X-Ray Photoelectron Spectroscopy (XPS) and X-Ray Absorption Spectroscopy (XAS) provide unique knowledge on the electronic structure and chemical properties of materials.
Unfortunately this information is scarce when investigating solid/liquid interfaces, chemical or photochemical reactions in ambient conditions because of the short electron inelastic mean free path (IMFP) that requires a vacuum environment, which poses serious limitation on the application of XPS and XAS to samples operating in atmosphere or in the presence of a solvent. One promising approach to enable the use of conventional electron spectroscopies is the use of thin membrane, such as graphene (Gr), which is transparent to both X-ray photons and photoelectrons. For these purposes, this work proposes an innovative system based on sealed Gr nanobubbles (GNBs) on a titanium dioxide TiO2 (100) rutile single crystal filled with the solution of interest during the fabrication stage (Figure 1a).
The formation of irregularly shaped vesicles with an average height of 6 nm and lateral size of a few hundreds of nanometers was proved by using a multi-technique approach involving Atomic Force Microscopy (AFM, see Figure 1b,c,d), Raman (Figure 1e) and synchrotron radiation spectroscopies (Figure 2), which have unequivocally demonstrated the presence of water inside the GNBs and the transition to a flat Gr layer after water evaporation by thermal heating up to 350 °C in ultra high vacuum (UHV).