1. Surface Analysis Laboratory INFN Roma Tre, via della Vasca Navale 84, Rome 00146, Italy
2. Department of Mathematics and Physics, Roma Tre University, via della Vasca Navale 84, Rome 00146, Italy
3. CNR-IMM, via del Fosso del Cavaliere 100, Rome 00133, Italy
4. Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Institute for Solar Fuels (EE-IF), Hahn-Meitner-Platz 1, D-14109 Berlin, Germany
5. Department of Physics, Politecnico di Milano, Piazza Leonardo da Vinci 32, I-20133 Milano, Italy
6. Department of Science, Roma Tre University, via della Vasca Navale 84, Rome 00146, Italy