We present the design and construction of a laboratory apparatus that provides advanced undergraduates with hands-on observations of electron quantum tunneling and the electronic density of states of various materials. The instrument is inspired by the scanning tunneling microscope (STM), but its implementation is simplified by limiting the tip motion to the single dimension along the tip-sample separation (z-axis); we refer to the device as the z-axis tunneling microscope (ZTM). Students are able to use the ZTM to measure electron tunneling probability as a function of barrier width, estimate relative material work functions, and observe differences in local electronic structure among metals, semimetals, and semiconductors. We share results obtained by third-year undergraduate physics students using the instrument for their final projects in an advanced instructional lab course.
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