Strain at junctions in multidomain configurations

This article deals with the determination of multidomain configurations in ferroics taking into account the elastic compatibility of the neighbouring domains. The proposed method is based on transformation matrices, which describe the spacial relationship of two crystal lattice bases for coherent domain pairs. The matrices are calculated using the symmetry operations between domains and lattice parameters. The principle point of this method is the comparison of the product of transformation matrices and the unity matrix. For example, by using this method it was shown that the junction of three and five orientation domains is strained whereas the encounter of four domains is strain free in three different ferroelastic perovskite phases. The derived allowed four-domain configurations are confirmed by experimental data.     

Lattice orientations of driven vortex matter in amorphous MoGe films

We have investigated the lattice orientation of driven vortex matter in amorphous MoGe films. Mode locking experiments in the flux flow state reveal that in addition to the theoretically predicted lattice orientation parallel to the flow direction also the perpendicular orientation occurs. Mapping out the orientations in a phase diagram, the perpendicular orientation is found to dominate the phase diagram covering a wide field and temperature range. Scanning tunneling microscopy images of the vortex lattice frozen from the flux flow state confirm the switching between parallel and perpendicular orientations in the phase diagram. The effect is possibly caused by the influence of the sample edge.     

Discrete and dipole-mode gap solitons in higher-order nonlinear photonic lattices

We investigate the formation of fundamental discrete solitons and dipole-mode gap solitons in triangular photonic lattices imprinted in photorefractive nonlinear media. These lattices are strongly affected by the photorefractive anisotropy, resulting in orientation-dependent refractive index structures with reduced symmetry. It is demonstrated that two different orientations of the lattice wave enable the formation of fundamental discrete solitons in the total internal reflection gap. Furthermore, it is shown that one lattice orientation additionally supports dipole-mode solitons in the Bragg reflection gap. The experimental results are corroborated by numerical simulations using the full anisotropic model. PACS 42.65.Tg; 42.65.Wi; 42.70.Qs     

CdTe and PbTe nanostructures on the oxidized pentagonal surface of an icosahedral AlPdMn quasicrystal

By means of congruent evaporation, we have deposited CdTe and PbTe onto the oxidized fivefold-symmetry surface of an icosahedral AlPdMn quasicrystal. This procedure results in the formation of nanocrystals in both cases. While the azimuthal orientations of the crystallites are random, the polar orientations are well defined. The crystalline CdTe and PbTe domains expose their (1 1 1) and (0 0 1) faces, respectively, which are aligned parallel to the pentagonal surface of the quasicrystal. The nanometric size of the domains is not a result of the lattice mismatch between the growing film and the substrate as usually observed in molecular-beam epitaxy, but of the limited size of the oxide domains of the substrate surface.     

Enlargement of absolute photonic band gap in modified 2D anisotropic annular photonic crystals

We analyze the absolute photonic band gap in two dimensional (2D) square, triangular and honeycomb lattices composed of air holes or rings with different geometrical shapes and orientations in anisotropic tellurium background. Using the numerical plane wave expansion method, we engineer the absolute photonic band gap in modified lattices, achieved by addition of circular, elliptical, rectangular, square and hexagonal air hole or ring into the center of each lattice unit cell. We discuss the maximization of absolute photonic band gap width as a function of main and additional air hole or ring parameters with different shapes and orientation.     

Orientation and alignment during materials processing under high magnetic fields

The characteristics of lattice structures can make crystal possess distinct anisotropic features, such as the varying magnetism in different crystal orientations and different directions. The anisotropic magnetism can also cause the free energy to vary in different orientations of crystal in a magnetic field(magnetic anisotropy energy). Magneto-anisotropy can make the crystal rotate by the magnetic force moment on the crystal with the easy axis towards the direction of the magnetic field, and can also promote the preferential growth along a certain crystal direction at the lowest energy state.By solidification, vapor-deposition, heat treatment, slip casting and electrodeposition under magnetic field, the crystal structure with high grain orientation is obtained in a variety of binary eutectics, peritectic alloys, multicomponent alloys and high temperature superconducting materials. This makes it possible to fabricate texture-functional material by using high magnetic field and magneto-crystalline anisotropy of crystal. The purpose of this article is to review some recent progress of the orientation and alignment in material processing under a high magnetic field.     

Simulation of thickness dependence in ferroelectric thin films

The thickness dependence of coercive field (E_C) and remanent polarization (P_r) in ferroelectric thin films has been numerically simulated using a two-dimensional four-state Potts model. In this model, each of the dipoles in the film is assigned to one of the four states corresponding to the four different mutually perpendicular orientations. Neighboring dipoles with the same orientation are then grouped together to form a domain. Four different kinds of domains exist. In the presence of the surface layer near the electrode/film interface, the thickness dependence of both coercive field and remanent polarization are simulated.     

Synthesis,structure, and electrochemical properties of epitaxial perovskite La0.8Sr0.2CoO3 film on YSZ substrate

Epitaxial films of the perovskite, La_0.8Sr_0.2CoO₃ (LSC), for SOFCs cathode were deposited on yttria-stabilized zirconia (YSZ) single crystals by pulsed laser deposition method. The films were characterized by thin-film X-ray diffraction measurement, atomic force microscopy (AFM), transmission electron microscope (TEM), and ac impedance spectroscopy. The film orientations depend on the substrate planes. The LSC films on the YSZ (100) and (111) substrates showed the (110) orientation with different twin structures, while those on the YSZ (110) had (100) and (112) orientations. Surface morphology of the films also depends on the substrate orientations. These films showed different electrode properties depending on the orientations. The relationships between the properties, the film orientations, surface morphology, and lattice misfit are discussed.     

Effect of surface lay in the surface roughness evaluation using machine vision

This work explores the influence of orientation of surface lay pattern of the machined components, while quantifying the surface roughness using machine vision approach. The surface images are captured from milled low carbon steel specimens with different roughness values using a vision system with coaxial lighting arrangement at different angular orientations of the work pieces (0°, 30°, 45°, 60°, 90°, 120°, 135°, 150°, and 180°). The captured images are subjected to preprocessing in order to retain the frequency components that attribute to roughness using a Gaussian filter by adapting the filtering procedures specified in ISO 4288. Numerous image based parameters such as gray level average (G_a), gray level co-occurrence matrix based image quantification parameters namely contrast, correlation, energy or uniformity, maximum probability and differential box courting based fractal dimension are computed from the surface images captured at different angular positions of the work piece. The computed vision based parameters are compared and correlated with the roughness average (R_a) obtained using a stylus instrument and the results are analyzed. The results clearly indicated that it is important to consider the orientation of the work piece when the machine vision approach is used to quantify the surface texture parameters.     

Spatially resolved twin domain distribution and lattice parameter variations in the near-surface region of SrTiO<Subscript>3</Subscript> single crystals

We investigated the twin domain distribution and lattice parameter variations associated with the displacive phase transition in SrTiO₃ by means of X-ray diffraction with high spatial resolution. By using 4.5-keV photons, the probed region is the first micrometer near the surface. We find a very inhomogeneous domain distribution, showing both regions with large monodomains and highly twinned regions, as well as large needle domains. Also, the lattice parameters in these different regions vary substantially.     

Remanenz und Ummagnetisierungsbeginn in Nickeleinkristallen

The hysteresis, especially the remanence, and the magnetostriction of nickel single crystal rods of 〈110〉, 〈111〉, 〈100〉 and medium orientation are measured at room temperature in a magnetic joke and their dependence on plastic deformation is investigated. In undeformed crystals the nucleation of reverse domains needs a negativeH-field several times the coercivity, thus causing an “overshooting” of the hysteresis. Very small plastic deformations initiate the formation of the reverse domains and destroy the overshooting. Similar to polycrystals, the remanence of the single crystals — except those with 〈100〉 as axis — falls steeply at the beginning of plastic deformation to about 40% of its initial value. The magnetization reversal and the role of nucleation processes are discussed for the different orientations.     

Morphological instabilities of a thin film on a Penrose lattice: A Monte Carlo study

We computed by a Monte Carlo method derived from the solid on solid model, the thermal relaxation of a polycrystalline thin film deposited on a Penrose lattice. The thin film was modeled by a 2-dimensional array of elementary domains, which have each a given height. During the Monte Carlo process, the height of each of these elementary domains is allowed to change as well as their crystallographic orientation. After equilibrium is reached at a given numerical temperature, all elementary domains have changed their orientation into the same one and small islands appear, preferentially on the domains of the Penrose lattice located in the center of heptagons. This method is a numerical approach to study the influence of the substrate and its defects on the islanding process of polycrystalline films.     

Differential-aperture X-ray structural microscopy: a submicron-resolution three-dimensional probe of local microstructure and strain

A recently developed differential-aperture X-ray microscopy (DAXM) technique provides local structure and crystallographic orientation with submicron spatial resolution in three-dimensions; it further provides angular precision of approximately 0.01 degrees and local elastic strain with an accuracy of approximately 1.0 x 10(-4) using microbeams from high brilliance third generation synchrotron X-ray sources. DAXM is a powerful tool for inter- and intra-granular studies of lattice distortions and lattice rotations on mesoscopic length scales of tenths of microns to hundreds of microns that are largely above the range of traditional electron microscopy probes. Nondestructive, point-to-point, spatially resolved measurements of local lattice orientations in bulk materials provide direct information on geometrically necessary dislocation density distributions through measurements of the lattice curvature in plastically deformed materials. This paper reviews the DAXM measurement technique and discusses recent demonstrations of DAXM capabilities for measurements of microtexture, local elastic strain, and plastic deformation microstructure.     

Growth and ordering of Ni(II) diphenylporphyrin monolayers on Ag(111) and Ag/Si(111) studied by STM and LEED

The room temperature self-assembly and ordering of (5,15-diphenylporphyrinato)nickel(II) (NiDPP) on the Ag(111) and Ag/Si(111)-(√3 × √3)R30° surfaces have been investigated using scanning tunnelling microscopy and low-energy electron diffraction. The self-assembled structures and lattice parameters of the NiDPP monolayer are shown to be extremely dependent on the reactivity of the substrate, and probable molecular binding sites are proposed. The NiDPP overlayer on Ag(111) grows from the substrate step edges, which results in a single-domain structure. This close-packed structure has an oblique unit cell and consists of molecular rows. The molecules in adjacent rows are rotated by approximately 17° with respect to each other. In turn, the NiDPP molecules form three equivalent domains on the Ag/Si(111)-(√3 × √3)R30° surface, which follow the three-fold symmetry of the substrate. The molecules adopt one of three equivalent orientations on the surface, acting as nucleation sites for these domains, due to the stronger molecule-substrate interaction compared to the case of the Ag(111). The results are explained in terms of the substrate reactivity and the lattice mismatch between the substrate and the molecular overlayer.     

The effect of solvent upon molecularly thin rotaxane film formation

We have investigated variations in molecularly thin rotaxane films deposited by solvent evaporation, using atomic force microscopy (AFM). Small changes in rotaxane structure result in significant differences in film morphology. The addition of exo-pyridyl moietes to the rotaxane macrocycle results in uniform domains having orientations corresponding to the underlying substrate lattice, while a larger, less symmetric molecule results in a greater lattice mismatch and smaller domain sizes. We have measured differences in film heights both as a function of the solvent of deposition and as a function of surface coverage of rotaxanes. Based on these observations we describe how the use of solvents with higher hydrogen-bond basicity results in films which are more likely to favour sub-molecular motion.     

Spatial confinement of ferromagnetic resonances in honeycomb antidot lattices

We report on a theoretical investigation of the magnetic static and dynamic properties of a thin ferromagnetic film with honeycomb lattice of circular antidots using micromagnetic simulations and analytical calculations. The theoretical model is based on the Landau–Lifshitz equations and directly accounts for the effects of the magnetic state nonuniformity. A direct calculation of local dynamic susceptibility tensor yields that the resonance spectra consist of four different quasi-uniform modes of the magnetization precession related to the confinement of magnetic domains by the hole mesh. Three of four resonant modes follow a two-fold variation with respect to the in-plane orientation of the applied magnetic field. The easy axes of these modes are mutually rotated by 60° and combine to yield the apparent six-fold configurational anisotropy. Additionally, a mode with intrinsic six-fold symmetry behavior exists, as well. Micromagnetic calculations of the local dynamic susceptibility tensor allow identifying the magnetic unit cell areas/domains responsible for each resonance mode.     

Percolation Clusters as Generators for Orientation Ordering

Needles at different orientations are placed in an i.i.d. manner at points of a Poisson point process on \(\mathbb {R}^2\) of density \(\lambda \). Needles at the same direction have the same length, while needles at different directions maybe of different lengths. We study the geometry of a finite cluster when needles have only two possible orientations and when needles have only three possible orientations. In both these cases the asymptotic shape of the finite cluster as \(\lambda \rightarrow \infty \) is shown to consists of needles only in two directions. In the two orientations case the shape does not depend on the orientation but just on the i.i.d. structure of the orientations, while in the three orientations case the shape depend on all the parameters, i.e. the i.i.d. structure of the orientations, the lengths and the orientations of the needles. In both these cases we obtain a totally ordered phase where all except one needle are bunched together, with the exceptional needle binding them together.     

Imaging nanoscale electronic inhomogeneity in the lightly doped Mott insulator Ca(2-x)NaxCuO2Cl2

The spatial variation of electronic states was imaged in the lightly doped Mott insulator Ca(2-x)NaxCuO2Cl2 using scanning tunneling microscopy or spectroscopy. We observed nanoscale domains with a high local density of states within an insulating background. The observed domains have a characteristic length scale of 2 nm (approximately 4-5a, a: lattice constant) with preferred orientations along the tetragonal [100] direction. We argue that such spatially inhomogeneous electronic states are inherent to slightly doped Mott insulators and play an important role for the insulator to metal transition.     

Effects of Field Orientation on the Driven Lattice Gas

Steady states of the driven lattice gas (DLG) on triangular, hexagonal and square lattices with the field at several fixed orientations to the principal lattice vectors were studied by Monte Carlo simulation. In most cases a strong field suppressed change to a low-temperature ordered phase. On each lattice, one field orientation that caused nonequilibrium ordering was identified. On triangular and hexagonal lattices, dependence of energy and anisotropy on field strength was studied at those orientations. Anisotropic ordering along the field developed at intermediate temperatures under weak fields. Partial ordering along the field persisted to low temperature under strong fields.     

On crystal shear,lattice rotation and constraint stress in (1 1 0) channel die compression: rate-independent and viscoplastic analyses and predictions compared

Rate-independent crystal plasticity theory and a classic viscoplastic power-law are investigated, contrasted and compared for finite deformation analysis of fcc crystals in channel die compression, including full consideration of lattice straining. Both experiment-based anisotropic and isotropic (Taylor) hardenings are evaluated in rate-independent theory; and an unlimited range of power-law exponent n is considered in viscoplasticity. The focus is on predictions of lateral constraint stress, lattice rotation and crystal shear, and their comparison with experiment. General elastic-plastic equations (for both theories) are given for the range of unstable lattice orientations in (1?1?0) compression (‘range I’) and evaluated before and after a finite rotation of the lattice about the load axis. Equations also are given and evaluated for the ‘Brass’ orientation. It is shown that the theories can be in close agreement at the onset of finite deformation in range I, but that viscoplasticity gives results (for any n) after finite rotation that are in sharp contrast to rate-independent theory. The latter’s predictions for crystal shear and lattice rotation are in good to very good agreement with finite deformation experiments on aluminium and copper. The inclusion of lattice elasticity is found to have a negligible effect in range I. In contrast, for finite deformation in the stable Brass orientation, elastic-viscoplastic theory can be made to agree very closely with rate-independent theory and with experiment.