[1] Xidian Univ, Sch Adv Mat & Nanotechnol, Xian 710071, Peoples R China
[2] CSIC, Inst Ciencia Mat Madrid ICMM, 2D Foundry, E-28049 Madrid, Spain
[3] Shaanxi Univ Sci & Technol, Coll Bioresources Chem & Mat Engn, Xian 710026, Peoples R China
[4] King Saud Univ, Coll Sci, Dept Chem, Riyadh 11451, Saudi Arabia
[5] King Saud Univ, Coll Sci, Dept Phys & Astron, Riyadh 11451, Saudi Arabia
[6] Univ Munster, Inst Phys, D-48149 Munster, Germany
[7] Univ Munster, Ctr Nanotechnol, D-48149 Munster, Germany
[8] Univ Nevada, Dept Phys & Astron, Las Vegas, NV 89154 USA