Deborah Perco
(University of Trieste)

Describing the oxidation of solid surfaces can be straightforward, with X-ray Photoelectron Spectroscopy (XPS) being one of the most widely used experimental techniques for probing the chemical environment of atoms. However, when the size of the system is reduced to the sub-nanoscale, new complexities arise. In this seminar, I will focus on the study of the oxidation of size-selected tungsten (W), molybdenum (Mo) and tantalum (Ta) nanoclusters supported on epitaxial graphene and oxide surfaces, comparing these findings with the behavior of bulk matter. Metal nanoclusters were generated by means of ENAC (Exact Number of Atoms in each Cluster), the source developed by the Nanoscale Materials Laboratory which allows to precisely select size and charge of the desired clusters. By combining High-Resolution synchrotron-based XPS and ab initio DFT calculations, we observed that W clusters on graphene exhibit a strong relationship between core level binding energies and W-O bond lengths, driven by the non-crystallinity of the system which makes challenging assigning a proper oxidation state to W atoms. In contrast, the deposition and oxidation of W, Mo and Ta clusters on Fe3O4(001) result in a spontaneous fragmentation of the clusters, a process that occurs without the need for external driving forces. Eventually, I will discuss the future directions of this research, particularly the selection of suitable substrates for clusters deposition, with a focus on graphene grown on Ir(311) as a promising candidate.
 

Zoom registration link:
https://zoom.us/meeting/register/QRB8vEGlQPqfDMUvdEGF5w