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2
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6
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&
Journal of Material Sciences and Engineering| ISSN: 2169-0022 | GDCSM-2018 | Volume: 7
Converting glassy carbon into amorphous diamond
Zhidan Zeng
1
, Jianguo Wen
2
, Qiaoshi Zeng
1
, Hongwei Sheng
1
, Wenge Yang
1
and
Ho-kwang Mao
1, 3
1
Center for High Pressure Science and Technology Advanced Research (HPSTAR), China
2
Argonne National Laboratory, USA
3
Carnegie Institution of Washington, USA
D
iamond 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 sp3-
bonded 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 π 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 “amorphous
diamond”. 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.govJ Material Sci Eng 2018, Volume: 7
DOI: 10.4172/2169-0022-C3-098