Microstructural evolution of diamond films from CH4/H2/N2 plasma and their enhanced electrical properties

Abstract

The influence of N 2 concentration in CH 4 /H 2 /N 2 plasma on microstructural evolution and electrical properties of diamond films is systematically investigated. While the diamond films grown in CH 4 / H 2 plasma contain large diamond grains, for the diamond films grown using CH 4 /H 2 /(4%)N 2 plasma, the microstructure drastically changed, resulting in ultra-nanosized diamond grains with Fd3m structure and a 0 ¼ 0.356 nm, along with the formation of n-diamond (n-D), a metastable form of diamond with space group Fm3m and a 0 ¼ 0.356 nm, and i-carbon (i-C) clusters, the bcc structured carbon with a 0 ¼ 0.432 nm. In addition, these films contain wide grain boundaries containing amorphous carbon (a-C). The electron field emission (EFE) studies show the best EFE behavior for 4% N 2 films among the CH 4 /H 2 /N 2 grown diamond films. They possess the lowest turn-on field value of 14.3 V/lm and the highest EFE current density value of 0.37 mA/cm 2 at an applied field of 25.4 V/lm. The optical emission spectroscopy studies confirm that CN species are the major criterion to judge the changes in the microstructure of the films. It seems that the grain boundaries can provide electron conduction networks to transport efficiently the electrons to emission sites for field emission, as long as they have sufficient thickness. Whether the matrix nano-sized grains are 3C-diamond, n-D or i-C is immaterial. V C 2015 AIP Publishing LLC.

Vertically aligned diamond-graphite hybrid nanorod arrays with superior field electron emission properties

“…15 The grain boundaries contain a large proportion of sp 2 -carbon and amorphous carbon (a-C) phases, which are susceptible to O 2 plasma etching than the diamond materials. At the initial stage of the etching process, ND particles sitting on top of the NCD pads mask the NCD films from the ion bombardment.…”

“…The NCD films were deposited using a CH 4 (6%)/H 2 (89%)/N 2 (5%) plasma with a microwave power of 3000 W, where 5% N 2 was added in CH 4 /H 2 plasma to achieve nano-sized diamond grains for NCD films. 15 The flow rate and the pressure were maintained at 300 SCCM and 40 mbar, respectively, during the growth of NCD films. The substrates were heated up due to the bombardment of the plasma species and the growth temperature was estimated to be around 540°C, which was measured in situ using an infrared optical fiber pyrometer (Williamson PRO 9240C, USA).…”

Ellipsometric investigation of nitrogen doped diamond thin films grown in microwave CH4/H2/N2 plasma enhanced chemical vapor deposition

“…Nitrogen incorporation results in significant mechanical stress and increases the number of vacancy defects due to distortion of the diamond lattice. [9][10][11] Several articles were published on the influence of nitrogen on the growth rate and quality of diamond films. [10][11][12][13][14] These 15 experiments were done using gas mixtures of CH 4 /H 2 /N 2 in microwave plasma reactors.…”

“…18 Microwave plasma enhanced CVD (MW PECVD) process results in polycrystalline nitrogen-doped diamond (NDD) films with high sp 3 content possessing low electrical conductivity and superior field emission properties. 9 In majority, the previous investigations have been focused on the use of surface morphology, microstructure, and bonding structure modified due to the addition of nitrogen species into the CH 4 /H 2 plasma. Nevertheless, the conductive NDD films attracting great interest in the field of optical applications including energy conversion 19 or biosensing.…”

“…The details of the growth is reported elsewhere. 9 Mixtures of CH 4 , H 2 , and N 2 were used as the reactant gases for the microwave discharges. The grown samples were designated as "NDD_z" films, where z is the percentage concentration of N 2 in a gas phase varying from 0 to 10 sccm (0% to 8% of total).…”