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 P_s 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.     

Dynamic systems of concentric ring magnetic domains in a highly anisotropic garnet ferrite film in magnetic fields at infrasonic frequencies

Dynamic domain structures in a garnet ferrite film with perpendicular anisotropy are investigated in magnetic fields at infrasonic frequencies for the first time. It is revealed that the multidomain film exists in the anger state and that stable dynamic structures with unusual properties are formed in ac magnetic fields at frequencies of 2–3 Hz.     

Periodic domain structures formed under electron-beam irradiation in LiNbO3 plates and Ti:LiNbO3 planar waveguides of the Y cut

Regular domain structures on the Y cuts of the LiNbO₃ substrates and Ti:LiNbO₃ waveguide structures based on these substrates have been fabricated under electron-beam irradiation. It has been revealed that the domains in undoped and titanium-doped LiNbO₃ crystals are formed as a result of different processes. It has been demonstrated using chemical etching and waveguide second-harmonic generation that regular domain structures in the Ti:LiNbO₃ waveguides are formed at a depth of approximately 8 μm from the surface, where the titanium concentration does not exceed 2 mol %. The quasi-synchronous waveguide optical second harmonic generation with an efficiency of 8.8% has been obtained using the fabricated structures.     

Domain structures of ultrathin magnetic nanobelts

We use a simple magnetization model to determine domain structures of ultrathin magnetic nanobelts. A train of alternate domains are formed along the length direction. Optimal domain length decreases with belt width. Experimental domain length distributions of Fe bilayer nanobelts can be naturally explained. This approach should be applicable to similar nanomagnets.     

Effect of roughness on the magnetic structure of ferro/antiferromagnetic interface

Spin structures at the ferro/antiferromagnetic interfaces perturbed by defects such as atomic high steps are analytically investigated. A two-dimensional model is proposed to describe the spin distribution formed on the interfacial step at the domain wall. A criterion of the domain wall configuration relative to the interface is found, defined by the magnetic and geometrical characteristics of the interface and the magnet.     

Formation of nanodomain structures in lithium niobate as a result of pulsed laser irradiation

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.     

Stable multidomain structures formed in the process of magnetization reversal in GaMnAs ferromagnetic semiconductor thin films

The process of magnetization reversal in ferromagnetic Ga(1-x)Mn(x)As epilayers has been systematically investigated using the planar Hall effect (PHE). Interestingly, we have observed a pronounced asymmetry in the PHE hysteresis when the range of the field scan is restricted to fields below the final magnetization transition. The observed behavior indicates that (a) multidomain structures are formed as M undergoes a reorientation, (b) the domain landscape formed in this way remains stable even after the magnetic field is switched off, and (c) the reorientation of magnetization directions corresponding to the transition points in PHE takes place separately within each domain.     

Rheed evidence for a domain structure of GaAs(001)−2 × 4 AND −4 × 2 reconstructed surfaces

Curved streaks in RHEED patterns from MBE-prepared reconstructed (001)GaAs surfaces are shown to originate from antiphase domains formed by tilted As-As dimer chains. Several possible domain boundary configurations are proposed, including both coplanar and stepped structures.     

PZT铁电薄膜纳米尺度畴结构的扫描力显微术研究

利用扫描力显微术中压电响应模式原位研究了（111）择优取向的PZT60/40铁电薄膜的纳米尺度畴结构及其极化反转行为.铁电畴图像复杂的畴衬度与晶粒中的畴排列和晶粒的取向密切相关.直接观察到极化反转期间所形成的小至30nm宽的台阶结构，该台阶结构揭示了（111）取向的PZT60/40铁电薄膜在极化反转期间其畴成核与生长机理主要表现为铁电畴的纵向生长机理. 关键词： 畴结构 反转机理 PZT薄膜 扫描力显微术     

PT/PZT/PT铁电薄膜的铁电畴和畴壁

用sol-gel法制备出了具有良好铁电性、纯钙钛矿结构的PbTiO₃/Pb(Zr_0.3Ti_0.7)O₃/PbTiO₃(PT/PZT/PT)新型夹心结构铁电薄膜.用扫描力显微镜(SFM)的压电响应模式获得了薄膜铁电畴的垂直于膜平面方向(OPP)、膜平面内(IPP)及OPP的相位和幅度图像，结合理论分析指出薄膜的电畴主要由c畴和偏离垂直于膜平面方向上的c畴构成，薄膜取向的复杂性导致了复杂的畴结构.对于［111］取向的薄膜，当偏离垂直于膜平面方向上的c畴在垂直膜平面方向和面内方向都相反时构成180°的畴壁，在垂直膜平面方向上相同、面内方向相反或由垂直膜平面方向上相反、面内方向相同时构成90°畴壁. 关键词： 铁电薄膜 PT/PZT/PT 电畴和畴壁 扫描力显微镜(SFM)     

High resolution measurement and modelling of magnetic domain structures in epitaxial FePd (0 0 1) L10 films with perpendicular magnetisation

Magnetic domain structures in two 50 nm thick chemically-ordered FePd (0 0 1) epitaxial films with different perpendicular anisotropies have been studied using Lorentz microscopy. Domain and domain wall structures vary significantly according to the magnitude of the anisotropy. For lower anisotropy films, a stripe domain structure with a period of ≈100 nm is formed in which there is a near-continuous variation in orientation of the magnetisation vector. By contrast, in the film with higher anisotropy, a maze-like domain structure is supported. The magnetisation within domains is perpendicular to the film plane and adjacent domains are separated by narrow walls, less than 20 nm wide. Micromagnetic modelling is generally in good quantitative agreement with experimental observations and provides additional information on the domain wall structure.     

Characterization of periodic domain structures in lithium niobate crystals by scanning electron microscopy and X-ray diffraction analysis

Congruent lithium niobate crystals with periodic domain structures formed by the method of thermoelectric postgrowth treatment have been investigated. Periodic domain structures in the samples of polar ZY-, YZ-, and YX-cuts were characterized by scanning electron microscopy, high resolution x-ray diffractometry, and topography. The evaluation and comparison of the secondary electron (SE) signal cycling, electron emission coefficient, and charge value to equalize the differences in the SE signal have allowed us to specify the features of ZY-and YZ-cut structures. A correlation between the crystal lattice distortions near domain boundaries and the type of domain walls has been found. The domain walls separating the areas with the tail-to-tail P _s vectors not only cause stronger crystal lattice distortions near them, but also are charged less quickly under electron irradiation.     

Threshold fluence for domain reversal directly induced by femtosecond laser in lithium niobate

Fabricating domain reversal directly induced by femtosecond laser is a novel and promising method to induce micron-period or even submicron-period inverted domain structure for it averts the domain spreading and mergence which is hard to avoid by traditional electric-field poling method. In this paper, the domain reversal process in lithium niobate crystal by irradiation of femtosecond pulses whose spatial and temporal distributions are taken into consideration is numerically simulated in the framework of Fahy’s model. The simulation results manifest the domain inversion window theory and predict the threshold reversal fluence. The experiment to form domain reversal via direct illumination with femtosecond laser in Y-cut lithium niobate samples was conducted at room temperature. The multi-ring-like structures on the processed samples tally with the inversion window theory and the calculated threshold reversal fluence is well within the scope obtained by simulation, which serves as a corroborative evidence to prove the domain reversals can be formed by direct irradiation with femtosecond laser in lithium niobate.     

Surface antiferromagnetic domain structures of NiO (0 0 1) studied using UV photoemission electron microscope

Direct observation of the antiferro (AF) magnetic domain structures of a NiO (0 0 1) surface is found to be possible using a spectroscopy photoelectron low-energy electron microscope (SPELEEM) and a commercial UV Hg excitation light source without using any polarizers. The principle is based on the magnetic linear dichroism (MLD) effect, where different domain contrasts are produced according to the relative angle between the antiferromagnetic axis and the linearly polarized light. The observed AF magnetic domain structures are strongly affected by both bulk AF magnetic domain structures and the stresses induced during the sample cleaving process. Moreover, the AF magnetic domain structures are found to be irreversible when the sample is heated to over its Néel temperature and then cooled. The possibility of imaging AF magnetic domain structures without using synchrotron radiation or a polarizer is attractive.     

Magnetic Bloch oscillations in nanowire superlattice rings

The recent growth of semiconductor nanowire superlattices encourages hope that Bloch-like oscillations in such structures formed into rings may soon be observed in the presence of a time-dependent magnetic flux threading the ring. These magnetic Bloch oscillations are a consequence of Faraday's law; the time-dependent flux produces an electromotive force around the ring, thus leading to the Bloch-like oscillations. In the spectroscopic domain, generalized Wannier-Stark states are found that are manifestations of the emf-induced localization of the states.     

Amorphization of biperiodic domain structures in quasi-uniaxial magnetic films with a critical thickness

The behavior of biperiodic stripe domain structures in quasi-uniaxial magnetic films with a near-critical thickness is studied by scanning magnetic force microscopy and magnetooptical diffraction. In these films, antiphase and hybrid biperiodic domain structures are found to be absent, and the phase transitions between monoperiodic and in-phase biperiodic domain structures are shown to proceed through two-dimensional domain arrays that are amorphized in the arrangement of near-surface distortions in the domain-wall profile.     

Rotating surface soliton complexes in annular waveguides

We address surface soliton complexes formed at the edge of annular guiding structures containing several concentric rings. Such soliton complexes feature a π-phase difference between neighboring spots. It is shown that the multipole-mode solitons can rotate steadily upon propagation, and the existence domain is strongly affected by the rotation frequency. The rotation may enhance the stabilization of surface multipole-mode solitons.     

Steps on current-voltage characteristics of a silicon quantum dot covered by natural oxide

Considering a double-barrier structure formed by a silicon quantum dot covered by natural oxide with two metallic terminals, we derive simple conditions for a steplike voltage-current curve. Due to standard chemical properties, doping phosphorus atoms located in a certain domain of the dot form geometrically parallel current channels. The height of the current step typically equals (1.2 pA)N, where N=0, 1, 2, 3... is the number of doping atoms inside the domain, and only negligibly depends on the actual position of the dopants. The found conditions are feasible in experimentally available structures.     

Formation of two-dimensional crystal-like structures from inclusions in smectic C films

The structures formed by inclusions in smectic C (SmC) free-standing films are investigated using polarized light microscopy. The domains confined in these two-dimensional (2D) systems induce distortion of the inplane orientational order, which governs the elastic interaction between the inclusions. The balance between long-range quadrupolar attraction and short-range repulsion gives rise to a nontrivial collective behavior of domains. Various 2D structures are created as a function of the concentration and size of inclusions. We observe the formation of chains and then a 2D square lattice when the concentration of domains increases. Further increase in the domain size leads to the transition from square to hexagonal close-packed structure.     

Specific features of structural defects in twisted nematic liquid crystals under conditions of electrohydrodynamic instability

The influence of inhomogeneous boundary conditions (director orientation) on the specific features of the formation and evolution of structural defects in 90·-twisted nematic liquid crystals (twisted structures) is investigated in the regime of electrohydrodynamic instability. It is found that, unlike the domain structure of nematic liquid crystals with a planar orientation, in which defects with topological indices of ±1 are formed under conditions of electrohydrodynamic instability, the domain structure of twisted nematic liquid crystals contains both the above defects and defects with a topological index of 0. It is shown that structural defects with a topological index of 0 are stable and that the existence of these defects is associated with the axial velocity u_a of nematic liquid-crystal flow in the domains.