Fabrication of 15NV− centers in diamond using a deterministic single ion implanter

At a Glance

Metadata	Details
Publication Date	2021-06-01
Journal	New Journal of Physics
Authors	Karin Groot-Berning, Georg Jacob, Christian Osterkamp, Fedor Jelezko, F. Schmidt‐Kaler
Institutions	Universität Ulm, Alpine Quantum Technologies (Austria)
Citations	28
Analysis	Full AI Review Included

Technical Documentation & Analysis: Deterministic ¹⁵NV^- Center Fabrication

This document analyzes the research paper “Fabrication of ¹⁵NV^- centers in diamond using a deterministic single ion implanter” and outlines how 6CCVD’s advanced MPCVD diamond materials and customization capabilities directly support and extend this critical quantum technology research.

Executive Summary

The research successfully demonstrates a scalable, maskless method for deterministically creating single Nitrogen Vacancy (NV) centers in diamond, a crucial step toward solid-state quantum processors and high-resolution sensing arrays.

Deterministic Source: Utilized a sympathetically laser-cooled single ¹⁵N₂⁺ molecular ion in a Paul trap, enabling single-ion-level dose control.
High Resolution: Achieved a lateral implantation resolution (spot size) of 121(35) nm without requiring nanofabricated masks or apertures.
Shallow Implantation: Used low kinetic energy (3 keV per atomic ¹⁵N ion) resulting in extremely shallow NV centers (4.2 nm penetration depth).
Material Requirement: Required ultra-low nitrogen concentration, electronic grade Type IIa diamond to minimize background ¹⁴NV centers.
Performance Validation: Confirmed the presence of ¹⁵NV^- centers via Optically Detected Magnetic Resonance (ODMR), showing the characteristic 3.1 MHz hyperfine splitting.
Coherence Results: Measured coherence times (T₂) up to 1.56 µs, demonstrating functional quantum emitters despite the challenges associated with shallow implantation.
Future Scalability: The method is highly encouraging for building scalable quantum processors requiring nanometer-accurate NV arrays (10-20 nm pitch).

Technical Specifications

The following hard data points were extracted from the experimental results, highlighting the precision required for deterministic NV fabrication.

Parameter	Value	Unit	Context
Implanted Ion Species	¹⁵N₂⁺	-	Molecular ion source
Atomic Implantation Energy	3	keV	Energy per atomic ¹⁵N ion (SRIM simulation)
Implantation Depth (Shallow)	4.2	nm	Penetration depth (SRIM simulation)
Lateral Resolution (Spot Size, σ)	121(35)	nm	Achieved resolution for ¹⁵N₂⁺ ions
Annealing Temperature (Max)	900	°C	Used for vacancy mobilization and NV formation
Annealing Vacuum	10^-7	mbar	Ultra-high vacuum (UHV) requirement
NV Creation Yield	0.6	%	Calculated for Region F (low energy, no co-implantation)
NV^- Zero Phonon Line (ZPL)	637	nm	Characteristic optical readout wavelength
NV^- Zero Field Splitting	2.87	GHz	Confirms NV^- charge state
¹⁵N Hyperfine Splitting	3.1	MHz	Measured via Pulsed ODMR
Coherence Time (T₂)	0.66 to 1.56	µs	Measured via Hahn echo (Region A)
Substrate Purity (Native ¹⁴N)	0.27	ppt	Concentration of native NV^- centers (1 NV^- per 100 µm²)

Key Methodologies

The deterministic fabrication process relies on precise control over the ion source, implantation parameters, and post-processing steps, particularly high-temperature annealing and surface treatment.

Ion Source Preparation: Single ¹⁵N₂⁺ molecular ions were loaded into a linear Paul trap, where they were sympathetically cooled via Coulomb interaction with laser-cooled ⁴⁰Ca⁺ ions.
Deterministic Extraction: The single ion was extracted by applying high voltage pulses to a pierced endcap electrode, accelerating the ion to a total energy of 5.9 keV.
Beam Focusing: The ion beam was focused using an Einzel-lens to achieve the required lateral resolution (121 nm spot size) and steered using deflection electrodes.
Implantation: Ions were implanted into a commercial Type IIa electronic grade diamond substrate in a 5x5 grid pattern with 2 µm separation. The dose was controlled deterministically from 1 to 20 ions per spot.
Pre-Annealing Cleaning: The sample was acid cleaned in a 1:1:1 mixture of sulfuric, nitric, and perchloric acid, heated to 130 °C for 2 hours, to remove surface contamination.
NV Activation Annealing: A UHV annealing procedure was performed: 250 °C for 1 hour, followed by ramping to 900 °C and holding for 2 hours (10^-7 mbar vacuum) to mobilize vacancies and form stable NV centers.
Surface Termination: A final acid boiling step was included to ensure oxygen termination of the diamond surface, which is essential for preserving the NV^- charge state of the shallow centers.
Characterization: NV centers were detected using confocal microscopy (518 nm laser) and characterized using pulsed ODMR to confirm the ¹⁵N hyperfine coupling and Hahn echo measurements to determine the T₂ coherence time.

6CCVD Solutions & Capabilities

This research highlights the critical dependence of quantum emitter performance on the quality and purity of the diamond substrate. 6CCVD is uniquely positioned to supply the advanced materials and customization services required to replicate, optimize, and scale this deterministic implantation technique.

Applicable Materials

To replicate and extend this high-precision quantum research, the highest purity diamond is mandatory.

6CCVD Material	Description & Application	Relevance to Deterministic Implantation
Optical Grade Single Crystal Diamond (SCD)	Ultra-low nitrogen (sub-ppb) electronic grade material.	Direct Requirement: Essential for minimizing native ¹⁴N impurities (P1 centers) that limit T₂ coherence time, especially for shallow NVs (Ref. [38]).
Custom Doped SCD	SCD intentionally doped with specific elements (e.g., Sulfur, Phosphorous, or controlled Boron).	Yield Optimization: Enables replication of advanced techniques like pre-implantation co-doping (Ref. [17]) to boost NV creation yield from 0.6% up to 75%.
High Purity Polycrystalline Diamond (PCD)	Available for large-area sensing applications where ultra-low nitrogen is less critical than size/cost.	Large-Scale Arrays: Suitable for scaling up NV arrays for sensing or simulator platforms where plates up to 125mm are required.

Customization Potential

The paper identifies challenges related to yield, coherence, and future readout architectures (p. 9, 10). 6CCVD’s customization services directly address these limitations.

Research Challenge / Future Need	6CCVD Customization Service	Benefit to Researcher
Substrate Dimensions (UHV/Trap Compatibility)	Custom Dimensions & Thickness: Plates/wafers up to 125mm (PCD). SCD thicknesses from 0.1 µm to 500 µm, and substrates up to 10mm thick.	Ensures perfect fit for specialized UHV chambers, Paul traps, and cryogenic stages used in the experimental setup.
Shallow NV Coherence (Surface Effects)	Ultra-High Polishing (Ra < 1 nm): SCD surfaces polished to atomic smoothness.	Minimizes surface damage and defects, which are the primary source of paramagnetic noise limiting T₂ coherence for shallow NV centers (4.2 nm depth).
Electrical Readout Architectures (10-20 nm pitch)	In-House Metalization: Deposition of custom metal stacks (Au, Pt, Pd, Ti, W, Cu) for nano-wire integration.	Facilitates the implementation of electrical readout schemes (Ref. [39]) necessary to overcome the optical diffraction limit for dense NV qubit arrays.
Patterning & Alignment	Precision Laser Cutting & Shaping: Custom substrate shapes and alignment features.	Provides pre-patterned substrates compatible with high-resolution ion beam referencing and positioning systems (Ref. [16]).

Engineering Support

6CCVD understands that the success of deterministic single ion implantation hinges on the quality of the starting material.

Material Consultation: 6CCVD’s in-house PhD team offers expert consultation on material selection, specifically advising on the optimal nitrogen purity, crystal orientation, and surface termination methods required for high-yield, high-coherence Deterministic Quantum Emitter projects.
Process Optimization: We assist researchers in defining specifications for custom-doped SCD necessary to implement advanced techniques like co-implantation (P, S) or high-temperature annealing (up to 1500 °C suggested in the paper) to maximize NV yield and T₂ coherence.
Global Logistics: We ensure reliable, global shipping (DDU default, DDP available) of sensitive, high-purity diamond materials directly to your research facility.

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

View Original Abstract

Abstract Nitrogen vacancy (NV) centers in diamond are a platform for several important quantum technologies, including sensing, communication and elementary quantum processors. In this letter we demonstrate the creation of NV centers by implantation using a deterministic single ion source. For this we sympathetically laser-cool single <mml:math xmlns:mml=“http://www.w3.org/1998/Math/MathML” display=“inline” overflow=“scroll”> <mml:mmultiscripts> <mml:mrow> <mml:mi mathvariant=“normal”>N</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> </mml:mrow> <mml:mprescripts/> <mml:none/> <mml:mrow> <mml:mn>15</mml:mn> </mml:mrow> </mml:mmultiscripts> </mml:math> molecular ions in a Paul trap and extract them at an energy of 5.9 keV. Subsequently the ions are focused with a lateral resolution of 121(35) nm and are implanted into a diamond substrate without any spatial filtering by apertures or masks. After high-temperature annealing, we detect the NV centers in a confocal microscope and determine a conversion efficiency of about 0.6%. The 15 NV centers are characterized by optically detected magnetic resonance on the hyperfine transition and coherence time.

Tech Support

Original Source

DOI: https://doi.org/10.1088/1367-2630/ac0753