Scanning nitrogen-vacancy magnetometry down to 350 mK
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2022-05-30 |
| Journal | Applied Physics Letters |
| Authors | Patrick Scheidegger, S. Diesch, Marius L. Palm, Christian L. Degen |
| Institutions | ETH Zurich |
| Citations | 25 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Sub-Kelvin Scanning NV Magnetometry
Section titled “Technical Documentation & Analysis: Sub-Kelvin Scanning NV Magnetometry”This document analyzes the research paper “Scanning nitrogen-vacancy magnetometry down to 350 mK” to identify material requirements and align them with 6CCVD’s advanced MPCVD diamond capabilities, focusing on single-crystal diamond (SCD) for quantum sensing applications.
Executive Summary
Section titled “Executive Summary”- Sub-Kelvin Quantum Sensing: The research successfully demonstrates robust scanning Nitrogen-Vacancy (NV) magnetometry in single-crystal diamond (SCD) tips down to a base temperature of 350 mK in a dry dilution refrigerator.
- Material Stability: NV centers in the SCD tips maintained stable spin and optical properties (PL contrast and linewidth) across the critical temperature range of 0.35 K to 3 K, confirming diamond’s suitability for extreme cryogenic quantum applications.
- High Sensitivity Achieved: An optimized magnetic field sensitivity of 3 µT/√Hz was achieved, enabling non-invasive imaging of nanoscale magnetic phenomena.
- Pulsed ODMR Implementation: Pulsed Optically Detected Magnetic Resonance (ODMR) was employed to mitigate laser- and microwave-induced heating, a critical challenge for millikelvin NV magnetometry.
- Application Validation: The system successfully imaged superconducting vortices in 50-nm-thin aluminum micro-discs, validating the technique for studying Type II superconductivity and other low-temperature quantum materials (e.g., twisted bilayer graphene).
- Diamond Specification: The scanning probe utilized a monolithic SCD tip with a {100} surface orientation, requiring ultra-precise surface preparation and controlled shallow NV implantation (7 keV).
Technical Specifications
Section titled “Technical Specifications”The following hard data points were extracted from the experimental results:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Base Operating Temperature | 350 | mK | Achieved in dry dilution refrigerator |
| Optimized Magnetic Field Sensitivity | 3 | µT/√Hz | Achieved via line scans at 1 mT bias field |
| Initial Magnetic Field Sensitivity | 14 | µT/√Hz | Normalized pixel-by-pixel variation (1-second integration) |
| NV Center Stability Range | 0.35 - 3 | K | PL contrast and linewidth independent of temperature |
| Aluminum Film Critical Temperature (Tc) | 1.25 | K | Expected Tc for 50 nm thin film |
| Aluminum Film Thickness | 50 | nm | Superconducting test structure |
| Co-Planar Waveguide (CPW) Thickness | 150 | nm | Used for microwave delivery |
| NV Center Implantation Energy | 7 | keV | Used for creating shallow NV centers in the tip |
| NV-to-Sample Distance | ~110 | nm | Estimated distance during scanning |
| AFM Vertical Stability (RMS) | ~2.5 | nm | Measured stability despite pulse tube vibrations |
Key Methodologies
Section titled “Key Methodologies”The successful implementation of sub-Kelvin scanning NV magnetometry relied on precise material fabrication and specialized cryogenic techniques:
- Diamond Tip Fabrication: Monolithic single-crystal diamond (SCD) tips were fabricated using a series of dry etching steps, ensuring a {100} surface orientation for optimal NV alignment and performance.
- NV Center Creation: Shallow NV centers were created via low-energy ion implantation (7 keV) into the SCD tip, followed by standard annealing processes (implied) to activate the defects.
- Cryogenic Integration: The AFM/Confocal Microscope (AFM/CFM) was rigidly suspended from the cold insert of a dry dilution refrigerator (Leiden Cryogenics) to minimize thermal anchoring issues and reach 350 mK.
- Microwave Delivery: Microwave (MW) pulses were guided to the sample via a co-planar waveguide (CPW) patterned onto the sapphire substrate, requiring precise metal deposition and impedance matching.
- Detection Scheme: Pulsed Optically Detected Magnetic Resonance (ODMR) was utilized, employing specific pulse sequences (tπ, tlaser, tset) to reduce the duty cycle of laser and MW irradiation, thereby mitigating local heating effects.
- Distance Control: A quartz tuning fork oscillator attached to the diamond tip provided distance control for contact mode scanning, achieving high spatial resolution (pixel size down to 133 nm).
6CCVD Solutions & Capabilities
Section titled “6CCVD Solutions & Capabilities”6CCVD is uniquely positioned to supply the advanced MPCVD diamond materials and customization services required to replicate and extend this pioneering sub-Kelvin quantum sensing research.
Applicable Materials
Section titled “Applicable Materials”To achieve the high spin coherence and surface quality necessary for shallow NV centers operating at cryogenic temperatures, the following 6CCVD material is required:
- Optical Grade Single Crystal Diamond (SCD): We supply high-purity, low-strain SCD wafers with nitrogen concentrations optimized for NV creation.
- Orientation Control: Guaranteed {100} surface orientation, essential for the tip geometry used in this study.
- Thickness Control: Available in thicknesses from 0.1 µm up to 500 µm, allowing researchers to optimize the thermal mass and mechanical stability of the scanning probe.
Customization Potential
Section titled “Customization Potential”The research highlights the need for precise integration of the diamond tip with custom electronics and sample structures. 6CCVD offers comprehensive fabrication support:
| Research Requirement | 6CCVD Customization Service | Benefit to Researcher |
|---|---|---|
| Ultra-Smooth Tip Surface (Ra < 2.5 nm stability required) | Precision Polishing (Ra < 1 nm) | Ensures minimal surface noise and reliable contact mode AFM operation, crucial for maintaining the 110 nm NV-to-sample distance. |
| Custom Sample Structures (Al CPW, micro-discs) | Custom Metalization (Au, Ti, Pt, Cu, W) | We can deposit the necessary metal stacks directly onto diamond or sapphire substrates for optimized microwave delivery (CPW fabrication) and thermal anchoring. |
| Tip Integration & Mounting | Custom Dimensions & Laser Cutting | We provide SCD plates/wafers cut to specific geometries required for mounting onto quartz tuning forks or complex nano-positioner stacks, minimizing vibrational coupling. |
| Future BDD Applications (e.g., SQUID complement) | Boron-Doped Diamond (BDD) | For future work complementing SQUID or exploring BDD-based quantum devices, we offer highly conductive BDD films (PCD or SCD) up to 500 µm thick. |
Engineering Support
Section titled “Engineering Support”The challenges identified in the paper—specifically improved probe thermalization, efficient microwave delivery, and material selection for low-temperature stability—are core areas of expertise for 6CCVD.
- Thermal Management: Our in-house PhD team can assist researchers in selecting optimal SCD thicknesses and metalization schemes to improve thermal anchoring and reduce heat load transmission through the probe, potentially enabling operation below the current 350 mK limit.
- Quantum Sensing Optimization: We provide consultation on material specifications (e.g., nitrogen concentration, isotopic purity) to maximize NV spin coherence time (T2) and PL contrast for similar quantum sensing projects.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
We report on the implementation of a scanning nitrogen-vacancy (NV) magnetometer in a dry dilution refrigerator. Using pulsed optically detected magnetic resonance combined with efficient microwave delivery through a co-planar waveguide, we reach a base temperature of 350 mK, limited by experimental heat load and thermalization of the probe. We demonstrate scanning NV magnetometry by imaging superconducting vortices in a 50-nm-thin aluminum microstructure. The sensitivity of our measurements is approximately 3 μT per square root Hz. Our work demonstrates the feasibility for performing noninvasive magnetic field imaging with scanning NV centers at sub-Kelvin temperatures.
Tech Support
Section titled “Tech Support”Original Source
Section titled “Original Source”References
Section titled “References”- 2022 - Nanoscale magnetic field imaging for 2D materials [Crossref]
- 2008 - Scanning magnetic field microscope with a diamond single-spin sensor [Crossref]
- 2012 - A robust scanning diamond sensor for nanoscale imaging with single nitrogen-vacancy centres [Crossref]
- 2017 - Real-space imaging of non-collinear antiferromagnetic order with a single-spin magnetometer [Crossref]
- 2019 - Nanomagnetism of magnetoelectric granular thin-film antiferromagnets [Crossref]
- 2021 - Coexistence of Bloch and Neél walls in a collinear antiferromagnet [Crossref]
- 2021 - Characterization of room-temperature in-plane magnetization in thin flakes of CrTe2 with a single-spin magnetometer [Crossref]
- 2017 - Nanoscale imaging of current density with a single-spin magnetometer [Crossref]
- 2017 - Quantum imaging of current flow in graphene [Crossref]
- 2020 - Imaging viscous flow of the Dirac fluid in graphene [Crossref]