Chemically resolved nuclear magnetic resonance spectroscopy by longitudinal magnetization detection with a diamond magnetometer

At a Glance

Metadata	Details
Publication Date	2025-03-03
Journal	arXiv (Cornell University)
Authors	Jānis Šmits, Yaser Silani, Zaili Peng, Bryan A. Richards, Andrew F. McDowell
Analysis	Full AI Review Included

Technical Documentation: High-Resolution NV NMR Spectroscopy via Ramsey-M_z Protocol

This document analyzes the research paper “Chemically resolved nuclear magnetic resonance spectroscopy by longitudinal magnetization detection with a diamond magnetometer” (arXiv:2503.02140v1) to provide technical specifications and highlight how 6CCVD’s advanced MPCVD diamond solutions can enable replication and extension of this high-impact quantum sensing research.

Executive Summary

Core Achievement: Demonstration of high-resolution Nuclear Magnetic Resonance (NMR) spectroscopy utilizing Nitrogen-Vacancy (NV) centers in diamond via a novel Ramsey-M$_{z}$ protocol.
Resolution: Achieved a fractional spectral resolution of $\sim$350 ppb (parts-per-billion) at a moderate magnetic field of B$_{0}$ = 0.32 T, representing a $\sim$3-fold improvement over previous NV NMR experiments.
Application: Successfully resolved the chemical shift structure of ethanol in a sub-nanoliter ($\sim$1 nL) detection volume, crucial for microfluidic metabolomics.
Methodology: The Ramsey-M${z}$ protocol detects longitudinal nuclear magnetization, overcoming the technical challenges associated with detecting transverse magnetization (M${\perp}$) at high magnetic fields (B$_{0}$ $\ge$ 0.3 T).
Material Requirement: The experiment relies on a thin, high-quality, $^{12}$C-enriched Single Crystal Diamond (SCD) membrane to minimize magnetic gradients and maximize coherence time.
Projected Performance: With optimized sensor design (e.g., using composite pulses and higher B$_{0}$ up to 3 T), the protocol is projected to achieve $\sim$1 ppb resolution and a concentration sensitivity of $\sim$40 mMs$^{1/2}$ for sub-nanoliter analyte volumes.

Technical Specifications

The following hard data points were extracted from the experimental results and projections detailed in the research paper.

Parameter	Value	Unit	Context
Magnetic Field (B$_{0}$) Used	0.32	T	Applied by electromagnet; stability limited resolution.
Diamond Cut/Orientation	[110]	N/A	Used in experiment; (111) projected as optimal geometry.
Diamond Membrane Dimensions	$\sim$250 x 250 x 60	µm$^{3}$	$^{12}$C-enriched, NV concentration $\sim$4 ppm.
Effective Analyte Volume (V$_{sens}$)	$\sim$1	nL	Volume contributing $\ge$50% of the M$_{z}$ NMR signal.
Achieved Fractional Resolution	$\sim$350	ppb	FWHM linewidth of $0.35 \pm 0.07$ ppm for water.
Projected Fractional Resolution	$\sim$1	ppb	Feasible with sensor design improvements.
Achieved Magnetometer Sensitivity	$\sim$100	pTs$^{1/2}$	Using CW-ODMR protocol.
Projected Magnetometer Sensitivity	$\sim$0.1	pTs$^{1/2}$	Using Ramsey-ENDOR with repetitive readout.
Projected Concentration Sensitivity (SNR=3)	$\sim$40	mMs$^{1/2}$	For 0.7 nL analyte volume at B$_{0}$ = 3 T.
Proton T$_{1}$ (TEMPOL doped)	$\sim$0.6	s	Longitudinal spin relaxation time.
RF Pulse Frequency	$\sim$13.8	MHz	Used to drive proton spins.
NV Zero-Field Splitting (D)	$\approx$ 2.87	GHz	Intrinsic property of the NV center.

Key Methodologies

The experiment relies on precise material engineering and complex quantum control sequences to achieve high-resolution detection of longitudinal nuclear magnetization (M$_{z}$).

Diamond Material Selection: A thin, [110]-cut, $^{12}$C-enriched Single Crystal Diamond (SCD) membrane ($\sim$60 µm thick) with an NV concentration of $\sim$4 ppm was used to minimize magnetic field gradients and maximize sensor proximity to the analyte.
Microwave Trace Fabrication: Copper microwave traces (2 µm thick on a 10 nm Ti adhesion layer) were thermally evaporated and etched onto a glass slide to drive NV spin transitions and facilitate Overhauser Dynamic Nuclear Polarization (DNP).
Magnetic Field Alignment: The B$_{0}$ bias field (0.32 T) was aligned along one of the in-plane NV crystallographic axes. The setup included first- and second-order gradient shim coils for field homogeneity.
Continuous-Wave ODMR (CW-ODMR): A broadband diamond magnetometer continuously recorded the local magnetic field. Microwave tones were applied simultaneously at all six $f_{\pm,i}$ resonance frequencies, frequency-modulated at 10.1 kHz.
Magnetic Field Stabilization: A low-frequency feedback loop used the demodulated CW-ODMR signal to drive secondary trim coils, compensating for environmental field drift and stabilizing B$_{0}$ to $\le$ 350 ppb over several hours.
Ramsey-M$_{z}$ Sequence: The protocol utilized two phase-coherent Radio-Frequency (RF) $\pi$/2 pulses, separated by a variable time $\tau$, to convert the analyte’s transverse spin precession into a longitudinal magnetization (M$_{z}$) amplitude.
M$_{z}$ Detection: A subsequent train of phase-cycled resonant RF $\pi$ pulses modulated the M$_{z}$ signal into an AC magnetic field, which was then detected by the lock-in amplifier output of the diamond magnetometer.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the advanced diamond materials and customization services required to replicate, optimize, and scale this cutting-edge NV NMR research.

Applicable Materials

To achieve the projected sub-ppb spectral resolution and high sensitivity, the research requires ultra-high purity, low-strain diamond with controlled isotopic composition.

Research Requirement	6CCVD Material Solution	Technical Advantage
High Purity / Low Strain	Optical Grade Single Crystal Diamond (SCD)	SCD wafers with extremely low defect density (N < 1 ppb) ensure long NV electron spin coherence times (T$_{2}$).
Isotopic Enrichment	Isotopically Pure SCD ($^{12}$C)	Available with $>99.99%$ $^{12}$C enrichment, critical for maximizing nuclear spin dephasing time (T$_{2}$*) and achieving projected ppb resolution.
Optimal Geometry	Custom SCD Substrates (e.g., (111) or (110) orientation)	We provide precise orientation control, including the optimal (111)-cut projected for maximum weighted signal strength (Bnuc$\sqrt{\delta}/\rho$) in M$_{z}$ detection.
Thin Membrane/Substrate	SCD Wafers (0.1 µm to 500 µm)	We supply thin membranes (down to 0.1 µm) necessary for maximizing the NV sensor proximity to the sub-nanoliter analyte volume.

Customization Potential

The experimental setup requires highly specific dimensions and integrated metalization for microwave delivery. 6CCVD offers comprehensive in-house services to meet these needs:

Custom Dimensions and Thickness: 6CCVD can supply SCD wafers up to 500 µm thick, and substrates up to 10 mm, cut to precise dimensions (e.g., the $\sim$250x250 µm$^{2}$ used in the paper) using advanced laser cutting techniques.
Advanced Metalization Services: The experiment utilized copper microwave traces on a glass slide. 6CCVD offers internal metalization capabilities, including deposition of Ti, Pt, Au, Pd, W, and Cu stacks directly onto the diamond surface, ensuring superior adhesion and electrical performance for integrated quantum devices.
Surface Preparation: We provide ultra-smooth polishing (Ra < 1 nm for SCD) essential for minimizing surface noise and ensuring a planar, low-strain interface for microfluidic integration.

Engineering Support

6CCVD’s in-house PhD team provides expert consultation to accelerate quantum sensing projects:

Material Optimization: We assist researchers in selecting the optimal diamond specifications (NV concentration, isotopic purity, and crystallographic orientation) required to replicate or extend high-field NV NMR spectroscopy projects.
Design for Coherence: Consultation services focus on maximizing T${2}$ and T${2}$* coherence times, which are the fundamental limits on magnetometer sensitivity and spectral resolution.
Global Logistics: We ensure reliable global shipping (DDU default, DDP available) for sensitive, high-value diamond materials.

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

View Original Abstract

Non-inductive magnetometers based on solid-state spins offer a promising solution for small-volume nuclear magnetic resonance (NMR) detection. A remaining challenge is to operate at a sufficiently high magnetic field to resolve chemical shifts at the part-per-billion level. Here, we demonstrate a Ramsey-M_z protocol that uses Ramsey interferometry to convert an analyte’s transverse spin precession into a longitudinal magnetization (M_z), which is subsequently modulated and detected with a diamond magnetometer. We record NMR spectra at B0=0.32 T with a fractional spectral resolution of ~350 ppb, limited by the stability of the electromagnet bias field. We perform NMR spectroscopy on a ~1 nL detection volume of ethanol and resolve the chemical shift structure with negligible distortion. Through simulation, we show that the protocol can be extended to fields up to B0=3 T, with minimal spectral distortion, using composite nuclear-spin inversion pulses. For sub-nanoliter analyte volumes, we estimate a resolution of ~1 ppb and concentration sensitivity of ~40 mM s^{1/2} is feasible with improvements to the sensor design. Our results establish diamond magnetometers as high-resolution NMR detectors in the moderate magnetic field regime, with potential applications in metabolomics and pharmaceutical research.

Tech Support

Original Source

DOI: None