags the sluggish screening charges, while the second regime appears for high domain wall velocity, when the delay of sluggish screening charges are essential and the wall depolarization field is screened by the instant free charges located at the electrode. The integral and approximate analytical expressions for electric field and algebraic equation for the domain wall velocity are derived. It is shown that in the local-field limit the motion can be unstable, since the internal field at the wall-surface junction decreases for larger domain wall velocities, making possible self-acceleration of the wall near the top surface. The instability may lead to the domain wall-surface bending and actual broadening in thick samples, as well as formation of periodic domain structures in the direction of wall motion. The motion in the limit of the averaged effective field is always stable.

The formation of nano-domain structure as a result of pulsed laser irradiation of lithium niobate single crystals has been studied experimentally applying optical and atomic force microscopy for visualization of nano-domain patterns. The observed growth of oriented nano-domain rays was considered as a manifestation of polarization reversal in highly nonequilibrium switching conditions. The results of computer simulation of nano-domain kinetics under the action of pyroelectric field during cooling after pulsed heating were used for explanation of the studied peculiarities of nano-domain kinetics. The screening effect retardation was taken into account. The main predictions of the simulations were confirmed experimentally.

The polarization reversal process under pulsed laser irradiation without application of electric field was investigated in single crystalline congruent and MgO doped lithium niobate LiNbO3. The nano-domain structures obtained in different experimental conditions were statistically analyzed and characterized in terms of domain growth anisotropy.

Pulsed implantation of Cu ions into single crystalline congruent lithium niobate resulted in extraordinary effects. First, surface nano-domain structures consisting of star-like domains with rays oriented along three Y directions were induced under the action of the pyroelectric field appeared during cooling after implantation pulse. These nano-domains served as nucleation sites for subsequent polarization reversal under external field. Second, jump-like domain wall motion led to formation of residual domain arrays along the staying positions of the wall. Third, the implantation led to suppression of screening of depolarizing field, due to formation of surface layer with suppressed polarization or non-ferroelectric.

A review of recent theoretical studies of the effects of a surface state and the screening on the nucleation and growth of artificial nanodomains in ferroelectrics-semiconductors. The obtained results prove that the formation of nanodomains caused by the inhomogeneous electric field of a biased force microscope probe is a first-order phase transition, since the domains with finite radii appear at the critical voltage applied to the probe. The critical voltage depends on the probe geometry, films thickness, surface state, and screening effects. The activation barrier height and domain nucleus critical sizes strongly depend on the surface charge state: a value and the distribution of charge density that screen the spontaneous polarization outside the sample.

The surface nanodomain structures formed in lithium niobate single crystals as a result of pulsed irradiation of polar surfaces with UV and IR lasers have been investigated. The structures formed have been classified. The main features of the domain kinetics during one-dimensional growth at strong deviation from equilibrium have been revealed. A mechanism of polarization switching is proposed and discussed.

Thin films of supersaturated Zn x Pb1 − x S solid solutions containing up to 4.1 mol % ZnS have been obtained by hydrochemical deposition. The dependence of the material structure and surface morphology on the film composition has been studied. It is established that an increase in the content of zinc sulfide leads to the growth of grains with a more complicated crystalline structure, the formation of grain boundary fragments with dimensions from 60 to 100 nm, and a modification of the electrical properties of deposited layers.

We consider the polar properties of the ferroelectric nanotubes within the framework of Landau-Ginzburg-Devonshire phenomenology. The approximate analytical expression for the paraelectric-ferroelectric transition temperature dependence on the radii of nanotube, polarization gradient, extrapolation length, elastic stresses and strains arising from surface tension and thermal expansion mismatch, and electrostriction coefficient was derived. We calculated effective local piezoresponse of the ferroelectric nanotube within decoupling approximation of electric and elastic problem. Obtained results explain the ferroelectricity conservation in Pb(Zr,Ti)O-3 and BaTiO3 nanotubes observed by using Piezoelectric Force Microscopy.