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6CCVD Research

Sluggish Electron Transfer of Oxygen-Terminated Moderately Boron-Doped Diamond Electrode Induced by Large Interfacial Capacitance between a Diamond and Silicon Interface

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2024-03-08
JournalJACS Au
AuthorsAtsushi Otake, Taiki Nishida, Shinya Ohmagari, Yasuaki Einaga
InstitutionsKeio University, National Institute of Advanced Industrial Science and Technology
Citations4
AnalysisFull AI Review Included

Executive Summary

Section titled “Executive Summary”

This study investigates the critical influence of substrate material and surface termination on the electrochemical performance of Boron-Doped Diamond (BDD) electrodes, providing guidelines for optimal material selection.

  • Core Finding: Oxygen-terminated BDD (O-BDD) with moderate boron doping (0.1% B/C ratio) synthesized on a Silicon (Si) substrate exhibits significantly sluggish electron transfer kinetics.
  • Mechanism Identified: The sluggishness is induced by a large interfacial capacitance (CSub/BDD) resulting from a wide depletion layer (10.0 nm) generated at the p-Si/p-BDD semiconductor heterojunction.
  • Performance Comparison: The charge transfer resistance (Rct) for O-0.1%BDD/Si (~1500 Ω) was three times greater than that observed for O-0.1%BDD on metal substrates (W, Nb, Mo) (~500 Ω).
  • Doping Effect: Highly doped (1.0% B/C) BDD electrodes showed rapid, quasi-reversible electron transfer regardless of surface termination or substrate material, due to high carrier concentration minimizing depletion layer effects.
  • Termination Effect: H-terminated BDDs consistently showed rapid, surface state-mediated electron transfer, independent of doping level or substrate.
  • Engineering Insight: For applications requiring moderately doped BDD (e.g., specific sensing or electroanalysis), metal substrates (W, Nb, Mo) are superior to Si substrates, especially when the diamond surface is O-terminated.

Technical Specifications

Section titled “Technical Specifications”
ParameterValueUnitContext
Boron Doping Levels (B/C ratio)0.1% and 1.0%atomic ratioCVD feed gas mixture
Boron Concentration (0.1% BDD)3.3 x 1020cm-3Estimated via SIMS/GDOES
Boron Concentration (1.0% BDD)1.9 x 1021cm-3Estimated via SIMS/GDOES
Diamond Bandgap (Eg,D)5.47eVIntrinsic diamond property
Si Bandgap (Eg,Si)1.12eVUsed in p-Si/p-BDD band diagram model
Depletion Layer Width (W) - O-0.1%BDD/Si10.0nmCalculated for p-Si/p-BDD heterojunction
Depletion Layer Width (W) - O-0.1%BDD/Metal1.4 to 1.7nmCalculated for metal/p-BDD Schottky junction
Charge Transfer Resistance (Rct) - O-0.1%BDD/Si~1500ΩMeasured via EIS (Fe(CN)63-/4-)
Charge Transfer Resistance (Rct) - O-0.1%BDD/Metal~500ΩMeasured via EIS (Fe(CN)63-/4-)
Si Substrate Resistivity0.005-0.01Ω·cmp-type single-crystalline Si (100)
CVD Microwave Voltage2kWMWPCVD system (AX6500X)
CVD Chamber Pressure30TorrHydrogen plasma environment
C-V Measurement Frequency1000HzUsed for capacitance-voltage characterization

Key Methodologies

Section titled “Key Methodologies”
  1. Film Synthesis: Boron-doped diamond (BDD) thin films were grown using Microwave Plasma-Assisted Chemical Vapor Deposition (MWPCVD).
  2. Substrate Preparation: Substrates included p-type Si (100), W, Nb, and Mo metals. All were seeded via ultrasonication in a nanodiamond suspension.
  3. Doping Control: Boron doping was controlled by supplying trimethylboron (B(CH3)3) and methane (CH4) into the hydrogen plasma at B/C atomic ratios of 0.1% and 1.0%.
  4. Surface Termination:
    • H-termination: Exposure to H2 plasma (2 kW, 30 Torr).
    • O-termination: Anodic oxidation using Cyclic Voltammetry (CV) in 0.1 M H2SO4 (30 total cycles up to 3.5 V).
  5. Electrochemical Analysis: CV and Electrochemical Impedance Spectroscopy (EIS) were performed using standard redox couples (Fe(CN)63-/4- and Ru(NH3)62+/3+) in 1 M KCl electrolyte.
  6. Structural and Compositional Analysis: Raman spectroscopy, Scanning Electron Microscopy (SEM), and X-ray Photoelectron Spectroscopy (XPS) were used to confirm film quality, morphology, and surface termination state.
  7. Electrical Property Measurement: Current-Voltage (I-V) curves and Capacitance-Voltage (C-V) characteristics were measured on BDD films and fabricated BDD mesa structures to validate proposed band diagrams and conduction pathways.

Commercial Applications

Section titled “Commercial Applications”

The findings regarding substrate selection and interfacial control are crucial for optimizing BDD performance in various high-demand electrochemical and electronic fields.

  • Electroanalysis and Sensing: Utilizing BDD’s wide potential window and low background current for high-sensitivity detection (e.g., environmental monitoring, biomedical sensors).
  • Wastewater Treatment: Employing BDD as a robust anode material for electrochemical oxidation of persistent organic pollutants, where long-term stability is paramount.
  • High-Power Semiconductor Devices: Integrating BDD films into Si-based electronics (e.g., MOSFETs, Schottky diodes) requires precise control over the BDD/Si heterojunction properties, as detailed by the depletion layer analysis.
  • Energy Storage and Conversion: Using BDD as a stable, high-performance electrode in advanced battery systems or fuel cells, where minimizing interfacial resistance (Rct) is critical for rapid charge/discharge rates.
  • Corrosion Resistance: Leveraging the chemical stability of diamond electrodes in harsh environments, particularly when synthesized on robust metal substrates like W or Mo.
View Original Abstract

[Image: see text] Boron-doped diamond (BDD) has tremendous potential for use as an electrode material with outstanding characteristics. The substrate material of BDD can affect the electrochemical properties of BDD electrodes due to the different junction structures of BDD and the substrate materials. However, the BDD/substrate interfacial properties have not been clarified. In this study, the electrochemical behavior of BDD electrodes with different boron-doping levels (0.1% and 1.0% B/C ratios) synthesized on Si, W, Nb, and Mo substrates was investigated. Potential band diagrams of the BDD/substrate interface were proposed to explain different junction structures and electrochemical behaviors. Oxygen-terminated BDD with moderate boron-doping levels exhibited sluggish electron transfer induced by the large capacitance generated at the BDD/Si interface. These findings provide a fundamental understanding of diamond electrochemistry and insight into the selection of suitable substrate materials for practical applications of BDD electrodes.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 2005 - Diamond Electrochemistry

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