Studies of model systems based on cerium oxide are important to improve current understanding of the properties of ceria-based materials, which find wide application based on the ability of cerium oxide to store, release, and transport oxygen. We report a study of CeO2 ultrathin films grown on the Pt(111) surface by reactive deposition of Ce using molecular or atomic oxygen as the oxidizing gas. High-temperature treatments in O-2 allowed us to obtain epitaxial structures with a very good quality in terms of morphology, stoichiometry, and structure. The cerium oxide films have a very flat morphology with terraces several tens of nanometers wide. The stoichiometry of the films is mainly CeO2, and the concentration of Ce3+ ions in the film can be reversibly increased by temperature treatments. We propose that the Pt substrate oxidation has a determinant role for the epitaxial stabilization of ceria films

NA62 is a fixed-target experiment at the CERN SPS dedicated to measurements of rare kaon decays. Such measurements, like the branching fraction of the K+ → π+ ν ν̄ decay, have the potential to bring significant insights into new physics processes when comparison is made with precise theoretical predictions. For this purpose, innovative techniques have been developed, in particular, in the domain of low-mass tracking devices. Detector construction spanned several years from 2009 to 2014. The collaboration started detector commissioning in 2014 and will collect data until the end of 2018. The beam line and detector components are described together with their early performance obtained from 2014 and 2015 data.

Thin MgO films with a nominal thickness ranging between 1 to 60 ML have been gr own on a Mo(001) surface. The film morphology was studied by LEED and STM, revealing the presence of a coincidence pattern with the Mo support in the low coverage regime, a dislocation network at medium thickness and a rather flat and defect-poor MgO surface for thicker layers. The MgO optical properties were investigated as a function of film thickness by analyzing electroluminescence spectra obtained via electron injection from the STM tip into well-defined surface areas. The spectra are characterized by two distinct emission bands at 3.1 and 4.4 eV. Their origin is discussed in the light of earlier photo-luminescence measurements on MgO nanocubes and smokes.

Ag nanoparticles have been deposited on stoichiometric and reduced thin CeO2 films grown on Pt(111). The nucleation and growth of the Ag nanoparticles has been characterized by STM and XPS (X-ray photoemission spectroscopy) measurements complemented with DFT calculations on Ag atoms, clusters, and extended layers deposited on slab models of the CeO2(111) surface. The XPS spectra clearly show a reduction of the ceria support by Ag deposition (formation of Ce3+ ions). This is accompanied by a positive shift of the Ag 3d core levels, in which final state effects related to the finite size of the Ag deposits come into play. The DFT calculations support the view of a direct electron transfer from the Ag clusters and nanoparticles to the ceria support. Other possible origins of the reduction of the ceria substrate, like the occurrence of oxygen reverse spillover on the Ag nanoparticles, are ruled out based on energy considerations.