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

Executive Summary

This study investigates the influence of three types of hydrogenated nanodiamond (H-ND) seeding layers on the morphology and electrical properties (sheet resistance, R_s) of boron-doped diamond (BDD) films grown by microwave plasma-enhanced chemical vapor deposition (MPCVD).

Superior Seeding Material: Novel bottom-up synthesized hydrogenated boron-doped nanodiamonds (H-BNDs) were identified as the most effective seeding material, yielding BDD films with the lowest sheet resistance (440 ohm/sq).
Morphological Improvement: BDD films grown on H-BND seeds exhibited the largest crystals (up to 1000 nm) and the lowest concentration of defects (e.g., twin boundaries), correlating directly with the superior electrical performance.
Mechanism Confirmation: Secondary Ion Mass Spectrometry (SIMS) confirmed that the boron concentration was nearly identical across all films, proving that the seed quality (crystal perfection and shape homogeneity), rather than doping efficiency, was the dominant factor determining the final film properties.
H-BND Characteristics: H-BNDs are monocrystalline and possess a highly uniform particle shape, in contrast to the polycrystalline and defective H-DNDs or the irregularly shaped TD_HPHT H-NDs.
Colloidal Stability: Oxidized BND (O-BND) was successfully hydrogenated at 700 °C, reversing its zeta potential from negative (-32 mV) to highly positive (+44 mV), which is crucial for achieving dense, homogeneous seeding layers on negatively charged substrates (Si/SiO₂).
Growth Consistency: Despite significant variation in initial surface coverage (13% for H-DND vs. 24-25% for H-BND/TD_HPHT H-ND), all seeding layers facilitated the growth of fully closed BDD films approximately 1 µm thick.

Technical Specifications

Parameter	Value	Unit	Context
Lowest Sheet Resistance (R_s)	440	ohm/sq	BDD film grown on H-BND seeding (H-terminated)
Highest Sheet Resistance (R_s)	~17	KΩ/sq	BDD film grown on H-DND seeding (O-terminated)
BDD Film Thickness	~1	µm	All films grown for 1 hour
Largest Crystal Size	500-1000	nm	BDD film grown on H-BND seeding
H-BND Zeta Potential (Hydrogenated)	+44	mV	Positive charge enabling electrostatic seeding
O-BND Zeta Potential (Oxidized)	-32	mV	Negative charge prior to hydrogenation
H-BND Seeding Coverage	24	%	High coverage achieved
H-DND Seeding Coverage	13	%	Lowest coverage achieved
CVD Gas Mixture	H₂/CH₄/TMB	N/A	TMB: Trimethylboron
B/C Ratio (CVD Gas)	5000	ppm	Constant doping level for all films
CVD Chamber Pressure	8 (60)	kPa (Torr)	Growth pressure
CVD Substrate Temperature	~500	°C	Growth temperature
H-BND Synthesis Temperature	1250	°C	HPHT synthesis from 9BBN precursor
H-BND Hydrogenation Temperature	700	°C	Thermal treatment to achieve positive zeta potential
FTIR C(111)-H Stretch Peak	2835	cm^-1	Characteristic of uniform H-BND facets
FTIR C(100):H Stretch Peak	2915	cm^-1	Characteristic of uniform H-BND facets

Key Methodologies

BND Synthesis and Oxidation: Boron-doped nanodiamonds (BND) were synthesized using the HPHT method (8.5-9 GPa, 1250 °C) from the 9-borabicyclo[3.3.1]nonane dimer (9BBN) precursor. The resulting powder was purified and oxidized by boiling in a 3:1 sulfuric/nitric acid mixture for 6 hours, yielding O-BND.
Hydrogenation: O-BND powder was thermally annealed in a tube furnace at 700 °C for 3 hours under atmospheric hydrogen pressure to produce H-BND, reversing the zeta potential from negative to positive.
Reference ND Preparation: Commercial H-DND dispersion was diluted. TD_HPHT H-ND powder (milled HPHT microcrystals) was purified by air annealing (450 °C, 5 h) and subsequently hydrogenated (800 °C, 6 h) to achieve a positive zeta potential.
Seeding Solution Preparation: H-ND powders (H-BND, TD_HPHT H-ND) were dispersed in DI water (2 mg/ml) using a Hielscher UP200S ultrasonic processor (120 W, 1 h). TD_HPHT H-ND dispersion was centrifuged to remove large aggregates.
Substrate Seeding: Cleaned Si(100) and fused SiO₂ substrates were immersed in the respective H-ND colloidal solutions and sonicated (10 min) to deposit dense seeding layers via electrostatic self-assembly.
BDD Film Growth (MPCVD): Films were grown simultaneously on seeded SiO₂ and Si substrates in a SEKI SDS6K reactor. Constant parameters included 5% CH₄ concentration, B/C ratio of 5000 ppm (using TMB), 8 kPa pressure, and a substrate temperature of ~500 °C for 1 hour.
Surface Termination: Films were H-terminated using a final hydrogen plasma treatment (10 min) or O-terminated using ICP RF plasma (100 W, O₂ flow) for comparative electrical measurements.
Characterization: Film morphology and defectiveness were assessed by SEM and boundary analysis. Electrical properties (R_s) were measured using a four-point probe. Boron incorporation was verified by SIMS depth profiling. Nanoparticle structure and size were analyzed using HRTEM, SAXS, DLS, and FTIR.

Commercial Applications

The successful growth of high-quality BDD films with low sheet resistance using H-BND seeding is highly relevant for advanced diamond technology applications:

High-Performance Electrodes: The low R_s (440 ohm/sq) and high crystal quality make these BDD films ideal for use as robust electrodes in electrochemistry, including water treatment, harsh environment sensing, and high-sensitivity biosensors.
Diamond-Based RF and Power Electronics: Minimizing defects (especially twin boundaries) is crucial for maximizing carrier mobility. H-BND seeding provides the structural quality necessary for developing high-frequency (RF) and high-voltage complementary circuits based on BDD.
Thin Film Device Manufacturing: The ability to grow fully closed, low-defect BDD films approximately 1 µm thick on non-diamond substrates (Si, SiO₂) is essential for integrating diamond into semiconductor manufacturing processes.
Controlled Doping and Color Centers: The bottom-up HPHT synthesis method used for H-BND is a highly controllable technique, which can be adapted to incorporate other dopants (like Si or Ge) to create specific color centers (SiV, GeV) for potential use in quantum sensing and information processing applications.

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
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