Development of diamond cathode materials for enhancing the electron field emission and plasma characteristics using two-step microwave plasma enhanced chemical vapor deposition process

Abstract

The enhancement on the plasma illumination characteristics of a cylindrical microplasma device due to the utilization of hybrid-diamond (HiD) films as cathode was systematically investigated. The improved plasma illumination behavior was closely related to the enhanced electron field emission (EFE) properties of the diamond films. The HiD films, which possessed better EFE properties, including lower turn-on field for inducing the EFE process [(E0)efe = 2.7 V/μm] and higher EFE current density [(Je)efe = 2.8 mA/cm2, at 10.6 V/μm], resulted in superior illumination performance for the microplasma devices. The plasma can be triggered at a low threshold field of (Eth)pl. = 0.166 V/μm, attaining a large plasma current density of (Je)pl. = 9.6 mA/cm2 at an applied field of 0.266 V/μm (plasma density of ne = 1.70 × 1015 cm−3). The better EFE for the HiD films is ascribed to the unique granular structure of the films. Transmission electron microscopic studies revealed that the HiD films contained large diamond aggregates evenly distributed among the ultrasmall grain matrix. There presents a-few-layer graphite, surrounding the large aggregates that formed electron transport networks and improved the EFE properties for the HiD films. The superior EFE properties for the HiD cathode materials are the prime factor for improving plasma illumination characteristics for the cylindrical microplasma devices.