Energy dispersive x-ray reflectometry as a unique laboratory tool for investigating morphological properties of layered systems and devices

The principles and technical aspects of the laboratory energy dispersive x-ray reflectometry technique (EDXR) are reviewed. X-ray reflectometry enables us to retrieve information on the morphological parameters (film thickness, surface and interface roughness) of thin films, layered materials and devices at the angstrom resolution. In the energy dispersive mode it makes use of a polychromatic beam and the energy scan is carried out by means of an energy sensitive detector, allowing us to keep the experimental geometry unchanged during data collection. The advantages offered by the technique, in particular when accurate time-resolved studies are to be performed, are outlined. An overview of the most significant works in the field is also reported, in order to present the wide range of its possible applications. The paper was written taking into account the necessity to provide a comprehensive description of this unusual laboratory technique. The first part of the manuscript is, therefore, devoted to the general aspects of EDXR: theoretical bases, experimental characteristics, advantages and drawbacks in comparison with alternative techniques, instrumental effects that may occur and information that can be gained by its application. In the second part of the paper, we resume the main literature results obtained by applying it to a variety of systems, to show examples of the possibilities it offers. Among the experiments reported, in particular much emphasis is given to the time-resolved in situ ones (for example, devices upon working and systems undergoing morphological modifications), which probably represents the most original use of this method.