Scanning Tunneling Microscopy (STM)

This instrument uses the phenomenon of quantum mechanical electron tunneling between a sharp metallic tip
and a flat sample separated by a distance of about 0.5 nm. The electron tunneling current (I_t) depends exponentially
on the distance between the tip and sample (d) which makes I_t very sensitive to small changes in d.
 
I_t ~ exp(-kd) where k is related to the work function.

Click on image to see the imaging mode

The high sensitivity of the tunnel current to the tip-sample distance results in the high spatial resolution of the STM.
Some examples are shown below:

The bumps are Mn atoms in a hole-doped manganite single crystal. Ref. Biswas et al., Phys. Rev. B 59, 5368 (1999)


The STM is beautiful in its simplicity. The basic microscope looks deceptively uncomplicated.

For more STM images follow the links:

Images of the high Tc superconductor BSCCO

Moving atoms, one at a time