Long spin coherence times of nitrogen vacancy centers in milled nanodiamonds
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2022-05-02 |
| Journal | Physical review. B./Physical review. B |
| Authors | Benjamin D. Wood, G. A. Stimpson, J. E. March, Yashna Lekhai, Colin Stephen |
| Institutions | Cardiff University, University of Warwick |
| Citations | 48 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Long Spin Coherence Times in Milled Nanodiamonds
Section titled âTechnical Documentation & Analysis: Long Spin Coherence Times in Milled NanodiamondsâReference: Wood et al., Long spin coherence times of nitrogen vacancy centers in milled nanodiamonds (arXiv:2112.01899v2, 2022).
Executive Summary
Section titled âExecutive SummaryâThis research validates the use of high-volume milling techniques on Chemical Vapor Deposition (CVD) diamond to produce nanodiamonds (NDs) suitable for advanced quantum applications, achieving record spin coherence times (T2) for this fabrication method.
- Record Coherence Time: Achieved an electron spin coherence time (T2) exceeding 400 ”s (specifically 462 ± 130 ”s using XY8-4 dynamical decoupling) at room temperature.
- Material Source: High-purity, low-nitrogen CVD bulk diamond (121 ppb single substitutional N, natural 13C abundance) was used as the starting material.
- Fabrication Advantage: Si3N4 ball milling was employed, enabling high-volume, 3D conversion of bulk material into NDs, overcoming the limitations of low-throughput etching methods.
- Validation for Quantum Sensing: The achieved T2 times are comparable to or longer than those previously reported for etched NDs, validating milled NDs for high-sensitivity AC magnetometry (sensitivity estimated at 100 nT Hz-1/2).
- Methodological Breakthrough: The study successfully correlated T2 measurements with Scanning Electron Microscopy (SEM) images of the exact nanodiamonds using etched silicon grid mapping, providing crucial size and location data (e.g., ND1 Rmax = 106 ± 2 nm).
- Core Application Focus: The results directly support applications in localized biological sensing and macroscopic quantum experiments, such as nanodiamond levitation.
Technical Specifications
Section titled âTechnical SpecificationsâExtracted hard data points and performance metrics from the research paper.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Maximum T2 Coherence Time (ND1) | 462 ± 130 | ”s | Room temperature, XY8-4 dynamical decoupling |
| Hahn Echo T2 (ND1) | 177 ± 24 | ”s | Room temperature |
| Average Hahn Echo T2 (7 NDs) | 51 | ”s | Room temperature |
| Source Nitrogen Concentration | 121 | ppb | Single substitutional N in bulk CVD diamond |
| Final Expected NV Concentration | ~1 | ppb | After 4.5 MeV electron irradiation and annealing |
| Single NV Confirmation (g(2)(0)) | 0.39 ± 0.02 | N/A | Hanbury Brown-Twiss (HBT) measurement (ND1) |
| Nanodiamond Size (ND1 Rmax) | 106 ± 2 | nm | Estimated maximum distance from surface via SEM |
| Maximum Annealing Temperature | 1200 | °C | Used for NV center formation |
| External Magnetic Field Range | 26 to 50 | mT | Applied during T2 measurements |
Key Methodologies
Section titled âKey MethodologiesâThe following steps outline the material preparation and measurement sequence used to achieve long T2 times in milled nanodiamonds.
- Source Material Preparation: Single-crystal CVD diamond (natural 13C, 121 ppb N) was selected.
- Vacancy Creation: The bulk diamond was irradiated with 4.5 MeV electrons for one minute to generate vacancies.
- NV Center Formation: A multi-step annealing process was performed: 3 hours at 400°C, 4 hours at 800°C, and 2 hours at 1200°C.
- Nanodiamond Fabrication: Si3N4 ball milling was used to convert the bulk material into nanodiamonds, avoiding magnetic contamination associated with steel milling.
- Surface Cleaning: The milled NDs were acid cleaned (H3PO4, NaOH) to remove Si3N4 contaminants, followed by an air anneal, resulting in a largely oxygen-terminated surface (C-Si, COOH, C=O, C-O, C=C, and C-C bonds).
- Sample Deposition: NDs were suspended in methanol (1 mg ml-1) and sprayed via nebulizer onto n-type silicon wafers featuring plasma-etched photolithography grids.
- Single NV Identification: Confocal Fluorescence Microscopy (CFM) and Hanbury Brown-Twiss (HBT) measurements (g(2)(0) < 0.5) were used to identify individual nanodiamonds containing a single NV- center.
- T2 Measurement: Spin-echo decay experiments (Hahn echo, XY8-1, XY8-4) were performed at room temperature, with evolution times specifically chosen to match the peaks of the intrinsic 13C revivals to simplify fitting.
- Physical Correlation: Scanning Electron Microscopy (SEM) was used in conjunction with the silicon grid markings to measure the size (Rmax) of the exact nanodiamonds for which T2 was measured.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe success of this research hinges on the quality and purity of the starting CVD diamond material and the ability to precisely control dimensions and defects. 6CCVD is uniquely positioned to supply the next generation of materials required to replicate and extend these record-breaking results, particularly for scaling up production or achieving even longer coherence times.
Applicable Materials for Replication and Extension
Section titled âApplicable Materials for Replication and ExtensionâThe paper utilized low-nitrogen CVD diamond with natural 13C abundance. To push T2 times further, researchers must minimize both nitrogen and the decoherence effects of the 13C nuclear spin bath.
| Research Requirement | 6CCVD Material Solution | Technical Advantage |
|---|---|---|
| High-Purity Bulk Material | Optical Grade Single Crystal Diamond (SCD) | Ultra-low defect density and nitrogen concentration (N < 1 ppb available), ideal for subsequent irradiation and high-volume milling. |
| Maximum Coherence Time | Isotopically Purified SCD | Available with 13C concentration < 100 ppm. Minimizing the 13C spin bath is critical for achieving T2 times in the millisecond range, essential for advanced quantum computing and sensing. |
| High-Volume Production | Polycrystalline Diamond (PCD) Substrates | Available in large formats (up to 125mm diameter) and thicknesses (up to 10mm), providing cost-effective bulk material for large-scale nanodiamond milling operations. |
Customization Potential & Engineering Support
Section titled âCustomization Potential & Engineering Supportâ6CCVDâs in-house capabilities directly address the material engineering challenges inherent in NV center research, particularly in preparing substrates for post-processing.
- Custom Dimensions and Thickness: The paper relies on bulk material. 6CCVD offers custom SCD plates and PCD wafers up to 125mm in diameter and substrates up to 10mm thick, ensuring sufficient volume for large-scale milling runs.
- Surface Engineering: While the paper used acid cleaning and air annealing for oxygen termination, 6CCVD offers precision polishing (Ra < 1nm for SCD, < 5nm for inch-size PCD) and custom metalization (Au, Pt, Pd, Ti, W, Cu) for researchers requiring specific surface terminations or integrated microwave/ODMR structures on their bulk diamond prior to milling or etching.
- Defect Control Consultation: The precise control of nitrogen concentration (121 ppb used here) and subsequent irradiation dose is crucial for optimizing the final NV concentration (~1 ppb). 6CCVDâs in-house PhD team can assist with material selection and specification to optimize the starting material purity for specific NV creation recipes (e.g., for high-density NV ensembles or single-NV applications like nanodiamond levitation).
- Global Logistics: We provide reliable, global shipping (DDU default, DDP available) for sensitive, high-value diamond materials, ensuring rapid delivery to research facilities worldwide.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Nanodiamonds containing negatively charged nitrogen vacancy centres\n(${\text{NV}}^{-}$) have applications as localized sensors in biological\nmaterial and have been proposed as a platform to probe the macroscopic limits\nof spatial superposition and the quantum nature of gravity. A key requirement\nfor these applications is to obtain nanodiamonds containing ${\text{NV}}^{-}$\nwith long spin coherence times. Using milling to fabricate nanodiamonds\nprocesses the full 3D volume of the bulk material at once, unlike etching, but\nhas, up to now, limited ${\text{NV}}^{-}$ spin coherence times. Here, we use\nnatural isotopic abundance nanodiamonds produced by\n${\text{Si}}{3}{\text{N}}{4}$ ball milling of bulk diamond grown by chemical\nvapour deposition with an average single substitutional nitrogen concentration\nof $121 ~\text{ppb}$. We show that the electron spin coherence times of\n${\text{NV}}^{-}$ centres in these nanodiamonds can exceed $400 ~\mu\text{s}$\nat room temperature with dynamical decoupling. Scanning electron microscopy\nprovides images of the specific nanodiamonds containing ${\text{NV}}^{-}$ for\nwhich a spin coherence time was measured.\n