Surface charge arising from element

A SSIMS spectrum, like any other mass spectrum, consists of a series of peaks of dif ferent intensity (i. e. ion current) occurring at certain mass numbers. The masses can be allocated on the basis of atomic or molecular mass-to-charge ratio. Many of the more prominent secondary ions from metal and semiconductor surfaces are singly charged atomic ions, which makes allocation of mass numbers slightly easier. Masses can be identified as arising either from the substrate material itself from deliberately introduced molecular or other species on the surface, or from contaminations and impurities on the surface. Complications in allocation often arise from isotopic effects. Although some elements have only one principal isotope, for many others the natural isotopic abundance can make identification difficult. 

CsCl at 200°C for 14 days, is shown in Figure 4. Before this spectrum was collected, the cube was sputtered with Ar ions to remove surface contamination. Two Cs MNN transitions arise at 554 and 566 eV (6) and the larger 0 KLL peak is at 506 eV. Superimposed on Figure 4 is a spectrum of natural pollucite, recorded under the same instrument conditions and corrected for a -4 eV positional difference observed in each of the three peaks. The same charging shift was observed in the Si peaks (not shown in Figure 4), which were found at 76 eV (cube) and 72 eV (natural pollucite). Transitions from four elements, Al, Si, 0, and Cs, were observed in both spectra. Potassium was not detected in either spectrum. 

The work of charging the ion is 8 J(E /8n) dV, where E is the ionic field and dV is the volume element in which polarization due to the ionic field arises. For the volume above the surface, the charging energy contribution, if it were still the fluid of dielectric constant 8, is seen from Fig. 7 to be... 

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