Grazing incidence X-ray fluorescence

Bensaid A, Patrat G, Brunei M, de Bergevin F, Herino R (1991) Characterization of porous silicon layers by grazing- incidence X-ray fluorescence and diffraction. Solid State Commun 79 923-928... 

Grazing-incidence X-ray Fluorescence (GIXRF) E, layer thickness 3 nm-1 /zm 0.3-100 nm 1 cm ZJ... 

Fig. I. Schematic sketch of the grazing incidence X-ray fluorescence experiment.

The surface composition of alkali-halide mixtures has been determined using grazing incidence X-ray fluorescence in Ref. 28. Salts of high... 

Grazing incidence X-ray fluorescence is able to directly determine the surface composition for concentrations ranging from 0.01 M to 1 M under ambient conditions. Coupled with competitive adsorption in mixtnres of salts, this method has the unique ability to distinguish very short-range couplings at the A level. However, it lacks depth sensitivity below abont 5 nm. At solid/solution interfaces, such a sensitivity can be obtained by using the X-ray standing waves technique. 

An advantage of the technique is that different spectroscopies, e.g. fluorescence or photoelectrons, can be used. In case fluorescence is used, a full spectrum including fluorescence and elastic scattering is recorded for each value of the grazing angle of incidence 9 as previously described for the grazing incidence X-ray fluorescence at the air-solntion interface. 

Grazing-incidence X-ray Absorption Emission Spectroscopy 307 interface fluorescence vs. incidence angle... 

Posedel D, Turkovic A, Dubcek P, Cmjak-Orel Z (2002) Grazing-incidence X-ray reflectivity on nanosized vanadium oxide and V/Ce films. Mat. Sci. Eng. 90 154-162 Prange A, Boddeker H, Kramer (1993) Determination of trace elements in river water using total-reflection X-ray fluorescence. Spectrochim Acta 48 207-215 Prange A, Kramer K, Reus U (1993) Boron nitride carriers for total reflection X-ray fluorescence. Spectrochim Acta 48 153-161... 

It needs to be mentioned here that many other experimental techniques are available for studying monolayers at the air-water interface. Most frequently, surface potential is measured to evaluate the molecular orientation of amphiphiles at the interface. This method is, however, better suited to the study of small molecules. Polymeric amphiphiles, due to their conformational dynamics, are difficult to analyze and simple dielectric layer models do not apply, or produce large errors. Grazing incidence X-ray diffraction provides information on molecular packing, and spectroscopic methods are used to study molecular interactions and the structural changes of molecules upon compression. Fluorescence microscopy is useful for studying two-dimensional organization of small molecular mass amphiphiles however, it is not applied to polymer monolayers. For a more comprehensive overview of experimental methods used to study monolayers at the air-water interface, the reader is referred to more specialized articles, e.g. [18]. 

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. 

We prepared thin film Pt alloy electrodes by Ar-sputtering Pt and the second metal targets simultaneously onto a disk substrate at room temperature (thickness approximately 200 nm). The resulting alloy composition was determined by gravimetry and X-ray fluorescent analysis (EDX). Grazing incidence (i7= 1°) X-ray diffraction patterns of these alloys indicated the formation of a solid solution with a face-centered cubic (fee) crystal stmeture. 

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... 

Schwenke H, Beaven PA, Knoth J (1999) Applications of total reflection X-ray fluorescence spectrometry in trace element and surface analysis. Fresenius J Anal Chem 365 19-27 Towle SN, Brown GE, Parks GA (1999a) Sorption of Co(II) on metal oxide surfaces I. Identification of specific binding sites of Co(II) on (110) and (001) surfaces of Ti02 (rutile) by grazing-incidence XAFS spectroscopy. J Coll Interface Sci 217 299-311... 

A narrow beam of X-rays is directed at a flat sample at grazing incidence, typically less than 10 mrad, so that total external reflection of the X-rays occurs. As a result the X-rays only penetrate the top few atomic layers, where they excite X-ray fluorescence. The emitted photons are then detected with a Si(U) detector. Fluorescence detection is extremely sensitive to very low content (1 part in 10 for transition... 

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