[B._Beckhoff,_et_al.]_Handbook_of_Practical_X-Ray_(b-ok.org).pdf

Lateral resolution at the micron scale is now reached

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Lateral resolution at the micron scale is now reached with a wide vari- ety of modern techniques. Secondary ion mass spectroscopy (SIMS) [44, 45] offers this resolution with excellent depth resolution as well, but is destruc- tive and quantification is difficult in many cases. Laser ablation microprobe mass analysis (LAMMA) [46, 47] is a very useful technique but suffers from the nonreproductive character of the laser-induced ionization and difficulties are often encountered in interpreting the mass spectra. Electron probe mi- croanalysis (EPMA) [48] presents extremely high lateral resolution (few nm).
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Methodological Developments and Applications 475 Unfortunately, due to the spread of the electron beam below the surface of the sample, the X-ray fluorescence spectrum arises from a sphere of about 1 µ m radius or larger. Moreover, this technique is limited to the determina- tion of major constituents because of the high background generated by the incident and secondary electrons as they slow down through the sample and only probe the surface layers due to the limited penetration depth of electrons. Micro-PIXE offers high sensitivity (down to the ppm range) and can reach the micron scale in lateral resolution [49–51] but with severe damage to sensitive samples. Micro-PIXE, however, can be easily coupled with nuclear reaction analysis (NRA) for the determination of light elements, and with Rutherford back scattering (RBS) for depth profile determination, which is of great in- terest in the characterization of many samples. Finally, all these techniques require the sample to be in vacuum which may be impossible with some very volatile, too large, or living samples. Sub µ m spatial resolution is now achievable in the hard X-ray range thanks to the advent of new X-ray optics in conjunction with SR. Thus microsyn- chrotron radiation X-ray fluorescence (micro-SRXRF) has appeared in recent years as an interesting quantitative microanalytical technique with high sen- sitivity that can be used on any kind of samples in air (except for the lightest elements). Moreover, by associating it to other techniques such as extended X- ray absorption fine structure (EXAFS), X-ray absorption near edge structure (XANES), diffraction or computed tomography (CT), very useful structural, chemical and morphological information can be obtained. 7.2.2 The General Setup The general setup of about all photon microprobes installed on synchrotron beamlines is presented in Fig. 7.24 Most of the components have been descri- bed in great detail in this book so we will only briefly justify the choices made. The Photon Source In this chapter, we only consider photon microprobes installed on SR facil- ities. As a matter of fact the brilliance of these third generation machines is so high that they represent the best sources for a very sensitive photon microprobe. Nevertheless, bending magnets or insertion devices deliver quite different X-ray beams and this has to be taken into account.
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