Kα Source Research Articles

Quantitative analysis of atomic disorders in full-Heusler Co2FeSi alloy thin films using x-ray diffraction with Co Kα and Cu Kα sources

The authors developed a new analysis technique for atomic disorder structures in full-Heusler alloys using x-ray diffraction (XRD) with Co Kα and Cu Kα sources. The technique can quantitatively evaluate all the atomic disorders for the exchanges between X, Y, and Z atoms in full-Heusler X2YZ alloys. In particular, the technique can treat the DO3 disorder that cannot be analyzed by ordinary Cu Kα XRD. By applying this technique to full-Heusler Co2FeSi alloy thin films formed by rapid thermal annealing (RTA), RTA-temperature (TA) dependence of the atomic disorders was revealed. The site occupancies of Co, Fe, and Si atoms on their original sites were 98%, 90%, and 93%, respectively, for the film formed at TA=800 °C, indicating that the RTA-formed Co2FeSi film had the L21 structure with the extremely high degree of ordering.

Focusing of millijoule picosecond Kα radiation from 100 TW laser-solid interaction

A calibrated x-ray spectrometer was used to characterize an intense 4.5 keV Kα source. Generated from the interaction of 30 J-320 fs laser pulses focused on 25 μm thick Ti foils, the conversion efficiency into Ti Kα line is estimated to (9±6)×10−5. Highly efficient collection, monochromatization and focusing were achieved using an ellipsoidally bent highly oriented pyrolytic graphite crystal. The measured 700 μm full width half maximum (FWHM) focal spot leads to a fluence of (3.0±2.1) mJ/cm2 hence paving the way to the study of intense x-ray pulse interaction with matter as demonstrated by a first simple experiment.

Size shift of XPS lines observed from PbS nanocrystals

AbstractCrystals of PbS with different sizes were obtained by chemical deposition from aqueous solution (chemical bath deposition technique) onto undoped Si (100) substrate. The morphology and size of crystals were analyzed by high resolution scanning electron microscopy. The fine structure of Pb 4f and S 2p photoelectron lines was measured by X‐ray photoelectron spectroscopy with monochromatic Al Kα source (hν = 1486.6 eV). The phenomenon of size shift, i.e. growth of binding energies for both donor Pb 4f and acceptor S 2p photoelectron lines with decreasing nanocrystals' size, was found and quantified as a function of nanocrystals' size. The size shift values of the Pb 4f5/2 and 4f7/2 lines were determined for nanocrystals with a size from 20 to 250 nm. The interband and intraband electronic transitions were investigated by high resolution electron energy losses spectroscopy. It was shown that width and spatial anisotropy of the band gap depend on the size of PbS nanocrystals. The dependence of size shift from nanocrystals' size, the nature of this phenomenon, and a role of changes in fine structure of electronic states near the band gap are discussed in the report. Copyright © 2010 John Wiley & Sons, Ltd.

LaMnO3: Influence of the Addition of Ba and Sr

The present work focuses on lanthanum manganite-based materials obtained by citrate (LaMnO3 and La0.6Sr0.4MnO3) and Pechini (La0.6Ba0.4MnO3) methods. The influence of the addition of barium and strontium is studied. The surface properties of LaMnO3, La0.6Ba0.4MnO3 and La0.6Sr0.4MnO3 powders are investigated by means of XPS using a standard Al Kα source. Besides the wide scan spectra, detailed spectra for the La 3d, Mn 2p, O 1s, Sr 3d and Ba 3d regions and related data are presented and discussed.

Core level photoelectron spectromicroscopy with Al Kα 1 excitation at 500 nm spatial resolution

Core level photoelectron spectromicroscopy in laboratory conditions (XPS imaging) with standard Al Kα 1 excitation (1486.6 eV), either in scanning or parallel imaging mode, is currently limited to a spatial resolution of ∼4 μm. Using energy-filtered X-ray photoelectron emission microscopy (XPEEM) and a bright monochromated Al Kα source (photon flux ∼10 12 photons/(s mm 2)), we demonstrate refined results regarding lateral and energy resolutions on cross-sectioned epitaxial Si/SiGe layers imaged with photoelectrons of 266.4 eV energy referred to the Fermi level of the sample (Ge 2p 3/2 transition). Despite an elemental contrast of only 50%, XPS imaging performed this way has an edge lateral resolution of 480 nm and an energy resolution of 0.56 eV, the spectroscopic information being available at the decanometric scale. Since the lateral resolution is only limited by the counting statistics due to a modest illumination flux, this method paves the way to laterally resolved XPS and UPS in the 100 nm range.

Evaluation of uncertainties in X‐ray photoelectron spectroscopy intensities associated with different methods and procedures for background subtraction. I. Spectra for monochromatic Al X‐ray

AbstractWe report uncertainties in X‐ray photoelectron spectroscopy (XPS) intensities arising from commonly used methods and procedures for subtraction of the spectral background. These uncertainties were determined from a comparison of XPS intensities reported by volunteer analysts from 28 institutions and the corresponding intensities expected for a set of simulated XPS spectra. We analyzed peak intensities from 32 sets of data for a group of 12 spectra that had been simulated for a monochromated Al Kα source. Each reported intensity was compared with an expected intensity for the particular integration limits chosen by each analyst and known from the simulation design. We present ratios of the reported intensities to the expected intensities for the background‐subtraction methods chosen by the analysts. These ratios were close to unity in most cases, as expected, but deviations were found in the results from some analysts, particularly if the main peak was asymmetrical or if shakeup was present. We showed that better results for the Shirley, Tougaard, and linear backgrounds were obtained when analysts determined peak intensities over certain energy ranges or integration limits. We then were able to recommend integration limits that should be a useful guide in the determination of peak intensities for other XPS spectra. The use of relatively narrow integration limits with the Shirley and linear backgrounds, however, will lead to measures of peak intensities that are less than the total intensities. Although these measures may be satisfactory for some quantitative analyses, errors in quantitative XPS analyses can occur if there are changes in XPS lineshapes or shakeup fractions with change of chemical state. The use of curve‐fitting equations to fit an entire spectrum will generally exclude the shakeup contribution to the intensity of the main peak, and no account will be taken of any variation in the shakeup fraction with change of chemical state. Published in 2009 by John Wiley & Sons, Ltd.Certain commercial products are identified to specify the formats in which the test spectra were distributed and the software with which the test spectra were analyzed by participants. This identification does not imply that the products are endorsed or recommended by the National Institute of Standards and Technology, or that they are necessarily the most suitable for the purposes described.

Penumbral imaging of Kα radiation source

At the SILEX-Ⅰlaser facility， penumbral imaging technique was used to record a Kα source in two dimensions. Due to the fact that the source was produced via the interaction between ultrashort-ultraintensity laser and ‘Velvet’ target， we can obtain high quality Kα source images. More details about the source spatial distributions can be deduced from the two-dimensional imaging than that from the one-dimensional imaging such as knife edge imaging.

A continuous kilohertz Cu Kα source produced by submillijoule femtosecond laser pulses for phase contrast imaging

We report a continuously operated Cu Kα x-ray source produced by a commercial kilohertz submillijoule femtosecond laser system. The source has an x-ray conversion of ∼4×10−5 into Kα line emission at 8.05 keV. The microplasma x-ray source has a size of 8 μm (full width at half maximum) produced by focusing 260 μJ laser pulses on a moving Cu-wire target. An average photon flux of ∼1.1×109 photons/sr/s is obtained using the above laser pulses. The source has been used to record phase contrast images of test samples. This compact x-ray source can serve as a low cost operating system for phase contrast imaging in clinical applications.

High-resolution 17–75keV backlighters for high energy density experiments

17 – 75 keV one- and two-dimensional high-resolution (<10μm) radiography has been developed using high-intensity short pulse lasers. High energy Kα sources are created by fluorescence from hot electrons interacting in the target material after irradiation by lasers with intensity IL>1017W∕cm2. High-resolution point projection one- and two-dimensional radiography has been achieved using microfoil and microwire targets attached to low-Z substrate materials. The microwire size was 10μm×10μm×300μm on a 300μm×300μm×5μm polystyrene substrate. The radiography experiments were performed using the Titan laser at Lawrence Livermore National Laboratory. The results show that the resolution is dominated by the microwire target size and there is very little degradation from the plasma plume, implying that the high-energy x-ray photons are generated mostly within the microwire volume. There are enough Kα photons created with a 300J, 1-ω, 40ps pulse laser from these small volume targets, and that the signal-to-noise ratio is sufficiently high, for single shot radiography experiments. This unique technique will be used on future high energy density experiments at many new high-power laser facilities.

Hard x-ray radiography for density measurement in shock compressed matter

In this letter we report on the direct density measurement in a shock compressed aluminum target using hard x-ray radiography. Experimental data employing a molybdenum Kα source at 17.5keV, generated with a short pulse laser are presented. High spatial resolution was obtained thanks to a new design for the backlighter geometry. Density values deduced from radiography are compared to predictions from hydrodynamic simulations, which have been calibrated in order to reproduce shock velocities measured from a rear-side self-emission diagnostic. Our results reveal the great potential of this technique as a diagnostic tool for direct density measurements in dense high-Z opaque materials.

X-ray photoelectron studies of clean and oxidized α-GeTe(111) surfaces

Clean and oxidized (104–1015 L of O2) surfaces of α-GeTe have been investigated with x-ray photoelectron spectroscopy by using the synchrotron radiation facility BESSY II as well as an Al Kα source. To understand the first steps of oxidation, complementary quantum chemical calculations were performed. The cleaved surfaces of α-GeTe were found to be rumpled with (111) domains that can be related to the domain (twin) structure of the bulk. Both the Ge 3d and the Te 4d spectra of freshly cleaved surfaces exhibit at least three components, which are explained by a Ge or Te termination of the surface domains with possible contributions of a surface reconstruction. The surface oxidation starts at exposures of 104 L and proceeds via several steps. At low exposures, only changes in the Ge spectra are observed. Consequently, the first step of the reaction is associated with the formation of intermediate peroxidelike structures, wherein both oxygen atoms are bonded to germanium atoms. In the range of exposures between 1010 and 1015 L, a layer of a relatively stable oxidation product with the approximate stoichiometry Ge1+δ+4Te1−δ0O2(1+δ)2− is formed, which shows growth kinetics that obey a time-logarithmic law. At this stage, the peroxidelike structures are still present at the oxide/crystal interface. Once the oxidized layer exceeds a thickness of ≈2.5 nm at ∼1013 L, a transformation of the Te0 state into the Te+4 state is observed at the surface of the oxide layer. The final oxidation product can be described as mGeO2×nTeO2.

Multi-kilohertz, ultrafast hard X-ray K α source

We report on the performance of a femtosecond laser-based hard X-ray Kα source operating up to 10 kHz repetition rate. Using chromium- or iron-containing tapes, spectrally narrow band Kα1 and Kα2 radiation at about 5.4 and 6.4 keV is generated. Employing up to 1 mJ pulse energy in the fundamental more than 109 Kα photons s-1 are generated in 4π steradian.

Monte Carlo simulation of Kα source produced by ultrashort and ultrahigh laser interaction with Cu target

超短超强激光打靶产生的超热电子，与固体靶相互作用时会产生Kα线辐射.由经典定标律给出了法线方向超热电子的温度.利用蒙特卡罗方法，对超热电子在固体靶中的传输进行了研究，模拟了不同靶厚度情况下Kα产额和角分布及不同电子温度下Kα光子的转化效率.计算结果与实验符合较好.结果表明：在一定电子温度下，随着靶厚度的增加Kα光子产额会达到饱和，并会使Kα光子发射的各向异性变得更加严重；存在最佳的电子温度，使Kα线转化效率最高.

Density Measurements of Shock Compressed Matter Using Short Pulse Laser Diagnostics

In this paper, experimental results on X-ray and proton radiography of shock compressed matter are presented. It has been performed at the Rutherford Appleton Laboratory (RAL) using three long pulse beams to generate a shock wave in a multi-layer foil and a short pulse beam to create either an X-ray or protons source for a transverse radiography. Depending on the probe material (aluminium or carbon foam) a Molybdenum Kα source or a proton beam are used. Density data of the shocked aluminium, in the multimagabar regime are presented.

Study of forward accelerated fast electrons in ultrashort Ti K α sources

The results of an experiment aimed at studying hot electrons emerging from a target rear side in ultrashort laser-based []Kα sources are described. In particular, forward accelerated fast electrons propagating through a Ti foil are found to be emitted in a cone perpendicular to the target surface. The energy of these electrons is estimated as well as their divergence. A comparison of the experimental findings with the results of a PIC simulation is also reported, aimed at identifying the physical processes responsible for the production of this forward propagating electron population.

High-energy Kα radiography using high-intensity, short-pulse lasers

The characteristics of 22–40keV Kα x-ray sources are measured. These high-energy sources are produced by 100TW and petawatt high-intensity lasers and will be used to develop and implement workable radiography solutions to probe high-Z and dense materials for the high-energy density experiments. The measurements show that the Kα source size from a simple foil target is larger than 60μm, too large for most radiography applications. The total Kα yield is independent of target thicknesses, verifying that refluxing plays a major role in photon generation. Smaller radiating volumes emit brighter Kα radiation. One-dimensional radiography experiments using small-edge-on foils resolved 10μm features with high contrast. Experiments were performed to test a variety of small volume two-dimensional point sources such as cones, wires, and embedded wires, measured photon yields, and compared the measurements with predictions from hybrid-particle-in-cell simulations. In addition to high-energy, high-resolution backlighters, future experiments will also need imaging detectors and diagnostic tools that are workable in the high-energy range. An initial look at some of these detector issues is also presented.

Conversion of Magnetron Deposited TiC Films into Rutile TiO2

AbstractSummary: TiO2 films can be obtained by a wide variety of technologies ranging from thermal oxidation, through PVD methods to a direct CVD growth. In this work, we report a two‐step fabrication of thin films of TiO2 (rutile). For the first time as a starting material were used TiC films deposited on monocrystalline silicon wafers by magnetron DC‐sputtering. The results of treatment of TiC thin films by an H2O/HCl gas mixture and Ar as a carrier gas at temperatures up to 1 000 °C and atmospheric pressure are presented. TiC films were converted into thin rutile films with traces of carbon. The microstructure and composition of the as‐deposited TiC films and of the films after treatment were investigated by scanning electron microscopy (SEM), by X‐ray diffraction (XRD) with a Co Kα (λ = 0.179 nm) and a Cu Kα source (λ = 0.154 nm) and by Raman spectroscopy.A SEM image of the treated TiC film.imageA SEM image of the treated TiC film.

Zeus-2D Simulations of Laser-Driven Radiative Shock Experiments

A series of experiments is underway using the Omega laser to examine radiative shocks of astrophysical relevance. In these experiments, the laser accelerates a thin layer of low-Z material, which drives a strong shock into xenon gas. One-dimensional numerical simulations using the HYADES radiation hydrodynamics code predict that radiation cooling will cause the shocked xenon to collapse spatially, producing a thin layer of high density (i.e., a collapsed shock). Preliminary experimental results show a less opaque layer of shocked xenon than would be expected assuming that all the xenon accumulates in the layer and that the X-ray source is a pure Kα source. However, neither of these assumptions is strictly correct. Here we explore whether radial mass and/or energy transport may be significant to the dynamics of the system. We report the results of two-dimensional numerical simulations using the ZEUS-2D astrophysical fluid dynamics code. Particular attention is given to the simulation method.

Characteristics of high energy Kα and Bremsstrahlung sources generated by short pulse petawatt lasers

We have measured the characteristics of high energy Kα sources created with the Vulcan Petawatt laser at RAL and the JanUSP laser at Lawrence Livermore National Laboratory. High energy x-ray backlighters will be essential for radiographing high energy-density experimental science targets for NIF projects especially to probe implosions and high areal density planar samples. Hard Kα x-ray photons are created through relativistic electron plasma interactions in the target material after irradiated by short pulse high intensity lasers. For our Vulcan experiment, we employed a CsI scintillator charge coupled device (CCD) camera for imaging and a CCD camera for single photon counting. We have directly measured the 22 keV Ag Kα source size using the RAL petawatt laser and performed knife-edge measurements of a 40 keV Sm Kα source using the JanUSP laser. The measured source sizes are both ∼60 μm full width half maximum. We have also measured the Ag Kα conversion efficiencies. At laser intensities of 1×1018 W/cm2 range, the conversion efficiency at 22 keV is ∼1×10−4.

Imaging detectors for 20–100 keV x-ray backlighters in high-energy-density experimental science petawatt experiments

We are developing a petawatt laser for use as a high-energy backlighter source in the 20–100 keV range on the National Ignition Facility (NIF). High-energy x-ray backlighters will be essential for radiographing high-energy-density experimental science (HEDES) targets, especially to probe implosions and high areal density planar samples. For these high energy backlighter imaging experiments, we are developing two types of detectors: a columnar grown CsI scintillator coupled to a 2 K×2 K charge-coupled device camera, and a CdTe crystal with special application specific integrated circuit readout electronics in a 508×512 format array. We characterized these sensors using Cd109 and Am241 radioactive isotopes. In addition, we employed them to measure the Sm Kα source size generated by the short pulse laser, JanUSP, at Lawrence Livermore National Laboratory. The CsI camera performed well, allowing a measurement of the Sm Kα source size. Calibration of this camera has shown that it has low noise and good resolution. The new CdTe camera performed well, however the noise level was too high for single photon counting. Some modifications to the camera will also be necessary in order to meet the needs of future hard x-ray experiments. Both cameras showed considerable promise as diagnostic tools for future high-energy x-ray backlighters for NIF HEDES experiments. This article will present the results of our characterizations of these detectors, and initial results from the JanUSP experiments.