Multilayers for light element electron probe microanalysis
| Autor: | Stephen J. B. Reed |
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| Rok vydání: | 2008 |
| Předmět: | |
| Zdroj: | Microchimica Acta. 161:433-437 |
| ISSN: | 1436-5073 0026-3672 |
| DOI: | 10.1007/s00604-007-0892-y |
| Popis: | Synthetic multilayers consisting of alternating layers of materials with different X-ray scattering power take the place of ‘real’ crystals in wavelength-dispersive spectrometers for wavelengths greater than about 20 A and are used for analysing light elements (Z = 4–9). Their characteristics can be varied through the choice of the spacing, thickness and composition of the layers, and thus can be optimised not only for specific elements but also for high intensity or high resolution. Reflectivity may approach 100% in principle, but in practice is lower owing to the strong absorption suffered by long-wavelength X-rays. For maximum intensity extra-large multilayers would be advantageous but incompatible with normal spectrometer designs. Resolution is determined mainly by the number of layers contributing to the reflection of the X-ray beam, and is governed by the interplay of the relevant factors, namely the strength of the reflection by each layer and the progressive decrease in the intensity of the incident and reflected X-rays owing to absorption. Ideally a separate multilayer for each light element is desirable, but is impractical in a conventional general-purpose electron-probe microanalyser. Resolution can be enhanced by etching grooves in the multilayer, in order to reduce the mean density and allow more layers to contribute. Background caused by specular (non-Bragg) reflection of long-wavelength X-rays is also reduced. This and other advanced types of multilayer, including some which have been developed for other X-ray optical purposes, could usefully be applied in electron-probe microanalysis. |
| Databáze: | OpenAIRE |
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