High-Pressure Tetrahedral Amorphous Carbon Synthesized by Compressing Glassy Carbon at Room Temperature

Tetrahedral amorphous carbon(ta-C) thin films with high sp(3) fraction have extraordinary mechanical properties and wide applications. Despite intensive effort to increase the thickness of ta-C thin films in the past decades, bulk ta-C has not been achieved until date. In this study, by compressing a sp(2)-bonded amorphous carbon (glassy carbon) up to 93 GPa, we demonstrate that the formation of bulk ta-C is possible at high pressures and room temperature. We studied the atomic structure, stability, and mechanical properties of the ta-C synthesized under high pressure using in situ high-pressure X-ray diffraction and large-scale first-principles calculations. The high-pressure ta-C is mainly tetrahedrally bonded, with relatively large distortions in the sp(3) C-C bonds. It can be preserved to approximately 8.5 GPa during pressure release, below which it transforms to disordered glassy carbon, accompanied by sp(3)-to-sp(2) transition. Moreover, both the experiment and simulation show that the high-pressure ta-C has a high bulk modulus (363 +/- 29 GPa, experimental) even comparable to diamond. These results deepen our understanding of amorphous carbon and help guide the synthesis of novel carbon materials using high pressure.