Investigation of the Nitrogen Bonding Configuration at Near-Surface and Subsurface of Low-Energy N₂⁺ Implanted Polycrystalline Diamond

The negatively charged nitrogen vacancy (NV^-) center in diamond is an excellent single photon emitter¹ and thus it has brought revolution in quantum sensing technologies,² biomarking,³ and as a sensitive probe to magnetic field.⁴ To achieve its best performance in quantum devices, we need to get an exact picture of the near-surface and subsurface region of nitrogen-populated diamond. This is essential since nitrogen-induced defects may be responsible for charge trapping which may destabilize the NV^- center.⁵ On the other hand, the chemical composition of the diamond surface can cause the shifting of the Fermi level beyond the NV^- center.⁶ Hence, one’s aim should be the creation of nitrogen terminated diamond, without forming substantial defect. Over the years, we achieved to the conclusion that, focused ion beam implantation is a profitable technique to get enriched N-terminated diamond of high purity.^7-9 Location and density of N atoms can be precisely controlled on the diamond surface through ion implantation, leading to the formation of long coherence time.¹⁰
In this work, considerable low energy (100 eV) positive nitrogen ions (N₂⁺) are irradiated on chemical-vapor-deposited (CVD-grown) polycrystalline diamond thin films at room temperature. We altered the ion dose within the range of 1 × 10¹⁴ ions.cm^-2 to 2 × 10¹⁵ ions.cm^-2. The bonding configuration of carbon and nitrogen and the chemical composition of the implanted layer are thoroughly scrutinized using X-Ray Photoelectron Spectroscopy (XPS). The thermal stability of the implanted layer and its different bonding configuration has also been examined. The results indicate that the controlled N₂⁺ dose of low ion energy can populate the near surface region effectively, with creating minimal defect and variable intensities of the different C-N components.

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