Role of Q-Carbon in the Wafer-Scale Growth of High-Quality Diamond Films

Quenched-in-carbon (Q-carbon) is a new allotrope of carbon with intriguing structural and functional properties. It consists of randomly packed diamond tetrahedra with sp³-bonded carbon atoms (80–85%) within the tetrahedra and a mixture of sp²- and sp³-bonded atoms between the tetrahedra. This distinct arrangement yields a 40-60% higher number density of covalently bonded carbon atoms in the diamond cubic lattice, with an 80% increase in the packing efficiency compared to diamond. As a result, undoped Q-carbon exhibits exceptional characteristics, including hardness higher than diamond, high radiation resistance, robust ferromagnetism, and superconductivity upon doping with boron. In addition to higher hardness, toughness, and adhesion, Q-carbon is biocompatible and shows enhanced resistance to bacterial growth, making it a great choice of coating material for biomedical implant devices. Moreover, as a wide bandgap semiconductor, Q-carbon offers cost-effective solutions for diamond film seeding, expanding its applications across various domains.

Considering diamond is metastable at ambient temperatures and pressures, the equilibrium synthesis requires extremely high temperatures (5000 K) and pressures (12 GPa). This process yields phase-pure diamonds but with limited scalability and undesirable grit formation. Moreover, the lack of diamond nucleation sites required for diamond growth poses a formidable challenge for the growth of continuous and adherent diamond films on practical substrates. Q-carbon, comprising of diamond unit cells, overcomes this challenge by enabling the barrierless nucleation of diamonds. Consequently, large-scale deposition of Q-carbon facilitates wafer-scale integration of high-quality diamond films with reduced processing times. In this work, we describe the formation of pristine Q-carbon films via a non-equilibrium plasma-enhanced chemical vapor deposition (PECVD) process, employing low-energy Ar⁺ ion bombardment using appropriate values of negative biasing. We discuss the formation mechanism of Q-carbon and demonstrate the feasibility of PECVD for large-area deposition of high-quality Q-carbon films on substrates up to 12” in diameter, paving the way for wafer-scale integration of diamond films for next-generation solid-state devices.

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