A new high-brightness stepped-crystal diffractor for X-ray microanalysis

An electron-probe X-ray microanalyzers, the characteristic X-ray radiation is generated within a small volume of sample and the emitting surface area is on the order of 1 μm². For a distance to analyzer of approximately 0.5 m, this small emitting area can be considered as a point source. Practical implementations of the electron-probe X-ray microanalysis (EPMA) require a high spectral resolution and sufficient intensity.     

Testing of a microanalysis system

During the testing of microsystems, one has to cope with many problems resulting from inaccessibility, different technologies, and nonelectrical failure modes. A number of mixed-signal test techniques have been applied to test a new advanced microsystem. The choices on testing are directly dependent on implementation form and application area of the microsystem. Mixed-signal testing approaches are a key factor in this environment     

Selection and preparation of standard specimens for x-ray spectrum microanalysis

Translated from Izmeritel'naya Tekhnika, No. 6, pp. 57–58, June, 1989.     

Grazing exit electron probe microanalysis for surface and particle analysis

We developed a new method of grazing exit electron probe microanalysis (GE-EPMA) and applied it to analyze both Si surfaces and Mg-salt particles. In conventional EPMA, X-rays are detected at an exit (takeoff) angle of approximately 45°. Therefore, when particles collected on a sample carrier are analyzed by EPMA, the X-rays from both the particles and the carrier are detected, although we need only the X-rays emitted from the particle itself. In contrast to this, the X-rays are detected at grazing exit angles in GE-EPMA. The X-rays emitted from deep inside of the sample are not detected under grazing exit conditions, and only X-rays emitted from the surface and the particle are measured. It was found that surface-sensitive analysis of a Si wafer was possible with low background at grazing exit angles. The intensity ratio of O Kα to Si Kα increased near zero degrees, indicating that the Si wafer is covered with a native Si oxide. Moreover, Mg Kα X-rays from a Mg-salt particle, which was deposited on the Si wafer, were detected with a small Si Kα intensity at grazing exit angles of less than 0.5°. By decreasing the exit angle to less than zero, only the top of the particle was observed; therefore, GE-EPMA measurement would make it possible to investigate the surface layer of one particle.     

Development of a film microanalysis method

One of the most recent and interesting fields of research in X-ray microanalysis is the elemental characterization of thin films. Our aim is to develop a quantitative analytical procedure. In this paper a new technique for thin film microanalysis is described. This method takes the small value of the emitted X-ray intensity into account. The atomic number and absorption corrections are calculated as functions of the angle at which electrons penetrate an isotropic and homogeneous target and the angle at which X-rays emerge from the surface. Two phenomena, acting in opposite directions, occur when the electron beam incidence angle decreases. The absorption of the X-rays generated in the target diminishes with the average distance travelled by the electrons which are inducing the ionizations, whilst electron backscattering increases with decreasing angle of incidence. Between the two extremes of normal and grazing incidences there is a pair of incidence and emergence angles that maximize the intensity of the emitted radiation. The difficulty commonly met with in the microanalysis method is that the X-ray production is weak. In order to increase the intensity we present a development of the technique originally proposed by Castaing for the case of normal beam incidence. We study the corrections that modify the relationships between concentration and intensity in particular conditions of microanalysis. The influence of the geometrical conditions is characterized by a physical model dealing with the effects of the electron beam incidence angle and the initial energy. The reason for a theoretical approach is the lack of adequate experimental data for the thin film concentration calculations.     

Electron probe microanalysis of Nicalon fibres

Electron probe microanalysis of a sample of Nicalon fibre showed it to consist of 54.9 wt% Si, 32.1 wt% C and 11.6 wt% O. Studies of the fine structure of the X-ray emission bands suggested these elements were combined as 46 vol% silicon carbide, 34 vol% silicon oxycarbide and 20 vol% free carbon, with the oxycarbide in the outermost regions of the fibre being significantly richer in oxygen. The silicon carbide was composed of microcrystallites several micrometres in diameter and the remaining material formed an amorphous network of material surrounding the microcrystallites.     

Radiography and local microanalysis for detection and examination of actinide-containing microparticles

A procedure was proposed for examination of the spatial microdistribution of fissile actinide isotopes (²³⁵U, ²³⁹Pu) in various environmental objects (soils, bottom sediments, aerosols, colloid material). Complex analysis of natural actinide-containing microparticles involves α-track radiography (ATR) and neutron-induced fission track radiography (NITR), highly sensitive nondestructive methods for determining the spatial microdistribution of α-emitting and fissile actinides, respectively, and scanning electron microscopy with energy-dispersive spectrometry (SEM-EDS) and secondary ion mass spectrometry (SIMS) for local microanalysis of the general elemental and isotope composition of the particles and determination of the morphology and size of the particles. The actinide-containing particles were localized using an SEM microgrid with electrodeposited ²³⁹Pu. Particles characterized by a high concentration of actinides were detected by SEM and SIMS, while those with a low content of actinides, by track radiography followed by fragmentation of the sample for subsequent analysis (γ-ray spectrometry etc.).     

X-ray microanalysis in the transmission electron microscope

The technique of x-ray microanalysis of thin specimens in the transmission electron microscope is well established. Quantitative analyses can be obtained by converting observed x-ray intensity ratios into weight fraction ratios by incorporating suitable correction factors. Flourescence corrections in thin specimens are always significantly less than in bulk specimens and, except where strong characteristic radiation fluorescence enhancement is predicted in the bulk, can be safety ignored. As analysis probes less than 100 Å diameter have become available, the beam spreading has become an important parameter in determining the spatial resolution for analysis. Present developments are directed at improving the quality of the analyses which can be obtained. This requires the generation of high quality correction factors, particularly forZ<13, rapid and accurate methods of determining sample thickness, so that absorption corrections can be made, and the development of reliable procedures for determining the shape of the activated volume in a thin specimen.     

Atom-probe microanalysis of a tempered high-speed steel

A powder metallurgical high-speed steel containing (wt%) 2.3C, 4.2Cr, 6.7W, 7.0Mo, 6.4V, and 10.3Co was quenched from 1180°C and triple tempered for 1 hour at 560°C to secondary hardness maximum. Some of the resulting types of carbide precipitates were analysed using atom-probe field-ion microscopy. The following preliminary results were obtained:

• 1.1. The martensite contained plate-shaped MC-type precipitates, 1–2 nm thick and up to 20 nm in diameter. The composition obtained corresponds to the approximate formula: (V_0.32Mo_0.39W_0.07Cr_0.21)C_0.86
• 2.2. The martensite also contained a high density of thin precipitate platelets, many only a few atomic planes thick and with a largest dimension of typically 5 nm. These precipitates were rich in Fe, Mo and Cr, and their C content suggests a structure M₂C or M₃C.
• 3.3. One type of primary carbide, M₆C, was analysed. The composition may be written: (Fe, Co, Cr, Si, V)_3.55(Mo, W)_2.45C which is within the stability range of the η₁-phase.

     

Electron-probe microanalysis of oxygen in heat-treated Orlon fibres

A method of using electron probe microanalysis to measure oxygen contents of heat treated Orlon fibres is described. The method utilizes specimens in the form of thin sections (～ 1 μm thick) which are coated with a thin layer of gold prior to analysis. It is shown that by comparing oxygen X-ray spectra obtained from inner and outer regions of certain heat-treated fibres the presence of oxygen gradients may be established. The findings are discussed in relation to rate controlling processes occurring during oxidation.     

Direct measurement of decomposition on crystallisation of metglasR 2826A by X-ray microanalysis in stem

X-ray microanalysis in a STEM with field emission gun (ELMISKOP ST 100 F) was employed succesfully for elemental composition measurements on small crystals (25 nm) growing in amorphous metal. A direct and rapid differentiation between “polymorphous” and “primary” crystallisation was possible. Considerable differences in the composition of crystals and the glassy matrix proved the crystallisation to be of the primary type.     

Microstructure and microanalysis of hardened ordinary Portland cement pastes

Hardened ordinary Portland cement pastes of various ages have been examined by analytical transmission electron microscopy (TEM) and electron microprobe analysis (EMPA). The stability of the various hydrate phases in the electron microscope is discussed. Although all are subject to damage in varying degrees, even the least stable phase, AFt, can be recognized in relict form in the TEM. The basic framework of the microstructure and the differentiation into inner and outer hydration product are well-established at 24 h hydration. Although the dominant inner product formed within the boundaries of the original anhydrous grains is C-S-H gel, particles of AFt, AFm, Ca(OH)₂, a magnesium-rich phase and an iron-rich phase are occasionally observed within the inner product. The CaSi ratio of the C-S-H gel determined by TEM shows significant variation from one region to another in a given paste. There is no relationship between the average CaSi ratio of the C-S-H and the maturity of the paste, although young pastes appear to show a bimodal distribution. Microanalysis by EMPA gives CaSi ratios in substantial agreement with those found by TEM but it is essentially impossible to obtain by EMPA analyses of outer product C-S-H without admixture of other phases, particularly sulphoaluminate phases. Despite the presence of small amounts of embedded phases as revealed by TEM, single-phase inner product C-S-H can be analysed by EMPA. The compositions of AFt and AFm phases have been obtained by TEM and the results do not require the substitution of silicon in the formulae.     

The problem of standard samples in electron probe microanalysis

The specific character of requirements for standard and reference samples in electron probe X-ray microanalysis (EPMA) defined by locality of the method is considered. It is noted that availability of standard samples for all necessary and possible determinations using EPMA is a rather acute problem. Possible ways of examining the suitability of substances for the use in EPMA as reference and standard samples are described.     

New trends in X-ray microanalysis of minerals (Review)

Central tendencies of the development of X-ray microanalysis of minerals are considered. The development of X-ray microanalysis passed through a number of stages. The present stage is characterized by production of computer-controlled microanalyzers capable of maintaining high stability of the electron beam at a high probe current for a long time. This provides powerful technical support of high-current X-ray microanalysis of minerals, which is currently becoming widespread. Microanalysis at high currents and long counting times improves the measurement reproducibility and makes it possible to lower the detection limit in trace analysis.