INTERACTION OF NITROGEN PLASMA WITH DIAMOND SURFACES STUDIED BY DENSITY FUNCTIONAL THEORY

Interaction of Nitrogen Plasma with Diamond Surfaces

Studied by Density Functional Theory

Yusen Zheng

Under supervision of Prof. Alon Hoffman (Technion) and Prof. Kai Huang (GTIIT)

Layer-by-layer construction of diamond devices for spin-sensing calls for atomistic understanding of the nitrogen species on diamond surfaces.^[i] As motivated by recent experiments,^[ii] I conducted density functional theory simulations to examine the adsorption and thermal evolution of the nitrogen species on the bare and hydrogenated diamond surfaces by nitrogen plasma, as below.

My work launched upon the (001) facet of diamond. On the bare diamond(001),^[iii] we find that nitrogen species favor to attack the C=C dimers, forming nitrogen-dimers in a horizontal configuration, h-N₂(ad). The formation of h-N₂(ad) is capable of resolving some discrepancy in the literature. On the hydrogenated diamond(001),^[iv] by contrast, there emerges a new state of nitrogen-dimers in a vertical configuration, v-N₂(ad), in addition to h-N₂(ad). Consequently, the desorption barriers of N₂ is altered, i.e. Ea=0.91 eV on bare diamond(001) versus Ea=2.36 eV on hydrogenated diamond(001).

In the remaining work, I made a comparative study on the nitridation of bare and hydrogenated diamond(111). The bare diamond(111) surface was represented by the (2×1) Pandey chain and the graphitized model, whereas the hydrogen diamond(111) surface was described by the (1×1)-H or (2×1)-H or model.[v] On the bare diamond(111) surface, we find the formation of horizontal N₂(ad) that features the C-N and N=N bonding at the surface. On the hydrogenated diamond(111) surfaces, it becomes evident that N₂ plasma is capable of inserting itself into surface C-H bonds to form C-N-H bonds. Consequently, the as formed surface species is N₂H₂(ad) that features the formation of C-N, N-N and N-H bonds. Of the four models, we find that the (2×1)-H model is the most plausible, because the computed desorption barrier of 2.90 eV is in the best agreement with the experimental value of 2.55 eV by temperature programmed desorption. Additionally, vibration of surface nitrogen species was computed under the harmonic oscillator model and compared with the prior results by high resolution electron energy loss spectroscopy, calling for re-interpretation of some spectroscopic features.

([i]). Jaffe, T.; Attrash, M.; Kuntumalla, M. K.; Akhvlediani, R.; Michaelson, S.; Gal, L.; Felgen, N.; Fischer, M.; Reithmaier, J. P.; Popov, C.; Hoffman, A.; Orenstein, M. Novel ultra localized and dense nitrogen delta-doping in diamond for advanced quantum sensing. Nano Lett. 2020, 20, 3192−3198.

([ii]). Attrash, M.; Kuntumalla, M. K.; Michaelson, S.; Hoffman, A. Nitrogen-terminated polycrystalline diamond surfaces by microwave chemical vapor deposition: thermal stability, chemical states, and electronic structure. J. Phys. Chem. C. 2020, 124, 5657−5664.

([iii]). Zheng, Y.; Hoffman, A.; Huang, K.  Atomistic insight into nitrogen-terminated Diamond (001) surfaces by the adsorption of N, NH, and NH₂: a density functional theory study. Langmuir. 2021, 37, 6248-6256.

([iv]). Zheng, Y.; Kuntumalla, M. K.; Attrash, M.; Hoffman, A.; Huang, K. Effect of Surface Hydrogenation on the Adsorption and Thermal Evolution of Nitrogen Species on Diamond (001) by Microwave N₂ Plasma. J. Phys. Chem. C. 2021, 125, 28157–28161.

([v]). Kuntumalla, M. K.; Zheng, Y.; Attrash, M.; Gani, G.; Michaelson, S.; Huang, K.; Hoffman, A. Microwave N2 plasma nitridation of H-diamond (111) surface studied by ex situ XPS, HREELS, UPS, TPD, LEED and DFT. Appl. Surf. Sci., 2022, 600, 154085.