In CVD diamond growth, what is the substrate?

• A. An abrasive material used to shape the diamond.
• B. A template or seed for new CVD diamond growth.
• C. A protective coating applied after growth.
• D. A chemical catalyst used during growth.

Answer: (B)

In CVD diamond growth, the substrate is the surface that supports and directs the deposition—the seed or template for the crystal to form on. A tiny diamond seed crystal or a seed layer sits on a heat‑resistant substrate, and carbon-rich gas is activated so carbon is deposited onto that seed, growing the diamond outward. The seed determines the crystal orientation and helps ensure high-quality, single‑crystal or well‑controlled polycrystalline growth; without a seed, nucleation would occur everywhere and you’d get a rough, poorly controlled film. The substrate must withstand the high temperatures and not contaminate the diamond, so common choices include silicon, silicon carbide, or pre-existing diamond. The other options don’t fit the role of the substrate: an abrasive shapes the diamond, a protective coating is applied after growth, and a chemical catalyst is not the substrate in the typical CVD process.