Influence of (N,H)-terminated surfaces on stability, hyperfine structure, and zero-field splitting of NV centers in diamond
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2022-02-17 |
| Journal | Physical review. B./Physical review. B |
| Authors | Wolfgang Körner, Reyhaneh Ghassemizadeh, Daniel F. Urban, Christian ElsÀsser |
| Institutions | Fraunhofer Institute for Mechanics of Materials, University of Freiburg |
| Citations | 17 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis DFT analysis investigates the stability and quantum properties of shallow Nitrogen-Vacancy (NV-) centers in diamond near mixed (N,H)-terminated surfaces, providing critical guidelines for quantum device engineering.
- Stability Requirement: A minimum of 25% substitutional Nitrogen termination on the diamond surface is required to maintain the stable negative charge state (NV-) of the defect complex.
- Optimal Configuration: Axial NV centers near a flat 100% N-terminated (111) surface are the ideal choice for quantum sensing, as their high symmetry minimizes disturbance from surface proximity.
- Bulk-Like Performance Distance: NV centers achieve bulk-like functional properties (ZFS and HFS) when situated at a distance of 8 A or greater from the surface.
- Surface Chemistry Influence: Above the 25% N threshold, the specific N:H ratio and the surface orientation ((001) vs. (111)) have only a minor effect on the NV centerâs ground state properties.
- Parameter Sensitivity: The Zero-Field Splitting (ZFS) axial component (D) is the most sensitive parameter, showing a reduction of up to 25% near the surface, while Hyperfine Structure (HFS) constants converge rapidly (within 4 A).
- Electron Affinity (EA) Control: The EA changes from negative (H-rich) to positive (N-rich) at approximately 33% N for the (111) surface and 25% N for the (001) surface.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Minimum N Termination for Stable NV- | 25 | % | Required N concentration to bind the extra electron. |
| Critical N Termination for Positive EA (001) | ~25 | % | Threshold for Electron Affinity sign change. |
| Critical N Termination for Positive EA (111) | ~33 | % | Threshold for Electron Affinity sign change. |
| Distance for Bulk-like Properties | > 8 | A | Minimum distance for marginal surface disturbance. |
| Distance for Bulk-like HFS | > 4 | A | Hyperfine Structure constants converge quickly. |
| Maximum ZFS (D) Reduction | 25 | % | Reduction observed for shallow NV centers near surfaces. |
| Bulk ZFS (Dzz) (Experimental) | 2.872 (±0.002) | GHz | Reference value for the 3A2 ground state. |
| 13C Hyperfine Constant (A11) (Bulk) | ~100 | MHz | Typical bulk value for 13C HFS. |
| 14N Hyperfine Constant (A11) (Bulk) | -2.16 | MHz | Typical bulk value for 14N HFS. |
| DFT Plane-Wave Cutoff Energy | 420 | eV | VASP calculation parameter. |
| DFT Force Relaxation Threshold | < 0.03 | eV/A | Maximum residual force during structural relaxation. |
| Diamond Lattice Constant (Bulk) | 3.567 | A | Used for supercell model construction. |
Key Methodologies
Section titled âKey Methodologiesâ- Simulation Framework: Density Functional Theory (DFT) calculations were performed using the Vienna Ab Initio Simulation Package (VASP).
- Exchange-Correlation Functional: The Generalized Gradient Approximation (GGA) using the Perdew, Burke, and Ernzerhof (PBE) functional was employed.
- Supercell Model Construction: Atomistic slab models were built for (111) and (001) diamond surfaces, containing approximately 1000 atoms plus a vacuum region (10-12 A).
- Surface Termination Study: Surfaces were modeled with pure H, pure N, and mixed (N,H) terminations, specifically investigating N concentrations of 16.7%, 20%, 25%, 50%, and 100%.
- NV Center Placement: All symmetry-inequivalent NV positions (axial and basal orientations) were tested relative to the surface, up to a maximum depth of 14 A.
- Charged Defect Modeling: The negatively charged NV- center was simulated using the charged supercell approach (adding one extra electron to the system) to ensure charge neutrality of the overall slab.
- Structural Relaxation: Atomic positions were relaxed until residual forces were less than 0.03 eV/A, using a plane-wave cutoff energy of 420 eV.
- Property Evaluation: Key quantum parameters calculated included formation energy, electronic Density of States (DOS), Hyperfine Structure (HFS) tensors (AIij), and Zero-Field Splitting (ZFS) tensors (Dij).
Commercial Applications
Section titled âCommercial ApplicationsâThe findings directly support the engineering and optimization of diamond-based quantum devices, particularly those requiring NV centers located extremely close to the surface.
- Quantum Magnetometry: Utilizing shallow NV- centers as atomic magnetic-field probes for high spatial resolution sensing (spatial-atomic-resolution quantum magnetometry).
- Solid-State Quantum Computing: Employing NV centers as stable qubits (functional elements) in diamond crystal structures for quantum information processing.
- Scanning Magnetic-Field Sensors: Developing high-sensitivity sensors where the atomic probe must be positioned as close as possible (less than 10 A) to the external magnetic field source.
- Optimized Diamond Growth: Providing specific N:H ratio targets (e.g., > 25% N) and surface orientation preferences ((111) N-terminated) for experimental diamond growth processes aimed at creating stable, shallow NV centers.
- Surface Spin Noise Mitigation: Designing surfaces (e.g., flat, 100% N-terminated) that avoid unpaired surface spins, thereby reducing a major source of decoherence noise (T2 time limitation) in NV-based sensors.
View Original Abstract
We present a density functional theory analysis of the negatively charged\nnitrogen-vacancy (NV$^-$) defect complex in diamond located in the vicinity of\n(111)- or (100)-oriented surfaces with mixed (N,H)-terminations. We assess the\nstability and electronic properties of the NV$^-$ center and study their\ndependence on the H:N ratio of the surface termination. The formation energy,\nthe electronic density of states, the hyperfine structure and zero-field\nsplitting parameters of an NV$^-$ center are analyzed as function of its\ndistance and orientation to the surface. We find stable NV$^-$ centers with\nbulk-like properties at distances of at least $\sim8$ Angstroem from the\nsurface provided that the surface termination consists of at least 25\%\nsubstitutional nitrogen atoms. Our results indicate that axial NV centers near\na flat 100\% N-terminated (111) surface are the optimal choice for NV-based\nquantum sensing applications as they are the least influenced by the proximity\nof the surface.\n