Abstract: Pair distribution function (PDF) analysis has become a widely used and most effective tool to study the local structure of materials that exhibit some degree of disorder. With the increasing availability of high-energy X-ray sources equipped with large and fast area detectors, PDF has advanced into the field of in situ and operando studies. Nowadays, PDF is indispensable for following processes in manifold bulk-type systems such as chemical reactors, electrochemical cells, and mechanical testing setups.
More recently, the PDF technique has also been used to investigate thin films. Different approaches to thin-film PDF have been applied, including the exfoliation of the film from the substrate to grind it up into a powder, as well as measuring the film on the substrate in transmission under normal incidence on the surface. While both of these methods are experimentally similar to bulk measurements with respect to data collection and evaluation, they have particular drawbacks. For the first method, film-specific features such as preferred orientation may be lost and the structure modified by the mechanical treatment,. The seconed method provides an unfavorable signal-to-background ratio, given that the scattering from both the film and the substrate is collected, and the thickness ratio is typically of the order of a factor 1000 (nanometer vs. micrometer range).
In this presentation, we demonstrate the advantages of surface diffraction type PDF measurements under grazing incidence (GIPDF) to quantitatively analyze thin films with thicknesses down to a few nanometers. In contrast to previous GIPDF studies, we use micro-focused high-energy X-rays (> 60 keV) and a fast area detector to obtain high-quality PDF data on the time scale of seconds to enable in situ and operando studies of thin films in real time. In a first, in situ PDF analysis of thin-film deposition, we followed the growth and strain evolution of sputtered platinum layers. This presentation highlights perspectives and challenges for future applications of GIPDF to operando and in situ thin-film studies.