Control of the Growth Regimes of Nanodiamond and Nanographite in Microwave Plasmas

Moderate-pressure microwave plasmas are used to deposit functional nanomaterials consisting of nanodiamond (ND) and/or nanographite. The growth conditions of ND, carbon nanowalls (CNWs), and ND/CNW composite films are categorized in a process map as functions of substrate temperature and Ar concentration with or without scratching pretreatment using diamond powder. Addition of high fractions of Ar to CH₄ plasmas facilitates the formation of C₂ radicals, which is responsible for decreasing the diamond grain size in ND film and enhancing graphitization into the form of graphitic walls in CNWs. The deposition of ND film is limited by substrate surface condition (scratching and seeding) rather than gas-phase condition, whereas that of CNWs is governed by gas-phase condition. A combination of a C₂-rich plasma with scratching pretreatment results in ND/CNW composite film, which increases the space between the walls favorably for better performance of field emission. Based on the insights into gas-phase and surface processes, the deposition mechanism of ND/CNW composite film is discussed to explore the possibility of controlling nano-arrangement of the walls.