The micron-scale diamond film was prepared using hydrogen and methane as the mixed gas supplies via self-developed 3 kW/2,450 MHz microwave plasma chemical vapor deposition (MPCVD) equipment. On this basis, the evolution of the surface morphology, hydrophobicity, and electrical properties of samples under different hydrogen plasma etching times was investigated. The results indicate that the crystal edge and the top of the diamond grain were preferentially etched when etching time is less than 30 min. The surface roughness reduced from 0.217 to 0.205 μm, and the resistance value decreases from 3.17 to 0.35 MΩ. However, as the etch time increases to 120 min, the etching depth increases, and the surface roughness was increased. Simultaneously, the contact angles increased from 62.8° to 95.9°, which indicates that the surface of the diamond films exhibits more pronounced hydrophobicity. The treatment time of hydrogen plasma has no significant effect on the resistance value in the range of 0.26–0.50 MΩ. The mechanism of surface etching by hydrogen plasma was also discussed.

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The porous diamond film was fabricated via a self-developed microwave plasma chemical vapor deposition (MPCVD) system in H2/Ar plasma by utilizing micrometer-sized diamond films coated with nickel as the starting material. Scanning electron microscopy and Raman spectroscopy were used to evaluate the evolution of the morphology and sp3 phase of porous diamond with changes in the surface treatment process parameters, including the etching temperature and time. The results indicate that once the etching temperature exceeds 700°C, the pitting etching phenomenon can be observed on the surface of the diamond film. In a certain range, increasing the etching time increases the depth of surface holes on diamond film, whereas the microporous density exhibits an inverted parabolic change pattern. The porous diamond films with uniform pores structure can be obtained by adopting optimal etching process parameter when the H2/Ar plasma temperature is determined at 900°C for 30 min. The porous formation mechanism of diamond film is attributed to the nickel particles' heterogeneous catalysis behavior, which promotes the transition route from diamond phase to graphite phase, followed by the preferential etching of graphite phase by H2/Ar plasma.

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