Effects of Thermal Oxidation and Proton Irradiation on Optically Detected Magnetic Resonance Sensitivity in Sub-100 nm Nanodiamonds
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2025-03-30 |
| Journal | ACS Applied Materials & Interfaces |
| Authors | Pietro AprĂ , G. Zanelli, Elena Losero, Nour-Hanne Amine, Greta Andrini |
| Institutions | Torino e-district, Istituto Nazionale di Fisica Nucleare |
| Analysis | Full AI Review Included |
Technical Analysis: Optimizing Nanodiamonds for Quantum Sensing
Section titled âTechnical Analysis: Optimizing Nanodiamonds for Quantum SensingâExecutive Summary
Section titled âExecutive SummaryâThis document analyzes the research paper, âEffects of Thermal Oxidation and Proton Irradiation on Optically Detected Magnetic Resonance Sensitivity in Sub-100 nm Nanodiamonds,â focusing on the material science and processing techniques used to optimize nanodiamonds (NDs) for quantum sensing in biological environments.
- Core Achievement: The study successfully developed a protocol combining thermal oxidation and proton irradiation to produce ultra-small nanodiamonds (average diameter < 20 nm) while retaining high Optically Detected Magnetic Resonance (ODMR) temperature sensitivity.
- Key Metric: The resulting sub-20 nm NDs achieved a shot-noise-limited temperature sensitivity of approximately ~10 K/âHz, which is the best reported sensitivity for NDs in this size range.
- Processing Strategy: The method utilized high-temperature annealing (800 °C) and controlled thermal oxidation (500 °C) for purification and size reduction, followed by 2 MeV proton irradiation (up to 4 x 1016 cm-2 fluence) to enhance Nitrogen-Vacancy (NV) center density.
- Surface Optimization: Oxidation proved crucial for promoting oxygen-containing surface terminations, which stabilize the negatively charged NV- state (optimal for sensing) over the neutral NV0 state.
- Biological Relevance: Achieving high sensitivity in sub-20 nm particles is critical for minimally invasive, high-spatial-resolution quantum sensing within biological systems, such as monitoring cellular membrane channels.
- Material Limitation: The study utilized commercial HPHT NDs, noting that MPCVD (CVD) NDs are particularly promising for future work due to their superior purity and control over nitrogen incorporation.
Technical Specifications
Section titled âTechnical SpecificationsâThe following table summarizes the critical material and performance parameters extracted from the research:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Initial Median ND Size (HPHT) | ~55 | nm | Starting material |
| Final Average ND Size (IrrhighND) | 18.5 ± 0.4 | nm | Maximum height via AFM, post-processing |
| ODMR Temperature Sensitivity (η) | ~10 | K/âHz | Shot-noise limited sensitivity (best for sub-20 nm) |
| High Proton Irradiation Fluence (F) | 4 x 1016 | cm-2 | Used for IrrhighND sample |
| Low Proton Irradiation Fluence (F) | 1 x 1015 | cm-2 | Used for IrrlowND sample |
| Proton Irradiation Energy | 2 | MeV | H+ beam energy |
| Initial Annealing Temperature | 800 | °C | 2 hours in N2 flow (sp2 carbon removal) |
| Oxidation Temperature | 500 | °C | In air environment (surface termination/size reduction) |
| Optimal NV-/NV0 Ratio | ~3.5 | Ratio | Achieved with 3h oxidation (OxlowND) |
| Native Nitrogen Concentration | ~100 | ppm | Present in HPHT starting material |
Key Methodologies
Section titled âKey MethodologiesâThe optimization protocol relies on precise thermal and irradiation steps to control surface chemistry, reduce particle size, and maximize the concentration of stable NV- centers:
- Initial Annealing (Purification):
- Conditions: 800 °C for 2 hours in N2 flow.
- Purpose: Convert amorphous sp2 carbon phases covering the ND surface into graphite (AnnND).
- Surface Oxidation (Size Reduction & NV- Stabilization):
- Conditions: Thermal etching at 500 °C in air environment.
- Durations: 3 hours (OxlowND) or 36 hours (OxhighND).
- Purpose: Selectively etch graphitic phases, reduce size distribution, and introduce oxygen-containing chemical groups to favor the NV- charge state.
- Proton Irradiation (Vacancy Creation):
- Conditions: 2 MeV H+ beam applied to ND layers (~30 ± 10 ”m thick) deposited on Si substrates.
- Fluences: 1 x 1015 cm-2 (IrrlowND) or 4 x 1016 cm-2 (IrrhighND).
- Purpose: Create lattice vacancies uniformly across the ND layer thickness.
- Post-Irradiation Annealing (NV Formation):
- Conditions: 800 °C for 4 hours in N2 flow.
- Purpose: Promote the migration of proton-induced vacancies to couple with native nitrogen impurities, forming additional NV centers.
- Final Oxidation (Surface Refinement):
- Conditions: 500 °C for 12 hours in air.
- Purpose: Remove surface graphitization induced by the post-irradiation annealing and achieve the final, highly reduced particle size (< 20 nm).
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe research demonstrates a successful pathway for creating high-performance quantum sensors from nanodiamonds. However, the paper notes that commercial HPHT NDs, while available, are typically not optimal and suggests that CVD NDs are particularly promising. 6CCVD specializes in high-purity MPCVD diamond, offering superior control and scalability necessary to advance this research.
| Research Requirement | 6CCVD Solution & Value Proposition |
|---|---|
| High Purity Starting Material: HPHT NDs were used, but CVD NDs are cited as having better quantum performance potential. | Optical Grade SCD/PCD: 6CCVD provides high-purity Single Crystal Diamond (SCD) and Polycrystalline Diamond (PCD) wafers grown via MPCVD. These materials offer significantly lower intrinsic defects and superior crystal quality compared to HPHT, minimizing background noise (NV0) and maximizing NV- stability. |
| Controlled Nitrogen Doping: Native nitrogen (~100 ppm) was relied upon for NV formation. | Custom Doping Control: We offer precise, controlled nitrogen incorporation during MPCVD growth. Engineers can specify exact nitrogen concentrations (ppm level) to optimize the precursor density, ensuring maximum NV center yield and enhanced ODMR contrast following irradiation. |
| Substrate for Irradiation: NDs were deposited on Si substrates for 2 MeV H+ irradiation. | Large-Area Diamond Substrates: 6CCVD supplies robust, thermally stable diamond substrates (up to 125mm PCD wafers or SCD substrates up to 10mm thick) ideal for uniform, large-scale ion irradiation and subsequent high-temperature annealing (800 °C). |
| Advanced Processing & Metalization: Future work may require tracking or functionalization (e.g., Ti/Pt/Au contacts). | Custom Metalization & Polishing: 6CCVD offers in-house metalization services (Au, Pt, Pd, Ti, W, Cu) for creating planar antennas or contacts directly on diamond substrates. We also provide ultra-smooth polishing (Ra < 1nm for SCD, < 5nm for PCD) essential for high-resolution optical setups. |
| Scalability and Uniformity: Need reproducible results across large batches for commercial viability. | Custom Dimensions & Global Supply: We provide custom dimensions and thicknesses for both SCD and PCD, ensuring material uniformity and scalability for industrial or large-scale research projects. Global shipping (DDU/DDP) ensures reliable delivery worldwide. |
Engineering Support
Section titled âEngineering Supportâ6CCVDâs in-house PhD team specializes in defect engineering and surface chemistry of MPCVD diamond. We can assist researchers and engineers in selecting the optimal starting material (SCD vs. PCD), defining precise nitrogen doping levels, and designing custom metalization schemes required for similar NV quantum sensing projects.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
In recent decades, nanodiamonds (NDs) have emerged as innovative nanotools for weak magnetic fields and small temperature variation sensing, especially in biological systems. At the basis of the use of NDs as quantum sensors are nitrogen-vacancy center lattice defects, whose electronic structures are influenced by the surrounding environment and can be probed by the optically detected magnetic resonance technique. Ideally, limiting the NDsâ size as much as possible is important to ensure higher biocompatibility and provide higher spatial resolution. However, size reduction typically worsens the NDsâ sensing properties. This study endeavors to obtain sub-100 nm NDs suitable to be used as quantum sensors. Thermal processing and surface oxidations were performed to purify NDs and control their surface chemistry and size. Ion irradiation techniques were also employed to increase the concentration of the nitrogen-vacancy centers. The impact of these processes was explored in terms of surface chemistry (diffuse reflectance infrared Fourier transform spectroscopy), structural and optical properties (Raman and photoluminescence spectroscopy), dimension variation (atomic force microscopy measurements), and optically detected magnetic resonance temperature sensitivity. Our results demonstrate how surface optimization and defect density enhancement can reduce the detrimental impact of size reduction, opening to the possibility of minimally invasive high-performance sensing of physical quantities in biological environments with nanoscale spatial resolution.