High Sensitivity Spin Defects in Carbon Implanted Diamond

At a Glance

Metadata	Details
Publication Date	2025-04-21
Journal	Advanced Optical Materials
Authors	X.D. Chai, Haidong Liang, Chengyuan Yang, Vinh X. Ho, Ee Jin Teo
Institutions	National University of Singapore, Australian Nuclear Science and Technology Organisation
Analysis	Full AI Review Included

High Sensitivity Spin Defects in Carbon Implanted Diamond

Executive Summary

The TR12 color center, a self-interstitial spin defect in diamond, has been optimized for quantum sensing, demonstrating performance metrics significantly exceeding prior literature.

Record Sensitivity Achieved: A shot-noise-limited magnetic sensitivity of 1.2 nT/sqrt(Hz) was achieved in TR12 ensembles, representing an improvement of three orders of magnitude over previously reported TR12 sensitivity (3.9 µT/sqrt(Hz)).
Fabrication Method: High-quality TR12 ensembles were created using 25 MeV Carbon (C⁺) focused ion microbeam line-scan irradiation on E-grade HPHT synthetic diamond.
Spatial Optimization: Cross-sectional 2D photoluminescence (PL) mapping along the ion cascade revealed that optimal optically detected magnetic resonance (ODMR) properties (high contrast, narrow linewidth) do not correlate directly with the highest defect density, but rather with specific regions near the surface or end-of-range (EOR) depending on the implantation fluence.
High Contrast and Linewidth: Optimal ODMR contrast reached 22.2% and minimum linewidth was 4.28 MHz at lower fluences (1 x 10¹⁴ ions cm^-2), while the highest sensitivity was achieved at the highest fluence (5 x 10¹⁴ ions cm^-2) due to significantly higher photon count rates.
Coherent Manipulation: Coherent spin manipulation was demonstrated via Rabi oscillations, yielding decoherence times (T₂^Rabi) of approximately 0.47 µs near the surface and 0.42 µs at the EOR region in the as-implanted state.
Competitive Advantage: TR12 offers a high Debye-Waller factor (DWF = 0.1, compared to 0.04 for NV centers) and maintains high ODMR contrast even in strong off-axis magnetic fields, positioning it as a strong alternative to NV centers for vector magnetometry.

Technical Specifications

Parameter	Value	Unit	Context
Magnetic Sensitivity (Optimal)	1.2	nT/sqrt(Hz)	Shot-noise-limited sensitivity, 5 x 10¹⁴ ions cm^-2 fluence
Ion Species / Energy	Carbon (C⁺)	25 MeV	Focused ion microbeam irradiation
Diamond Grade	E-grade	Type IIa HPHT	Substrate material
Irradiation Fluence Range	1 to 5	x 10¹⁴ ions cm^-2	Line-scan irradiation range
TR12 ZPL Wavelength	470.2	nm	Zero-Phonon Line (ZPL) emission
TR12 DWF (Debye-Waller Factor)	0.1 (10%)	(unitless)	Higher than NV center (0.04 or 4%)
TR12 Triplet State D (ZFS)	1636.6	MHz	Zero-Field Splitting (ZFS) parameter
TR12 Triplet State E	869.6	MHz	ZFS parameter
ODMR Detection Frequency	740	MHz	Primary transition used for measurement
Maximum ODMR Contrast	22.2	%	Achieved at 1 x 10¹⁴ ions cm^-2 fluence
Minimum ODMR Linewidth	4.28	MHz	Achieved at 1 x 10¹⁴ ions cm^-2 fluence
Rabi Decoherence Time (Surface)	~0.47	µs	As-implanted state, near surface region
Rabi Decoherence Time (EOR)	~0.42	µs	As-implanted state, End-of-Range region
Post-Irradiation Annealing	460	°C	Performed for 3 hours in vacuum

Key Methodologies

The TR12 ensembles were fabricated and characterized using a multi-step process focusing on precise ion implantation and advanced optical/magnetic resonance measurements.

Substrate Preparation:
- Material: E-grade type IIa HPHT synthetic diamond plate (4 x 4 x 0.5 mm³), polished on all surfaces.
- Defect Type: Carbon ions (C⁺) were chosen as the irradiation species due to the TR12 defect’s proposed self-interstitial nature.
Ion Implantation (ANSTO SIRIUS Microprobe):
- Species/Energy: 25 MeV Carbon ions (C⁺).
- Pattern: Focused ion microbeam line-scan irradiation, extending across the lateral edge of the diamond to allow cross-sectional viewing of the cascade.
- Beam Parameters: Microbeam focused to approximately 1.5 µm; line pixel size approximately 2 µm.
- Fluences: Three primary fluences were studied: 1 x 10¹⁴, 3 x 10¹⁴, and 5 x 10¹⁴ ions cm^-2.
Post-Irradiation Treatment (Optional):
- Annealing: Performed on a subset of samples at 460 °C for 3 hours in a vacuum environment to investigate stability improvement.
Optical Characterization (PL Mapping):
- Setup: Homebuilt confocal scanning fluorescence microscope.
- Excitation: 405 nm Continuous Wave (CW) laser.
- Mapping: Cross-sectional PL scans were used to map the spatial distribution of TR12 (ZPL at 470.2 nm), 3H (503.5 nm), and GR1 (741.1 nm) defects along the ion cascade.
ODMR Measurement:
- Setup: Diamond placed on a copper waveguide (microwave chip).
- Excitation/Detection: 405 nm laser excitation; PL emission detected in the 464 nm to 473 nm range (TR12 ZPL).
- Frequency: Microwave frequency swept around 740 MHz to measure the ODMR signal.
- Optimization: ODMR contrast and linewidth were measured as a function of laser power and microwave power at three distinct locations along the cascade for each fluence.
Coherent Manipulation:
- Measurement: Rabi oscillation measurements were performed between metastable states T_x and T_y.
- Analysis: Damped Rabi oscillations were fitted to an exponentially decaying sinusoid to extract the Rabi decoherence time (T₂^Rabi).

Commercial Applications

The demonstrated high sensitivity and robust performance of the TR12 center make it highly suitable for advanced quantum sensing applications, particularly where high magnetic fields or vector measurements are required.

Vector Magnetometry: TR12’s high ODMR contrast and wide acceptance angles in strong off-axis magnetic fields allow for atomic-scale vector magnetometry, overcoming limitations faced by NV centers in high-field environments.
Quantum Sensing and Metrology: The high sensitivity (1.2 nT/sqrt(Hz)) is competitive with or superior to many other solid-state spin defects (e.g., hBN, some SiC defects), enabling high-precision measurements of magnetic fields, temperature, and pressure.
Quantum Information Processing: The demonstrated coherent spin manipulation (Rabi oscillations) indicates potential for use as qubits or quantum memory elements in solid-state quantum computing architectures.
Medical and Biological Imaging: High-sensitivity magnetometers are critical for detecting weak magnetic signals in biological systems, such as magnetic resonance imaging (MRI) or magnetoencephalography (MEG) at the nanoscale.
Geological and Navigation Systems: The ability to sense magnetic fields of arbitrary orientation makes TR12 suitable for advanced inertial navigation systems and geological surveying equipment.

View Original Abstract

Abstract The TR12 color center in diamond is a self‐interstitial spin defect capable of room‐temperature atomic‐scale vector magnetometry for detecting magnetic fields of arbitrary orientation and magnitude. Measurements using the TR12 center show that the sensing dynamic range can potentially outperform that of NV centers in diamond. The powerful quantum sensing capabilities of TR12 place it as a strong alternative candidate for quantum sensing in diamond, especially in extreme magnetic fields. However, its sensitivity in existing literature is relatively low in the µT/√Hz range. This work examines the spatial distributions of TR12 centers fabricated by high‐energy carbon irradiation on an E‐grade diamond along the ion irradiation cascade. A detailed study of photoluminescence intensity, optically detected magnetic resonance contrast, and linewidth is conducted. By varying locations along ion cascades of line irradiations with different fluences, the highest sensitivity of 1.2 nT/√Hz is achieved at three orders of magnitude higher than demonstrated in existing literatures. Coherent manipulation of triplet spin states in these ensembles is evident from Rabi oscillation measurements, with decoherence times of ≈0.47 µs at the surface and ≈ 0.42 µs at the end‐of‐range. These findings significantly enhance the potential of TR12 for quantum sensing applications.

High Sensitivity Spin Defects in Carbon Implanted Diamond

At a Glance