Scattered ion intensity

Practically it is more convenient to measure intensity ratios instead of absolute intensities. Thus, e.g., Cu may serve as a reference material, relative to which the ion intensities back-scattered from the atoms of the surface under consideration are measured ... 

We discuss briefly the factors that determine the intensity of the scattered ions. During collision, a low energy ion does not penetrate the target atom as deeply as in RBS. As a consequence, the ion feels the attenuated repulsion by the positive nucleus of the target atom, because the electrons screen it. In fact, in a head-on collision with Cu, a He+ ion would need to have about 100 keV energy to penetrate within the inner electron shell (the K or Is shell). An approximately correct potential for the interaction is the following modified Coulomb potential [lj ... 

In ISS, like in SIMS, gas ions such as helium or neon are bombarded on the sample surface at a fixed angle of incident. The ISS spectrum normally consists of a single peak of backscattered inelastic ion intensity at an energy loss that is characteristic of the mass of surface atom. From the pattern of scattered ion yield versus the primary ion energy, information about elements present on the sample surface can be obtained at ppm level. 

The spectrometer is used to record the intensity of the scattered ions as a function of their energy. 

Figure 8.4 Distribution of peptide cluster intensities for control and PMA-treated U937 cells (w = 3). (a) Scatter plot of ion intensity for peptide clusters reproducibly detected in at least 2 replicates. The dotted lines show the 3-fold change in abundance, (b) Expression plot showing the number of down-regulated (30.0%), up-regulated (24.6%) and unaffected (45.6%) peptide clusters from a total of 9756 peptide clusters. Conditions as for Figure 8.3 for SCX/C18 separation. Replicate injections of 1.5 pg of protein digest from control and PMA-treated U937 cells were injected on two-dimensional nanoLC-chip-MS systems.

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