SNMS, analytical method

If the secondary ion component is indeed negligible, the measured SNMS ion currents will depend only on the ionizing mode, on the atomic properties of the sputtered atoms, and on the composition of the sputtered sample. Matrix characteristics will have no effect on the relative ion currents. SNMS analysis also provides essentially complete coverage, with almost all elements measured with equal facility. All elements in a chemically complex sample or thin-film structure will be measured, with no incompleteness due to insensitivity to an important constituent element. Properly implemented SNMS promises to be a near-universal analytical method for solids analysis. 

The application of SIMS, SNMS, SSMS and GDMS in quantitative trace analysis for conducting bulk material is restricted to matrices where standard reference materials (SRMs) are available. For quantification purposes, the well characterized multi-element SRMs (e.g., from NIST) are useful. In Table 9.5 the results of the analysis by SNMS and the RSCs (relative sensitivity coefficients) for different elements in a low alloy steel standard (NBS 467) are compared with those of SSMS. Both solid-state mass spectrometric techniques with high vacuum ion sources allow the determination of light non-metals such as C, N, and P in steel, and the RSCs for the elements measured vary from 0.5 to 3 (except C). RSCs are applied as a correction factor in the analytical method used to obtain... 

In general, the nnmber of experimental points m is larger (often mnch larger) than the nnmber of adjustable parameters. The resulting function is not an exact fit to each point bnt represents a best overall fit in the sense that the snm of the sqnares of the deviations [y,(obs) ycaic( i)] is a minimnm, hence the name. The fitting function y(x) obtained by least sqnares can be differentiated, integrated, set eqnal to zero and solved to find roots, etc., by analytical methods. Thns there is no need for the apphcation of other numerical methods imless the function is very awkward to handle analytically in closed form. 

The SIMS analytical ion signal of a specific element or isotope also can be enhanced by selective ionization of particular atoms, and the detection limit for that element thereby improved. This mode of SNMS is important to specific applications, but it lacks the generality inherent in nonselective SNMS methods. The focus of this article will be on the methods for obtaining complete, accurate, and matrix-independent compositions of chemically complex thin-film structures and materials. 

Different analytical procedures have been developed for direct atomic spectrometry of solids applicable to inorganic and organic materials in the form of powders, granulate, fibres, foils or sheets. For sample introduction without prior dissolution, a sample can also be suspended in a suitable solvent. Slurry techniques have not been used in relation to polymer/additive analysis. The required amount of sample taken for analysis typically ranges from 0.1 to 10 mg for analyte concentrations in the ppm and ppb range. In direct solid sampling method development, the mass of sample to be used is determined by the sensitivity of the available analytical lines. Physical methods are direct and relative instrumental methods, subjected to matrix-dependent physical and nonspectral interferences. Standard reference samples may be used to compensate for systematic errors. The minimum difficulties cause INAA, SNMS, XRF (for thin samples), TXRF and PIXE. 

For the general case where axx ocyy, there are no analytical solutions, and the only possible approach to determine the quantized subband energy Snm from Eq. (5) is through numerical methods (Lin etal, 2000c). In this instance, a mesh consisting of M concentric circles and N sectors is created within the wire cross section, as shown in Fig. 13. The differential equation of Eq. (5) is then transformed to a set of difference equations based on the grid points on... 

In recent years, SNMS has evolved into an important tool for the characterisation of surfaces and thin films [210-217]. Mathieu et al. [217] have reviewed the different post-ionisation methods and the analytical use of SNMS in comparison with SIMS. A textbook is also available [5]. 

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