Benefits from bremsstrahlung distribution evaluation to get unknown information from specimen in SEM and TEM

15th European Workshop on Modern Developments and Applications in Microbeam Analysis; 7th Meeting of the International union of Microbeam Analysis Societies

材料科学;物理学

Eggert, F.^1 ; Camus, P.P.^1 ; Schleifer, M.^1 ; Reinauer, F.^1

EDAX Inc., AMETEK Materials Analysis Division, 91 McKee Drive, Mahwah

NJ

07430, United States^1

关键词: Background approximation;    Bremsstrahlung spectrum;    Characteristic x rays;    Energy dispersive x-ray spectrometers;    Quantification methods;    Quantification model;    Scanning and transmission electron microscopes;    Wavelength dispersive x-ray spectrometers;   

Others  :  https://iopscience.iop.org/article/10.1088/1757-899X/304/1/012005/pdf
DOI  :  10.1088/1757-899X/304/1/012005

学科分类：材料科学（综合）

来源: IOP

【 摘 要 】

The energy-dispersive X-ray spectrometer (EDS or EDX) is a commonly used device to characterise the composition of investigated material in scanning and transmission electron microscopes (SEM and TEM). One major benefit compared to wavelength-dispersive X-ray spectrometers (WDS) is that EDS systems collect the entire spectrum simultaneously. Therefore, not only are all emitted characteristic X-ray lines in the spectrum, but also the complete bremsstrahlung distribution is included. It is possible to get information about the specimen even from this radiation, which is usually perceived more as a disturbing background. This is possible by using theoretical model knowledge about bremsstrahlung excitation and absorption in the specimen in comparison to the actual measured spectrum. The core aim of this investigation is to present a method for better bremsstrahlung fitting in unknown geometry cases by variation of the geometry parameters and to utilise this knowledge also for characteristic radiation evaluation. A method is described, which allows the parameterisation of the true X-ray absorption conditions during spectrum acquisition. An 'effective tilt' angle parameter is determined by evaluation of the bremsstrahlung shape of the measured SEM spectra. It is useful for bremsstrahlung background approximation, with exact calculations of the absorption edges below the characteristic peaks, required for P/B-ZAF model based quantification methods. It can even be used for ZAF based quantification models as a variable input parameter. The analytical results are then much more reliable for the different absorption effects from irregular specimen surfaces because the unknown absorption dependency is considered. Finally, the method is also applied for evaluation of TEM spectra. In this case, the real physical parameter optimisation is with sample thickness (mass thickness), which is influencing the emitted and measured spectrum due to different absorption with TEM measurements. The effects are in the very low energy part of the spectrum, and are much more visible with most recent windowless TEM detectors. The thickness of the sample can be determined in this way from the measured bremsstrahlung spectrum shape.