Relaxometry and Dephasing Imaging of Superparamagnetic Magnetite Nanoparticles Using a Single Qubit
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2015-07-28 |
| Journal | Nano Letters |
| Authors | Dominik Schmid-Lorch, Thomas HĂ€berle, Friedemann Reinhard, Andrea Zappe, Michael Slota |
| Institutions | University of Stuttgart, Max Planck Institute for Solid State Research |
| Citations | 61 |
| Analysis | Full AI Review Included |
6CCVD Technical Documentation: Nanoscale Magnetic Imaging via NV Center Relaxometry
Section titled â6CCVD Technical Documentation: Nanoscale Magnetic Imaging via NV Center RelaxometryâExecutive Summary
Section titled âExecutive SummaryâThis paper demonstrates a novel, ambient-condition nanoscale magnetometry technique using a shallow Nitrogen-Vacancy (NV) center in diamond to image the dynamic magnetic fluctuations of superparamagnetic magnetite nanoparticles. This research validates the utility of high-coherence MPCVD Single Crystal Diamond (SCD) in advancing quantum sensing for applications in materials science and nanomedicine.
- Core Achievement: Successful application of T1 relaxometry and T2 dephasing imaging to characterize a single 10 nm magnetite nanoparticle, extracting key metrics (diameter, NV distance) at the nanoscale.
- Material Requirement: The technique relied on high-quality bulk (100) SCD hosting shallow NV centers (approximately 5 nm below the surface) to ensure long intrinsic spin lifetimes.
- Dynamic Range: Magnetic spin noise from the nanoparticle dramatically reduced the NV coherence times by factors up to 30 (T2) and two orders of magnitude (T1), confirming strong spin-noise coupling.
- Frequency and Spatial Anisotropy: The combined T1 (sensitive to transverse magnetic noise, B⊥) and T2 (sensitive to longitudinal magnetic noise, B∥) measurements provided anisotropic information on magnetic fluctuations across different frequency ranges.
- Ambient Conditions Advantage: Unlike cryogenic methods (SQUID), this NV-based approach operates under ambient conditions, making it an ideal, viable screening method for future biomedical agents (e.g., MRI contrast agents like ferritin).
- 6CCVD Relevance: Replication and extension of this research necessitates high-purity, low-strain SCD substrates with precise crystallographic orientation, core capabilities of 6CCVDâs MPCVD manufacturing process.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| NV Center Depth (Nominal) | ~5 | nm | Below diamond surface (100 orientation) |
| Applied DC Magnetic Field (B0) | 13 | mT | Aligned with the NV axis direction |
| Scan Area / Pixel Size | 500 x 500 / 10 | nm / nm | Spatial imaging resolution |
| Intrinsic T1 Lifetime (Retracted) | 2713 ± 311 | ”s | SCD material limit (Intrinsic decoherence) |
| Intrinsic T2 Lifetime (Retracted) | 19 ± 1 | ”s | SCD material limit (Intrinsic decoherence) |
| Engaged T1 Lifetime (Minimum) | 31 ± 6 | ”s | Maximum T1 decoherence induced by particle |
| Engaged T2 Lifetime (Minimum) | 0.49 ± 0.05 | ”s | Maximum T2 decoherence induced by particle |
| Fitted Nanoparticle Diameter (r) | 7.06 ± 0.4 | nm | Derived from Ornstein-Uhlenbeck fit |
| Fitted Vertical Distance (z) | 16.3 ± 4.7 | nm | Distance between NV center and particle |
| Magnetite Anisotropy Constant (K) | 26 | kJ/m3 | Chosen for fit based on literature values |
| Max Second Moment (B⊥2) | 8.8 | mT2 | Transverse noise measured by T1 |
| Max Second Moment (B∥2) | 1.8 | mT2 | Longitudinal noise measured by T2 |
Key Methodologies
Section titled âKey MethodologiesâThe experiment successfully characterized the magnetic dynamics of superparamagnetic magnetite nanoparticles using pulsed optically detected magnetic resonance (ODMR) protocols on a single NV center.
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Substrate & Setup:
- A commercial Atomic Force Microscope (AFM) was used, operating under ambient conditions (critical for bio-applications).
- The base material was a bulk (100) Single Crystal Diamond plate containing shallow NV centers located approximately 5 nm from the surface.
- A constant magnetic field of 13 mT was applied, aligned parallel to the NV center axis.
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Sample Preparation & Scanning:
- Superparamagnetic magnetite nanoparticles (initial diameter 8 ± 3 nm) were diluted in sodium silicate.
- This matrix served to firmly attach the particles to the AFM cantilever and act as a spacer.
- The particle-loaded cantilever was scanned in contact mode over a fixed, individual NV center on the diamond surface.
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Spin Lifetime Measurement Protocols:
- T1 Relaxometry (Longitudinal Relaxation):
- The polarization is initialized and analyzed along the NV axis.
- The T1 sequence is primarily sensitive to magnetic field fluctuations perpendicular (transverse) to the NV axis (B⊥).
- It detects noise components at the NV centerâs Larmor frequency (high frequency range).
- T2 Dephasing (Transversal Relaxation via Spin Echo, SE):
- The polarization is flipped into the transversal plane using a $\pi$/2 microwave pulse.
- The SE method is mainly sensitive to low frequency magnetic field fluctuations along (longitudinal) the NV axis (B∥).
- T1 Relaxometry (Longitudinal Relaxation):
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Modeling and Data Extraction:
- Magnetic field fluctuations were modeled using an Ornstein-Uhlenbeck process incorporating the NĂ©el relaxation time ($\tau$N) and anisotropy energy barrier (E = KV).
- Decoherence rates ($\Gamma$tot) were calculated as the sum of intrinsic diamond lattice decoherence ($\Gamma$int, due to 13C) and external nanoparticle-induced decoherence ($\Gamma$ext).
- Simulations were fitted to fluorescence contrast images (T1 and T2 maps) simultaneously to determine the particle radius (r) and the minimum vertical distance (z) to the NV center.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThis quantum sensing research confirms the critical role of high-purity, highly coherent Single Crystal Diamond (SCD) as the fundamental platform. 6CCVD is an expert technical partner for synthesizing and preparing the custom SCD materials required to replicate or significantly enhance this work.
Applicable Materials for NV Center Magnetometry
Section titled âApplicable Materials for NV Center Magnetometryâ| Material Requirement (Paper) | 6CCVD Material Solution | Relevance & Advantages |
|---|---|---|
| High Coherence / Low Strain | Optical Grade SCD (High Purity) | Guaranteed low concentrations of substitutional nitrogen (P1 centers) and other contaminants, maximizing intrinsic T1 (up to milliseconds) and T2 (up to tens of microseconds) lifetimes. Essential for high-sensitivity measurements. |
| Specific Orientation | Custom Oriented SCD Plates | The paper utilized (100) diamond. 6CCVD offers wafers with custom crystallographic orientation, including (111), which the paper notes would hypothetically yield better anisotropy control (Δ = 0.0). |
| Substrate Size & Bulk | SCD Substrates up to 500 ”m thick | We provide robust, large-area SCD substrates, ensuring stability and homogeneity for sophisticated scanning probe setups like the AFM used here. |
| Improved SNR (Future Work) | SCD Templates for Nanopillars | The paper suggests improving signal-to-noise ratio (SNR) using nanopillars. 6CCVD supplies the high-purity SCD material necessary for subsequent high-resolution etching processes. |
Customization Potential for Advanced Research
Section titled âCustomization Potential for Advanced ResearchâThe ability to finely control material properties is paramount for replicating and advancing NV-center-based quantum sensing experiments.
- Custom Dimensions: While this experiment used a small bulk sample, 6CCVD can supply SCD or PCD substrates in custom sizes and shapes, with polishing available up to inch-size PCD (Ra < 5 nm) and sub-nanometer roughness for SCD (Ra < 1 nm), crucial for high-precision AFM scanning.
- Precision Thickness Control: We offer SCD material with thickness control ranging from 0.1 ”m films up to 500 ”m bulk plates, providing engineering flexibility for integrating diamond films into complex quantum devices.
- Metalization Services: Although not explicitly used on the diamond in this paper, NV quantum sensing often requires precise microwave delivery or electrical contacts. 6CCVD provides in-house metalization (Au, Pt, Pd, Ti, W, Cu) for creating optimized microstrip lines or electrodes directly onto the SCD surface.
Engineering Support & Application Extension
Section titled âEngineering Support & Application Extensionâ6CCVDâs in-house PhD team specializes in defect engineering and MPCVD growth parameters tailored for quantum applications. We can assist researchers in selecting materials specifically optimized for:
- Shallow NV Optimization: Achieving the requisite ~5 nm depth for sensing external nanoparticles, a process highly dependent on the quality of the SCD starting material and subsequent implantation/annealing.
- Biomedical Applications: Supporting material selection and design for novel MRI contrast agents or particle-aided tumor hyperthermia studies that require ambient-condition, nanoscale magnetic screening.
- Relaxometry Refinement: Consulting on how different crystallographic orientations and intrinsic defect levels impact the anisotropy ($\varepsilon$) observed in T1 and T2 relaxometry images.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly. We ship globally (DDU default, DDP available) to support your cutting-edge research.
View Original Abstract
To study the magnetic dynamics of superparamagnetic nanoparticles, we use scanning probe relaxometry and dephasing of the nitrogen vacancy (NV) center in diamond, characterizing the spin noise of a single 10 nm magnetite particle. Additionally, we show the anisotropy of the NV sensitivityâs dependence on the applied decoherence measurement method. By comparing the change in relaxation (T1) and dephasing (T2) time in the NV center when scanning a nanoparticle over it, we are able to extract the nanoparticleâs diameter and distance from the NV center using an Ornstein-Uhlenbeck model for the nanoparticleâs fluctuations. This scanning probe technique can be used in the future to characterize different spin label substitutes for both medical applications and basic magnetic nanoparticle behavior.