1. Department of Physics and Research Centre OPTIMAS, University of Kaiserslautern, Erwin-Schrödinger-Straße, 67663 Kaiserslautern, Germany
2. Institute for Surface and Thin Film Analysis (IFOS) GmbH and Research Centre OPTIMAS, Trippstadter Straße 120, 67663 Kaiserslautern, Germany
3. Department of Operative Dentistry and Periodontology, University Hospital of the Saarland, 66421 Homburg, Germany