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Electrochemical Wet Etching of Silver STM Tips

Electrochemical Wet Etching of Silver STM Tips . Presentation By: Anthony R. Davis Senior Electrical Engineering Major Hampton University Mentor: Dr. Wilson Ho Graduate Student: Xiuwen Tu. Outline. Background (Tips, STM) Research Inspiration (Why Silver Tips) Process/Results/Findings

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Electrochemical Wet Etching of Silver STM Tips

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  1. Electrochemical Wet Etching of Silver STM Tips Presentation By: Anthony R. Davis Senior Electrical Engineering Major Hampton University Mentor: Dr. Wilson Ho Graduate Student: Xiuwen Tu

  2. Outline • Background (Tips, STM) • Research Inspiration (Why Silver Tips) • Process/Results/Findings • Future Applications • Acknowledgements

  3. What are “tips” • Used in STMs • Atomic-sized radius of curvature • Etched using electrochemistry • Usually made of tungsten metal

  4. Tips usage in STMs

  5. Atomic Mapping: The Art of Drawing Atoms

  6. Outline • Background (Tips, STM) • Research Inspiration (Why Silver Tips) • Process/Results/Findings • Future Applications • Acknowledgements

  7. Ho Lab Group Goals & Research Inspiration • Nanoscale Chemical & Physical Phenomena • Detailed Descriptions of Individual Molecules and Atoms

  8. What’s Special About Silver Tips? • Research suggests that Ag tips have higher photon-coupling efficiency than tungsten tips • Enhanced Photo-Induced Tunneling yields more comprehensive data from specimens scanned

  9. Why is Etching Silver Tips so Challenging Compared to Etching other Metal Tips? • Malleable/Soft composure of Ag • Quick evaporation of electrolyte Solution • Appearance of AgOH reside • Silver tip etching is relatively new; etching methods are primitive • Well known methods & commerical kits are available for etching other metals tips (W, Au, Pt-Ir); but not Ag

  10. Outline • Background (Tips, STM) • Research (Why Silver Tips) • Process/Results/Findings • Future Applications • Acknowledgements

  11. Primary Objective of Research The challenge presented is optimizing the procedure and parameters for etching silver tips to ensure efficiency and reproducibility.

  12. 2-Step Electrochemical Etching 2nd Etch 1st Etch

  13. Setup of Primary Etch System(Electropolishing) Graphite Tip Electrolyte

  14. Objectives for Optimizing 1st Etch • Prevent Solution concentration for changing • Retard electrolyte evaporation • Increase Speed of First Etch • Obtain & interpret voltage vs. time data • Automate tip etching to increase efficiency • Create circuitry to monitor current flow through tip over time

  15. Stabilize that Solution • Began using a new recipe NH4:C2H6:H2O2to prevent evaporation • This solution works just as well as NH4 • Needs to be replenished after 3 hours • Liquid Levels are consistent over time

  16. DC Voltage Slows and Speeds Etching

  17. A Need For Automation • The electrochemical reaction is lengthy & subtle • Visual Inspection Required • Cannot Perform both 1st and 2nd Etches at the same Time

  18. What’s the “Current” Trend?

  19. How Can we Measure It? Measure voltage Across a Resistor using a Voltmeter Use LabVIEW software to analyze signal Current I R Voltmeter Resistor

  20. The New System: From Idea to Reality Triggered Alarms I = 0 mA I < 2 mA

  21. Variation in Apex Shape After First Etch

  22. Secondary Etch Setup Diagram DC Voltage 5-12V Tip NH4

  23. Second Etch: Useful Findings

  24. Outline • Background (Tips, STM) • Research (Why Silver Tips) • Process/Results/Findings • Future Applications • Acknowledgements

  25. Innovation Future Possibilities/Applications: Chemical/Optical Sensors High Density Data Storage Nanoelectronic Circuit Components Bio-toxin & Pollution Removal Quantum Computing

  26. Acknowledgements University of California, Irvine National Science Foundation (NSF) The UROP Team Department of Engineering Department of Physics & Astronomy Mentor: Dr. Wilson Ho Graduate Student: Xiuwen Tu

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