Optical Synchrotron Research Articles

High-pressure radiative conductivity of dense silicate glasses with potential implications for dark magmas.

The possible presence of dense magmas at Earth's core-mantle boundary is expected to substantially affect the dynamics and thermal evolution of Earth's interior. However, the thermal transport properties of silicate melts under relevant high-pressure conditions are poorly understood. Here we report in situ high-pressure optical absorption and synchrotron Mössbauer spectroscopic measurements of iron-enriched dense silicate glasses, as laboratory analogues for dense magmas, up to pressures of 85 GPa. Our results reveal a significant increase in absorption coefficients, by almost one order of magnitude with increasing pressure to ~50 GPa, most likely owing to gradual changes in electronic structure. This suggests that the radiative thermal conductivity of dense silicate melts may decrease with pressure and so may be significantly smaller than previously expected under core-mantle boundary conditions. Such dark magmas heterogeneously distributed in the lower mantle would result in significant lateral heterogeneity of heat flux through the core-mantle boundary.

Hexatic and blue phases in a chiral liquid crystal: optical polarizing microscopy, synchrotron radiation and dielectric study

Phase behavior, structure and molecular dynamics of a chiral liquid crystalline compound, which exhibits SmG*, SmJ*, SmF*, SmI*, SmC*, SmA*, N* and BP*, have been investigated. Observed optical textures, synchrotron radiation diffraction data and frequency dependent dielectric spectroscopic study clearly depict the temperature evolution of the different hexatic smectic phases along with cholesteric and blue phase in a single compound. In hexatic phases dielectric absorption spectra show one low frequency relaxation process, related to the phase fluctuation of the bond orientational order, and one high frequency process related to amplitude fluctuation of the bond orientational order coupled with the polarization and tilt of the molecules. Goldstone and soft mode relaxation processes are detected, respectively, in SmC* and SmA* phases.

Deflection of threading dislocations in patterned 4H–SiC epitaxial growth

Deflection of threading dislocations in patterned 4H–SiC epitaxial growth is investigated by applying multiple dry etching to create stair-like patterns growing toward <11¯00> on <112¯0> off-cut Si-face and C-face substrates. Forced deflection of most threading dislocations in the substrate is accomplished in the patterned C-face epitaxial growth; although no remarkable deflection of threading dislocations takes place in the patterned Si-face growth. The morphology of the patterned steps and behavior of threading and deflected dislocations are examined by optical microscopy and synchrotron X-ray topography, respectively. The interactions between the patterned steps and dislocations as well as the dependency of the deflection ratios of threading dislocations on the morphology of patterned steps are discussed.

Study of V and Y Shape Frank-Type Stacking Faults Formation in 4H-SiC Epilayer

Nomarski optical microscopic, KOH etching and synchrotron topographic studies are presented of faint needle-like surface morphological features in 4H-SiC homoepitaxial layers. Grazing incidence synchrotron white beam x-ray topographs show V shaped features which transmission topographs reveal to enclose 1/4[0001] Frank-type stacking faults. Some of these V-shaped features have a tail associated with them and are referred to as Y-shaped defects. Geometric analysis of the size and shape of the V-shaped faults indicates that they are fully contained within the epilayer and appear to be nucleated at the substrate/epilayer interface. Detailed analysis shows that the positions of the V-shaped stacking faults match with the positions of c-axis threading dislocations with Burgers vectors of c or c+a in the substrate and thus appear to result from the deflection of these dislocations onto the basal plane during epilayer growth. Similarly, the Y-shaped defects match well with the substrate surface intersections of c-axis threading dislocations with Burgers vectors of c or c+a in the substrate which were deflected onto the basal plane during substrate growth. Based on the observed morphology of these defect configurations we propose a model for their formation mechanism.

FERMI RULES OUT THE INVERSE COMPTON/CMB MODEL FOR THE LARGE-SCALE JET X-RAY EMISSION OF 3C 273

The X-ray emission mechanism in large-scale jets of powerful radio quasars has been a source of debate in recent years, with two competing interpretations: either the X-rays are of synchrotron origin, arising from a different electron energy distribution than that producing the radio to optical synchrotron component, or they are due to inverse Compton scattering of cosmic microwave background photons (IC/CMB) by relativistic electrons in a powerful relativistic jet with bulk Lorentz factor Gamma ~ 10-20. These two models imply radically different conditions in the large-scale jet in terms of jet speed, kinetic power, and maximum energy of the particle acceleration mechanism, with important implications for the impact of the jet on the large-scale environment. A large part of the X-ray origin debate has centered on the well-studied source 3C 273. Here we present new observations from Fermi which put an upper limit on the gamma-ray flux from the large-scale jet of 3C 273 that violates at a confidence greater that 99.9% the flux expected from the IC/CMB X-ray model found by extrapolation of the UV to X-ray spectrum of knot A, thus ruling out the IC/CMB interpretation entirely for this source when combined with previous work. Further, this upper limit from Fermi puts a limit on the Doppler beaming factor of at least delta < 9, assuming equipartition fields, and possibly as low as delta < 5, assuming no major deceleration of the jet from knots A through D1.

Optical observations of PSR J0205+6449 – the next optical pulsar?

PSR J0205+6449 is a young ({\approx} 5400 years), Crab-like pulsar detected in radio and at X and {\gamma}-ray energies and has the third largest spin-down flux among known rotation powered pulsars. It also powers a bright synchrotron nebula detected in the optical and X-rays. At a distance of {\approx} 3.2 kpc and with an extinction comparable to the Crab, PSR J0205+6449 is an obvious target for optical observations. We observed PSR J0205+6449 with several optical facilities, including 8m class ground-based telescopes, such as the Gemini and the Gran Telescopio Canarias. We detected a point source, at a significance of 5.5{\sigma}, of magnitude i {\approx} 25.5, at the centre of the optical synchrotron nebula, coincident with the very accurate Chandra and radio positions of the pulsar. Thus, we discovered a candidate optical counterpart to PSR J0205+6449. The pulsar candidate counterpart is also detected in the g ({\approx}27.4) band and weakly in the r ({\approx}26.2) band. Its optical spectrum is fit by a power law with photon index {\Gamma}0 = 1.9{\pm}0.5, proving that the optical emission if of non-thermal origin, is as expected for a young pulsar. The optical photon index is similar to the X-ray one ({\Gamma}X = 1.77{\pm}0.03), although the optical fluxes are below the extrapolation of the X-ray power spectrum. This would indicate the presence of a double spectral break between the X-ray and optical energy range, at variance with what is observed for the Crab and Vela pulsars, but similar to the Large Magellanic Cloud pulsar PSR B0540-69.

Standard specimens of Au and ZnO nanoparticles for low-angle x-ray diffractometer calibration

Standard specimens based on Au and ZnO nanoparticles are developed for calibration of low-angle x-ray diffractometers. Structural parameters of the standard specimens obtained are measured by means of transmission electron microscopy. Average values of nanoparticle dimensional parameters are confirmed, and additional characterization of standard specimens is achieved using a set of research methods, including optical spectroscopy, x-ray analysis, and synchrotron radiation.

Isothermal and nonisothermal crystallization of isotactic polypropylene/graphene oxide nanosheet nanocomposites

Isothermal and nonisothermal crystallization of isotactic polypropylene (iPP)/graphene oxide nanosheet (GONS) nanocomposites were investigated by differential scanning calorimetry, polarizing optical microscopy and synchrotron wide-angle X-ray diffraction. Nonisothermal crystallization measurement revealed that GONSs significantly elevated crystallization peak temperature of iPP. Nucleating activity of the nanocomposites containing 0.05 wt% and 0.1 wt% GONSs was 0.61 and 0.56, respectively, indicating strong nucleation ability of GONSs. Induction period and half crystallization time of nanocomposites was greatly reduced during isothermal crystallization process. Moreover, only 0.05 wt% and 0.1 wt% caused less temperature dependence of crystallization kinetics in a wide temperature range of 132–140 °C. A very low GONS loading provided sufficient surface area for crystallite nucleation. Polarized optical microscopy showed that nucleation density of nanocomposites was much larger than that of neat iPP, accelerating overall spherulite growth rate. Crystal structure of iPP was not affected by GONSs, confirming the α-nucleating ability of GONSs.

Pedogenic hematitic concretions from the Triassic New Haven Arkose, Connecticut: Implications for understanding Martian diagenetic processes

The Triassic New Haven Arkose locally contains mm-scaled pedogenic hematitic concretions, within red arkosic sandy mudstones, that provide insights into concretion-forming processes on Earth and Mars. Concretions represent ~8% of the sediment by mass (~7% by volume), are irregularly distributed and have a near-normal size distribution with a mean diameter of 1.53mm and graphic standard deviation of 0.64mm. X-ray diffraction (XRD) and attenuated total reflectance (ATR) spectroscopy indicate that the concretions are composed of ambient sediments: quartz, montmorillonite, and feldspar, and a minor phosphatic phase that is also implied by geochemistry; however, the concretions preferentially exclude coarser grain sizes, and are cemented by hematite and goethite. Optical observations and synchrotron X-ray fluorescence (XRF) chemical mapping indicate that concretions are massive to weakly zoned with respect to hematitic cements. Compared to the surrounding sediments, concretion rare earth elements (REE) are elevated in total abundances, exhibit light rare earth element (LREE)-enrichment, and possess negative Ce-anomalies; Th/U ratios are lower due to elevated U. Mass balance calculations indicate that ~20% of the concretions are composed of iron oxides and that ~30mm3 of ambient sediment is required to provide the hematitic cement in a single 1.5mm diameter concretion. Element mobility during concretion formation was tested assuming different immobile elements (Al, Ti, Zr). Assuming Zr immobility provides intermediate results, and indicates the following gains in concretions: Pb (572%), Fe (322%), Mn (142%), REE (438–116%), V (138%), U (124%), Ni (84%), and Nb (58%); other elements show either gains or losses of less than ±50%. Ce-anomalies, low Th/U, and elevated V and U abundances point to a significant redox influence on element distributions in the concretions. High iron content, crude internal concentric banding, and redox controls suggest that the concretions are formed in seasonally variable, but generally moist, soil conditions with annual precipitation >130cm. Trace element enrichment patterns are broadly consistent with derivation from downward percolating weathering fluids. Although the New Haven Arkose pedogenic concretions have significant differences and were clearly formed by different mechanisms than hematitic spherules discovered on Mars, they nevertheless exhibit a number of textural (e.g., sphericity, size distributions) and geochemical (e.g., Ni enrichments) similarities that support models suggesting that the Martian spherules are formed as sedimentary concretions.

The changes of crystalline structure of cellulose during dissolution in 1-butyl-3-methylimidazolium chloride

The morphology and crystalline structure changes of cellulose during dissolution in 1-butyl-3-methylimidazolium chloride [(BMIM)Cl] were investigated by optical microscopy and synchrotron radiation wide-angle X-ray diffraction (WAXD). Neither swelling nor dissolution of cellulose was observed under the melting point of [BMIM]Cl. While the temperature was elevated to 70 °C, the swelling phenomenon of cellulose happened with the interplanar spacing of (\( 1\bar{1}0 \)) and (020) planes increased slightly. With the temperature further going up to 80 °C, cellulose was dissolved gradually with the crystallinity (Wc,x) and crystalline index (CrI) of cellulose decreased rapidly, which indicated the crystalline structure of cellulose was destroyed completely and transformed into amorphous structure.

The Ammonia–Hydrogen System under Pressure

Binary mixtures of hydrogen and ammonia were compressed in diamond anvil cells to 15 GPa at room temperature over a range of compositions. The phase behavior was characterized using optical microscopy, Raman spectroscopy, and synchrotron X-ray diffraction. Below 1.2 GPa we observed two-phase coexistence between liquid ammonia and fluid hydrogen phases with limited solubility of hydrogen within the ammonia-rich phase. Complete immiscibility was observed subsequent to the freezing of ammonia phase III at 1.2 GPa, although hydrogen may become metastably trapped within the disordered face-centered-cubic lattice upon rapid solidification. For all compositions studied, the phase III to phase IV transition of ammonia occurred at ~3.8 GPa and hydrogen solidified at ~5.5 GPa, transition pressures equivalent to those observed for the pure components. A P-x phase diagram for the NH(3)-H(2) system is proposed on the basis of these observations with implications for planetary ices, molecular compound formation, and possible hydrogen storage materials.

High-Pressure Synthesis and Correlation between Structure, Magnetic, and Dielectric Properties in LiNbO3-Type MnMO3 (M = Ti, Sn)

LiNbO(3)-type MnMO(3) (M = Ti, Sn) were synthesized under high pressure and temperature; their structures and magnetic, dielectric, and thermal properties were investigated; and their relationships were discussed. Optical second harmonic generation and synchrotron powder X-ray diffraction measurements revealed that both of the compounds possess a polar LiNbO(3)-type structure at room temperature. Weak ferromagnetism due to canted antiferromagnetic interaction was observed at 25 and 50 K for MnTiO(3) and MnSnO(3), respectively. Anomalies in the dielectric permittivity were observed at the weak ferromagnetic transition temperature for both the compounds, indicating the correlation between magnetic and dielectric properties. These results indicate that LiNbO(3)-type compounds with magnetic cations are new candidates for multiferroic materials.

Chelating oleyl-EDTA amphiphiles: self-assembly, colloidal particles, complexation with paramagnetic metal ions and promise as magnetic resonance imaging contrast agents

Chelating amphiphiles with N, N′-ethylene diamine tetraacetic acid (EDTA) conjugated via an ester bond to one or two oleyl chain/s (EDTA-MO and EDTA-BO) have been found to be capable of chelating a variety of metal ions including paramagnetic metal ions such as Manganese (Mn) and Gadolinium (Gd). Thermal behavior and stability were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). X-ray diffraction (XRD), polarizing optical microscopy (POM) and synchrotron small and wide angle X-ray scattering (SWAXS) were used to examine the neat and lyotropic liquid crystalline phases of these amphiphiles. Aqueous colloidal dispersions of EDTA-MO and EDTA-BO and their paramagnetic metal ion chelates were examined by synchrotron SAXS, cryogenic transmission electron microscopy (cryo-TEM) and light scattering. The complexed colloidal particles were evaluated as contrast enhancement agents (CEAs) for magnetic resonance imaging (MRI) using low field NMR. Neat EDTA-MO and EDTA-BO displayed lamellar crystalline structures at room temperature. EDTA-MO in excess water or sodium acetate solution exhibited a lamellar liquid crystalline phase (Lα) across a broad range of temperatures, whereas EDTA-BO displayed a very rich polymorphism from lamellar to inverse cubic and inverse hexagonal phases depending on the ionic strength of the aqueous solution and temperature employed. Dispersion of the bulk lyotropic liquid crystalline phases of both amphiphiles in aqueous Na-acetate solution yielded stable and predominantly liposomal particles at room temperature. Complexation of an EDTA-MO colloidal dispersion with Mn(II) or Gd(III) ions resulted in liposomal particles with significantly enhanced relaxivity values when compared with their low molecular weight counterparts Mn-EDTA and Gd-EDTA. In contrast, complexation of the EDTA-BO colloidal dispersion with Mn(II) altered the liposomal structure to highly ordered cylindrical multi-wall lipid nanotubes (MWLNTs). Again the relaxivity values were enhanced significantly in comparison with the Mn-EDTA analogue. In particular, the transverse relaxivity value of these complexed colloidal particles was enhanced significantly, which suggests that these MWLNTs have potential for use as both T1 and T2-weighted contrast agents.

Characterization of Pd Impurities and Finite-Sized Defects in Detector Grade CdZnTe

ABSTRACTSynthetic CdZnTe or “CZT” crystals are highly suitable for γ-spectrometers operating at the room temperature. Secondary phases (SP) in CZT are known to inhibit detector performance, particularly when they are present in large numbers or dimensions. These SP may exist as voids or composites of non-cubic phase metallic Te layers with bodies of polycrystalline and amorphous CZT material and voids. Defects associated with crystal twining may also influence detector performance in CZT. Using transmission electron microscopy, we identify two types of defects that are on the nano scale. The first defect consists of 40 nm diameter metallic Pd/Te bodies on the grain boundaries of Te-rich composites. Although the nano-Pd/Te bodies around these composites may be unique to the growth source of this CZT material, noble metal impurities like these may contribute to SP formation in CZT. The second defect type consists of atom-scale grain boundary dislocations. Specifically, these involve inclined “finite-sized” planar defects or interfaces between layers of atoms that are associated with twins. Finite-sized twins may be responsible for the subtle but observable striations that can be seen with optical birefringence imaging and synchrotron X-ray topographic imaging.

OPTICAL SPECTRAL VARIABILITY OF THE VERY HIGH ENERGY GAMMA-RAY BLAZAR 1ES 1011+496

We present results of five years of optical (UBVRI) observations of the very-high-energy gamma-ray blazar 1ES 1011+496 at the MDM Observatory. We calibrated UBVRI magnitudes of five comparison stars in the field of the object. Most of our observations were done during moderately faint states of 1ES 1011+496 with R > 15.0. The light curves exhibit moderate, closely correlated variability in all optical wavebands on time scales of a few days. A cross-correlation analysis between optical bands does not show significant evidence for time lags. We find a positive correlation (Pearson's r = 0.57; probability of non-correlation P(>r) ~ 4e-8) between the R-band magnitude and the B - R color index, indicating a bluer-when-brighter trend. Snap-shot optical spectral energy distributions (SEDs) exhibit a peak within the optical regime, typically between the V and B bands. We find a strong (r = 0.78; probability of non-correlation P (>r) ~ 1e-15) positive correlation between the peak flux and the peak frequency, best fit by a relation $\nu F_{\nu}^{\rm pk} \propto \nu_{\rm pk}^k$ with k = 2.05 +/- 0.17. Such a correlation is consistent with the optical (synchrotron) variability of 1ES 1011+496 being primarily driven by changes in the magnetic field.

Characterization of the carrot defect in 4H-SiC epitaxial layers

Characterization of the epitaxial defect known as the carrot defect was performed in thick 4H-SiC epilayers. A large number of carrot defects have been studied using different experimental techniques such as Nomarski optical microscopy, KOH etching, cathodoluminescence and synchrotron white beam X-ray topography. This has revealed that carrot defects appear in many different shapes and structures in the epilayers. Our results support the previous assignment of the carrot defect as related to a prismatic stacking fault. However, we have observed carrot defects with and without a visible threading dislocation related etch pit in the head region, after KOH etching. Polishing of epilayers in a few μm steps in combination with etching in molten KOH and imaging using Nomarski optical microscope has been used to find the geometry and origin of the carrot defects in different epilayers. The defects were found to originate both at the epi-substrate interface and during the epitaxial growth. Different sources of the carrot defect have been observed at the epi-substrate interface, which result in different structures and surfaces appearance of the defect in the epilayer. Furthermore, termination of the carrot defect inside the epilayer and the influence of substrate surface damage and growth conditions on the density of carrot defects are studied.

PROBING THE INNER JET OF THE QUASAR PKS 1510–089 WITH MULTI-WAVEBAND MONITORING DURING STRONG GAMMA-RAY ACTIVITY

We present results from monitoring the multi-waveband flux, linear polarization, and parsec-scale structure of the quasar PKS 1510-089, concentrating on eight major gamma-ray flares that occurred during the interval 2009.0-2009.5. The gamma-ray peaks were essentially simultaneous with maxima at optical wavelengths, although the flux ratio of the two wavebands varied by an order of magnitude. The optical polarization vector rotated by 720 degrees during a 5-day period encompassing six of these flares. This culminated in a very bright, roughly 1 day, optical and gamma-ray flare as a bright knot of emission passed through the highest-intensity, stationary feature (the "core") seen in 43 GHz Very Long Baseline Array images. The knot continued to propagate down the jet at an apparent speed of 22c and emit strongly at gamma-ray energies as a months-long X-ray/radio outburst intensified. We interpret these events as the result of the knot following a spiral path through a mainly toroidal magnetic field pattern in the acceleration and collimation zone of the jet, after which it passes through a standing shock in the 43 GHz core and then continues downstream. In this picture, the rapid gamma-ray flares result from scattering of infrared seed photons from a relatively slow sheath of the jet as well as from optical synchrotron radiation in the faster spine. The 2006-2009.7 radio and X-ray flux variations are correlated at very high significance; we conclude that the X-rays are mainly from inverse Compton scattering of infrared seed photons by 20-40 MeV electrons.

Erratum: The structure of the jet in 3C 15 from multiband polarimetry

Our observations have constrained the differences in polarization position angle between the optically and radio bright regions of the jet. If these arise predominantly from regions of different velocity (as in a spine–sheath model), relativistic aberration of the polarization position angle may be large. In order to test such a model is not ruled out by the data, we attempt to model the jet as two components: a central high-velocity spine emitting optical synchrotron radiation, and an outer sheath of radio-emitting plasma. Our model has a magnetic field with components (B x, B ′ y, B ′ z) in the jet frame, where the z-axis is parallel to the jet direction, and the xy-plane is transverse to the jet. For a Lorentz factor γ in the z-direction, and an angle φ between the z-axis and the line of sight, the observer will see a projected magnetic field in the plane of the sky Bu = γB ′ x cosφ + B ′ z sinφ, (1)

Prompt optical emission and synchrotron self-absorption constraints on emission site of GRBs

We constrain the distance of the Gamma-Ray Burst (GRB) prompt emission site from the explosion centre, R, by determining the location of the electron's self absorption frequency in the GRB prompt optical-to-X/gamma-ray spectral energy distribution, assuming that the optical and the gamma-ray emissions are among the same synchrotron radiation continuum of a group of hot electrons. All possible spectral regimes are considered in our analysis. The method has only two assumed parameters, namely, the bulk Lorentz factor of the emitting source Gamma, and the magnetic field strength B in the emission region (with a weak dependence). We identify a small sample of 4 bursts that satisfy the following three criteria: (1) they all have simultaneous optical and gamma-ray detections in multiple observational time intervals; (2) they all show temporal correlations between the optical and gamma-ray light curves; and (3) the optical emission is consistent with belonging to the same spectral component as the gamma-ray emission. For all the time intervals of these 4 bursts, it is inferred that R \geq 10^{14} (Gamma/300)^{3/4} (B/10^5 Gauss)^{1/4} cm. For a small fraction of the sample, the constraint can be pinned down to R \approx 10^{14} - 10^{15} cm for Gamma ~ 300. For a second sample of bursts with prompt optical non-detections, only upper limits on R can be obtained. We find no inconsistency between the R-constraints for this non-detection sample and those for the detection sample.

TIDALLY INDUCED OUTBURSTS IN OJ 287 DURING 2005-2008

The blazar OJ 287 has produced two major optical outburst events during the years 2005-2008. These are the latest in a series of outbursts that have occurred repeatedly at 12 year intervals since early 1900s. It has been possible to explain the historical light fairly well by using a binary black hole model where the secondary black hole impacts the accretion disk of the primary twice during the 12 year orbital cycle. We will ask here how well does the latest light-curve fit with this model. We use a 10 million particle disk to model the accretion disk of the primary black hole. The rate of transfer of particles through the 10 Schwarzschild radius cylinder around the primary is followed. The secondary induces an inward flow through this surface. The inward flow rate is compared with the historical light as well as with the most recent observations reported in this paper. The observations have been carried out by using a number of small and medium size telescopes in different locations in order to ensure a dense light-curve coverage. The inflow light curve and the optical light of OJ 287 have a close resemblance to each other. It suggests that the tidally induced accretion flow is responsible for the main features of the optical light curve, with the exception of the quasi-periodic double peaks. It implies a close connection between the accretion disk and the jet where the optical synchrotron emission is presumably generated.