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	Ghent University, Zhengzhou University
Citations	2
Analysis	Full AI Review Included

Executive Summary

This research investigates the realization of enhanced light extraction from single crystal diamond (SCD) using nanofabricated photonic structures and surface chemistry control targeting negatively charged nitrogen vacancies (NV^-).

Core Achievement: Successful top-down nanofabrication (nanopillars) on CVD-grown SCD containing naturally occurring NV^- centers to leverage the waveguiding effect for potential light extraction enhancement.
NV Center Source: NV^- centers were generated in situ during CVD growth; the diamond was neither implanted with ¹⁴N⁺ nor subjected to post-growth annealing.
Spin Manipulation Proof: Optically Detected Magnetic Resonance (ODMR) confirmed the characteristic 2.87 GHz spin transition of the NV^- center at room temperature.
Novel Treatment: A dedicated 0 V bias SF₆ ICP plasma was applied for surface fluorination, confirmed by X-ray Photoelectron Spectroscopy (XPS).
Unexpected Result: Contrary to expectations that fluorination stabilizes the NV^- charge state, the 0 V SF₆ plasma caused irreversible, selective deactivation (quenching) of the NV^- centers, resulting in a photoluminescence drop by an order of magnitude.
Deactivation Mechanism: The deactivation is attributed to the thermodynamic instability of the naturally generated NV^- centers combined with the strong electron-withdrawing effect of the halogenide surface termination.

Technical Specifications

Parameter	Value	Unit	Context
Diamond Material	Single Crystal Diamond (SCD)	N/A	Grown by Chemical Vapor Deposition (CVD)
Diamond Orientation	(400)	N/A	Confirmed by X-ray Diffraction (XRD)
NV Center Type	NV^-	N/A	Naturally grown-in, unannealed
NV^- ODMR Transition	2.87	GHz	Ground state m_s = ±1 → m_s = 0 cycling
ODMR Measurement Resolution	7	MHz	Actual area of interest for ODMR measurements
Excitation Laser Wavelength	519	nm	Continuous diode-pumped solid-state laser (DPSS)
PL Detection Filter	650	nm	Longpass filter applied for NV^- detection
Theoretical Optical Resolution	324	nm	Calculated using 0.8 NA objective and 519 nm laser
Plasma Bias Voltage (Fluorination)	0	V	Dedicated SF₆ ICP plasma treatment
Diamond Band Gap	5.5	eV	Intrinsic property of diamond
Raman Diamond Line	1332.25	cm^-1	Used to confirm lack of underetching (D-band splitting)
Microwave Frequency Range	2.700 to 3.100	GHz	Applied for spin manipulation (ODMR)

Key Methodologies

The experiment involved a precise top-down nanofabrication and surface modification sequence:

CVD Growth: Single crystal diamond was grown via CVD, incorporating nitrogen impurities that formed NV^- centers in situ during the high-temperature growth process.
Cleaning and Preparation: The SCD was subjected to standard acid cleaning (HNO₃, H₂SO₄, HClO₄).
Mask Deposition: A 25 nm thick polycrystalline silicon (Si) layer was evaporated as an adhesive layer, followed by spin-coating of FOX16 negative tone resist.
Electron Beam Lithography (EBL): EBL was used to write the nanopillar mask structures onto the resist layer.
Dry Etching (ICP-RIE): The structures were etched using a highly anisotropic pure oxygen (O₂) RIE/ICP plasma to create the nanopillars, preceded by a short SF₆ pulse.
Selective Fluorination: A novel 0 V bias SF₆ ICP plasma was applied to the etched diamond surface. A quartz plate was used to selectively shield certain areas, allowing quantification of the fluorination effect.
Mask Removal: The mask and adhesive layer were removed using wet chemical etching (HF-based buffered oxide etchant and 3M KOH bath).
Characterization: Photoluminescence (PL) spectroscopy and Optically Detected Magnetic Resonance (ODMR) were performed at room temperature to assess light extraction efficiency and spin coherence.

Commercial Applications

The technology developed in this study, focusing on nanofabricated diamond structures and NV^- center control, is critical for several high-tech sectors:

Quantum Sensing and Metrology:
- Products: High-sensitivity magnetometers, gyroscopes, and thermometers based on the NV^- spin state.
- Value Proposition: Diamond NV^- centers offer robust, room-temperature quantum sensing capabilities, essential for medical diagnostics (e.g., MRI contrast agents) and geological surveys.
Quantum Information Processing (QIP):
- Products: Solid-state qubits and single-photon emitters (SPEs).
- Value Proposition: Nanopillars act as photonic waveguides, significantly increasing the collection efficiency of single photons emitted by NV^- centers, a key requirement for scalable quantum networks and computing architectures.
Advanced Semiconductor Fabrication:
- Products: High-power electronic devices and UV detectors utilizing diamond’s wide bandgap.
- Value Proposition: The demonstrated EBL and highly anisotropic ICP-RIE techniques provide reliable methods for patterning diamond, overcoming challenges associated with its insulating properties and hardness.
Surface Chemistry Engineering:
- Products: Diamond surfaces with tailored electronic properties (e.g., p-type surface conductivity via termination).
- Value Proposition: Understanding the charge state switching induced by halogen termination (like fluorine) is crucial for controlling the stability and functionality of near-surface quantum defects in commercial devices.

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

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