Magnetic imaging with an ensemble of nitrogen-vacancy centers in diamond

At a Glance

Metadata	Details
Publication Date	2015-06-29
Journal	The European Physical Journal D
Authors	Mayeul Chipaux, Alexandre Tallaire, Jocelyn Achard, Sébastien Pezzagna, Jan Meijer
Institutions	Université Paris-Sud, Centre National de la Recherche Scientifique
Citations	101
Analysis	Full AI Review Included

6CCVD Technical Analysis: Vectorial Magnetic Imaging using Ensemble NV Centers

This analysis reviews the experimental methodology and results of the paper “Magnetic imaging with an ensemble of Nitrogen Vacancy centers in diamond,” demonstrating high-sensitivity, high-resolution vectorial magnetic field mapping using Optically Detected Magnetic Resonance (ODMR) in Chemical Vapor Deposition (CVD) diamond.

Executive Summary

This research validates high-density ensemble Nitrogen Vacancy (NV) centers in CVD Single Crystal Diamond (SCD) as robust, room-temperature magnetic sensors, achieving quantitative vectorial field mapping.

Core Achievement: Quantitative, vectorial reconstruction of a magnetic field (produced by a DC current in a copper wire) using the response of the four intrinsic NV center orientations within the diamond lattice.
Methodology: Utilizes a maximum-likelihood algorithm applied to Optically Detected Magnetic Resonance (ODMR) spectra acquired over a thin, implanted NV layer (8 ± 2 nm deep) in (100) oriented SCD.
Material Basis: Ultra-pure, 250 µm thick CVD diamond plate required high-quality optical polishing on all faces to enable total internal reflection (TIR) for efficient green laser pumping.
Sensitivity: Achieved a minimum detectable magnetic field sensitivity of 2.0 µT · µm/√Hz (for a 1 µm² area, equivalent to ~10⁴ NV centers), confirming shot-noise limited performance.
Resolution: Demonstrated a spatial resolution of 480 nm, limited by the numerical aperture (N.A. = 1.35) of the optical collection system.
Improvement Potential: Suggested enhancements include using high-purity, isotopically enriched ¹²C SCD and controlling nitrogen doping for preferential NV orientation to maximize contrast and reduce the electron spin bath noise.

Technical Specifications

The following key parameters and performance metrics were established using the MPCVD diamond platform:

Parameter	Value	Unit	Context
Diamond Material	SCD (Single Crystal)	N/A	Ultra-pure, grown by plasma-assisted CVD on HPHT substrate.
Crystallographic Orientation	(100)	N/A	Defined the laboratory frame for vector reconstruction.
Plate Dimensions (Active Area)	3 x 3	mm²	Sample size optimized for experiment.
Plate Thickness	250	µm	Allows for objective working distance (320 µm) viewing through the diamond.
Surface Polishing Requirement	High Optical Quality	N/A	Required for Total Internal Reflection (TIR) side pumping.
Implantation Species / Dose	¹⁵N⁺ at 10¹⁴	N/cm²	High-density ensemble NV creation.
NV Layer Depth	8 ± 2	nm	Result of 5 keV implantation energy.
NV Surface Concentration	~10⁴	NV/µm²	Derived from 1% conversion yield after annealing.
Annealing Parameters	800 °C for 2 hours	Vacuum	Induces vacancy diffusion for NV formation.
Excitation Wavelength (Pump)	532	nm	Green laser (e.g., Coherent Verdi V5).
ODMR Zero-Field Splitting (v₀)	2.88	GHz	Characteristic frequency of ground state spin triplet.
ODMR Linewidth (Δv)	6.8	MHz	Limited by power broadening and high N concentration spin bath.
Maximum Sensitivity ($\eta_{\text{max}}$)	2.0	µT · µm/√Hz	Achieved using the differential acquisition method.
Spatial Resolution	480	nm	Limited by optical diffraction limit (N.A. = 1.35).
DC Current Measured (Source)	10.5	mA	Reconstructed value from a 12 mA target current.

Key Methodologies

The experiment relies on precision material engineering and advanced microwave/optical protocols:

Material Preparation:
- Growth of ultra-pure SCD diamond via MPCVD on an HPHT substrate, ensuring a (100) surface orientation.
- Precision cutting (3 x 3 mm²) and thickness reduction (250 µm).
- High-quality optical polishing applied to both main faces and the four lateral faces to enable efficient light propagation via Total Internal Reflection (TIR).
NV Center Creation:
- Uniform ¹⁵N⁺ ion implantation at 5 keV energy to create a highly localized NV layer 8 nm below the surface (10¹⁴ N/cm² dose).
- High-temperature vacuum annealing (800 °C) to mobilize vacancies, ensuring the formation of negatively charged NV^- centers.
Optical and Microwave Setup:
- Green laser (532 nm, 150 mW) coupled into the diamond via a polished side face, exploiting TIR for non-destructive pumping of the active NV layer.
- Photoluminescence (600-800 nm) collected via a high N.A. (1.35) objective.
- Microwave excitation supplied via a lithographed short-circuit omega antenna placed near the diamond surface, sweeping frequency around v₀ = 2.88 GHz.
Data Acquisition (ODMR Spectroscopy):
- Static magnetic field applied to lift the degeneracy between the four possible NV orientations, resulting in four pairs of resonance lines in the ODMR spectrum for each pixel.
- High-volume data acquisition creating a 3D volume (x, y, frequency).
Vectorial Reconstruction:
- Levenberg-Marquardt fitting of the multi-Lorentzian ODMR spectrum at each pixel to determine the Zeeman shift (D) for all four NV axes (m_a, m_b, m_c, m_d).
- Application of a Maximum-Likelihood algorithm to reconstruct the full vectorial magnetic field components (B_x, B_y, B_z) in the laboratory frame, exploiting the known symmetry relationships of the four NV orientations.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the advanced MPCVD diamond materials necessary to replicate and significantly extend this state-of-the-art quantum sensing research. The requirements outlined in this paper—ultra-high purity, custom dimensions, and critical surface quality—are central to our specialized manufacturing capabilities.

Applicable Materials for NV Center Magnetometry

Requirement from Paper	Recommended 6CCVD Material & Specification	Technical Justification & Value Proposition
Ultra-pure, Low-Defect Diamond	Optical Grade SCD (Single Crystal Diamond)	Essential for minimizing background noise and maximizing T₂^* coherence time. Our MPCVD process delivers exceptionally low inherent nitrogen and defect concentrations, crucial for maximizing NV sensor performance.
High Sensitivity/Long Coherence	Isotopically Enriched SCD (e.g., ¹²C > 99.99%)	The paper identifies the ¹³C nuclear spin bath as a sensitivity limit. Isotopically enriched diamond dramatically reduces this noise source, enabling sensitivities in the targeted nT/√Hz range for superior quantum sensing.
Heavy Doping/Ensemble NV	Custom N-doped SCD or High-Density PCD	For researchers requiring high NV concentration ensembles for greater signal-to-noise ratios (SNR) over larger areas, 6CCVD offers precision control over nitrogen incorporation during CVD growth.

Customization Potential & Technical Support

To address the specific engineering challenges presented by this ODMR setup, 6CCVD provides comprehensive customization:

Precision Substrate Dimensions: The experiment required a precisely cut 3 x 3 mm², 250 µm thick plate. 6CCVD delivers custom dimensions and thickness for both SCD (up to 500 µm) and PCD (up to 10mm substrates, wafers up to 125mm). This allows engineers to optimize substrates for specific objective working distances (as was done in this paper) or integrated chip designs.
Critical Optical Polishing: The success of the TIR side-pumping technique hinged on high-quality optical faces. 6CCVD specializes in Ultra-Low Roughness Polishing (Ra < 1 nm for SCD), ensuring minimal scattering losses and optimal light coupling for high-efficiency optical systems. We can polish both the main and lateral faces upon request.
Integrated Microwave Structures: The paper used an external omega antenna. For advanced, integrated sensors, 6CCVD offers in-house custom metalization (Au, Pt, Ti, Cu, W) services. We can lithographically pattern critical microwave structures directly onto the diamond surface to maximize microwave field uniformity and efficiency across the NV layer.
Engineering Support: 6CCVD’s in-house PhD team provides expert consultation on material selection, doping strategies (e.g., optimizing ¹⁵N implantation depth and dose), and crystal orientation selection (e.g., (111) for preferential NV alignment) to replicate or extend current magnetic imaging and quantum sensing projects.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

Tech Support

Original Source

DOI: https://doi.org/10.1140/epjd/e2015-60080-1