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)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)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/FindingsProcess/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 1 st Etch 2 nd Etch

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

14. Objectives for Optimizing 1 st 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 NH 4 :C 2 H 6 :H 2 O 2 to prevent evaporation This solution works just as well as NH 4 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 1 st and 2 nd 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 R I Current 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 NH 4

23. Second Etch: Useful Findings

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

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

27. 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