Undercooling driven growth of Q-carbon, diamond, and graphite
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Research Letter
Undercooling driven growth of Q-carbon, diamond, and graphite Siddharth Gupta, Department of Materials Science and Engineering, Centennial Campus, North Carolina State University, Raleigh, NC 27695-7907, USA Ritesh Sachan, Department of Materials Science and Engineering, Centennial Campus, North Carolina State University, Raleigh, NC 27695-7907, USA; Materials Science Division, Army Research Office, Research Triangle Park, NC 27709, USA Anagh Bhaumik, Punam Pant, and Jagdish Narayan, Department of Materials Science and Engineering, Centennial Campus, North Carolina State University, Raleigh, NC 27695-7907, USA Address all correspondence to Jagdish Narayan at [email protected] (Received 29 January 2018; accepted 10 April 2018)
Abstract We provide insights pertaining the dependence of undercooling in the formation of graphite, nanodiamonds, and Q-carbon nanocomposites by nanosecond laser melting of diamond-like carbon (DLC). The DLC films are melted rapidly in a super-undercooled state and subsequently quenched to room temperature. Substrates exhibiting different thermal properties—silicon and sapphire, are used to demonstrate that substrates with lower thermal conductivity trap heat flow, inducing larger undercooling, both experimentally and theoretically via finite element simulations. The increased undercooling facilitates the formation of Q-carbon. The Q-carbon is used as nucleation seeds for diamond growth via laser remelting and hot-filament chemical vapor deposition.
Introduction Carbon as an element has carved its niche in the materials world due to its immense pliability to be morphed into numerous allotropes. Among these allotropes, diamond is a prominent crystalline phase with 100% sp3 bonding which induces extraordinary properties like extreme hardness and thermal conductivity. Due to the increasing applications of pristine and N–V centers in diamonds, there is a need to fabricate diamonds with controlled introduction of defects without utilizing detrimental techniques like detonation and ion implantation which generate Frenkel pairs, creating disorder in the lattice. By laser annealing amorphous carbon with nanosecond laser pulses, Narayan et al. demonstrated its conversion into diamonds.[1,2] Due to the susceptibility of carbon towards sublimation at higher temperatures, nanosecond laser annealing is ideal for melt processing carbon, as it completes the regrowth process in 16 m/s).[3] The Q-carbon is different from other forms of carbon—graphite, diamond, and melt state.[5,6] It has a high sp3 content (75– 85%), and possesses novel physical, chemical, mechanical, and catalytic properties.[2,7,8] When DLC is melted in the
undercooled state and quenched back to form Q-carbon, there is a significant reduction in the specific volume. At intermediate regrowth rates, nanodiamonds nucleate due to relatively lower undercooling. Different phases can be grown in this regime due to the competing forces of kinetic growth rate and the nucleation at the mobile melt front. The formation of Q-carbon and diam
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