1. Thin Film Physics Division, Department of Physics (IFM), Linköping University, SE-581 83 Linköping, Sweden
2. Materials Science Department and Frederick Seitz Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801
3. Department of Physics, University of Illinois, Urbana, Illinois 61801
4. Department of Materials Science and Engineering, National Taiwan University of Science and Technology, Taipei 10607, Taiwan