Designing a two-stage acceleration lens for a 100 keV single-ion implantation system

At a Glance

Metadata	Details
Publication Date	2025-09-25
Journal	The European Physical Journal Plus
Authors	Y. Ishii, Yosuke Yuri, Nobumasa Miyawaki, Shinobu Onoda, Kazumasa Narumi
Institutions	National Institutes for Quantum Science and Technology
Analysis	Full AI Review Included

Technical Documentation & Analysis: High-Precision Single-Ion Implantation Substrates

Reference Paper: Ishii et al., Designing a two-stage acceleration lens for a 100 keV single-ion implantation system, Eur. Phys. J. Plus (2025) 140:916.

Executive Summary

This research details the successful redesign of a two-stage acceleration lens critical for a 100 keV Single-Ion Implantation System (SIIS). The system is designed for the deterministic fabrication of Nitrogen-Vacancy (NV) center arrays in diamond, a foundational step for quantum device engineering.

Core Achievement: Successful design of a two-stage electrostatic lens achieving a focused beam width (FWHM) of 12.0 nm for 100 keV N⁺ ions.
Quantum Application: Enables deterministic, nanometer-scale implantation of single nitrogen ions into diamond to create high-yield NV center arrays.
Critical Specifications Met: The lens achieved a long Working Distance (WD) of 113.0 mm (target > 100 mm) to accommodate in-situ quantum effect detectors.
Material Requirement: The success of this SIIS relies entirely on the quality of the diamond substrate, requiring high-purity, low-defect Single Crystal Diamond (SCD) capable of supporting 100 keV implantation at a precise depth of 100 nm.
Design Methodology: Optimization was performed via numerical simulations (MUNRO and TriComp codes) to balance the inherent trade-off between beam width and working distance while avoiding collimators to ensure 100% transmittance.
6CCVD Value Proposition: 6CCVD provides the necessary Optical Grade SCD substrates, polished to Ra < 1 nm, ensuring the atomically flat surface required for nanometer-scale implantation accuracy.

Technical Specifications

The following hard data points define the performance targets and achieved results of the 100 keV SIIS lens configuration, directly impacting the requirements for the diamond substrate.

Parameter	Value	Unit	Context
Target Ion Species	N⁺	Ion	Nitrogen for NV center formation
Final Beam Energy	100	keV	Required for 100 nm penetration depth in diamond
Focused Beam Width (FWHM)	12.0	nm	Achieved final specification (< 50 nm target)
Working Distance (WD)	113.0	mm	Achieved final specification (> 100 mm target)
Ion Penetration Depth Target	100	nm	Required depth for optimal NV center quantum performance
1st Lens Applied Voltage	30.5	kV	Optimized voltage for WD control
2nd Lens Applied Voltage	69.5	kV	Optimized voltage for 100 keV acceleration
Voltage Stability (HVPS)	1 x 10^-6	V/V	Used in chromatic aberration calculations
2nd Lens Bore Diameter (B)	5	mm	Optimized parameter for long WD
Injected Beam Radius	0.54	µm	Input from LPTLC-IS

Key Methodologies

The two-stage acceleration lens (STAL) was designed using rigorous numerical analysis to meet the stringent requirements for deterministic single-ion implantation without using collimators.

Initial Conditions Setting: The injection beam energy was fixed at 5 keV (N⁺ ions) with an initial beam radius of 0.54 µm, based on the performance of the Linear Paul-Trap Laser-Cooling Ion Source (LPTLC-IS).
Simulation Tools: The MUNRO code was used for preliminary analysis of lens parameters, while the TriComp simulation code (field precision) was used for cross-checking the WD via finite element methods.
Aberration Modeling: Beam width ($\Phi_{f}$) calculations incorporated both spherical ($\Phi_{sp}$) and chromatic ($\Phi_{ch}$) aberrations, using the high voltage stability of the power supplies (1 x 10^-6 V/V) as the limiting factor for energy spread.
2nd Lens Optimization: The 2nd acceleration lens was the primary focus of redesign. Key parameters were systematically varied to optimize the WD and beam width simultaneously:
- Bore Diameter (B): Optimized to 5 mm.
- Electrode Distance (D): Optimized to 10 mm.
- Lens Separation (L): Optimized to 155 mm, resulting in the final WD of 113.0 mm.
Voltage Application: The final configuration utilized 30.5 kV on the 1st lens and 69.5 kV on the 2nd lens to achieve the 100 keV final energy and desired WD.

6CCVD Solutions & Capabilities

The successful implementation of this 100 keV SIIS for deterministic NV center fabrication requires diamond substrates of the highest quality and precision. 6CCVD is uniquely positioned to supply the necessary materials and customization services.

Applicable Materials for Quantum Implantation

Material Grade	Specification	Relevance to Research
Optical Grade Single Crystal Diamond (SCD)	Low-defect, high-purity (low N content), typically < 1 ppb N.	Essential host material for maximizing NV center coherence time and yield during deterministic implantation.
High-Purity Polycrystalline Diamond (PCD)	Wafers up to 125 mm diameter, high thermal conductivity.	Suitable for large-scale prototyping or applications where the SIIS is used for general high-power beam focusing or thermal management studies.

Customization Potential

The nanometer-scale precision of the SIIS demands perfect substrate preparation. 6CCVD’s in-house capabilities ensure the diamond material does not introduce additional error or scattering.

Ultra-Precision Polishing: Achieving a 12.0 nm beam width requires an atomically flat surface. 6CCVD guarantees SCD polishing to Ra < 1 nm and inch-size PCD polishing to Ra < 5 nm, minimizing surface roughness that could scatter the focused 100 keV ion beam.
Custom Dimensions and Thickness: We provide SCD plates and wafers in custom dimensions up to 125 mm (PCD) and thicknesses ranging from 0.1 µm to 500 µm (SCD/PCD), allowing precise integration into the SIIS vacuum chamber and detector setup.
Integrated Metalization: If the diamond substrate requires integrated electrodes, alignment marks, or heat sinks for the quantum effect detector, 6CCVD offers in-house metalization using Au, Pt, Pd, Ti, W, and Cu, applied with nanometer precision.

Engineering Support

6CCVD’s in-house PhD team offers specialized consultation to researchers working on deterministic single-ion implantation projects.

Material Selection for Quantum Applications: We assist in optimizing diamond properties, such as isotopic purity (e.g., ¹²C enrichment) and crystal orientation, which are critical for achieving long coherence times in fabricated NV center arrays.
Substrate Preparation: Consultation on surface termination (e.g., H-termination, O-termination) to optimize charge state control and minimize surface damage during 100 keV N⁺ implantation.
Global Logistics: We ensure reliable, fast global shipping (DDU default, DDP available) of sensitive 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 An array of color centers, each known as an NV center formed by a single-nitrogen atom and a vacancy, spaced at intervals of several tens of nanometers in a diamond exhibits quantum entanglement effects and indicates potential for quantum device applications. To fabricate such an array by implanting single-nitrogen ions into a diamond, a 100 keV single-ion implantation system (SIIS) has been developed by combining a linear Paul-trap laser-cooling ion source (LPTLC-IS) with a sympathetically cooled ion technique and a two-stage acceleration lens. So far, the LPTLC-IS and the two-stage acceleration lens have been refined as individual elemental technologies. However, for deterministic single-ion implantation, the SIIS must meet the following ion beam conditions: implantation with nanometer accuracy, a long working distance exceeding 100 mm to accommodate a quantum effect detector, and a penetration depth of approximately 100 nm in a diamond. These requirements necessitate the development of a two-stage acceleration lens capable of focusing the ion beam to a width of < 50 nm without a collimator when using a 100 keV ion beam. In this study, the two-stage acceleration lens, comprising 1st and 2nd acceleration lenses, was redesigned using numerical simulations to optimize lens parameters. Our primary redesign focus was the 2nd acceleration lens, which was redesigned based on the configuration of the previously developed lens. The resulting two-stage acceleration lens successfully met the target beam conditions for the SIIS.

Tech Support

Original Source

DOI: https://doi.org/10.1140/epjp/s13360-025-06750-x

References

1975 - Eric Munro: a set of computer programs for calculating the properties of electron lenses