1. Key Laboratory for Advanced Materials Processing TechnologyMinistry of Education of ChinaState Key Laboratory of TribologyDepartment of Mechanical EngineeringTsinghua University Beijing 100084 P. R. China
2. Department of ChemistryTsinghua University Beijing 100084 P. R. China
3. School of Chemistry and Chemical EngineeringBeijing Institute of Technology Beijing 100081 P. R. China