Production of single crystal diamond needles by a combination of CVD growth and thermal oxidation

Single crystal diamond needles were produced by combining chemical vapor deposition of a thin polycrystalline diamond film and its subsequent thermal oxidation. The deposition process has been carried out in a direct discharge activated hydrogen–methane gas mixture with parameters providing (100) textured diamond film growth. The oxidation has been performed by heating the deposited film in an air atmosphere with a temperature allowing the selective etching of the smallest fraction of the diamond crystallites in the film. As a result of this procedure, perfectly shaped micrometer sized single crystal diamond pyramids were obtained. The pyramids have a rectangular base plane with an apex tip curvature radius of about 2 to 10 nm. The atomic structure of the pyramids was established using high resolution transmission electron microscopy. We propose a model explaining the mechanism of the pyramids' formation.