Self-assembled Domain Structures Research Articles

Shape instability of the moving wavy domain wall in uniaxial ferroelectric

ABSTRACTIn this paper, we consider the shape instability of ferroelectric wavy domain wall that moves uniformly in the ferroelectric capacitor under the constant uniform electric field. The retardation of the bulk screening of residual depolarization field and existing of the surface dielectric layers were taken into account. It was shown that the spatial distribution of the electric field in the ferroelectric plate led to topological instability of the moving wavy domain wall. The obtained results are important for the formation of the self-assembled domain structures in ferroelectrics.

Formation of self-assembled micro- and nano-domain structures in uniaxial ferroelectrics

We present the experimental study of appearance of domain wall shape instabilities and self-assembled domain structures in uniaxial ferroelectrics lithium niobate and lithium tantalate covered by artificial dielectric layer. The domain structure evolution has been considered as a manifestation of nucleation processes similar to the first order phase transformation. The necessary conditions for formation of self-assembled domain structures including the highly non-equilibrium switching conditions and stability of concave angles were proposed. The formation of the self-assembled domain shape instabilities under application of the uniform external electric field during switching (domain growth) and backswitching (domain shrinkage) has been studied experimentally with these conditions fulfilled. The formation of the bumps at the vortexes of hexagon domain for diameter above 3 - 5 μm with subsequent oriented growth was obtained in stoichiometric lithium tantalate. The formation of quasi-regular fish-bone domain structure has been revealed during spontaneous backswitching in Mg doped lithium niobate. The resulted structure consisted of the narrow residual domains with width from 200 to 500 nm appeared as a result of finger growth to the center of hexagon domain. The obtained decreasing of the number of the residual domains during growth has been attributed to strong electrostatic interaction of domain walls.

Formation of self-assembled domain structures in single crystals of lithium tantalate with artificial dielectric layer

ABSTRACTThe polarization reversal was studied in single crystals of lithium tantalate with intermediate deviation from stoichiometric composition (([Li]/([Li]+[Ta]) = 48.9%) with and without surface photoresist layer. The switching current was analyzed according to the stages of domain structure evolution revealed during in situ visualization of domain kinetics. The characteristic times of the switching process were extracted by fitting of the experimental data using modified Kolmogorov-Avrami model. The formation of the self-assembled domain chains was observed during polarization reversal with photoresist dielectric layer on one polar surface.

Self-assembled domain structures: From micro- to nanoscale

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.

Formation of Self-Assembled Domain Structures in MgOSLT

The formation of self-organized structures of submicron domains under application of the uniform electric field was studied in single crystals of magnesium doped near stoichiometric lithium tantalate grown by double crucible Czochralski method. It was shown that the period of the domain structure (about 1 μm) appeared on Z− polar surface after polarization reversal was almost independent on the electric field. This fact confirms the self-organized nature of the phenomenon. The obtained dependence of the structure geometry on the switching conditions was discussed. The noticeable increase of the low-frequency dielectric permittivity was demonstrated in the samples with charged domain walls.

Formation of Self-Assembled Domain Structures in Lithium Niobate Modified by Ar Ions Implantation

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.

Molecular Transfer Printing Using Block Copolymers

Soft lithographic techniques augment or enhance the capabilities of traditional patterning processes and expand the diversity of materials that can be patterned. Realization of robust parallel techniques for creating chemical patterns at the nanoscale has been challenging. Here we present a method for creating and replicating chemical patterns that uses functionalized homopolymer inks that are preferentially segregated into the nanodomains of phase-separated diblock copolymer films. The inks are transferred by reaction to substrates that are brought into contact with block copolymer films, creating chemical patterns on the substrate that mirror the domain structure present at the film surface with high fidelity and resolution. In addition to printing from self-assembled domain structures, we can also direct the assembly of the block copolymer films from which transfer occurs using lithographically defined masters so as to replicate and transfer patterns of inks with controlled and well-defined geometries. The transferred patterns may be at higher resolution than the lithographically defined master, and the process can be repeated to create multiple copies of identical replicas. Transfer of one ink from one block of the copolymer is also possible, and filling the interspatial regions of the pattern with a second ink provides a pathway toward creating patterns with diverse chemical functionalities.

Shape Evolution of Isolated Micro-Domains in Lithium Niobate

The varieties of domain shapes produced in single crystals of lithium niobate LiNbO 3 family by application of the uniform electric field have been revealed. The crucial role of predetermined nucleation effect representing the step generation at vertices of polygon domain and step growth in three Y directions was discussed. We put emphasis on formation of unusual domain shapes created by switching in non-equilibrium conditions arisen due to retardation of the screening of depolarization field. Formation of oriented fingers and dendrite self-assembled domain structures during switching with artificial surface dielectric layer and during spontaneous backswitching was considered.

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.

Thermal motion and energetics of self-assembled domain structures: Pb on Cu(111).

Low energy electron microscope measurements of the thermal motion of 50-200 nm diameter Pb islands on Cu(111) are used to establish the nature and determine the strength of interactions that give rise to self-assembly in this two-dimensional, two-phase system. The results show that self-assembled patterns arise from a temperature-independent surface stress difference of approximately 1.2 N/m between the two phases. With increasing Pb coverage, the domain patterns evolve in a manner consistent with models based on dipolar repulsions caused by elastic interactions due to a surface stress difference.

Scanning force microscopy characterization of thin lipid films on a substrate

The surface morphology and frictional property of self-assembled domains of ultrathin organic films adsorbed on a solid substrate have been studied by a commercially available scanning probe microscopy with an operation mode of simultaneous atomic force microscopy and lateral force microscopy measurements. Two lipid film systems have been studied; one is a film system formed from synthetic dialkyl lipid, N, N-dioctadecylsuccinamic acid, and the other is films formed from biological phospholipids such as dipalmitoylphosphatidylcholine (DPPC), phosphatidylcholine, and phosphatidylethanolamine. The characteristic self-assembled domain structures as well as the local friction behaviors of the lipid films are presented. A preliminary result is also shown which suggests the hydrophobic alkyl tail groups appeared on multilamellar surfaces of DPPC film can be distinguished from the other hydrophilic polar headgroups.