Surface chemistry changes, SIMS

In summary, these SIMS studies have shown that reproducible measurements of some surface chemistry changes are possible following very early attack of glass surfaces by water. Early depletions of sodium and more surprisingly, boron, are indicated even after a few minutes of leaching time. The apparent effects of surface hydration on the SIMS relative ion yields also warrants further investigation. 

On the other hand, SIMS takes advantage of the destructive nature of the ion probe. Atoms can be knocked free (sputtered) from the surface by the bombarding ions and those that become ionized are analyzed by conventional mass spectrometry I70). A large number of different kinds of ions can be emitted from the surface. The resolution is also quite good. Thus, although SIMS is not as surface sensitive as ISS, it does provide more detailed information about the surface chemistry. ISS and SIMS, therefore, complement one another. Furthermore, since the ion probe sputters away the surface that is being analyzed, the change in the chemistry of the surface as a function of depth below the surface can be studied by these techniques. 

Two types of SIMS experiment can be carried out static SIMS and dynamic SIMS. In the former case, the surface is bombarded with low energy ions and molecular and atomic fragments are produced without the experiment changing the nature of the surface appreciably the surface chemistry can therefore be investigated. Dynamic SIMS uses high energy ions to obtain highly sensitive elemental data down to ppb levels, but the structural information is lost. 

A great deal of effort has been invested in recent years in the study of the surface chemistry of Uthiated carbon anodes in Li battery electrol)de solutions. Fortunately, the basic surface reactions of a large variety of nonaqueous Li salt solutions on Li, Li-C, and noble metal electrodes polarized cathodically are very similar. The tools for the study of the surface chemistry of these systems included XPS [53], AES [54], FTIR [55], Raman [56], EDAX [57], and, recently, SIMS-TOF [58], The study of the surface chemistry of the composite electrodes used in Li-ion batteries is difficult. Hence, a previous study of the surface chemistry developed on noble metal and Li electrodes in the solutions of interest may be very helpful. It should be emphasized that the use of XPS, AES, Raman (laser beam needed), and SIMS-TOF may lead to changes in the surface species during the measurements due to further surface reactions induced by X-rays, laser beams, or bombardment by ions. 

The most common application of dynamic SIMS is depth profiling elemental dopants and contaminants in materials at trace levels in areas as small as 10 pm in diameter. SIMS provides little or no chemical or molecular information because of the violent sputtering process. SIMS provides a measurement of the elemental impurity as a function of depth with detection limits in the ppm—ppt range. Quantification requires the use of standards and is complicated by changes in the chemistry of the sample in surface and interface regions (matrix efiects). Therefore, SIMS is almost never used to quantitadvely analyze materials for which standards have not been carefiilly prepared. The depth resoludon of SIMS is typically between 20 A and 300 A, and depends upon the analytical conditions and the sample type. SIMS is also used to measure bulk impurities (no depth resoludon) in a variety of materials with detection limits in the ppb-ppt range. 

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