X-ray fluorescence total reflection

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. 

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. 

XRF is closely related to the EPMA, energy-dispersive X-Ray Spectroscopy (EDS), and total reflection X-Ray Fluorescence (TRXF), which are described elsewhere in this encyclopedia. Brief comparisons between XRF and each of these three techniques are given below. 

Vol. 140. Total Reflection X-Ray Fluorescence Analysis. By Reinhold Klockenkamper... 

Method abbreviations D-AT-FAAS (derivative flame AAS with atom trapping), ETAAS (electrothermal AAS), GC (gas chromatography), HGAAS (hydride generation AAS), HR-ICP-MS (high resolution inductively coupled plasma mass spectrometry), ICP-AES (inductively coupled plasma atomic emission spectrometry), ICP-MS (inductively coupled plasma mass spectrometry), TXRF (total reflection X-ray fluorescence spectrometry), Q-ICP-MS (quadrapole inductively coupled plasma mass spectrometry)... 

XiE M, Von Bohlen A, Klockenkamper R, Jian X, Gunther K (1998) Multielement analysis of Chinese tea (Camellia sinensis) by total reflection X-ray fluorescence. Z Lebensm Unters Forsch 207A 3i-38. 

Kelko-Levai, A., Varga, I., Zih-Perenyi, K., and Lasztity, A., Determination of trace elements in pharmaceutical substances by graphite furnace atomic absorption spectrometry and total reflection X-ray fluorescence after flow injection ion-exchange preconcentration, Spectrochim. Acta Pt. B, 54, 827, 1999. 

Prange et al. [809,810] carried out multielement determinations of the stated dissolved heavy metals in Baltic seawater by total reflection X-ray fluorescence (TXRF) spectrometry. The metals were separated by chelation adsorption of the metal complexes on lipophilised silica-gel carrier and subsequent elution of the chelates by a chloroform/methanol mixture. Trace element loss or contamination could be controlled because of the relatively simple sample preparation. Aliquots of the eluate were then dispersed in highly polished quartz sample carriers and evaporated to thin films for spectrometric measurements. Recoveries (see Table 5.10), detection limits, and reproducibilities of the method for several metals were satisfactory. 

Haarich et al. [ 811 ] applied total reflection X-ray fluorescence spectrometry to the determination of a wide range of miscellanous metals in seawater. 

Fluorescence, 3 256 22 716. See also EDXRF instruments Micro X-ray fluorescence (MXRF) analysis Total reflection X-ray fluorescence spectrometry micro X-ray, 26 437-439 Raman scattering and, 21 324, 325 sensors using, 22 271... 

Total reflection X-ray fluorescence spectrometry, 26 435-437 Total sideband suppression (TOSS) technique, 23 741 Total site pinch analysis, 20 751 Total solids flux, in thickener design and scale-up, 22 58... 

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... 

Fig. 7.18. Instrumental arrangement for the measurement of total reflection x-ray fluorescence. The x-rays from the source (A) are allowed to impinge on the sample mounted on a reflector plate (B). Most of the incident radiation bounces off the sample (C), but some results in the production of XRF (D), which is measured by the detector (E).

Garcia-Heras, M., Blackman, M. J., Fernandez-Ruiz, R., and Bishop, R. L. (2001). Assessing ceramic compositional data a comparison of total reflection X-ray fluorescence and instrumental neutron activation analysis on Late Iron Age Spanish Celtiberian ceramics. Archaeometry 43 323-347. 

Vazquez C, Boeykens S, Bonadeo H (2002) Total reflection X-ray fluorescence polymer spectra classification by taxonomy statistic tools. Talanta 57 1113-1117... 

In addition to the electrochemical techniques, many surface analytical techniques are constantly in use, such as ellipsome-try for the surface thin oxide thickness, multiple reflection infrared spectroscopy (MIR), and X-ray photoelectron spectroscopy (XPS) for surface layer composition, total reflection X-ray fluorescence spectroscopy (TXRFS) for the metal surface contaminants, and naturally atomic force microscopy (AFM) for the surface roughness profile. 

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... 

---