Study of LiNbO3 single crystals with a regular domain structure by piezoresponse force microscopy

Lithium niobate crystals with a regular domain structure have been studied by piezoresponse force microscopy. The period of regular domains and the domain-wall width (w = 45 nm) have been calculated for Z- and Y-cut crystals based on an analysis of two-dimensional images of the domain-structure piezoresponse. It is shown that for the Y-cut crystal, both positive and negative domain boundaries can be identified when recording the lateral component of piezoresponse.     

The 30° rotation domains in wurtzite ZnO films

The 30° rotation domains in ZnO films were studied by transmission electron microscopy (TEM) and high-resolution electron microscopy (HREM). The cross-section and plane-view observations reveal that the 30° rotation domains have elliptical cylindrical shape, with the longitude axis along one of the 1 1 2¯ 0 directions and the short axis along one of the 1¯ 1 0 0 orientations, respectively. The volume fraction of the 30° rotation domains is about 1%. Due to the elliptical shape of the domain boundaries along the [0 0 0 1]_ZnO direction, partially disordered superlattice-like structures are formed. As shown by the HREM images and Zn elemental mapping, these super-lattices are most likely caused by periodical segregation and depletion of Zn along the domain boundary for compensating the mismatched lattice strain.     

Supramolecular structure formation of Langmuir-Blodgett films of comblike precursor and polyimide

The surface structure of Langmuir-Blodgett films of a comblike polyimide precursor—a rigid-chain polyamic acid alkylamine salt bearing multichains of tertiary amine—and films of the corresponding polyimide were studied by atomic force microscopy (AFM). An analysis of the images of the surface of three-layer films revealed a domain structure. It was found that the Langmuir-Blodgett film formation of the precursor occurs as a result of the layer-by-layer deposition of two-dimensional domains (composed of polyamic acid salt molecules on the water surface) onto a substrate. The formation of domains in a monolayer is associated with the chemical structure of the precursor, to be more precise, with the rigidity of the main chain and the presence of closely spaced aliphatic side chains in the polymer chain, whose total cross-section area is close to the surface area of the projection onto the plane of the repeating unit of the main chain. Polyimide films inherit the domain structure of the precursor films; the inhomogeneity of the film thickness substantially decreases, whereas the domain size and character of their distribution in the film remain unchanged.     

Application of the Fourier transforms for analysis of the domain structure images of uniaxial ferroelectric

The formation of ferroelectric domains in triglycine sulfate crystal in the para–ferroelectric phase transition has been investigated in situ by piezoresponse force microscopy. The domain structure has been analyzed using the images of Fourier transforms of the scanned (010) surface of natural cleavage. The formation of a quasi-periodic one-dimensional structure of 180° domains with dominant components of one sign below T _C near the transition point is revealed and crystallographic reference to the laboratory coordinate system is performed.     

Investigation of domain structures in PZNT93/7 crystals by chemical etching

The domain structures in 0.93Pb (Zn_1/3Nb_2/3)O₃‐0.07PbTiO₃ (PZNT93/7) crystals were investigated by chemical etching technique. Original antiparallel 180° domains of size 20–40 μm were observed on the surface of as‐grown PZNT93/7 crystal. It was found the domain states are sensitive to the stress field induced by mechanical processing or impurities. As the composition of PZNT93/7 crystal was located near the morphotropic phase boundary, various domain configurations were observed. On the <001>‐oriented wafer, the etched a ‐ and c ‐domains revealed homogenous and island‐like patterns. The c ‐domains consist of upper and lower height regions corresponding to the tail and head of the polarization, respectively. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of Co substitution for Ni on the microstructure and magnetic properties of (Fe, Ni)-based amorphous alloys produced by melt spinning

Transmission electron microscopy with selected area electron diffraction, and X-ray diffraction were applied to study the effect of Co substitution for Ni in (Fe, Ni)-based amorphous alloys. The investigation was performed to obtain information on correlations between microstructure and magnetic properties of the (Fe, Ni, Co)-based amorphous alloys. The examination of the microstructure reveals that there are small crystallized free surface regions because the actual quenching rate is distributed inhomogeneously over the cross-section of the ribbon. Since in the free surface region, the solidification rate is lower, a spontaneous annealing process occurs at the top surface of the ribbon. The crystallization degree of the free surface region is higher for alloy ribbons that contain Co up to a 15 at.% concentration. Magnetic domains pattern are sensitive to the surface crystallization and Co content of the (Fe, Ni)-based alloy ribbons. Fine-scaled stripe domains were evidenced on the free ribbon surface while on contact surface stress domain pattern appeared. With the increase of the Co content, the domain width became small and long stripes appeared. The striped domains are responsible for an increased coercivity of the ribbons. However, there is a critical Co content (x_Co = 10) for which spontaneous narrow stripe domains are no longer more energetically favourable for ribbons with specific magnetic applications.     

Study of the surface heterogeneity of topographic and electric nature by atomic force microscopy by the example of triglycine sulfate

Triglycine sulfate crystals with an ideal (010) cleavage plane are used as model objects to reveal problems in interpreting atomic force microscopy (AFM) images of surfaces with nonuniform charge distribution. Specific microrelief features of two types are found: lenslike formations with different contrast and rounded protrusions/valleys of different size but fixed height. An analysis of their evolution with a change in temperature and under an electric field and mechanical impacts has made it possible to separate relief elements from the crystal domain structure. The interpretation proposed is confirmed by the multimode AFM data. The specific features of the images of dynamic domains and aged domains (which cannot undergo polarization reversal) are studied. The domain-wall width found in the AFM measurements depends on the technique used and the specificity of probe-surface interaction; it varies from 9 to 2000 nm. The most reliable data on the domain-wall width in triglycine sulfate crystals are provided by piezoelectric force microscopy, according to which the wall width does not exceed 30 nm.     

Domain structure and properties of triglycine sulfate crystals with profile <Emphasis Type="Italic">D</Emphasis>,<Emphasis Type="Italic">L</Emphasis>-α- and <Emphasis Type="Italic">L</Emphasis>-α-alanine-doped layers

A complex investigation of the domain structure and dielectric properties of triglycine sulfate (TGS) crystals containing profile layers doped with D,L-α-alanine (DLATGS) and L-α-alanine (LATGS) impurities is carried out. The images of the DLATGS and LATGS layers and ferroelectric domains are obtained by piezoelectric force microscopy; the parameters of the domain structure and the degree of unipolarity are determined. It is established that DLATGS layers are multidomain and LATGS stripes are mainly single-domain. The experimental data on the macroscopic dielectric properties of the crystals are compared with the results of a microscopic analysis of the domain structure.     

Further Experimental Evidence for the Wall Structure of the Flexoelectric Domains in Symmetrically Weakly-Anchored MBBA Layers

An attempt for measuring of the penetration non-critical length of MBBA flexoelectric surface-induced domains is made. The disappearance of the domains into subcritical regions is related to the strong nonhomogeneity of the electric field around the gap which is able to inhibit the flexoelectric domain formation. The disappearance of the electrohydrodynamic domains generated from the flexoelectric ones, on the other hand, shows their secondary character as well. The existence of the penetration non-critical length of the flexoelectric domains is further confirmed with the observation of the corresponding supercritical influence length of side walls or air bubbles.

The behavior of the flexoelectric domains in an additionally applied magnetic field reveals their wall structure and permits the determination of the value and sign of the two MBBA flexoelectric coefficients of bend e _3x and splay e _1z, when the value and sign of the total flexoelectric coefficient ( e _z, + e _3x) are known.     

准同型相界组分PMNT弛豫铁电单晶的畴结构与极化特性

采用坩埚下降法生长了具有准同型相界(MPB)组分的65Pb(Mg1/3Nb2/3)O3-35PbTiO3 (PMNT65/35)弛豫铁电单晶.用偏光显微镜研究了(001)、(110)和(111)三个结晶学取向的铁电畴结构,观察到明暗交替的变化.通过对极化前后电畴形状的比较,分析了极化前后铁电畴形态的变化原因.晶片极化条件为:600 V/mm 的电场并保持10～15 min.研究了极化介质不同对极化后晶片压电性能的影响.     

Fabrication of a GaN lateral polarity junction by metalorganic chemical vapor deposition

A fabrication process for growth of GaN lateral polarity junctions consisting of Ga-polar and N-polar domains grown simultaneously side-by-side on c-plane sapphire was developed using the polarity control scheme. An ammonia-annealing step following deposition and patterning of a thin low-temperature AlN nucleation layer played a crucial role in avoiding mixed-polarity growth of the remaining AlN nucleation layer, as well as in nitriding the bare sapphire surface to facilitate growth of N-polar GaN. The achievement of both polar domains, free from inversion domains within a contiguous domain, led to Ga-polar domain exhibiting featureless morphology with highly resistive characteristics, while N-polar domains exhibited hexagonally faceted morphology and were highly conductive.     

The stress birefringence images of low angle grain boundaries in 6H‐SiC single crystals

Low angle grain boundaries, also referred to as domain walls, is one of the major structural defects in c‐axis physical vapor transport (PVT) grown hexagonal Silicon Carbide. To investigate the nature of the low angle boundaries, polarized optical microscope was used. The low angle boundary gives bright stress birefringence images under polarizing optical microscope. Periodic extinction of the stress birefringence images occurs when the (0001)‐face SiC is rotated under polarizing optical microscope. The micro‐structure of the low angle boundary is proposed. Using dislocation elastic theory, it is theoretically confirmed that the domains consist of uniform pure edge dislocations with Burgers vectors perpendicular to the dislocation arrays. The simulation results coincide with the experimental observations.     

Scanning Capacitance Microscopy of Triglycine Sulfate Crystals with the Profile Chromium Distribution

The spatial capacitance distribution, domain wall configuration, and impurity composition of triglycine sulfate TGS–TGS + Cr crystals with a growth periodic impurity structure have been investigated using scanning capacitance microscopy and X-ray fluorescence and topography. The chromium ion concentration in the strips emerging to the surface has been determined, and the periodic impurity distribution has been established. The difference between the chromium concentrations in nominally pure and impurity strips was found to be ~0.08 wt %, which is reflected in a variation in the capacitance image contrast by 0.17%. It is shown that capacitance images carry information about localization of the impurity gradient regions and domain walls and make it possible to establish a correlation between the defect and domain structures of a ferroelectric crystal.     

An investigation of the magnetic domains in the stressed amorphous FeCoSiB magnetoelastic films

The effects of tensile and compressive stress on the magnetic domains of amorphous FeCoSiB films are investigated. It is observed that the unstressed sample consists of irregular domains while the stressed samples show stripe domains. With the increase of the tensile stress, the stripe domain of the stressed films tends to align parallel to the direction of the stress, while with the increase of the compressive stress the stripe domain of the stressed films tends to align perpendicular to the direction of the stress. The magnetic domain and its evolution under the stress are explained by introducing the magnetoelastic anisotropy induced by the stress.     

A study of ferroelectric domain patterns in orthorhobic KNbO3 with optical microscopy

Ferroelectiric domain patterns in natural surface layers of Czochralski as-grown crystals are very complicated. The inner domain patterns are comparatively simple and consist of a regular arrays of so-called thin lens-like 90° domains. Only few inner 60° and 120° domains crossing the 90° domain arrays are observed. The inversion or 180° domains are shape-like separated islands. The 60° microdomains are easily introduced into the surface layers during the specimen processing. There are some elastic interactions between the different kinds of ferroelectric domain walls, the orientations of which are in good coincidence with the theory proposed by Janovec.     

ELECTRIC FIELD-INDUCED DIRECTOR ORIENTATION OF SMECTIC-A DOMAINS IN AN ISOTROPIC PHASE

Abstract

Electric field-induced director orientation of smeetic-A phase in an isotropic phase has been studied with a polarizing microscope using the binary mixture of octyloxycyanobiphenyl and dodecyl alcohol. Electric field is applied to the samples in which spherical smectic-A domains with and without defects in an isotropic phase are observed. Field-induced orientation of smectic-A director is observed for spherical smectic-A domains with defects but not observed for those without defects below electric field strength of 1.0 V/μm, indicating that the presence of defects facilitates the director orientation. The threshold field for the smectic-A director orientation varies from smectic-A domain to domain, suggesting that the threshold field is dependent on the structure of defects.     

The influence of a ferroelectric domain wall on the fabrication of a pyroelectric laser energymeter

A region across a ferroelectric domain wall has been scanned, using an Nd:YAG laser beam (beam size 440 μm), in a thin crystal of TGS (triglycine sulphate), cut normal to the polar axis and the pyroelectric response of the crystal has been recorded. If a laser pulse of fixed beam size falls on the domain completely, then the output pyroelectric signal is maximum. But when the laser beam (diameter of beam greater than width of domain wall) falls on the domain wall, the pyroelectric signals from two opposite domains tries to cancel each other and net signal depends on the position of laser beam across the domain wall. When the domain wall lies in the middle of the laser beam the output pyroelctric signal will be zero. In our experiment when beam of size 440 μm falls on positive domain the pyroelectric voltage of ‐2.76 mV recorded and when beam starts crossing the domain wall (i.e from positive domain to negative domain), the pyoelectric signal changes its sign from negative to positive through zero. After 220 μm the signal decreased to minimum and again increases to maximum (+2.46 mV) in opposite direction after 440 μm i.e when beam falls on the negative domain completely. This shows that the polarization in the domain wall region (separating two domains) is zero i.e the paraelectric nature of domain wall. So before detector fabrication the sample must be poled sufficiently to avoid the non uniformity of pyroelectric signal due to the domain wall. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Image enhancement of nano-dispersed N-(p-n-decyloxybenzylidene)-p-n-hexyloxy aniline using combined unsharp masking

The main objective of the image enhancement is to process an image with suitable technique to produce better visibility for a specific application. To identify key features like transition temperatures, clear phase identification in the liquid crystalline images, we require some novel image processing techniques. Characterisation and mesomorphic behaviour in pure and 1% ZnO nano-dispersed liquid crystalline N-(p-n-decyloxybenzylidene)-p-n-hexyloxy anilines, 10O.O6 compounds are carried out using a polarising microscope and images are preserved for enhancement. Both the compounds exhibits NACIG (nematic, smectic-A, smectic-C, smectic-I, smectic-G) phases and the transition temperatures of the 1% ZnO nano-dispersed 10O.O6 are reduced compared with pure 10O.O6. Further, in this paper, a novel image enhancement technique of combined unsharp masking is proposed on pure and 1% ZnO nano-dispersed 10O.O6 liquid crystalline compounds for better visibility of phases at transition temperatures. The proposed method is used to identify the uniform regions and to detect the defects which may not be clearly observed from the textures that are recorded by polarising microscope.     

Formation of unusual nonferroic domains in TeO2 single crystals under external electric field

The formation of unusual slowly relaxing domains under an external dc electric field has been revealed in paratellurite (TeO₂) crystals. These domains differ from those arising in ferroics (ferromagnets, ferroelectrics, ferroelastics, etc.). The effect is characterized by the existence of a threshold field strength (at which domains begin to be formed) and long equilibrium settling times (up to a few hours, depending on the electric field strength). A crystal returns to the initial single-domain state also after a few hours after the field is switched off. High-resolution triple-crystal X-ray diffractometry has revealed that domains retaining the paraelastic tetragonal phase rotate with respect to each other in space without changing their lattice parameter. The domain sizes are 2–4 mm, depending on the field strength. Currently, the exact mechanisms of domain formation are unclear. Possible reasons for the formation of these defects and an analogy of the observed effects with the behavior of liquid crystals under electric field are discussed.     

Stability of magnetic domains inside the core of amorphous wire

The size and energy of domains inside the core of an amorphous Fe-based wire was estimated. The influence of magnetic field, coercitivities and lengths of the domain on the wire radius is confirmed. Domains consisting of a cylindrical part with cone-shaped domain tops exibit the lowest energy and greatest stability to a magnetic field.