The STM probe is brought very close to the sample surface, only a few angstroms away. When a voltage is applied between the probe and the sample, electrons tunnel through the vacuum between them, creating a tunneling current. This current is highly sensitive to the distance between the probe and the sample, allowing for precise imaging of the surface's atomic structure. By scanning the probe across the surface and maintaining a constant tunneling current, a topographic map of the surface can be constructed.
