Total Reflection X-ray Fluorescence Analysis TXRF

Since then, TXRE has become the standard tool for surface and subsurface microanalysis [4.7-4.11]. In 1983 Becker reported the angular dependence of X-ray fluorescence intensities in the range of total reflection [4.12]. Recent demands have set the pace of further development in the field of TXRE - improved detection limits [4.13] in combination with subtle surface preparation techniques [4.14, 4.15], analyte concentrations extended even to ultratraces (pg) of light elements, e. g. A1 [4.16], spe-dation of different chemical states [4.17], and novel optical arrangements [4.18] and X-ray sources [4.19, 4.20]. 

Eor information on both the history and principles of, and future trends in, XRE, please refer to the artide by Jenkins in this book. Eor TXRE see the outstanding handbook by Klockenkamper [4.21] and current reviews [4.22-4.24]. This contribution relies extensively on these referenced works. 

The basis of XRE analysis is the photoelectric absorption and the subsequent emission of X-ray photons characteristic of the fingerprints of analyte atoms in the sample. Element composition can be quantified by the relative intensities of the indivi- 

In X-ray spectrometry, attenuation, deflection and interference must be considered. Attenuation is described by the well-known Lambert-Beer law and the mass attenuation coefficient as given for conventional XRF. 

Practical X-ray energies do not exceed 100 keV. The primary beam is mainly attenuated by the photoelectric effect. Scattering, both elastic (Rayleigh) and inelastic (Compton), represents a minor contribution to attenuation at energies below 100 keV. 

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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. 

Similar to the analytical procedure for trace analysis in high purity GaAs wafers after matrix separation, discussed previously,52 the volatilization of Ga and As has been performed via their chlorides in a stream of aqua regia vapours (at 210 °C) using nitrogen as the carrier gas for trace/matrix separation.58 The recoveries of Cr, Mn, Fe, Ni, Co, Cu, Zn, Ag, Cd, Ba and Pb determined after a nearly quantitative volatilization of matrix elements (99.8 %) were found to be between 94 and 101 % (except for Ag and Cr with 80 %). The concentrations of impurities measured by ICP-DRC-MS (Elan 6100 DRC, PerkinElmer Sciex) after matrix separation were compared with ICP-SFMS (Element 2, Thermo Fisher Scientific) and total reflection X-ray fluorescence analysis (TXRF Phillips). The limits of detection obtained for trace elements in GaAs were in the low ngg-1 range and below.58... 

The loaded filters were digested with nitric acid under pressure at 160 °C. The quantitative determination of the concentrations of 23 trace elements (As, Ba, Ca, Cd, Cr, Cu, Fe, K, Mn, Mo, Ni, Pb, Rb, S, Sb, Se, Sn, Sr, Ti, V, Y, Zn, and Zr) was performed by total-reflection X-ray fluorescence analysis (TXRF) after addition of an internal Co standard [STOSSEL, 1987 MICHAELIS, 1988]. Further details of the sampling method and the trace analysis were given in [MICHAELIS and PRANGE, 1988]. 

Neumann, C., Eichinger, P. (1991) Ultra-trace analysis of metaUic contaminations on silicon wafer surfaces by vapour phase decomposition/total reflection X-ray fluorescence (VPD/TXRF). Spectrochimica Acta Part B Atomic Spectroscopy, 46,1369-1377. 

Analysis by total-reflection X-ray fluorescence spectrometry (TXRF)... 

Three techniques involving the use of X-ray emission to obtain quantitative elemental analysis of materials are described in this chapter. They are X-Ray Fluorescence, XRF, Total Reflection X-Ray Fluorescence, TXRF, and Particle-Induced X-Ray Emission, PIXE. XRF and TXRF use laboratory X-ray tubes to excite the emission. PIXE uses high-energy ions from a particle accelerator. 

Total reflection x-ray fluorescence (TXRF) has become very popular for the conduct of microanalysis and trace elemental analysis [77-79]. TXRF relies on scatter properties near and below the Bragg angle to reduce background interference, and to improve limits of detection that can amount to an order of magnitude or moreover more traditional XRF measurements. As illustrated in Fig. 7.18, if x-rays are directed at a smooth surface at a very small angle, virtually all of the radiation will be reflected at an equally small angle. However, a few x-rays will excite atoms immediately at the surface, and those atoms will emit their characteristic radiation in all directions. One obtains very clean... 

Detection limits are presented for 61 elements by ten analytical determinative methods FAAS flame atomic absorption spectrometry ETAAS electrothermal atomization atomic absorption spectrometry HGAAS hydride generation atomic absorption spectrometry including CVAAS cold vapor atomic absorption spectrometry for Hg ICPAES(PN) inductively coupled plasma atomic emission spectrometry utilizing a pneumatic nebulizer ICPAES(USN) inductively coupled plasma atomic emission spectrometry utilizing an ultrasonic nebulizer ICPMS inductively coupled plasma mass spectrometry Voltammetry TXRF total reflection X-ray fluorescence spectrometry INAA instrumental activation neutron analysis RNAA radiochemical separation neutron activation analysis also defined in list of acronyms. 

Klockenkamper R, von Bohlen A (1996) Elemental analysis of environmental samples by total reflection X-ray fluorescence—a review. X-ray Spectrom. 25 156-162 Knoth J, Prange A, Reus U, Schwenke H (1999) A formula for the background in TXRF as a function of the incidence angle and substrate material. Spectrochim Acta 54 1513-1515 Krivan V, Schneider G, Baumann H, Reus U (1994) Multi-element characterization of tobacco smoke condensate. Fresenius J Anal Chem 348 218-225... 

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... 

In order to evaluate possible hazards for the enviroiunent and human health it is crucial to develop analytical strategies for fast and easy quantification of traces and ultra-traces of Pd in environmental matrices as well as biological tissues and fluids. Despite the efforts of numerous workgroups, a reliable method for the determination of Pd in all environmental matrices has yet to be developed. Up to date, the most important analytical methods for this task are electrothermal atomic absorption spectrometry (ETAAS), inductively coupled plasma-mass spectrometry (ICP-MS) and isotope dilution (ID)-ICP-MS, also strategies involving inductively coupled plasma-atomic emission spectrometry (ICP-AES), and electrochemical methods like anodic stripping voltammetry (ASV) have been described. Furthermore, total reflection X-ray fluorescence (TXRF) and instrumental neutron activation analysis (INAA) have been successfully employed for the determination of PGE in enviromnental matrices. 

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