Characteristic X-ray production cross-sections for standardless elemental analysis in EDX

Measurements have been made of cross-sections for the production of X-rays following ionization of the K-shell by fast electrons for a range of elements and incident electron energies. These data have been fitted to a simple functional expression for the ionization cross-section. This model, the Bethe model, includes two empirical fitting parameters. We found that a single universal pair of parameters may be used to allow the model to predict cross-sections with a mean error of ～ 7% and a maximum error of ～ 20% over the range of conditions considered. A relativistic form of the Bethe model yields a small improvement in accuracy for higher incident electron energies. Measurements have also been made of L-shell production cross-sections. It is expected that the Bethe model will apply also to the L-shell. Comparison of experimental and calculated K/L-shell cross-section ratios generally supports this, but uncertainties in the values in the literature for L-shell fluorescence yields precludes the drawing of any firm conclusions here.     

A study of factors influencing the accuracy of quantitative X-ray analysis of thin foil specimens

Needle-shaped specimens were used to determine experimental values of X-ray intensity ratios for L/K and M/L lines. These ratios can be used to determine k_AB factors for L and M lines. They also provide necessary data for absorption correction with the X-ray intensity ratio method. Recent theoretical calculations of k_AB factors are evaluated and new constants in the parametrization of ionization cross-sections for L and M lines are presented. The average X-ray production per unit thickness has been measured as a function of mass thickness for a stainless steel specimen using acceleration voltages of 100 and 200 kV. An increase in X-ray production by more than 20% was found at 100 kV for mass thicknesses up to 1 mg/cm² while at 200 kV the increase was about 5%. The contamination spot method for thickness measurements has also been investigated using needle-shaped specimens. The reported overestimate of thickness using this method can be explained by the formation of broad contamination layers around the deposited spots.     

MEASUREMENT OF FOIL AND CABLE THICKNESSES BY A TRANSMISSION METHOD

X-ray fluorescence analysis techniques can be applied to determine sample thickness by either absolute or relative methods. An absolute method for thickness determination by x-ray fluorescence analysis has been devised, based on two types of independent measurements of the fluorescence intensity of the constituents of the sample and performance of transmission and reflection irradiation setups.

In the present work, a method for determination of the average thickness of material between a gamma-ray source and a detector is presented. The thicknesses of Au, Ag, and Cu foils, and Cu cables have been calculated by a transmission method. An Am-241 radioisotope source and a Si(Li) detector have been used.

The method has high accuracy and is easy to use, it is non-destructive towards the sample, and it allows one to the control the sample thickness. To assess the reliability of the method, the results obtained are compared with the results obtained with a micrometer. The results are in good agreement with each other, within the estimated experimental error     

单通道和多通道毛细管光学元件－技术发展水平和应用

毛细管光学元件在X射线分析中的应用已有20多年的历史,在这段时间里,毛细管光学元件的制作技术发生了很大的变化。上世纪90年代初,使用的是组装的毛细管光学元件,目前,集成的多通道毛细管光学元件已广泛地应用于市场销售的X射线分析设备中。这些元件的毛细管直径在微米量级,其光学性质可以根据几何光学的光线追迹计算进行描述。最近,由于多通道毛细管制作技术的改进,已成功制成了200 nm及以下通道尺寸的毛细管光学元件。在这样小的通道尺寸下,观察到了X射线辐射的波动效应。最后文章介绍了毛细管光学元件在X射线微荧光分析和微衍射方面的应用。     

弯晶X射线光学

近年来,人们付出很大精力研制新的具有独特性能的同步辐射装置和自由电子激光器,而飞秒激光等离子源可提供具有高峰值亮度的超短X射线脉冲,用来作为波荡器辐射的补充X射线源。此外,所有最新型的X射线源的诊断和应用也都需要专用X射线光学元件或仪器。X射线光谱测量是激光聚变应用中最重要的等离子诊断方法之一,该方法根据实验目的,可获得单色X射线图像或与空间或时间分辨相组合的高分辨率图像。已经研制出拥有多达10个环状弯晶的高精单色成像仪,用以研究激光聚变实验中的内爆过程并通过获得的数据对等离子体参数的时间分辨图做出评估。大功率飞秒激光器可提供实用的相对价格不高的大功率X射线脉冲源,但需要有发光效率,能量分布,以及热电子传输方面的信息来实现理想K层辐射线或者连续X射线输出的最大化,以便得到相当于同步辐射输出的峰值亮度。把这些新的射线源与弯晶光学元件相组合,可完成亚皮秒时间量级的衍射实验。激光泵浦的X射线探针实验已经展示了若干晶体在250 fs内的结构变化。作者所在研究所使用光线追踪和布拉格反射方法设计了1D或2D或1D与2D结合的弯晶X射线光学仪器。在仪器制备过程中,非常注重晶体完整,反射选择的优化,弯曲精确,以及成像和反射特性的测量,还使用X射线形貌相机和衍射仪对分析器晶体的相关特性做了测试。     

Application of diamond-like carbon coatings to elastomers frictional surfaces

Nitrile-butyl rubber-like materials were coated with amorphous hydrogenated diamond-like carbon (DLC) coatings in order to modify their surface and tribological properties. Measurements of water contact angle were performed by the sessile drop method and showed that the coated samples are more hydrophobic with water contact angles up to 116°. The surface free energy of the elastomers was calculated by the acid-base regression method considering polar and dispersive contributions and the results were correlated with changes in the surface chemistry measured by X-ray photoelectron spectroscopy. It has been found that the lower presence of oxygen functional groups on the elastomer surfaces led to lower surface free energies, even though the polar contribution was not predominant. We also found that the DLC coatings led to a significant decrease of the surface free energy (up to 16%) and that there is a good correlation between the surface free energy values and the corresponding water contact angle values. The coefficient of friction was also measured and presented a significant decrease after coating with DLC.     

A coherence approach to phase-contrast microscopy II: Experiment

We report an experimental investigation of the optical transfer functions for an X-ray microscope operated in defocus phase-contrast mode. The results are compared with a theoretical model of partially coherent image formation and are found to be in excellent agreement.     

High resolution protein localization using soft X-ray microscopy

Soft X-ray microscopes can be used to examine whole, hydrated cells up to 10 µm thick and produce images approaching 30 nm resolution. Since cells are imaged in the X-ray transmissive 'water window', where organic material absorbs approximately an order of magnitude more strongly than water, chemical contrast enhancement agents are not required to view the distribution of cellular structures. Although living specimens cannot be examined, cells can be rapidly frozen at a precise moment in time and examined in a cryostage, revealing information that most closely approximates that in live cells. In this study, we used a transmission X-ray microscope at photon energies just below the oxygen edge (λ = 2.4 nm) to examine rapidly frozen mouse 3T3 cells and obtained excellent cellular morphology at better than 50 nm lateral resolution. These specimens are extremely stable, enabling multiple exposures with virtually no detectable damage to cell structures. We also show that silver-enhanced, immunogold labelling can be used to localize both cytoplasmic and nuclear proteins in whole, hydrated mammary epithelial cells at better than 50 nm resolution. The future use of X-ray tomography, along with improved zone plate lenses, will enable collection of better resolution (approaching 30 nm), three-dimensional information on the distribution of proteins in cells.     

Solute-enriched surface layers and X-ray microanalysis of thin foils of a commercial aluminium alloy

Thin foils of the commercial Al alloy 7075 were subjected to X-ray microanalysis in a Jeol 100 CX TEMSCAN using a modified double-tilting stage. The ratio of the Cu K_x and Al K_x peaks, I_cu/I_Al, was found to decrease rapidly with increasing foil thickness, t, in regions thinner than about 200 nm. This was attributed to the formation of surface layers enriched in Cu during electropolishing, consistent with the findings of other investigators. An equation predicting the variation of I_B/I_A with t in an A-rich alloy in which B (or additional solute elements) is dilute is derived for a sample with surface layers enriched in B. The derivation predicts that I_B/I_A should vary linearly with t^?1, and that the intercept of such a plot should be positive. It is suggested that consistency with this prediction serves as a criterion for true surface enrichment. Our data on Cu obey these predictions, and further analysis indicates that the layers on both surfaces are enriched by a factor of about 5.6. The ratio of the intensities of the Zn K_x and Al K_x X-ray peaks was found to be nearly independent of foil thickness to t?400 nm. This result, combined with additional analysis, indicates that the apparent enrichment observed by other investigators is most likely due to the influence of instrumental factors.     

Analysis of 3D elemental mapping artefacts in biological specimens using Monte Carlo simulation

In this paper, we present Monte Carlo simulation results demonstrating the feasibility of using the focused ion beam based X-ray microanalysis technique (FIB-EDS) for the 3D elemental analysis of biological samples. In this study, we used a marine diatom Thalassiosira pseudonana as our model organism and NISTMonte for the Monte Carlo simulations. We explored several beam energies commonly used for the X-ray microanalysis to examine their effects on the resulting 3D elemental volume of the model organism. We also performed a preliminary study on the sensitivity of X-ray analysis for detecting nanoparticles in the model. For the conditions considered in this work, we show that the X-ray mapping performed using the 5 keV beam energy results in 3D elemental distributions that closely reflect the elemental distributions in the original model. At 5 keV, the depth resolution of the X-ray maps is about 250 nm for the model organism. We also show that the nanoparticles that are 50 nm in diameter or greater are easily located. Although much work is still needed in generating more accurate biological models and simulating experimental conditions relevant to these samples, our results indicate that FIB-EDS is a promising technique for the 3D elemental analysis of some biological specimens.     

Scanning luminescence X-ray microscopy: Imaging fluorescence dyes at suboptical resolution

Scanning luminescence X-ray microscopy is based on the use of the very small focused probe of a scanning X-ray microscope to stimulate visible light emission from phosphors and dyes. Using an undulator X-ray source and a Fresnel zone plate to produce a focused X-ray probe, images of P31 phosphor grains with a resolution of 50–75 nm have been obtained, and luminescence from polystyrene spheres loaded with 50–100 μmol/g of fluorescent dye has been imaged. The resolution was not limited by the focused X-ray probe (the microscope has imaged features at 36-nm spacing in transmission mode) but by dark noise and the low net efficiency of the luminescence detection system used for this investigation. This technique may make it possible to image dye-tagged sites of biochemical activity at the resolution of the X-ray microscope in wet, unsectioned, and unfixed cells, especially with soft X-ray optimized dyes. Because the image is formed from the detection of signal against a dark background, calculations suggest that the radiation dose for luminescence imaging of dye-tagged features should be 2–22 times lower than it is in transmission X-ray microscopy. A possible extension of the technique for three-dimensional imaging at the transverse resolution of the X-ray microscope is described, where visible light collection optics might be used to obtain submicrometre axial resolution.     

The continuum normalization method for quantification of X-ray spectra in biological microanalysis. 1. Generalized bremsstrahlung production cross-sections and analysis using standards

The thin self-supporting biological specimens used for quantitative X-ray microanalysis are problematical because the sections are most unlikely to be uniform in thickness or density, so the intensities of the characteristic lines alone are not a good measure of composition. The method developed to overcome these problems was introduced by T. A. Hall in 1971 and uses the bremsstrahlung or continuum intensity recorded in the X-ray spectrum to normalize each characteristic line, and hence is frequently referred to as the continuum normalization (CN) procedure.
  Reformulating the CN method of quantification in terms of generalized cross-sections and calculating more accurate values of bremsstrahlung production using a formula allows us a better understanding of the options open to the analyst of biological thin sections by which the errors in the measurement may be reduced. If one chooses to use the original Hall (1971 ) method using Kramers cross-sections, the window measuring the continuum for normalization should be set in the 4–7 keV region for typical scanning electron microscope and microprobe beam energies, 20–40 kV, and above 10 keV for transmission electron microscope energies of 80 kV and above. Although it is clear that peak counts must not contribute to the white count, the window should be as wide as possible to reduce statistical errors.     

Flat-response, subkiloelectronvolt x-ray detector with a subnanosecond time response

A detector that has a flat response to x rays with energies between 100 eV and 1.5 keV has been built. It has been used to measure x rays emitted from gold disks irradiated by the Argus laser at Lawrence Livermore Laboratory. Results from this detector are in good agreement with results from other techniques.     

Preparation and Evaluation of Tribological Properties of Cu Nanoparticles Surface Modified by Tetradecyl Hydroxamic Acid

Oil-soluble Cu nanoparticles without phosphorus and sulphur elements were prepared using in situ surface-modification technique with hydrazine hydrate as a reductant and tetradecyl hydroxamic acid (THA) as a modifier. The phase composition, microstructure, and chemical structure of as-synthesized Cu nanoparticles (coded as THA-capped Cu or THA-capped nano-Cu) were analyzed by means of X-ray diffraction, transmission electron microscopy, and Fourier transform infrared spectrometry. The thermal stability of THA-capped Cu was examined using thermogravimetric analysis and differential thermal analysis. The antiwear ability of THA-capped Cu as an additive in liquid paraffin was examined using a four-ball machine, and the morphology of worn steel balls was examined using a scanning electron microscope, an energy dispersive spectrometer and an X-ray photoelectron spectroscopy. It has been found that THA-capped Cu can be well dispersed in some organic solvents. As-synthesized THA-capped Cu as an environmentally friendly additive in liquid paraffin shows excellent antiwear ability for the steel–steel contact. Besides, Cu nanoparticles are able to deposit and fill up micropits and grooves on steel sliding surfaces under a higher load and hence greatly reduced wear of the steel–steel pair thereat by way of self-repairing of worn surfaces of the steel–steel frictional pair, showing promising application as an environmentally acceptable lubricating oil additive.     

A physical approach to the radiation damage mechanisms induced by X-rays in X-ray microscopy and related techniques

A physical approach is used to analyse the various mechanisms induced by the absorption of X-ray photons of energies in the 0.2–20 keV range. At the atomic scale, besides the (Auger and photo) electron transport in the bulk or the ejection into the surrounding media, special attention is devoted to the specific consequences of the initial Auger decay mechanism. At the macroscopic scale, the decisive role of the poor electronic conductivity of the radiation-sensitive materials is outlined and it is shown that the damaging effects occur in irradiated insulators because the lack of conduction electrons prevents the initial charge of the excited atoms being quickly restored. Correlating irradiation conditions and physical properties of the specimen, various expressions are proposed for the first time to quantify these effects. Some are neither dose- nor dose-rate-dependent and the influence of the surrounding medium is also considered. The fundamental mechanisms investigated here hold for a wide variety of specimens or components investigated in X-ray microscopy. Their consequences can be easily transposed to other techniques using transmitted X-rays.     

用热解石墨晶体作色散和聚焦光学元件的激光等离子体源的超快X射线光谱仪

由于激光等离子X射线源的光子通量显著低于同步辐射源的光子通量且射线为所有方向的各向同性辐射,所以,很需要具有大的集光立体角和高的积分反射率的光学元件,用热解石墨(PG)晶体作色散和聚焦元件可满足上述要求。由于PG晶体为嵌镶结构,所以可给出很高的积分反射率,而PG薄膜还可安装在任意形状的模具上构成任意形状的光学元件。此外,特殊形状的嵌镶聚焦使这些晶体甚至在弯曲的情况下,也可作为高分辨率X射线光学元件。基于上述元件特性,可以设计出有高集光效率的色散光学元件,用于激光等离子体源超快X射线光谱检测。文中描述了PG弯晶在一台改型的von HAMOS光谱仪中的应用,使用这台光谱仪,测量了飞秒激光器产生等离子体发射的X射线的光谱分布。讨论了产生的X射线在时间分辨扩展X射线吸收精细结构(EXAFS)分析中的应用。实验表明,通过优化晶体特性和光谱仪几何设置,可以实现对过渡金属K边的高分辨率EXAFS测量。     

Minipal4便携X射线荧光光谱仪现场快速测定水系沉积物中多种元素

直接使用粉末样品,用Minipal 4便携式能量色散X射线荧光光谱仪现场测定水系成积物样品中的Cu、Zn、AS、Ba、Ni、Co、Mo、Mn等元素,方法简便、快速,把采到的样品再送到实验室内进行测量,两者的分析结果基本符合;精密度试验结果,除Mo以外,各组分的RSD(n=12)均小于5%,能满足矿山和野外现场快速测定的要求。     

A multielectrode X-ray detector

A multielectrode vacuum photoemission detector for X-ray tomography of plasmas at the ITER facility is described. The detector characteristics have been investigated with an X-ray source. The spectral response of the detector to X-ray photons with energies of 3–30 keV has been determined. The spatial and angular dependences of the X-ray detection efficiency are presented. The useful signal of the ITER facility has been estimated.     

Absolute calibration of X-ray optical elements and detectors at a wavelength of 46.9 nm

The results are presented of the absolute calibration of X-ray optical elements (diffraction gratings and Sc/Si multilayers) and detectors (an УΦ-4 photographic film and a vacuum X-ray diode) used in diagnostic devices to study generation of X-ray laser radiation in an argon plasma of a capillary discharge (λ = 46.9 nm). The measurements have been performed at the soft X-ray and vacuum UV station of the VEPP-4 storage ring at the Siberian International Center of Synchrotron Radiation. An absolutely calibrated AXUV 100G photodiode has been used as a reference detector. The relative error of calibration is 10%. The measured reflectances of the multilayer mirrors and gratings are in good agreement (within the limits of errors) with the results of their calibration at the RKK-1-100 X-ray calibration facility.     

Chemomechanical Properties of Antiwear Films Using X-ray Absorption Microscopy and Nanoindentation Techniques

The first chemomechanical comparison between an antiwear film formed from a solution containing zinc dialkyl-dithiophophates (ZDDPs) to a solution containing ZDDP plus a detergent (ZDDPdet) has been performed. X-ray absorption near-edge structure (XANES) analysis has shown a difference in the type of polyphosphate between each film. The ZDDPdet film has been found to contain short-chain polyphosphates throughout. X-ray photoelectron emission microscopy (X-PEEM) has provided detailed spatially resolved microchemistry of the films. The large pads in the ZDDP antiwear film have long-chain polyphosphates at the surface and shorter-chain polyphosphates are found in the lower lying regions. The spatially resolved chemistry of the ZDDPdet film was found to be short-chain calcium phosphate throughout. Fiducial marks allowed for the re-location of the same areas with an imaging nanoindenter. This allowed the nanoscale mechanical properties, of selected antiwear pads, to be measured on the same length scale. The indentation modulus of the ZDDP antiwear pads were found to be heterogeneous, ~120 GPa at the center and ~90 GPa at the edges. The ZDDPdet antiwear pads were found to be more uniform and have a similar indentation modulus of ~90 GPa. A theory explaining this measured difference, which is based on the probing depths of all techniques used, sheds new insight into the structure and mechanical response of ZDDP antiwear films.