Charge state dynamics and optically detected electron spin resonance contrast of shallow nitrogen-vacancy centers in diamond
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-08-18 |
| Journal | Physical Review Research |
| Authors | Zhiyang Yuan, Mattias Fitzpatrick, Lila V. H. Rodgers, Sorawis Sangtawesin, Srikanth Srinivasan |
| Institutions | Princeton University |
| Citations | 39 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research investigates the critical degradation of shallow Nitrogen-Vacancy (NV) center performance near the diamond surface, a major hurdle for nanoscale quantum sensing applications.
- Core Problem Identified: The Optically Detected Electron Spin Resonance (OD-ESR) contrast (CESR) of shallow NV centers is significantly decreased due to surface-dependent charge state dynamics.
- Mechanism of Degradation: Contrast loss stems from two effects: (1) increased background fluorescence due to a higher steady-state population of the neutral charge state (NV0), and (2) fast charge conversion rates (ionization/recombination) that compete with the intrinsic NV spin polarization and readout dynamics.
- Surface Dependence: A contaminated sample (Sample F, exhibiting ~4% boron surface contamination via XPS) showed markedly lower CESR (below 0.3) and much faster charge conversion rates compared to a cleaner sample (Sample A).
- Kinetic Interference: In Sample F, charge conversion rates under green illumination reached up to 7.5 x 106 s-1, comparable to the NV spin polarization rate, actively interfering with spin readout.
- Modeling Achievement: A coupled rate equation model successfully quantified the relative contributions of static NV0 population and dynamic charge conversion interference to the overall CESR reduction.
- Engineering Implication: The findings emphasize that meticulous surface preparation and engineering (e.g., optimal termination) are essential for stabilizing the desired negative charge state (NV-) and achieving robust nanoscale quantum sensing.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Typical OD-ESR Contrast (Sample A) | 0.38 to 0.42 | Arb. | High-contrast NV centers |
| Typical OD-ESR Contrast (Sample F) | 0.15 to 0.17 | Arb. | Low-contrast NV centers |
| Spin Coherence Time (T2) | < 4 | ”s | Observed in low-contrast Sample F |
| N Ion Implantation Energy (Sample A) | 3 | keV | NV center formation |
| N Ion Implantation Energy (Sample F) | 1.5 | keV | NV center formation (expected shallower depth) |
| N Ion Implantation Dose (Sample A) | 5 x 108 | cm-2 | |
| N Ion Implantation Dose (Sample F) | 1 x 109 | cm-2 | |
| Boron Surface Contamination (Sample F) | ~4 | % | Atomic percentage of a surface monolayer (via XPS) |
| Dark Charge Conversion Time (Sample F) | 11 to 300 | ms | Timescale for NV- population decay in the dark |
| Dark Charge Conversion Time (Sample A) | > 1 | s | NV- population stability in the dark |
| Max Charge Conversion Rate (Sample F) | Up to 7.5 x 106 | s-1 | Under green illumination (P532 up to 400 ”W) |
| Green Excitation Wavelength | 532 | nm | Optically pumping and readout |
| Orange Excitation Wavelength | 590 | nm | Preferential excitation of NV- for charge state readout |
| Excited State Lifetime (ES0 Ï) | 10 to 13 | ns | Fitted intrinsic NV parameter (Table S2) |
Key Methodologies
Section titled âKey MethodologiesâThe NV centers were fabricated and characterized using a multi-step process focusing on surface control and time-resolved optical measurements:
- Substrate Preparation: Electronic grade diamond was scaife polished (RMS roughness < 1 nm).
- Damage Removal: Inductively-coupled plasma reactive ion etching (ICP-RIE) was performed, followed by high-temperature (1200 °C) vacuum annealing to remove surface/subsurface damage.
- Initial Cleaning (Triacid): Samples were cleaned in a refluxing mixture of concentrated sulfuric, nitric, and perchloric acids to remove amorphous carbon.
- NV Center Formation: Nitrogen ion implantation (1.5 keV or 3 keV energy) was used, followed by vacuum annealing (800 °C) to form NV centers.
- Surface Termination: Samples A, C, D, E, and F underwent oxygen annealing (440 °C - 460 °C) to create well-ordered oxygen-terminated diamond surfaces.
- Final Cleaning (Piranha): Oxygen-annealed samples were cleaned in Piranha solution (1:2 hydrogen peroxide:concentrated sulfuric acid).
- Surface Characterization: X-ray photoelectron spectroscopy (XPS) was used to confirm surface contamination (e.g., persistent boron contamination in Sample F).
- Optical Measurement Setup: A home-built confocal microscope (Nikon Plan Fluor 100x, N.A. = 1.30 oil immersion objective) was used for photoluminescence (PL) and OD-ESR measurements.
- Time-Resolved Dynamics: Time-resolved PL traces were measured using a PicoHarp (128 ps sampling resolution) and analyzed using a coupled 7-level rate equation model that incorporated both NV- spin dynamics and NV0 charge states, including ionization (Îion) and recombination (Îrec) rates.
Commercial Applications
Section titled âCommercial ApplicationsâThe stabilization of shallow NV centers is crucial for advancing diamond-based quantum technologies, particularly in sensing and information processing.
- Nanoscale Quantum Sensing: Enabling high-sensitivity, high-resolution magnetometry and electric field sensing for material science, biological imaging, and defect analysis, especially within 10 nm of a surface.
- Solid-State Qubits: Providing a pathway for stabilizing the NV- charge state, which is necessary for utilizing NV centers as robust, room-temperature solid-state qubits in quantum computing architectures.
- Quantum Information Processing (QIP) Interfaces: Developing reliable interfaces between NV centers and external quantum systems (e.g., superconducting circuits or molecules) by ensuring high spin readout fidelity near the surface.
- Diamond Surface Engineering: Establishing best practices for post-processing treatments (cleaning, annealing, termination) to mitigate surface charge traps and contaminants (like boron), thereby maximizing NV performance metrics (CESR and T2).
- Advanced Material Characterization: Using NV centers as internal probes to study charge trap dynamics and noise mechanisms at the diamond-environment interface.
View Original Abstract
Nitrogen-vacancy (NV) centers in diamond can be used for nanoscale sensing\nwith atomic resolution and sensitivity; however, it has been observed that\ntheir properties degrade as they approach the diamond surface. Here we report\nthat in addition to degraded spin coherence, NV centers within nanometers of\nthe surface can also exhibit decreased fluorescence contrast for optically\ndetected electron spin resonance (OD-ESR). We demonstrate that this decreased\nOD-ESR contrast arises from charge state dynamics of the NV center, and that it\nis strongly surface-dependent, indicating that surface engineering will be\ncritical for nanoscale sensing applications based on color centers in diamond.\n