Pulsed magnetic field gradient on a tip for nanoscale imaging of spins
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2025-03-10 |
| Journal | Communications Physics |
| Authors | Leora Schein-Lubomirsky, Yarden Mazor, Rainer Stöhr, Andrej Denisenko, Amit Finkler |
| Institutions | University of Stuttgart, Academic College of Tel Aviv-Yafo |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Pulsed Magnetic Field Gradient for Nanoscale Spin Imaging
Section titled âTechnical Documentation & Analysis: Pulsed Magnetic Field Gradient for Nanoscale Spin ImagingâSource Paper: Pulsed magnetic field gradient on a tip for nanoscale imaging of spins (Communications Physics, 2025)
Executive Summary
Section titled âExecutive SummaryâThis research demonstrates a significant advancement in Nanoscale Magnetic Resonance Imaging (nanoMRI) by integrating a switchable, current-controlled magnetic field gradient onto a scanning tip, utilizing Nitrogen-Vacancy (NV) centers in diamond as the sensor.
- Core Achievement: Successful implementation of a pulsed magnetic field gradient (up to 1 ”T nm-1 measured) using a metallic microwire on a quartz tip positioned above a high-purity CVD diamond NV sensor.
- Resolution Milestone: The achieved gradient enables electron spin mapping with a projected 1 nm spatial resolution, overcoming limitations associated with static permanent magnets.
- Dynamic Control: The current-controlled gradient is switchable in < 600 ns, allowing for advanced pulse sequences (e.g., Fourier imaging) and enhancing NV contrast by switching the field off during spin readout.
- Material Foundation: The device relies on high-quality, electronic-grade CVD Single Crystal Diamond (SCD) membranes with shallow 15N+ implantation, a core material specialty of 6CCVD.
- Rabi Power Modulation: The metallic tip proximity provides a localized Rabi power enhancement factor of x3.5, enabling selective spin manipulation and reducing the need for high-power microwave (MW) sources, thereby mitigating thermal management issues.
- Sales Proposition: 6CCVD is uniquely positioned to supply the high-coherence SCD substrates, custom thin membranes, and specialized metalization required to replicate and scale this cutting-edge quantum sensing technology.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Spatial Resolution (Electron Spin) | 1 | nm | Achieved using NV center sensor. |
| Measured Magnetic Field Gradient (Max) | 0.95 - 1 | ”T nm-1 | Measured at 1.54 mA current. |
| Projected Magnetic Field Gradient (Max) | 3.3 | ”T nm-1 | Potential with 5-fold higher current density. |
| Gradient Switching Time (Rise/Fall) | < 600 | ns | Current-controlled pulsing capability. |
| NV Sensor Material | e6 [100] | - | Electronic-grade CVD diamond. |
| Diamond Membrane Thickness | 30 | ”m | Thinned for integration with co-planar waveguide. |
| NV Dephasing Time (T*) | ~3 | ”s | Corresponds to 100 kHz spectral resolution limit. |
| Rabi Power Modulation Factor | x3.5 | - | Enhancement due to metallic tip proximity (156 nm distance). |
| Tip Apex Diameter | ~1 | ”m | Optimized geometry for gradient strength vs. Joule heating. |
| Metalization Stack (Leads/Apex) | Cr/Au | nm | Chromium (Cr) adhesion layer, Gold (Au) conductor. |
| Working Magnetic Field (Max) | 259 | ”T | Measured field strength, weak relative to zero-field splitting. |
Key Methodologies
Section titled âKey MethodologiesâThe experiment relies on precise material engineering of the diamond sensor and complex fabrication of the current-focusing tip.
- Diamond Substrate Preparation:
- Used e6 [100] electronic-grade CVD diamond.
- Overgrown with solid-state boron rod doping.
- Shallow 15N+ implantation (5 keV energy) followed by vacuum annealing at 950 °C to create NV centers.
- Diamond Structuring:
- Boron-doped layer etched using Inductively Coupled Plasma (ICP).
- Diamond thinned down to a 30 ”m membrane.
- Nanopillar arrays etched into the membrane using Electron Beam Lithography and ICP to enhance photon collection.
- Tip Fabrication (Current Focusing Device):
- Quartz solid rod pulled to form two tapers.
- Three-step self-aligned metal deposition process (Cr/Au).
- Focused Ion Beam (FIB) used to cut the apex, creating a 1 ”m diameter tip for current focusing.
- Final metal stack: 7 nm Cr / 120 nm Au (apex) and 7 nm Cr / 50 nm Au (leads).
- Sensing and Measurement:
- Optically Detected Magnetic Resonance (ODMR) pulse sequence used.
- Current pulse (1.54 mA) through the tip is interleaved with the ODMR sequence, ensuring the magnetic field is applied during spin manipulation but turned off during readout.
- Atomic Force Microscopy (AFM) feedback (using a tuning fork) maintains a fixed vertical distance (e.g., 300 nm) between the tip and the diamond surface.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThis research highlights the critical need for high-quality, custom-engineered diamond materials and precise metalization for next-generation quantum sensing and nanoMRI devices. 6CCVD is the ideal partner to supply the foundational materials required to replicate and advance this work.
Applicable Materials
Section titled âApplicable Materialsâ| Research Requirement | 6CCVD Material Recommendation | Rationale for Selection |
|---|---|---|
| High-Coherence NV Host | Optical Grade Single Crystal Diamond (SCD) | Provides the ultra-low defect density and high isotopic purity (e.g., 12C enrichment available) necessary to maximize the NV center dephasing time (T*), which directly limits the achievable spectral and spatial resolution. |
| Thin, Integrated Sensor Layer | Custom SCD Plates (0.1 ”m - 500 ”m) | We supply SCD wafers in the precise thickness range (e.g., 30 ”m membranes) required for integration with co-planar waveguides and subsequent nanopillar etching, ensuring optimal MW delivery and photon collection. |
| High-Current Substrate | High Thermal Conductivity Substrates (up to 10 mm) | While quartz was used for the tip, replacing it with SCD or high-purity PCD substrates (up to 10 mm thick) can significantly improve heat dissipation, enabling the higher current densities (3.3 ”T nm-1 projected gradient) necessary for sub-nanometer resolution. |
Customization Potential
Section titled âCustomization PotentialâThe success of this device hinges on precise geometry and electrical conductivity, areas where 6CCVD offers comprehensive in-house engineering support:
- Custom Metalization: The paper utilized a Cr/Au stack for the current leads. 6CCVD offers internal metalization capabilities including Au, Pt, Pd, Ti, W, and Cu. We can deposit custom multi-layer stacks to optimize conductivity, adhesion, and thermal performance for high-current applications, including potential use of superconducting films at cryogenic temperatures.
- Precision Polishing: Achieving stable AFM feedback and minimizing tip-to-surface distance requires an extremely flat diamond surface. 6CCVD guarantees SCD polishing to Ra < 1 nm and Inch-size PCD polishing to Ra < 5 nm, ensuring optimal conditions for nanoscale proximity sensing.
- Custom Dimensions and Structuring: We supply SCD and PCD plates up to 125 mm in diameter. Our substrates are ready for advanced post-processing techniques like the nanopillar etching and membrane thinning described in the paper.
Engineering Support
Section titled âEngineering Supportâ6CCVDâs in-house PhD team specializes in the material science of diamond for quantum applications. We can assist researchers and engineers with:
- Material Selection: Consulting on the optimal diamond grade (SCD vs. PCD, isotopic purity, doping levels) for specific nanoMRI or quantum sensing projects.
- Integration Challenges: Providing guidance on achieving robust metalization stacks and surface preparation for integration with complex scanning probe microscopy (SPM) and microwave (MW) systems.
- Replication and Scaling: Supporting the transition from proof-of-concept (single NV) to scalable sensor arrays using large-area PCD or customized SCD wafers.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Abstract Nanoscale magnetic resonance imaging (nanoMRI) is crucial for advancing molecular-level structural analysis, yet existing techniques relying on permanent magnets face limitations in controllability and resolution. This study addresses the gap by introducing a switchable magnetic field gradient on a scanning tip, enabling localized, high-gradient magnetic fields at the nanoscale. Here, we demonstrate a device combining a metal microwire on a quartz tip with a nitrogen-vacancy (NV) center in diamond, achieving gradients up to 1 ÎŒT nmâ1 at fields below 200 ÎŒT. This allows electron spin mapping with 1 nm resolution, overcoming challenges like emitter contrast and sample preparation rigidity. The current-controlled gradient, switchable in 600 ns, enhances precision and flexibility. Additionally, the metallic tip modifies Rabi power spatially, enabling selective spin manipulation with varying microwave effects. This innovation paves the way for advanced nanoMRI applications, including high-resolution imaging and targeted spin control in quantum sensing and molecular studies.