Microwave and millimeter-wave processing of materials, in particular diamonds, is an important research and industrial method that was reviewed by authors44. CVD techniques, in particular that is based upon microwave-assisted approach, have become one of the most superior methods in the manufacturing of materials, involving different carbon nanoforms, and are well explained in a series of books.
The experimental detection give a fundamental perception about the plasma chemistry of hydrocarbon/Ar-rich plasma environment that are used for growing ND films, were discussed. Both main ND types, NCD and UNCD, were obtained via this route45. Between the series of associated works, the NCD (40–400 nm) were grown without the help of initial nucleation sites on Ni substrates in a microwave plasma reactor (400 to 600? C) using hexane/nitrogen-based CVD. In a associated work, NCD thin films were produced and characterized with the help of MPCVD. Ultra smooth nanostructured diamond (USND) coatings were deposited by MPCVD technique by using He/H2/CH4/N2 gas mixture that is used as a precursor46. Different characteristics of CVD applications for ND materials were studied in detail by Butler et al.47, in particular the growth and characteristics of NCD thin films with thicknesses from 20 nm to <5 µm containing 95->99.9% diamond crystallites.
It was shown that the UNCD was usually produced in argon-rich, H-poor CVD environments, and that may contain up to 95–98% sp3-bonded C. Effect of gas (mixture of methane and hydrogen) on flow rate of diamond deposition on mirror-polished silicon substrates in a microwave plasma reactor was studied by Chen et al48. At low gas flow rates (30–300 sccm) microcrystalline diamond thin films were obtained, while at higher gas flow rates (>300 sccm) NCD thin films with cauliflower-like morphology were obtained. This result may be assigned to the improvement of diamond secondary nucleation occur from the increase in the flux rate of carbon-accomadating radicals reaching the diamond growth surface49. A series of copyright are devoted to different presentations of microwave equipment for the fabrication of different diamond forms.
Thus, the equipment for MWCVD processing was patented by Nanba et al50. The apparatus had a dielectric window for introducing microwave in a vacuum chamber and an antenna part with an edge electrode for initiate microwave in the chamber, whereas the window is sandwiched between the chamber inner surface and the electrode. These apparatus was appropiate for forming a large-area high-quality semiconductor diamond film51.
Another microwave CVD apparatus precisely for the formation of diamond, containing a globe-shaped discharge chamber and a coaxial antenna for sustain microwave into the chamber, with the antenna tip equipped with a work holder, positioned in the centre of the globe, was proposed by authors46.