Out of all the carbon-based nanomaterials studied in recent years, diamond thin films stand out due to their endless range of applications and physical properties [1-2]. Diamond’s unique properties such as high bulk modulus (445 GPa), thermal conductivity (2200 W/m K), hardness (120 GPa), along with its small value of thermal expansion coefficient (1.1*10-8/K), [1-2] and also, its biocompatible nature makes it promising for applications on extreme environments such as outer space and heavy machinery. Diamond lattice is amenable to doping and it is possible to dope diamond with other atoms such as B, P, N, and Si. Even though the pure form of diamond is highly insulating (1011-1018 Ωm), incorporation of such dopants in nanodiamonds has been found to induce the insulating nature leading to metallic transition for nanodiamonds and even superconductivity has been observed in some cases [3]. Specifically, the introduction of nitrogen-vacancy (NV) defects and silicon-vacancy (SiV) defects have shown to give excellent optical properties to diamond, which is promising in the fabrication of devices such as magnetometers, quantum bits, single-photon sources, and detectors [4]. In terms of electronic applications, even though the p-type doping of boron in diamond is well established, the hunt for a suitable n-type dopant is still on. The objective of this work is to explore the possibilities of using different defects on micro/nanocrystalline diamonds and the resultant changes in their physical properties, specifically adsorption, electrical conductivity, optical and magnetic properties. Not only conventional methods such as phase addition of dopants, and ion implantation will be explored, but also alternate doping approaches will be tried along with co-doping of different elements. As a starting point, the morphology and crystalline quality of polycrystalline diamond samples were studied by systematically varying the flow rate of nitrogen gas in microwave plasma. A slight improvement in both crystallite size and in terms of quality is observed for a low concentration of 0.5 sccm nitrogen. With a further increase in nitrogen concentration, the diamond switches from micro-crystalline (MCD) to nanocrystalline (NCD) with a nitrogen flow of 2.5 sccm (10 % of methane concentration). The surface roughness of the sample is found to depend strongly on the crystallite size of the sample. Extensive spectroscopic studies have been used to understand the presence and formation of different defect complexes in diamond. The presence of nitrogen-containing defect complexes has been studied thoroughly and their concentration has been found to be limited by the solubility limit rather than the availability of reactants in the gas environment. In contrast, the effect these complexes have on the diamond crystal in terms of strain is found to be negligible. Optical emission spectroscopy of the plasma reveals the presence of C2 dimers as well as C-N radicals. However, they have little role in modifying diamond morphology or quality

1. Das, Dhruba, et.al, Journal of Physics D: Applied Physics, 2022.
2. Mallik, Awadesh Kumar, JCST 2016,3
3. Kumar, Dinesh, et.al, 2018 J. Phys. Commun. 2 045015
4. N. Yang, Springer, 2016, pp 1 284.