Structural, Raman and photoluminescence studies on nanocrystalline diamond films - Effects of ammonia in feedstock

At a Glance

Metadata	Details
Publication Date	2020-04-17
Journal	Diamond and Related Materials
Authors	K. Ganesan, P.K. Ajikumar, S.K. Srivastava, P. Magudapathy
Institutions	Indira Gandhi Centre for Atomic Research
Citations	20
Analysis	Full AI Review Included

Technical Documentation & Analysis: Optimized N-Doped Nanocrystalline Diamond for Optical Sensing

Executive Summary

This research successfully demonstrates the optimization of nitrogen doping in Nanocrystalline Diamond (NCD) films to enhance structural quality and photoluminescence (PL) emission, directly supporting applications in radiation detection.

Optimal Doping Identified: The highest structural quality (largest crystallite size, lowest XRD FWHM) and maximum PL enhancement were achieved at an optimal feedstock N/C ratio of 0.35.
Structural Quality Control: Addition of NH₃ significantly reduced the amorphous carbon background observed in undoped films, improving overall material quality.
Compressive Strain Management: Raman analysis confirmed that N-doped NCD films exhibit compressive strain, which increases monotonically up to an N/C ratio of 0.50.
Defect Engineering: A unique Raman mode at 1195 cm^-1 confirms significant nitrogen incorporation via C=N-H bonding, crucial for defect formation.
Enhanced Optical Emission: Optimal doping drastically increased room temperature PL intensity at two key wavelengths: ~505 nm (attributed to H3 centers, N-V-N) and ~700 nm (attributed to N-aggregate defects).
Target Application: The resulting N-doped NCD films, combining enhanced PL with diamond’s inherent radiation hardness, are highly suitable for luminescence-based radiation detectors operating in extreme environments.

Technical Specifications

Parameter	Value	Unit	Context
Synthesis Method	HFCVD	N/A	Hot Filament Chemical Vapor Deposition
Substrate Material	Si (111)	N/A	Chemo-mechanically polished prior to growth
Substrate Temperature	800	°C	Constant temperature maintained during synthesis
Operating Pressure	30	mbar	Fixed process parameter
Optimal N/C Ratio (Feedstock)	0.35	N/C ratio	Yielded optimal structural quality (N35 sample)
Maximum Crystallite Size	16.3	nm	Achieved at N/C = 0.35
Film Thickness Range	1.1 - 2.7	µm	Measured by SEM
Characteristic Raman Mode	1195	cm^-1	Corresponds to C=N-H vibrations
Optimal PL Emission (UV Excitation)	~505	nm	H3 color center (N-V-N), 355 nm laser excitation
Optimal PL Emission (Visible Excitation)	~700	nm	N-aggregate defects, 532 nm laser excitation
Compressive Strain Trend	Monotonic Increase	N/C ratio	Observed up to N/C ratio of 0.50

Key Methodologies

The nanocrystalline diamond films were synthesized using a custom Hot Filament Chemical Vapor Deposition (HFCVD) system under controlled conditions:

Substrate Preparation: Si (111) wafers were prepared by chemo-mechanical polishing using micron-level diamond paste.
Gas Feedstock: Undoped and N-doped NCD films were grown using mixtures of CH₄, H₂, and NH₃. The nominal N/C ratio in the feedstock was systematically varied (0, 0.13, 0.35, 0.50, and 0.75).
Process Environment: The operating pressure was maintained constant at 30 mbar.
Thermal Control: Substrate temperature was held constant at 800 °C using an additional resistive heater.
Growth Duration: All growth experiments were conducted for a fixed duration of 6 hours to ensure consistency and avoid instrumental parameter variation.
Characterization: Films were analyzed using X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and micro-Raman/Photoluminescence (PL) spectroscopy utilizing 355 nm (UV) and 532 nm (visible) diode lasers.

6CCVD Solutions & Capabilities

The research demonstrates the critical role of precise nitrogen doping in Nanocrystalline Diamond (NCD) for advanced optical applications, specifically luminescence-based radiation detection. 6CCVD specializes in providing high-quality, custom-engineered diamond materials via Microwave Plasma CVD (MPCVD), offering superior purity and scalability compared to the HFCVD method used in this study.

Applicable Materials

To replicate or extend this research, 6CCVD recommends the following materials, optimized for controlled defect incorporation and high optical performance:

Optical Grade Polycrystalline Diamond (PCD): Ideal for NCD/UNCD applications requiring large area coverage (up to 125mm wafers) with controlled grain boundaries and high sp² content management.
Nitrogen-Doped PCD: We offer precise nitrogen incorporation during MPCVD growth to stabilize specific color centers (like the H3 center, N-V-N) necessary for the enhanced PL emission observed at 505 nm and 700 nm.

Customization Potential

6CCVD’s advanced MPCVD platform and post-processing capabilities directly address the specific requirements of NCD film development:

Research Requirement	6CCVD Customization Capability	Benefit to Client
Thickness Control (1.1 - 2.7 µm films)	Custom PCD thickness from 0.1 µm to 500 µm.	Allows engineers to specify exact film depth for optimal X-ray penetration and detector efficiency.
Large Area Substrates (Scalability)	PCD plates/wafers up to 125 mm diameter.	Enables scalable production of large-area radiation detectors, moving beyond lab-scale HFCVD samples.
Surface Finish (Optical Coupling)	Polishing services achieving Ra < 5 nm on inch-size PCD.	Minimizes surface scattering and absorption, crucial for maximizing PL signal collection in optical sensors.
Defect Engineering (N-V-N, H3 Centers)	Precise gas flow control in MPCVD for controlled N-doping profiles.	Ensures reproducible creation of specific N-related color centers, guaranteeing consistent optical output (PL intensity and wavelength).
Substrate Compatibility	Ability to grow on various substrates (Si, Mo, etc.) or provide free-standing diamond.	Offers flexibility for integration into complex device architectures, including MEMS or high-power electronics.

Engineering Support

The successful development of luminescence-based radiation detectors requires precise control over defect chemistry and structural quality. 6CCVD’s in-house PhD team specializes in:

Dopant Optimization: Assisting researchers in translating HFCVD N/C ratios to optimized MPCVD recipes for superior material purity and defect concentration control.
Optical Characterization: Providing consultation on material selection to maximize specific color center yields (e.g., H3, NV^-, SiV^-) for targeted emission wavelengths (380-700 nm range).
Radiation Hardness Design: Supporting the design of diamond components for extreme environments, leveraging the inherent radiation hardness of our SCD and PCD materials.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly. Global shipping (DDU default, DDP available) ensures rapid delivery of your custom diamond solutions.

Tech Support

Original Source

DOI: https://doi.org/10.1016/j.diamond.2020.107872

References

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