Effects of Laser Photolysis of Hydrocarbons at 193 and 248 nm on Chemical Vapor Deposition of Diamond Films

In this work, the influence of ultraviolet (UV) laser photolysis of hydrocarbons on combustion chemical vapor deposition of diamond films was investigated at 193 and 248 nm. Although the output fluence of the 193 nm laser was 1 order of magnitude lower than that of the 248 nm laser, UV laser irradiations at 193 and 248 nm led to similar enhancement of diamond growth: a 2-fold increase in the diamond deposition rate and a 3% increase in diamond quality compared to those obtained without laser irradiation. In situ thermionic measurement of emission currents revealed that the diamond nucleation time was reduced from 9.5 min without laser irradiation to 4.2 and 7.0 min, respectively, with UV laser irradiations at 193 and 248 nm. These results suggest the advantages of using UV laser photolysis in diamond deposition achieved by suppressing nondiamond carbon accumulation. Spectroscopic investigation of the flame chemistry showed that UV laser irradiations of the diamond-forming combustion flames led to photogenerated reactive species, OH, CH, and C₂, which play critical roles in diamond growth. The more pronounced flame chemistry change and diamond growth enhancement with UV laser irradiation at 193 nm than 248 nm is attributed to a higher photon energy, 6.4 eV, which is above the energetic dissociation threshold of most hydrocarbons for more efficient photodissociation.