Surface Engineering on Diamond for Nitrogen-Vacancy Quantum Sensing Application: A Density Functional Theory Study

金剛石表面工程對碳氮空位色心量子傳感應用的密度泛函理論研究

Student thesis: Doctoral Thesis

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Award date5 May 2020

Abstract

The nitrogen vacancy (NV) color center in diamond is a prominent candidate as a solid−state quantum defect. Owing to the ease of manipulation and readout, long coherence times and high fidelity at room temperature, NV center have recently been extensively characterized and used in quantum information processing and nanosensing applications.

These diverse utilities rely on the electron spin state of the NV center which is very sensitive to the ambient condition. To achieve high sensitivity and spatial resolution, the color centers should be placed close proximity to the surface. However, NV centers near the diamond surface suffer from short spin coherence times due to surface spin noise, permanent bleaching caused by surface states intrusion, and low photon collection efficiency due to nonoptimal crystal orientation. Therefore, to stabilize and improve the performance of shallow NV centers, surface functionalization is an imperative step. Here in this thesis, using first principles calculations, we investigate the interaction of surface terminations with NV defect on specified diamond surfaces and find certain type of surface terminators are ideal for NV center nanosensing applications.

First, here we study the geometric and electronic structure of (113) diamond surface with various types of terminators. Results indicate that complete oxygen termination of (113) diamond creates positive electron affinity with neither strain on the surface nor ii in−gap levels. This is a very surprising result as the commonly employed oxygenated (001) diamond surface is often defective due to the disorder created by the strain of ether groups at the surface that seriously undermine the coherence properties of the shallow NV centers. The special atomic configurations on (113) diamond surface are favorable for oxygen bonding, in contrast to (001) and (111) diamond surfaces. These simulations imply that oxygenated diamond (113) surface can be produced by conventional diamond chemical vapor deposition growth.

Based on the above result on (113) diamond surface, we then demonstrate the oxygenated 2×1 (111) diamond surface which has the similar epoxide configuration could also server as potential host for NV center. The wide band gap property can be well preserved and there is no surface states intrusion. The proposed surface shows robust stability by evaluating the Gibbs free energy and experimental data.

Finally, the stability and electronic structures of NV centers with different charged state in (111) and (113) diamond have been investigated. The formation energy as a function of doping depth shows different evolution pattern for different charged states. The formation energy converges to same value with the increase of doping depth of neutral NV center while converges to different values for the negatively charged state based on the terminators. The surface dipole layer induces electrostatic potential change and plays a very important role in this non−decaying effect. Especially, we find the oxygenated diamond surface has the most dramatical effect on stabilizing the negatively charge state which matches the previous experimental result. Furthermore, compared iii to the (111) surface, the (113) surface has less surface related resonance states even for ultra−shallow doping.