Grazing geometry

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 27.7 Grazing incidence X-ray scattering geometry. The X-rays are incident on the sample at an angle (j) and are detected at a combination of two angles 29 and 2c ). ... 

Very thin films exhibit special structure because of their confined geometry between substrate and surface. Their structure cannot be studied in a normal setup. In order to obtain enough photons on the detector, the X-ray beam must impinge on them under grazing incidence (Cf. Sects. 7.6.3.1,1.63.2, 8.8). This technique is suitably combined with microbeams. Current effort is focusing both on progress of the instrumentation and on the development of adapted analysis methods. 

Ruland and Smarsly [9,84,240] can analyze their recorded data in the classical Born approximation, but have to correct for the special geometry of the grazing incidence experiment. They propose not to carry out the necessary corrections in a... 

PBDS will also be useful in a related area for the examination of catalysts which are opaque not because of high unit absorption but because they are physically large, i.e., entire catalyst pellets. This is made possible by the favourable geometry of the apparatus and detection device. As indicated schematically in Fig. 1, the sample is merely placed at the focus of the IR beam (an off-axis elliptical mirror is used to focus the IR beam about 1 cm from the edge of the mirror) and a laser beam grazes the surface. The "sample space of the spectrometer is thus of indefinite volume and can be made as large as needed to examine massive objects (in the present apparatus, a sphere of about 20 cm diameter could be accomodated). An example is shown in Fig. 8. 

Figure 3.2 The effect of glancing incidence geometry, calculated for a 150 nm lno.5i77Gao. 4823As film on a (001) InP substrate. The symmetric 004 and the grazing incidence 044 curves are shown...

Figure 3.7 (a) Grazing incidence geometry, (b) Grazing exit geometry, (c) Symmetric scan. (Coustesy K.M.Matney)... 

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