Impact of gate electrode on free chlorine sensing performance in solution-gated graphene field-effect transistors
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2024-01-01 |
| Journal | RSC Advances |
| Authors | Masato Sugawara, Takeshi Watanabe, Yasuaki Einaga, Shinji Koh |
| Institutions | Keio University, Aoyama Gakuin University |
| Citations | 4 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive Summaryâ- Core Innovation: The study optimizes solution-gated Graphene Field-Effect Transistors (GFETs) for highly sensitive free chlorine (FC) sensing by focusing on the electrochemical properties of the gate electrode.
- Sensing Mechanism: FC acts as a p-dopant on the graphene channel, causing a shift in the Dirac Point Voltage (VDP). This shift is governed by the Nernst equation and the voltage distribution across the electric double layers (EDLs).
- Performance Enhancement: Gate electrodes with low electric double-layer capacitance (CGE) and wide potential windows (Graphene and Boron-Doped Diamond, BDD) significantly amplify the VDP shift, improving sensitivity.
- Material Comparison: Graphene (1.65 ”F cm-2) and BDD (2.68 ”F cm-2) gates demonstrated superior performance compared to the standard Au gate (27.3 ”F cm-2), especially at low concentrations.
- Low Concentration Sensitivity: The absence of interfering surface redox species on carbon-based electrodes (Graphene/BDD) allows for accurate sensing in the low concentration range (0.1-0.2 ppm), suitable for tap water.
- Durability Potential: BDD is highlighted as an ideal gate material due to its chemical stability and resistance to fouling, suggesting potential for durable, long-term continuous monitoring sensors.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Graphene Growth Temperature | 1000 | °C | CVD process on Cu substrate |
| CH4 Flow Rate | 20 | sccm | CVD reaction source gas |
| H2 Flow Rate | 2 | sccm | CVD reaction source gas |
| Drain-Source Voltage (VDS) | 0.1 | V | Fixed voltage for transfer curve measurement |
| Au Gate EDL Capacitance (CGE) | 27.3 | ”F cm-2 | Measured in 0.1 M PBS (pH 7) |
| Graphene Gate EDL Capacitance (CGE) | 1.65 | ”F cm-2 | Measured in 0.1 M PBS (pH 7) |
| BDD Gate EDL Capacitance (CGE) | 2.68 | ”F cm-2 | Measured in 0.1 M PBS (pH 7) |
| BDD Boron-to-Carbon (B/C) Ratio | 1 | % | Used for BDD gate electrode deposition |
| Graphene 2D/G Intensity Ratio | 2.4 | N/A | Characteristic of single-layer graphene |
| Carrier Density Increase (10 ppm FC) | 34 | % | Measured via Hall effect on graphene channel |
| FC Detection Limit (Graphene/BDD) | 0.1-0.2 | ppm | Suitable for drinking water monitoring |
| FC Detection Limit (Au) | 0.5 | ppm | Lower sensitivity due to surface oxides |
| Standard Redox Potential (HClO) | 1.40 | V | Against Standard Hydrogen Electrode (SHE) |
Key Methodologies
Section titled âKey Methodologiesâ- Graphene Channel Fabrication (CVD): Single-layer graphene was grown on a 35 ”m thick copper (Cu) substrate at 1000 °C using CVD with CH4 (20 sccm) and H2 (2 sccm).
- Transfer and Device Assembly: Graphene was transferred onto a quartz substrate using a PMMA-assisted wet etching process (0.5 M iron nitrate). Cr/Au (10 nm/40 nm) source and drain electrodes were evaporated to define the channel (7.5 mm length, 15 mm width).
- Gate Electrode Preparation:
- Graphene Gate: Fabricated via the same CVD/transfer process, with an Au/Cr contact.
- BDD Gate: Deposited on silicon wafers using Microwave Plasma-Assisted CVD (MPCVD) with methane and trimethyl boron (1% B/C ratio).
- Au Gate: Fabricated by vacuum evaporation of Cr (10 nm)/Au (100 nm) on SiO2/Si substrates.
- Electrochemical Characterization: Cyclic Voltammetry (CV) was used to assess the potential window and stability of the gate electrodes. Electrochemical Impedance Spectroscopy (EIS) was used to quantify the electric double-layer capacitance (CGE).
- Sensing Protocol: Transfer curves (IDS vs. VGS) were measured in 0.1 M Phosphate Buffer Solution (PBS, pH 7). Free chlorine concentration was adjusted stepwise by adding standardized sodium hypochlorite (NaClO) solution.
- Signal Analysis: Free chlorine concentration was correlated with the shift in the Dirac Point Voltage (VDP) on the transfer curves, demonstrating the doping effect.
Commercial Applications
Section titled âCommercial Applicationsâ- Drinking Water Safety: Continuous, highly sensitive monitoring of residual free chlorine (0.2-0.5 ppm range) at the point of delivery, crucial for public health and regulatory compliance.
- Industrial Water Treatment: Real-time control and measurement of disinfection levels in food processing, beverage production, and industrial wastewater streams.
- Durable Sensor Technology: Utilizing Boron-Doped Diamond (BDD) as the gate electrode material provides a platform for robust, long-lifetime sensors resistant to surface fouling and oxidation, reducing maintenance needs.
- Advanced Sensor Integration: The GFET platform is suitable for integration with statistical methods like machine learning (ML) and multi-signal integration (e.g., dual-gate configurations) to enhance accuracy and robustness against interfering redox species.
- Extended-Gate FET (EGFET) Design: The findings advocate for an EGFET structure using BDD, separating the sensitive graphene channel from direct liquid contact to improve long-term durability and practicality in liquid environments.
View Original Abstract
We investigated the role of gate electrodes in solution-gated graphene field-effect transistors for sensing free chlorine. Graphene and boron-doped diamond exhibit suitable electrochemical properties for gate electrodes.
Tech Support
Section titled âTech SupportâOriginal Source
Section titled âOriginal SourceâReferences
Section titled âReferencesâ- 2022 - Guidelines for Drinking-Water Quality