High-resolution X-ray Spectroscopy Research Articles

HREM and EDS analysis of (La, M)TiO3 (M = Zn, Mn) prepared by M/Li ion exchange

High-resolution electron microscopy (HREM) and energy dispersive X-ray spectroscopy (EDS) studies of (La, M)TiO3 (M = Zn, Mn) prepared by M/Li ion exchange were performed to clarify the microscopic mechanism of ion-exchange reactions. At a macroscopic level, EDS analysis revealed that Zn and Mn atoms were homogeneously dispersed in matrix grains of (La, Zn)TiO3 and (La, Mn)TiO3 samples, respectively. EDS analysis also revealed that no segregation of Zn and Mn atoms was observed even in the vicinity of grain boundary regions. HREM and EDS analysis demonstrated that the microscopic mechanism of ion-exchange reactions was different by the ion-exchanged metals.

A Superconducting Tunnel Junction X-Ray Spectrometer Without Liquid Cryogens

Superconducting tunnel junctions (STJs) are being developed as X-ray detectors because they combine the high energy resolution of cryogenic detector technologies with the high count rate capabilities of athermal devices. We have built STJ spectrometers for chemical analysis of dilute samples by high-resolution soft X-ray spectroscopy at the synchrotron. The instruments use 36 pixels of 200 mum times 200 mum Nb-Al-AlOx-Al-Nb STJs with 165 nm thick Nb absorber films. They have achieved an energy resolution of ~ 10-20 eV FWHM for X-ray energies below 1 keV, and can be operated at a total count rate of ~ 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> counts/s. For increased user-friendliness, we have built a liquid-cryogen-free refrigerator based on a two-stage pulse tube cryocooler in combination with a two-stage adiabatic demagnetization stage. It holds the STJ detector at the end of a 40-cm-long cold finger, and attains the required operating temperature of ~ 0.3 K at the push of a button. We describe the instrument performance and present speciation measurements on Eu dopant activators in the novel scintillator material SrI <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> to illustrate the potential for STJ spectrometers at the synchrotron.

Synthesis and room-temperature ferromagnetism of cobalt-doped SnO2 nanowires

We have observed ferromagnetism in dilute cobalt-doped SnO2 nanowires at room temperatures. The Co-doped SnO2 nanowires with an average diameter of ∼50 nm were synthesized by the thermal chemical vapor transport method. High-resolution transmission electron microscopy and energy-dispersive x-ray spectroscopy analyses demonstrate that the nanowires are single-crystal structures and Co is homogeneously doped into the SnO2 lattice. The ferromagnetic hysteresis curves and temperature-dependent magnetization measurement provide evidence for ferromagnetic properties with a Curie temperature above room temperature. Oxygen annealing has been performed to study the roles played by the oxygen vacancies in determining the ferromagnetic properties of the nanowires.

An efficient X-ray spectrometer based on thin mosaic crystal films and its application in various fields of X-ray spectroscopy

X-ray optics with high energy resolution and collection efficiency are required in X-ray spectroscopy for investigations of chemistry and coordination. This is particularly the case if the X-ray source emits a rather weak signal into a large solid angle. In the present work the performance of a spectrometer based on thin mosaic crystals was investigated for different spectroscopic methods using various X-ray sources. It was found that, even with low-power X-ray sources, advanced high-resolution X-ray spectroscopy can be performed.

On nanoscale Al precipitates forming in eutectic Si particles in Al–Si–Mg cast alloys

Nanoscale Al precipitates with satellite-like outgrowths have been observed in eutectic Si particles in Al–Si–Mg alloys. Investigation by high-resolution transmission electron microscopy and energy dispersive X-ray spectroscopy indicates that the outgrowth is a void in the aluminium. The void interface plane in the Al crystal is {1 1 1} and is parallel with {0 0 1} Si. It is very likely that the outgrowth is related to the precipitation of Al in the Si particles and to the stability of the Al precipitates.

DoubleK-shell ionization of Al induced by photon and electron impact

This paper reports on the investigation of the double $K$-shell ionization of metallic aluminum induced by photon and electron impact. The experimental method consisted to measure the $K\ensuremath{\alpha}$ hypersatellite spectra resulting from the radiative decay of double $1s$ vacancy states by means of high-resolution x-ray spectroscopy using a Bragg-type von Hamos crystal spectrometer. Measurements of the photon-induced spectra were carried out at the European Synchrotron Radiation Facility, Grenoble, France, while those of the electron-induced spectra were performed at the University of Fribourg. The double $1s$ ionization probabilities and cross sections were derived from the $K{\ensuremath{\alpha}}_{2}$ hypersatellite to diagram line intensity ratios for photon beam energies ranging between 3.1 and 5.5 keV and for different incident electron-beam energies ranging between 4 and 20 keV. The energy and linewidth of the $K{\ensuremath{\alpha}}_{2}$ hypersatellite x-ray line were also determined for which consistent results were obtained from the photon and electron-beam measurements.

Observation of ion cyclotron range of frequencies mode conversion plasma flow drive on Alcator C-Mod

At modest H3e levels (n3He/ne∼8%–12%), in relatively low density D(H3e) plasmas, n¯e≤1.3×1020 m−3, heated with 50 MHz rf power at Bt0∼5.1 T, strong (up to 90 km/s) toroidal rotation (Vϕ) in the cocurrent direction has been observed by high-resolution x-ray spectroscopy on Alcator C-Mod. The change in central Vϕ scales with the applied rf power (≤30 km s−1 MW−1), and is generally at least a factor of 2 higher than the empirically determined intrinsic plasma rotation scaling. The rotation in the inner plasma (r/a≤0.3) responds to the rf power more quickly than that of the outer region (r/a≥0.7), and the rotation profile is broadly peaked for r/a≤0.5. Localized poloidal rotation (0.3≤r/a≤0.6) in the ion diamagnetic drift direction (∼2 km/s at 3 MW) is also observed, and similarly increases with rf power. Changing the toroidal phase of the antenna does not affect the rotation direction, and it only weakly affects the rotation magnitude. The mode converted ion cyclotron wave (MC ICW) has been detected by a phase contrast imaging system and the MC process is confirmed by two-dimensional full wave TORIC simulations. The simulations also show that the MC ICW is strongly damped on H3e ions in the vicinity of the MC layer, approximately on the same flux surfaces where the rf driven flow is observed. The flow shear in our experiment is marginally sufficient for plasma confinement enhancement based on the comparison of the E×B shearing rate and gyrokinetic linear stability analysis.

Synthesis and Characterization of Functionalized Ionic Liquid-Stabilized Metal (Gold and Platinum) Nanoparticles and Metal Nanoparticle/Carbon Nanotube Hybrids

Carboxylic acid- and amino-functionalized ionic liquids were used as the stabilizer for the systhesis of metal nanoparticles in aqueous solution. Smaller gold nanoparticles (3.5 nm) and platinum nanoparticles (2.5 nm) were prepared with NaBH4 as the reductant. Larger gold nanospheres (23, 42, and 98 nm) were synthesized using different quantities of trisodiumcitrate reductant. The morphology and the surface state of the metal nanoparticles were characterized by high-resolution transmission electron microscopy, UV-visible spectroscopy, and X-ray photoelectron spectroscopy. X-ray photoelectron spectroscopy spectra indicated that binding energies of C 1s and N 1s from ionic liquids on the surface of metal nanoparticles shifted negatively compared with that from pure ionic liquids. The mechanism of stabilization is proposed to be due to the interactions between imidazolium ions/functional groups in ionic liquids and metal atoms. Resonance Rayleigh scattering property of the functionalized ionic liquid-stabilized metal nanoparticles was also explored. It was found that amino-functionalized ionic liquid-stabilized gold nanoparticles exhibited lower resonance Rayleigh scattering intensity than trisodiumcitrate stabilized gold nanoparticles, which is expected to decrease the background of the resonance Rayleigh scattering intensity in the determination of various analytes. Moreover, it was found that all the as-prepared metal nanoparticles could be easily assembled on the multiwalled carbon nanotubes, which was confirmed by high-resolution transmission electron microscopy and energy dispersive X-ray spectroscopy. In this case, ionic liquids acted as a linker to connect metal nanoparticles with carbon nanotubes. The imidazolium ring moiety of ionic liquids might interact with the pi-electronic nanotube surface by virtue of cation-pi and/or pi-pi interactions, and the functionalized group moiety of ionic liquids might interact with the metal NPs surface. Finally, it was observed that plantinum nanoparticle/multiwalled carbon nanotube hybrids could be well dispersed in water, which may find future applications in fields such as catalysis, nanoscale electronics, as well as sensors.

Physics and applications of metallic magnetic calorimeters for particle detection

An increasing number of experiments and applications employ low temperature particle detectors. Following the calorimetric detection principles, the energy released in the detector leads to a temperature increase which is measured by a very sensitive sensor. Metallic magnetic calorimeters are composed by an energy absorber, optimized for the particles to be detected, in good thermal contact with a metallic paramagnetic sensor positioned in a weak magnetic field. A change in the sensor magnetisation follows the change of the detector temperature. High energy resolution can be obtained by using a low-noise, high-bandwidth DC-SQUID to measure the corresponding change of flux. We discuss the thermodynamic properties, the energy resolution, the microfabrication and general design considerations of magnetic calorimeters as well as their application in high resolution x-ray spectroscopy, beta spectroscopy and absolute activity measurements.

High-resolution X-ray spectroscopy of the low and high states of the Seyfert 1 galaxy NGC 4051 with Chandra LETGS

Context. With the new generation of high-resolution X-ray spectrometers the understanding of warm absorbers in active galactic nuclei has improved considerably. However, the important questions regarding the distance and structure of the photoionised wind remain unsolved. Aims. To constrain the distance of the photoionised wind, we study the variability of the continuum, absorption, and, emission in one of the brightest and most variable low-luminosity AGN: the narrow-line Seyfert galaxy NGC 4051. Methods. We analyse two observations taken with the Low Energy Transmission Grating Spectrometer of Chandra. We investigated the spectral response to a sudden flux decrease by a factor of 5, which occurred during the second observation. Results. We detect a highly ionised absorption component with an outflow velocity of −4670 km s −1 , one of the highest outflow velocity components observed in a Seyfert 1 galaxy. Furthermore, this is one of the only observations whereby the X-ray observed absorption component is unaccompanied by a corresponding UV absorption component with the same outflow velocity. The spectra contain a relativistic O viii Lyα line with properties similar to those determined for this source with XMM-Newton, and four absorption components spanning a range in ionisation parameter ξ between 0.07 and 3.19 (log values, and units of 10 −9 W m). An emission component producing radiative recombination continua of C vi and C v appears during the low state. The black body temperature decreases with the drop in flux observed in the second observation. Conclusions. For all absorber components we exclude that the ionisation parameter linearly responded to the decrease in flux by a factor of 5. The variability of the absorber suggest that at least three out of four detected components are located in the range 0.02−1 pc. For one component we only have a lower limit of 0.3 pc. These distances are different from earlier suggestions.

Modeling energy dependence of the inner-shell x-ray emission produced by femtosecond-pulse laser irradiation of xenon clusters

We employ the Los Alamos suite of atomic physics codes to model the inner-shell x-ray emission spectrum of xenon and compare results with those obtained via high-resolution x-ray spectroscopy of xenon clusters irradiated by 30fs Ti:Sapphire laser pulses. We find that the commonly employed configuration-average approximation breaks down and significant spin-orbit splitting necessitates a detailed level accounting. We reproduce an interesting spectral trend for a series of experimental spectra taken with varying pulse energy for fixed pulse duration. To simulate the experimental measurements at increasing beam energies, we find that spectral modeling requires an increased hot electron fraction, but decreased atomic density and bulk electron temperature. We believe these latter conditions to be a result of partial cluster destruction due to the increased energy in the laser prepulse.

Vibrational dynamics of very high density amorphous ice studied by high-resolution x-ray spectroscopy

We report results from high-resolution inelastic x-ray scattering experiments on very high density amorphous (vHDA) water ice samples. The inelastic response of the amorphous structures has been sampled with high accuracy in the momentum $Q$ range of the first pseudo-Brillouin zone. Well distinguished crystal-like phonons have been observed, and excitations of longitudinal and transverse polarization as well as acoustic and optic character are discerned. An averaged longitudinal velocity of sound of about 4050 m/s is established, exceeding the values of high density amorphous (HDA) and low density amorphous ice modifications reported in prior studies. In general, the dynamic features observed in the homogeneous vHDA structure appear to be better resolved and distinguished than the inelastic characteristics found in the heterogeneous structure of HDA.

Formation and Microstructural Properties of Locally Distributed ZnSiO3 Nanoparticles Embedded in a SiO2 Layer by Using a Focused Electron Beam

Locally distributed crystalline ZnSiO3 nanoparticles embedded in a SiO2 layer inserted between the ZnO thin film and the Si substrate were formed using transmission electron microscopy (TEM) with a focused electron beam irradiation process. High-resolution TEM (HRTEM) images and energy dispersive X-ray spectroscopy (EDS) profiles showed that ZnSiO3 nanocrystals with a size of approximately 6 nm were formed in the SiO2 layer. The formation mechanisms of the ZnSiO3 nanocrystals in the SiO2 layer are described on the basis of the HRTEM images and the EDS profiles.

Spatially resolved high resolution x-ray spectroscopy for magnetically confined fusion plasmas (invited)

The use of high resolution x-ray crystal spectrometers to diagnose fusion plasmas has been limited by the poor spatial localization associated with chord integrated measurements. Taking advantage of a new x-ray imaging spectrometer concept [M. Bitter et al., Rev. Sci. Instrum. 75, 3660 (2004)], and improvements in x-ray detector technology [Ch. Broennimann et al., J. Synchrotron Radiat. 13, 120 (2006)], a spatially resolving high resolution x-ray spectrometer has been built and installed on the Alcator C-Mod tokamak. This instrument utilizes a spherically bent quartz crystal and a set of two dimensional x-ray detectors arranged in the Johann configuration [H. H. Johann, Z. Phys. 69, 185 (1931)] to image the entire plasma cross section with a spatial resolution of about 1 cm. The spectrometer was designed to measure line emission from H-like and He-like argon in the wavelength range 3.7 and 4.0 A with a resolving power of approximately 10,000 at frame rates up to 200 Hz. Using spectral tomographic techniques [I. Condrea, Phys. Plasmas 11, 2427 (2004)] the line integrated spectra can be inverted to infer profiles of impurity emissivity, velocity, and temperature. From these quantities it is then possible to calculate impurity density and electron temperature profiles. An overview of the instrument, analysis techniques, and example profiles are presented.

High-resolution X-ray spectroscopy ofθ Carinae

Context : The peculiar hot star Theta Car in the open cluster IC2602 is a blue straggler as well as a single-line binary of short period (2.2d). Aims : Its high-energy properties are not well known, though X-rays can provide useful constraints on the energetic processes at work in binaries as well as in peculiar, single objects. Methods : We present the analysis of a 50ks exposure taken with the XMM-Newton observatory. It provides medium as well as high-resolution spectroscopy. Results : Our high-resolution spectroscopy analysis reveals a very soft spectrum with multiple temperature components (1--6MK) and an X-ray flux slightly below the `canonical' value (log[L_X(0.1-10.)/L_{BOL}] ~ -7). The X-ray lines appear surprisingly narrow and unshifted, reminiscent of those of beta Cru and tau Sco. Their relative intensities confirm the anomalous abundances detected in the optical domain (C strongly depleted, N strongly enriched, O slightly depleted). In addition, the X-ray data favor a slight depletion in neon and iron, but they are less conclusive for the magnesium abundance (solar-like?). While no significant changes occur during the XMM-Newton observation, variability in the X-ray domain is detected on the long-term range. The formation radius of the X-ray emission is loosely constrained to <5 R_sol, which allows for a range of models (wind-shock, corona, magnetic confinement,...) though not all of them can be reconciled with the softness of the spectrum and the narrowness of the lines.

High Spatial Resolution X-Ray Spectroscopy of Cas A with Chandra

We present high spatial resolution X-ray spectroscopy of the supernova remnant Cassiopeia A with the Chandra observations. The X-ray emitting region of this remnant was divided into 38 × 34 pixels of 10''× 10'' each. Spectra of 960 pixels were created and fitted with an absorbed two component non-equilibrium ionization model. From the results of the spectral analysis we obtained maps of absorbing column density, temperatures, ionization ages, and the abundances of Ne, Mg, Si, S, Ca and Fe. The Si, S and possibly Ca abundance maps show obvious jet structures, while Fe does not follow the jet but seems to be distributed perpendicular to it. The abundances of Si, S and Ca show tight correlations between one another over a range of about two dex. This suggests that they are ejecta from explosive O-burning and incomplete Si-burning. Meanwhile, the Ne abundance is well correlated with that of Mg, indicating them to be the ashes of explosive C/Ne burning. The Fe abundance is positively correlated with that of Si when the latter is lower than 3 times the solar value, and is negatively correlated when higher. We suggest that such a two phase correlation is due to the different ways in which Fe was synthesized.

X‐Atlas: An Online Archive ofChandra's Stellar High‐Energy Transmission Grating Observations

The high-resolution X-ray spectroscopy made possible by the 1999 deployment of the Chandra X-ray Observatory has revolutionized our understanding of stellar X-ray emission. Many puzzles remain, however, particularly regarding the mechanisms of X-ray emission from OB stars. Although numerous individual stars have been observed in high resolution, realizing the full scientific potential of these observations will necessitate studying the high-resolution Chandra data set as a whole. To facilitate the rapid comparison and characterization of stellar spectra, we have compiled a uniformly processed database of all stars observed with the Chandra High-Energy Transmission Grating (HETG). This database, known as X-Atlas, is accessible through a Web interface with searching, data retrieval, and interactive plotting capabilities. For each target, X-Atlas also features predictions of the low-resolution ACIS spectra convolved from the HETG data for comparison with stellar sources in archival ACIS images. Preliminary analyses of the hardness ratios, quantiles, and spectral fits derived from the predicted ACIS spectra reveal systematic differences between the high- and low-mass stars in the atlas and offer evidence for at least two distinct classes of high-mass stars. A high degree of X-ray variability is also seen in both high- and low-mass stars, including Capella, long thought to exhibit minimal variability. X-Atlas contains over 130 observations of approximately 25 high-mass stars and 40 low-mass stars and will be updated as additional stellar HETG observations become public. The atlas has recently expanded to nonstellar point sources, and Low-Energy Transmission Grating (LETG) observations are currently being added as well.

Synthesis of ZnO/cubic (Zn, Mg)O heterostructure nanorods

ZnO/cubic (Zn, Mg)O core–shell heterostructure nanorods with wire-shaped tips have been synthesized via a catalyst-free thermal evaporation process on Si substrates. The average diameters were about 180 nm for nanorods and about 20 nm for tips. Transmission electron microscopy (TEM) investigations revealed that the tip was a single-crystalline cubic structure and grew along the [2 0 0] direction. A two-step growth process was used to synthesize the ZnO/(Zn, Mg)O heterostructure nanorods; that is, Zn and Mg powders were first evaporated at 630 °C and then the temperature was raised to 750 °C. High-resolution TEM and energy dispersive x-ray spectroscopy analysis confirmed that the product is pure ZnO at the first step. X-ray diffraction, photoluminescence and TEM results indicated that a final heterostructure nanorod consisted of a wurtzite ZnO core and a cubic (Zn, Mg)O shell. The growth temperature and process control were suggested to be responsible for the formation of heterostructure nanorods.

Abundance variations and first ionization potential trends during large stellar flares

Context. In the solar corona, elements of low first ionization potential (FIP 10 eV) are enriched relative to their abundances in the photosphere, while high-FIP abundances remain unchanged. This was labeled as the Solar FIP effect. High-resolution X-ray spectroscopy has revealed that active stellar coronae show an opposite effect, which was labeled the inverse-FIP (IFIP) effect. The correlation found between coronal activity and the FIP/IFIP bias suggests that flaring activity is involved in switching from FIP to IFIP.Aims. This work aims at a more systematic understanding of the FIP trends during stellar flares and complements an earlier study based on Chandra alone.Methods. The eight brightest X-ray flares observed with XMM-Newton are analyzed and compared with their respective quiescence states. Together with six previous flares observed with Chandra , this establishes the best currently available sample of flares. We look for abundance variations during the flare and their correlation with FIP. For that purpose, we define a new FIP bias measure.Results. A trend is found where coronae that are IFIP-biased in quiescence, show a FIP bias during flares relative to their quiescence composition. This effect is reversed for coronae that are FIP-biased in quiescence. The observed trend is thus consistent with chromospheric evaporation rather than with a FIP mechanism operating during flares. It also suggests that the quiescent IFIP bias is real and that the large flares are not the direct cause of the IFIP effect in stellar coronae.

Carbon submicrotubes synthesized on carbon microfibers

Carbon submicrotubes were synthesized on carbon microfibers by floating catalyst method, and carbon nanotubes were also observed to grow on the rough surface of carbon submicrotubes. The morphology, microstructure and composition of the obtained products were characterized by field emission scanning electron microscopy, high-resolution transmission electron microscopy, Raman spectroscopy and energy dispersive X-ray spectroscopy. The growth of carbon submicrotubes on carbon microfibers was attributed to the pretreatment of carbon microfibers, which gave rise to catalyst areas, while the secondary growth of carbon nanotubes could be related to the defects of hexagonal graphite on the surface of carbon submicrotubes.