1. Conditions for using X-rays to study surfaces and interfaces

To obtain usable information, we have already mentioned the need to excite only the layers studied and close to the surface. Initially, we will consider the case of a perfectly flat homogeneous surface. This unrealistic case simplifies the presentation of the principle of the analysis methods and the parameters or orders of magnitude of the variables considered. In the following paragraphs, we will consider more realistic cases, i.e. surfaces with defects or superimposed layers.