SchoolofMaterialsScienceandEngineering;
HebeiUniversityofTechnology;
Tianjin300130;
China;
DepartmentofAppliedPhysics;
HebeiUniversityofScienceandTechnology;
Shijiazhuang050018;
China;
DepartmentofMaterialsScienceandEngineering;
ColumbiaUniversity;
NewYork10027;
U.S.A.;