SSIMS characteristics

In conclusion, SSIMS spectra provide not only evidence of all the elements present, but also detailed insight into molecular composition. Quasimolecular ions can be desorbed intact up to 15000 amu, depending on the particular molecule [3.17] and on whether an effective mechanism of ionization is present. Larger molecules can be identified from fragment peak patterns which are characteristic of the particular molecules. If the identity of the material being analyzed is completely unknown, spectral interpretation can be accomplished by comparing the major peaks in the spectrum with those in a library of standard spectra. 

The basic instrumental set-up for dynamic SIMS is the same as for SSIMS (Sect. 3.1.2). Depending on the intensity, beam diameter, and ion species needed, dif ferent ion sources are used. Several mass analyzers with different characteristics enable a broad field of applications. 

In a more recent application of SSIMS, the ratios M02 /M0 and M03 /MO for transition metal oxides of the type MxOy were measured to demonstrate a fingerprint spectrum characteristic of the oxidation state of the metal. The data for iron oxide were then compared to oxide found on a steel sample with an oxide film 4 nm thick. The best match was to Fe203 [115]. 

The SSIM is an objective image quality metric used for the measmement of similarity between two images based on the characteristics of the human visual system. It measures the structural similarity rather than error visibility between two images. SSIM is defined as... 

Table 1..1 lists the most relevant performance characteristics of SSIMS and SNMS, correct at the time of writing. Instrumental performance (e.g., mass resolution, lateral resolution, etc.) is always likely to improve progressively with time. 

The usefulness of SSIMS in the field of catalysis-related surface science is already well known. SSIMS studies of CO adsorption on single-crystal surfaces of Cu, Ru. Ni, Pd and Pt have been summarized briefly [45). The ob.ser-vation that different CO adsorption structures (linearly bonded, bridged, triple bridged and mixed states) can be distinguished by the characteristic MeiCO+ (-V = 1, 2, 3) secondary cluster-ion yield fractions in the SSIMS spectra, i.e.. by fingerprinting, confirms that these rather delicate structures can be identified by the method. 

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