1. Surface Analysis Laboratory, Department of Mathematics and Physics and INFN; Roma Tre University; Via della Vasca Navale 84 00146 Rome Italy
2. Department of Engineering and INFN; Roma Tre University; via Vito Volterra 62 00146 Rome Italy
3. Department of Industrial Engineering; University of Rome Tor Vergata; via del Politecnico 1 00133 Rome Italy
4. Istituto Superiore per la Conservazione ed il Restauro; Via di San Michele 23 00153 Rome Italy