Microwave-free imaging magnetometry with nitrogen-vacancy centers in nanodiamonds at near-zero field
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2025-03-03 |
| Journal | Physical Review Applied |
| Authors | Saravanan Sengottuvel, Omkar Dhungel, Mariusz MrĂłzek, Arne Wickenbrock, Dmitry Budker |
| Institutions | GSI Helmholtz Centre for Heavy Ion Research, Helmholtz Institute Mainz |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research introduces a novel, wide-field magnetometry technique utilizing Nitrogen-Vacancy (N-V) centers in nanodiamonds (NDs), specifically engineered for microwave-free operation in zero- and low-field environments.
- Microwave-Free Operation: The system exploits the N-V zero-field cross-relaxation feature, eliminating the need for complex and potentially invasive microwave components required by traditional Optically Detected Magnetic Resonance (ODMR).
- High Sensitivity Imaging: Achieved a mean per-pixel magnetic field sensitivity of 4.5 ”T/âHz using 140 nm ND ensembles under ambient conditions.
- Wide-Field Mapping: Demonstrated real-time, parallel mapping of magnetic fields generated by a 65 ”m wide current-carrying copper cross pattern.
- Versatile Substrate Use: Utilizes nanodiamonds deposited via drop-casting onto a transparent PET substrate, allowing for imaging on arbitrarily shaped or non-smooth surfaces.
- Low-Field Suitability: The technique is ideal for applications involving biological systems, high-Tc superconductors, or ultra-low-field Nuclear Magnetic Resonance (NMR) where external magnetic fields or high-power microwaves are detrimental.
- Key Parameter Characterization: Successfully mapped the magnetic field shift (ÎB), contrast (C), and linewidth (w) of the zero-field feature across the field of view (FOV).
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| N-V Material Type | Carboxylated fluorescent NDs | N/A | Commercially available (Adamas Nanotechnologies) |
| N-V Nanodiamond Size | 140 | nm | Mean size of particles used |
| Substrate Material | PET | N/A | Transparent polyethylene terephthalate |
| Substrate Thickness | 0.11 | mm | Thickness of the PET film |
| Excitation Wavelength | 532 | nm | Green LED pump source |
| Excitation Power | 60-70 | mW | Total power used for illumination |
| Copper Wire Width | 65 | ”m | Width of the conductive cross pattern |
| Maximum Applied Current | 0.5 | A | Maximum DC current used for field generation |
| Background Field Scan Range | -4.0 to +4.0 | mT | Range of the scanned bias field (Bz) |
| Mean Per-Pixel Sensitivity | 4.5 | ”T/âHz | Estimated photon shot-noise limited sensitivity |
| Camera Field of View (FOV) | 384 x 321 | ”m | Area imaged by the CMOS camera |
| Binned Pixel Size | 0.15 x 0.15 | ”m | Effective spatial resolution per binned pixel |
| Zero-Field Linewidth (w) | ~2.0 | mT | FWHM of the cross-relaxation feature in NDs |
| Zero-Field Contrast (C) | 1-2 | % | Contrast of the cross-relaxation feature in NDs |
| Total Acquisition Time | ~20 | min | Time required for 10 averaged scans to generate maps |
Key Methodologies
Section titled âKey Methodologiesâ- Nanodiamond Deposition: 140 nm carboxylated fluorescent nanodiamonds (NDs) were suspended in deionized water and deposited onto a 0.11 mm thick transparent PET substrate using the drop-casting (âsalt-and-pepperâ) technique.
- Current Pattern Integration: A 65 ”m wide copper cross pattern was printed on the reverse side of the PET substrate and connected to a power source via a Printed Circuit Board (PCB).
- Wide-Field Optical Setup: A home-built wide-field fluorescence microscope was used. The ND layer was illuminated with 60-70 mW of 532 nm green light (LED). Red fluorescence was collected using a 40x objective (NA 0.65) and imaged onto a 12-bit CMOS camera.
- Magnetic Field Scanning: A DC current (up to 0.5 A) was applied to the copper cross pattern. A background magnetic field (Bz), perpendicular to the ND layer, was systematically scanned from -4.0 mT to +4.0 mT using an external coil.
- Data Acquisition and Binning: Fluorescence images were captured sequentially across the B-field scan range. To improve the signal-to-noise ratio (SNR) and reduce processing load, images were spatially binned (16 x 16 pixels).
- Spectral Fitting: The zero-field cross-relaxation spectrum was extracted for each binned pixel. This spectrum was fitted using a Gaussian function (Equation 1) to determine the three key parameters: the center shift (ÎB), the contrast (C), and the width (w).
- Magnetic Field Mapping: The resulting ÎB map directly visualizes the magnetic field generated by the current-carrying cross pattern, while C and w maps provide complementary information on N-V concentration and transverse field components.
Commercial Applications
Section titled âCommercial Applicationsâ- Biomagnetometry and Cellular Imaging: The microwave-free nature is critical for sensing magnetic fields generated by biological systems (e.g., neuronal activity) and for real-time magnetometry in living cells, where traditional ODMR techniques are invasive or cause heating.
- Zero- and Low-Field Quantum Sensing: Applications in specialized magnetic resonance techniques, such as Zero- to Ultra-Low-Field Nuclear Magnetic Resonance (ZULF NMR), where the presence of high-power microwaves is detrimental to the measurement.
- Micro- and Nano-Electronics Testing: Wide-field, non-contact imaging of current distribution and magnetic fields in integrated circuits, thin conductive films (e.g., graphene), and micro-wires for quality control and failure analysis.
- Materials Characterization: Mapping magnetic properties of novel materials, including two-dimensional magnetic materials and high-transition-temperature (Tc) superconductors, without interference from RF fields.
- Arbitrary Surface Magnetometry: The use of nanodiamond coatings allows the sensor layer to be applied to non-planar or complex geometries (e.g., fiber tips), expanding the utility beyond flat bulk diamond substrates.
View Original Abstract
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