A z-axis tunneling microscope for undergraduate labs

We describe the development of an advanced laboratory apparatus inspired by the scanning tunneling microscope (STM) but simplified to one dimension: the z-axis tunneling microscope (ZTM). This device allows undergraduate experimentation on electron quantum tunneling and electronic density of states. Student data from an advanced lab course show qualitative differences in density of states between metals, semimetals, and semiconductors. Students also observe that the tunneling current is exponentially dependent on the tip-sample separation. The ZTM is a simple device providing access to condensed matter physics in the undergraduate lab curriculum.