Direct formation of nitrogen-vacancy centers in nitrogen doped diamond along the trajectories of swift heavy ions

At a Glance

Metadata	Details
Publication Date	2021-02-22
Journal	Applied Physics Letters
Authors	Russell E. Lake, Arun Persaud, Casey Christian, Edward S. Barnard, Emory M. Chan
Institutions	GSI Helmholtz Centre for Heavy Ion Research, National University of Singapore
Citations	12
Analysis	Full AI Review Included

Technical Documentation & Analysis: Direct NV Center Formation via SHI

This document analyzes the research paper “Direct formation of nitrogen-vacancy centers in nitrogen doped diamond along the trajectories of swift heavy ions” to provide technical specifications and demonstrate how 6CCVD’s advanced MPCVD diamond materials and processing capabilities can support and extend this critical quantum research.

Executive Summary

This research demonstrates a highly efficient, one-step method for creating high-density, quasi-one-dimensional (1D) registers of negatively charged Nitrogen-Vacancy (NV$^{-}$) centers in synthetic Single Crystal Diamond (SCD) using Swift Heavy Ion (SHI) irradiation.

Novel Formation Mechanism: NV$^{-}$ centers are formed directly along the ion tracks where electronic stopping (energy deposition) dominates, rather than solely relying on the end-of-range nuclear stopping (vacancy creation).
Material Requirement: The process requires high-quality, Type Ib synthetic SCD uniformly doped with nitrogen (100 ppm concentration).
High Qubit Density: The method creates quasi-1D chains of NV centers with an average spacing of a few nanometers (nm), potentially enabling the fabrication of registers containing over 1,000 coupled qubits over 10 µm distances.
Conversion Efficiency: An estimated NV conversion efficiency of 15% to 20% from SHI irradiation was achieved, significantly higher than many conventional implantation techniques.
Processing Insight: Thermal annealing (800 °C) further increases NV yield, particularly activating vacancies created by nuclear stopping near the end of the ion range (34 µm).
Application: This technique is crucial for developing scalable, high-resolution spin-photon qubit registers for quantum computing and sensing applications.

Technical Specifications

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

Parameter	Value	Unit	Context
Diamond Material	Type Ib Synthetic SCD	N/A	Grown with nitrogen doping
Nitrogen Concentration	100	ppm	Uniformly doped during growth
Incident Ion Species	${}^{197}\text{Au}$ (Gold)	N/A	Swift Heavy Ion (SHI)
Ion Energy	1.1	GeV	Irradiation source energy
Ion Fluence	$1 \times 10^{12}$	ions/cm$^{2}$	Total irradiation dose
Ion Flux	$6 \times 10^{9}$	ions/cm$^{2}$/s	Irradiation rate
Ion Range (in diamond)	34	µm	Calculated stopping depth (SRIM)
Annealing Temperature	800	°C	Post-irradiation thermal treatment
Annealing Duration	1	hour	Performed in high vacuum
PL Excitation Wavelength	532	nm	Confocal microscopy laser source
NV Center Yield (Estimated)	15 - 20	%	SHI conversion factor
Qubit Spacing (Average)	Few	nm	Along quasi-1D tracks
Track Length	10 to 30	µm	Length of percolation chains

Key Methodologies

The experiment focused on controlled SHI irradiation of pre-doped SCD followed by depth-resolved optical analysis.

Material Preparation: Type Ib synthetic SCD was grown with a uniform nitrogen concentration of 100 ppm.
Masking: The sample was masked with a thick metallic grid to create adjacent irradiated and nonirradiated (pristine) regions for comparative analysis.
SHI Irradiation: Irradiation was performed using 1.1 GeV ${}^{197}\text{Au}$ ions in high vacuum at nominal room temperature, achieving a fluence of $1 \times 10^{12}$ ions/cm$^{2}$.
Initial PL Measurement: Room temperature photoluminescence (PL) spectra were collected using a custom confocal setup (532 nm excitation) to confirm direct NV center formation in the irradiated regions without annealing.
Depth Profiling: Depth-resolved PL measurements were performed by scanning the sample stage (z-axis) and converting the stage position to actual depth using the diamond refractive index ($n = 2.4$).
Thermal Annealing: The sample was subsequently annealed in high vacuum at 800 °C for 1 hour to study the activation and diffusion effects on NV center yield and distribution.
Post-Anneal Analysis: PL depth profiles were measured again to compare the effects of SHI irradiation alone versus SHI irradiation followed by annealing.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the foundational materials and custom processing required to replicate and advance this research into scalable quantum registers.

Applicable Materials

To replicate the high-efficiency, quasi-1D NV center formation demonstrated in this paper, researchers require high-quality, nitrogen-doped SCD with precise concentration control.

6CCVD Material Solution	Specification Match	Customization Potential
Optical Grade SCD	Type Ib Synthetic Diamond	Required for high-coherence quantum applications.
Controlled Nitrogen Doping	Target 100 ppm N (or custom range)	6CCVD offers precise control over nitrogen incorporation during MPCVD growth to match specific experimental requirements (e.g., 1 ppm to >100 ppm).
Ultra-Low Roughness Polishing	Ra < 1 nm (SCD)	Essential for high-fidelity optical excitation and collection (532 nm laser) in depth-resolved confocal microscopy.
Custom Thickness	0.1 µm to 500 µm	We can provide SCD plates tailored to the specific ion range (34 µm in this study) or for subsequent device integration.

Customization Potential

The research highlights the need for precise material handling and future device integration (e.g., lift-out techniques for quasi-1D chains). 6CCVD offers comprehensive post-growth processing services:

Custom Dimensions: While the paper does not specify dimensions, 6CCVD provides SCD wafers and plates in custom sizes, ensuring compatibility with existing ion beam and optical setups.
Advanced Metalization: Future integration of these quasi-1D qubit registers with microwave sources and magnetic fields requires robust electrical contacts. 6CCVD offers in-house metalization services, including Ti, Pt, Au, Pd, W, and Cu deposition, crucial for creating stable ohmic contacts or protective layers.
Precision Laser Cutting: We provide high-precision laser cutting services to define specific sample geometries or to prepare samples for lift-out techniques mentioned in the paper (e.g., for isolating single 1D chains).

Engineering Support

The successful creation of high-density NV centers relies heavily on the quality and purity of the starting diamond material and the precise control of nitrogen concentration.

Material Selection for Quantum Applications: 6CCVD’s in-house PhD team specializes in optimizing MPCVD growth recipes to achieve the specific defect concentrations and crystal quality required for Quantum Sensing and Quantum Communication projects.
Process Optimization: We can assist researchers in selecting the optimal material parameters (e.g., nitrogen concentration, crystal orientation, surface termination) to maximize NV conversion efficiency and coherence time for similar Swift Heavy Ion Implantation projects.
Global Logistics: We ensure reliable global shipping (DDU default, DDP available) to research facilities worldwide, including those performing high-energy ion irradiation experiments like GSI.

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

View Original Abstract

We report depth-resolved photoluminescence measurements of nitrogen-vacancy (NV−) centers formed along the tracks of swift heavy ions (SHIs) in type Ib synthetic single crystal diamonds that had been doped with 100 ppm nitrogen during crystal growth. Analysis of the spectra shows that NV− centers are formed preferentially within regions where electronic stopping processes dominate and not at the end of the ion range where elastic collisions lead to the formation of vacancies and defects. Thermal annealing further increases NV yields after irradiation with SHIs preferentially in regions with high vacancy densities. NV centers formed along the tracks of single swift heavy ions can be isolated with lift-out techniques for explorations of color center qubits in quasi-1D registers with an average qubit spacing of a few nanometers and of order 100 color centers per micrometer along 10 to 30-μm-long percolation chains.

Tech Support

Original Source

DOI: https://doi.org/10.1063/5.0036643

References

2016 - Quantum nanophotonics in diamond [invited] [Crossref]
2018 - Quantum internet: A vision for the road ahead [Crossref]
2013 - Room-temperature entanglement between single defect spins in diamond [Crossref]
2014 - Formation of NV centers in diamond: A theoretical study based on calculated transitions and migration of nitrogen and vacancy related defects [Crossref]
2005 - Generation of single color centers by focused nitrogen implantation [Crossref]
2014 - Local formation of nitrogen-vacancy centers in diamond by swift heavy ions [Crossref]
2010 - Chip-scale nanofabrication of single spins and spin arrays in diamond [Crossref]
2005 - Progress in the study of warm dense matter [Crossref]
2012 - Nano-hillock formation in diamond-like carbon induced by swift heavy projectiles in the electronic stopping regime: Experiments and atomistic simulations [Crossref]
2007 - Atomistic simulations of swift ion tracks in diamond and graphite [Crossref]