Single-Crystal Diamond Needle Fabrication Using Hot-Filament Chemical Vapor Deposition

At a Glance

Metadata	Details
Publication Date	2021-04-29
Journal	Materials
Authors	Р. Р. Исмагилов, Sergei Malykhin, Aleksey P. Puzyr, А. Б. Логинов, Victor I. Kleshch
Institutions	Institute of Biophysics, University of Eastern Finland
Citations	21
Analysis	Full AI Review Included

Technical Documentation & Analysis: Single-Crystal Diamond Needle Fabrication

Executive Summary

This research successfully demonstrates a scalable, large-area method for fabricating single-crystal diamond (SCD) needles using Hot-Filament Chemical Vapor Deposition (HF CVD) combined with selective thermal oxidation. This approach offers significant advantages for industrial and quantum applications:

Scalable Production: HF CVD enables deposition on areas up to 3000 cm², far exceeding the typical limits of plasma-enhanced CVD (PE CVD) systems (up to 100 cm²).
High-Quality Morphology: The resulting SCD crystallites are perfect pyramids with sharp apexes and smooth {100} basal planes, ideal for field emission and sensing applications.
Quantum Defect Integration: Successful, albeit uncontrolled, incorporation and activation of critical quantum defects, specifically the Silicon-Vacancy (SiV^-) center (738 nm ZPL) and Nitrogen-Vacancy (NV) centers.
Process Control Advantage: The relatively low growth rate (~500 nm/h) facilitates fine-tuning of process parameters, crucial for precise control over impurity introduction and structural modifications.
Selective Purification: Thermal oxidation at 580 °C effectively removes the non-diamond carbon matrix, isolating the high-quality SCD needles and significantly enhancing the collection efficiency of the SiV quantum signal.

Technical Specifications

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

Parameter	Value	Unit	Context
Filament Temperature	~2300	°C	Hot-Filament CVD (W filaments)
Substrate Temperature Range	740 to 800	°C	Gradient across the stair-like quartz holder
CVD Pressure	5.5	Torr	Operating pressure of gas mixture
Methane Concentration	2.7	%	CH₄ in H₂ gas mixture
Total Gas Flow Rate	822	sccm	H₂/CH₄ flow
Growth Duration	~8	h	CVD deposition time
Thermal Oxidation Temperature	580	°C	Selective removal of non-diamond carbon matrix
Thermal Oxidation Duration	22	h	Performed in air at normal pressure
Typical Needle Growth Rate	~500	nm/h	Estimated via film thickness (low rate for fine-tuning)
SiV Zero-Phonon Line (ZPL)	738	nm	Negatively charged Silicon-Vacancy center
Diamond Raman Peak	1331	cm^-1	First-order diamond line
Maximum Deposition Area Potential	~3000	cm²	Potential area of the HF CVD setup used

Key Methodologies

The fabrication of single-crystal diamond needles involved a two-step process combining HF CVD growth and post-growth purification:

Substrate Preparation and Seeding:
- Mirror-polished Si (100) substrates (20 x 20 mm², 0.5 mm thickness) were cleaned in ethanol.
- Substrates were seeded using an ethanol suspension of detonation nanodiamonds (DND) to promote nucleation.
- Seeded substrates were dried using a spin drier at 1000 rpm for 1 minute.
Hot-Filament CVD Growth:
- Growth was performed in an HF CVD reactor equipped with 31 straight tungsten filaments (Ø 0.127 mm).
- Filament temperature was maintained at approximately 2300 °C.
- Substrates were placed on a stair-like quartz holder, resulting in a substrate temperature gradient between 740 °C and 800 °C.
- The gas mixture was 2.7% CH₄ in H₂, maintained at 5.5 Torr pressure and 822 sccm total flow rate.
- Growth duration was 8 hours, resulting in polycrystalline films containing embedded single-crystal pyramids.
Selective Thermal Oxidation:
- As-grown films were heated in a tube oven in air at normal atmospheric pressure.
- The oxidation parameters were fixed at 580 °C for 22 hours.
- This process selectively gasified and removed the disordered carbon material (amorphous, graphitic, and nanodiamond matrix), leaving behind free-standing SCD needles.
Characterization:
- Morphology was confirmed using Scanning Electron Microscopy (SEM).
- Structural quality and purification were monitored via Raman spectroscopy (1331 cm^-1 diamond peak).
- Quantum defect presence was confirmed using Photoluminescence (PL) spectroscopy (738 nm SiV^- ZPL).

6CCVD Solutions & Capabilities

The successful replication and advancement of this research—particularly in achieving controlled quantum defect incorporation and maximizing scalability—requires high-precision CVD materials and engineering support. 6CCVD is uniquely positioned to supply the necessary components.

Applicable Materials

To replicate or extend this research, especially concerning quantum applications, researchers require high-purity diamond with controlled doping:

Optical Grade SCD: For applications requiring the highest structural quality and lowest intrinsic defect density, 6CCVD offers Single Crystal Diamond (SCD) wafers up to 500 µm thick, providing an ideal foundation for subsequent needle growth or direct device integration.
Custom Doped SCD (Si/N/B): The paper noted that SiV and NV centers were incorporated via uncontrolled etching of the Si substrate and quartz holder. 6CCVD offers precise, controlled doping during the MPCVD process, allowing for:
- Controlled SiV Creation: Direct introduction of silicon precursors to achieve homogeneous or spatially localized SiV^- centers, eliminating reliance on substrate etching.
- Controlled NV Creation: Nitrogen doping for high-density NV centers, critical for magnetic sensing and quantum memory applications.
Polycrystalline Diamond (PCD) Substrates: For maximizing the large-area potential demonstrated by HF CVD, 6CCVD supplies large-format PCD plates up to 125 mm in diameter, suitable for high-throughput industrial processes.

Customization Potential

The research highlights the need for precise dimensional control and integration capabilities. 6CCVD’s in-house services directly address these requirements:

Research Requirement	6CCVD Customization Service	Technical Benefit
Large-Scale Substrates: Need for deposition areas far > 100 cm².	Custom Dimensions: Plates/wafers available up to 125 mm (PCD) and custom-sized SCD substrates (up to 10 mm thickness).	Facilitates the industrial scaling and mass production of diamond needle arrays.
Surface Quality: Need for smooth basal planes for controlled growth.	Precision Polishing: SCD surfaces polished to ultra-low roughness (Ra < 1 nm); Inch-size PCD polished to Ra < 5 nm.	Ensures optimal nucleation control and minimizes surface defects that interfere with quantum coherence.
Device Integration: Future devices (e.g., field emitters) require electrical contacts.	Custom Metalization: Internal capability for depositing standard and exotic metals (Au, Pt, Pd, Ti, W, Cu).	Allows for rapid prototyping and functionalization of diamond needle arrays into integrated electronic or quantum devices.
Thickness Control: Needle length depends on CVD duration (0.1 µm to several µm).	Precise Thickness Control: SCD and PCD films available from 0.1 µm up to 500 µm, allowing researchers to define the exact film thickness required for specific needle lengths.	Enables fine-tuning of crystallite length for optimized performance in sensing or field emission applications.

Engineering Support

The challenges faced in this paper—specifically the uncontrolled introduction of silicon impurities via quartz/substrate etching—underscore the complexity of CVD diamond growth for quantum applications.

6CCVD’s in-house PhD engineering team specializes in optimizing MPCVD recipes for advanced applications. We offer consultation and support for similar Quantum Sensing and Field Emission projects, focusing on:

Precursor Optimization: Designing gas chemistries to ensure controlled, homogeneous doping of Si and N, eliminating reliance on reactor component etching.
Process Transfer: Assisting clients in transferring lab-scale recipes to large-area, high-throughput production using our scalable SCD and PCD substrates.
Defect Engineering: Providing expertise in post-growth annealing and surface termination techniques to maximize the stability and coherence of SiV and NV centers.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly. We ship globally (DDU default, DDP available).

View Original Abstract

Single-crystal diamonds in the form of micrometer-scale pyramids were produced using a combination of hot-filament (HF) chemical vapor deposition (CVD) and thermal oxidation processes. The diamond pyramids were compared here with similar ones that were manufactured using plasma-enhanced (PE) CVD. The similarities revealed in the morphology, Raman, and photoluminescent characteristics of the needles obtained using the hot-filament and plasma-enhanced CVD are discussed in connection with the diamond film growth mechanism. This work demonstrated that the HF CVD method has convincing potential for the fabrication of single-crystal diamond needles in the form of regularly shaped pyramids on a large surface area, even on non-conducting substrates. The experimental results demonstrated the ability for the mass production of the single-crystal needle-like diamonds, which is important for their practical application.

Tech Support

Original Source

DOI: https://doi.org/10.3390/ma14092320

References

2006 - Processing quantum information in diamond [Crossref]
2017 - Submillihertz magnetic spectroscopy performed with a nanoscale quantum sensor [Crossref]
2018 - A 4.5 μm PIN diamond diode for detecting slow neutrons [Crossref]
2018 - Determination of minority carrier lifetime of holes in diamond p-i-n diodes using reverse recovery method [Crossref]
2018 - Material platforms for spin-based photonic quantum technologies [Crossref]
2010 - Thermal oxidation of CVD diamond [Crossref]