Affiliation: | 1. Physics Department, Universtiy of Siegen, Walter‐Flex Str. 3, 57072 Siegen (Germany), Fax: (+49)?271‐740 37 63;2. Chemical Technology of Advanced Materials, University of WürzburgD‐97070 Würzburg (Germany);3. LDM, NUM Department, Paul Scherrer Institute, CH‐5232 Villigen‐PSI, Switzerland;4. Physics Department, Bergische University of Wuppertal, Gau?stra?e 20,D‐42097 Wuppertal (Germany) |