Plasma Treatments and Light Extraction from Fluorinated CVD-Grown (400) Single Crystal Diamond Nanopillars

At a Glance

Metadata	Details
Publication Date	2020-06-03
Journal	C – Journal of Carbon Research
Authors	Mariusz Radtke, Abdallah Slablab, Sandra Van Vlierberghe, Chaonan Lin, Ying‐Jie Lu
Institutions	Zhengzhou University, Ghent University
Citations	2
Analysis	Full AI Review Included

Technical Documentation & Analysis: Plasma Treatments for Single Crystal Diamond Quantum Emitters

This document analyzes the research paper “Plasma Treatments and Light Extraction from Fluorinated CVD-Grown (400) Single Crystal Diamond Nanopillars” to provide technical specifications and align the findings with 6CCVD’s advanced MPCVD diamond capabilities.

Executive Summary

This research successfully demonstrates the integration of naturally grown-in Nitrogen Vacancy (NV^-) centers into Single Crystal Diamond (SCD) photonic nanostructures, a critical step for quantum sensing and photonics.

Core Achievement: Successful top-down nanofabrication of SCD nanopillars using Electron Beam Lithography (EBL) and Inductively Coupled Plasma/Reactive Ion Etching (ICP-RIE) to enhance light extraction.
Material Basis: High-quality, CVD-grown SCD plate (2.3 cm thick, (400) orientation) containing stable, naturally generated NV^- centers.
Quantum Control: Spin manipulation of the NV^- centers was confirmed via Optically Detected Magnetic Resonance (ODMR) at the characteristic 2.87 GHz transition frequency at room temperature.
Surface Termination Study: Investigation into 0 V bias SF₆ plasma fluorination, intended to stabilize the NV^- charge state, yielded the surprising result of selective, irreversible deactivation (NV^- switching to the optically dormant NV⁰ state).
Deactivation Mechanism: The deactivation is attributed to thermodynamic instability of the unannealed NV centers combined with strain induced by heavy SF₆ plasma ions, causing a charge state switch facilitated by the electron-withdrawing effect of fluorine.
6CCVD Relevance: The project highlights the need for ultra-high-purity, precisely oriented SCD substrates and advanced post-processing control, areas where 6CCVD offers industry-leading customization and material engineering support.

Technical Specifications

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

Parameter	Value	Unit	Context
Diamond Material	Single Crystal Diamond (SCD)	N/A	Grown via Chemical Vapor Deposition (CVD).
Substrate Thickness	2.3	cm	Thickness of the CVD-grown diamond plate used.
Crystal Orientation	(400)	N/A	Confirmed by X-ray Diffraction (XRD) peak at 119.8°.
NV Center Type	Naturally Grown-In NV^-	N/A	No ¹⁴N⁺ implantation or post-growth annealing performed.
Excitation Wavelength	519	nm	Continuous diode-pumped solid-state laser (DPSS) used for PL/ODMR.
NV^- Zero Phonon Line (ZPL)	637	nm	Purely electronic transition observed in PL spectrum.
ODMR Transition Frequency	2.87	GHz	Characteristic frequency for the $m_s = \pm 1 \rightarrow m_s = 0$ cycling transition.
ODMR Frequency Range	2.700 to 3.100	GHz	Range used for optically detected magnetic resonance acquisition.
Plasma Chemistry (Fluorination)	SF₆	N/A	Used at 0 V bias for surface termination.
Microscope Numerical Aperture (NA)	0.8	N/A	Used in custom-built confocal microscope setup.
Surface Polishing Requirement	Ra < 5	nm	Required for successful EBL/RIE nanofabrication (implied by methodology).

Key Methodologies

The experiment involved a multi-step process combining advanced material growth, nanofabrication, and quantum characterization:

CVD Diamond Growth: SCD was grown via CVD, generating naturally occurring nitrogen vacancies (NV^-) in-situ during the growth process without subsequent high-temperature annealing.
Nanofabrication Mask Preparation:
- A 25 nm thick polycrystalline silicon layer was evaporated onto the SCD surface to serve as an adhesive layer.
- Negative tone resist (FOX16) was spin-coated onto the silicon layer.
Patterning: Electron Beam Lithography (EBL) was used to write the mask structures defining the nanopillars.
Dry Etching (ICP-RIE):
- A short SF₆ pulse was applied, followed by highly anisotropic pure oxygen RIE/ICP plasma etching to create the light-focusing nanopillars.
Mask Removal and Cleaning: Wet chemical etching (HF-based buffered oxide etchant, 3M KOH bath) and subsequent acid cleaning (1:1:1 HNO₃, H₂SO₄, HClO₄) were performed.
Surface Fluorination: A dedicated 0 V bias SF₆ ICP plasma was used to fluorinate the diamond surface, targeting NV^- charge state stabilization.
Characterization: Photoluminescence (PL) spectroscopy and Optically Detected Magnetic Resonance (ODMR) were performed at room temperature using a 519 nm laser and microwave control (20 µm thick gold wire).

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the high-specification diamond materials and custom engineering services required to replicate, optimize, and extend this research into scalable quantum devices.

Applicable Materials

To achieve the high-fidelity quantum control and nanofabrication success demonstrated in this paper, researchers require materials with exceptional purity and precise crystallographic control.

Optical Grade Single Crystal Diamond (SCD): 6CCVD offers high-purity SCD wafers, essential for minimizing background noise and maximizing the coherence time of NV centers.
Custom Crystal Orientation: The paper utilized a (400) orientation. 6CCVD routinely supplies SCD plates with precise (100) and (111) orientations, and can provide custom (400) oriented substrates necessary for optimizing light extraction and NV alignment in photonic structures.
Controlled Nitrogen Doping: While the paper used naturally grown-in NV centers, 6CCVD can supply SCD with controlled nitrogen concentrations (Type Ib) to optimize NV density for high-yield quantum emitter arrays.

Customization Potential

The nanofabrication and characterization steps demand specific material preparation that aligns perfectly with 6CCVD’s core capabilities:

Research Requirement	6CCVD Customization Service	Value Proposition
Ultra-Smooth Surface Finish	Precision Polishing: SCD wafers polished to Ra < 1 nm.	Ensures compatibility with high-resolution Electron Beam Lithography (EBL) and minimizes scattering losses in etched nanopillars.
Integrated Microwave Structures	Custom Metalization: Internal capability to deposit thin films of Au, Pt, Ti, W, or Cu.	Allows researchers to integrate high-performance microwave striplines directly onto the diamond surface, replacing external wires and improving ODMR signal fidelity.
Custom Dimensions & Thickness	Large Area Substrates: SCD plates available up to 500 µm thick; PCD plates up to 125 mm diameter. Substrates up to 10 mm thick.	Provides flexibility for scaling up photonic arrays or integrating diamond into complex device architectures.
Nanofabrication Support	Laser Cutting and Shaping: Precise laser cutting services for creating custom shapes and dimensions compatible with RIE/ICP tools.	Delivers ready-to-use substrates optimized for specific nanofabrication processes.

Engineering Support

The unexpected deactivation of NV^- centers upon SF₆ plasma fluorination highlights the complexity of diamond surface chemistry and defect engineering.

Defect Engineering Consultation: 6CCVD’s in-house PhD team specializes in the thermodynamics and kinetics of diamond defect formation. We can assist researchers in designing optimized CVD growth recipes and post-growth annealing protocols to maximize the stability and yield of the desired NV^- charge state, mitigating the thermodynamic instability observed in this study.
Surface Termination Optimization: We offer consultation on alternative surface terminations (e.g., controlled oxygen or hydrogen termination) and plasma chemistries to achieve charge state stabilization without inducing the physical strain and irreversible deactivation caused by heavy SF₆ ions.

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

View Original Abstract

We investigate the possibilities to realize light extraction from single crystal diamond (SCD) nanopillars. This was achieved by dedicated 519 nm laser-induced spin-state initiation of negatively charged nitrogen vacancies (NV−). We focus on the naturally-generated by chemical vapor deposition (CVD) growth of NV−. Applied diamond was neither implanted with 14N+, nor was the CVD synthesized SCD annealed. To investigate the possibility of light extraction by the utilization of NV−’s bright photoluminescence at room temperature and ambient conditions with the waveguiding effect, we have performed a top-down nanofabrication of SCD by electron beam lithography (EBL) and dry inductively-coupled plasma/reactive ion etching (ICP-RIE) to generate light focusing nanopillars. In addition, we have fluorinated the diamond’s surface by dedicated 0 V SF6 ICP plasma. Light extraction and spin manipulations were performed with photoluminescence (PL) spectroscopy and optically detected magnetic resonance (ODMR) at room temperature. We have observed a remarkable effect based on the selective 0 V SF6 plasma etching and surprisingly, in contrast to literature findings, deactivation of NV− centers. We discuss the possible deactivation mechanism in detail.

Tech Support

Original Source

DOI: https://doi.org/10.3390/c6020037

References

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2014 - Magnetical and Optical Properties of Nanodiamonds Can Be Tuned by Particles Surface Chemistry: Theoretical and Experimental Study [Crossref]
2019 - Ab initio theory of the nitrogen-vacancy center in diamond [Crossref]
2019 - Nanoscale sensing based on nitrogen vacancy centers in single crystal diamond and nanodiamonds: Achievements and challenges [Crossref]