Impact of surface and laser-induced noise on the spectral stability of implanted nitrogen-vacancy centers in diamond
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2021-08-24 |
| Journal | Physical review. B./Physical review. B |
| Authors | Srivatsa Chakravarthi, Christian Pederson, Zeeshawn Kazi, A. D. Ivanov, KaiâMei C. Fu |
| Institutions | University of Washington |
| Citations | 25 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Spectral Stability of Implanted NV Centers
Section titled âTechnical Documentation & Analysis: Spectral Stability of Implanted NV CentersâReference: Chakravarthi et al., Impact of surface and laser-induced noise on the spectral stability of implanted nitrogen-vacancy centers in diamond (arXiv:2105.09483v2, 2021).
Executive Summary
Section titled âExecutive SummaryâThis research successfully demonstrates the viability of ion implantation for creating optically stable Nitrogen-Vacancy (NV) centers in high-purity Single Crystal Diamond (SCD), while critically identifying surface proximity as the dominant source of optical decoherence for shallow defects.
- Core Achievement: Creation of 15NV centers via ion implantation (85 keV) and high-temperature annealing, achieving near lifetime-limited optical linewidths (< 60 MHz) for centers implanted at ~100 nm depth.
- Critical Finding: NV centers implanted shallowly (~20 nm) exhibited significantly reduced optical coherence (median linewidths 0.5 GHz to 1.2 GHz), implying that surface charge traps are a greater source of perturbation than bulk implantation damage.
- Material Requirement: Electronic-grade SCD with ultra-low native nitrogen (N < 1 ppb) and boron (B < 1 ppb) concentrations is essential to ensure NV formation is dominated by implanted 15N.
- Processing Necessity: Rigorous surface preparation, including deep plasma etching (~5 ”m removal) to eliminate polishing damage and subsequent high-temperature (1100 °C) vacuum annealing, is required for defect activation.
- Stability Demonstrated: Long-term spectral stability (variation < 100 MHz) was observed for deeper NV centers, supporting their use in scalable quantum networking protocols.
- 6CCVD Value Proposition: 6CCVD provides the necessary ultra-high purity SCD substrates and expert consultation on surface preparation (Ra < 1 nm polishing) and post-processing requirements to replicate and advance this critical quantum research.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the experimental methodology and results:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Initial Substrate Material | Electronic Grade SCD | N/A | N < 1 ppb, B < 1 ppb |
| Crystallographic Orientation | (100) | N/A | Used for all samples |
| Initial Surface Roughness (Ra) | < 1 | nm | As-purchased polished surface |
| Post-Etch Surface Roughness (Ra) | 0.43 to 0.63 | nm | After Ar/Cl2 and O2 plasma etch |
| Ion Implantation Species | 15N | N/A | Used for deterministic NV creation |
| Ion Energy | 85 | keV | Fixed energy for primary samples |
| Implantation Dose | 3e9 | ions/cm2 | Effective beam dosage |
| Normal Implant Depth (7°) | 100 ± 20 | nm | Deeper, stable NV centers (Sample A) |
| Oblique Implant Depth (85°) | 21 ± 13 | nm | Shallower, unstable NV centers (Sample B) |
| High-Temperature Annealing | 1100 | °C | Vacuum ( < 1.4x10-7 mbar), 2 hours |
| Surface Termination Annealing | 435 | °C | O2 flow, 2 hours (NV- charge stabilization) |
| Stable NV Linewidth (Median) | < 60 | MHz | Near lifetime-limited (100 nm depth) |
| Unstable NV Linewidth (Median) | 0.5 to 1.2 | GHz | Broadened due to surface proximity (20 nm depth) |
| Long-Term Spectral Stability | < 100 | MHz | Variation between re-pump pulses (100 nm depth) |
| ZPL Distribution FWHM (Sample B) | 126 | GHz | Broadest distribution, indicating residual strain/surface effects |
Key Methodologies
Section titled âKey MethodologiesâThe experiment relied on precise material preparation and controlled post-growth processing to achieve high-coherence NV centers.
- Substrate Preparation: Electronic grade SCD with (100) surface was polished to Ra < 1 nm.
- Damage Removal Etch: Approximately 5 ”m of diamond was removed via plasma reactive-ion etching (RIE) to eliminate subsurface polishing damage.
- Cleaning Protocol: Samples were cleaned in a boiling 1:1:1 acid mixture (H2SO4, HNO3, HClO4) at 260 °C for 1 hour to remove organic and graphitic contaminants.
- Two-Step Plasma Etch:
- Step 1 (Physical): Ar/Cl2 plasma (45 min) for physical sputtering/etching (RF 240 W, ICP 320 W, DC bias 530 V).
- Step 2 (Chemical): O2 plasma (20 min) for chemical etching/oxidation (RF 50 W, ICP 1500 W, DC bias 150 V).
- Ion Implantation: 15N ions were implanted at 85 keV with a dose of 3e9 ions/cm2. Depth was controlled by angle: 7° (100 nm deep) or 85° (20 nm deep).
- NV Formation Annealing: Samples were vacuum annealed ( < 1.4x10-7 mbar) at 1100 °C for 2 hours to mobilize vacancies and form NV centers.
- Charge State Stabilization: A final anneal was performed at 435 °C under O2 flow for 2 hours to oxygen terminate the surface and stabilize the negative NV charge state (NV-).
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe findings of this research underscore the critical role of high-quality, ultra-pure diamond substrates and precise surface engineering in achieving optically coherent NV centers for quantum applications. 6CCVD is uniquely positioned to supply the materials and processing support necessary to replicate and scale this work.
Applicable Materials
Section titled âApplicable MaterialsâTo replicate the high-coherence results achieved in Sample A (100 nm depth), researchers require material with extremely low native defect density.
| Research Requirement | 6CCVD Solution | Technical Specification |
|---|---|---|
| Ultra-Low Native Defects | Optical Grade SCD | N < 1 ppb, B < 1 ppb (Electronic Grade Equivalent) |
| Crystallographic Control | Custom Orientation | Standard (100) or custom (111) for enhanced NV alignment |
| Thickness Control | SCD Wafers | Thicknesses available from 0.1 ”m up to 500 ”m |
Customization Potential
Section titled âCustomization PotentialâThe study highlights that surface quality (Ra < 1 nm) and the removal of polishing damage (~5 ”m etch) are non-negotiable for achieving stable shallow NV centers. 6CCVD offers tailored material preparation services to meet these stringent demands:
- Precision Polishing: We guarantee SCD surfaces with roughness Ra < 1 nm, matching or exceeding the starting material quality used in this study.
- Custom Dimensions: While the paper used small samples, 6CCVD can provide SCD plates and PCD wafers up to 125 mm in diameter, enabling large-scale device fabrication and integration.
- Pre-Etched Substrates: We can supply substrates pre-thinned or pre-etched to specific depths, reducing the need for complex in-house RIE processing and ensuring the removal of subsurface damage layers.
- Metalization Services: For future integration into hybrid materials platforms or photonic structures (as discussed in the paperâs introduction), 6CCVD offers in-house metalization capabilities, including Ti/Pt/Au, Pd, W, and Cu thin films.
Engineering Support
Section titled âEngineering SupportâThe central conclusionâthat surface proximity is the dominant source of decoherenceârequires careful mitigation strategies. 6CCVDâs in-house PhD engineering team specializes in defect engineering and surface science for quantum applications.
- Defect Engineering Consultation: We assist clients in optimizing implantation parameters (energy, dose, angle) and post-processing recipes (annealing temperature, vacuum level, gas termination) to maximize NV yield and spectral stability.
- Surface Termination Optimization: We provide guidance on achieving optimal surface termination (e.g., oxygen termination via 435 °C O2 anneal) to stabilize the NV- charge state, a critical step demonstrated in this research.
- Global Logistics: We offer reliable global shipping (DDU default, DDP available) to ensure sensitive materials arrive safely and promptly for time-critical research.
For custom specifications or material consultation regarding NV center creation, surface preparation, or quantum device integration, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Scalable realizations of quantum network technologies utilizing the nitrogen vacancy center in diamond require creation of optically coherent NV centers in close proximity to a surface for coupling to optical structures. We create single NV centers by $^{15}$N ion implantation and high-temperature vacuum annealing. Origin of the NV centers is established by optically detected magnetic resonance spectroscopy for nitrogen isotope identification. Near lifetime-limited optical linewidths ($<$ 60 MHz) are observed for the majority of the normal-implant (7$^\circ$, $\approx$ 100 nm deep) $^{15}$NV centers. Long-term stability of the NV$^-$ charge state and emission frequency is demonstrated. The effect of NV-surface interaction is investigated by varying the implantation angle for a fixed ion-energy, and thus lattice damage profile. In contrast to the normal implant condition, NVs from an oblique-implant (85$^\circ$, $\approx$ 20 nm deep) exhibit substantially reduced optical coherence. Our results imply that the surface is a larger source of perturbation than implantation damage for shallow implanted NVs. This work supports the viability of ion implantation for formation of optically stable NV centers. However, careful surface preparation will be necessary for scalable defect engineering.