Shallow Nitrogen Vacancy Color Centers in Diamond by Ion Implantation

At a Glance

Metadata	Details
Publication Date	2025-06-11
Journal	Advanced Quantum Technologies
Authors	G. Speranza, Alessandro Cian, B. Perlingeiro Corrêa, Elena Missale, Andrea Pedrielli
Institutions	Fondazione Bruno Kessler, Netherlands Organisation for Applied Scientific Research
Analysis	Full AI Review Included

Technical Documentation & Analysis: Shallow NV Centers in Diamond

Executive Summary

This research successfully demonstrates a highly controlled method for fabricating shallow Nitrogen-Vacancy (NV) color centers in high-purity Single Crystal Diamond (SCD) using ion implantation through a screening layer. This achievement is critical for advancing nanoscale quantum sensing and computing applications.

Core Achievement: Fabrication of NV defects confined to the first 30 nm of the diamond subsurface, with the highest concentration confirmed at depths less than 5 nm.
Methodology: Utilized 30 keV N+ broad-beam ion implantation through a 100 nm PECVD SiO₂ screening layer on electronic grade SCD.
Depth Control: Demonstrated precise modulation of the nitrogen distribution and penetration depth by adjusting the ion beam incidence angle (7° vs. 45°).
Material Requirement: Confirmed the necessity of ultra-low nitrogen background SCD substrates (N < 5 ppb) to ensure optimal NV formation yield (FY) and high-quality quantum properties.
Charge State Control: Observed that shallower implantation (45° incidence) resulted in a higher NV⁰/NV⁻ ratio, emphasizing the need for advanced surface passivation techniques to stabilize the desired NV⁻ charge state.
Performance: The 7° incidence angle sample (D1) exhibited significantly higher overall Photoluminescence (PL) emission intensity (150.2 kcts s⁻¹), indicating a greater density of functional NV centers compared to the 45° sample (D2).

Technical Specifications

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

Parameter	Value	Unit	Context
Substrate Material	Single Crystal Diamond (SCD)	N/A	Electronic Grade, N background < 5 ppb
Substrate Orientation	(100)	N/A	Used for implantation
Surface Roughness (Ra)	< 0.5	nm	Post-finishing
Screening Layer Thickness	100 ± 2	nm	PECVD SiO₂
Ion Implantation Energy	30	keV	N+ ions
Ion Fluence (Total)	9.0 x 10¹⁴	ions cm^-2	Used for both D1 and D2 samples
Incidence Angle (D1)	7	°	Normal incidence (Higher PL yield)
Incidence Angle (D2)	45	°	Oblique incidence (Shallower R_p)
Projected Range (R_p) D1	[1-5]	nm	Below screening oxide
Projected Range (R_p) D2	[0-2.6]	nm	Below screening oxide (Shallower)
Peak N Concentration (D1)	≈2.0 x 10²⁰	atoms cm^-3	Simulated at diamond surface
Annealing Temperature	1000	°C	For NV center formation
Annealing Duration	3	hours	High vacuum (10^-6 mbar)
Shallow NV Depth Achieved	0 to 30	nm	Confirmed by ToF-SIMS depth profiling
NV^- ZPL Wavelength	≈637	nm	Confirmed by PL spectroscopy
PL Intensity (D1 Average)	150.2 ± 95.7	kcts s^-1	Confocal PL map average

Key Methodologies

The experimental process flow utilized a combination of advanced deposition, implantation, and thermal treatment techniques:

Substrate Selection: Electronic grade SCD diamond wafers (100)-oriented were chosen, characterized by ultra-low nitrogen content (< 5 ppb) and highly polished surfaces (Ra < 0.5 nm).
Screening Layer Deposition: A 100 nm thick SiO₂ screening layer was deposited onto the diamond surface using Plasma-Enhanced CVD (PECVD).
N+ Ion Implantation: Broad-beam N+ ions were implanted at 30 keV energy and a fluence of 9.0 x 10¹⁴ ions cm^-2. Two incidence angles (7° and 45°) were tested to control the nitrogen penetration depth and suppress ion channeling effects.
Screening Layer Removal: The sacrificial SiO₂ layer was removed using a conventional chemical process (HF etching) without affecting the underlying diamond surface quality.
Thermal Annealing: Samples were annealed at 1000 °C for 3 hours under high vacuum (10^-6 mbar) to mobilize vacancies, allowing them to combine with substitutional nitrogen atoms to form NV color centers.
Depth Profiling: Nitrogen distribution and depth were verified using Angle-Resolved X-ray Photoelectron Spectroscopy (ARXPS) for surface analysis (< 4 nm depth) and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) for deeper profiling (up to 30 nm).
Optical Characterization: Confocal Raman and Photoluminescence (PL) spectroscopy were used to confirm the formation and quantify the density of NV⁰ (575 nm) and NV⁻ (637 nm) centers.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the foundational materials and advanced processing required to replicate and extend this research into scalable quantum device fabrication. Our MPCVD diamond substrates meet or exceed the stringent purity and surface requirements demonstrated in this study.

Research Requirement / Challenge	6CCVD Material Solution	6CCVD Capability Alignment
High-Purity Substrate: Need for electronic grade SCD with N < 5 ppb for optimal NV⁻ formation yield and long coherence times (T₂).	Optical Grade Single Crystal Diamond (SCD): We provide ultra-low nitrogen concentration SCD substrates, ensuring minimal native defects and maximizing the quality of implanted NV centers for quantum sensing.	Custom Thickness: SCD wafers are available from 0.1 µm up to 500 µm, allowing precise control over the bulk material properties and integration with specific ion implantation energies.
Precise Surface Quality: Requirement for Ra < 0.5 nm to minimize surface-induced decoherence and charge instability in shallow NV centers.	Precision Polishing Services: Guaranteed SCD surface roughness of Ra < 1 nm, and inch-size PCD polishing to Ra < 5 nm, ensuring atomically smooth surfaces critical for shallow NV applications.	Orientation Control: SCD substrates are available in high-precision (100) orientation, matching the requirements of this study, as well as (110) and (111) for deterministic NV alignment strategies.
Advanced Device Integration: Future need for on-chip microwave delivery structures and electrical contacts for Optically Detected Magnetic Resonance (ODMR).	Custom Metalization: Internal capability to deposit standard quantum stack materials including Ti, Pt, Au, Pd, W, and Cu. This enables researchers to integrate microwave antennas directly onto the diamond surface for high-fidelity spin control.	Custom Dimensions & Shaping: We offer plates and wafers up to 125 mm (PCD) and custom laser cutting services, supporting both R&D and scalable manufacturing of diamond quantum chips.
Engineering Support: Need for optimization of material selection and post-processing steps (e.g., surface termination) to maximize the critical NV⁻/NV⁰ ratio.	In-House PhD Engineering Team: 6CCVD provides expert consultation on material selection, surface termination (e.g., oxygen or hydrogen termination), and substrate preparation to maximize the stability and performance of shallow NV centers for nano-NMR projects.	Global Shipping: Reliable global shipping (DDU default, DDP available) ensures rapid delivery of high-value diamond materials to research facilities worldwide.

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

View Original Abstract

Abstract Recent advancements in quantum technologies are fueled by the ability to engineer materials with specific quantum properties, enabling various applications. The nitrogen‐vacancy (NV) center in diamond is a key system for nanoscale sensors, capable of detecting weak magnetic fields with nanotesla‐range sensitivity. To achieve high spatial resolution and sensitivity, NV centers must be placed near the diamond surface. This study investigates the creation of NV defects in a pure chemical vapor deposition (CVD) diamond single crystal via broad‐beam ion implantation. The implantations are performed through thin (100 nm) SiO 2 layers deposited by plasma‐enhanced CVD (PECVD). Both normal and oblique ion beam incidences are used, with the oblique incidence chosen to reduce the nitrogen ion penetration depth. Simulations show a subsurface NV center distribution, with the highest concentration near the surface; the expected trends are confirmed by angle‐resolved X‐ray photoelectron spectroscopy (ARXPS) and time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS). This distribution extends to a depth of 30 nm. By adjusting the ion beam incidence angle, NV center density can be modulated. This work contributes to optimizing the fabrication process for shallow color centers through ion implantation using a screening layer.

Tech Support

Original Source

DOI: https://doi.org/10.1002/qute.202500080

References

2013 - Second Edition, Spin Dynamics: Basics of Nuclear Magnetic Resonance