Converting glassy carbon into amorphous diamond

Joint Event on 2^nd Edition of Graphene & Semiconductors | Diamond Graphite & Carbon Materials Conference & 6^th Edition of Smart Materials & Structures Conference

April 16-17, 2018 Las Vegas, Nevada, USA

Zhidan Zeng, Jianguo Wen, Qiaoshi Zeng, Hongwei Sheng, Wenge Yang and Ho-kwang Mao

Center for High Pressure Science and Technology Advanced Research (HPSTAR), China
Argonne National Laboratory, USA
Carnegie Institution of Washington, USA

Posters & Accepted Abstracts: J Material Sci Eng

Abstract :

Diamond owes its unique mechanical, thermal, optical, electrical, chemical, and biocompatible materials properties to its complete sp3-carbon network bonding. Crystallinity is another major controlling factor for materials properties. Although other Group-14 elements silicon and germanium have complementary crystalline and amorphous forms consisting of purely sp3 bonds, purely sp3-bonded tetrahedral amorphous carbon has not yet been obtained. In 2011, Lin et al found that glassy carbon was converted into a new carbon allotrope with a fully sp3-bonded amorphous structure under high pressure of about 45 gpa. However, the transition was reversible upon releasing pressure. In this study, by using a diamond anvil cell coupled with in situ laser heating, we explore a P-T range rarely studied before for the carbon system. Using glassy carbon as a starting material, we synthesize an sp3bonded tetrahedral amorphous carbon which can be recovered to ambient conditions, i.e. Quenchable amorphous diamond. With the aberration-corrected TEM, some fragmented curved graphene can be observed in the amorphous carbon (Fig. 1a). The EELS of glassy carbon shows a sharp pre-peak at ~285 ev that corresponds to Ï�? bonding, as a result of its nearly 100% sp2 bonds. This pre-peak is not present in the EELS of the nanocrystalline diamond due to its purely sp3 bonds. Similarly, the EELS pattern of the recovered carbon sample has no pre-peak, implying its atoms should be fully sp3-bonded like those in crystalline diamond. This amorphous carbon form converted from glassy carbon is fully sp3-bonded, optically transparent, dense, and is named quenchable â�?�?amorphous diamondâ�?. The structure, bonding, and properties of quenchable amorphous diamond are investigated using XRD, high-resolution transmission electron microscopy, electron energy loss spectroscopy, and ab initio molecular dynamics simulation. Amorphous diamond is optically transparent, dense, and shows ultrahigh incompressibility (bulk modulus) comparable to crystalline diamond. Jwen@anl.gov