In situ optimization of co-implantation and substrate temperature conditions for Nitrogen-Vacancy center formation in single crystal diamonds

At a Glance

Metadata	Details
Publication Date	2016-06-20
Authors	J Schwartz, P Michaelides, C D Weis, T Schenkel
Citations	2
Analysis	Full AI Review Included

In Situ Optimization of NV-Center Formation in Single Crystal Diamond

Document ID: 6CCVD-NV-LBNL-072023 Source: J. Schwartz et al., Lawrence Berkeley National Laboratory (LBNL) Application Focus: Quantum Sensing and Defect Engineering

Executive Summary

This study focuses on optimizing the creation of Nitrogen-Vacancy (NV) color centers in single crystal diamond (SCD) through dynamic annealing protocols using ion co-implantation. The findings are highly relevant to engineers seeking reliable, scalable methods for high-fidelity quantum device fabrication.

Core Achievement: Demonstrated enhanced NV-center formation efficiency (measured by Photoluminescence, PL) by utilizing in situ heating (dynamic annealing) during ion co-implantation.
Optimal Result: Co-implantation of Carbon (C) ions at a fluence of 10¹² cm^-2 while maintaining the diamond substrate at 780° C enhanced NV-PL intensity by up to 25% compared to N-only implants.
Critical Mechanism: Dynamic annealing effectively increases the conversion of substitutional nitrogen into stable NV-centers by promoting vacancy mobility while concurrently repairing lattice damage below the threshold for graphitization (10²² vacancies/cm³).
Material Requirement: The success of this technique relies heavily on the use of Electronic Grade Single Crystal CVD Diamonds with ultra-low native nitrogen concentrations (P1 centers <5 ppb).
Implication for Quantum Technologies: The use of low-energy (7.7 keV) implantation combined with dynamic annealing enables the creation of highly localized, shallow NV centers with enhanced reliability, crucial for next-generation quantum sensors and solid-state qubits.

Technical Specifications

Parameter	Value	Unit	Context
Substrate Temperature (Dynamic Annealing)	780	° C	Temperature during co-implantation
NV Formation Enhancement (C Co-implant)	Up to 25	%	Relative PL intensity increase (10¹² C/cm²)
Primary Implant Energy	7.7	keV	Used for all ion species (N, H, He, C)
Nitrogen (N⁺) Dose Fluence	10¹³	cm^-2	Fixed dose for baseline comparison
Optimal Carbon (C⁺) Co-implant Fluence	10¹²	cm^-2	Yielded maximum NV enhancement at 780° C
Carbon Ion Vacancy Creation Estimate	56	vacancies/ion	Calculated via SRIM, resulting in 4x10²⁰ vacancies/cm³
Graphitization Damage Threshold	10²²	vacancies/cm³	Critical limit for irreversible lattice degradation
Initial Substrate Purity	<5	ppb	Background nitrogen concentration (P1 centers)
N Ion Range (Simulated)	11.5	nm	Shallow implantation depth for 7.7 keV N⁺
Annealing Time (Post-Implant)	Up to 120	minutes	Follow-up annealing cycles at 780° C
Excitation Laser Wavelength	532	nm	Photoluminescence (PL) spectroscopy excitation

Key Methodologies

The experiment utilized an in situ processing chamber allowing for ion implantation, dynamic temperature control, and immediate optical characterization, enabling rapid optimization of the NV creation recipe.

Substrate Selection: Electronic grade Single Crystal Diamond (SCD) with ultra-low native nitrogen content (<5 ppb) and (100) orientation was used to minimize background defects and maximize spin coherence.
Ion Beam Configuration: Ions (N⁺, H⁺, He⁺, C⁺) were generated, mass-selected via an ExB filter, and delivered at a uniform energy of 7.7 keV. Beam intensity was maintained at <10 nA/cm² to prevent localized beam heating and dose rate effects.
Implantation Profile: Shallow nitrogen implants (peak range 11.5 nm) were performed, followed by co-implantation of H, He, or C ions to generate additional vacancies.
Dynamic Annealing Protocol: Samples were heated to a uniform temperature of 780° C using a heatable goniometer during the co-implantation process. This in situ heating (dynamic annealing) allows vacancies to become mobile (typically >600° C) immediately upon creation, favoring NV formation and damage repair.
Optical Characterization (PL): NV-center formation was tracked by monitoring the Photoluminescence (PL) intensity of the NV⁰ (575 nm) and NV⁻ (637 nm) Zero Phonon Lines (ZPLs) using a 532 nm fiber-coupled excitation laser.
Fluence Optimization: Fluences for co-implantation were systematically varied (10¹¹ to 10¹³ cm^-2) to identify the critical fluence where damage accumulation begins to decrease NV yield (observed above 10¹² cm^-2 for all co-implanted species).

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the advanced diamond materials and integrated processing capabilities required to replicate, scale, and extend the LBNL research into commercial quantum and sensing platforms.

Applicable Materials

To achieve optimal NV-center formation and coherence, the highest purity substrates are mandatory.

Material Recommendation: Optical Grade Single Crystal Diamond (SCD)
- Purity Guarantee: Our MPCVD growth process yields SCD with ultra-low nitrogen incorporation (well below the <5 ppb specified in the research), drastically reducing unwanted P1 centers which degrade NV spin coherence.
- Crystallographic Control: Available in high-quality (100) and (111) orientations, enabling engineers to select the optimal surface for specific channeling or device integration requirements.

Material Requirement (Paper)	6CCVD Standard Capability	Advantage for Replication
Ultra-low N background (<5 ppb)	SCD, P1 Concentration Control	Maximized spin coherence and spectral stability for qubits and sensors.
(100) Orientation, High Quality	SCD Plates up to 125mm	Guaranteed crystal structure necessary for precision ion channeling effects.
High Surface Finish	SCD: Ra < 1 nm	Essential for shallow implantation consistency and subsequent lithography/metalization steps.

Customization Potential

NV-based quantum devices often require integration with surface electronics and precise placement controls. 6CCVD offers full customization for downstream processing.

Precision Processing: We offer high-resolution laser cutting and shaping to achieve custom dimensions beyond standard plates, facilitating integration into microfluidic or specific cryogenic environments.
Depth Control Optimization: While the paper used 7.7 keV implants (11.5 nm depth), 6CCVD supplies SCD wafers with thickness control from 0.1 µm up to 500 µm, allowing researchers flexibility for future experiments involving deeper implants or thin membranes.
Integrated Device Fabrication: We provide robust in-house metalization services, including Ti, W, Pt, Pd, Au, and Cu layers. This is critical for translating fundamental NV research into functional devices requiring surface gate electrodes for controlled charge state management (e.g., stabilizing NV⁻).
Charge State Engineering (BDD): For studies requiring controlled band structure modification—especially relevant given the paper’s discussion on NV charge state conversion (NV⁺, NV⁰, NV⁻)—6CCVD supplies Boron-Doped Diamond (BDD) films. BDD allows for precise local Fermi level control, a necessary pathway for optimizing NV⁻ ratios.

Engineering Support

NV-center defect engineering requires deep expertise in both material growth and processing kinematics.

6CCVD’s in-house PhD engineering team specializes in MPCVD growth parameters and defect generation/annealing protocols. We can assist in optimizing substrate choice and pre-treatment conditions (e.g., surface termination) to ensure maximum NV conversion efficiency for shallow implantation projects targeting quantum sensing or solid-state qubit arrays.
Our support minimizes the material variability and processing uncertainty that often limits the reproducibility of complex recipes like dynamic annealing.

For custom specifications or material consultation on optimizing NV-center formation through advanced CVD diamond substrates, visit 6ccvd.com or contact our engineering team directly.

Tech Support

Original Source

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