Solution nuclear magnetic resonance spectroscopy on a nanostructured diamond chip

At a Glance

Metadata	Details
Publication Date	2017-08-04
Journal	Nature Communications
Authors	Pauli Kehayias, Andrey Jarmola, Nazanin Mosavian, Ilja Fescenko, Francisco Benito
Institutions	University of New Mexico, Harvard University
Citations	83
Analysis	Full AI Review Included

Technical Documentation & Sales Analysis: Nanostructured Diamond Chips for Picoliter NMR Spectroscopy

6CCVD Analysis Reference: Kehayias et al., Nature Communications, DOI: 10.1038/s41467-017-00266-4

Executive Summary

This paper demonstrates a significant breakthrough in small-volume Nuclear Magnetic Resonance (NMR) spectroscopy using nanostructured diamond chips embedding Nitrogen-Vacancy (NV) centers. The results confirm the critical role of ultra-high-purity Single Crystal Diamond (SCD) substrates supplied by specialized CVD manufacturers like 6CCVD.

Sensitivity Milestone: Achieved nearly two orders of magnitude improvement in concentration sensitivity over prior NV-based picoliter NMR studies.
Detection Limit: Demonstrated detection of $4 \pm 2 \times 10^{12}$ ¹⁹F spins in a 1 pL volume with a Signal-to-Noise Ratio (SNR) of 3 in 1 second of integration.
Material Strategy: Success relies on starting with electronic-grade, [100]-oriented Single Crystal Diamond (SCD) substrates suitable for deep-UV lithography and subsequent high-temperature annealing.
Structural Innovation: Nanogratings (400 nm pitch, up to 3 µm depth) fabricated via interferometric lithography and plasma etching increased the sensor-analyte contact area by $\geq 15\times$, boosting fluorescence detection efficiency by 20-50 times.
Core Material Requirement: The precise control over diamond surface orientation, purity, and polish quality is fundamental for the successful fabrication of near-surface NV ensembles with long coherence times (T₂).
6CCVD Value Proposition: 6CCVD specializes in supplying the foundation material—high-purity, low-strain MPCVD SCD—necessary for replicating and advancing these complex quantum sensing platforms.

Technical Specifications

Parameter	Value	Unit	Context
Minimum Detectable Spins (P_min)	4 ± 2 x 10¹²	spins	¹⁹F in 1 pL volume (SNR=3, 1s)
Concentration Sensitivity (P_min)	6 ± 2 x 10²⁴	spins per liter	CsF/glycerol solution at 40.5 mT
Sensitivity Improvement	2x	Factor	Better than Fomblin® oil measurements
Concentration Improvement	Nearly two orders of magnitude	Factor	Over previous picoliter NMR studies
Operating Temperature	Room	°C	Ambient (non-cryogenic)
Operating Magnetic Field (B₀)	20 - 50	mT	Low field
Substrate Material	[100] SCD	-	Electronic-grade diamond (1.1% ¹³C abundance)
Substrate Dimensions (Initial)	2 x 2 x 0.5	mm³	-
Nanograting Pitch	400	nm	-
Nanograting Depth	Up to 3	µm	High-aspect-ratio
Surface Area Enhancement	≥15	Factor	Nanostructuring vs. flat surface
NV Implantation Energy	20, 60, or 200	keV	Corresponding to 5 - 20 nm simulated NV depth
Annealing Temperature (Max)	1100	°C	Vacuum environment

Key Methodologies

The fabrication of the nanostructured diamond chip requires specialized high-purity diamond material and precise recipe control over plasma etching and implantation:

Substrate Preparation: Used $2 \times 2 \times 0.5 \text{ mm}^3$ electronic-grade [100]-polished SCD chips. Cleaning involved a rigorous triacid mixture (nitric:perchloric:sulfuric acids) at 200 °C for 7 hours to ensure an atomically clean, oxygen-terminated surface.
Patterning: Optical interferometric lithography created periodic nanostructures with a $\sim 400 \text{ nm}$ period and controllable duty cycles (20-80%).
Mask Creation: A custom metal mask was deposited, consisting of $3-5 \text{ nm}$ Cr (adhesion layer) followed by $70 \text{ nm}$ Au.
Deep Plasma Etching: A highly anisotropic ICP etch (Oxygen/Argon chemistry) was applied for 40 minutes to form nanogratings up to $3 \text{ µm}$ deep, necessary for high-aspect-ratio sensing walls.
Nitrogen Implantation: ¹⁵N⁺ ions were implanted at shallow depths (20-200 keV, $5-20 \text{ nm}$ depth) at a 4° angle relative to the surface normal, ensuring doping along the nanograting sidewalls.
NV Center Formation: Post-implantation vacuum annealing was performed in a multi-step process ($800 ^\circ \text{C}$ for 4 h, followed by $1100 ^\circ \text{C}$ for 2 h) to form NV centers and maximize yield while minimizing unwanted paramagnetic impurities.

6CCVD Solutions & Capabilities

The successful implementation of this high-sensitivity NV NMR chip hinges on utilizing ultra-pure, defect-controlled Single Crystal Diamond (SCD) material capable of supporting advanced nanofabrication, high-energy implantation, and high-temperature processing. 6CCVD is uniquely positioned to supply and enhance the critical diamond material components required for this research.

Applicable Materials

Research Requirement	6CCVD Material Solution	Specification Match / Advantage
Substrate: Electronic-Grade [100] Diamond	Optical Grade SCD Wafers	Ultra-low strain and high purity (PPM level N, low other defects). [100] orientation guaranteed for optimal implantation geometry.
Material Thickness/Volume	SCD Substrates up to 500 µm	Allows for replication of the $0.5 \text{ mm}$ thickness used, or delivery of custom thicknesses (e.g., thinner for heat dissipation or thicker for robustness).
Doping Requirement	As-Grown Intrinsic/N-Doped SCD	We supply the ideal platform before implantation. Alternatively, we offer low-PPM intrinsic SCD perfect for controlled ¹⁵N⁺ implantation and NV formation yield maximization.
Advanced Sensing/Electrochemistry	Boron-Doped Diamond (BDD)	For extensions of this research into electrochemical sensing or high-Q microwave delivery, 6CCVD offers custom BDD films (PCD/SCD) with controllable conductivity.

Customization Potential

The experimental workflow in this paper highlights several opportunities where 6CCVD’s in-house customization capabilities can accelerate research and device integration:

Custom Dimensions and Dicing: The paper used small $2 \times 2 \times 0.5 \text{ mm}^3$ chips. 6CCVD provides precision laser cutting and dicing services to produce custom small-format chips from large SCD/PCD wafers (up to 125mm) with extreme dimensional accuracy.
Surface Finishing: The complex lithography requires extremely flat surfaces. 6CCVD guarantees Ra < 1nm polishing for SCD substrates, ensuring the lowest possible surface roughness for high-resolution photoresist adhesion and subsequent etching uniformity.
Metalization Services: The research utilized a $3-5 \text{ nm}$ Cr / $70 \text{ nm}$ Au mask. 6CCVD offers full, in-house metalization capabilities, including Au, Pt, Pd, Ti, W, and Cu deposition. We can provide substrates with pre-patterned metal masks or contact pads optimized for the microwave interrogation loops, reducing researcher fabrication time and improving device reliability.
Optimized Etch Preparation: 6CCVD can supply substrates pre-processed with precise surface terminations (e.g., oxygen or hydrogen terminated) to optimize subsequent steps, such as photoresist adhesion or post-annealing chemical cleaning.

Engineering Support

6CCVD’s in-house PhD-level material science team understands the intricate interplay between CVD growth parameters, defect engineering (like NV centers), and advanced nanofabrication. We can assist engineers and scientists working on similar NV NMR Spectroscopy projects by:

Material Selection: Guiding the choice between different SCD grades (low strain vs. ultra-pure) based on target T₂ coherence times and maximum NV density requirements.
Process Compatibility: Consulting on optimal substrate dimensions and surface finish necessary to interface seamlessly with high-throughput interferometric lithography systems.
Global Supply Chain: Providing rapid, reliable global shipping (DDU default, DDP available) to ensure uninterrupted research schedules worldwide.

Call to Action

To achieve two orders of magnitude sensitivity improvement in quantum sensing requires foundation materials of uncompromising quality. 6CCVD delivers the high-purity MPCVD diamond substrates essential for next-generation quantum technologies.

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/s41467-017-00266-4