Diamond

Industrial process selection must balance stable operation, maintenance accessibility, control system coordination and on-site media conditions.

Chemical vapor deposition (CVD) is the mainstream route to high-quality synthetic diamond. The core principle uses methane as the carbon source and excess hydrogen as the carrier gas at low pressure (~0.1 atm) and high temperature (~800–1000°C), dissociating H₂ into highly reactive atomic hydrogen. Atomic hydrogen preferentially etches non-diamond carbon (graphite) while stabilizing the diamond lattice so carbon atoms attach correctly. Methods are classified by energy input: microwave plasma CVD (MPCVD), hot-filament CVD (HFCVD), and DC-arc plasma jet CVD.

MPCVD generates an electrode-free plasma ball at 2.45 GHz, minimizing contamination and yielding electronic- and gem-grade diamond. Typical recipes use H₂ 300 sccm, CH₄ 15–18 sccm, substrate 700–800°C, chamber pressure 14–15 kPa, growing at 1–5 µm/h. HFCVD decomposes gas on filaments at 2000–2400°C; it is simple, low-cost, and scalable to large areas for tool coatings and polycrystalline diamond, with methane typically 1–1.5% of total flow.

The methane-to-hydrogen ratio is decisive for film quality: too little carbon lowers nucleation density; too much turns grains spherical and raises non-diamond content. Flow must therefore be precise and stable — small drift accumulates into visible composition error over long growth runs.

Epitaxial single-crystal growth demands even tighter stability. In a Shanghai Jiao Tong University HFCVD study, at filament 2200°C, carbon source 4%, and chamber pressure 4 kPa, single crystals grew at 3.41 µm/h with quality exceeding the seed — placing extreme demands on long-term flow stability and repeatability of CH₄ and H₂.

HNR supplies mass flow control, pressure regulation, and gas blending for MPCVD, HFCVD, and arc-jet systems, helping diamond producers and researchers stabilize their process window and improve crystal quality.