Small-angle Reflection Research Articles

Small grazing angle reflection and the sound siphon effect over a low velocity layer of sediments.

The low-order normal modes with small grazing angles (SGA) often control long-range sound field characteristics in shallow water. The SGA reflection loss from a half-space low-velocity bottom (LVB) is independent of the sound attenuation, except around the angle of complete transmission; the SGA bottom reflection loss (BRL) from a seafloor with a top low-velocity layer is very insensitive to the LVB attenuation also, except around a few selected frequencies. Thus, the "seafloor velocity-attenuation coupling" problem will be more fatal for LVB geo-acoustic inversions. The dispersion equation of the normal modes in the LVB layer is coincidentally the same as the singularity expression of the SGA reflection coefficient in the water column, resulting in a sound siphon effect that causes the abnormally high SGA BRL and transmission loss in the water at the siphon frequencies. The siphon effect is very sensitive to seafloor acoustic parameters, might offer a physical base for geo-acoustic inversion, and show a dim light in a "gray area" for inverting the LVB sound attenuation at low to mid frequencies. As an example, the acoustic siphon effect and related seafloor geophysical parameters forming it in the Yellow Sea are reported in this paper.

Correlation between biological activity and physicochemical properties of sodium dodecylbenzenesulfonate in aqueous solutions

The purpose of this study was to establish a correlation between the effect of the pollutant content on the dimensional and physicochemical characteristics of the investigated solutions and its effect on aquatic organisms. To this end, the surface tension, electrical conductivity, pH, and redox potential of aqueous solutions of sodium dodecylbenzenesulfonate were measured in a wide concentration range (10–710–2 М). The change in the size and number of optical inhomogeneities was investigated using the small-angle reflection method in the micron range. In addition, the behavior of aquatic biological objects (Daphnia Magna) was studied in the investigated solutions. It was shown that the investigated concentration dependences (including the behavior of biological objects) are non-linear: they have either a stepped character or clearly expressed extremes and are well correlated with each other. A comfortable concentration range of sodium dodecylbenzenesulfonate for daphnia (all daphnia are active within 58 hours of the experiment) was established (0.018–0.037 mM). The correlation and nature of the concentration dependences indicate that at critical concentrations, structural rearrangements occur in sodium dodecylbenzenesulfonate solutions, not only the formation of micelles and pre-micelles, but also structural rearrangements of the solvent (water) itself. Thus, it has been experimentally shown that the change in the structure of water during interaction with pollutants can significantly affect both the physicochemical properties of aqueous solutions and the behavior of aquatic biological objects.

A Novel Transient Electric Field Measurement for Low Kerr Constant Liquid Dielectrics Based on Concave Spherical Mirror Conjugate Structure

This article proposes a Kerr effect electric field measurement method based on a concave spherical mirror conjugate structure (CSM CS) for a transient electric field in low Kerr constant liquid dielectrics. The accuracy of transient electric field measurement can be greatly improved in a limited space by multiple small-angle reflections. To verify the effect of the proposed structure, the electric field distribution is measured in propylene carbonate (PC) with a high Kerr constant at a switching overvoltage. The measurement results show that the electric field error of a PC under an extremely low electric field is only about 2%. The novel structure improves the electric field measurement accuracy of a liquid with a high Kerr constant. Then, the whole device is applied to the transformer oil, and the accuracy of the measured electric field is also greatly improved. At the same electrode size, the sensitivity of measuring the electric field with the proposed structure is three times that without it. The analysis results show that the introduction of the proposed structure has little effect on the electric field measurement. The proposal and application of the proposed CSM CS further expand the electric field measurement range based on the Kerr effect and improves the electric field measurement accuracy.

Disordering of β-Ga2O3 upon irradiation with Si+ ions: Effect of surface orientation

Development of gallium oxide-based devices is one of the most promising areas of modern electronic technology. The method of ion implantation is widely used in electronic engineering; however, it has not yet been sufficiently studied for gallium oxide from a physical point of view. One of the interesting questions is the possible impact of surface orientation of β-Ga2O3 single crystals on the structural damage upon ion irradiation. In this work, the effect of Si+ ion irradiation on the structural properties of β-Ga2O3 crystals with (−201) and (010) surface orientations has been investigated by X-ray diffraction and small-angle reflection electronography. It is established that mechanical stresses in the irradiated layer depend on surface orientation: in the case of (−201) orientation, the stress in lateral to the surface direction is compressive, while it is tensile for the (010) orientation. At one and the same irradiation dose, the degree of damage for (010) orientation is shown to be stronger than that for (−201). Possible explanation is suggested for the surface orientation effect.

Design and Performance of a Full Functional Electrochemical Cell for Lab Scale in-Situ GI-XRD Instruments

In-situ XRD may support electrochemical measurements by delivering analytical information about electrochemical processes. Since structural changes at the electrode/electrolyte interface are of specific interest, measurements are done usually in small angle reflection mode geometry. The surface sensitive grazing incidence – XRD (GI-XRD) in-situ technique allows the detection of short-lived electrode reaction products or products sensitive to ambient atmosphere exposure. This method finds applications for quite a number of investigations of electrochemical processes including corrosion, film growth and deposition, reconstruction of superficial regions, ion insertion battery materials, etc. The common cell designs for lab scale XRD equipment use thin electrolyte layers to avoid unacceptable beam intensity loss through water. The use of synchrotron radiation would reduce this shortcoming to some extent but is much less accessible.In 1986, Fleischmann et al. presented an in-situ XRD thin layer cell in reflection as well as in transmission mode, where a X-ray transparent Mylar foil was used as window material [1]. However, this geometry restricts the positioning of counter and reference electrodes and therefore has unfavorable current density distribution, has very small electrolyte volume, is vulnerable to side reactions with gas evolution and does not allow high flow rates for the solution. Thus, the general applicability is limited.In our proposed in-situ cell design for GI-XRD, the electrochemical cell is fully functional, avoiding all of the above mentioned drawbacks [2]. The solution of this issue is the "backside-illumination" (or "inverse" illumination) of a thin film working electrode applied on a thin polymer foil as a support by the X-ray beam at a small incident angle. On the opposite side a conventional electrochemical cell with reference electrode and counter electrode and sufficient solution volume can be used. The big advantage of this design is that the X-ray only has to penetrate the foil and the thin layer of electrode material resulting in high signals from the region of interest. It is used with a conventional laboratory X-ray source and does not need high intensity synchrotron radiation. With this cell design, problems with bulk solution resistance, inhomogeneous current-density distribution, insufficient bath agitation or gas evolution as side reaction are eliminated.In this contribution, details of the cell design, analysis of current density distribution within the thin current collector and the electrochemical cell, results of calibration measurements and measurements on copper as an example for a galvanic deposition/dissolution process are presented.[1] M. Fleischmann, A. Oliver, and J. Robinson, ‘In Situ X-ray diffraction studies of electrode solution interfaces’, Electrochimica Acta, vol. 31, no. 8, pp. 899–906, (1986)[2] S. Reither, W. Artner, A. Eder, S. Larisegger, M. Nelhiebel, C. Eisenmenger-Sittner, G. Fafilek, ‘On the In-Situ Grazing Incidence X-Ray Diffraction of Electrochemically Formed Thin Films’, ECS Transactions, 80 (10) 1231-1238, (2017) 10.1149/08010.1231ecst Figure 1

Quantum Theory of X-ray Radiation by Relativistic Electrons at Small-Angle Reflection from Crystals

In the framework of quantum electrodynamics the theory of a new type of X-ray radiation emitted by relativistic electrons at channeling conditions is developed beyond the dipole approximation. This radiation takes place when the electron is reflected by or crossed the crystal surface which coincides with one of the crystallographic planes. It is shown that in this case one reveals two kinds of radiation: channeling radiation by reflected particles and diffracted channeling radiation by passed particles. The radiation can be applied for investigation of the crystal surface.

Quantum size effect observed during the small-angle reflection of an electron beam incident onto a single-crystal film with allowance for the average internal lattice potential

Analytical formulas are derived and used to perform calculations. The solution to the problem of the quantum size effect arising when a moderate- or high-energy electron beam is reflected from a thin single-crystal film at a small glancing angle of incident electrons is graphically illustrated. The average internal potential of the crystal lattice of the film material is taken into account. Experimental methods for observing the aforementioned effect are proposed.

Reverse time migration of multiples: Applications and challenges

Marine seismic acquisitions record both primary and multiple wavefields. In a typical processing sequence, multiple energy is removed from the data before migration. However, valuable information might be contained in the multiple wavefield. A modification is proposed to the standard reverse time migration (RTM) algorithm to enable correct imaging between the primary wavefield and the first-order multiple wavefield. The advantages of this modification, reverse time migration of multiples (RTMM), are evaluated through three real data-processing projects and identified three key advantages. First, RTMM can recover small-angle reflections critical for shallow-water imaging that are missing in the primary wavefield. Second, RTMM has a wider illumination coverage, which significantly extends the image for an ocean-bottom node (OBN) project. Third, RTMM produces an image complementary to the primary image in a complex geologic setting, possibly assisting with interpretation. In addition, a synthetic study is presented of two types of cross-talk noise that hinder the full potential of RTMM, and corresponding practical strategies are proposed to handle them.

Lensless X-ray imaging in reflection geometry

Lensless X-ray imaging techniques such as coherent diffraction imaging1,2,3,4,5,6,7,8 and ptychography9,10,11, and Fourier transform holography12,13,14,15,16,17 can provide time-resolved, diffraction-limited images. Nearly all examples of these techniques have focused on transmission geometry, restricting the samples and reciprocal spaces that can be investigated. We report a lensless X-ray technique developed for imaging in Bragg and small-angle scattering geometries, which may also find application in transmission geometries. We demonstrate this by imaging a nanofabricated pseudorandom binary structure in small-angle reflection geometry. The technique can be used with extended objects, places no restriction on sample size, and requires no additional sample masking. The realization of X-ray lensless imaging in reflection geometry opens up the possibility of single-shot imaging of surfaces in thin films, buried interfaces in magnetic multilayers, organic photovoltaic and field-effect transistor devices, or Bragg planes in a single crystal. Many X-ray imaging techniques require transmission geometries, which place severe restrictions on the samples being imaged. Here, a reflection geometry lensless X-ray imaging method is demonstrated. This technique may allow single-shot imaging of surfaces and films such as organic photovoltaic materials and field-effect transistor devices, or Bragg planes in a single crystal.

Collapsed Octacalcium Phosphate Stabilized by Ionic Substitutions

We have explored the possibility of introducing biologically relevant ions, namely Sr2+, Mg2+, and Mn2+, into the structure of octacalcium phosphate (OCP). OCP with partial substitutions of Sr2+ and Mg2+ for Ca2+ up to 7.4 and 1.0 at%, respectively, was successfully synthesized. On the contrary, Mn2+ completely inhibits OCP crystallization, and it promotes the precipitation of brushite. The incorporation of Sr2+ and Mg2+ disturbs the shape of the crystals and reduces the stability of OCP structure. The analysis of the structural modifications occurring during heat treatment puts into evidence that the transformation of OCP into apatite involves a crystalline phase, “collapsed OCP”, resulting from loss of structural water molecules. The main characteristic features of this phase are the small angle reflection at about and 17.0 Å (2θ = 5.2°) and the reflection at 8.6 Å (2θ = 10.3°). Due to the destabilizing effect of the foreign ions, in the temperature range of 170−250 °C, Mg- and Sr-OCP contain “collapsed OCP” but no OCP, which allowed us to calculate the unit cell of this new phase characterized by a slightly reduced a-axis and a wider γ angle with respect to OCP.

Long N-acyl fatty acids on sphingolipids are responsible for miscibility with phospholipids to form liquid-ordered phase

The structure and thermotropic phase behaviour of aqueous dispersions of dipalmitoylphosphatidylcholine and glucosylceramide rich in C-24 fatty acyl residues was investigated by synchrotron X-ray diffraction methods. Binary mixtures comprised of molar ratios 2.5:100, 6.5:100, 12.6:100, 25:100, 40:100 and 50:100, glucolipid:phospholipid were examined in heating and cooling scans of 2°/min between 25 and 85 °C. Small-angle reflections indicated coexisting lamellar structures over the entire temperature range investigated. Reversible thermotropic changes were observed in one lamellar structure that is consistent with transitions between gel, ripple and fluid lamellar phases of pure phospholipid. The temperature of these transitions, however, were progressively shifted up by about 5 °C in the mixture containing the highest proportion of glucolipid and coincided with a published endothermic peak observed in this mixture. A higher-temperature endotherm was associated with molecular rearrangements on transition of the gel phase phospholipid to the fluid phase. This rearrangement was associated with the appearance of identifiable transient intermediate structures in the small-angle scattering region. The glucolipid formed stoichiometric mixtures with the phospholipid at all temperatures investigated and there was no evidence of phase separation of pure glucolipid. Analysis of the wide-angle scattering profiles during an initial heating scan of a binary mixture comprised of 40:60 glucolipid:phospholipid was consistent with a phase transition of pure phospholipid at about 43 °C coexisting with a liquid-ordered phase formed from the two lipids. This was confirmed by analysis of the small-angle scattering peaks of this mixture recorded at 25 and 65 °C which showed that a glucolipid-rich phase coexisted with almost pure bilayers of phospholipid at both temperatures. The glucolipid-rich phase consisted of 45:55 mole ratio glucolipid:phospholipid at 25 °C with pure phospholipid in gel phase and 42:58 mole ratio at 65 °C when the phospholipid was in the fluid phase. The results are discussed with reference to the role of the length of the N-acyl substituent of the sphingolipids in formation of complexes with phospholipids.

Quality evaluation of quick-frozen biological specimens by simultaneous microbeam SAXS/WAXS recordings

The quality of small-angle X-ray scattering (SAXS) patterns from quick-frozen hydrated biological specimens was correlated with the extent of ice crystal formation by simultaneously recording wide-angle X-ray scattering (WAXS) of ice, at a micrometer-order spatial resolution by using X-ray microbeams. Flight muscle fibers from a giant waterbug, Lethocerus, known to generate well defined small-angle reflection spots originating from the hexagonal lattices of myofilaments, were quick-frozen in the presence or absence of various cryoprotectants. Freezing without a cryoprotectant resulted in massive ice-crystal formation at almost all depths of the specimen, and the occurrence of reflection spots was limited to the region close to the specimen surface. Inclusion of 20% dimethyl sulfoxide or methylpentanediol ensured ideal vitreous ice formation and good diffraction qualities for up to 100 microm from the specimen surface. Glycerol and sucrose were found to be inferior at a 20% concentration, but left the reflection spots observable at depths of up to 100 microm. Thus, the microbeam SAXS/WAXS recording offers a high-spatial-resolution means of evaluating the extent of structure preservation of quick-frozen biological specimens. The technique presented here may also provide useful information in cryoelectron microscopy.

Thickness dependence of microstructures in La 0.9Sr 0.1MnO 3 thin films grown on exact-cut and miscut SrTiO 3 substrates

The thickness dependence of microstructures of La 0.9Sr 0.1MnO 3 (LSMO) thin films grown on exact-cut and miscut SrTiO 3 (STO) substrates, respectively, was investigated by high-angle X-ray diffraction (HXRD), X-ray small-angle reflection (XSAR), X-ray reciprocal space mapping and atomic force microscopy (AFM). Results show that the LSMO films are in pseudocubic structure and are highly epitaxial [0 0 1]-oriented growth on the (0 0 1) STO substrates. The crystalline quality of the LSMO film is improved with thickness. The epitaxial relationship between the LSMO films and the STO substrates is [0 0 1] LSMO∥[0 0 1] EXACT-STO, and the LSMO films have a slight mosaic structure along the q x direction for the samples grown on the exact-cut STO substrates. However, an oriented angle of about 0.24° exists between [0 0 1] LSMO and [0 0 1] MISCUT-STO, and the LSMO films have a mosaic structure along the q z direction for that grown on the miscut STO substrates. The mosaic structure of both groups of the samples tends to reduce with thickness. The diffraction intensity of the (0 0 4) peaks increases with thickness of the LSMO film. The XSAR and AFM observations show that for both groups, the interface is sharp and the surface is rather smooth. The mechanism was discussed briefly.

Small-angle AVO response of PS-waves in tilted transversely isotropic media

Field records for small source-receiver offsets often contain intensive converted PS-waves that may be caused by the influence of anisotropy on either side of the reflector. Here, we study the small-angle reflection coefficients of the split converted [Formula: see text]- and [Formula: see text]-waves ([Formula: see text] and [Formula: see text]) for a horizontal interface separating two transversely isotropic (TI) media with arbitrary orientations of the symmetry axis. The normal-incidence reflection coefficients [Formula: see text] and [Formula: see text] vanish when both half-spaces have a horizontal symmetry plane, which happens if the symmetry axis is vertical or horizontal (i.e., if the medium is VTI or HTI). For a tilted symmetry axis in either medium, however, the magnitude of the reflection coefficients can reach substantial values that exceed 0.1, even if the anisotropy strength is moderate. To study the influence exerted by the orientation of the symmetry axis and the anisotropy parameters, we develop concise weak-contrast, weak-anisotropyapproximations for the PS-wave reflection coefficients and com-pare them with exact numerical results. In particular, the analytic solutions show that the contributions made by the Thomsen parameters [Formula: see text] and [Formula: see text] and the symmetry-axis tilt [Formula: see text] to the coefficients [Formula: see text] and [Formula: see text] can be expressed through the first derivative of the P-wave phase velocity at normal incidence. If the symmetry-axis orientation and anisotropy parameters do not change across the interface, the normal-incidence reflection coefficients are insignificant, regardless of the strength of the velocity and density contrast. The AVO (amplitude variation with offset) gradients of the PS-waves are influenced primarily by the anisotropy of the incidence medium that causes shear-wave splitting and determines the partitioning of energy between the [Formula: see text] and [Formula: see text] modes. Because of their substantial amplitude, small-angle PS reflections in TI media contain valuable information for anisotropic AVO inversion of multicomponent data. Our analytic solutions provide a foundation for linear AVO-inversion algorithms and can be used to guide nonlinear inversion that is based on the exact reflection coefficients.

Effect of Eu 2CuO 4/Yttrium-stabilized Z rO 2 buffer layers on YB 2Cu 3O 7− x thin films grown on Si substrates

The microstructure and crystallinity of epitaxial YB 2Cu 3O 7− x (YBCO) thin films grown on a silicon using a buffer of Eu 2CuO 4 (ECO)/Yttrium-stabilized Z rO 2 (YSZ) were investigated by X-ray high-resolution diffraction, small angle reflection, and reciprocal space map, as well as atomic force microscopy. The results showed that YBCO films with a buffer of ECO/YSZ were well oriented in the [00L] direction perpendicular to the substrate surface. The rocking measurements for the YBCO films grown on ECO/YSZ buffered Si show a smaller value of the full widths at half maximum (∼2.07°) in comparing with that of the YBCO with a single YSZ buffer (∼4.48°). Moreover, the surface morphology of YBCO films with an ECO/YSZ buffer is significantly improved. The average size of grains on the surface was much smaller, indicating that growth of YBCO on Si with such a buffer of ECO/YSZ is highly epitaxial.

X-ray evidence for a "super"-secondary structure in silk fibers.

X-ray studies on degummed B. mori silk fibers and on hydrogels prepared under a variety of conditions reveal moderately small angle reflections. These reflections are often highly oriented and are correlated to silk II lattice reflections. A superstructure can explain these features. Silk fibroin hydrogels were monitored as they dried to form the silk II structure. The silk II wide angle and moderately small angle patterns obtained from dried hydrogels and silk fibers are identical. The "superstructure" reflections at moderately small angle (3-7 nm) were first to appear, followed by the "intersheet" spacing, and then the remainder of the silk II wide angle scattering pattern. Thus, any superstructure hypothesized for the hydrogels (and for Silk II in fibers) must be both stable in a highly hydrated environment and must convert to silk II with little large scale diffusion. A folded structure, similar to amyloids and cross-beta-sheets but with much longer beta-strand stems, is proposed for silk II in fibers.

Improved Epitaxy and Surface Morphology in YBa2Cu3Oy Thin Films Grown on Double Buffered Si Wafers

Highly epitaxial thin films of YBCO have been obtained on silicon wafers using a Eu 2 CuO 4/ YSZ (yttrium-stabilized ZrO 2) double buffer. Our results showed that application of such a double buffer can significantly enhance the epitaxy of grown YBCO. It also leads to an excellent surface morphology. The average surface roughness was found less than 5 nm in a large range. The results of X-ray small angle reflection and positron spectroscpy demonstrate a very clear and flat interface between YBCO and buffer layers. The Eu 2 CuO 4/ YSZ double buffer could be promising for coating high-TC superconducting films on various reactive substrates.

Change of coercivity of magnetic thin films with non-magnetic layers and applications to spin valve

Co and NiFe thin films were deposited on various buffer layers such as Ta, Cu and Cr to study dependence of coercivity on the buffer layers. It has been found that coercivity of the magnetic layers could be favorably reduced when grown on Ta buffer layer. In contrast, the coercivity was enhanced for the films with Cr buffer layer. X-ray diffraction and small-angle reflection analysis revealed that the change of coercivity with various buffer layers was closely linked with structure of the magnetic films. In addition, magnetoresistance of the sandwiches with the structure of Co/NM/NiFe on different non-magnetic buffer layers has been investigated. The result indicated that spin valve effect for the sandwiches without exchange-biased field can be obtained by selecting appropriate non-magnetic layer.

Nano-segregated structures of hydrogen-bonded mesogens with perfluorinated moieties: cubic phase formation and first order smectic A to smectic C phase transition

Two series of mesogenic compounds having both a perfluorinated substituent and a hydrogen bonding active site were synthesized and their phase behavior investigated. Due to the chemical architecture of these materials exhibiting amphiphilic character, structures of nano-segregation are expected to form. We found a thermotropic cubic phase with Ia3d symmetry in one of the acid/base hydrogen-bonded complexes, which is a nano-segregated structure. Moreover materials exhibiting a first order smectic A to smectic C phase transition were found, which was ascertained by differential scanning calorimetry measuring a large latent heat, and X-ray diffraction experiments observing abrupt changes of physical properties at the phase transition, i.e. the tilt angle, the intensity and the half-width of the small angle reflection. This first order phase transition occurs due to the frustration of nano-segregated structures of lamellar phases.

Influence of emulsifiers on the crystallization of solid lipid nanoparticles

The crystallization temperature and polymorphism of tripalmitin nanoparticles in colloidal dispersions prepared by melt-homogenization and stabilized with different pharmaceutical surfactants (sodium glycocholate, sodium oleate, tyloxapol, Solutol HS 15, Cremophor EL) and their combinations with soybean phospholipid (Lipoid S100) were investigated to establish the influence of the emulsifiers on these parameters. There were no major effects on the crystallization temperature but remarkable differences in the time-course of polymorphic transitions after crystallization of the triglyceride particles indicate interaction between the surfactant layer and the triglyceride matrix. The metastable alpha-modification was most stable in dispersions solely stabilized with glycocholate. Upon fast cooling from the melt, these dispersions form an uncommon type of alpha-modification that displays only a very weak small-angle reflection indicating poor ordering between triglyceride layers. Slow crystallization of these glycocholate-stabilized nanoparticles yields the usual alpha-form. Electron microscopic investigations reveal that, in both cases, the particles in the alpha-modification are less anisometric than those of the stable beta-form. These results indicate that major rearrangements still may take place in solid lipid nanoparticles after recrystallization.