A cost-efficient approach for simultaneous scanning electrochemical microscopy and scanning ion conductance microscopy
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-06-17 |
| Journal | Monatshefte fĂŒr Chemie - Chemical Monthly |
| Authors | Stefan Wert, Simona BaluchovĂĄ, Karolina SchwarzovĂĄâPeckovĂĄ, Silvia SedlĂĄkovĂĄ, Andrew Taylor |
| Institutions | University of Regensburg, Charles University |
| Citations | 4 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis paper presents a novel, cost-efficient method for fabricating dual-function probes capable of simultaneous Scanning Electrochemical Microscopy (SECM) and Scanning Ion Conductance Microscopy (SICM).
- Core Value Proposition: The method uses simple photoresist deposition onto platinum-coated fused silica capillaries, avoiding complex techniques like Atomic Layer Deposition (ALD) or Focused Ion Beam (FIB) milling, thus lowering the barrier to entry for combined SECM/SICM studies.
- Probe Design: The resulting probe is a pipette structure with an integrated ring ultramicroelectrode (UME), enabling non-contact acquisition of both electrochemical activity (SECM) and topographical information (SICM).
- Performance Validation: Probes were successfully characterized using Cyclic Voltammetry (CV) and Probe Approach Curves (PACs), demonstrating typical positive (conductor) and negative (insulator) SECM feedback, alongside SICM current decrease due to hindered ion migration.
- Model Substrate Results: The dual probes successfully resolved and distinguished the topography and electrochemical activity at the edge of a screen-printed gold/polymer sensor.
- Advanced Application: The technique was applied to porous Boron-Doped Diamond (BDD) samples, revealing that variations in SECM current were caused by a combination of inhomogeneous topography, porosity, and non-uniform boron doping distribution within the BDD layer.
- Key Achievement: This approach facilitates widespread use of combined SECM/SICM for simultaneous, non-contact investigation of topographical and electrochemical surface properties.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Ring UME Diameter (Polished) | 25 | ”m | SECM/SICM Probe Characterization |
| Ring UME Diameter (Unpolished) | 2 | ”m | SECM/SICM Probe Characterization |
| Platinum Film Thickness | <50 | nm | Estimated thickness of the UME film |
| SECM Potential (Model Substrate) | +0.3 | V | Applied to probe (FcMeOH mediator) |
| SICM Potential (Model Substrate) | +0.2 | V | Applied to probe |
| SECM Scan Rate (Model Substrate) | 40 | ”m s-1 | Imaging speed |
| SECM Current Increase (Conductor PAC) | 135 | % | Relative to bulk current |
| SECM Current Decrease (Insulator PAC) | 85 | % | Relative to bulk current |
| Redox Mediator (Model) | 1.5 | mmol dm-3 | Ferrocenemethanol (FcMeOH) |
| Redox Mediator (BDD) | 1.5 | mmol dm-3 | Hexaamineruthenium(III) chloride (Ru(NH3)6Cl3) |
| Supporting Electrolyte Concentration | 0.2 | mol dm-3 | KNO3 or KCl |
| BDD Deposition Temperature | ca. 750 | °C | Substrate temperature |
| BDD Microwave Power | 1150 | W | During deposition |
| BDD Gas Pressure | 50 | mbar | During deposition |
| BDD Gas Composition | 0.5% CH4 in H2 | N/A | Methane concentration |
| Boron Doping Ratio (B/C) | 4000 | ppm | Trimethylboron addition in gas phase |
| BDD Porous Template Thickness | 4-5 | ”m | 3D template layer |
| BDD SECM Potential (Probe) | -0.4 | V | Applied to probe (Ru(NH3)6Cl3 mediator) |
| BDD SICM Potential (Probe) | +0.2 | V | Applied to probe |
| BDD Scan Rate | 30 | ”m s-1 | Imaging speed |
Key Methodologies
Section titled âKey MethodologiesâI. Cost-Efficient Dual-Probe Fabrication (SECM/SICM)
Section titled âI. Cost-Efficient Dual-Probe Fabrication (SECM/SICM)âThe probes were fabricated by modifying commercial platinum-coated fused silica emitters for electrospray ionization.
- Electrical Contacting: A copper tube (1.1 mm ID) was pushed over the capillary. Silver conductive paint and adhesive were used to establish contact between the copper and the platinum coating.
- Photoresist Application: A 10:1 mixture of SU8.5 photoresist and ethanol was applied under N2 flow to the tip.
- Curing: The photoresist was cured using UV light (350 nm) for 30 s.
- Heating/Solvent Evaporation: The tip was heated in an oven at 95 °C for 5 min.
- Coating Check and Repetition: Cyclic voltammetry (CV) was used to check the insulation quality; steps 2-4 were repeated if currents were too high.
- Tip Polishing (for larger probes): If larger ring diameters (e.g., 25 ”m) were desired, the tips were polished using 0.3 ”m alumina lapping sheets while water was flushed through the pipette to prevent clogging.
- Final Assembly: The finished pipette was filled with supporting electrolyte (KNO3 or KCl), and a Ag/AgCl wire was inserted to serve as the quasi-reference/counter electrode for SICM.
II. Porous Boron-Doped Diamond (BDD) Synthesis
Section titled âII. Porous Boron-Doped Diamond (BDD) SynthesisâPorous BDD samples were prepared via a two-step diamond deposition process on conductive p-Si wafers.
- Base Layer Deposition: A planar BDD base layer was grown using Microwave Plasma Chemical Vapor Deposition (MPCVD).
- Template Preparation: A 4-5 ”m thick 3D template, comprising nanodiamond-seeded SiO2 nanofibers in a polymer solution, was spin-coated (3000 rpm for 30 s) onto the BDD base layer and dried.
- Porous Layer Growth: A second diamond deposition step was performed for 5 h, using the following MPCVD conditions:
- Gas Phase: 0.5% Methane (CH4) in Hydrogen (H2).
- Doping: Trimethylboron added to achieve a B/C ratio of 4000 ppm.
- Conditions: 50 mbar pressure, 1150 W microwave power, ca. 750 °C substrate temperature.
- Surface Termination: The fabricated porous BDD samples were hydrogen terminated (as-grown).
Commercial Applications
Section titled âCommercial ApplicationsâThe simultaneous SECM-SICM technique and the materials investigated (BDD) are highly relevant across several advanced engineering and materials science sectors:
- Electrocatalysis and Energy Storage:
- High-resolution mapping of electrocatalytic activity on novel electrode materials (like BDD) for fuel cells, water splitting, or CO2 reduction.
- Investigating local current density variations in battery or supercapacitor electrodes to optimize charge/discharge kinetics.
- Corrosion Science:
- Non-contact, simultaneous monitoring of localized corrosion processes (electrochemical activity) and resulting surface damage (topography) on metal alloys or protective coatings.
- Biosensing and Biomedical Engineering:
- Characterization of cell membranes or biological surfaces, where SICM provides high-resolution topography of soft samples without contact damage, while SECM monitors local biochemical reactions (e.g., neurotransmitter release).
- Advanced Materials Characterization:
- Quality control and failure analysis of microelectronic devices, particularly distinguishing between structural defects (topography) and functional defects (electrochemical short circuits or activity variations) on complex patterned surfaces.
- Diamond Technology (BDD):
- Development and optimization of BDD electrodes for harsh environment sensing and wastewater treatment, where understanding the relationship between surface morphology (porosity) and electrochemical uniformity (doping distribution) is critical for performance and longevity.
View Original Abstract
Abstract A novel and cost-efficient probe fabrication method yielding probes for performing simultaneous scanning electrochemical microscopy (SECM) and scanning ion conductance microscopy (SICM) is presented. Coupling both techniques allows distinguishing topographical and electrochemical activity information obtained by SECM. Probes were prepared by deposition of photoresist onto platinum-coated, pulled fused silica capillaries, which resulted in a pipette probe with an integrated ring ultramicroelectrode. The fabricated probes were characterized by means of cyclic voltammetry and scanning electron microscopy. The applicability of probes was demonstrated by measuring and distinguishing topography and electrochemical activity of a model substrate. In addition, porous boron-doped diamond samples were investigated via simultaneously performed SECM and SICM. Graphic abstract
Tech Support
Section titled âTech SupportâOriginal Source
Section titled âOriginal SourceâReferences
Section titled âReferencesâ- 2012 - Scanning electrochemical microscopy