Formation mechanism of diamond nanotips by plasma enhanced vapour processes

摘要

Synthesis of diamond nanotip arrays was investigated using plasma enhanced hot filament chemical vapour deposition (HFCVD) and microwave plasma enhanced chemical vapour deposition (MPCVD) under different conditions. Well-aligned diamond nanotip arrays were synthesized on silicon wafers precoated with diamond thin films with substrates negatively biased in a plasma in the HFCVD reactor with a negative bias voltage above 300V and the operation pressure below 2 kPa. The alignment orientation of the nanotips is parallel to the electric field lines on the sample surface. All the nanotips synthesized have nanometre-size tips and micrometre-size roots. The apex angle of the nanotips is similar under the same conditions regardless of the size of the nanotips. However, only flat diamond thin films were obtained when MPCVD was used regardless of the processing conditions. The experimental results indicate that the formation of nanotips strongly depends on ion bombardment and the nanotip apex angle is determined mainly by ion bombardment conditions regardless of the size of the nanotips. An angle dependent ion sputtering mechanism was proposed to explain the formation of nanotips. Furthermore, controlled ion beam sputtering of precoated diamond thin films was conducted in an ion beam deposition system to verify the formation mechanism.