Improvement of morphology and electrical properties of boron-doped diamond films via seeding with HPHT nanodiamonds synthesized from 9-borabicyclononane

At a Glance

Metadata	Details
Publication Date	2025-02-19
Journal	Diamond and Related Materials
Authors	Štěpán Stehlík, Štěpán Potocký, Kateřina Aubrechtová Dragounová, Petr Bělský, Rostislav Medlín
Citations	3
Analysis	Full AI Review Included

Technical Documentation & Analysis: High-Quality Boron-Doped Diamond Films

Executive Summary

This research successfully demonstrates that the quality of nanodiamond (ND) seeding material is the dominant factor determining the morphology and electrical performance of Boron-Doped Diamond (BDD) films grown by Microwave Plasma-Enhanced Chemical Vapor Deposition (MPCVD).

Core Achievement: Novel HPHT-synthesized, hydrogenated Boron-Doped Nanodiamonds (H-BND) were used as a seeding layer, resulting in BDD films with superior crystal quality and electrical properties compared to conventional Detonation ND (H-DND) and Top-Down HPHT ND (TD_HPHT H-ND).
Performance Metric: BDD films grown on H-BND exhibited the lowest sheet resistance (440 ohm/sq), correlating directly with the lowest defect concentration and largest crystal size (up to 1000 nm).
Material Mechanism: The superior performance is attributed to the H-BND’s monocrystalline character, uniform particle shape, and narrow size distribution, which promotes highly ordered homoepitaxial growth.
Seeding Control: Thermal hydrogenation successfully reversed the zeta potential of the BNDs from negative (-32 mV) to positive (+44 mV), enabling dense, uniform electrostatic seeding on negatively charged substrates (Si/SiO₂).
Growth Consistency: Despite variations in initial seeding coverage (13% to 25%), all ND types facilitated the growth of fully closed BDD films approximately 1 µm thick, confirming seed quality, not just density, is critical.
Application Potential: These findings establish H-BND as a promising material for growing high-quality BDD films essential for advanced electronic devices and high-performance electrochemical electrodes.

Technical Specifications

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

Parameter	Value	Unit	Context
B/C Ratio (Gas Phase)	5000	ppm	CVD growth parameter (Trimethylboron, TMB)
Substrate Temperature	~500	°C	MPCVD growth temperature
Chamber Pressure	8	kPa (60 Torr)	MPCVD growth pressure
CVD Growth Time	1	h	Time required to achieve ~1 µm film thickness
Final BDD Film Thickness	~1	µm	Thickness of fully closed BDD films
Lowest Sheet Resistance (R_s)	440	ohm/sq	Achieved using H-BND seeding (Hydrogenated surface)
Highest Sheet Resistance (R_s)	~20	KΩ/sq	Achieved using H-DND seeding (Hydrogenated surface)
Largest Crystal Size (H-BND)	500-1000	nm	Observed via SEM analysis
O-BND Zeta Potential	-32	mV	Oxidized BND colloidal dispersion (mildly acidic pH 4-5)
H-BND Zeta Potential	+44	mV	Hydrogenated BND colloidal dispersion (pH 5-6)
H-BND Particle Size (R_g)	1.3	nm	Gyration radius (SAXS analysis)
H-BND Surface Coverage	24	%	Seeding layer density on Si/SiO_x

Key Methodologies

The high-quality BDD films were produced using a tightly controlled MPCVD process combined with novel nanodiamond seeding preparation:

BND Synthesis: Boron-doped nanodiamonds (BND) were synthesized using the High-Pressure High-Temperature (HPHT) method from a 9-Borabicyclo[3,3,1]nonane dimer (9BBN) precursor at 8.5-9 GPa and 1250 °C.
Oxidation and Purification: The synthesized powder was cleaned by boiling in a 3:1 mixture of sulfuric and nitric acids for 6 hours, yielding oxidized BND (O-BND) with minimal sp²-C content.
Hydrogenation: O-BND powder was thermally annealed in a tube furnace under atmospheric hydrogen pressure at 700 °C for 3 hours to achieve hydrogen termination (H-BND) and reverse the zeta potential.
Substrate Preparation: Si(100) and fused SiO₂ substrates were cleaned using standard ultrasonic baths (acetone, isopropyl alcohol, DI water).
Seeding Layer Deposition: Substrates were immersed in the H-ND colloidal solutions (H-BND, H-DND, TD_HPHT H-ND) and sonicated for 10 minutes to achieve electrostatic self-assembly of the positive NDs onto the negative substrate surfaces.
MPCVD Growth: Films were grown in a SEKI SDS6K MPCVD reactor using a gas mixture of H₂, CH₄, and Trimethylboron (TMB).
- Recipe Parameters: 5% CH₄, B/C ratio of 5000 ppm, total flow rate 250 sccm, 8 kPa pressure, and substrate temperature ~500 °C.
Surface Termination: The final step included a 10-minute hydrogen plasma treatment to ensure hydrogen termination of the BDD film surface.

6CCVD Solutions & Capabilities

This research validates the critical importance of high-quality, monocrystalline diamond material for achieving optimal electronic performance in BDD films. 6CCVD is uniquely positioned to support the replication and industrial scaling of this technology through our advanced MPCVD capabilities.

Research Requirement	6CCVD Solution & Capability	Technical Advantage for Replication/Scaling
Applicable Materials	Heavy Boron-Doped PCD (BDD)	We specialize in high-purity Polycrystalline Diamond (PCD) films with precise, heavy boron doping (BDD) necessary for metallic conductivity (R_s < 1 KΩ/sq). Our MPCVD process ensures the low defect density and large grain size (500-1000 nm) demonstrated as critical by the H-BND seeding results.
Thin Film Thickness Control (Target: 1 µm)	Precision Thickness Range	6CCVD offers PCD films with thickness control from 0.1 µm up to 500 µm (and substrates up to 10 mm). We guarantee the precise 1 µm thickness required for thin-film electrodes and electronic applications.
Customization Potential (Scaling & Integration)	Large Area Wafers & Custom Metalization	We provide custom dimensions for PCD plates/wafers up to 125 mm in diameter, enabling industrial scale-up of high-quality BDD electrodes. We offer in-house metalization services (Au, Pt, Pd, Ti, W, Cu) for robust electrical contact integration, crucial for electrochemical devices.
Surface Quality (Critical for sensing/electronics)	Ultra-Smooth Polishing	Our advanced polishing capabilities achieve surface roughness of Ra < 5 nm for inch-size PCD wafers, ensuring optimal interface quality for subsequent device fabrication steps (e.g., lithography or biosensing).
Engineering Support	In-House PhD Team Consultation	6CCVD’s expert material scientists can assist researchers in selecting the optimal BDD material specifications (doping level, thickness, crystal orientation) for similar thin diamond electrode or electronic device projects, ensuring the highest possible crystal quality and lowest sheet resistance.

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

Tech Support

Original Source

DOI: https://doi.org/10.1016/j.diamond.2025.112127

References

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2022 - Structural and electrochemical heterogeneities of boron-doped diamond surfaces
2009 - Fabrication of boron-doped diamond nanorod forest electrodes and their application in nonenzymatic amperometric glucose biosensing [Crossref]
2024 - Heavily boron-doped polycrystalline diamond films: microstructure, chemical composition investigation and plasma in-situ diagnostics [Crossref]
2023 - Effect of boron doping levels on the microstructure and characteristics of high-quality boron-doped diamond electrodes prepared by MPCVD [Crossref]
2000 - Surface morphology and electrical properties of boron-doped diamond films synthesized by microwave-assisted chemical vapor deposition using trimethylboron on diamond (100) substrate [Crossref]
2013 - Diamond nucleation and seeding techniques for tissue regeneration
2015 - Appropriate salt concentration of nanodiamond colloids for electrostatic self-assembly seeding of monosized individual diamond nanoparticles on silicon dioxide surfaces [Crossref]
2020 - Mixed-size diamond seeding for low-thermal-barrier growth of CVD diamond onto GaN and AlN [Crossref]