Orientation Of Crystallographic Axes Research Articles

Determination of the internal structural heterogeneity of natural diamond: Methodological aspects of using confocal Raman spectroscopy with polarization analysis

Aim. To describe a technique for studying the internal structural heterogeneity of natural diamond crystals, based on confocal Raman spectroscopy with polarization analysis, including angular resolution, at high spectral (0.5–0.6 cm–1) and spatial (1 μm) resolution. Results. The parameters of the F2g vibrational mode in diamond (position, width, intensity, shape, including the Gaussian and Lorentzian contributions to the broadening) are determined by the superposition influence of a number of factors, including the type and content of structural stresses, deformations, various types of defects, as well as orientation of crystallographic axes of the crystal relative to the directions of incident and scattered rays and the directions of their electric polarization vectors. The proposed analytical technique includes: (1) analysis of the crystallographic orientation of the sample in the spectrometer coordinate system and possible misorientations of its fragments with an error of ≈8–15°; (2) visualization of the distribution of structural stresses, deformations, twins, impurity defects and their associates based on sample surface mapping by spectral parameters of the F2g vibration mode; (3) obtaining statistical characteristics of the internal structural heterogeneity of the samples based on diagrams of spectral parameter frequency with a statistically significant number (≈103): unimodality (uni-, bimodal distributions) and distribution dispersion (from ≈0.1 to ≈0.6 cm–1 for width and from ≈0.04 to ≈0.6 cm–1 for line position). The procedure was tested using two synthetic CVD diamond single crystals doped with nitrogen and boron. The possibility of typification of natural samples by statistical characteristics of internal heterogeneity is considered using the example of samples from kimberlite pipes of Yakutia and placers of the Western Cis-Urals. Conclusions. A method for determining the internal structural heterogeneity of natural diamond crystals based on confocal Raman spectroscopy with polarization analysis is proposed. The possibility of using statistical characteristics of heterogeneity as a typomorphic feature of the original diamond source is demonstrated. The proposed diagrams are promising for sample comparison and typification.

Polarization Distortions Caused by Strong Thermal Stress-Induced Birefringence in Uniaxial Crystals and Their Elimination Using Dedicated Orientations

The polarization distortions of radiation, which arise when it passes through optical elements cut from uniaxial crystals in the regime of strong thermally induced birefringence, are studied. The presented theoretical description of the effect convincingly corresponds to the results of the experiment carried out for verification purposes. The problem of the existence of critical orientations of crystallographic axes in an optical element, at which polarization distortions do not occur, is studied for uniaxial crystals of all symmetry groups. Criteria for the existence of critical orientations are defined; approaches to finding these orientations are presented.

Experimental fracture sealing in reservoir sandstones and its relation to rock texture

Faults and fractures are important fluid pathways in subsurface energy reservoirs. Especially in geothermal energy production, hydrocarbon production, and energy storage in the subsurface, fractures can enhance reservoir quality and production or storage potential. However, mineral precipitations often reduce available fracture apertures, and thus fracture porosity and permeability. Hydrothermal experimental setups, natural samples, and numerical simulations have been studied to great extent. In fractured sandstones, the main focus has been on only some controlling factors, e.g. fracture opening rate and the orientation of crystallographic axes in substrates. Furthermore, substrates have mostly been fairly homogeneous or sediment textures have not been explicitly considered. Here, fracture sealing experiments are performed on a homogeneous, massive marine sandstone and heterogeneous, laminated fluvial sandstone. Hydrothermal flow-through experiments are performed at 421 ± 1 °C and 30.5 ± 0.5 MPa for 72 h to compare resulting precipitated quartz cement textures on fracture surfaces on natural sandstones. Results indicate a strong impact of grain size variations associated with lamination on observed syntaxial quartz crystal dimensions on fracture surfaces. In layers of finer grain sizes, smaller cement overgrowths develop, as opposed to coarser grained laminae in the same sample. In homogeneous sandstones, the overgrowths appear more uniform, apart from the differences induced by varying c-axis orientations. Some open fracture porosity may be preserved in areas of finer grained laminae, as opposed to coarser grained laminae. Additionally, the potential to stabilize fractures by cement growth spanning the aperture could preserve fracture porosity and permeability in generally unfavorable stress regimes. Furthermore, the relative abundance of suitable syntaxial precipitation sites and additional mineral dissolution as a function of varying detrital compositions appears to influence the mineralogy of the precipitate. If samples are rich in quartz grains, the largest quantity of precipitate will be quartz, due to the large supersaturation in the input solution. If samples contain less quartz by volume, the same solution additionally precipitates phyllosilicates, implying that some structural-diagenetic mineral phases are a function of heterogeneity of the host rock, rather than a result of variable external fluid compositions entering the formation. The phyllosilicates additionally act as nucleation discontinuities, reducing the size of surfaces available for syntaxial precipitation of quartz. Results may be applicable in fractured sandstone lithologies, which have been in the focus of energy storage and production.

Thermal lens astigmatism in glass and in cubic crystals with [001] orientation.

The thermal lens was investigated in CaF2 and Tb3Ga5O12 cubic crystals with [001] crystallographic axes orientation and in magneto-optical glass MOG103 by the method of phase-shifting interferometry. It was demonstrated experimentally that the thermal lens has astigmatism determined by the incident radiation polarization state and by the optical anisotropy parameter ξ. A method of ξ determination by measuring thermal lens astigmatism in cubic crystals with [001] orientation was proposed and verified. It was shown that thermally induced depolarization and the amplitude of phase astigmatism depend on the position of the crystal with [001] orientation in antiphase.

Thermal Lens Astigmatism Induced by the Photoelastic Effect in m3m, 432, and 43m Symmetry Cubic Crystals

The expressions for the thermal lens of linearly polarized radiation arising in m3m, 432 and $\bar {4}3\text{m}$ cubic crystals with arbitrary crystallographic axes orientation in the presence of circular birefringence $\delta _{\mathbf {c}}$ are analyzed. It is shown that the thermal lens may have astigmatism the magnitude of which is proportional to the power of heat generation. The Euler angles determining the crystallographic axes orientation [P] are found and the conditions for the material constant – optical anisotropy parameter $\xi $ – under which the thermal lens astigmatism in active and magneto-active optical elements can be eliminated, are formulated. It is demonstrated that the orientation [P] depends only on optical anisotropy parameter $\xi $ of the crystal and on circular birefringence $\delta _{\mathbf {c}}$ .

Band-edge field enhanced nonlinear cross-polarized wave generation in photonic band-gap structure.

We report on the enhancement of nonlinear cross-polarized wave (XPW) generation in a one-dimensional photonic band-gap structure, which is composed of two periodic arrangements of barium-fluoride and silicon-dioxide through numerical simulations. By detuning the pump-field wavelength to the band-edge position of the photonic band-gap spectrum, the electric field at this wavelength would be resonant and then the field enhancement mechanism arises immediately. Under band-edge field enhancement condition, we found that the conversion efficiencies of XPW generation was implicitly enhanced even without phase-matched condition from the exact angle of crystallographic axis orientation.

Analysis of molecular orientation in polymeric spherulite using polarized micro attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopic imaging

Micro ATR-FTIR spectroscopic imaging enables the visualization of two-dimensional chemical distribution at a higher spatial resolution than macro-transmission FTIR imaging approach. In this study, micro ATR-FTIR imaging was applied for analysis of a specific morphology in a spherulite of poly(3-hydroxybutyrate) (PHB). The PHB spherulites crystallized at an isothermal condition, showed the fine band structure due to the twisting lamellar crystals during the spherulite growth under the polarized optical microscope (POM). In addition, the band structure observed in the PHB spherulite was the double band pattern in which the higher and lower birefringence banded areas alternatively appear due to the three-dimensional orientation of crystallographic axes and the biaxial refractive index ellipsoid of PHB crystalline structure. Micro ATR-FTIR spectroscopic imaging was employed for detecting the double band structure in the PHB spherulite. However, the obtained spectral images did not indicate any band structures.To detect the difference of molecular orientation among the double band structures, the micro ATR-FTIR imaging was performed with a linear polarizer at four different angles.The mean values of absorbance in each measured area changed depending on the polarizer angle. The in-plane molecular orientation to the tangential direction of spherulite, caused by the dependence of the average absorbance on the polarizer angles, was determined by the position of measured area in the spherulite and the linear dicroism of each of the spectral band used. To visualize the small difference of molecular orientation in the double band structure, micro ATR-FTIR images of the dichroic differences at three spectral bands were calculated from two different sets of polarizer angles. The micro ATR-FTIR images representing the dichroic differences displayed their corresponding distributions among three spectral bands. The complementary distributions of the dichroic difference were caused by the crystallographic orientation of b- and c-axes and were successfully visualized to reveal the pattern with the features less than 10 μm in size. The results achieved in this study were due to two advantages of the polarized micro ATR-FTIR imaging: the high spatial resolution of micro ATR-FTIR imaging technique, and the high sensitivity of polarization measurements. Thus, this work demonstrates the power of this spectroscopic approach for such analytical investigation.

Characterization of terbium containing cubic zirconia crystal for high power laser applications

A magneto-active terbium containing cubic zirconia crystal is an attractive material for creating Faraday isolators thanks to a high value of its Verdet constant and low absorption coefficient. The optical anisotropy parameter of this crystal which shows the distribution of orientations of the axes of thermally induced birefringence in a thermally loaded optical element has negative value. It means that there exists a dedicated orientation of crystallographic axes, at which the axes of thermally induced birefringence are arranged in the one direction and thermally induced depolarization may be reduced substantially. For assessing potential of this crystal for high-power applications we have investigated its temperature dependence of the Verdet constant that proved to correspond to the paramagnetic behavior. Thermo-optical characteristics are also of principal importance when operating with high-power laser radiation. We present results of measurements of thermo-optical characteristics Q and P which determines values of polarization and phase distortions of passing laser radiation. Measured values can be used to determine the characteristics of Faraday isolators based terbium containing cubic zirconia crystals in various implementations of their optical schemes for various parameters of laser radiation.

Spectral, magneto-optical and thermo-optical properties of terbium containing cubic zirconia crystal

This letter presents the investigation of magneto-active media based on a cubic zirconia crystal. We studied spectral, magneto-optical and thermo-optical characteristics of a terbium containing cubic zirconia (TCZ) crystal aiming to estimate its applicability in magneto-optic applications. This crystal has significant advantages over the popular TGG crystal. The value of its Verdet constant for the radiation at the wavelength of 1075 nm is 31% higher than that of a TGG crystal. The value of the absorption coefficient is rather small and typical for commercially available TGG crystals. Its transmission spectrum is typical for terbium containing magneto-active media. The dispersion dependence of the Verdet constant had been measured for visible and near-IR ranges and presented in this paper. The optical anisotropy parameter which shows the distribution of orientations of the axes of thermally induced birefringence in a thermally loaded optical element had also been determined. Unlike a TGG crystal, the optical anisotropy parameter of a TCZ crystal is negative, which means that there exists a dedicated orientation of crystallographic axes, at which the axes of thermally induced birefringence are arranged in one direction and thermally induced depolarization may be reduced substantially. Such a combination of characteristics makes the TCZ crystal a very promising material for magneto-optical applications, for example, for creating Faraday isolators, including those with a high maximum permissible operating power.

Features of Thermally Induced Depolarization in Magneto-Active Media With Negative Optical Anisotropy Parameter

The dependence of thermally induced depolarization on crystallographic axis orientation in crystal materials with negative optical anisotropy parameter in the presence of Faraday rotation has been analyzed. The orientation at which thermally induced depolarization is minimal has been found. The contributions to thermally induced depolarization of linear birefringence caused by photoelastic effect, of the temperature dependence of Verdet constant, and of the temperature dependence of optical anisotropy parameter are assessed. Three magneto-optical materials with negative optical anisotropy parameter have been compared with a currently widely used TGG crystal from the viewpoint of their prospective application in Faraday devices for powerful laser radiation. It has been demonstrated that these magneto-optical materials are undoubtedly superior to a TGG crystal.

The dependence of optical anisotropy parameter on dopant concentration in Yb:CaF2 and Tb:CaF2 crystals

Optical anisotropy parameters of Yb3+:CaF2 with different concentrations of Yb3+ ions (2.6, 3, 4.2 at.% Yb3+) and 10 at.% Tb3+:CaF2 crystals were determined from measurements of thermally induced depolarization. It was shown that the optical anisotropy parameter depends on dopant, if its concentration is sufficiently high. The crystallographic axes orientation at which there is no thermally induced depolarization was found for each studied crystal.

Highly Ordered Organic Ferroelectric DIPAB-Patterned Thin Films.

Ferroelectric molecular compounds present great advantages for application in electronics because they combine high polarization values, comparable to those of inorganic materials, with the flexibility and low-cost properties of organic ones. However, some limitations to their applicability are related to the high crystallinity required to deploy ferroelectricity. In this article, highly ordered ferroelectric patterned thin films of diisopropylammonium bromide have been successfully fabricated by a lithographically controlled wetting technique. Confinement favors the self-organization of ferroelectric crystals, avoiding the formation of polymorphs and promoting the long-range orientation of crystallographic axes. Patterned structures present high stability, and the polarization can be switched to be arranged in stable domain pattern for application in devices.

Quantum size effect in single-crystalline bismuth nanorods

In a metal sample, where at least one of the dimensions is comparable with the de Broglie wavelength of conduction electrons, the quantum size effects (QSE) should be observed. QSEs manifest themselves as non-monotonic dependencies of various material properties as function of relevant dimension. QSE should be particularly noticeable in materials with charge carrier(s) effective mass less than the free electron mass. Bismuth is one of the most suitable semi-metal to observe QSE due to small effective masses and small the Fermi energy. However, bismuth has a high anisotropic energy spectrum. Hence to observe QSE which can be interpreted with reasonable accuracy, it is mandatory to fabricate single-crystal nanostructure with known orientation of crystallographic axes. In this paper several short bismuth nanowires (nanorods) were investigated, and oscillating dependence of electric resistance on effective cross section was found. Theoretical calculations provide a reasonable agreement with experiment. The quantum-size phenomena are important for operation of a wide spectrum of nanolelectronic devices.

Temperature dependence of optical anisotropy parameter of CaF2, BaF2 and SrF2 materials

Thermally induced depolarization in undoped CaF2, BaF2 and SrF2 crystals was measured. The obtained results were used to determine temperature dependence of the optical anisotropy parameter ξ of these materials in the 80–300 K range. Temperature dependence of the orientation of crystallographic axes corresponding to the “zero depolarization” orientation was found. It was revealed that thermally induced depolarization in the studied materials cooled to 80 K reduces by more than 100 times, with changes in the parameter ξ being 5.8%, 6.4% and 28%, respectively.

Non-stationary response of sapphire rod on longitudinal impact. Theory and experiment

The response of a finite-length elastic sapphire rod to low-velocity longitudinal impact is investigated theoretically and experimentally. Deformation and wave propagation processes in a sapphire rod are considered. Several theoretical approaches, based on one-dimensional and three-dimensional models, are considered to analyze of rod response. An analytical-numerical solution of the problem is offered. The orientation of crystallographic axes on the velocity of propagation of strain waves in sapphire rods is investigated. Experimental data are obtained using dynamic broadband strain gauge measurements. Theoretical and experimental results are compared, and they are found to be in good agreement.

The Influence of Azimuth Orientation of Crystallographic Axes on Thermoelastic State of a Gte Blade with a Vortex Cooling System

The paper addresses the temperature and thermoelastic states of a single-crystal blade with a complex vortex cooling system and passages for cooling air outflow. The problem of determination of stress-strain state of the blade at hand under the action of temperature fields and centrifugal forces is solved by the finite element method. The authors study the influence of azimuth orientation of crystallographic axes on the distribution and magnitude of thermoelastic stresses in the blade volume.

Germanium-on-Silicon Waveguide Engineering for Third Harmonic Generation in the Mid-Infrared

In this paper, we propose the rigorous and sophisticated engineering of germanium-on-silicon waveguides for the efficient wavelength conversion from 10.60 to 3.53 μm and from 6 to 2 μm by means of third harmonic generation. In our investigation, the influence of waveguide fabrication tolerances, sidewall tilting angles, crystallographic axis orientation, laser wavelength drifts, and chromatic dispersion on the phase matching between the pump and harmonic optical modes, has been taken into account. Finally, conversion efficiencies as high as −35.68 and −23.46 dB have been achieved theoretically in optimized straight waveguides and resonant microcavities, respectively, with a pump wavelength of 10.60 μm.

CaF2, BaF2 and SrF2 crystals’ optical anisotropy parameters

Using the original method, based on measurements of thermally induced depolarization, the optical anisotropy parameters of CaF2, BaF2 and SrF2 cubic crystals were measured and compared with what is known from the literature. Euler angles of crystallographic axis orientation [C], in which the thermally induced depolarization is minimal, were determined using experimental results for studied fluorides.

Evidence of melting, melt percolation and deformation in a supra-subduction zone (Marum ophiolite complex, Papua New Guinea)

New geochemical and microstructural data are presented for a suite of ultramafic rocks from the Marum ophiolite in Papua New Guinea. Our results describe a piece of most depleted mantle made essentially of dunite and harzburgite showing compositions of supra-subduction zone peridotite. Strong olivine crystallographic preferred orientations (CPOs) in dunite and harzburgite inferred the activation of both (001)[100] and (010)[100] slip systems, which are activated at high-temperature and low-stress conditions. Clinopyroxene and orthopyroxene CPOs inferred the activation of (100)[001] and (010)[001] slip systems, which are common for pyroxenes deformed at high temperature. This plastic deformation is interpreted to have developed during the formation of the Marum ophiolite, prior to melt percolation. The orientation of the foliation and olivine [100] slip directions sub-parallel to the subduction zone indicates that mantle flow was parallel to the trench pointing a fast polarisation direction parallel to the arc. This provides new evidence that fast polarisation direction parallel to the arc could be caused by anisotropic peridotite and not by olivine [001] slip. After its formation, Marum ophiolite has been fertilised by diffuse crystallisation of a low proportion of clinopyroxene (1–2 %) (P1) and formation of cm-scale ol-clinopyroxenite and ol-websterite veins cross-cutting the foliation (P2). This percolating melt shows silica-rich magnesian affinities (boninite-like) related to supra-subduction zone in a young fore-arc environment. The peridotite has also been percolated by a melt with more tholeiite affinities precipitating plagioclase-rich wehrlite and thin gabbroic veins (P3); these are interpreted to form after the boninitic event. The small proportion of newly crystallised pyroxene in the dunite shows similar orientation of crystallographic axes to the host dunite ( ol parallel to cpx–opx). In contrast, the pyroxenes in ol-clinopyroxenite, ol-websterite and the thin gabbroic veins in the wehrlite, record their own orientation with axes at 45°–60° to olivine axes. Our results indicate that for low melt proportion the crystallisation is governed by epitaxial growth, and when the proportion of melt is higher the newly formed minerals record syn-kinematic crystallisation. This switch of crystallographic axes orientation of newly formed minerals indicates a reorientation of the constraints during the boninitic and tholeiitic melts event probably due to a variation of lateral mantle flow within the fore-arc area. The variation of the crystallographic axes orientation could be an indicator for the development of a young fore-arc mantle in supra-subduction zone.

Probing Symmetry Properties of Few-Layer MoS2 and h-BN by Optical Second-Harmonic Generation

We have measured optical second-harmonic generation (SHG) from atomically thin samples of MoS2 and h-BN with one to five layers. We observe strong SHG from materials with odd layer thickness, for which a noncentrosymmetric structure is expected, while the centrosymmetric materials with even layer thickness do not yield appreciable SHG. SHG for materials with odd layer thickness was measured as a function of crystal orientation. This dependence reveals the rotational symmetry of the lattice and is shown to provide a purely optical method of determining the orientation of crystallographic axes. We report values for the nonlinearity of monolayers and odd-layers of MoS2 and h-BN and compare the variation as a function of layer thickness with a model that accounts for wave propagation effects.