Nanoscale microwave imaging with a single electron spin in diamond

At a Glance

Metadata	Details
Publication Date	2015-11-04
Journal	New Journal of Physics
Authors	Patrick Appel, Marc Ganzhorn, Elke Neu, Patrick Maletinsky
Institutions	Saarland University, University of Basel
Citations	85
Analysis	Full AI Review Included

6CCVD Technical Documentation: Nanoscale Microwave Imaging

Research Paper Analysis: Nanoscale microwave imaging with a single electron spin in diamond (Appel et al., arXiv:1508.02719v2, 2015)

Executive Summary

This paper validates the use of single Nitrogen Vacancy (NV) centers in diamond as highly sensitive, nanoscale magnetometers for imaging microwave (MW) magnetic fields at room temperature. The results establish a path toward next-generation quantum sensing devices.

Nanoscale Resolution: Achieved spatial resolution of approximately 25 nm, limited by the NV-to-sample distance (d), enabling near-field analysis of MW circuits.
High Sensitivity: Demonstrated a photon shot noise limited MW magnetic field sensitivity of 680 nT/√Hz at 2.825 GHz.
Current Measurement: The system was used to image the MW stray field around a Pd stripline, yielding a high MW current sensitivity of ~300 nA/√Hz.
Advanced Material Requirements: The technique relies fundamentally on the long spin coherence times (T_R = 4 µs) provided by high-purity single crystal diamond (SCD) material.
Broadband Potential: The platform is projected to extend detection bandwidth up to frequencies exceeding 20 GHz by implementing strong static magnetic fields.
Core Technology: The measurement utilizes optically detected magnetic resonance (ODMR) via coherent Rabi oscillations driven by the MW field.

Technical Specifications

The following table summarizes the key performance metrics and material specifications extracted from the research demonstrating nanoscale MW imaging.

Parameter	Value	Unit	Context
Spatial Resolution (d)	~25	nm	Determined by NV spin distance to stripline surface
MW Magnetic Field Sensitivity (Shot Noise Limit)	680	nT/√Hz	Measured at 2.825 GHz, room temperature
MW Current Sensitivity	~300	nA/√Hz	Sensitivity for an infinitely thin, current-carrying wire
Operating Frequency (Tested)	2.825	GHz	NV center transition frequency
Potential Max Frequency	>20	GHz	Requires strong external magnetic biasing
Rabi Decay Time (T_R)	4	µs	Extracted from Rabi oscillation fit (Crucial for sensitivity)
Fluorescence Contrast (C)	0.095	-	(F₀ - F₁)/F₀
Stripline Conductor Width	2.5	µm	Prototype test structure dimension
Stripline Conductor Thickness	60	nm	Palladium (Pd) layer thickness
Fitted Current Density (J)	3.9 - 4.05	mA/µm²	Extracted from analytical model fit

Key Methodologies

The experiment combined advanced nanofabrication of the NV probe with high-precision scanning magnetometry techniques.

Step	Parameter / Condition / Component	Recipe Details
Diamond Probe Fabrication	All-diamond scanning probe	Involves low energy ion implantation (N or C/N co-implantation), electron beam lithography (EBL), and inductively coupled reactive ion etching (ICP-RIE).
Material Requirement	Single Crystal Diamond (SCD)	Used to host the single NV center and ensure exceptionally long coherence times (T_R).
MW Device Fabrication	Pd Stripline	60 nm thick Pd patterned via EBL and evaporation onto a 300 nm SiO₂ layer on an undoped Si substrate.
MW Input Signal	Frequency: 2.825 GHz	MW input power tested at 7.5 dBm and 12.5 dBm.
Sensing Technique	Coherent Rabi Oscillations (ODMR)	Pulsed MW sequence drives transitions between the
Imaging System	Combined Confocal Microscope (CFM) & AFM	AFM maintains precise distance (d) control, while CFM optically reads the spin state via fluorescence.
Data Acquisition	Normalized Differential Fluorescence (∆F)	Used to map equi-magnetic field lines (isofield imaging).
Modeling & Validation	Finite Element Simulation (COMSOL)	Used to validate B’_-,MW profiles, confirming current density homogeneity within the stripline.

6CCVD Solutions & Capabilities

6CCVD is an indispensable partner for replicating and advancing this nanoscale MW imaging research, particularly in optimizing diamond material performance, geometry, and device integration.

Applicable Materials

To achieve and surpass the demonstrated sensitivity and coherence times, 6CCVD recommends:

Ultra-Pure Single Crystal Diamond (SCD): Required for the scanning probe tip to host single NV centers with maximum spin coherence time (T₂*/T_R). We guarantee CVD growth resulting in intrinsic nitrogen concentration < 5 ppb.
Isotopically Enriched SCD (¹²C): The paper explicitly notes that sensitivity could be enhanced by improving the Rabi decay time (T_R) using isotopically enriched diamond [21, 35]. 6CCVD offers high-purity ¹²C enriched SCD wafers, drastically reducing decoherence caused by naturally abundant ¹³C nuclear spins.
Polycrystalline Diamond (PCD) Substrates: For scalability or integration into larger electronic platforms, 6CCVD offers PCD plates up to 125mm in diameter, with thickness control ranging from 0.1 µm to 500 µm.

Customization Potential

The success of this experiment hinges on highly specific material geometries and integration, areas where 6CCVD excels:

Research Requirement	6CCVD Capability	Value Proposition for Researchers
Scanning Probe Geometry	Custom Thickness & Etching	We supply SCD plates/wafers (0.1 µm - 500 µm thick) engineered for subsequent fabrication steps (like RIE etching for probe tips), guaranteeing optimal NV placement depth.
Device Substrates	Large Format Diamond Plates	Plates and substrates are available up to 10 mm in thickness for complex thermal management or supporting highly integrated MW electronics.
Metalization Integration	In-House Metalization Services	The stripline used 60 nm of Palladium (Pd). 6CCVD offers deposition of Pd, Au, Pt, Ti, W, and Cu with precise layer control, crucial for minimizing impedance mismatch and near-field effects.
Surface Finish	Ultra-Low Roughness Polishing	For optimizing the critical NV-to-sample distance (d ~ 25 nm), 6CCVD provides SCD surfaces polished to Ra < 1 nm, reducing non-ideal spacing layers caused by surface contaminants or defects.

Engineering Support

6CCVD’s in-house team of PhD material scientists specializes in optimizing diamond characteristics for quantum applications, including NV center magnetometry and spin-wave analysis. We offer consultation on:

Isotope selection for maximizing T₂*.
CVD growth parameters for controlling intrinsic defect concentration.
Material dimensioning to interface seamlessly with existing lithographic and scanning probe systems (AFM/CFM).

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

View Original Abstract

We report on imaging of microwave (MW) magnetic fields using a magnetometer\nbased on the electron spin of a nitrogen vacancy center in diamond. We\nquantitatively image the magnetic field generated by high frequency (GHz) MW\ncurrent with nanoscale resolution using a scanning probe technique. We\ndemonstrate a MW magnetic field sensitivity in the range of a few\nnT/$\sqrt{\text{Hz}}$, polarization selection and broadband capabilities under\nambient conditions and thereby establish the nitrogen vacancy center a\nversatile and high performance tool for the detection of MW fields. As a first\napplication of this scanning MW detector, we determine the MW current density\nin a stripline and demonstrate a MW current sensitivity of a few\nnA/$\sqrt{\text{Hz}}$\n

Tech Support

Original Source

DOI: https://doi.org/10.1088/1367-2630/17/11/112001