Nanoimplantation and Purcell enhancement of single nitrogen-vacancy centers in photonic crystal cavities in diamond

At a Glance

Metadata	Details
Publication Date	2015-06-01
Journal	Applied Physics Letters
Authors	Janine Riedrich‐Möller, Sébastien Pezzagna, Jan Meijer, Christoph Pauly, Frank Mucklich
Institutions	Leipzig University, Element Six (United Kingdom)
Citations	71
Analysis	Full AI Review Included

6CCVD Technical Analysis & Quantum Material Solutions

Analysis of “Nanoimplantation and Purcell enhancement of single NV centers in photonic crystal cavities in diamond”

This analysis details the fabrication and characterization of deterministically placed Nitrogen-Vacancy (NV) centers within high-quality diamond photonic crystal (PhC) cavities, demonstrating Purcell enhancement of spontaneous emission. This research validates the need for ultra-high purity, engineered single crystal diamond (SCD) material capable of integration into complex quantum photonic circuits.

Executive Summary

The following points summarize the core technical achievement and material requirements of the research:

Deterministic Quantum Emitter Creation: Achieved controlled placement of single NV centers at the maximum electric field of pre-fabricated diamond PhC cavities using collimated 5 keV ¹⁵N⁺ nanoimplantation through a pierced AFM tip.
Material Purity Requirement: The experiment relied upon ultra-high purity, Single Crystal Diamond (SCD) with Nitrogen concentrations below 5 ppb to minimize native defect interference.
Optimal Placement Recipe: An optimal ion dose of $1 \times 10^{13}$ ions/cm² was determined, yielding $0.8 \pm 0.2$% NV creation efficiency for the targeted formation of a single optically active NV center.
Photonic Integration Success: Demonstrated successful coupling of the broad NV emission (Phonon Side Band, PSB) to the M1 cavity mode, resulting in a measurable Purcell enhancement factor of 1.24.
Membrane Technology Validation: PhC structures were etched into ultra-thin (220 nm) SCD membranes, confirming the viability of precision MPCVD diamond for advanced integrated quantum optics platforms.
Fundamental Step for Scalability: This methodology is cited as an essential step toward building scalable, solid-state quantum networks and repeaters based on NV-nanocavity systems.

Technical Specifications

Parameter	Value	Unit	Context
Diamond Material	Single Crystal Diamond (SCD)	N/A	High Purity (< 5ppb N)
Membrane Thickness	220	nm	Final PhC membrane thickness
Starting Substrate Thickness	10	µm	Initial bulk thickness after polishing
Implantation Ion	¹⁵N⁺	N/A	Nitrogen isotope for NV center formation
Ion Energy	5	keV	Used for nanoimplantation
Implantation Depth (Average)	8	nm	Monte Carlo simulation (SRIM)
Ion Straggle	3	nm	Lateral and vertical uncertainty
Optimal Single NV Dose	$1 \times 10^{13}$	ions/cm²	Targeted creation of one single NV center
NV Creation Yield	$0.8 \pm 0.2$	%	Percentage yield at 5 keV
Annealing Temperature	800	°C	Required post-processing for NV formation
Cavity Type	M1, M3, M7	N/A	One, three, or seven-hole defects
Lattice Constant (a)	220 - 240	nm	PhC dimensions
Quality Factor (Q)	150 - 1200	N/A	Experimental Q-factors of PhC modes
Mode Volume (V)	$\approx 1(1/n)$³	N/A	$n=2.4$ refractive index
NV ZPL Wavelength	637	nm	Zero-Phonon Line (ZPL)
Purcell Enhancement ($I_{on}/I_{off}$)	1.24 (Experimental)	N/A	Measured intensity enhancement
Emission Efficiency ($\beta$)	0.31 (Experimental)	N/A	Ratio of intensity channeled into mode C1

Key Methodologies

The successful integration of quantum emitters required meticulous material preparation and precise processing steps:

SCD Substrate Preparation:
- High purity, synthetic single crystal diamond (< 5ppb Nitrogen) was grown via MPCVD (Microwave Assisted Chemical Vapor Deposition).
- The as-grown (001) diamond was processed using standard lapidary and scaife polishing to thin the material to 10 µm.
Membrane Fabrication:
- The SCD was bonded to a silicon substrate using a spin-on-glass layer (HSQ).
- The silicon substrate was partially removed to create a free-standing diamond membrane.
- Reactive Ion Etching (RIE) in an oxygen plasma thinned the membrane down to the target 220 nm.
Photonic Crystal (PhC) Patterning:
- A triangular lattice of air holes (lattice constant $a=220-240$ nm, radii $R=80-83$ nm) was patterned into the 220 nm membrane.
- Patterning was executed using Focused Ion Beam (FIB) milling with $30$ keV Ga⁺ ions.
High-Resolution Nanoimplantation:
- The nanoimplanter setup combined a nitrogen ion beam (5 keV ¹⁵N⁺) with an Atomic Force Microscope (AFM).
- A small hole (< 30 nm diameter) drilled in the AFM tip served as an aperture for ion beam collimation and lateral positioning.
- Targeted dose was applied to the PhC cavity center, aiming for $1 \times 10^{13}$ ions/cm² for single NV creation.
Post-Processing and Activation:
- The sample was annealed at $800$ °C for 2 hours in vacuum to mobilize lattice vacancies, allowing them to diffuse and combine with implanted Nitrogen ions to form optically active NV centers.
- Final cleaning involved boiling the sample in a mixture of nitric, sulfuric, and perchloric acids to oxidize graphite-like residuals and convert the NV centers to the desirable negative charge state (NV^-).

6CCVD Solutions & Capabilities

This demanding research requires materials and precision services perfectly aligned with 6CCVD’s core competencies. Replication or extension of this work depends on starting with the highest quality MPCVD diamond.

Applicable Materials

The successful creation of NV-PhC systems is critically dependent on the purity and surface quality of the substrate.

Research Requirement	6CCVD Material Solution	Rationale
Ultra-High Purity SCD	Optical Grade SCD (Sub-5 ppb Nitrogen)	Essential for minimizing native defects and ensuring long coherence times necessary for quantum applications. Our material matches or exceeds the purity specification (< 5 ppb N) used in the paper.
Thin Membranes	SCD Wafers (Substrate or Polished)	We offer SCD polished down to 0.1 µm. We provide the 10 µm starting material required, or we can supply wafers pre-thinned to customized specifications, reducing customer processing complexity.

Precision Processing and Engineering Support

Replicating the PhC structures (lattice constant 220-240 nm, membrane 220 nm) demands world-class polishing and thinning capabilities, which 6CCVD delivers in-house.

Polishing Quality: The PhC fabrication process (FIB milling) is highly sensitive to surface roughness. 6CCVD guarantees Ra < 1 nm for Single Crystal Diamond (SCD), ensuring the prerequisite atomically smooth surface needed for high-Q cavity performance.
Custom Dimensions and Etch Preparation: We supply custom wafers and plates up to 125 mm (PCD) and offer (001) orientation diamond suitable for membrane fabrication and subsequent RIE thinning.
Metalization Potential: While the paper focused on ion implantation, future scaling or integration of charge control gates often requires conductive layers. 6CCVD provides custom metalization services including Au, Pt, Pd, Ti, W, and Cu, suitable for defining implantation masks or electrical contacts.
Doping for Advanced Control: For applications requiring electrochemical sensing or integrated contacts (not used in this specific paper, but relevant for NV control), 6CCVD offers Boron-Doped Diamond (BDD) wafers.

Engineering Support

NV-center research involves highly specialized fabrication recipes, including high-temperature annealing ($800$ °C) and aggressive acid cleaning. 6CCVD’s in-house PhD team provides expert consultation on:

Material Selection: Guiding customers on selecting the optimal SCD grade based on target NV coherence time, required impurity levels, and mechanical tolerance for subsequent PhC etching.
Post-Growth Processing: Advising on material preparation, orientation, and cleaning protocols to maximize NV creation yield and convert centers to the desired NV^- charge state for quantum applications.

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

View Original Abstract

We present the controlled creation of single nitrogen-vacancy (NV) centers via ion implantation at the center of a photonic crystal cavity which is fabricated in an ultrapure, single crystal diamond membrane. High-resolution placement of NV centers is achieved using collimation of a 5 keV-nitrogen ion beam through a pierced tip of an atomic force microscope. We demonstrate coupling of the implanted NV centers’ broad band fluorescence to a cavity mode and observe Purcell enhancement of the spontaneous emission. The results are in good agreement with a master equation model for the cavity coupling.

Tech Support

Original Source

DOI: https://doi.org/10.1063/1.4922117