Ultrathin boron-doped diamond – surface-wave-plasma synthesis of semi-conductive nanocrystalline boron-doped diamond layers at low temperature

At a Glance

Metadata	Details
Publication Date	2025-01-01
Journal	Materials Advances
Authors	P. Ashcheulov, M. Davydova, Taylor A, P. Hubík, A. Kovalenko
Institutions	Institute of Physics of the Slovak Academy of Sciences, Czech Academy of Sciences
Analysis	Full AI Review Included

Technical Documentation & Analysis: Ultrathin Semi-Conductive BDD Layers via SWP-PECVD

Executive Summary

This research successfully demonstrates the fabrication of highly tunable, ultrathin nanocrystalline Boron-Doped Diamond (BDD) layers using a low-temperature Surface-Wave-Plasma (SWP) Microwave Plasma Enhanced CVD (MW-LA-PECVD) technique.

Low-Temperature Synthesis: BDD layers were grown at a low substrate temperature of 500 °C (±20 °C), significantly expanding the range of compatible substrate materials for diamond coatings.
Ultrathin and Uniform Layers: Achieved highly uniform, nanocrystalline BDD films with thicknesses precisely controlled between 124 nm and 167 nm.
Tunable Electrical Properties: Electrical resistivity was systematically tuned across five orders of magnitude, ranging from 1.85 Ω cm (highly conductive) up to 303,500 Ω cm (semi-conductive), by varying the gas-phase B/C ratio and CO₂ concentration.
High Surface Quality: Fabricated layers exhibited excellent surface smoothness, with RMS roughness values consistently below 8 nm (6.2-7.6 nm), which is beneficial for opto-electronic applications by minimizing light scattering.
Wide Electrochemical Window: The resulting BDD electrodes demonstrated a wide electrochemical stability window of approximately 3.0 V in aqueous electrolytes, comparable to conventional thick microcrystalline BDD electrodes.
Scalability Potential: The SWP MW-LA-PECVD method is highlighted as a promising route for large-area, low-temperature BDD coatings on diverse substrates, addressing key limitations of conventional MW-PECVD (scalability and high temperature).

Technical Specifications

The following hard data points were extracted from the synthesis and characterization of the ultrathin nanocrystalline BDD layers:

Parameter	Value	Unit	Context
Synthesis Method	SWP MW-LA-PECVD	N/A	Low-temperature CVD
Substrate Temperature	500 ± 20	°C	Achieved via plasma heat (unassisted)
Layer Thickness Range	124 - 167	nm	Ultrathin nanocrystalline BDD
Maximum Growth Rate	< 30	nm h^-1	Calculated over 6-hour deposition
Electrical Resistivity (Range)	1.85 to 303,500	Ω cm	Tuned via B/C ratio and CO₂ content
Boron Concentration (Solid Phase)	6.07 x 10¹⁹ to 7.1 x 10²⁰	at. cm^-3	Estimated via GDOES
RMS Surface Roughness (Range)	6.2 to 7.6	nm	Measured via AFM
Electrochemical Stability Window	2.5 - 3.0	V	In 1 M KCl aqueous electrolyte
Microwave Power	2 x 3	kW	Total power applied
Process Pressure	0.25	mbar	N/A
Substrates Used	Si, Quartz, High-Temp Glass	N/A	10 x 10 mm² pieces

Key Methodologies

The ultrathin nanocrystalline BDD layers were fabricated using a custom-built Surface-Wave-Plasma (SWP) MW-LA-PECVD reactor optimized for low-temperature operation.

Substrate Preparation:
- Substrates (Si, quartz, glass) were thoroughly cleaned using standard chemical baths (acetone, IPA, H₂SO₄/H₂O₂).
- Si substrates received an additional HF acid treatment to remove the native SiO₂ layer, preventing a highly resistive interface.
- Substrates were seeded via spin coating using a nanodiamond dispersion (NanoAmando, 0.2 g L^-1).
Gas Phase Chemistry:
- The gas admixture consisted of H₂ (94-96%), CH₄ (4%), Diborane (B₂H₆, 7500 ppm in H₂) as the boron precursor, and CO₂ as the oxygen source.
- B/C Ratio Tuning: Varied substantially from 60 ppm (low doping) up to 60,000 ppm (high doping).
- CO₂ Tuning: Varied in a narrow range from 0.1% to 2% to suppress SiC formation and influence layer quality/boron incorporation.
Deposition Conditions:
- The synthesis was performed at a low temperature of 500 °C (±20 °C) using an unassisted substrate holder configuration.
- Microwave power was set to 2 x 3 kW at a process pressure of 0.25 mbar.
- All deposition cycles were fixed at 6 hours to allow for comparative analysis of growth rates and thickness.
Characterization:
- Thickness and morphology were assessed using cross-sectional SEM and AFM.
- Boron concentration was determined using Glow Discharge Optical Emission Spectroscopy (GDOES).
- Electrical characteristics (resistivity) were measured using the differential van der Pauw (vdP) method with evaporated Ti/Au triangle contacts.
- Electrochemical performance was evaluated using Cyclic Voltammetry (CV) with a Fe(CN)₆^3-/4- redox marker.

6CCVD Solutions & Capabilities

This research validates the critical role of highly controlled, low-temperature MPCVD for producing functional, ultrathin BDD layers with tunable semi-conductive properties, ideal for advanced electrochemical and opto-electronic devices. 6CCVD is uniquely positioned to supply and customize the required materials and specifications.

Applicable Materials

The paper requires Nanocrystalline Boron-Doped Diamond (BDD) layers with precise resistivity control. 6CCVD offers materials that directly meet these requirements, providing superior quality and scalability.

Research Requirement	6CCVD Material Solution	Key Benefit
Ultrathin BDD (124-167 nm)	Polycrystalline Diamond (PCD) / BDD	Precise thickness control from 0.1 µm (100 nm) up to 500 µm.
Tunable Semi-Conductive Range	Moderately Doped PCD/BDD	We specialize in tuning B/C ratios to achieve specific resistivity targets (e.g., 10 Ω cm to 100 kΩ cm) for sensing applications.
Highly Conductive BDD (1.85 Ω cm)	Heavy Boron Doped PCD/BDD	Guaranteed high doping levels for metallic-like conductivity, crucial for efficient charge transfer kinetics.
Smooth Surface (RMS < 8 nm)	Polished PCD/BDD Wafers	Standard polishing achieves Ra < 5 nm on inch-size PCD, surpassing the roughness achieved in this study for enhanced optical clarity and reduced scattering.

Customization Potential

The success of this research relies on precise control over dimensions, substrate preparation, and electrode integration—all core competencies of 6CCVD.

Scalability and Dimensions: While the paper used small 10 x 10 mm² samples, 6CCVD offers PCD/BDD wafers up to 125 mm in diameter. We provide custom laser cutting and shaping services to deliver BDD plates in any required geometry for large-scale device integration.
Substrate Compatibility: 6CCVD supports deposition onto diverse substrates, including Silicon, Quartz, and high-temperature Glass, matching the materials used in this study. We offer specialized substrate preparation (e.g., HF etching, seeding) to ensure optimal diamond adhesion and interface quality, critical for low-temperature growth.
Metalization Services: The researchers used Ti/Au contacts for electrical testing. 6CCVD provides in-house custom metalization using various materials (Au, Pt, Pd, Ti, W, Cu) to deliver fully integrated BDD electrodes or sensor arrays, ready for immediate electrochemical testing.

Engineering Support

The systematic optimization of gas chemistry (B/C ratio and CO₂ concentration) to control resistivity is a complex material science challenge.

6CCVD’s in-house PhD material science team specializes in optimizing MPCVD recipes to achieve specific functional requirements. We provide expert consultation on material selection, doping levels, and growth parameters to replicate or extend the low-temperature BDD synthesis demonstrated here for similar electrochemical, gas-sensing, or opto-electronic projects.
We offer global shipping (DDU default, DDP available) to ensure rapid delivery of custom diamond solutions worldwide.

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

View Original Abstract

Ultrathin boron-doped diamond layers, synthesized at 500 °C, provide a cost-effective, energy-efficient material with moderate semi-conductive properties for advanced functional uses.

Tech Support

Original Source

DOI: https://doi.org/10.1039/d5ma00238a