1. Department of Chemistry, MOE Key Laboratory of Bioorganic Phosphorus Chemistry & Chemical BiologyTsinghua University Beijing 100084 P. R. China
2. Applied Mechanics Laboratory, Department of Engineering Mechanics and Center for Nano and Micro MechanicsTsinghua University Beijing 100084 P. R. China
3. Key Laboratory of Bio-Inspired Smart Interfacial Science and Technology of Ministry of EducationSchool of ChemistryBeihang University Beijing 100191 P. R. China
4. Centre of Soft Matter Physics and Its ApplicationsBeihang University Beijing 100191 P. R. China
5. Key Laboratory for Advanced Materials Processing TechnologyMinistry of Education of ChinaState Key Laboratory of TribologyDepartment of Mechanical EngineeringTsinghua University Beijing 100084 P. R. China