How does a scanning tunneling microscope create images of individual atoms?

A scanning tunneling microscope (STM) creates images of individual atoms by utilizing the quantum mechanical phenomenon known as tunneling.12

The process works as follows:

• Proximity: A sharp tungsten needle tip is positioned just a few angstroms away from the sample surface.1
• Voltage and Current: A small voltage is applied between the tip and the surface, which allows electrons to "tunnel" across the gap—a process where electrons pass through a barrier that would be impassable under classical physics.12
• Sensitivity: The probability of this tunneling current is extremely sensitive to the distance between the tip and the surface. As the probe scans across the surface, it registers variations in the tunneling current.1
• Imaging: In semiconductors, the tunneling current measures electron density, which peaks at atomic sites and appears as bright spots. In metals, the interaction between the tip and the surface perturbs the electron density, causing the current to increase when the tip is directly above an atom.1

This data is processed to generate a topographical map, revealing the precise spatial distribution of individual atoms.1