Subsurface Nitrogen in Diamond(001)-2×1-H Studied by Density Functional Theory

Title

Subsurface Nitrogen in Diamond(001)-2×1-H Studied by Density Functional Theory

Speaker

Shicai Wang (2nd year MSc Student in Chemistry)

Time

Tuesday, September 17 2024, 20:30-21:30 (China time) or 15:30-16:30 (Israel time)

Zoom Meeting

https://technion.zoom.us/my/dgklab

Abstract

As the most common impurity in natural diamond, nitrogen could form a series of color centers that are of optical and spin properties suitable for applications in quantum computing, magnetometry, and biological sensing.[1] To populate nitrogen centers in the near-surface region of diamond, there has been recent effort [2-12] of using activated dinitrogen to impact fully hydrogenated diamond surfaces as synthesized by chemical vapor deposition. For example, Hoffman and co-workers [5] reported on the formation of surface nitrogen dimers on diamond(001)-2×1-H by microwave N2 plasma. By contrast, there is implication [7-8] of nitrogen into the subsurface region (depth: 6 ± 5 Å) of the same diamond(001)-2×1-H by low energy N2+ ions. It remains, however, unclear about the atomistic understanding into the configuration and bonding of the nitrogen species in the subsurface region of diamond(001)-2×1-H.

Here, I present studies into subsurface nitrogen in diamond (001)-2×1-H by density functional theory simulations, revealing in each case information regarding structure, energy and vibration that depend on the atomistic coordination as detailed below.

1.Interstitial Ni Species.

We have studied 10 configurations of a single interstitial nitrogen in the topmost 3 layers of diamond (001)-2×1-H. In all configurations, the carbon network is strongly distorted by an interstitial nitrogen atom, in which 2 carbon-carbon bonds are cleaved. The interstitial nitrogen is bound to 3 neighboring carbon atoms, of which one carbon becomes sp2 hybridized. The stability of the interstitial configuration depends on the location of nitrogen and the direction of the formed C(sp2)-N bond, exhibiting formation energies of +4.83 to +11.04 eV. The most characteristic mode of vibration arises from the C(sp2)-N bond, i. e., stretch (1530 to 1901 cm⁻¹/ 189.7 to 235.8 meV) and swing (1101 to 1389 cm⁻¹/ 136.6 to 172.2 meV). Migration of nitrogen interstitial is also evaluated, involving a series of steps and intermediates; the rate determining step is of a barrier of 6.02 eV.

2.Substitutional Ns Species.

We have also evaluated 3 configurations of a single substitutional nitrogen in the topmost 3 layers of diamond(001)-2×1-H. In all configurations, the carbon network is largely preserved, giving formation energy of +2.79 to +3.41 eV. The substitutional nitrogen is bound to four neighboring carbons, and the formed C-N bond is larger than a typical C-N single bond, giving the characteristic C-N swing vibration of 844 to 979 cm⁻¹ (105 to 121 meV).

3.Dinitrogen N2i Species.

We have finally evaluated 6 configurations of a pair of nitrogen atoms in the topmost 3 layers of diamond(001)-2×1-H. Our computations were restricted to the N2i species that mimics the encounter of an interstitial Ni and a substitutional Ns species. The formation energy depends on the location of N2i and the direction of the formed Ni-Ns bond, ranging from +4.12 to +9.71 eV. The most characteristic motions of vibration arise from N-N stretch mode of 1419 cm⁻¹ (176.0 meV), C-N swing mode of 968 cm⁻¹ (120 meV) and N-N swing mode of 471 cm⁻¹ (58.5 meV).

Reference

[1] Ashfold, M. N., Goss, J. P., Green, B. L., May, P. W., Newton, M. E., & Peaker, C. V. (2020). Nitrogen in diamond. Chemical reviews, 120(12), 5745-5794.

[2] Attrash, M., Kuntumalla, M. K., Michaelson, S., & Hoffman, A. (2020). Nitrogen-terminated polycrystalline diamond surfaces by microwave chemical vapor deposition: Thermal stability, chemical states, and electronic structure. The Journal of Physical Chemistry C, 124(10), 5657-5664.

[3] Attrash, M., Kuntumalla, M. K., Michaelson, S., & Hoffman, A. (2021). Nitrogen terminated diamond (111) by RF (N2) plasma–chemical states, thermal stability and structural properties. Surface Science, 703, 121741.

[4] Zheng, Y., Hoffman, A., & Huang, K. (2021). Atomistic insight into nitrogen-terminated diamond (001) surfaces by the adsorption of N, NH, and NH2: A density functional theory study. Langmuir, 37(20), 6248-6256.

[5] Zheng, Y., Kuntumalla, M. K., Attrash, M., Hoffman, A., & Huang, K. (2021). Effect of surface hydrogenation on the adsorption and thermal evolution of nitrogen species on diamond (001) by microwave N2 plasma. The Journal of Physical Chemistry C, 125(51), 28157-28161.

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

[7] Kuntumalla, M. K., Gani, G., Fischer, M., & Hoffman, A. (2023). Bonding, retention and thermal stability of shallow nitrogen in diamond (100) by low-energy nitrogen implantation. Surfaces and Interfaces, 37, 102649.

[8] Kuntumalla, M. K., Fischer, M., & Hoffman, A. (2024). Subsurface nitrogen bonding and thermal stability of low-energy nitrogen implanted H-Diamond (100) surfaces studied by XPS and HREELS. Surface Science, 739, 122399.

[9] Kuntumalla, M. K., Fischer, M., Gani, G., & Hoffman, A. (2024). Influence of 1 keV N2+ Implantation on Nitrogen Bonding, Defect Formation, and Thermal Stability of the Polycrystalline Diamond Near-Surface Region Studied by XPS, TPD, and HREELS. The Journal of Physical Chemistry C, 128(6), 2588-2603.

[10] Kuntumalla, Mohan Kumar, et al. “Bonding, Thermal and Ambient Stability of Nitrogen-Terminated Diamond (100) Surfaces by Plasma Exposure Studied by Ex-Situ XPS, HREELS, and DFT Modeling.” Novel Aspects of Diamond II: Science and Technology. Cham: Springer Nature Switzerland, 2024. 175-210.

[11] Fischer, M., Maity, S., Kuntumalla, M. K., Gani, G., & Hoffman, A. (2024). Subsurface nitrogen bonding, thermal stability, and retention of 200 eV N2+ implanted polycrystalline diamond studied by in situ X-ray photoelectron spectroscopy. Applied Surface Science, 657, 159740.

[12] Zheng, Y., Hoffman, A., & Huang, K. (2024). Nitridation of diamond (111) surface by density functional theory. The Journal of Chemical Physics, 160(21), 214713.