Imaging Of Domain Structures Research Articles

Three-dimensional imaging of ferroaxial domains using circularly polarized second harmonic generation microscopy

The spontaneous symmetry breakdown of matter is one of the most important concepts in materials physics and leads to a phase transition into an ordered phase and domain formation in its consequence. The so-called ‘ferroaxial order’ characterized by a rotational structural distortion with an axial vector symmetry has gained growing interest as a new class of ordered state. However, the observation of ferroaxial domain states, that is, clockwise and counterclockwise rotational states, is not straightforward and has been little investigated. Here, we propose that the circular intensity difference in second harmonic generation (CID-SHG) offers an experimental technique to investigate ferroaxial order and its domain states through the transition process of higher-order multipoles such as magnetic-dipole and electric-quadrupole. By using CID-SHG microscopy, we successfully visualize three-dimensional images of ferroaxial domain structures in NiTiO3. Our results indicate that CID-SHG is a sensitive probe of ferroaxial order and opens possibilities for the use of ferroaxial materials in nonlinear optical manipulations.

Dimerization processes for light-regulated transcription factor Photozipper visualized by high-speed atomic force microscopy

Dimerization is critical for transcription factors (TFs) to bind DNA and regulate a wide variety of cellular functions; however, the molecular mechanisms remain to be completely elucidated. Here, we used high-speed atomic force microscopy (HS-AFM) to observe the dimerization process for a photoresponsive TF Photozipper (PZ), which consists of light–oxygen–voltage-sensing (LOV) and basic-region-leucine-zipper (bZIP) domains. HS-AFM visualized not only the oligomeric states of PZ molecules forming monomers and dimers under controlled dark–light conditions but also the domain structures within each molecule. Successive AFM movies captured the dimerization process for an individual PZ molecule and the monomer–dimer reversible transition during dark–light cycling. Detailed AFM images of domain structures in PZ molecules demonstrated that the bZIP domain entangled under dark conditions was loosened owing to light illumination and fluctuated around the LOV domain. These observations revealed the role of the bZIP domain in the dimerization processes of a TF.

Computer-aided characterization of ferroelectric phase transitions and domain structures using polarizing light microscopy

Optical microscopy is an essential characterization technique that is used as an initial step in the study of domain structures and phase transitions of ferroelectric materials. Image analysis aided by advanced computer algorithms is urgently required to enable an improved accuracy and higher efficiency of data processing. In this study, an automatic full-angle light intensity detection algorithm is developed to study polarizing light microscopy images of domain structures and the phase evolution process is decoded using the scale invariant feature transform method. This data processing algorithm is then used to characterize the phase transition process in relaxor ferroelectric PMN-0.29PT single crystals with complex domain structures. An emerging in-plane tetragonal phase is tracked during the rhombohedral (R) to tetragonal (T) phase transition, which is associated with peaks present in the temperature-dependent dielectric curve. Compared to the traditional polarizing light microscopy characterization method, this computer-aided algorithm enables a quicker and more informative analysis of domain evolutions in ferroelectric single crystals.

Humidity Effects on Domain Structure and Polarization Switching of Pb(Zn1/3Nb2/3)O3-x%PbTiO3 (PZN-x%PT) Single Crystals.

The effect of relative humidity on the domain structure imaging and polarization switching process of Pb(Zn1/3Nb2/3)O3-x%PbTiO3 (PZN-x%PT) ferroelectric single crystals has been investigated by means of the piezoresponse force microscopy (PFM) and piezoresponse force spectroscopy (PFS) techniques. It was found that the PFM amplitude increases with the relative humidity, and that the ferroelectric hysteresis loops at different relative humidity levels show that the coercive bias decreases with the increase in relative humidity. These observed phenomena are attributed to the existence of the water layer between the probe tip and the sample surface in a humid atmosphere, which could affect the effect of the electric field distribution and screening properties at the ferroelectric sample surface. These results provide a better understanding of the water adsorption phenomena at the nanoscale in regard to the fundamental understanding of ferroelectrics’ properties.

Carbon tip aperture cantilevers: Fabrication & features in near-field magneto-optical imaging

Improving the ways of magnetic structure investigation with the lowest possible resolution is important in the study and practical implementation of fundamental magnetism. Here we discuss one of the most modern magneto-optical method of domain structure (DS) imaging, scanning near-field magneto-optical microscopy (SNMOM), and propose the new technology based on focused ion beam (FIB) treatment to produce aperture cantilevers with carbon hollow pyramid tip (ACCT). Estimated ACCT light transmission coefficients show better results compare to commonly used aperture silicon cantilevers. By measuring the polarization characteristics of aperture with diameter from 83 to 263 nm, we illustrate the possibility of ACCT to maintain a liner polarization of transmitted light. Testing of ACCT in atomic-force and SNMOM modes shows that ACCT are the effective tool in near-field imaging. Features of morphology and DS of Bi-substituted iron garnet (Bi: IG) films synthesized and used as the test objects, including DS peculiarities of 100 nm-size, is revealed.

Giant magnetoimpedance and magneto-optical Kerr effects in (Co63Ni37)75Si15B10 amorphous ribbon

The Giant magneto-impedance (GMI) effect in the frequency range 10–1000 MHz and surface magnetic characterization using the magneto-optical Kerr effect (MOKE) in (Co63Ni37)75Si15B10 amorphous ribbon were studied. The GMI ratio increases with a frequency up to around 500 MHz followed by a slow decrease. Observed dependence of GMI ratio is discussed by considering the frequency dependencies of the skin depth penetration and magnetic permeability. MOKE in the transverse and longitudinal applied magnetic field to the ribbon direction configurations provides images of magnetic domain structure and hysteresis loops of the two surface sides of the ribbon. An inclined magnetic structure with respect to the longitudinal direction of the ribbon was observed. This inclined magnetic structure is related to a significant transverse component of the magnetic susceptibility tensor, which is a prerequisite to observe GMI effect. The magnetic anisotropy field evaluated from the hysteresis loop with the transverse applied magnetic field configuration is in agreement with the longitudinal magnetic field necessary to obtain the maximum GMI ratio. The MOKE characteristic of two sides ribbon is quite vertical associated to large Barkhausen jumps because the anisotropy axis is, in this configuration, parallel to the applied magnetic field.

Enhancement of piezoelectric properties of lithium niobate thin films by different annealing parameters

Piezoelectric materials with useful properties find a wide range of applications including opto- and acousto- electronics. Lithium niobate in the form of a thin film is one of those promising materials and has a potential to improve ferroelectric random access memories devices, optical waveguides or acoustic delay lines by virtue of its physical characteristics, e.g. electro-optic coefficient, acoustic velocity, refractive indices etc. The key challenge to overcome is lithium nonstoichiometry as it leads to the appearance of parasite phases and thus aggravates physical and structural properties of a film. According to literature data, in order to obtain microcrystalline piezoelectric phase in previously amorphous films a set of methods is used. In our case we tried to synthesize LN films using congruent target and non-heated silicon substrate and then attain the piezoelectric phase by different annealing parameters. Afterwards LN films were compared to the ones synthesized on the silicon substrate with an additional buffer layer of platinum. Samples were studied by scanning probe microscope. Self-polarization vectors were defined. Based on domain structure images, the histograms of distribution of piezoresponse signals were built.

Advanced aperture cantilevers made by focused ion beam for both magnetic domain structure and morphology investigation in high resolution magneto optical microscopy

Magneto-optical microscopy is a well-known and widely used method of magnetic domain structure investigation. Spatial resolution is limited by diffraction limit of the light and practically not exceed 0.5μm. Possibility to overcome diffraction limit by combination of magneto-optical microscopy and magnetic-force microscopy was showed earlier [1]. Aperture cantilever was used to light up the sample in near-field mode. In this paper, authors review most popular technology for aperture cantilever production with its advantages and disadvantages. Authors propose new technology based on focused ion beam treatment for creation aperture cantilevers with advanced parameters such as small aperture size and light throughput. Bi-substituted yttrium iron garnet (Bi: YIG) thin films with high magneto-optical activity and different period of domain structure were used as test objects. High resolution images of both morphology and domain structure obtained with new advanced aperture cantilevers are shown.

Abnormal kinetics of domain structure in KTA single crystals

Single crystals of potassium titanyl phosphate (KTiOPO4, KTP) family (MTiOXO4, where M is K, Rb, or Cs, and X is P or As) with periodical domain structures have emerged as one of the key platforms for enabling nonlinear photonics applications. Potassium titanyl arsenate (KTiOAsO4, KTA) crystals possess nonlinear optical properties outperforming those of KTP. However, domain kinetics in KTA, being the crucial element for periodical poling, lacks comprehensive studies. We present the results of in situ imaging of domain kinetics in KTA with high temporal resolution. The analysis of a set of instantaneous domain structure images (kinetic map) has allowed reliable revealing of the slow and fast domain walls, similar to KTP. The mobility and the threshold fields for the domain walls have been estimated. The main stages of the domain structure evolution have been revealed. The original hatching stage representing the formation of quasiperiodic structure of the narrow stripe domains has been discovered. The relative input of the hatching stage has increased with external field. The obtained qualitative difference in the domain structure evolution, compared with KTP, has been attributed to a six times larger ratio of fast to slow wall mobility in KTA. This fact results in suppression of the undesirable broadening of the stripe domains thus making KTA crystals very attractive for periodical poling.

Micro-Raman Imaging of Ferroelectric Domain Structures in the Bulk of PMN-PT Single Crystals

We demonstrate the application of confocal Raman microscopy (CRM) for nondestructive imaging of ferroelectric domains both at the surface and in the bulk of lead magnesium niobate-lead titanate (PMN-PT) ferroelectric single crystals. The studied model periodical domain structure was created at a [001] cut of tetragonal-phase PMN-PT crystal by the electron beam patterning technique. It was shown that the surface CRM domain image coincides in details with the image obtained by piezoresponse force microscopy.

Kink–Antikink Interaction in a Linear Defect of the Electroconvective Structure of a Nematic

Features of the interaction of two dislocations in a new type of a singular defect appearing in a one-dimensional domain structure at electroconvection in π/2-twisted nematic liquid crystals have been studied experimentally and theoretically. This type of defects is characterized by a quite extended strain field or the degree of “dissociation.” In this case, domains above the core of the defect are shifted with respect to domains below the core of the defect by half the spatial period. Hydrodynamic flows in domains of twisted nematics have not only the tangential velocity component but also the axial component whose directions in neighboring rolls are opposite. The axial component is responsible for specific features in the oscillation dynamics of various types of defects in twisted nematics. Above a certain critical applied voltage, the defect begins to oscillate so that domains with codirected axial components are closed. As a result, so-called “zigzag” oscillations appear. Simultaneously, a pair of dislocations with opposite topological charges S = ±1 is generated at the edges of the oscillating defect; these dislocations move toward each other. Using the demodulation technique of initial images of domain structures, it has been shown that the collision of dislocations in the extended defect is well described by a two-kink solution of the sine-Gordon equation.

Potential Images of Ferroelectric Domain Structures Formed by Electron Beam in Lithium Niobate Crystals

Ferroelectric domain structures formed by an electron beam in lithium niobate crystals are studied using low-voltage SEM microscopy. The structures are formed in crystals with different conductivity, including samples with high-resistance congruent composition (CLN) and samples with conductivity increased by reductive annealing (RLN). The potential nature of the contrast of the domain structures observed in the secondary electron mode depending on the conductivity of the samples and the direction of spontaneous polarization of the domains is analyzed. It is assumed that the domain contrast in CLN crystals is associated with long-lived charges localized near domain walls and in the irradiated areas. The recorded domain structures in the CLN crystals are visualized on polar and nonpolar cuts. In the RLN crystals with improved conductivity compared to CLN, the potential contrast of the periodic domain structures is found only on the polar cuts, where vector Ps of the domains is perpendicular to the irradiated surface. This contrast is likely because the field of the spontaneous electric polarization charges influences the secondary electrons.

Magnetic domain structure imaging near sample surface with alternating magnetic force microscopy by using AC magnetic field modulated superparamagnetic tip

For magnetic domain imaging, with a very high spatial resolution magnetic force microscope, the tip-sample distance should be as small as possible. However, magnetic imaging near the sample surface is very difficult with conventional magnetic force microscopy (MFM) because the interactive forces between the tip and sample include van der Waals and electrostatic forces along with a magnetic force. In this study, we proposed alternating MFM which only extracts a magnetic force near the sample surface without any topographic and electrical crosstalk. In the present method, the magnetization of an FeCo–GdOx superparamagnetic tip is modulated by an external AC magnetic field in order to measure the magnetic domain structure without any perturbation from the other forces near the sample surface. Moreover, it is demonstrated that the proposed method can also measure the strength and identify the polarities of the second derivative of the perpendicular stray field from a thin film permanent magnet with a DC demagnetized state and remanent state.

Three-dimensional imaging of ferroelectric domain structure in periodically poled lithium niobate using digital holographic tomography

An experimental method for three-dimensional (3D) imaging of ferroelectric domain patterns using digital holographic tomography is presented. The implementation of this method employs the curvilinear filtered back-projection. Our experimental method has been demonstrated on the imagining of the domain structure in a periodically poled lithium niobate single crystal. The developed method allows fast and accurate 3D observations of ferroelectric domain structures in the whole volume of the ferroelectric single crystals on the millimeter scale.

Nearly Diffraction-Free Nonlinear Imaging of Irregularly Distributed Ferroelectric Domains.

Second-harmonic generation is used experimentally for the nonlinear imaging of two-dimensional irregular domain structures. Analytical solutions and simulation results for the Fresnel distribution of domain walls are obtained. The results show that the domain wall plays an important role in the imaging process and the corresponding diffraction effect is greatly suppressed (we call it a nearly diffraction-free effect), thus providing a simple way to realize high-resolution imaging for ferroelectric domains.

Magnetic resonance force microscopy using ferromagnetic resonance of a magnetic tip excited by microwave transmission via a coaxial resonator

The present work proposes magnetic resonance force microscopy (MRFM) based on ferromagnetic resonance (FMR) modulation of a magnetic tip using microwave transmission via a coaxial resonator instead of using conventional microwave irradiation by an external antenna. In this MRFM, the coaxial resonator is electrically connected to the magnetic cantilever tip, which enables simple implementation of FMR excitation of a magnetic tip in conventional magnetic force microscopy. The FMR frequency of the tip can be easily extracted from the reflection spectrum of a transmission line connected to the magnetic tip. The excitation of tip FMR is confirmed from the microwave frequency dependence of the mechanical response of the tip oscillation. This MRFM is effective for extracting the magnetic interaction force near a sample surface without perturbation of its magnetic state. Nanometer-scale imaging of magnetic domain structures on a demagnetized thin-film permanent magnet is successfully demonstrated.

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.

MOKE Study of Amorphous Microwires for Temperature Sensors

We report investigations on temperature-induced transformation of magnetic domain structures and magnetization reversal process in as-cast and annealed co-rich amorphous glass covered microwires. The images of domain structures and hysteresis loops were obtained using magneto-optical Kerr microscopy. The directed shift of the hysteresis loop along the field axis was observed during the temperature increase and decrease in the annealed wire. The mechanism of the observed effect is based on the strong influence of the temperature-induced transformation of the internal stresses in the outer shell of the microwire. The studied microwires could be considered as candidates for the active element of the temperature sensor.

Ferroelectric Domain Structure and Local Piezoelectric Properties of Lead-Free (Ka0.5Na0.5)NbO₃ and BiFeO₃-Based Piezoelectric Ceramics.

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.

Fractal parameterization analysis of ferroelectric domain structure evolution induced by electron beam irradiation

The article presents some results of fractal analysis of ferroelectric domain structure images visualized with scanning electron microscope (SEM) techniques. The fractal and multifractal characteristics were estimated to demonstrate self-similar organization of ferroelectric domain structure registered with static and dynamic contrast modes of SEM. Fractal methods as sensitive analytical tools were used to indicate degree of domain structure and domain boundary imperfections. The electron irradiation-induced erosion effect of ferroelectric domain boundaries in electron beam-stimulated polarization current mode of SEM is characterized by considerable raising of fractal dimension. For dynamic contrast mode of SEM there was revealed that complication of domain structure during its dynamics is specified by increase in fractal dimension of images and slight raising of boundary fractal dimension.