Backscattering analysis limitations

Ion Induced x-ray. Auxiliary techniques may be used to obviate some of the difficulties or limitations of backscattering analysis outlined above. One such technique is ion induced x-ray analysis, a relatively simple technique to apply in an... 

Because X-ray counting rates are relatively low, it typically requires 100 seconds or more to accumulate adequate counting statistics for a quantitative analysis. As a result, the usual strategy in applying electron probe microanalysis is to make quantitative measurements at a limited collection of points. Specific analysis locations are selected with the aid of a rapid imaging technique, such as an SEM image prepared with backscattered electrons, which are sensitive to compositional variations, or with the associated optical microscope. 

In the analysis of EXAFS data on bimetallic clusters, we consider two EXAFS functions, one for each component of the clusters (8,12-15.17). If the treatment is limited to contributions of near-est neighbor backscattering atoms, each of the functions will consist of two terms. For a bimetallic cluster composed of elements a and b, the EXAFS associated with element a is given by the expression ... 

The distribution of species normal to the surface can be obtained nondestructively by variation of the emission angle in XPS or AES (limited to a total depth of about 50 nm), by Rutherford backscattering spectrometry (applying only to elements with Z > 10) and by nuclear reaction analysis (Z < 20 only). Depth resolution in both RBS and NRA is in the range 5-50 nm. 

This group of techniques is based upon the analysis of electrons backscattered or emitted from metal surfaces. The shallow escape depths of these particles make their use most suitable for interfacial studies since the information they bear are characteristic only of the near-surface layers on the other hand, the short mean-free paths necessitate a high-vacuum enviromnent. The major limitation has always been the possibility of stractural and compositional changes upon emersion (removal from solution under potential control) and transfer of the electrode into the UHV environment. However, numerous studies have established that the compact layer remains largely unperturbed upon emersion, " unless the emersed layer contains feebly bound non-condensed species. 

Eo, in general Rj values can be determined to an accuracy of about 0.02 A. The atomic number of the backscattering atoms cannot usually be determined to a precision better than 1, because (7t) and dj [Eq. (4)] do not show a marked dependence on Z. The present limitations in the accuracy with which Nj and Z values can be determined are especially frustrating for the characterization of metal centers in proteins. Therefore, wherever possible, the information obtained from other spectroscopic and structural techniques should be incorporated into the EXAFS analysis to help remove ambiguity. 

X-ray absorption spectroscopy is a powerful tool for nanoparticle analysis due to its selectivity and independence of sample physical state. It is limited in range to the region within about 0.5-0.7 nm of a particular (chosen) absorber atom in the structure, but can be applied to amorphous or even liquid samples. The basic theory behind the origins and analysis of the extended X-ray absorption fine structure (EXAFS) has been well described by Sayers et al. (1970, 1971) and Lee et al. (1981). with mineralogical applications detailed by Brown et al. (1988). The crucial aspect of the EXAFS spectrum is that it is formed by an electron backscattering process in the vicinity of the absorber... 

The application of ion beam analysis techniques to determine pore size and pore volume or density of thin silica gel layers was first described by Armitage and co-workers [114]. These techniques are non-destructive, sensitive and ideally suited for the analysis of thin porous films such as membrane layers (dense support is needed for backscattering). However, apart from a more recent report on ion-beam analysis of sol-gel films [115] using Rutherford backscattering and forward recoil spectrometry, ion beam techniques have not been developed further despite their potential for membrane characterisation. This is probably due to the limited availability of ion beam sources, such as charged particles accelerators. 

SIMS Is more sensitive than the other common surface or Interface analysis techniques of Auger X-ray Photoelectron Spectroscopy Rutherford BackscatterIng Spectroscopy or Energy Dispersive X-ray Analysis. Detection limits and background signal levels for a large number of semiconductor materials have been reported under typical operating conditions (Ji). Table I lists the detection limits for a number of dopants used In semiconductors obtained under optimized conditions. 

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