Nanoscale electrical conductivity imaging using a nitrogen-vacancy center in diamond

At a Glance

Metadata	Details
Publication Date	2018-06-13
Journal	Nature Communications
Authors	Amila Ariyaratne, Dolev Bluvstein, Bryan A. Myers, Ania C. Bleszynski Jayich, Amila Ariyaratne
Institutions	University of California, Santa Barbara
Citations	112
Analysis	Full AI Review Included

Technical Analysis and Commercial Solutions: Nanoscale Conductivity Imaging via NV Centers

6CCVD, an expert provider of tailored MPCVD diamond solutions, has analyzed the publication, “Nanoscale electrical conductivity imaging using a nitrogen-vacancy center in diamond” (Nature Communications, 2018). This research validates the critical role of highly customized diamond platforms in advancing quantum sensing and condensed matter physics research.

The experiment successfully employed ultra-shallow Nitrogen-Vacancy (NV) centers in isotopically purified Single Crystal Diamond (SCD) to achieve unprecedented nanoscale, non-invasive imaging of electrical conductivity via monitoring thermal magnetic fluctuations (Johnson-Nyquist noise).

Executive Summary

Core Breakthrough: Demonstration of quantitative, non-invasive electrical conductivity imaging utilizing the spin relaxation rate (T₁) of atom-sized Nitrogen-Vacancy (NV) centers in diamond.
Resolution and Sensitivity: Achieved 40 nm spatial resolution, with theoretical projections demonstrating feasibility down to 5 nm, enabling the study of nanoscale phase separation in complex oxides.
Material Requirement: Requires ultra-high quality, isotopically pure (99.99% ¹²C) Single Crystal Diamond (SCD) platforms suitable for extremely shallow NV implantation (~7 nm depth).
Imaging Speed Enhancement: Realized a crucial 25-fold increase in imaging speed by implementing Spin-to-Charge Conversion (SCC) readout techniques for shallow NV centers.
Mechanism: Measurement relies on the NV center sensing fluctuating magnetic fields generated by thermal electron motion in adjacent conductors.
Platform Integration: The setup integrates a highly stable, scanning probe microscope (AFM) geometry with confocal optics for NV initialization and readout, operating robustly in ambient conditions.
6CCVD Value Proposition: 6CCVD provides the necessary core materials (High-Purity SCD wafers, custom thicknesses, and required metalization layers) essential for replicating and scaling this advanced quantum sensing technology.

Technical Specifications

The following hard data points define the parameters and outcomes of the NV-based conductivity imaging technique:

Parameter	Value	Unit	Context
Spatial Resolution	40	nm	Achieved resolution, set by NV-metal separation.
Projected Resolution	5	nm	Resolution achievable with optimized alignment and shallower NVs.
NV Center Depth (Shallow)	~7	nm	Target depth via ¹⁴N implantation at 4 keV.
Diamond Film Thickness	50	nm	99.99% ¹²C isotopically purified film.
Substrate Thickness	150	µm	Supporting SCD plate thickness.
Magnetic Field (Applied)	20	G	Small applied field for experiments (ambient conditions).
Intrinsic Relaxation Rate ($\Gamma_{NV,int}$) ($1/T_{1}$)	~200	Hz	Intrinsic background relaxation rate ($T_{1}$ ~5 ms).
Imaging Speed Improvement	25-fold	Ratio	Achieved using Spin-to-Charge Conversion (SCC) readout.
Thermal Drift Correction Error	~1	nm	Achieved using PL-based image registration.
Conductivity (Ag, measured)	$2.3 \times 10^{5}$	$\Omega$^-1cm^-1	Conductivity of 85 nm Ag film (2.7x lower than bulk).
Conductivity (Al, measured)	$2.0 \times 10^{5}$	$\Omega$^-1cm^-1	Conductivity of 85 nm Al film (1.7x lower than bulk).
Metal Film Thickness	85	nm	Thickness of Ag, Al, and Ti films studied.

Key Methodologies

The experimental success hinges on precise diamond preparation, NV center formation, and multi-modal microscope integration.

Diamond Substrate Preparation:
- Starting Material: Element 6 electronic grade (100) SCD substrate.
- Film Growth: 50 nm thick, 99.99% ¹²C isotopically purified film deposited via CVD.
- Cleaning: Initial ArCl₂ plasma etch (1 µm depth) to mitigate polishing damage, followed by boiling acid cleaning (H₂NO₃:H₂SO₄).
NV Center Implantation:
- Ion Source: ¹⁴N ion implantation.
- Parameters: 4 keV energy, 7° tilt angle, $5.2 \times 10^{10}$ ions/cm² dosage.
- Target Depth: Expected depth of ~7 nm below the surface (critical for nanoscale sensing).
Annealing and Activation:
- Process: Annealed in vacuum (< $10^{-6}$ Torr) at 850 °C for 2.5 hours, with a 40-min temperature ramp.
- Post-Anneal Clean: Cleaned in boiling acid mixture (HClO₄:H₂NO₃:H₂SO₄).
Device Patterning and Integration:
- MW Delivery: 300 nm thick waveguide evaporated onto the diamond surface for coherent spin manipulation.
- Photon Collection: 400 nm diameter, 500 nm tall nanopillars patterned on the diamond surface to enhance photon collection efficiency (up to 5x amplification).
Conducting Sample Fabrication:
- Conductor Geometry: 85 nm thick Ag, Al, or Ti films thermally evaporated onto custom-fabricated silicon scanning probe tips (flat plateau region, ~3 µm diameter).
Measurement Techniques:
- Setup: Custom confocal microscope integrated with a tuning fork-based Atomic Force Microscope (AFM).
- Spin Readout: Used 532 nm laser for initialization/readout. Spin-to-Charge Conversion (SCC) readout technique utilized to significantly reduce measurement time.
- Drift Correction: Active drift correction (image registration) implemented to maintain ~1 nm error stability.

6CCVD Solutions & Capabilities

This research relies fundamentally on a highly specialized SCD platform. 6CCVD excels in providing the custom diamond materials, fabrication services, and expert technical support necessary to replicate this methodology and push the boundaries of NV quantum sensing.

Applicable Materials

To achieve the required coherence and sensitivity for conductivity imaging, researchers require diamond substrates engineered for minimal noise and precise defect location.

Research Requirement	6CCVD Material Solution	Optimization Notes
Isotopically Purified Thin Film	Optical Grade SCD (99.999% ¹²C enrichment)	Crucial for extending spin coherence time ($T_{2}$) and minimizing strain noise, supporting ultimate 5 nm resolution goals.
Shallow NV Implantation	SCD Wafers (Custom Thicknesses 0.1 µm - 500 µm)	Providing ultra-smooth, near-surface SCD ensures maximum yield and minimal variability for few-nm depth NV centers.
Mechanical Substrate	SCD Substrates (Up to 10 mm thick)	Supplied with precise (100) crystal orientation, polished, and ready for deposition, implantation, and subsequent fabrication steps.

Customization Potential

The experiment requires complex integration of optics, waveguides, and precise metal structures. 6CCVD’s in-house capabilities streamline this supply chain.

Wafer Dimensions & Thickness: While the paper used 150 µm thick plates, 6CCVD supplies custom SCD plates from 0.1 µm up to 500 µm thick, and substrates up to 10 mm, tailored to specific cantilever or probe holder geometries.
Precision Polishing: Achieving ultra-shallow NVs requires an exceptionally clean, flat surface. 6CCVD guarantees Ra < 1 nm polishing for SCD, reducing surface-related magnetic noise and improving implantation uniformity.
Integrated Metalization & Patterning: The experiment requires a 300 nm microwave waveguide and metal features (Ag, Al, Ti) for calibration. 6CCVD offers custom, high-precision thin-film metalization using common NV contact metals (Au, Pt, Pd, Ti, W, Cu) applied directly to the diamond surface.

Engineering Support

NV-based conductivity imaging, particularly using advanced SCC readout, presents unique engineering challenges involving material choice and processing (e.g., implantation, annealing recipe optimization).

6CCVD’s in-house PhD team provides specialized consultative support for quantum sensing projects, assisting engineers and scientists in:

Selecting the optimal ¹²C enrichment level and thickness for minimizing magnetic noise and maximizing $T_{1}$ and $T_{2}$ performance.
Tailoring substrate specifications to ensure compatibility with complex setups, such as integrated AFM-confocal systems used for nanoscale current mapping and phase separation studies (e.g., Mott insulators or LAO/STO interfaces).
Developing custom metalization stacks for optimized waveguide performance and high-frequency microwave delivery.

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/s41467-018-04798-1