Maskless Plasma Etching of Diamond Cones: The Role of CH₄ Gas and Enhanced Field Emission Property

Diamond cone arrays were formed by plasma etching of diamond films in a hot filament chemical vapor deposition (HFCVD) system. The role of CH4 in the formation of diamond cone arrays was investigated. It was found that addition of CH4 to H2 plasma could enhance the plasma intensity and hence the etching efficiency to improve the formation of diamond cones with high aspect ratio and controllable density. The microscopic measurement of the as-formed diamond cones shows that they have an inner core of polycrystalline structure and an outer layer of amorphous carbon. These as-formed diamond cones have exhibited field emission current density of 1 μA/cm2 at threshold field of 5 V/μm. For an applied field of 12 V/μm, the emission current density can rapidly reach as high as 560 μA/cm2. The property of high field electron emission is attributed to the high aspect ratio of as-formed diamond cones and the appropriate cone density as well as the outer amorphous carbon layer which acts as a pathway for electron-hopping conduction during field electron emission.