Nano-tip diamond-like carbon fabrication utilizing plasma sheath potential drop technique

Microwave plasma chemical vapor deposition (MPCVD) system with microwave frequency 2.45 GHz was used for exciting mixed reaction gases of methane and hydrogen to produce plasma. The p-type (1 0 0) silicon substrate surface was put to contact with plasma to induce plasma sheath potential drop. It introduces an electric field to accelerate positive and lighter hydrogen ions (H+) to etch out sp2 clusters and amorphous carbons anisotropically. Besides, high-energy ions, hydrocarbon species and hydrogen atoms (H) are diffused to etch out sp2 clusters and amorphous carbons isotropically. Without externally applying negative bias, nano-tip diamond-like carbon (DLC) film with a few nano-size diamonds and many sp3 bonding was successfully deposited under the competition of etching and deposition. SEM study shows that the density of DLC nano-tips is up to 20×108 cm−2. Its length, bottom diameter and top diameter are about 1.5–2 μm, 300–400 nm, and 20–30 nm, respectively. The deposited film was analyzed by energy dispersion spectrometer (EDX). The result shows that there is no transition metal incorporated in the film. This suggests that the DLC nano-tip growing mechanism is not similar to general growing mechanism of carbon nanotubes. X-ray diffraction spectrometer (XRD) was applied to confirm that a few nano-size diamonds are contained in the film. Finally, Raman spectrometer and Auger electron spectrometer (AES) were used to confirm that a larger amount of sp3 bonding is incorporated in the film.