Synthesis of diamond hexagonal nanoplatelets by microwave plasma chemical vapor deposition

Variation of diamond deposition with temperature gradient was studied using standing-up substrates embedded within the plasma ball in microwave plasma chemical vapor deposition (MPCVD). The substrate is a polycrystalline diamond coated with a 30-nm thick iron film before deposition. Surface morphologies of the deposits and their crystalline characteristics were characterized by scanning electron microscopy, transmission electron microscopy (TEM), and selected area diffraction. On the upper area of the specimen near the center of the plasma ball where the temperature is the highest (>1100 °C), formation of diamond nanoplatelets in hexagonal shape with a thickness of 20–60 nm and side length of several hundreds of nanometers is found. In the middle region, diamond nanoplatelets with some iron nanoparticles are observed. Around the bottom region with low temperature near the edge of the plasma ball, nanodiamonds, Fe nanoparticles, and carbon nanotubes coexisted. The relative temperature distributions of diamond and carbon nanotube growth are briefly discussed.