High-Temperature Oxidation of Heavy Boron-Doped Diamond Electrodes - Microstructural and Electrochemical Performance Modification

At a Glance

Metadata	Details
Publication Date	2020-02-21
Journal	Materials
Authors	Jacek Ryl, Mateusz Cieślik, A. Zieliński, Mateusz Ficek, Bartłomiej Dec
Institutions	Gdańsk University of Technology
Citations	26
Analysis	Full AI Review Included

Technical Analysis & Documentation: High-Temperature BDD Electrodes

Executive Summary

This research details the critical degradation mechanisms of heavy Boron-Doped Diamond (BDD) electrodes when subjected to high-temperature oxidation (600 °C in air). The findings underscore the necessity of highly stable, customized MPCVD diamond materials for harsh environment applications.

Irreversible Corrosion: High-temperature treatment causes permanent structural defects, including etch pits, leading to irreversible corrosion and degradation of electrochemical activity, even after subsequent plasma rehydrogenation.
Rapid Performance Decay: Electrochemical activity (standard rate constant, kº) is significantly hindered, with anodic peak current decreasing by a factor of four after only 10 minutes of oxidation.
Surface Resistance Spike: Mean surface resistance (Rs) increases drastically by over 100 times (from 0.15 MΩ to 16.1 MΩ) due to the transition from highly conductive Hydrogen-Terminated (HT-BDD) to less conductive Oxygen-Terminated (OT-BDD).
Heterogeneity Challenge: Oxidation is highly heterogeneous and crystallographic-orientation dependent, resulting in localized variations in charge transfer kinetics and electrical conductivity across the electrode surface.
6CCVD Value Proposition: 6CCVD specializes in engineering high-purity, heavy BDD films with optimized grain structure and custom metalization (e.g., Ti/Pt/Au) to maximize stability and minimize performance drift in high-temperature, corrosive environments, ensuring reliable operation where standard BDD fails.

Technical Specifications

Data extracted from CV, SSRM, and XPS analyses of BDD electrodes.

Parameter	Value	Unit	Context
Oxidation Temperature	600	°C	Treatment environment: Air
Boron Doping Concentration ([B]/[C] gas phase)	10,000	ppm	Heavy doping level used for synthesis
Boron Doping Density (Estimated)	2 x 10²¹	atoms cm^-3	High electrical conductivity requirement
Untreated Mean Surface Resistance (Rs)	0.1505	MΩ	Measured by SSRM
90 min Oxidized Mean Surface Resistance (Rs)	16.1148	MΩ	Demonstrates severe conductivity loss
Untreated Standard Rate Constant (kº)	3.58 x 10^-3	cm/s	Initial electrochemical activity
90 min Oxidized Standard Rate Constant (kº)	1.91 x 10^-3	cm/s	Reduced activity post-corrosion
Untreated Peak Separation (ΔE)	0.35	V	At 50 mV/s scan rate
30 min Oxidized Peak Separation (ΔE)	1.04	V	Indicates highly irreversible process
Dominant Oxidized Species (XPS)	Hydroxyl (C-OH)	%	Confirmed dominant surface termination

Key Methodologies

The following parameters and processes were critical to the BDD synthesis and high-temperature testing:

CVD Synthesis: Microwave Plasma-Assisted Chemical Vapor Deposition (MPCVD).
Deposition Parameters:
- Chamber Stage Temperature: 700 °C.
- Growth Time: 6 hours.
Pre-Treatment Cleaning (Hydrogen Termination):
1. Hot aqua regia (HNO₃:HCl/1:3).
2. Hot “piranha” solution (H₂O₂:H₂SO₄/1:3) at 90 °C.
3. Microwave hydrogen plasma treatment (1000 W, 300 sccm H₂, 10 min).
High-Temperature Oxidation:
- Medium: Air.
- Temperature: 600 °C.
- Durations Tested: 3 min, 10 min, 30 min, 90 min.
Reversibility Test: Subsequent rehydrogenation via plasma treatment on oxidized samples.
Electrochemical Analysis: Cyclic Voltammetry (CV) and Scanning Electrochemical Microscopy (SECM) using the [Fe(CN)₆]^3-/4- redox couple.
Microstructural Analysis: Scanning Spreading Resistance Microscopy (SSRM), X-ray Photoelectron Spectroscopy (XPS), SEM, and AFM.

6CCVD Solutions & Capabilities

The findings of this paper—specifically the need for highly conductive, structurally stable BDD films resistant to high-temperature corrosion—align perfectly with 6CCVD’s core MPCVD capabilities.

Applicable Materials

To replicate or extend this research into stable high-temperature electrochemical devices, 6CCVD recommends:

Heavy Boron-Doped Polycrystalline Diamond (PCD): 6CCVD can precisely match the high doping density (up to 10²¹ atoms cm^-3) required for low resistance and high electrochemical activity, ensuring the starting material exceeds the quality of the “as-prepared” electrodes in the study.
Optimized PCD Substrates: We offer PCD films with controlled grain orientation and minimized sp²-carbon content, crucial for maximizing corrosion resistance and minimizing the formation of etch pits observed at 600 °C.
BDD Thickness Control: We supply BDD films in thicknesses ranging from 0.1 µm to 500 µm, allowing researchers to optimize the conductive layer depth for specific device requirements (e.g., minimizing silicon substrate diffusion mentioned in the paper).

Customization Potential

The study utilized small, 0.25 cm² exposed areas. 6CCVD offers unparalleled flexibility for scaling and integration:

Requirement from Research	6CCVD Customization Capability	Technical Advantage
Small, Custom-Cut Electrodes	Precision laser cutting of plates/wafers.	Supply BDD plates up to 125mm (PCD) or custom dimensions for array fabrication.
Need for Stable Electrical Contacts	In-house metalization services.	Deposition of high-temperature stable contacts (Ti, Pt, Au, W) directly onto the BDD surface, essential for reliable electrical testing at elevated temperatures (e.g., for Schottky barrier diodes or heat spreaders).
Surface Quality (Ra)	Advanced Polishing Services.	Polishing of PCD surfaces to Ra < 5 nm (inch-size), ensuring minimal surface defects that could act as nucleation sites for etch pits and heterogeneous oxidation.
Global Logistics	Global Shipping (DDU/DDP).	Fast, reliable delivery of sensitive diamond materials worldwide, simplifying procurement for international research teams.

Engineering Support

The observed irreversible degradation of BDD structure and electrochemical properties at 600 °C highlights a critical engineering challenge for high-power electronics and harsh environment sensors.

Corrosion Mitigation: 6CCVD’s in-house PhD team specializes in optimizing MPCVD growth recipes to produce BDD films with enhanced resistance to thermal oxidation and chemical corrosion. We can assist researchers in selecting the optimal BDD grade and surface termination strategy for High-Temperature Electrochemistry projects.
Process Replication: We provide materials grown under highly controlled conditions, ensuring batch-to-batch consistency, which is vital for studies investigating subtle, heterogeneous effects like those observed via SECM and SSRM.

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

View Original Abstract

In this work, we reveal in detail the effects of high-temperature treatment in air at 600 °C on the microstructure as well as the physico-chemical and electrochemical properties of boron-doped diamond (BDD) electrodes. The thermal treatment of freshly grown BDD electrodes was applied, resulting in permanent structural modifications of surface depending on the exposure time. High temperature affects material corrosion, inducing crystal defects. The oxidized BDD surfaces were studied by means of cyclic voltammetry (CV) and scanning electrochemical microscopy (SECM), revealing a significant decrease in the electrode activity and local heterogeneity of areas owing to various standard rate constants. This effect was correlated with a resultant increase of surface resistance heterogeneity by scanning spreading resistance microscopy (SSRM). The X-ray photoelectron spectroscopy (XPS) confirmed the rate and heterogeneity of the oxidation process, revealing hydroxyl species to be dominant on the electrode surface. Morphological tests using scanning electron microscopy (SEM) and atomic force microscopy (AFM) revealed that prolonged durations of high-temperature treatment lead not only to surface oxidation but also to irreversible structural defects in the form of etch pits. Our results show that even subsequent electrode rehydrogenation in plasma is not sufficient to reverse this surface oxidation in terms of electrochemical and physico-chemical properties, and the nature of high-temperature corrosion of BDD electrodes should be considered irreversible.

Tech Support

Original Source

DOI: https://doi.org/10.3390/ma13040964

References

2019 - Boron-doped diamond: Current progress and challenges in view of electroanalytical applications [Crossref]
2019 - Environmental Applications of Boron-Doped Diamond Electrodes: 1. Applications in Water and Wastewater Treatment [Crossref]
2018 - Nanocrystalline Boron-Doped Diamond as a Corrosion-Resistant Anode for Water Oxidation via Si Photoelectrodes [Crossref]
2020 - Effect of reactor configuration on the kinetics and nitrogen byproduct selectivity of urea electrolysis using a boron doped diamond electrode [Crossref]
2018 - The Dependence of Oxidation Parameters and Dyes’ Molecular Structures on Microstructure of Boron-Doped Diamond in Electrochemical Oxidation Process of Dye Wastewater [Crossref]
2016 - Beyond Thermal Management: Incorporating p-Diamond Back-Barriers and Cap Layers Into AlGaN/GaN HEMTs [Crossref]