Fundamental Discovery of Q-Phases and Direct Conversion of Carbon into Diamond and h-BN into c-BN
This article reviews the discovery of new phases of carbon (Q-carbon) and BN (Q-BN) and addresses critical issues related to direct conversion of carbon into diamond and h-BN into c-BN at ambient temperatures and pressures in air without any need for catalyst and presence of hydrogen. The Q-carbon and Q-BN are formed as a result of quenching from super undercooled state by using high-power nanosecond laser pulses. We discuss the equilibrium phase diagram (P vs. T) of carbon, and show that by rapid quenching kinetics can shift thermodynamic graphite/diamond/liquid carbon triple point from 5000 K/12 GPa to super undercooled (4000 K) carbon at atmospheric pressure in air. Similarly, the hBN-cBN-Liquid triple point is shifted from 3500 K/9.5 GPa to as low as 2800 K and atmospheric pressure. It is shown that nanosecond laser heating of amorphous carbon and nanocrystalline BN on sapphire, glass and polymer substrates can be confined to melt in a super undercooled state. By quenching this super undercooled state, we have created a new state of carbon (Q-carbon) and BN (Q-BN) from which nanocrystals, microcrystals, nanoneedles, microneedles and thin films are formed. The large-area epitaxial diamond and c-BN films are formed, when appropriate planar matching or lattice matching template is provided for growth from super undercooled liquid state. Scale-up processing of diamond, c-BN and diamond/c-BN heterostructures and related nanostructures such as nanodots, microdots, nanoneedles, microneedles and large-area single-crystal thin films will have tremendous impact on applications ranging from abrasive and tool coatings to high-power devices and myriad of biomedical applications.
KeywordsCarbon phase diagram Raman spectroscopy Diamond/c-BN heterostructures
We are grateful to Fan Family Foundation Distinguished Chair Endowment for Professor J. Narayan, and this research was partly funded by the National Science Foundation. We are also very pleased to acknowledge technical help and useful discussions with John Prater, and Ki Wook Kim.
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