1. Institut d'Electronique Fondamentale, Université Paris-Sud, UMR CNRS 8622, 91405 Orsay, France
2. Laboratorio MDM, IMM-CNR, Via C. Olivetti 2, 20864 Agrate (MB), Italy
3. Singulus Technology AG, Hanauer Landstrasse 103, 63796 Kahl am Main, Germany