Investigation of Room Temperature Formation of the Ultra-Hard Nanocarbons Diamond and Lonsdaleite

Diamond is an attractive material due to its extreme hardness, high thermal conductivity, quantum optical, and biomedical applications. There is still much that is not understood about how diamonds form, particularly at room temperature and without catalysts. In this work, a new route for the formation of nanocrystalline diamond and the diamond-like phase lonsdaleite is presented. Both diamond phases are found to form together within bands with a core-shell structure following the high pressure treatment of a glassy carbon precursor at room temperature. The crystallographic arrangements of the diamond phases revealed that shear is the driving force for their formation and growth. This study gives new understanding of how shear can lead to crystallization in materials and helps elucidate how diamonds can form on Earth, in meteorite impacts and on other planets. Finally, the new shear induced formation mechanism works at room temperature, a key finding that may enable diamond and other technically important nanomaterials to be synthesized more readily.Portions of this work were performed at HPCAT (Sector 16) and GeoSoilEnviroCARS (The University of Chicago, Sector 13), Advanced Photon Source (APS), Argonne National Laboratory. HPCAT operations were supported by DOE-NNSA under Award No. DE-NA0001974, with partial instrumentation funding by NSF. GeoSoilEnviroCARS is supported by the National Science Foundation – Earth Sciences (EAR – 1634415) and Department of Energy- GeoSciences (DE-FG02-94ER14466). The Advanced Photon Source is a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. D.G.M., B.H., R.B. and D.R.M. would like to acknowledge the support from the Australian Research Council (ARC) Discovery Project scheme (DP170102087). J.E.B. would like to acknowledge the Australian Research Council (ARC) for ARC Discovery Project scheme (DP190101438). B.H. and R.B. were supported by resources at the Spallation Neutron Source (SNS) and the High Flux Isotope Reactor (HFIR), DOE Office of Science User Facilities operated by the Oak Ridge National Laboratory (ORNL). ORNL is funded under DOE-BES contract number, DE-AC05-00OR2272