Photoelectron Spectromicroscopy Through Graphene of Oxidised Ag Nanoparticles

Abstract: Performing electron based spectroscopies at ambient pressure environments, for instance, to investigate catalytic reactions, when the energy of the electrons is below 1.5 keV is extremely challenging. This limitation, known as the "pressure gap", was to some extent overcome about 15 years ago for X-ray photoelectron spectroscopy (XPS) experiments made at near ambient pressure, but only recently the first pioneering experiments at true ambient pressure with XPS have been realized. These investigations use graphene (Gr)-sealed cells to separate the ambient and vacuum environments by exploiting the properties of Gr to create a barrier for the transmission of liquids or gases and to be partially transparent to low energy photoelectrons. In such cells, the Gr membrane can be used as a bare substrate for other materials or can be an active part of a system. When nanoparticles are deposited or grown on the Gr membrane and exposed to an ambient pressure environment a raising question is if the areas of the nanoparticles directly in contact with Gr will experience the same environment conditions as the areas freely exposed to the atmospheric pressure. To answer to this question we have designed a pilot experiment where Ag nanoparticles are grown on one side of the Gr and ex-situ exposed to molecular oxygen to investigate the oxidation rate of the Ag atoms in contact with the Gr and those directly exposed to the oxygen molecules. Spatially resolved photoemission and high resolution scanning electron microscopy measurements have demonstrated that also the Ag atoms at the interface between Gr and Ag nanoparticles experiences the environment, showing, in our case, an oxidation comparable with that of the other areas of the nanoparticles. Graphical Abstract: [Figure not available: see fulltext.] © 2018, Springer Science+Business Media, LLC, part of Springer Nature.