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6CCVD Research

Engineering the collapse of lifetime distribution of nitrogen-vacancy centers in nanodiamonds

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2021-06-28
JournalApplied Physics Letters
AuthorsH. Li, J.Y. Ou, B. Gholipour, J.K. So, D. Piccinotti
InstitutionsNanyang Technological University, University of Southampton
Citations3
AnalysisFull AI Review Included

Executive Summary

Section titled “Executive Summary”

This research demonstrates a novel engineering approach to dramatically improve the statistical uniformity and speed of Nitrogen-Vacancy (NV) centers in nanodiamonds (NDs) by embedding them in thin chalcogenide films.

  • Distribution Collapse: The lifetime distribution spread of NV0 centers was narrowed by over five times, reducing the spread from >7 ns (reference sample) to approximately 1 ns (embedded sample).
  • Lifetime Shortening: The average lifetime of NV0 centers was shortened by a factor of two, converging from ~20 ns to a uniform average of 11 ns across various dielectric environments.
  • Mechanism 1: Non-Radiative Enhancement: The lossy chalcogenide film (Antimony Telluride, SbTe) substantially enhances non-radiative decay, which dominates the relaxation process in embedded NDs.
  • Mechanism 2: Orientation Insensitivity: Embedding the NDs renders the total decay rate (Ytot) almost insensitive to the random orientation of the NV center’s electric dipole moment, eliminating a major source of lifetime variation in ensembles.
  • Brightness Uniformity: Similar improvements were observed in brightness statistics, with the spread narrowing by at least a factor of three for embedded NDs, despite an overall five-fold decrease in average brightness.
  • Tunable Platform: The use of chalcogenides allows for active control over emission statistics, as their optical constants can be tuned continuously (from plasmonic to dielectric) via stoichiometric or phase engineering.

Technical Specifications

Section titled “Technical Specifications”
ParameterValueUnitContext
ND Average Size120nmNanodiamonds used (Sigma Aldrich)
NV0 Centers per ND~1200centersNeutral NV centers per nanodiamond
Reference Average Lifetime~20nsNDs deposited on SbTe film
Embedded Average Lifetime11nsNDs embedded in SbTe film
Lifetime Spread Reduction>5timesRatio of spread (reference / embedded)
Embedded Lifetime Spread~1nsSpread around 11 ns average (SPL/WPL areas)
NV0 Zero Phonon Line (ZPL)575nmWavelength used for filtering
SbTe Deposition Vacuum< 10-8mbarPhysical Vapor Deposition (PVD) pressure
Sb/Te Source Purity> 99.9999%Purity of source materials
SbTe Film Thickness (d) Range40 to 100nmTotal thickness after two deposition rounds
SbTe Permittivity (Re Δ) Range-23 to 13N/AReal part, varying across composition
SbTe Permittivity (Im Δ) Range15 - 30N/AImaginary part (loss), high across all compositions
TR-CL SEM Voltage10kVScanning Electron Microscope operating voltage
TR-CL Beam Current1.7 - 1.9nAElectron beam current during measurement
Non-Radiative Decay Enhancement (Parallel Dipole)>18timesSimulated enhancement for embedded NDs vs. deposited NDs

Key Methodologies

Section titled “Key Methodologies”

The experiment relied on high-throughput physical vapor deposition (PVD) to create compositionally graded chalcogenide films, followed by precise integration and characterization of nanodiamond ensembles.

  1. Substrate Preparation and PVD (Layer 1): A thin film of Antimony Telluride (SbTe) (thickness d/2, 20 to 50 nm) was deposited onto a 28 mm x 28 mm silicon (Si) substrate.
  2. High-Throughput Synthesis: PVD utilized off-axis Knudsen cell sources under ultra-high vacuum (≀ 10-8 mbar) at room temperature. Fixed wedge shutters independently controlled the density gradients of Sb and Te, ensuring simultaneous mixing and the formation of an amorphous SbTe alloy.
  3. ND Integration: Nanodiamonds (120 nm average size) were dispersed in methanol and drop-cast onto the first SbTe layer.
  4. PVD (Layer 2) and Embedding: A second SbTe film (thickness d/2) was deposited over the ND dispersion using the same PVD procedure, resulting in NDs fully embedded within the SbTe film of total thickness d.
  5. Optical Characterization: Complex permittivity (Re Δ and Im Δ) maps were generated using variable angle spectroscopic ellipsometry at 575 nm (the NV0 ZPL wavelength) to identify areas of Strong Plasmonic (SPL, Re Δ = -15), Weak Plasmonic (WPL, Re Δ = -7), and Strong Dielectric (SDL, Re Δ = 7) response.
  6. Time-Resolved Cathodoluminescence (TR-CL): Lifetimes were measured using a 10 kV SEM in fixed-spot mode with a pulsed electron beam (beam current 1.7 - 1.9 nA). Photons were filtered at 575 nm and counted using time-correlated single-photon counting.
  7. Data Extraction: Lifetime histograms were fitted with a bi-exponential function, where the slow exponential term represented the decay rate of the NV0 centers.

Commercial Applications

Section titled “Commercial Applications”

The ability to engineer highly uniform and fast decay rates for NV centers addresses a critical challenge in scaling quantum technologies, particularly those relying on ensemble properties.

  • Scalable Quantum Photonics: Creating large ensembles of NV centers with uniform decay rates is essential for building robust, integrated quantum circuits, quantum repeaters, and photonic devices.
  • Uniform Single-Photon Sources (SPS): The collapse of the lifetime distribution enables the production of highly predictable and uniform SPS devices, crucial for quantum communication and quantum cryptography.
  • Fluorescence Lifetime Imaging Microscopy (FLIM): Uniform lifetime characteristics improve the accuracy and resolution of ND-based scanning probes used in bio-imaging and biological sensing applications.
  • Nanoscale Sensing Platforms: NV centers are widely used for sensing magnetic fields, temperature, and strain. Increased uniformity enhances the signal-to-noise ratio and reliability of ensemble-based sensors.
  • Active Optical Devices: Since chalcogenides are phase-change materials (tunable optically, electrically, or thermally), this platform offers a pathway for implementing active control over the emission statistics (e.g., switching or modulating the decay rate).
View Original Abstract

We demonstrate experimentally that the distribution of the decay rates of nitrogen-vacancy centers in diamond becomes narrower by over five times for nanodiamonds embedded in thin chalcogenide films.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 2013 - The nitrogen-vacancy colour centre in diamond [Crossref]
  2. 1997 - Scanning confocal optical microscopy and magnetic resonance on single defect centers [Crossref]
  3. 2000 - Stable Solid-State Source of Single Photons [Crossref]
  4. 2000 - Photon antibunching in the fluorescence of individual color centers in diamond [Crossref]
  5. 2001 - Nonclassical radiation from diamond nanocrystals [Crossref]
  6. 2015 - Lifetime investigation of single nitrogen vacancy centres in nanodiamonds [Crossref]
  7. 1989 - Cathodoluminescence of defects in diamond films and particles grown by hot-filament chemical-vapor deposition [Crossref]
  8. 2006 - Characterisation of high-quality thick single-crystal diamond grown by CVD with a low nitrogen addition [Crossref]
  9. 2012 - Spectrally and spatially resolved cathodoluminescence of nanodiamonds: Local variations of the NV(0) emission properties [Crossref]
  10. 2013 - Spatially resolved quantum nano-optics of single photons using an electron microscope [Crossref]

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