Detection angle resolved PIXE and the equivalent depth concept for thin film characterization
The characterization of thin films using PIXE, although basically a simple matter, in practice suffers from significant problems. Here two case studies are presented in which the use of grazing detection geometry is shown to be a good solution. The first case study, the analysis of GaSb-InAs films deposited on a GaSb substrate, relates to the measurement of elements of atomic number close to and below that of the substrate. Problems may be due to the tail of the peaks that correspond to x-rays emitted from the substrate, and also to the presence in the substrate of an element having large x-ray emission cross-sections. The use of the simulation capability implemented on the DATTPIXE package is shown to be of good help in the proper planning of the analysis procedure. In the second case study, the distinction between film contamination and substrate material contamination is discussed. In this case the characterization of a ZnO film deposited on sapphire is presented. The concept of equivalent depth is discussed and it is shown to be an important tool for a straightforward distinction between film and bulk contamination.