Highly Conductive Diamond–Graphite Nanohybrid Films with Enhanced Electron Field Emission and Microplasma Illumination Properties
2015
Saravanan, Adhimoorthy | Huang, Bohr-Ran | Sankaran, Kamatchi Jothiramalingam | Tai, Nyan-Hwa | Lin, Yinan
Bias-enhanced nucleation and growth of diamond–graphite nanohybrid (DGH) films on silicon substrates by microwave plasma enhanced chemical vapor deposition using CH₄/N₂ gas mixture is reported herein. It is observed that by controlling the growth time, the microstructure of the DGH films and, thus, the electrical conductivity and the electron field emission (EFE) properties of the films can be manipulated. The films grown for 30 min (DGHB₃₀) possess needle-like geometry, which comprised of a diamond core encased in a sheath of sp²-bonded graphitic phase. These films achieved high conductivity of σ = 900 S/cm and superior EFE properties, namely, low turn-on field of 2.9 V/μm and high EFE current density of 3.8 mA/cm² at an applied field of 6.0 V/μm. On increasing the growth time to 60 min (the DGHB₆₀), the acicular grain growth ceased and formed nanographite clusters or defective diamond clusters (n-diamond). Even though DGHB₆₀ films possess higher electrical conductivity (σ = 1549 S/cm) than the DGHB₃₀ films, the EFE properties degraded. The implication of this result is that higher conductivity by itself does not guarantee better EFE properties. The nanosized diamond grains with needle-like geometry are the most promising ones for the electron emission, exclusively when they are encased in graphene-like layers. The salient feature of such materials with unique granular structure is that their conductivity and EFE properties can be tuned in a wide range, which makes them especially useful in practical applications.
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