Scanned probe imaging of nanoscale magnetism at cryogenic temperatures with a single-spin quantum sensor

At a Glance

Metadata	Details
Publication Date	2016-04-29
Journal	Nature Nanotechnology
Authors	Matthew Pelliccione, Alec Jenkins, Preeti Ovartchaiyapong, Christopher Reetz, Eve Emmanouilidou
Institutions	University of California, Santa Barbara, University of California, Los Angeles
Citations	213
Analysis	Full AI Review Included

Technical Documentation: Cryogenic NV Scanning Magnetometry Probes

This documentation analyzes the requirements for fabricating high-performance Nitrogen-Vacancy (NV) diamond quantum sensors operating at cryogenic temperatures, based on the research paper “Scanned probe imaging of nanoscale magnetism at cryogenic temperatures with a single-spin quantum sensor.”

Executive Summary

The research successfully demonstrates the first cryogenic operation of an NV scanning magnetometer, a critical advancement for nanoscale magnetic imaging in condensed matter physics.

Core Achievement: First NV magnetic imaging demonstration down to 6 K, enabling the study of non-trivial magnetic order in solid-state systems (e.g., superconducting vortices).
Performance Metrics: Achieved 6 nm spatial resolution and 3 µT/√Hz DC field sensitivity.
Material Requirement: The technique relies exclusively on high-quality, monolithic Single Crystal Diamond (SCD) probes to ensure long spin coherence times (T₂*).
Probe Design: Nanofabricated SCD cantilevers with arrays of pillars (200 nm diameter) were used, requiring precise control over crystal orientation and surface quality.
Future Roadmap: Projected improvements aim for 3 nm spatial resolution and 10 nT/√Hz sensitivity, necessitating ultra-shallow NV centers (requiring superior surface polishing) and extended T₂* coherence times (> 100 µs).
6CCVD Value: 6CCVD provides the necessary high-purity, low-strain, (100) oriented SCD substrates and custom processing (polishing, metalization) required to meet these next-generation quantum sensing specifications.

Technical Specifications

The following hard data points were extracted from the research paper detailing the performance and fabrication parameters of the cryogenic NV sensor.

Parameter	Value	Unit	Context
Minimum Operating Temperature	6	K	Sample temperature during magnetic imaging.
Spatial Resolution (Achieved)	6	nm	Demonstrated resolution on magnetic hard disk features.
DC Field Sensitivity (Achieved)	3	µT/√Hz	Best sensitivity achieved using the faster contour imaging method.
DC Field Sensitivity (Full-Field)	30	µT/√Hz	Sensitivity using the full Electron Spin Resonance (ESR) method.
Target Spatial Resolution (Future)	3	nm	Requires reduced NV-sample separation (shallower NVs).
Target Field Sensitivity (Future)	10	nT/√Hz	Requires NV spin coherence time T₂* > 100 µs.
NV Implantation Dose (¹⁴N)	5E11/cm²	cm^-2	Dose used to yield approximately one NV center per pillar.
NV Implantation Energy	15	keV	Used to target NV depths of 15-20 nm.
Annealing Temperature	850	°C	Post-implantation annealing performed in vacuum.
Diamond Substrate Orientation	(100)	N/A	Orientation chosen for cantilever fabrication.
Cantilever Dimensions (Full)	150 x 20 x 3	µm	Typical dimensions of the fabricated SCD cantilever.
Pillar Dimensions	200 nm diameter, 1 µm tall, 1 µm pitch	nm / µm	Dimensions of the nanofabricated diamond tips.
Superconductor Critical Temperature (T_c)	30	K	Iron pnictide BaFe₂(As_0.7P_0.3)₂.

Key Methodologies

The fabrication and experimental setup relied on advanced diamond processing and custom cryogenic instrumentation.

Substrate Selection: Monolithic single-crystal diamond (SCD) was chosen for its superior coherence properties compared to diamond nanocrystals. The substrate was (100) oriented, 2 mm x 2 mm, and bonded to an oxidized silicon wafer using a Diamond-on-Insulator approach.
Nanostructure Fabrication: An array of diamond pillars (200 nm diameter, 1 µm tall) was formed using nanoimprint lithography with a Titanium (Ti) hard mask, followed by O₂ etching.
NV Center Creation: Nitrogen (¹⁴N) implantation was performed at 15 keV energy and a dose of 5E11/cm² to position the NV centers shallowly (15-20 nm depth).
Defect Activation & Cleaning: The implanted diamond was annealed at 850 °C in vacuum, followed by cleaning in a boiling sulfuric acid/nitric acid mixture to remove surface contamination and activate the NV centers.
Probe Integration: The SCD cantilever was attached to a quartz tuning fork, anchored in shear mode, and integrated into a custom-built, low-temperature Atomic Force Microscope (AFM).
Cryogenic Environment: The system utilized a closed-cycle cryostat (Montana Instruments) operating the sample at 6 K, with tip-sample vibration minimized to 0.72 nm RMS.
Sensing Protocol: NV spin state was read out via photoluminescence (532 nm green excitation) and manipulated using microwave (RF) excitation delivered via a gold wirebond located within 50 µm of the NV center.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the high-purity diamond materials and custom processing required to replicate and advance this cutting-edge quantum sensing research. The success of cryogenic NV magnetometry hinges on maximizing T₂* coherence time and minimizing NV-sample separation, both of which are directly controlled by the quality and preparation of the SCD substrate.

Research Requirement	6CCVD Solution & Value Proposition
Applicable Materials	Optical Grade SCD (Low Strain, Low N): The core requirement is high-purity, low-strain SCD to achieve the long spin coherence times (T₂* > 100 µs) necessary for the targeted 10 nT/√Hz sensitivity. 6CCVD specializes in MPCVD growth optimized for quantum applications.
Substrate Orientation & Size	Custom (100) SCD Substrates: We provide SCD plates with precise (100) orientation, essential for the nanofabrication process described. We offer custom dimensions, from small 2 mm x 2 mm pieces used here, up to large SCD plates (up to 500 µm thick) for scaling production.
Ultra-Shallow NV Placement	Precision Polishing (Ra < 1 nm): Achieving the target 3 nm spatial resolution requires NV centers closer to the surface (shallower implantation). 6CCVD guarantees ultra-low surface roughness (Ra < 1 nm for SCD), providing the ideal, damage-free surface necessary for highly controlled, shallow ion implantation.
Nanostructure Integration	Custom Thickness Control: We supply SCD material with thickness control from 0.1 µm to 500 µm, enabling researchers to optimize the Diamond-on-Insulator (DOI) approach for cantilever and pillar fabrication, ensuring high mechanical Q-factors and efficient waveguiding.
Microwave Circuit Integration	Integrated Custom Metalization: The experiment used a gold wirebond for RF delivery. 6CCVD offers in-house metalization capabilities (Au, Pt, Pd, Ti, W, Cu) to deposit integrated microwave striplines directly onto the diamond surface, improving RF coupling efficiency and simplifying probe assembly.
Scaling and Production	Large-Area PCD Wafers (up to 125 mm): While SCD was used for coherence, 6CCVD can provide large-area Polycrystalline Diamond (PCD) substrates (up to 125 mm diameter) for applications where large-scale integration or cost-efficiency is paramount.

Engineering Support

6CCVD’s in-house PhD team, experts in MPCVD growth and quantum defect engineering, can assist researchers with material selection, implantation strategy consultation (dose/energy optimization), and surface preparation protocols for similar Cryogenic NV Magnetometry projects.

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

Tech Support

Original Source

DOI: https://doi.org/10.1038/nnano.2016.68