TXRF spectrum

Depending on the X-ray source and the spectral modification devices, the LD are in the pg range for 2—3 kW X-ray tubes and in the fg range with excitation by means of synchrotron radiation. Figure 11.15 shows a typical TXRF spectrum the absolute detection limit values of typical TXRF instruments are shown in Fig. 11.10. Thus, TXRF permits to simultaneously determine trace elements in samples of small volume. Additional advantages are insensitivity to matrix effects, easy cahbration, fast analysis times and low cost. In practice, the method is in particular apphed for multi-element determinations in water samples of various nature and for the routine analysis of Si-wafer surfaces employed in the microelectronics industry. 

Big. 12-20. TXRF spectrum of a clean quartz glass carrier. 

A typical TXRF spectrum of a seawater sample prepared according to the procedure described here is shown in Fig. 12-29 (obtained from the seawater reference material CASS-1 see Section 12.1.6). 

Fig. 12-29. TXRF spectrum of the seawater reference material CASS-1 using W-excitation. The values are given in /

In Total Reflection X-Ray Fluorescence Analysis (TXRF), the sutface of a solid specimen is exposed to an X-ray beam in grazing geometry. The angle of incidence is kept below the critical angle for total reflection, which is determined by the electron density in the specimen surface layer, and is on the order of mrad. With total reflection, only a few nm of the surface layer are penetrated by the X rays, and the surface is excited to emit characteristic X-ray fluorescence radiation. The energy spectrum recorded by the detector contains quantitative information about the elemental composition and, especially, the trace impurity content of the surface, e.g., semiconductor wafers. TXRF requires a specular surface of the specimen with regard to the primary X-ray light. 

Figure 4 Direct TXRF (upper spectrum, recording time 3000 s) and VPD-TXRF (lower spectrum, recording time 300 s) on a silicon wafer surface. The sensitivity enhancement for Zn and Fe is two orders of magnitude. The measurements were made with a nonmonochromatized instrument.

Metrology and contamination analysis in particular have been decisive factors for profitable semiconductor production [4.47]. Semiconductor applications of TXRF go back to the late nineteen-eighties and were introduced by Eichinger et al. [4.48, 4.49]. Because of its high sensitivity, wide linear range, facile spectrum deconvolution, and... 

Lagarde P, Delaunay R, Flank AM, Jupille J (1993) Site of sulfur impurities in silicate glasses and REFLEXAFS studies around the Si -edge. Jap J Appl Phys 32 619-621 Lee PA, Citrin PH, Eisenberger PM (1981) Extended X-ray absoption fine structure-its strength and limitations as a structural tool. Rev Mod Phys 53 769-806 Lee JM, Yoo H-H, Joo M (1999) Numerical determination of a true absorption spectrum from grazing-incidence fluorescence EXAFS data. J Synchrotron Rad 6 244-246 Lieser KH, Flakowski M, Hoffman P (1994) Determination of trace elements in small water samples by total reflection X-ray fluorescence (TXRF) and by neutron activation analysis (NAA). Fresenius J Anal Chem 350 135-138... 

Fig. 11.15 Energy-dispersive XRF spectrum of a multi-element standard, obtained in a TXRF spectrometer.

The general instrumental set-up for TXRF spectrometry is quite simple with an X-ray source, a reflector or monochromator, a second reflector, acting as sample support or sample itself, and a detector. A low pass filter to reduce the high-energy part of the X-ray spectrum has to be inserted in the path of the... 

Figure 8.17 (a) Schematic drawing of a TXRF system. From left to right is the X-ray source, the synthetic multilayer monochromator (Section 8.2.3.2), the thin sample on a support, the silicon drift detector (SDD) above the sample, and finally a beam stop, (b) A commercial TXRF spectrometer, the Bruker S2 PICOFOX with its laptop computer. The displayed spectrum shows the high S/N ratio. ( 2013 Bruker, Inc. www.bruker.com. Used with permission.)... 

It is obvious that the sample preparation technique used influences the detection limits. Table 1 shows this influence on various samples from different fields of application. Table 2 gives an overview of applications of TXRF already analysed. Figure 3 shows a spectrum of a water standard reference sample (NIST 1643c) obtained with a TXRF vacuum chamber, constructed at Atominstitut, Vienna. Generally, an excellent field of application of TXRF in trace element analysis can be seen in liquid samples. All kinds of liquids, ranging from different kinds of water to acids and oils, as well as body fluids, can be analysed. Environmental samples, like airborne particles, plant material or medical and biological samples such as tissue can be analysed directly on a reflector. 

Figure 3 Spectrum of water sample, NIST 1643c standard reference material, 10 o,L, dried on a quartz reflector, measured with the TXRF vacuum chamber of Atominstitut, Mo monochromatic excitation, 40 kV, 50 mA, 1000 s concentration values of respective elements given in j.g L- ...

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