Fabrication of highly transparent ultrananocrystalline diamond films from focused microwave plasma jets

Abstract

This paper describes a particular class of highly transparent ultrananocrystalline diamond (UNCD) films synthesized from focused microwave plasma jet. The rapid transition in microstructure of diamond films from microcrystalline diamond (MCD) to UNCD was achieved by Ar addition from Ar/Ar+H2 0% to 90% in the plasma jet. This is due to the significant enhancement on activity and density of plasma species during synthesis, resulting from the excitation of focused microwave plasma jet. The evolution of transition from MCD to UNCD using focused plasma jet and induced effects on the optical transparency and mechanical properties of the as-grown diamond films were investigated. Synchrotron-based X-ray absorption near-edge structure (XANES) analysis was employed to thoroughly complete the confirmation of atomic bonding structure in the diamond films during transition from MCD to UNCD. The research results demonstrated that the optical transparency property of diamond films depended on the surface roughness more than on the nondiamond contents in films. The transmittance of diamond films was improved by films transition from MCD to UNCD. The significant decrease of light scattering from UNCD films is due to the ultra-smooth surface and ultra-nanosized crystallites. The UNCD film with a thickness ~300nm was synthesized on quartz substrate using the unique focused microwave plasma jet-enhanced growth, which produced films with high optical transmittance (~90% at 780nm), high hardness (~69Gpa), and extremely smooth surface morphology (~7.5nm rms).