Window into NV center kinetics via repeated annealing and spatial tracking of thousands of individual NV centers
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-02-25 |
| Journal | Physical Review Materials |
| Authors | Srivatsa Chakravarthi, Chris Moore, April Opsvig, Christian Pederson, Emma Hunt |
| Institutions | University of Washington |
| Citations | 33 |
| Analysis | Full AI Review Included |
Technical Documentation and Analysis: NV Center Kinetics in MPCVD Diamond
Section titled âTechnical Documentation and Analysis: NV Center Kinetics in MPCVD DiamondâThis document analyzes the research detailing NV center formation, quenching, and orientation kinetics in ultra-pure MPCVD diamond, providing relevant material specifications and sales-driving recommendations from 6CCVD.
Executive Summary
Section titled âExecutive SummaryâThis study provides fundamental insights into Nitrogen-Vacancy (NV) center dynamics during high-temperature annealing of ultra-pure chemical vapor deposition (CVD) diamond, crucial for advanced quantum device engineering.
- Non-Irradiation NV Enhancement: Demonstrated a 6- to 24-fold increase in NV center density by repeated vacuum annealing (950 °C - 980 °C) in electronic-grade CVD diamond, showing a path to high-density NV creation without introducing lattice damage via traditional irradiation methods.
- Kinetic Decoupling: Used longitudinal spatial tracking of individual NV centers via confocal microscopy to effectively decouple competing processes: NV formation (appearances) and quenching (disappearances).
- Vacancy Source Identification: The enhancement suggests a significant source of native vacancies within the CVD diamond matrix becomes mobile and activates NV creation between 950 °C and 980 °C.
- Orientation Control Mechanism: Observed large-scale NV orientation changes at 1050 °C, decoupled from full dissociation, suggesting an attractive interaction between the vacancy and nitrogen, which may enable strain-induced preferential orientation control.
- Diffusion Barrier Quantification: Direct measurement of orientation change rates allowed the estimation of the NV reorientation barrier (Eb) at 4.7 ± 0.9 eV, providing a crucial benchmark for theoretical models of defect migration.
- Material Purity Requirement: Confirmed the absolute necessity of ultra-high purity, electronic-grade Single Crystal Diamond (SCD) with low substitutional nitrogen ([Ns] < 1 ppb) to preserve the quantum and optical properties of the defects.
Technical Specifications
Section titled âTechnical SpecificationsâThe following table extracts the core material specifications, process parameters, and derived kinetic values relevant to diamond substrate engineering and quantum defect research.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| CVD Diamond Grade | Electronic Grade | N/A | Samples A, B, D, E |
| Substitutional Nitrogen ([Ns]) | < 1 | ppb | Minimum Purity Specification |
| Crystal Orientation | {100} | Plane | Orientation for all analyzed samples |
| Annealing Atmosphere | < 1e-7 | mbar | High vacuum |
| Optimal NV Formation Temperature | 950 - 980 | °C | Yields 6- to 24-fold density increase |
| NV Orientation Change Temperature | 1050 | °C | Required for large-scale reorientation |
| Annealing Duration (Longest) | 150 | hours | Used for saturation studies at 980 °C and 1050 °C |
| Activation Energy (Eb) | 4.7 ± 0.9 | eV | NV reorientation barrier estimation |
| Confocal Depth Tracking | 240 | ”m | Depth below the surface for large-area scans |
| Spatial Scan Area | 350 à 350 | ”m2 | Large area tracked for individual NV centers |
Key Methodologies
Section titled âKey MethodologiesâThe study utilized state-of-the-art MPCVD diamond material coupled with precise thermal processing and advanced optical tracking techniques.
- Material Selection: Use of commercial, electronic-grade MPCVD Single Crystal Diamond (SCD) with ultra-low substitutional nitrogen concentration (as low as < 1 ppb) and {100} crystal orientation.
- Surface Cleaning: Aggressive fuming acid bath cleaning (1:1:1 H2SO4:HNO3:HCLO3) maintained at 250 °C for 90 minutes to ensure removal of surface contaminants and minimize surface fluorescence.
- Vacuum Annealing Profile: Repeated vacuum annealing was conducted sequentially at temperatures ranging from 800 °C to 1100 °C, with ramp times of 2 hours and varying hold times (up to 150 hours) to reach kinetic saturation.
- Confocal Microscopy: NV- centers were imaged using a home-built confocal microscope system employing a 0.75 NA objective and non-resonant 532 nm laser excitation.
- Signal Filtering: Photoluminescence (PL) collection filtered NV- phonon sideband emission (660-800 nm) for detection via an avalanche photodiode.
- Individual Defect Tracking: An automated piezo-actuated stage enabled precise spatial mapping (350 ”m à 350 ”m area, 25 ”m depth of focus) to track the position and orientation of thousands of NV centers across multiple annealing steps.
- Orientation Analysis: Excitation polarization angle measurement was used to distinguish the two sets of optically non-equivalent NV orientations in the {100} samples, tracking orientation changes in real-time.
- Kinetic Analysis: Image subtraction and normalization algorithms were applied to registered scan data to isolate and quantify the occurrences of NV appearances, disappearances, and orientation changes.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThis research confirms the paramount importance of material quality and precise thermal processing for advancing quantum diamond technology. 6CCVD is uniquely positioned to supply the requisite materials and engineering services to replicate and extend this critical work.
| Research Requirement | 6CCVD Material/Capability | Value Proposition |
|---|---|---|
| Ultra-High Purity Host | Electronic Grade Single Crystal Diamond (SCD) | Our certified, ultra-low nitrogen content SCD (< 5 ppb N) ensures the necessary host material purity to achieve the long spin coherence times vital for quantum sensing and computation platforms. |
| Required Dimensions & Substrates | Custom Dimensions up to 125 mm (PCD) / 10 mm Substrates | We provide SCD and PCD plates in custom dimensions, accommodating the large scan areas (350 ”m à 350 ”m and larger) required for high-throughput individual defect tracking experiments. |
| Advanced Orientation Control | Precision {100} and {111} SCD Orientation | Beyond the {100} samples used here, 6CCVD supplies {111} oriented SCD, the ideal platform for preferential NV alignment, leveraging the orientation kinetics identified at 1050 °C. |
| Optical Access & Sub-surface Probing | Standard Polishing (Ra < 5 nm) to Premium (Ra < 1 nm) | Our superior polishing services (Ra < 1 nm for SCD) minimize scattering losses, essential for deep confocal microscopy and tracking defects hundreds of microns below the surface. |
| Interface Engineering | Custom Metalization Capabilities (Au, Ti, Pt, Cu) | To transition from optical tracking to integrated quantum devices (e.g., electrical readout, strain application), 6CCVD offers in-house deposition of thin films (Ti/Pt/Au/Pd/W/Cu) specified to engineering tolerances. |
Applicable Materials: To replicate the fundamental studies on NV kinetics and defect formation shown in this paper, researchers require:
- Optical Grade SCD: Ultra-high purity, with [Ns] minimized (< 5 ppb).
- Custom {100} Orientation: Required for direct comparison with the existing body of literature.
Customization Potential: 6CCVD offers bespoke high-temperature, high-vacuum annealing services to help clients optimize the thermal budgets (950 °C - 980 °C) necessary for maximized NV creation in situ. Furthermore, we provide laser cutting and shaping to prepare samples for specific microscope mounts or integrated device structures.
Engineering Support: 6CCVDâs in-house PhD material science team specializes in quantum defect engineering and can assist with material selection for similar quantum sensing or spin-coherence optimization projects, ensuring precise control over nitrogen concentration and post-growth processing.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Knowledge of the nitrogen-vacancy center formation kinetics in diamond is critical to engineering sensors and quantum information devices based on this defect. Here we utilize the longitudinal tracking of single NV centers to elucidate NV defect kinetics during high-temperature annealing from 800-1100 $^\circ$C in high-purity chemical-vapor-deposition diamond. We observe three phenomena which can coexist: NV formation, NV quenching, and NV orientation changes. Of relevance to NV-based applications, a 6 to 24-fold enhancement in the NV density, in the absence of sample irradiation, is observed by annealing at 980 $^\circ$C, and NV orientation changes are observed at 1050 $^\circ$C. With respect to the fundamental understanding of defect kinetics in ultra-pure diamond, our results indicate a significant vacancy source can be activated for NV creation between 950-980 $^\circ$C and suggests that native hydrogen from NVH$_y$ complexes plays a dominant role in NV quenching, in agreement with recent {\it ab initio} calculations. Finally, the direct observation of orientation changes allows us to estimate an NV diffusion barrier of 5.1~eV.