Transcript 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
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•
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•
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Background (Tips, STM)
Research Inspiration (Why Silver Tips)
Process/Results/Findings
Future Applications
Acknowledgements
What are “tips”
• Used in STMs
• Atomic-sized
radius of curvature
• Etched using
electrochemistry
• Usually made of
tungsten metal
Tips usage in STMs
Atomic Mapping: The Art of Drawing
Atoms
Outline
•
•
•
•
•
Background (Tips, STM)
Research Inspiration (Why Silver Tips)
Process/Results/Findings
Future Applications
Acknowledgements
Ho Lab Group Goals & Research
Inspiration
• Nanoscale
Chemical &
Physical
Phenomena
• Detailed
Descriptions of
Individual
Molecules and
Atoms
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
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
Outline
•
•
•
•
•
Background (Tips, STM)
Research (Why Silver Tips)
Process/Results/Findings
Future Applications
Acknowledgements
Primary Objective of Research
The challenge presented is optimizing the procedure and
parameters for etching silver tips to ensure efficiency and
reproducibility.
2-Step Electrochemical Etching
1st
Etch
2nd Etch
Setup of Primary Etch System
(Electropolishing)
Graphite
Tip
Electrolyte
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
Stabilize that Solution
• Began using a new recipe
NH4:C2H6:H2O2 to prevent
evaporation
• This solution works just as well as
NH4
• Needs to be replenished after 3
hours
• Liquid Levels are consistent
over time
DC Voltage Slows and Speeds Etching
Effect of Voltage on Etching Time
30
Time (minutes)
25
20
Time Trial 1
15
Time Trial 2
Time Trial 3
10
5
0
0
10
20
DC Voltage (Volts)
30
40
A Need For Automation
• The electrochemical reaction is lengthy
& subtle
• Visual Inspection Required
• Cannot Perform both 1st and 2nd Etches
at the same Time
What’s the “Current” Trend?
Current Flow Through Silver Tips
While Etching
Current (mA)
6
5
4
V=24V
3
V=30V
2
V=21V
1
0
0
10
20
Time (minutes)
30
How Can we Measure It?
Measure voltage
Across a Resistor
using a Voltmeter
Current
I
R
Use LabVIEW
software to
analyze signal
Voltmeter
Resistor
The New System: From Idea to Reality
Triggered
Alarms
I = 0 mA
I < 2 mA
Variation in Apex Shape After First Etch
Secondary Etch Setup Diagram
DC Voltage 5-12V
Tip
NH4
Second Etch: Useful Findings
Outline
•
•
•
•
•
Background (Tips, STM)
Research (Why Silver Tips)
Process/Results/Findings
Future Applications
Acknowledgements
Innovation
Future Possibilities/Applications:
Chemical/Optical Sensors
High Density Data Storage
Nanoelectronic Circuit Components
Bio-toxin & Pollution Removal
Quantum Computing
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