Enhanced concentrations of nitrogen-vacancy centers in diamond through TEM irradiation

At a Glance

Metadata	Details
Publication Date	2017-09-18
Journal	Applied Physics Letters
Authors	Demitry Farfurnik, Nir Alfasi, Sergei Masis, Yaron Kauffmann, E. Farchi
Institutions	Technion – Israel Institute of Technology, Hebrew University of Jerusalem
Citations	45
Analysis	Full AI Review Included

Enhanced NV Center Concentration in Diamond via 200 keV TEM Irradiation: A 6CCVD Analysis

This technical documentation analyzes the findings of “Enhanced concentrations of nitrogen-vacancy centers in diamond through TEM irradiation” (arXiv:1702.05332v3) to provide relevant material specifications and capabilities offered by 6CCVD for quantum sensing and solid-state physics applications.

Executive Summary

The research demonstrates a highly effective, localized method for enhancing Nitrogen-Vacancy (NV) center concentration in various CVD and HPHT diamond substrates using 200 keV Transmission Electron Microscopy (TEM) irradiation.

Order of Magnitude Improvement: Electron irradiation enhanced the NV concentration by more than an order of magnitude across all tested CVD and implanted CVD samples.
High Concentration Achieved: Peak NV concentrations reached up to ~ 10¹⁵ NV/cm³ (3D bulk samples) and ~ 10¹¹ NV/cm² (2D implanted layers).
Coherence Preservation: Crucially, the long spin coherence time (T₂ ≈ 180 µs) of the standard grade CVD sample was maintained post-irradiation, confirming viability for quantum applications.
Efficiency Maximization: Conversion efficiency of Nitrogen (P1 centers) to NV centers reached up to 10.6% in nitrogen-implanted CVD samples.
Enhanced Sensing: The resulting NV concentration increase translates to a potential magnetometric sensitivity improvement from ~ 7/√Hz to ~ 2.2/√Hz.
Practical Localized Method: TEM irradiation offers a practical, in-house nanotechnology tool for creating localized, high-density NV ensembles suitable for many-body physics and small-area sensing devices.

Technical Specifications

The following parameters summarize the key experimental results and material requirements defined in the paper.

Parameter	Value	Unit	Context
Electron Irradiation Energy	200	keV	TEM source
Tested Dose Range (TEM)	7.0 x 10¹⁷ to 1.3 x 10²⁰	e/cm²	Localized irradiation for NV creation
Target NV Concentration (3D)	~ 10¹⁵	NV/cm³	Achieved in Standard CVD bulk
Target NV Concentration (2D)	~ 10¹¹	NV/cm²	Achieved in N-Implanted CVD layer
Peak Conversion Efficiency	10.6	%	Achieved in N-Implanted CVD 1
N Concentration (Standard CVD)	~ 2 x 10¹⁶	N/cm³	Initial bulk material concentration
N Implantation Energy	20	keV	For creating 2D NV layer
N Implantation Depth	~ 100	nm	Limited by ion channeling
Coherence Time (T₂)	~ 180	µs	Standard CVD sample (maintained after irradiation)
Annealing Temperature	800	°C	Standard post-irradiation process
Annealing Vacuum	~ 7.5 x 10^-7	Torr	Required high-vacuum environment
Irradiated Spot Diameter	10 - 20	µm	Localized TEM irradiation area

Key Methodologies

The NV creation and enhancement procedure relies on precise material engineering (CVD growth and implantation) followed by controlled defect creation (TEM irradiation) and vacancy mobilization (annealing).

Material Selection: Use of high-quality CVD diamond:
- Standard Grade CVD (initial [N] ~ 2 x 10¹⁶ N/cm³).
- High Purity CVD (initial [N] ~ 2 x 10¹⁴ N/cm³).
Nitrogen Implantation (for 2D layers):
- Nitrogen ions implanted at 20 keV energy.
- Doses varied: 2 x 10¹¹ N/cm² and 2 x 10¹² N/cm².
- This creates a narrow, near-surface nitrogen layer (~100 nm deep).
Electron Irradiation:
- Performed using a standard 200 keV TEM (FEI Tecnai G2 T20 S-Twin).
- Irradiation dose tailored for concentration goals, ranging from 7.0 x 10¹⁷ to 1.3 x 10²⁰ e/cm².
- Localized irradiation diameter: 10 - 20 µm.
Post-Irradiation Annealing:
- Standard process applied to mobilize created vacancies.
- Recipe: 8 hours at 800 °C, under high vacuum (~ 7.5 x 10^-7 Torr).
Characterization:
- Confocal microscope used with a 532 nm laser for NV fluorescence mapping and concentration estimation.
- Hahn-Echo experiment [27] used to measure decoherence time (T₂).

6CCVD Solutions & Capabilities

6CCVD provides the high-specification diamond substrates necessary to replicate and extend this research, particularly focusing on materials required for advanced quantum sensing applications and achieving the maximum possible coherence times (T₂).

Applicable Materials for Enhanced NV Ensembles

Material Type	6CCVD Specification	Relevance to Research
Standard Grade CVD	N-doped MPCVD Single Crystal (SCD) or Polycrystalline (PCD) plates, initial [N] customizable from 10¹⁵ to 10¹⁷ N/cm³.	Required for replication of bulk NV creation experiments and achieving T₂ > 180 µs, as demonstrated in the paper.
High Purity CVD	SCD with ultra-low native nitrogen (< 5 ppb typical) for maximum coherence.	Ideal starting material for external ion implantation (2D layers) to ensure minimal P1 background defects, necessary for high-fidelity quantum experiments.
Isotopically Pure ¹²C SCD	SCD with < 1% ¹³C content, customizable thickness (0.1 µm to 500 µm).	Critical for achieving target T₂ times. The paper notes that using ¹²C diamond could increase T₂ from ~180 µs up to ~ 30 ms, enabling the NV-NV interaction-dominated regime for many-body physics.

Customization Potential for Quantum Device Engineering

The ability to control geometry, crystal orientation, and surface termination is vital for translating these high-density NV centers into functional quantum devices.

Custom Dimensions and Thickness: While TEM irradiation is localized, large area commercial implementation (2.8 MeV irradiation discussed in the paper) requires high-quality, large-format wafers. 6CCVD provides SCD/PCD plates up to 125mm diameter and precise thickness control from 0.1 µm to 500 µm, accommodating both bulk (3D) and thin film (2D, N-implanted) research geometries.
Precision Polishing: Achieving stable, near-surface 2D NV layers requires low surface roughness to minimize decoherence from surface effects [29]. 6CCVD guarantees Ra < 1 nm for Single Crystal Diamond (SCD) and Ra < 5 nm for inch-size PCD, supporting high-fidelity surface studies.
Metalization Services: While not central to NV creation, future device integration (e.g., microwave circuits for ODMR) requires reliable electrical contacts. 6CCVD offers internal thin film metalization capabilities, including common stacks like Ti/Pt/Au, as well as Pd, W, and Cu.
Laser Cutting and Etching: Custom shapes and precise mesa structures are essential for micro-sensing elements. 6CCVD offers advanced laser cutting and etching services to define the localized diamond volumes necessary for optimized NV ensemble sensors.

Engineering Support & Delivery

Expert Consultation: 6CCVD’s in-house PhD engineering team specializes in diamond defect engineering. We can assist researchers with material selection, optimizing initial nitrogen concentration, and defining specifications for post-growth treatments (e.g., implantation dose and energy) for similar NV quantum sensing and many-body physics projects.
Global Logistics: All custom materials are available for global shipping, with DDU default and DDP options, ensuring materials reach sensitive research facilities efficiently.

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

View Original Abstract

The studies of many-body dynamics of interacting spin ensembles, as well as quantum sensing in solid state systems, are often limited by the need for high spin concentrations, along with efficient decoupling of the spin ensemble from its environment. In particular, for an ensemble of nitrogen-vacancy (NV) centers in diamond, high conversion efficiencies between nitrogen (P1) defects and NV centers are essential while maintaining long coherence times of an NV ensemble. In this work, we study the effect of electron irradiation on the conversion efficiency and the coherence time of various types of diamond samples with different initial nitrogen concentrations. The samples were irradiated using a 200 keV transmission electron microscope. Our study reveals that the efficiency of NV creation strongly depends on the initial conversion efficiency and on the initial nitrogen concentration. The irradiation of the examined samples exhibits an order of magnitude improvement in the NV concentration (up to ∼1011 NV/cm2), without degradation in their coherence time of ∼180 μs. We address the potential of this technique toward the study of many-body physics of NV ensembles and the creation of non-classical spin states for quantum sensing.

Tech Support

Original Source

DOI: https://doi.org/10.1063/1.4993257