Three-dimensional magnetic resonance tomography with sub-10 nanometer resolution

At a Glance

Metadata	Details
Publication Date	2024-01-25
Journal	npj Quantum Information
Authors	Mohammad T. Amawi, Andrii Trelin, You Huang, Paul Weinbrenner, Francesco Poggiali
Institutions	Technical University of Munich, University of Rostock
Citations	4
Analysis	Full AI Review Included

Technical Documentation & Analysis: 3D Magnetic Resonance Tomography

Reference: Amawi et al., npj Quantum Information (2024) 10:16. Application: Three-dimensional magnetic resonance tomography with sub-10 nanometer resolution using NV centers in CVD diamond.

Executive Summary

This research demonstrates a breakthrough in nanoscale imaging, achieving three-dimensional magnetic resonance tomography (3D MRT) with super-resolution capabilities. The core findings and value proposition are summarized below:

Record Resolution: Achieved spatial resolution down to 5.9 ± 0.1 nm using Fourier-accelerated 3D MRT, comparable to the best super-resolution optical microscopy techniques (e.g., PALM/STORM).
Material Basis: The technique relies on Nitrogen-Vacancy (NV) centers embedded in a densely doped Chemical Vapor Deposition (CVD) diamond substrate (NV concentration ≈ 0.13 ppb).
Gradient Generation: High-magnitude, switchable magnetic field gradients (up to 2.10² T/m) are generated by a lithographically fabricated U-structure consisting of three independent gold microwires on the diamond surface.
Enhanced Coherence: Effective decoherence mitigation via hardware integration and post-processing resulted in a coherence time ($T_{2,\perp}$) of 8.64 ± 0.1 µs under high-gradient conditions.
Data Efficiency: A novel compressed sensing scheme (“Fourier zooming”) was implemented, exploiting aliasing to reduce the required data points by a factor of up to 18, significantly accelerating acquisition time.
Transformative Applications: This method establishes a pathway for 3D structure analysis of spin-labeled proteins, advanced quantum register addressing in dense NV ensembles, and nanoscale force tracking.

Technical Specifications

The following hard data points were extracted from the experimental results and device design:

Parameter	Value	Unit	Context
Spatial Resolution (Achieved)	5.9 ± 0.1	nm	3D Magnetic Resonance Tomography
NV Center Concentration	≈ 0.13	ppb	Densely doped CVD diamond substrate
Magnetic Field Gradient Magnitude	≈ 2 G/µm (2.10² T/m)	T/m	Generated by U-structure microwires
Coherence Time (T_2,⊥)	8.64 ± 0.1	µs	Measured under gradient current conditions
Bias Magnetic Field (B₀)	≈ 76	G	Applied along one of the four NV axes
Imaging Depth Below Surface	≈ 6	µm	Focal spot depth beneath the U-structure
Microwire Gold Film Thickness	200	nm	Au layer for high-conductivity gradient generation
Microwire Adhesion Layer	10	nm	Chromium (Cr) layer beneath Au
Microwire Arm Width	500	nm	Critical dimension for gradient localization
Data Acquisition Reduction Factor	18	Factor	Achieved via compressed sensing (6x and 3x undersampling)

Key Methodologies

The experiment successfully combined advanced MPCVD diamond material science with nanoscale lithography and high-speed quantum control techniques:

Substrate Selection: Utilized a densely doped CVD diamond substrate (Element Six General Grade, NV ≈ 0.13 ppb) to ensure a sufficient ensemble of NV centers within the confocal volume for signal detection.
Device Fabrication: A U-shaped microstructure consisting of three independent microwires was fabricated on the diamond surface using lift-off photolithography. The metal stack was 200 nm Gold (Au) on a 10 nm Chromium (Cr) adhesion layer.
Gradient Control: Fast switches (ic-Haus HGP) were used to pulse stable voltage sources, generating highly rectangular current pulses in the microwires. These currents created three linearly independent magnetic field gradients.
3D Phase Encoding: The standard Hahn Echo sequence was extended to include three consecutive magnetic gradient pulses ($I_1, I_2, I_3$), phase-encoding the position of the NV centers in three dimensions.
Decoherence Mitigation: Current fluctuations (a primary source of decoherence, $T_{2,\perp}$ shortening) were corrected by hardware-integrating the current pulse ($\int I(t)dt$) and using this value for post-processing correction of the time axis.
Image Reconstruction: The 3D spatial image was recovered by performing an inverse 3D Fourier Transform on the time-domain (k-space) data.
Compressed Sensing Implementation: A “Fourier zooming” technique was demonstrated by equidistant undersampling of k-space, leveraging aliasing to shift the signal band to a low-frequency window, enabling effective zoom and reducing data acquisition requirements.

6CCVD Solutions & Capabilities

The achievement of sub-10 nm resolution 3D MRT is highly dependent on the quality and customization of the diamond substrate and the precision of the surface metalization. 6CCVD is uniquely positioned to supply the materials and engineering services required to replicate, optimize, and scale this groundbreaking research.

Research Requirement	6CCVD Solution & Capability	Technical Advantage for Replication/Extension
Densely Doped CVD Diamond Substrate (NV ≈ 0.13 ppb)	Custom Single Crystal Diamond (SCD) Wafers	6CCVD offers precise, tailored nitrogen doping during MPCVD growth, allowing engineers to specify NV concentrations (e.g., 0.1 ppb to 10 ppm) to optimize SNR for ensemble sensing or isolate single NV centers for ultimate sensitivity.
High-Quality Surface Finish (Critical for 500 nm lithography)	Ultra-Low Roughness Polishing (Ra < 1 nm)	Our standard SCD polishing achieves Ra < 1 nm, ensuring superior surface quality necessary for reliable adhesion and patterning of nanoscale metal structures (e.g., 500 nm wide microwires) and minimizing strain near the surface.
Microfabricated Metal Structure (10 nm Cr / 200 nm Au stack)	Advanced Custom Metalization Services	We provide in-house deposition of multi-layer stacks (e.g., Cr/Au, Ti/Pt/Au, W/Cu) with precise thickness control (down to 0.1 µm). This capability is essential for generating stable, high-magnitude magnetic gradients (2.10² T/m) required for high spatial resolution.
Scaling and Integration	Large-Area PCD and Custom Dimensions	For scaling up device arrays or integrating complex quantum systems, 6CCVD provides PCD wafers up to 125mm diameter and SCD substrates up to 500 µm thick (or 10mm thick substrates), all with global shipping (DDU/DDP).
Future $T_2$ Optimization	High-Purity, Low-Strain SCD	While the paper achieved 8.64 µs $T_{2,\perp}$, future experiments requiring longer coherence times for enhanced spectral resolution (Δf) can utilize 6CCVD’s ultra-low strain, high-purity SCD material, minimizing background spin bath noise.

Engineering Support

6CCVD’s in-house PhD team specializes in the material science of diamond quantum sensors. We can assist researchers and engineers in selecting the optimal SCD or PCD material specifications (doping level, crystal orientation, surface termination, and metalization stack) required to replicate or extend this 3D Magnetic Resonance Tomography project, particularly for applications involving quantum registers or spin-labeled protein analysis.

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

View Original Abstract

Abstract We demonstrate three-dimensional magnetic resonance tomography with a resolution down to 5.9 ± 0.1 nm. Our measurements use lithographically fabricated microwires as a source of three-dimensional magnetic field gradients, which we use to image NV centers in a densely doped diamond by Fourier-accelerated magnetic resonance tomography. We also demonstrate a compressed sensing scheme, which allows for direct visual interpretation without numerical optimization and implements an effective zoom into a spatially localized volume of interest, such as a localized cluster of NV centers. It is based on aliasing induced by equidistant undersampling of k-space. The resolution achieved in our work is comparable to the best existing schemes of super-resolution microscopy and approaches the positioning accuracy of site-directed spin labeling, paving the way to three-dimensional structure analysis by magnetic-gradient based tomography.

Tech Support

Original Source

DOI: https://doi.org/10.1038/s41534-024-00809-w