Ion sputtering process

The examples cited above demonstrate a need for caution in the use of ion-sputtering as a cleaning technique in the preparation of sample surfaces for ESCA analysis the ion-sputtering process itself can produce chemical changes on the sample surface. 

Figure 32. Schematic diagram of the ion-sputtering process. (From Ref. 1(X).)...

The ion-sputtering process is statistical in nature in that the. second and subsequent atom layers may be depleted before the first layer is removed entirely. This fact leads to a progressive degradation in depth resolution with sputtering... 

Ion-beam lithography Ion beam mixing Ion beam processing Ion beams Ion-beam sputtering Ion channels Ion chromatogram Ion chromatography... 

The detection limit of each element depends upon the electron affinity or ionization potential of the element itself, the chemical nature of the sample in which it is contained, and the type and intensity of the primary ion beam used in the sputtering process. 

Because SIMS can measure only ions created in the sputtering process and not neutral atoms or clusters, the detection limit of a particular element is affected by how efficiently it ionizes. The ionization efficiency of an element is referred to as its ion yield. The ion yield of a particular element A is simply the ratio of the number of A ions to the total number of A atoms sputtered from the mixing zone. For example, if element A has a 1 100 probability of being ionized in the sputtering process—that is, if 1 ion is formed from every 100 atoms of A sputtered from the sample—the ion yield of A would be 1/100. The higher the ion yield for a given element, the lower (better) the detection limit. 

The sputtering process is frequendy used in both the processing (e.g., ion etching) and characterization of materials. Many materials develop nonuniformities, such as cones and ridges, under ion bombardment. Polycrystalline materials, in particular, have grains and grain boundaries that can sputter at different rates. Impurities can also influence the formation of surface topography. ... 

For the analysis of surfaces there are a group of ion bombardment techniques based on sputtering processes described in Ref 30 Since the spectra obtained consists mainly of adsorbed gases and radicals, these techniques are omitted from this discussion... 

Both positive and negative ions are produced during the sputtering process, and either can be recorded by an appropriate choice of instrumental parameters. Positive ions are the result of protonation, [M + H]", or cationiz-ation, [M +cation], whereas negative ions are preponderantly [M-H], but can also be formed by the addition of an anion, that is, [M+anion]". The type of pseudomolecular ion produced is governed by the chemical nature of the sample and by the composition of the matrix from which it is ionized. 

SIMS involves bombarding a material surface with a primary ion beam, with a typical energy in the keV range. Ion impacts on the surface induce a so-called collision cascade sputtering process, where the energy of the primary ions is transferred to the surface through nuclear collisions [Brunelle et al. 2005]. 

The Mg isotopic measurements were performed with a modified AEI IM-20 ion microprobe [13,14]. Secondary ions were generated by bombarding the sample with a focussed ion beam to excavate a small volume of the sample. A fraction of the sputtered material is ionized during the sputtering process and is drawn off into the mass spectrometer. A duoplasmatron ion source produces a... 

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