1. Department of MaterialsUniversity of Oxford Parks Road Oxford OX1 3PH UK
2. Institute of Materials Research and EngineeringAgency for Science, Technology and Research (A*STAR) 2 Fusionopolis Way 138634 Singapore
3. Clarendon LaboratoryDepartment of PhysicsUniversity of Oxford Parks Road Oxford OX1 3PU UK
4. Department of Engineering SciencesUniversity of Oxford Parks Road Oxford OX1 3PJ UK
5. Optoelectronics Research CentreUniversity of Southampton Southampton SO17 1BJ UK
6. Diamond Light SourceHarwell Science and Innovation Campus Didcot Oxfordshire OX11 0DE UK
7. Department of Materials Science and EngineeringNational University of Singapore 9 Engineering Drive 1 117575 Singapore