Scanning tunneling microscopy

Scanning tunneling microscopy and spectroscopy (STM/STS) allows to characterize the topographic as well as the electronic properties of the surface of (semi)-conducting crystals up to atomic resolution (10^-10 m). This method is based on the well-known quantum property called tunneling effect of electron between a sharp tip and the sample surface : the tunneling current is exponentially dependent on the distance between both electrodes.

A gap voltage is applied between tip and sample, and the tip scans the surface line by line. In the same time, an electronic feedback loop is used in order to keep the tunneling current constant. The tip has therefore to adapt its height in order to keep a constant distance to the sample surface according to its local topography. This height profile is recorded and after the complete scan a topographic image of the surface is obtained.

Our Omicron LT-STM setup needs perfectly clean and flat surfaces. It works in ultra-high vacuum (10^-11 mbar) and cryogenic conditions (4.5 K).