Scanning Tunneling Microscope

A Scanning Tunneling Microscope (STM) is a tool for atomic-scale surface imaging my team and I built under UC Davis Professor Chiang’s guidance. The STM operates by positioning a sharp tungsten tip within a few angstroms of a conductive sample surface and applying a small voltage to generate a current through quantum tunneling. The scanning tip is mounted on a piezoelectric disk, which expands or contracts with voltage, allowing movement in all directions. A PID feedback loop maintains a constant tunneling current by adjusting the tip-sample z-distance via piezoelectric voltage. Similarly, the piezoelectric disk moves the tip in x and y axes to scan the tip across the sample. Through this, we constructed atomic-scale topographic images of samples.

Subsystems:

Structural Damping System

• Three large springs hold up the scanner to isolate it from vibrations. Though there may be miniscule oscillations, the whole scanner subsystem oscillates as whole, maintaining tip-sample distance 
• Strong Magnets placed at the bottom and around the sides help minimize oscillations and swaying.
• Small pieces of rubber between large aluminum plates help minimize any last vibrations 

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Electronics

• Stepper motor lowers the tip close enough to the sample to begin tunneling
• Laptop and Teensy CPU to control voltage outputs, feedback loop, and record data
• Other: 15V Power Supply, Piezoelectric Disk, Motor Controller, Preamplifier, Green Amp, ADC

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Scanner

• Graphene sample
• Tungsten tip