Diamond as Insulation for Conductive Diamond—A Spotted Pattern Design for Miniaturized Disinfection Devices

At a Glance

Metadata	Details
Publication Date	2023-08-18
Journal	C – Journal of Carbon Research
Authors	Manuel Zulla, Vera Vierheilig, Maximilian Koch, Andreas Burkovski, Matthias Karl
Institutions	Friedrich-Alexander-Universität Erlangen-Nürnberg, Saarland University
Citations	1
Analysis	Full AI Review Included

Technical Documentation & Analysis: Double Diamond Laminate (DDL) for Miniaturized Disinfection

This document analyzes the research on using a Double Diamond Laminate (DDL) structure for miniaturized electrochemical disinfection devices. 6CCVD specializes in the precise growth and fabrication of MPCVD diamond materials necessary to replicate and advance this technology.

Executive Summary

The research successfully developed a polymer-free, miniaturized Boron-Doped Diamond (BDD) electrode insulated by Undoped Diamond (UDD) for in situ disinfection applications, such as root canal treatment.

Polymer-Free Insulation: Achieved stable electrical insulation by integrating a non-conductive UDD layer directly onto the conductive BDD layer, eliminating the drawbacks of polymeric insulators (detachment, non-biocompatibility).
Miniaturization: The resulting Double Diamond Laminate (DDL) electrode, coated on a Niobium wire, achieved a total diameter of approximately 55 µm, suitable for fine medical cannulas (e.g., 31 gauge).
Novel Fabrication Method: A selective growth technique utilizing a temporary Spotted Copper Deposition (SCD) intermediate layer was employed to inhibit UDD growth, creating a controlled “spotted pattern” of active BDD sites.
High Active Surface Area: Despite the insulation, the DDL maintained a high electrochemically active BDD surface area of approximately 80%.
Enhanced Efficiency (Microdistancing): The UDD insulation layer reduced the anode-cathode gap to a critical 3-5 µm distance, enabling efficient Electrochemical Advanced Oxidation Processes (EAOPs) in low-conductivity electrolytes (demineralized water) at low voltages (5-15 V).
Performance: Demonstrated significant oxidant production, achieving hydrogen peroxide (H₂O₂) concentrations up to 30 mg/L.

Technical Specifications

The following hard data points were extracted from the DDL fabrication and performance analysis:

Parameter	Value	Unit	Context
Substrate Material	Niobium (Nb)	N/A	Wire substrate
Substrate Diameter	50	µm	Niobium wire
Final DDL Diameter	~55	µm	BDD + UDD layers
BDD Layer Thickness	1-2	µm	First conductive layer (HFCVD)
UDD Layer Thickness	3-4	µm	Second insulating layer (HFCVD)
Required UDD Thickness	≥ 3	µm	Minimum for reliable insulation
Electrochemically Active Area	~80	%	Accessible BDD surface
Active Zone Length (Tested)	3	cm	Total length of coated wire
Active Surface Area (Tested)	~0.075	cm²	For 3 cm wire length
Anode-Cathode Gap (Minimum)	3-5	µm	Determined by UDD thickness (Microdistancing)
BDD Growth Temperature	~800	°C	HFCVD process
HFCVD Pressure	2	mbar	BDD coating
Operating Voltage Range	5-15	V	For oxidant production
Maximum H₂O₂ Production	30	mg/L	At 15 V, 20 mA
Current Density Range	0.01-0.27	A/cm²	Achieved during testing

Key Methodologies

The DDL fabrication relies on precise, multi-step CVD growth combined with selective electrochemical deposition and etching.

Conductive BDD Layer Deposition (HFCVD):
- Substrate: Niobium wire (50 µm diameter).
- Gas Phase: 1000 mL/min H₂, 16 mL/min CH₄, 0.15 mL/min Trimethyl Borate (TMB).
- Conditions: 800 °C, 2 mbar, 6 h duration.
- Result: 1-2 µm thick BDD layer with desired electrochemical properties.
Spotted Copper Deposition (SCD) Intermediate Layer:
- Setup: Simple galvanic cell using BDD-Nb wire as the working electrode (−) and BDD-Nb sheet counter electrodes (+).
- Electrolyte: Copper (II) sulfate pentahydrate solution (20 g/L).
- Process: Applied 50 mA current at ~1.5 V for 2-10 s.
- Function: Copper precipitates selectively inhibit subsequent diamond growth, creating the spotted pattern.
Non-Conductive UDD Layer Deposition (HFCVD):
- Gas Phase: 1000 mL/min H₂, 16 mL/min CH₄ (TMB dopant omitted).
- Conditions: Deposition time extended to 20 h for the final prototype.
- Result: 3-4 µm thick UDD layer, providing insulation while maintaining porosity over the copper spots.
Copper Etching and Activation (2-Step Process):
- Step 1 (Electrochemical Etching): Positively charged DDL reacted with a negatively charged BDD electrode in distilled water (electrolyte). Applied 10 V for 2 min.
- Step 2 (Acidic Etching): Used a mixture of Nitric acid (20%) and Hypochlorous acid (20%) (1:1 ratio), performed twice.
- Function: Complete removal of the copper intermediate layer, exposing the underlying BDD layer to the electrolyte and creating the active spotted pattern.

6CCVD Solutions & Capabilities

The successful fabrication of the Double Diamond Laminate (DDL) relies entirely on highly controlled MPCVD growth and advanced material processing. 6CCVD is uniquely positioned to supply the necessary materials and engineering services to industrialize or extend this research.

Applicable Materials for DDL Replication

To replicate the DDL structure, researchers require two distinct, high-quality CVD diamond materials grown sequentially with precise thickness control:

DDL Component	6CCVD Material Recommendation	Key Capability Match
Conductive Layer (BDD)	Heavy Boron-Doped PCD (Polycrystalline Diamond)	High conductivity required for EAOPs. 6CCVD offers PCD layers from 0.1 µm up to 500 µm, ensuring precise 1-2 µm thickness control.
Insulation Layer (UDD)	Optical Grade SCD (Single Crystal Diamond)	UDD must be a perfect electrical insulator (band gap 5.47 eV). 6CCVD’s high-purity SCD material provides superior insulating properties and controlled growth morphology (3-4 µm thickness).
Substrate Handling	Custom Substrate Processing	While the paper used 50 µm Nb wire, 6CCVD can handle custom substrates, including thin wires, rods, or complex geometries, for MPCVD coating.

Customization Potential & Advanced Fabrication

The DDL concept requires specialized processing steps beyond standard diamond growth. 6CCVD offers the in-house capabilities to support these complex requirements:

Precision Thickness Control: The success of the DDL hinges on controlling the BDD (1-2 µm) and UDD (3-4 µm) layers to the micrometer level. 6CCVD guarantees thickness control across our entire range (0.1 µm to 500 µm).
Custom Metalization Services: The research utilized a Copper (Cu) intermediate layer for selective growth inhibition. 6CCVD offers internal metalization capabilities including Au, Pt, Pd, Ti, W, and Cu, allowing for the precise deposition and patterning of intermediate layers or final contacts.
Advanced Polishing: For applications requiring minimal surface roughness (e.g., flow dynamics in miniaturized reactors), 6CCVD provides ultra-smooth polishing: Ra < 1 nm for SCD and Ra < 5 nm for inch-size PCD.
Large-Scale Prototyping: While this paper focused on miniaturization, 6CCVD can produce custom plates and wafers up to 125 mm in diameter, enabling the upscaling of BDD electrode arrays for industrial disinfection or water treatment systems.

Engineering Support

The DDL fabrication process—combining CVD growth, electrochemical deposition (SCD), and selective etching—is highly complex. 6CCVD’s in-house PhD engineering team specializes in optimizing diamond growth recipes for specific electrochemical and biomedical applications. We offer consultation on:

Optimizing TMB doping levels for specific BDD conductivity requirements.
Developing robust, scalable processes for selective growth inhibition (e.g., replicating the SCD technique).
Material selection and design for similar Miniaturized Electrochemical Disinfection projects.

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

View Original Abstract

Boron-doped diamond (BDD) electrodes are well known for the in situ production of strong oxidants. These antimicrobial agents are produced directly from water without the need of storage or stabilization. An in situ production of reactive oxygen species (ROS) used as antimicrobial agents has also been used in recently developed medical applications. Although BDD electrodes also produce ROS during water electrolysis, only a few medical applications have appeared in the literature to date. This is probably due to the difficulties in the miniaturization of BDD electrodes, while maintaining a stable and efficient electrolytic process in order to obtain a clinical applicability. In this attempt, a cannula-based electrode design was achieved by insulating the anodic diamond layer from a cathodic cannula, using a second layer of non-conducting diamond. The undoped diamond (UDD) layer was successfully grown in a spotted pattern, resulting in a perfectly insulated yet still functional BDD layer, which can operate as a miniaturized flow reactor for medical applications. The spotted pattern was achieved by introducing a partial copper layer on top of the BDD layer, which was subsequently removed after growing the undoped diamond layer via etching. The initial analytical observations showed promising results for further chemical and microbial investigations.

Tech Support

Original Source

DOI: https://doi.org/10.3390/c9030078

References

2019 - Environmental applications of boron-doped diamond electrodes: 1. Applications in water and wastewater treatment [Crossref]
2011 - Efficient electrochemical decomposition of perfluorocarboxylic acids by the use of a boron-doped diamond electrode [Crossref]
2019 - Elimination of bacterial contaminations by treatment of water with boron-doped diamond electrodes [Crossref]
2014 - Understanding persulfate production at boron doped diamond film anodes [Crossref]
2021 - Electrochemically generated sulfate radicals by boron doped diamond and its environmental applications [Crossref]
2019 - Use of boron-doped diamond electrodes in electro-organic synthesis [Crossref]
2012 - Boron-doped diamond electrodes for electroorganic chemistry
2020 - Research on the mechanism and reaction conditions of electrochemical preparation of persulfate in a split-cell reactor using BDD anode [Crossref]