AlGaN/GaN异质结构的X射线衍射研究

在(0001)取向的蓝宝石(α-A12O3)基片上用金属有机物化学气相沉积(MOCVD)方法生长了势垒层厚度为1000A的Al0．22Ga0．78N／GaN异质结构,利用高分辨X射线衍射(HRXRD)技术测量了样品的对称反射(0002)和非对称反射(1014)的倒易空间Mapping(RSM)。结果表明,样品势垒层的内部微结构与应变状态和下层i-GaN的微结构与应变状态互相关联。样品势垒层的微应变已经发生弛豫,而且具有一种“非常规”应变弛豫状态,这种弛豫状态的来源可能与n-AIGaN的内部缺陷以及i-GaN／α-Al2O3界面应变弛豫状态有关。掠入射X射线衍射研究表明样品内部的应变是不均匀的,由表层的横向压应变状态过渡到下层的张应变状态,与根据倒易空间Mapping分析得到的结果一致。     

A unique high pressure apparatus for X-ray diffraction studies of phase transitions up to 5 kbar

A new high pressure apparatus equipped with a beryllium pressure cell for X-ray diffraction experiments up to 5 kbar is described. The apparatus is especially designed for studying phase transitions in crystalline solids. The pressure generator has the capabilities of controlling pressure with precision of ± 2 bars and of performing a quick change in pressure applied to a sample. The beryllium miniature cell is press-fitted with a supporting jacket which has a large aperture for X-ray beams; therefore, a greater portion in reciprocal space can be surveyed. By using synchrotron radiation X-rays, we have carried out a test experiment on the incommensurate-commensurate phase transition in [N(CH₃)₄]₂MnCl₄.     

Positron annihilation and X-ray diffraction studies on tin oxide thin films

Positron annihilation spectroscopy along with glancing incidence X-ray diffraction have been used to investigate tin oxide thin films grown on Si by pulsed laser deposition. The films were prepared at room temperature and at 670 K under oxygen partial pressure. As-grown samples are amorphous and are found to contain large concentration of open volume sites (vacancy defects). Post-deposition annealing of as-grown samples at 970 K is found to drastically reduce the number of open volume sites and the film becomes crystalline. However, film grown under elevated temperature and under partial pressure of oxygen is found to exhibit a lower S-parameter, indicating lower defect concentration. Based on the analysis of experimental positron annihilation results, the defect-sensitive S-parameter and the overlayer thickness of tin oxide thin films are deduced. S-W correlation plots exhibit distinct positron trapping defect states in three samples.     

同位素源激发X荧光分析微量元素的实验研究

本文所介绍的实验工作主要有三部分。首先是实验条件的选择;其次是用AXIL软件包进行X射线能谱分析;第三部分是标准曲线及其修正,即如何确定内标法中的相对灵敏度因子。     

Thermal expansion studies on Inconel-600 by high temperature X-ray diffraction

The lattice thermal expansion characteristics of Inconel-600^® have been studied by high temperature X-ray diffraction (HT-XRD) technique in the temperature range 298-1200 K. Altogether four experimental runs were conducted on thin foils of about 75-100 μm thickness. The diffraction profiles have been accurately calibrated to offset the shift in 2θ values introduced by sample buckling at elevated temperatures. The corrected lattice parameter data have been used to estimate the instantaneous and mean linear thermal expansion coefficients as a function of temperature. The thermal expansion values estimated in the present study show a fair degree of agreement with other existing dilatometer based bulk thermal expansion estimates. The lattice parameter for this alloy at 300 K is found to be 0.3549(1) nm. The mean linear thermal expansivity is found to be 11.4 × 10⁻⁶ K⁻¹.     

便携式X射线荧光仪稳谱技术

介绍的应用于便携式Ｘ射线荧光仪的稳谱技术是利用Ｘ射线与物质作用产生的散射峰作为参考源实现稳谱，其方法简便，不附加参考辐射源，稳谱效果好，采用该技术的ＣＤ－４微机化Ｘ射线荧光仪稳定性好，整机性能明显改善。     

Characterisation of mineralisation of bone and cartilage: X-ray diffraction and Ca and Sr Kα X-ray fluorescence microscopy

Bone is a dynamic structure, constantly remodelling in response to changing mechanical and environmental factors. This is particularly evident in the mineral component encrusting the collagenous framework. The mineral is principally in the form of calcium apatite, but calcium can exchange with strontium, both during the cellular processes of mineralisation and resorption and by passive exchange with the deposited crystals. Mineralisation is generally characterized by densitometry, but because of the differences in absorption cross sections of calcium and strontium it can be misleading in studies of composition. In this work we have used X-ray diffraction to identify calcium and strontium apatite and X-ray fluorescence to quantify strontium and calcium distribution. With the beam characteristics available from synchrotron radiation, this has enabled us to obtain microscopic resolution on thin sections of bone and cartilage from the equine metacarpophalangeal joint. Two issues have been investigated; the first is the distribution of mineral in the bone-cartilage interface and within individual trabeculae. In trabecular bone the ratio of strontium to calcium concentration was typically 0.0035 ± 0.0020, and higher by a factor of ∼3 at the periphery than in the centre of a trabeculum (possibly reflecting the more rapid turnover of mineral in the surface layer). In the dense subchondral bone the ratio was similar, approximately doubling in the calcified cartilage. The second objective was to explore the changes in mineralisation associated with development of osteoarthrosis. We analysed lesions showing cartilage thinning and changes in the trabecular organization and density of the underlying bone. At the centre of the lesion the ratio of strontium to calcium was much lower than that in normal tissue, although the calcified cartilage still showed a higher ratio than the underlying bone. In the superficially normal tissue around the lesion the calcified cartilage returned to a normal ratio much more rapidly than the underlying bone. These data demonstrate the complex relationship between changes in cartilage and the underlying bone.     

A synchrotron radiation microprobe for X-ray fluorescence and microtomography at ELETTRA

A synchrotron radiation microscope based on X-ray fluorescence and computed microtomography for advanced applications in biomedicine, environmental sciences, geology and materials science is described. This microscope will utilize the radiation produced by a bending magnet of ELETTRA, the third-generation, high-brilliance synchrotron radiation facility being built in Trieste. Various wide-band-pass mirror systems operating in an energy range between 7 and 17 keV have been designed. For example, multilayer-coated mirrors in the Kirkpatrick-Baez configuration can produce a spatial resolution of 1 μm² for a flux in excess of 10⁸ photons per second on the sample (E = 12 keV, E/ΔE = 10). This X-ray microprobe will allow micrometric mapping of trace and minor elements and computed tomographic imaging with high resolution, opening a new realm of experiments in different fields of science, such as in vivo elemental scanning and microtomography of cultured cells, analysis of single atmospheric particulates, analysis of cosmic debris collected from the stratosphere and antarctic ice, etc. The preliminary design of the beam line and the performance of the microprobe are discussed.     

Applications of parametric X-rays for X-ray diffraction analysis

Until now parametric X-rays (PXR) have not had practical applications because of the lack of a modern compact accelerator providing the required beam current and consequently high X-ray photon flux. PXR sources even with the intensities achievable at present may be applied to a number of X-ray reflectometry and diffractometry measurements which are important for the characterization of crystals and multi-layer nanostructures. In the paper we present some proposals for possible PXR applications for a number of X-ray measurements based on the smooth energy tuning, high monochromaticity and directed emission of this radiation. The theoretical background and numerical evaluations for PXR applications for determining ingredient concentration in a solid solution in the range of anomalous dispersion of the defect atoms, determination of the phase structure of a crystal, and selective PXR action in organic compounds, important for medical and biological research, are considered.     

用于便携式X射线荧光仪的基体效应散射校正模型

本文论证了样品对入射射线的质量吸收系数(μ_O)与康普顿散射强度之倒数呈线性关系,提出并验证了样品对待测元素特征线的质量吸收系数(μ_K)与质量吸收系数(μ_O)以及待测元素含量之间呈线性多项式关系。并且给出了这些关系存在的条件。提出了一种适用于低能量分辨率的携带式X荧光仪的散射校正模型。并成功用于锡矿和某些铜矿分析中。     

Atomic data for accelerator-based X-ray fluorescence spectroscopy

For use in basic and applied research, an atomic data library with atomic-emission and -structure data was developed by using an EC 1055/56 computer facility. The data files contain X-ray transition data, orbital data. Auger-transition data and photon mass attenuation coefficients for all elements up to uranium. The data are stored in a generalized format that permits suitable data handling considering the features of atomic data sets. The data are available either in book form, computer listings or as files on magnetic tape. Computer codes for calculation of radiative and nonradiative transition probabilities have been developed and successfully tested for various configurations of neutral and ionized atoms.     

A method for forward energy-dispersive X-ray fluorescence analysis of thin and intermediate samples

The usefulness of forward geometry in Energy Dispersive X-Ray Fluorescence (EDXRF) analysis has been investigated both experimentally and theoretically. This work relates to milli- and micro-beams, which limits this work to tightly collimated incident X-ray beams (<1 mm). The use of forward geometry also limits the targets to be of thin and intermediate thickness. The advantages and the peculiarities of using a forward geometry for XRF are discussed. Forward X-Ray Fluorescence (FXRF) has features including: (a) high geometrical efficiencies when using tightly collimated primary beams; (b) a minimisation in the uncertainty in the interaction volume; (c) a sample thickness at which the production of characteristic X rays is maximised; and (d) a filtering action by intermediate thickness samples resulting in an enhancement of the sensitivity for higher atomic number elements with respect to lower atomic number elements. For thin and intermediate thickness samples simultaneous forward and backward geometry XRF can be used to correct for self-absorption effect.     

Study of transmission grating diffraction efficiencies for soft X—ray

Tansmission grating spectrometers are extensively used to measure absolute X-ray spectra in a photon-energy range below 1000eV.the transmission grating,as its dispersive element,must be calibrated to obtain its diffraction efficiencies.Calibrations of absolute diffraction efficiencies of the transmission grating at photon energy of 844eV have been caried out on Bejing synchrotron Radiation Facility.With the aid of grating model,all of the grating structure parameters have been determined and the absolute diffraction efficeencies in a photon-energy range below 2000eV have also been calculated and discussed.     

X射线衍射法研究刚玉注入层的结构

用Ｘ射线衍射法和ＰＯＷＤ１２理论计算程序探讨了多晶刚玉Ｆｅ离子注入层的结构变化。     

In situ characterization of ancient plaster and pigments on tomb walls in Egypt using energy dispersive X-ray diffraction and fluorescence

A portable type of energy dispersive X-ray diffraction and fluorescence (ED-XRDF) spectrometer was developed, whose operation mode is completely different from that of an X-ray diffractometer commercially available. The former is operated in energy dispersive mode but the latter in angle dispersive mode. The performance of the ED-XRDF spectrometer was tested in the field, i.e. in the tomb of Amenhotep III, built in 1364 B.C. or earlier in Egypt. The crystal structure and chemical composition of ancient plaster and pigments were successfully determined in the field using the spectrometer. The same areas investigated by the ED-XRDF spectrometer were also examined with an optical microscope. The plaster is found to be composed of anhydrite, calcite and quartz. White and yellow pigments were identified as huntite and orpiment, respectively. Egyptian blue and goethite were found in the green colored parts.     

A setup for probing ultra-short soft X-ray diffraction by means of curved multilayer structures

We propose an experimental setup allowing for measurement of the whole diffraction curve of a Bragg peak by single pulse exposure where a bended sample is illuminated by a set of parallel pencil beams under locally different angles of incidence. The feasibility is demonstrated probing the 1st order Bragg peak of Ru/B₄C multilayers for photon energies close to Boron K-edge. The evaluated optical parameters recorded from bent sample under fixed sample setting equals those obtained from a flat sample using angular dispersive recording. Subsequently our scheme is appropriate for solid state experiment using at high intense femtosecond pulses provided by free-electron laser sources.     

Techniques for depth heterogeneity identification in X-ray fluorescence

Two methods enabling depth heterogeneity to be recognized and taken into account in quantitative analysis have been elaborated and then applied to various samples. The first method involves predicting the Kα/Kβ (or L lines) ratios for all identified elements. The second method is based on comparing the spectra measured on different geometric arrangements. In particular, sample tilting makes identification of depth heterogeneities possible. If the sample is heterogeneous, the heights of some peaks in the X-ray spectra change according to the depth distribution of the corresponding elements. Monte Carlo simulations with the MCNP4C2 code can be used to predict these changes and interpret the experimental results.     

气固反应的同步辐射X射线衍射原位表征装置研制

腐蚀性气体参与的气固反应,其同步辐射原位X射线衍射（X-ray Diffraction,XRD）表征需要使用防腐蚀和泄露的装置。为此研发了两种用于气固反应XRD表征的原位装置,分别通过液体挥发和固体热处理来产生反应气体,具有装置结构紧凑、可拆卸和重复利用等优点,解决了特定气固反应原位XRD表征的需求。其中,基于液体挥发产生反应气体的原位装置适用于室温近常压气固反应,气体与固态样品发生反应可以通过精确控制液体的注入来控制反应的起始时间;基于固体热处理的原位反应装置主体采用石英材料制作,包括石英反应池和石英X窗等,适用于光子能量在18 keV以上的原位X射线衍射表征,工作温度可达450℃。这些实验装置有助于推动同步辐射技术在化学反应原位表征中的应用。