An example would be a scanning tunneling microscope. It has a tiny probe-tip of conducting wire mounted on a pizeoelectric arm, which enables the tip to be scanned over the sample surface at an atomic distance. If a small voltage is applied across the tip and sample, some electrons will quantum tunnel from the tip across the gap to the sample, thus creating a measurable current. As the tip scans the atoms, the current changes, and a graphical representation of that change can be created.