The plasma emission spectrum and polycrystalline diamond growth within 4 inches was studied by using a microwave plasma chemical vapor deposition (MPCVD) equipment with a microwave frequency of 2.45 GHz and a power of 10 kW

a 4-inch free-standing diamond thick film was prepared

and the growth uniformity

crystal quality at different positions

room temperature thermal conductivity

ultraviolet-visible-near infrared spectral transmittance and dielectric properties of diamond film were characterized. The results show that the freestanding diamond films are prepared with good uniformity and crystallinity at 10 kW power with high concentration and chemical activity of carbon and hydrogen active particles within the plasma diameter of about 100 mm. The thermal conductivity at room temperature reaches more than 1894 W/m·K

the infrared transmittance reaches more than 70%

the dielectric constant is 5.5

and the dielectric loss is 5.9 × 10

−5

. This study provides a theoretical possibility for the preparation of large-area high-quality diamond films in low-power MPCVD equipment.