[1] Dept. of Chem. Eng. and Technology, Roy. Inst. Technol. (KTH), S-100 44, Stockholm, Sweden
[2] Physics and Engineering Physics, Chalmers Univ. of Technol., S-412 96, Göteborg, Sweden
[3] Dept. of Mat. Sci. and Engineering, Univ. Sci. Technol. China, 230026 H., Anhui, China