Fabrication of all diamond scanning probes for nanoscale magnetometry

At a Glance

Metadata	Details
Publication Date	2016-06-01
Journal	Review of Scientific Instruments
Authors	Patrick Appel, Elke Neu, Marc Ganzhorn, Arne Barfuss, Marietta Batzer
Institutions	Saarland University, University of Basel
Citations	157
Analysis	Full AI Review Included

6CCVD Technical Documentation: All-Diamond Scanning Probes for Nanoscale Magnetometry

Executive Summary

This research validates an advanced, high-yield fabrication methodology for creating single-crystal, all-diamond scanning probes essential for state-of-the-art quantum magnetometry. The process requires ultra-high purity materials and precision engineering, aligning perfectly with 6CCVD’s core capabilities.

Core Achievement: Successful integration of single Nitrogen Vacancy (NV) centers into robust, miniaturized diamond scanning probes (200 nm diameter nanopillars on a <1 µm cantilever).
Performance: Achieved high AC magnetic field sensitivity ($N_{AC} \approx 50 \pm 20 \text{ nT}/\sqrt{\text{Hz}}$), enabled by excellent spin coherence times ($T_2 = 94 \pm 4 \text{ µs}$).
Material Necessity: Fabrication relies exclusively on ultra-high purity, electronic grade Single Crystal Diamond (SCD) to ensure long spin coherence, minimizing paramagnetic defects.
Engineering Challenge: The process demands extreme dimensional control, requiring SCD wafers to be polished to $R_a < 1 \text{ nm}$ and thinned via deep ICP-RIE etching to form thin membranes and high-aspect-ratio nanopillars.
Resolution: Nanoscale spatial resolution is confirmed by achieving NV-to-sample distances estimated in the tens of nanometers (as low as 10-25 nm demonstrated in related work).
6CCVD Advantage: 6CCVD is positioned to supply the required high-quality SCD substrates, custom thickness thinning, ultra-low roughness polishing, and pre-implantation preparation necessary to replicate and scale this complex quantum device fabrication.

Technical Specifications

Parameter	Value	Unit	Context
Material Grade	SCD, Electronic Grade	-	[N]<5 ppb, B<1 ppb
Initial Thickness (Plates)	500	µm	Commercially available starting material
Final Membrane Thickness	<1	µm	Formed via deep etching for cantilever structure
Nanopillar Diameter	200	nm	Key dimension for light extraction efficiency
Nanopillar Length	1 - 2	µm	Defined by etch depth
Ion Implantation Energy	6	keV	Nitrogen ions ($^{14}$N) for shallow NV creation
Ion Implantation Dose	$3 \times 10^{11}$	cm^-2	Target density for single NV per pillar
Estimated NV Stopping Depth	$9 \pm 4$	nm	Proximity to the diamond surface
Spin Coherence Time ($T_2$)	$94 \pm 4$	µs	Measured via Hahn Echo, critical for sensitivity
AC Magnetic Field Sensitivity ($N_{AC}$)	$50 \pm 20$	nT/&sqrt;Hz	Average sensitivity of single-NV probes
Initial RMS Surface Roughness ($R_a$)	0.7	nm	Required high-quality polish prior to processing
Post-Etch RMS Roughness ($R_a$)	0.3	nm	Surface quality maintained/improved after RIE
Standard Annealing Temperature	800	°C	2 hours in vacuum (Base pressure: $3\text{-}4 \times 10^{-7} \text{ mbar}$)

Key Methodologies

The fabrication of the all-diamond scanning probes consists of a rigorous 6-step process, focusing on precise material removal and defect engineering:

Diamond Preparation and Pre-Treatment

Initial Substrate Preparation: High-purity, (100) oriented Single Crystal Diamond (SCD) plates (500 µm thick) are mechanically polished, cut, and chemically cleaned (boiling tri-acid mixture).
Polishing Damage Removal: Approximately 3-4 µm of the damaged subsurface layer, introduced by polishing, is removed using Inductively Coupled Plasma Reactive Ion Etching (ICP-RIE) utilizing $\text{ArCl}_2$ plasma followed by $\text{O}_2$ plasma to prevent $\text{Cl}_2$ contamination.

NV Creation and Membrane Thinning

Shallow NV Center Creation: The etched surface is implanted with $^{14}$N ions (6 keV) to create a shallow layer of N defects, followed by high-vacuum annealing at $800^\circ \text{C}$ to mobilize vacancies and form the $\text{NV}^{-}$ centers.
Deep Etching/Membrane Formation: A second deep etch step, employing thin quartz cover slips as masks, reduces the diamond thickness from 50 µm to a thin membrane (<1 µm center thickness). Cyclic $\text{ArCl}_2$ and $\text{O}_2$ plasmas are used, requiring ceramic ($\text{Al}_2\text{O}_3$) carriers to mitigate silicon contamination risks.

Plasma Type	ICP Power [W]	RF Power / Bias [W/V]	Flux [sccm]	Pressure [Pa]	Etch Rate [nm/min]
$\text{ArCl}_2$ (Deep Etch)	400	100/220	Ar 25, $\text{Cl}_2$ 40	1	60
$\text{O}_2$ (Termination)	700	50/120	$\text{O}_2$ 60	1.3	150
$\text{ArO}_2$ (Pillar Etch)	500	200/120	Ar 50, $\text{O}_2$ 50	0.5	150

Structuring and Integration

Nanopillar and Cantilever Structuring: Two sequential electron beam lithography (EBL) steps using Hydrogen Silsesquioxane (HSQ) resist and $\text{ArO}_2$ plasma transfer the high-aspect-ratio features (200 nm nanopillars) onto the membrane, ensuring the NV centers are located near the pillar apex.
Transfer and Mounting: Characterized SCD cantilevers containing single NV centers are mechanically transferred using micromanipulators, UV curable glue, and attached to tuning fork based AFM heads for operational integration.

6CCVD Solutions & Capabilities

The successful replication and expansion of this cutting-edge nanoscale magnetometry technology depend on securing diamond materials with exceptional purity and precise engineering finishes. 6CCVD is uniquely equipped to meet these demanding requirements.

Applicable Materials for Quantum Sensing

To replicate the long coherence times ($T_2$) required for $N_{AC}$ sensitivity demonstrated in this paper, researchers must start with the highest quality material.

Optical Grade Single Crystal Diamond (SCD): We recommend our high-purity, low-birefringence SCD material. This material guarantees ultra-low native nitrogen content ([N] < 5 ppb), essential for minimizing the decoherence caused by proximal paramagnetic defects. This replicates the electronic grade material cited in the research paper.
Custom Thickness Substrates: 6CCVD offers custom slicing and polishing services to achieve the precise starting thickness required for deep etching protocols. We can supply SCD plates thinned to 50 µm (or custom ranges from 0.1 µm up to 500 µm), optimizing preparation for subsequent deep-RIE processing.

Customization Potential & Precision Engineering

The key material preparation steps mentioned in the paper—polishing, thinning, and structuring—are standard 6CCVD capabilities, allowing researchers to skip complex initial preparation steps.

Research Requirement	6CCVD Capability	Technical Specification
Initial Surface Quality	Ultra-Low Roughness Polishing	SCD substrates polished to $R_a < 1 \text{ nm}$, crucial for minimizing subsurface damage (up to $4 \text{ µm}$ deep) that degrades spin coherence.
Dimensional Control	Custom Wafer Sizing & Thinning	Plates/wafers available up to 125 mm (PCD/SCD) with guaranteed uniform thickness (up to 10 mm thick). Laser cutting services ensure precise substrate dimensions for RIE carrier mounting.
Material Structuring Precursor	Nanofabrication Readiness	We provide customized diamond etching (RIE) pre-treatment services to remove polishing damage (as described in Section II A), delivering a pristine lattice for direct ion implantation.
AFM Integration Support	Custom Metalization Services	Although primarily a mechanical transfer in this study, for integration with on-chip microwave circuits or resistive heaters, 6CCVD offers in-house metalization (Au, Pt, Pd, Ti, W, Cu) for contact pads or microstriplines.

Engineering Support

The complexity of shallow NV implantation and subsequent annealing protocols requires material substrates optimized for these specific conditions.

6CCVD’s in-house PhD engineering team can assist clients with material selection and pre-treatment planning for NV-center based quantum sensing projects, including guidance on surface orientation (e.g., preference for (111) vs. (100) for enhanced photonic properties) and preparing substrates for ion implantation or $\delta$-doping growth techniques.
We offer global shipping options (DDU default, DDP available), ensuring prompt and reliable delivery of custom quantum-grade diamond materials worldwide.

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

View Original Abstract

The electronic spin of the nitrogen vacancy (NV) center in diamond forms an atomically sized, highly sensitive sensor for magnetic fields. To harness the full potential of individual NV centers for sensing with high sensitivity and nanoscale spatial resolution, NV centers have to be incorporated into scanning probe structures enabling controlled scanning in close proximity to the sample surface. Here, we present an optimized procedure to fabricate single-crystal, all-diamond scanning probes starting from commercially available diamond and show a highly efficient and robust approach for integrating these devices in a generic atomic force microscope. Our scanning probes consisting of a scanning nanopillar (200 nm diameter, 1-2 μm length) on a thin (&lt;1 μm) cantilever structure enable efficient light extraction from diamond in combination with a high magnetic field sensitivity (ηAC≈50±20nT/Hz). As a first application of our scanning probes, we image the magnetic stray field of a single Ni nanorod. We show that this stray field can be approximated by a single dipole and estimate the NV-to-sample distance to a few tens of nanometer, which sets the achievable resolution of our scanning probes.

Tech Support

Original Source

DOI: https://doi.org/10.1063/1.4952953

References

**** - Quantitative nanoscale vortex imaging using a cryogenic quantum magnetometer [Crossref]