| Metadata | Details |
|---|
| Publication Date | 2025-10-26 |
| Journal | Advanced Optical Materials |
| Authors | Bradley T. Flinn, William J. Cull, Ian Cardillo‐Zallo, James Kerfoot, Benjamin L. Weare |
| Institutions | University of Nottingham |
| Analysis | Full AI Review Included |
- Core Objective: The study investigated the stability of Nitrogen-Vacancy (NV) photoluminescence (PL) and sensing contrast in fluorescent nanodiamonds (FNDs) under Transmission Electron Microscopy (TEM) electron beam (e- beam) irradiation across energies (20-200 keV) and fluences (103-107 e- nm-2).
- Optimal Imaging Conditions: Non-invasive imaging for Correlative Light-Electron Microscopy (CLEM) is achieved using a 200 keV e- beam at fluences less than 105 e- nm-2, ensuring the retention of PL and magnetic sensing properties.
- Damage Mechanism Elucidation: NV quenching occurs well below the displacement energy threshold (Ed ≈ 30 eV) for pristine bulk diamond, confirming a complex mechanism dominated by ionization-assisted Direct Knock-On (DKO) atomic displacement.
- Fluence Regime Dependence: In the low fluence regime (<106 e- nm-2), quenching is greatest at lower energies (80 keV) due to higher ionization cross-sections. In the high fluence regime (>106 e- nm-2), quenching is greatest at 200 keV due to higher DKO cross-sections.
- Sensing Stability: Optically Detected Magnetic Resonance (ODMR) and Magnetic Modulation (MM) sensing contrast generally track PL loss but show better preservation at 80 keV high fluence compared to PL intensity, reflecting the sensitivity of spin measurements to the broader distribution of spin-active defects.
- Nanofabrication Potential: The methodology enables controlled, top-down spatial patterning of diamond PL by selectively deactivating NVs, providing a route for nanofabricated NV structures.
| Parameter | Value | Unit | Context |
|---|
| Electron Beam Energies Tested | 20, 80, 100, 200 | keV | TEM accelerating voltages |
| Electron Fluence Range Tested | 103 to 107 | e- nm-2 | Range used for irradiation studies |
| Optimal Non-Invasive Fluence | <105 | e- nm-2 | Recommended for 200 keV CLEM imaging |
| FND Particle Diameter (Average) | ~100 | nm | Commercial HPHT FNDs (brFND-100) |
| FND Thickness (Average) | 40 ± 2 | nm | Estimated from 3D TEM tilt-series imaging |
| Pristine C Displacement Energy (Ed) | 30 | eV | Threshold for DKO in bulk diamond lattice |
| C-Vacancy Adjacent Ed (Lower Bound) | 2.3 | eV | Energy for anisotropic C-vacancy substitution |
| C-Vacancy Adjacent Ed (Upper Bound) | 13.0 | eV | Energy for isotropic C atom displacement |
| Maximum Transferable Energy (ETmax) | 43.7 | eV | At 200 keV beam energy |
| Ionization Cross Section (σi) Ratio (20/200 keV) | ~5 | orders of magnitude | Ionization is 5x greater at 20 keV than 200 keV |
| Residual PL (200 keV, Low Fluence) | 98 ± 1 | % | At 1.1 x 103 e- nm-2 |
| Residual ODMR (200 keV, High Fluence) | 5 ± 3 | % | At 9.0 x 106 e- nm-2 |
| Residual ODMR (80 keV, High Fluence) | 64 ± 4 | % | At 1.5 x 107 e- nm-2 (Significantly higher retention than 200 keV) |
| NV- ZPL Wavelength | 637 | nm | Corresponds to 1.95 eV |
| NV0 ZPL Wavelength | 575 | nm | Corresponds to 2.16 eV |
- Sample Preparation: Commercial NV-rich HPHT FNDs (~100 nm) were drop-cast onto TEM Au holey carbon finder grids for subsequent Correlative Light-Electron Microscopy (CLEM).
- Electron Beam Irradiation: Irradiation was performed using a JEOL 2100+ TEM at 20, 80, 100, and 200 keV. Electron flux was calibrated using a Faraday cup and Keithley 6485 Picoammeter to ensure accurate fluence control (103-107 e- nm-2).
- NV Sensing (ODMR and MM): PL and sensing contrast were measured using an inverted fluorescence microscope setup.
- ODMR involved sweeping the MW frequency (2.77-2.97 GHz) to probe the NV- ground state spin transitions.
- MM involved modulating an external off-axis magnetic field (0-40 mT) to measure PL contrast changes related to spin-noise.
- PL Mapping and Charge-State Analysis: A confocal Raman microscope was used to map PL intensity and determine the NV-/NV0 ZPL ratio before and after irradiation, confirming that PL quenching was not primarily due to simple, permanent charge-state conversion.
- Structural Characterization: Selected Area Electron Diffraction (SAED) and Electron Energy Loss Spectroscopy (EELS) were performed at 80 keV and 200 keV to confirm minimal bulk lattice damage or change in C bonding environment, supporting the localized defect mechanism.
- Theoretical Modeling: Monte Carlo CASINO simulations were used to model electron trajectories in the FNDs (~40 nm thickness). Atomic displacement (DKO) and ionization cross-sections were calculated to quantify the probability of proposed damage mechanisms (anisotropic low-E vacancy migration and isotropic high-E atomic displacement).
- Quantum Sensing Platforms: Provides the necessary engineering parameters (200 keV, <105 e- nm-2) for integrating TEM imaging into NV-based quantum sensing protocols, crucial for high-resolution CLEM of FNDs interacting with external spin-active materials.
- Nanofabrication of Diamond Devices: Enables a controlled, top-down approach for spatial patterning of NV PL properties by selectively deactivating NVs, which is essential for creating complex quantum circuits and engineered diamond structures.
- Diamond Platform Manufacturing: The ability to selectively deactivate NVs allows for the creation of non-fluorescent fiducial markers on diamond substrates, solving a key normalization problem in multi-step diamond sensing platform fabrication.
- Diamond Relaxometry: Opens avenues for engineering the diamond spin environment (T1 and T2 processes) through targeted e- beam irradiation, optimizing diamond materials for advanced magnetic and thermal sensing applications.
- High-Quality Nanodiamond Products: The research informs the stability and robustness of NV-rich HPHT nanodiamonds (such as those used in this study, e.g., brFND-100) under invasive imaging techniques, ensuring product reliability for quantum technology end-users.
View Original Abstract
Abstract Nitrogen‐vacancy (NV) photoluminescence (PL) in diamond is fundamental to its function as a color center, underpinning advances in sensing science and quantum technologies. The work herein provides critical insights into the atomistic mechanisms of electron beams interacting with NV centers, which are crucial for advancing robust quantum sensing at the nanoscale and controlling the functional properties of nanodiamonds. NV PL and sensing stability of NV‐rich fluorescent nanodiamonds (FNDs) under electron beam irradiation is probed, across a range of energies (20, 80, 100, and 200 keV) and fluences (≈10 3 to 10 7 e − nm −2 ). PL intensity, NV charge‐state ratios, and sensing contrast, as monitored via optically detected magnetic resonance (ODMR) and magnetic modulation (MM) of PL, are examined. Results reveal complex mechanisms governing interactions between NV‐centers and fast electrons, dominated by ionization and direct knock‐on (DKO) effects, which allow to establish optimum imaging conditions where FNDs can be imaged with sub‐nanometer resolution while preserving their PL and sensing properties (200 keV, <10 5 e − nm −2 ). This methodology enables controlled, top‐down spatial patterning of diamond PL by selectively deactivating NVs, providing novel routes to patterned NV creation.