Excitation of surface plasmon polariton modes with multiple nitrogen vacancy centers in single nanodiamonds

At a Glance

Metadata	Details
Publication Date	2015-12-21
Journal	Journal of Optics
Authors	Shailesh Kumar, Jens L. Lausen, Cesar E. Garcia‐Ortiz, Sebastian K. H. Andersen, Alexander S. Roberts
Citations	6
Analysis	Full AI Review Included

Technical Analysis: Excitation of Surface Plasmon Polariton Modes with Multiple Nitrogen Vacancy Centers in Single Nanodiamonds

This document analyzes the research detailing the coupling of high-density Nitrogen Vacancy (NV) centers in nanodiamonds (NDs) to Surface Plasmon Polariton (SPP) and Channel Plasmon Polariton (CPP) modes. This work is critical for advancing integrated quantum plasmonics, high-precision sensing, and stable solid-state quantum emitters.

Executive Summary

The research successfully demonstrates the integration of high-density NV centers (~400 per 100 nm ND) with metallic plasmonic waveguides (Silver-dielectric interfaces and Gold V-grooves). This integration is essential for scaling quantum technologies.

Core Achievement: Confirmed efficient coupling of multiple NV centers to propagating SPP and CPP modes, evidenced by fluorescence emission from distant waveguide termination mirrors.
Enhanced Emission: Observed significant shortening of NV center fluorescence lifetimes (e.g., $\tau_A$ reduced from 34.51 ns to 13.86 ns on flat gold, and further inside the V-groove), indicating enhanced spontaneous emission rates crucial for quantum applications.
Scalable Architecture: The use of V-grooves (VGs) fabricated via UV lithography and self-terminated silicon etching provides a robust, highly confined plasmonic channel suitable for integrated quantum circuits.
Material Requirement: The success hinges on high-quality diamond material containing stable, high-density NV centers, which 6CCVD specializes in providing via MPCVD.
6CCVD Value Proposition: 6CCVD offers the necessary high-purity Single Crystal Diamond (SCD) and large-area Polycrystalline Diamond (PCD) substrates, along with custom metalization (Au, Cr, Ti) and polishing services, required to transition this proof-of-concept into scalable, integrated quantum devices.

Technical Specifications

The following hard data points were extracted from the experimental methodology and results:

Parameter	Value	Unit	Context
Nanodiamond (ND) Average Diameter	100	nm	Source material (Adámas Nanotechnologies)
NV Center Density (per ND)	~400	centers	Used for high-sensitivity sensing/coupling
Excitation Wavelength	532	nm	Linearly polarized pulsed laser source
Laser Pulsewidth	~50	ps	Used for time-resolved fluorescence measurements
Objective Numerical Aperture (NA)	0.9	-	Used for excitation and collection
Silver Film Thickness (SPP Interface)	150	nm	Thermally evaporated on Si wafer
SiO₂ Sputtered Layer Thickness (SPP)	20	nm	Dielectric protection layer on Ag
Gold Layer Thickness (VG)	70	nm	Deposited via electron-beam evaporation
Chromium Adhesion Layer Thickness	5	nm	Used beneath Gold layer in VG fabrication
VG Etch Inclination Angle	55	°	Fixed angle from surface plane (KOH etch)
VG Thermal Oxidation Temperature	1150	°C	Used to sharpen V-shape geometry
Uncoupled NV Lifetime ($\tau_A$)	34.51	ns	On fused silica substrate (averaged over 10 NDs)
Coupled NV Lifetime ($\tau_A$)	13.86	ns	On flat gold-air interface
CPP Propagation Length (700 nm)	~10	µm	Simulated result (Figure 13(c))
ND Separation Distance (SPP coupling)	7 and 9	µm	Tested distances between source and scatterer NDs

Key Methodologies

The experiment involved precise nanofabrication of plasmonic structures and advanced optical characterization techniques:

SPP Interface Fabrication: Thermal evaporation of an optically thick (150 nm) Silver film on a silicon wafer, followed by sputtering a 20 nm amorphous SiO₂ layer in vacuum to minimize atmospheric reaction.
ND Deposition (SPP): NDs were periodically placed using PMMA, electron-beam lithography, and a lift-off process, ensuring controllable separation distances (7 and 9 µm).
V-Groove (VG) Fabrication (CPP):
- Patterning: UV lithography and reactive-ion etching (RIE) defined the perimeter of the VG devices in a 200 nm SiO₂ layer, aligned with the Si (100) crystal planes.
- Anisotropic Etching: VGs and termination mirrors were formed by anisotropic wet etching of exposed silicon in a Potassium Hydroxide (KOH) bath at 80 °C, yielding smooth (111) sidewalls and 55° inclination.
- Geometry Tailoring: Thermal wet oxidation (1150 °C for 9 h) created a 2320 nm SiO₂ layer, sharpening the interior angle to support the CPP mode.
- Metalization: Electron-beam evaporation deposited a 5 nm Chromium adhesion layer followed by a 70 nm Gold layer.
ND Manipulation: An Atomic Force Microscope (AFM) was used to physically push the NDs from the flat gold-air interface outside the VG to the inside of the VG for coupling studies.
Optical Characterization: A scanning confocal microscope utilized a 532 nm pulsed laser (50 ps pulsewidth) for excitation. Fluorescence was analyzed spectrally (EMCCD) and temporally (APD) to measure lifetimes and coupling efficiencies.

6CCVD Solutions & Capabilities

This research highlights the critical need for high-quality diamond materials and precision fabrication capabilities to realize integrated quantum plasmonic devices. 6CCVD is uniquely positioned to supply the necessary components for scaling this technology.

Applicable Materials

The successful integration of NV centers with plasmonic circuits requires diamond substrates optimized for NV creation, high purity, and compatibility with complex nanofabrication processes.

Research Requirement	6CCVD Solution	Material Specification
High-Density NV Emitters	High-Purity Polycrystalline Diamond (PCD)	Plates up to 125mm in diameter, ideal for large-scale fabrication of VG arrays and integrated circuits.
High Coherence/Single Emitters	Optical Grade Single Crystal Diamond (SCD)	SCD wafers (up to 500 µm thick) for precise NV implantation and superior spin coherence times, necessary for qubit applications.
Integrated Sensing	Boron-Doped Diamond (BDD)	Available for electrochemical sensing applications or as a conductive layer in complex device stacks.

Customization Potential

The fabrication of V-grooves and the use of specific metal layers (Cr/Au) demonstrate the need for highly customized substrates. 6CCVD provides end-to-end material engineering support:

Custom Dimensions: While the paper focuses on micron-scale features, scaling the VG arrays requires large substrates. 6CCVD offers PCD plates up to 125mm and SCD wafers up to 10mm thick, providing the foundation for industrial-scale production.
Precision Metalization: The experiment utilized a 5 nm Cr adhesion layer and a 70 nm Au layer. 6CCVD offers in-house metalization services including:
- Au, Pt, Pd, Ti, W, and Cu deposition.
- Custom layer thicknesses and multi-layer stacks (e.g., Ti/Pt/Au or Cr/Au) tailored for subsequent lithography and etching processes.
Surface Preparation: The plasmonic coupling is highly sensitive to surface roughness. 6CCVD guarantees ultra-low roughness: Ra < 1 nm for SCD and Ra < 5 nm for inch-size PCD, ensuring optimal plasmon propagation and minimal scattering losses in integrated circuits.
Thickness Control: 6CCVD provides precise thickness control for SCD and PCD layers, ranging from 0.1 µm to 500 µm, allowing researchers to optimize the diamond layer for specific NV depth or waveguide geometry requirements.

Engineering Support

6CCVD’s in-house PhD team specializes in material science and quantum applications, offering consultation for similar Quantum Plasmonics and NV-based Sensing projects. We assist clients in:

Selecting the optimal diamond grade (SCD vs. PCD) based on required NV density and coherence time.
Designing metalization schemes compatible with advanced lithography (UV, E-beam) and etching techniques (like the KOH etching used for VGs).
Specifying surface polishing requirements to minimize optical and plasmonic losses.

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

View Original Abstract

Nitrogen-vacancy (NV) centers in diamonds are interesting due to their\nremarkable characteristics that are well suited to applications in\nquantum-information processing and magnetic field sensing, as well as\nrepresenting stable fluorescent sources. Multiple NV centers in nanodiamonds\n(NDs) are especially useful as biological fluorophores due to their chemical\nneutrality, brightness and room-temperature photostability. Furthermore, NDs\ncontaining multiple NV centers also have potential in high-precision magnetic\nfield and temperature sensing. Coupling NV centers to propagating surface\nplasmon polariton (SPP) modes gives a base for lab-on-a-chip sensing devices,\nallows enhanced fluorescence emission and collection which can further enhance\nthe precision of NV-based sensors. Here, we investigate coupling of multiple NV\ncenters in individual NDs to the SPP modes supported by silver surfaces\nprotected by thin dielectric layers and by gold V-grooves (VGs) produced via\nthe self-terminated silicon etching. In the first case, we concentrate on\nmonitoring differences in fluorescence spectra obtained from a source ND, which\nis illuminated by a pump laser, and from a scattering ND illuminated only by\nthe fluorescence-excited SPP radiation. In the second case, we observe changes\nin the average NV lifetime when the same ND is characterized outside and inside\na VG. Fluorescence emission from the VG terminations is also observed, which\nconfirms the NV coupling to the VG-supported SPP modes.\n

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Original Source

DOI: https://doi.org/10.1088/2040-8978/18/2/024002