Scanning nitrogen-vacancy center magnetometry in large in-plane magnetic fields

At a Glance

Metadata	Details
Publication Date	2022-02-14
Journal	Applied Physics Letters
Authors	Pol Welter, J. Rhensius, Andrea Morales, M. S. Wörnle, Charles‐Henri Lambert
Institutions	ETH Zurich
Citations	21
Analysis	Full AI Review Included

Technical Documentation & Sales Analysis: Scanning NV Magnetometry in Large In-Plane Fields

This document analyzes the research detailing the fabrication and application of {110}-cut single-crystal diamond (SCD) probes for nitrogen-vacancy (NV) center magnetometry in large in-plane magnetic fields. This breakthrough is critical for spintronics and thin-film magnetism research, directly aligning with 6CCVD’s expertise in custom MPCVD diamond solutions.

Executive Summary

Breakthrough Material: The research successfully utilized {110}-cut Single Crystal Diamond (SCD) probes to align the NV center anisotropy axis (90°) with the sample plane, enabling in-plane magnetometry.
High-Field Performance: {110} probes maintained high Photo-Luminescence (PL) contrast (20-25%) and sensitivity in large in-plane bias fields (B_ip) up to 40 mT.
Limitation Overcome: Conventional {100}-cut probes lose sensitivity and PL contrast above ~15 mT in in-plane fields due to the 55° misalignment of the NV axis.
Application: Demonstrated quantitative scanning magnetometry of ferromagnetic domains in Co-NiO thin films, crucial for studying exchange bias and spintronic devices.
Fabrication Method: High-purity SCD was processed using ¹⁵N⁺ ion implantation (7 keV, 3·10¹⁰ ions per cm²) and vacuum annealing (880°C) to create shallow NV centers, followed by e-beam lithography and ICP etching for tip formation.
6CCVD Value Proposition: 6CCVD specializes in providing custom-oriented, ultra-high purity MPCVD SCD substrates (including {110} orientation) and advanced processing support required to replicate and scale this high-performance quantum sensing technology.

Technical Specifications

Parameter	Value	Unit	Context
Diamond Crystal Orientation (Probe)	{110}	Cut	Enables in-plane NV anisotropy (θ = 90°)
Maximum Operational Bias Field (B_ip)	40	mT	Field maintained with high sensitivity ({110} probe)
Sensitivity Loss Threshold ({100} Probe)	15	mT	Field where conventional probes lose PL contrast
Intrinsic Nitrogen Concentration (SCD)	< 5	ppb	Starting HPHT material purity
Ion Implantation Species	¹⁵N⁺	N/A	Used for controlled NV center creation
Ion Implantation Energy	7	keV	Determines NV depth
Ion Implantation Dose	3·10¹⁰	ions per cm²	N/A
Vacuum Annealing Temperature	880	°C	Required for NV formation
Spin Contrast (ε)	20-25	%	Measured PL contrast for {110} probes
Saturation Count Rate (I_sat)	800 - 1200	kCt/s	Photo-luminescence performance
Magnetic Structure Length Scale	100 - 200	nm	Typical domain size observed in Co film

Key Methodologies

The successful fabrication of high-performance {110}-cut NV probes relied on precise material selection and advanced nanofabrication techniques:

Material Selection: High-purity single-crystal diamond plates with a main {110} facet were used as the starting material. The intrinsic nitrogen concentration was verified to be extremely low (< 5 ppb).
NV Center Engineering: NV centers were created via ¹⁵N⁺ ion implantation at 7 keV (dose: 3·10¹⁰ ions per cm²).
Defect Activation: Samples underwent vacuum annealing at 880°C (p < 5·10^-8 mbar) for 2 hours to mobilize vacancies and form stable NV centers.
Tip Fabrication: A series of e-beam lithography and Inductively-Coupled Plasma (ICP) etching steps were employed to define the diamond paddle and create the sharp nanoscale NV tips.
Probe Assembly: The finished diamond paddle was glued to a silicon handle structure, which was attached to a quartz tuning fork for AFM position feedback.
Magnetometry: Optically-Detected Magnetic Resonance (ODMR) spectroscopy was performed using 520 nm laser excitation and confocal collection, with the in-plane bias field (B_ip) applied via a vector electromagnet or permanent magnets.

6CCVD Solutions & Capabilities

This research highlights the critical need for custom-oriented, ultra-high purity SCD substrates and precise fabrication support—areas where 6CCVD excels. We are uniquely positioned to supply the foundational materials and engineering services necessary to advance high-field NV magnetometry.

Applicable Materials

To replicate or extend this research, the following 6CCVD materials are required:

Material Specification	6CCVD Product Recommendation	Rationale
Crystal Orientation	Optical Grade SCD, Custom {110} Orientation	Essential for achieving the in-plane (90°) NV anisotropy axis required for high-field operation.
Purity	High-Purity SCD (N < 1 ppb)	Our MPCVD process delivers intrinsic nitrogen concentrations significantly lower than the < 5 ppb used in the study, ensuring maximum control over NV creation via implantation.
Thickness/Dimensions	SCD Plates (0.1 µm - 500 µm)	We provide custom thicknesses suitable for tip fabrication and integration into scanning probe setups.
Surface Quality	Polished SCD (Ra < 1 nm)	Ultra-smooth surfaces are critical for subsequent lithography, etching, and achieving high-resolution scanning performance.

Customization Potential

6CCVD offers comprehensive services to support the complex fabrication workflow demonstrated in this paper:

Custom Substrate Preparation: We supply SCD wafers cut to specific non-{100} orientations (e.g., {110} or {111}) and can provide laser cutting services to pre-shape diamond paddles, reducing post-processing time.
Advanced Polishing: We guarantee Ra < 1 nm polishing on SCD, ensuring the pristine surface quality necessary for high-resolution e-beam lithography and subsequent ICP etching steps used to define the nanoscale tips.
Metalization Services: While this study did not focus on metalization, 6CCVD offers in-house deposition of standard contacts (Au, Pt, Pd, Ti, W, Cu), which may be required for integrating microwave lines or electrical contacts in future NV sensing devices.
Defect Engineering Partnership: 6CCVD provides the ideal ultra-pure SCD starting material and can facilitate partnerships for precise ¹⁵N⁺ ion implantation and post-implantation annealing protocols required for optimized NV center creation.

Engineering Support

6CCVD’s in-house PhD team can assist with material selection and optimization for similar quantum sensing and spintronics projects. We provide consultation on:

Selecting the optimal crystal orientation ({110} vs. {111}) based on the required bias field direction (in-plane vs. out-of-plane).
Determining the appropriate SCD purity and thickness for specific NV depth requirements and probe geometries.
Integrating diamond materials into complex device architectures requiring custom metalization or bonding.

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

View Original Abstract

Scanning magnetometry with nitrogen-vacancy (NV) centers in diamond has emerged as a powerful microscopy for studying weak stray field patterns with nanometer resolution. Due to the internal crystal anisotropy of the spin defect, however, external bias fields—critical for the study of magnetic materials—must be applied along specific spatial directions. In particular, the most common diamond probes made from {100}-cut diamond only support fields at an angle of θ=55° from the surface normal. In this paper, we report fabrication of scanning diamond probes from {110}-cut diamond where the spin anisotropy axis lies in the scan plane (θ=90°). We show that these probes retain their sensitivity in large in-plane fields and demonstrate scanning magnetometry of the domain pattern of Co-NiO films in applied fields up to 40 mT. Our work extends scanning NV magnetometry to the important class of materials that require large in-plane fields.

Tech Support

Original Source

DOI: https://doi.org/10.1063/5.0084910

References

2017 - Purely antiferromagnetic magnetoelectric random access memory [Crossref]
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2018 - Nanoscale electrical conductivity imaging using a nitrogen-vacancy center in diamond [Crossref]
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2013 - Imaging currents in HgTe quantum wells in the quantum spin hall regime [Crossref]
2017 - Nanoscale imaging of current density with a single-spin magnetometer [Crossref]
2020 - Imaging viscous flow of the Dirac fluid in graphene [Crossref]