Enhancing the plasma illumination behaviour of microplasma devices using microcrystalline/ultra-nanocrystalline hybrid diamond materials as cathodes

Abstract

The properties of capacity-type microplasma devices were significantly enhanced due to the utilisation of hybrid diamond films as cathodes. The performance of the microplasma devices was closely correlated with the electron field emission (EFE) properties of the diamond cathode materials. The nanoemitters, which were prepared by growing duplex-structured diamond films [microcrystalline diamond (MCD)/ultra-nanocrystalline diamond (UNCD)] on Si-pyramid templates via a two-step microwave plasma enhanced chemical vapour deposition (MPE-CVD) process, exhibited improved EFE properties (E0 = 5.99 V μm(-1), J(e) = 1.10 mA cm(-2) at 8.50 V μm(-1) applied field), resulting in superior microplasma device performance (with a lower threshold field of 200 V mm(-1) and a higher plasma current density of 7.80 mA cm(-2)) in comparison with UNCD film devices prepared using a single-step MPE-CVD process. The superior EFE properties of the duplex-structured MCD-UNCD films relative to those of the UNCD films can be attributed to the unique granular structure of the diamond films. High-resolution transmission electron microscopy reveals that the MCD-UNCD films consisted of abundant graphitic phases located at the periphery of large diamond aggregates and at the boundaries between the ultra-small diamond grains. The presence of the graphite phase is presumed to be the prime factor that renders these films more conductive and causes these films to exhibit higher EFE properties, thus resulting in the improved plasma illumination properties of the microplasma devices.

Fast Photoresponse and Long Lifetime UV Photodetectors and Field Emitters Based on ZnO/Ultrananocrystalline Diamond Films

“…After removing the light source, the photocurrent decays quickly at first as ar esult of the recombination of free electron-hole pairs. [49] Apparently,t he prime factor that notably improves the electron transport and enhances the EFE properties of the UNCD is the formation of an a-C carbon or graphite phase aroundt he grain boundaries in the small-grain regions,which results in the formationo fi nterconnected paths for electrons transfer.T hese becomec onduction channels for the electrons to be transported from the bottom of the films to the top and then emitted into vacuum very effortlessly. In the operation of the ZNRs/UNCD PD, when the electrons recombine with holes the tunneling effect and trappinga nd de-trapping are simplyd ue to the ultra-small grain size of the UNCD films, which is more conductive than other diamond films.…”

Theory and analysis of operating modes in microplasmas assisted by field emitting cathodes

“…The recent field emitting cathodes are largely diamond-based nanomaterials that differ primarily in the techniques used to grow them. While the recent experiments [29][30][31][32][33][34][35][36][37][38][39][40] deal with $mm gaps operating at low pressures with cathodes characterized by field enhancement factors $1000, the theory 28 focused on microgaps operating at atmospheric pressures with cathode field enhancement factors $100. However, the common theme between them is the influence of field emission on microplasmas and therein lies the motivation for the current work.…”

“…In that work, the author predicted the existence of an abnormal glow mode with a positive differential resistance (dV=dI > 0) and an arc-like mode with a negative differential resistance (dV=dI < 0) in microgaps that are under the influence of field emission. More recently, there has been some experimental work [29][30][31][32][33][34][35][36][37][38][39][40] for field emission assisted microplasmas with novel cathodes that have excellent field emitting properties combined with longer lifetimes than other comparable cathodes, such as bare carbon nanotubes (CNTs). It should be noted that CNTs were proposed 41,42 to enhance the plasma densities in cavity microplasmas but suffered from extremely poor lifetimes.…”

Straight imaging and mechanism behind grain boundary electron emission in Pt-doped ultrananocrystalline diamond films

“…Cold cathode materials with excellent electron field emission (EFE) properties have great promise for use in vacuum electronic devices such as electron sources for electron microscopes, X-ray sources, high energy accelerators, cathode-ray tube monitors and microwave amplifiers [1][2][3]. Diamond is a good electronic candidate for solid-state electronic emitters because of its negative electron affinity (NEA) and low effective work function surface [4,5].…”