[1] Chalmers Univ Technol, Dept Appl Phys, SE-41296 Gothenburg, Sweden
[2] Univ Karachi, Dept Phys, Karachi 75270, Pakistan
[3] Polish Acad Sci, Inst Phys, PL-02668 Warsaw, Poland
[4] Lund Univ, MAX Lab, SE-22100 Lund, Sweden
[5] Univ Skovde, Dept Life Sci, SE-54128 Skovde, Sweden