The quantitative technique for the first atomic layer
Low Energy Ion Scattering (LEIS) yields quantitative information on the elemental composition (from Be) of the outermost atomic layer of a sample. It is the most surface specific chemical analysis technique of all.
Details on LEIS
Quantitative element compsition of the outer atomic layer
In LEIS analysis, the surface is bombarded with noble gas ions of a few keV energy. The energy of the ion after a collission with a surface atom is a measure for the mass of this atom. Therefore, the energy of the ions scattering from a surface is a measure of the elements (from Be) that are present. Detection limits in the ppm range for heavy and in the percentage range for light elements can be achieved, due to the use of modern double toroidal analyzers. Particles scattered from deeper layers (max. 10 nm) show up as background signals that are characteristic for the element occurance in these layers. As a result, the concentration profile of the element is accessible (static depth profiling), leading to valuable information, e.g. on the thickness of films.
Conducting LEIS analysis requires an ultra-high vacuum, so the samples must have sufficient vacuum compatibility. LEIS has no special requirements with regard to the sample topography. Therefore, atomically smooth single crystals as well as extremely rough catalyst powders can be analyzed without problems. Due to the high surface sensitivity of the method, hydrocarbons that have been adsorbed from the atmosphere during transport must usuallybe be removed from the samples. The equipment required for this pre-cleaning is an integral part of modern LEIS instruments.
- High-Sensitivity Low Energy Ion Scattering (HS-LEIS)
- Ion Scattering Spectroscopy (ISS)