Limitations in the X-ray microanalysis of thin foils in a scanning transmission electron microscope

The X-ray microanalysis of thin foils has been investigated using a scanning transmission electron microscope fitted with an energy dispersive spectrometer. Thin foils prepared from an iron-nickel and an aluminium-zinc-magnesium-copper alloy have been observed and analysed. For foil thicknesses between 200 and 300 nm the X-ray intenstiy ratios are consistent with X-ray absorption characteristics. For regions less than 200 nm thickness the measured intensity ratios increase by up to a factor of 5. These results have been explained in terms of a solute enriched or depleted surface layer developed during the preparation procedure.     

The use of the scanning electron microscope for the study of weathered wood

The use of the scanning electron microscope for the study of the changes in the structure and ultrastructure of weathered wood was evaluated in a study of wood exposed to natural weathering for several hundred years. Stereoscan photographs taken of the surface structure of wood revealed in detail the mechanism of the structural breakdown, which could not be found by using the light microscope or the conventional transmission electron microscope. The gradual and very slow deterioration and ultimate destruction of the middle lamella, the various layers of the cell wall and the cohesive strength of wood tissue as well as the wood fibres are illustrated by a serious of photographs. Since no preparative technique can be used which would interfere with the surface of the weathered wood and due to the deep three-dimensional change in the structure, the scanning electron microscope was found to be the ideal instrument for the study of the structure of weathered wood at both high and low magnification with excellent resolution of detail.     

The secondary fluorescence correction for X-ray microanalysis in the analytical electron microscope

A general formulation for the secondary fluorescence correction is presented. It is intended to give an intuitive appreciation for the various factors that influence the magnitude of the secondary fluorescence correction, the specimen geometry in particular, and to serve as a starting point for the derivation of quantitative correction formulae. This formulation is primarily intended for the X-ray microanalysis of electron-transparent specimens in the analytical electron microscope (AEM). The fluoresced intensity, I^Y_X, is expressed relative to the primary intensity of the fluorescing element, I_Y, rather than to that of the fluoresced element, I_X, as has been customary for microanalysis. The importance of this choice of I_Y as a reference intensity for the electron-transparent specimens examined in the AEM is discussed. The various factors entering the secondary fluorescence correction are grouped into three factors, representing the dependencies of the correction on specimen composition, X-ray fluorescence probability and specimen geometry. In principle, an additional factor should be appended to account for the difference in detection efficiencies of the fluoresced and fluorescing X-rays; however, this factor is shown to be within a few per cent of unity for practical applications of the secondary fluorescence correction. The absorption of secondary X-rays leaving the specimen en route to the detector is also accounted for through a single parameter. In the limit that the absorption of secondary X-rays is negligible, the geometric factor has the simple physical interpretation as the fractional solid angle subtended by the fluoresced volume from the perspective of the analysed volume. Studies of secondary fluorescence in the published literature are compared with this physical interpretation. It is shown to be qualitatively consistent with Reed's expression for secondary fluorescence in the electron probe microanalyser and with the specimen-thickness dependence of the Nockolds expression for the parallel-sided thin foil. This interpretation is also used to show that the ‘sec α’ dependence on specimen tilt in the latter expression is erroneous and should be omitted. The extent to which extrapolation methods can be used to correct for secondary fluorescence is also discussed. The notion that extrapolation methods, by themselves, can be used to correct for secondary fluorescence is refuted. However, extrapolation methods greatly facilitate secondary fluorescence correction for wedge-shaped specimens when used in conjunction with correction formulae.     

The measurement and calculation of the X-ray spatial resolution obtained in the analytical electron microscope

The X-ray microanalytical spatial resolution is determined experimentally in various analytical electron microscopes by measuring the degradation of an atomically discrete composition profile across an interphase interface in a thin-foil of Ni-Cr-Fe. The experimental spatial resolutions are then compared with calculated values. The calculated spatial resolutions are obtained by the mathematical convolution of the electron probe size with an assumed beam-broadening distribution and the single-scattering model of beam broadening. The probe size is measured directly from an image of the probe in a TEM/STEM and indirectly from dark-field signal changes resulting from scanning the probe across the edge of an MgO crystal in a dedicated STEM. This study demonstrates the applicability of the convolution technique to the calculation of the microanalytical spatial resolution obtained in the analytical electron microscope. It is demonstrated that, contrary to popular opinion, the electron probe size has a major impact on the measured spatial resolution in foils < 150 nm thick.     

The modification of the electron microscope for special crystallographic applications.

The conversion of the transmission electron microscope to a convergent-beam camera and shadow microscope with facilities for experiments using two specimens located in different planes is discussed, with particular reference to older models such as the Elmiskop 1. The conversion requires the removal of the intermediate lens in some microscopes and thus prevents them from operating in their original capacity. The Elmiskop 1 has a wide intermediate lens pole-piece which does not unduly restrict the diffraction angle. The smallest crystal spacing contributing to the convergent-beam diffraction pattern is 0.05 nm.     

The scanning low-energy electron microscope: First attainment of diffraction contrast in the scanning electron microscope

Using small Pb crystals deposited in situ on a partially contaminated Si (100) crystal, we demonstrate that a commercial scanning electron microscope (SEM) can easily be converted into a scanning low-energy electron microscope (SLEEM). Although the contrast mechanism is much more complicated than that in nonscanning LEEM because not only one diffracted monochromatic beam and its close environment are used for imaging, but several diffracted beams and a wide energy spectrum of electrons of different origin (secondary electrons, inelastically andelastically scattered electrons) are used, SLEEM is a valuable addition to the standard SEM because it provides an additional structure- and orientation-sensitive contrast mechanism in crystalline materials, a low sampling depth, and high intensity at low energies.     

在线分析仪表在有色冶炼过程中的应用

介绍了几种重要分析仪表的应用情况,探讨了分析仪表（系统）在选型、使用、改进及维护方面的一些问题.     

The application of analytical electron microscopy to the study of diseased biological tissue

A routine method is described for X-ray microanalysis of thin specimens of biological tissue containing mineral particles in cancerous growths. Such a method allows information to be obtained that relates pathological history to histology, electron microscopy and X-ray microanalysis. Classification of minerals is possible in a way that is not provided by bulk analysis. The technique provides baselines of elemental data of minerals from various sources that may be used to classify particles found present in certain tumour growths.     

The use of scanning electron microscope autoradiography to localize the blueberry shoestring virus in its aphid vector

Scanning electron microscopy autoradiography (SEM-AR) in conjunction with light microscope autoradiography (LM-AR) was used to follow the movement of ¹²⁵I-labeled blueberry shoestring virus (BBSSV) through its aphid vector Illinoia pepperi with varying acquisition access periods (AAP). At 6 hr AAP, the virus had reached the stomach; at 12 hr AAP, it had reached the anterior of the intestines, and after 48 hr, AAP was present throughout the aphid. SEM-AR using backscatter electron detection proved very useful because the sample bulk resulted in a shortened exposure time compared to LM sections, correlation of the autoradiograms could be made with fine structure, preparing large numbers of samples was easy, and examining whole longitudinal sections of aphids at low magnification with a clearly visible marker was possible. Limitations were mostly attributed to sample preparation and, in some cases, were easily remedied.