[B._Beckhoff,_et_al.]_Handbook_of_Practical_X-Ray_(b-ok.org).pdf

In many cases the energy resolution of the detector

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In many cases, the energy resolution of the detector is of secondary im- portance. However, with strong overlap of element lines in the spectrum, or when measuring very thin layers or low element contents, a better energy res- olution will result in a better repeatability. Of course, in addition, cost and handling (cooling, durability, stability) are of great significance in industrial manufacturing or quality control. Considering what has been said thus far, it is understandable that propor- tional counter tubes are commonly used. Although the energy resolution is relatively poor, with low costs they generally exhibit large active areas. Semi- conductor detectors (in layer analysis almost exclusively Si-PIN diodes and Si-drift chamber detectors are used) have a significantly better energy resolu- tion, however, costs are higher and the active areas are significantly smaller. Their use is therefore limited to applications where a high energy resolution, due to strong overlap of peaks in the spectrum or due to low detection lim- its, is required. The increasing complexity of the measurement applications and ever thinner layers will most likely lead to greater use of semiconductor detectors in the future.
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580 V. R¨oßiger and B. Nensel Anode Cathode Au = 751.3 X-ray tube Mirror Video camera Detector Sample Collimator Spectrum Fig. 7.97. XRFA instrument for layer analysis. Primary radiation generated by the X-ray tube is laterally limited by a collimator or an X-ray optics, such that a defined area of the sample is excited. Using a video camera, the sample can be observed dur- ing measurement. Instrument equipped with a programmable, motorized measuring stage, measurement can be easily automated to cover several samples or several spots of one sample. Detector registers fluorescence radiation that is converted into a spectrum by suitable electronics. Spectrum is used by evaluation program as the basis for the computation of the result values. Representing a typical instrument, the Fischerscope X-ray XDAL is shown above. Equipped with a PIN diode with Peltier cooling as the detector. X-ray source is a microfocus tube with a W-anode that operates at a maximum of 50 kV and 50 W. Measurement example of Fig. 7.89 as well as several applications of Sect. 7.4.4 refer to this instrument
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Methodological Developments and Applications 581 Fig. 7.98. Video image of a bond pad. Instrument: FISCHERSCOPE XDVM- µ . The size of the shown measurement spot is 0.04 mm × 0.05 mm Table 7.11. Comparison of proportional counter tubes and semiconductor detec- tors. The given numbers are typical values Proportional Si drift Property counter Si PIN chamber Si(Li) Energy resolution (FWHM) for Mn-K α 900 eV 180 eV 150 eV 125 eV Effective entrance window 10 cm 2 5–25 mm 2 5–10 mm 2 10–100 mm 2 Solid angle Ω 0.05 sr 0.005 sr 0.002 sr 0.01 sr Cooling None Peltier Peltier Liquid Nitrogen X-Ray Source – Beam Guidance and Measurement Spot The system consisting of X-ray source and beam guidance system determines the intensity of the fluorescence radiation emitted by the sample, and therefore the repeatability of the measurement. At the same time, they define size and
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