Resolution enhancement methods in optical microscopy for dimensional optical metrology

At a Glance

Metadata	Details
Publication Date	2025-01-01
Journal	Journal of the European Optical Society Rapid Publications
Authors	Bernd Bodermann, Mohammad Nouri, P. Olivero, Stefanie Kroker, Ivano Ruo Berchera
Citations	1
Analysis	Full AI Review Included

Resolution Enhancement Methods in Optical Metrology: Leveraging MPCVD Diamond for Super-Resolution Standards

Executive Summary

This technical documentation analyzes the research on resolution enhancement methods for dimensional optical nanometrology, focusing specifically on the application of Nitrogen-Vacancy (NV) centers embedded in artificial diamond substrates for Stimulated Emission Depletion (STED) microscopy.

Core Application: The research validates the use of NV centers in artificial diamond as stable, inorganic labels for Super-Resolution Microscopy (SRM), specifically STED, suitable for quantitative dimensional nanometrology.
Material Validation: Artificial diamond substrates (3 x 3 x 0.5 mm³) were successfully processed using 2 MeV proton irradiation and high-temperature annealing (800 °C) to create uniformly distributed NV centers.
Performance: STED mode provided superior contrast and resolution at feature borders compared to conventional confocal microscopy, resolving cross-shaped patterns with a width of 2.1 µm.
WISER Achievement: Wide-field Imaging with Super-resolution Enabled by Raman Scattering (WISER) achieved a 1.6x resolution improvement compared to the diffraction limit, demonstrating the potential of label-free techniques on carbon materials.
Critical Need: The paper highlights the immediate need for high-quality, traceable reference standards, including low-density NV-center samples for Point Spread Function (PSF) characterization and high-density, patterned substrates for metrology calibration.
6CCVD Value: 6CCVD is positioned to supply the necessary high-purity Single Crystal Diamond (SCD) substrates, custom dimensions, ultra-low roughness polishing (Ra < 1 nm), and integrated metalization required to manufacture these advanced optical standards.

Technical Specifications

The following hard data points were extracted regarding the materials, processing, and performance metrics relevant to the diamond substrate and super-resolution techniques:

Parameter	Value	Unit	Context
Diamond Substrate Dimensions	3 x 3 x 0.5	mm³	Artificial diamond sample used for STED
Nanocrystal Median Size (Small)	125	nm	NDs used for NV center enhancement
Proton Irradiation Energy (H+)	2	MeV	Ion beam used to create vacancies
Proton Irradiation Fluence	2 x 10¹⁶	cm^-2	Optimal fluence for NV concentration
Annealing Temperature (N₂)	800	°C	Promotes NV center formation
Oxidation Temperature (Air)	500	°C	Surface purification/graphitic layer removal
Excitation Wavelength (STED)	561	nm	Pulsed laser for excitation
STED Depletion Wavelength	775	nm	Pulsed laser for saturation depletion
Objective Numerical Aperture (NA)	1.4	-	Oil-immersion objective used for STED
NV⁰ Zero-Phonon Line (ZPL)	575	nm	Neutral charge state emission peak
NV^- Zero-Phonon Line (ZPL)	637	nm	Negative charge state emission peak
WISER Resolution Improvement	1.6	times	Improvement over diffraction limit
STED Feature Resolution (Case II)	2.1	µm	Width of cross-shaped pattern resolved

Key Methodologies

The preparation of the artificial diamond substrates with embedded NV centers involved precise, multi-step processing to optimize photoluminescence properties for STED microscopy:

Sample Acquisition: Diamond nanocrystals (NDs) with median sizes of 125 nm and 180 nm were acquired (Pureon® MSY 0-0.25 and 0-0.35).
Dispersion and Deposition: NDs were dispersed in isopropanol, sonicated, and drop-casted onto a silicon wafer substrate (0.5 x 0.5 cm²) to form a layer approximately 30 ± 10 µm thick.
Vacancy Creation: Proton (H+) irradiation was performed using a 2 MeV ion beam at a fluence of 2 x 10¹⁶ cm^-2 to introduce additional vacancies into the diamond lattice.
NV Center Formation (Annealing): High-temperature thermal annealing was conducted at 800 °C for 2 hours in N₂ flow, allowing the generated vacancies to couple with naturally present Nitrogen (N) impurities.
Surface Purification (Oxidation): Thermal oxidation was performed at 500 °C for 8 hours in an air environment to remove surface quenching phases (disordered sp²/sp³ carbon) and enhance photoluminescence stability.
Optical Characterization: Photoluminescence (PL) spectra were measured to confirm uniform NV center distribution and spectral resolution (peaks at 575 nm and 637 nm).
SRM Imaging: Fabricated patterns were imaged using a STED microscopy system equipped with 561 nm (excitation) and 775 nm (depletion) pulsed lasers and a vortex phase plate to generate the required donut-shaped beam.

6CCVD Solutions & Capabilities

The research demonstrates that high-quality diamond substrates are essential for developing next-generation optical metrology standards based on NV centers and label-free SRM techniques. 6CCVD is uniquely positioned to supply the foundational materials and precision fabrication services required to replicate and advance this work.

Applicable Materials

To achieve the high crystalline quality and stability required for NV center creation and high-power laser compatibility, the following 6CCVD materials are recommended:

Optical Grade Single Crystal Diamond (SCD): Provides the lowest defect density and highest purity, ensuring maximum stability and optimal NV center formation efficiency via post-processing (irradiation/annealing).
High-Purity Polycrystalline Diamond (PCD): For large-area metrology standards (up to 125 mm diameter) where the highest resolution is not strictly required, PCD offers cost-effective, large-format substrates compatible with high-power optical systems.
Boron-Doped Diamond (BDD): While not the focus of this paper, BDD substrates are available for researchers exploring alternative label-free SRM methods, such as those exploiting plasma dispersion effects in silicon-based nanostructures.

Customization Potential

The paper explicitly calls for tailored reference standards (Figure 17) and custom substrate dimensions. 6CCVD’s in-house capabilities directly address these needs:

Research Requirement	6CCVD Customization Service
Custom Substrate Dimensions: Need for specific sizes (e.g., 3 x 3 x 0.5 mm³) for system integration.	Precision Fabrication: We supply custom plates and wafers up to 125 mm (PCD) and substrates up to 10 mm thick, cut to precise dimensions using advanced laser processing.
Ultra-Low Surface Roughness: Required for high-fidelity optical measurements (TFM, STED) to minimize scattering.	Advanced Polishing: We guarantee ultra-smooth surfaces: Ra < 1 nm for SCD and Ra < 5 nm for inch-size PCD, ensuring compatibility with high-NA oil-immersion objectives.
Plasmonic SRM Integration: Need for metalized patterns (e.g., Ti/Pt/Au) for techniques like SUSI and SAX.	Integrated Metalization: 6CCVD offers internal deposition of Au, Pt, Pd, Ti, W, and Cu layers, enabling the fabrication of complex plasmonic nanostructures directly onto the diamond surface.
Calibration Standards: Need for patterned structures (line pairs, dots) for traceable resolution assessment.	Lithography Support: We provide engineering consultation and support for defining and fabricating custom patterns on diamond surfaces, essential for creating traceable SRM reference standards.

Engineering Support

6CCVD’s in-house PhD team specializes in the growth and characterization of MPCVD diamond materials. We offer expert consultation to assist researchers in:

Material Selection: Optimizing the SCD grade (e.g., nitrogen concentration, defect density) to maximize the yield and homogeneity of NV centers during post-processing (H+ irradiation and annealing).
Thermal Management: Providing diamond substrates with superior thermal conductivity, which is crucial for applications involving high STED laser power (up to 3 W pulsed) to prevent sample damage and maintain measurement stability.
Integration: Assisting with the design and fabrication of diamond components for integration into complex optical setups, such as STED microscopy systems.

Call to Action: For custom specifications or material consultation regarding NV center substrates, label-free SRM, or dimensional nanometrology projects, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

In this paper, we discuss several enhancement approaches to increase the resolution and sensitivity of optical microscopy as a tool for dimensional nanometrology. Firstly, we discuss a newly developed through-focus microscopy technique providing additional phase information from the afocal images to increase the nanoscale sensitivity of classical microscopy. We also explore different routes to label-free or semiconductor compatible labelling super-resolution microscopy suitable for a broad range of technical applications. We present initial results from, a new wide-field super-resolution imaging technique enabled by Raman scattering. In addition, we discuss super-resolution imaging using NV centres in nano-diamonds as labels and their application in future reference standards.

Tech Support

Original Source

DOI: https://doi.org/10.1051/jeos/2025002