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The formation of the ferroelectric domain structure as a result of irradiation by focused ion beam of [100]-cut 0.61Pb(Mg[Formula: see text]Nb[Formula: see text]O3–0.39PbTiO3 (PMN–PT) single crystals covered by surface artificial dielectric layer and with free surface was investigated. The dot irradiation resulted in formation of the wedge-like domains grown along [00[Formula: see text]] direction. For irradiation of the free surface, the domains are mainly located under the surface, while at the irradiated surface with an artificial dielectric layer the domains are located at the surface. It was shown that the subsurface wedge-shaped part of the domain is unstable and completely disappears after a month due to spontaneous backswitching under the action of the residual depolarization field. The revealed nonlinear dose dependence of the domain sizes was attributed to the distribution of the electric field using the point charge model. The domain interaction for the distance between irradiated dots below 30[Formula: see text][Formula: see text]m has been revealed in all samples. It was shown that the decrease of the distance between irradiated dots in the created domain row leads to an increase in the length of the central domains, which is explained by the contribution of all injected charges to the switching field.

Self-phase modulation (SPM) broadening of prompt laser spectra was studied in a transmission mode in natural and synthetic diamonds at variable laser wavelengths (515 and 1030 nm), pulse energies and widths (0.3–12 ps, positively chirped pulses), providing their filamentary propagation. Besides the monotonous SPM broadening of the laser spectra versus pulse energy, which was more pronounced for the (sub)picosecond pulsewidths and more nitrogen-doped natural diamond with its intra-gap impurity states, periodical low-frequency modulation was observed in the spectra at the shorter laser pulsewidths, indicating dynamic Bragg filtering of the supercontinuum due to ultrafast plasma and nanoplasmonic effects. Damping of broadening and ultra-modulation for the longer picosecond pulsewidths was related to the thermalized electron-hole plasma regime established for the laser pulsewidths longer, than 2 ps. Unexpectedly, at higher pulse energies and corresponding longer, well-developed microfilaments, the number of low-intensity, low-frequency sideband spectral modulation features counterintuitively increases, thus indicating dynamic variation of the periods in the longitudinal plasma Bragg gratings along the filaments due to prompt secondary laser–plasmon interactions. The underlying sub- and/or near-wavelength longitudinal nanoscale Bragg gratings produced by femtosecond laser pulses in this regime could be visualized in less hard lithium niobate by atomic force microscopy cross-sectional analysis in the correlation with the corresponding sideband spectral components, supporting the anticipated Bragg filtering mechanism and envisioning the corresponding grating periods.

The systematic imaging of the damaged tracks and domain patterns created in the MgOLN plates by one-step fs-laser irradiation at different depths was carried out. It is shown that the domains in the bulk have a spindle-like shape and start to grow in the Z− direction from the track ends. The domain shape changes from a spindle-like one with charged walls to a hexagonal prism with neutral walls after the domain reaches the polar surface. The length of the domains located in the bulk increases linearly with the pulse energy. The hexagonal domain shape at the surface is typical for the crystals of the lithium niobate family. The obtained effects have been considered in terms of the kinetic approach. After irradiation, the domains appear in the vicinity of the track ends with maximum electric field strength and grow under the action of a spatially nonuniform pyroelectric field. The key role of the pyroelectric field is confirmed by the creation of new domains at the surface without correlation with the position of the focusing point located at the vicinity of the surface. The 3D domain pattern was produced, which represented four layers of the regular matrices consisting of elongated domains about 100 μm in length.

Double-track microstructures were induced in the bulk of a z-cut lithium niobate crystal by 1030 nm 240 fs ultrashort laser pulses with a repetition rate of 100 kHz at variable pulse energies exceeding the critical Kerr self-focusing power. The microstructure topography was characterized by atomic force microscopy in piezoelectric response mode. The spatial positions of laser-induced modification regions inside lithium niobate in the case of laser beam propagation along the crystal optical axis can be directly predicted by simple analytical expressions under the paraxial approximation. A dimensional analysis of the morphology of the double-track structures revealed that both their length and width exhibit a monotonous increase with the pulse energy. The presented results have important implications for direct laser writing technology in crystalline dielectric birefringent materials, paving the way to control the high spatial resolution by means of effective energy deposition in modified regions.

Ferroelectric nanodomains were formed in bulk lithium niobate single crystals near nanostructured microtracks laser-inscribed by 1030-nm 0.3-ps ultrashort laser pulses at variable pulse energies in sub- and weakly filamentary laser nanopatterning regimes. The microtracks and related nanodomains were characterized by optical, scanning probe and confocal second-harmonic generation microscopy methods. The nanoscale material sub-structure in the microtracks was visualized in the sample cross-sections by atomic force microscopy (AFM), appearing weakly birefringent in polarimetric microscope images. The piezoresponce force microscopy (PFM) revealed sub-100 nm ferroelectric domains formed in the vicinity of the embedded microtrack seeds, indicating a promising opportunity to arrange nanodomains in the bulk ferroelectric crystal in on-demand positions. These findings open a new modality in direct laser writing technology, which is related to nanoscale writing of ferroelectric nanodomains and prospective three-dimensional micro-electrooptical and nanophotonic devices in nonlinear-optical ferroelectrics.

The possibility to control the charge, type, and density of domain walls allows properties of ferroelectric materials to be selectively enhanced or reduced. In ferroelectric–ferroelastic materials, two types of domain walls are possible: pure ferroelectric and ferroelastic–ferroelectric. In this paper, we demonstrated a strategy to control the selective ferroelectric or ferroelastic domain wall formation in the (111) single-domain rhombohedral PMN-PT single crystals at the nanoscale by varying the relative humidity level in a scanning probe microscopy chamber. The solution of the corresponding coupled electro-mechanical boundary problem allows explaining observed competition between ferroelastic and ferroelectric domain growth. The reduction in the ferroelastic domain density during local switching at elevated humidity has been attributed to changes in the electric field spatial distribution and screening effectiveness. The established mechanism is important because it reveals a kinetic nature of the final domain patterns in multiaxial materials and thus provides a general pathway to create desirable domain structure in ferroelectric materials for applications in piezoelectric and optical devices.

The features of nanodomain growth during local switching in X-cut lithium niobate on insulator (LNOI) were comprehensively studied using the biased tip of a scanning probe microscope. The obtained results were discussed in terms of the kinetic approach. The revealed differences in domain growth in bulk LN and LNOI were attributed to the higher bulk conductivity of LNOI. The obtained influence of humidity on the shape and growth of isolated domains was attributed to the water meniscus. Analysis of the transition between the “forward growth” and “sideways growth” stages was performed by switching to the stripe electrode. A sand-glass-shaped domain was formed due to growth in the opposite direction after the domain touched the electrode. Stable periodical domain structures down to 300 nm were created and characterized in LNOI. Highly ordered comb-like domains of various alternating lengths, including four- and eight-fold increase periods, were produced by performing biased tip scanning along the Y axis. The obtained knowledge is important for the future development of nanodomain engineering methods in monocrystalline ferroelectric thin films on insulators.

The recent achievements in studying the self-assembled evolution of micro- and nanoscale domain structures in uniaxial single crystalline ferroelectrics lithium niobate and lithium tantalate have been reviewed. The results obtained by visualization of static domain patterns and kinetics of the domain structure by different methods from common optical microscopy to more sophisticated scanning probe microscopy, scanning electron microscopy and confocal Raman microscopy, have been discussed. The kinetic approach based on various nucleation processes similar to the first-order phase transition was used for explanation of the domain structure evolution scenarios. The main mechanisms of self-assembling for nonequilibrium switching conditions caused by screening ineffectiveness including correlated nucleation, domain growth anisotropy, and domain–domain interaction have been considered. The formation of variety of self-assembled domain patterns such as fractal-type, finger and web structures, broad domain boundaries, and dendrites have been revealed at each of all five stages of domain structure evolution during polarization reversal. The possible applications of self-assembling for micro- and nanodomain engineering were reviewed briefly. The review covers mostly the results published by our research group.

We have studied experimentally the interaction of isolated needle-like domains created in an array via local switching using a biased scanning probe microscope (SPM) tip and visualized via piezoelectric force microscopy (PFM) at the non-polar cuts of MgO-doped lithium niobate (MgOLN) crystals. It has been found that the domain interaction leads to the intermittent quasiperiodic and chaotic behavior of the domain length in the array in a manner similar to that of polar cuts, but with greater spacing between the points of bias application and voltage amplitudes. It has also been found that the polarization reversal at the non-polar cuts and domain interaction significantly depend on humidity. The spatial distribution of the surface potential measured by Kelvin probe force microscopy in the vicinity of the charged domain walls revealed the decrease of the domain length as a result of the partial backswitching after pulse termination. The phase diagram of switching behavior as a function of tip voltage and spacing between the points of bias application has been plotted. The obtained results provide new insight into the problem of the domain interaction during forward growth and can provide a basis for useful application in nanodomain engineering and development of non-linear optical frequency converters, data storage, and computing devices.

Recent advances in the development of novel methods for the local characterization of ferroelectric domains open up new opportunities not only to image, but also to control and to create desired domain configurations (domain engineering). The morphotropic and polymorphic phase boundaries that are frequently used to increase the electromechanical and dielectric performance of ferroelectric ceramics have a tremendous effect on the domain structure, which can serve as a signature of complex polarization states and link local and macroscopic piezoelectric and dielectric responses. This is especially important for the study of lead-free ferroelectric ceramics, which is currently replacing traditional lead-containing materials, and great efforts are devoted to increasing their performance to match that of lead zirconate titanate (PZT). In this work, we provide a short overview of the recent progress in the imaging of domain structure in two major families of ceramic lead-free systems based on BiFeO3 (BFO) and (Ka0.5Na0.5)NbO3 (KNN). This can be used as a guideline for the understanding of domain processes in lead-free piezoelectric ceramics and provide further insight into the mechanisms of structure–property relationship in these technologically important material families.