Selective Oxidation of Graphite on Diamond Films Induced by UV Exposure

A selective oxidation technique for diamond films based on the extended exposure to UV light in air at room temperature was developed and studied by Raman Spectroscopy and Scanning Electron Microscopy. The diamond films were synthesized by the combustion flame technique in open atmosphere by using an oxy-acetylene gas mixture as the carbon source. A 125 W UV lamp was used to irradiate the films in the wavelength range of 180–250 nm, from 2 to 10 days. The Raman spectrum from the as-deposited diamond films shows the typical band at 1333 cm^–1, characteristic of the sp ³diamond structure, with a certain nondiamond or graphite content. After UV irradiation, graphite was selectively oxidized and partially removed without oxidation of diamond, indicating that the strong reaction of ozone (O₃) and atomic oxygen (O·) produced by the UV irradiation oxidized the graphite, even at room temperature, without the need of an additional heating source. The oxidation of graphite was best observed after 2 days of UV treatment. A sensible improvement in the diamond film quality was obtained after 2 days of irradiation, as revealed by the sharpening of the corresponding Raman band.