from http://ktgss.edu.hk/academic/physics/phyindex/files/PhyPicMonth.htm [May 2005]

Quantum Corral is a ring of 48 iron atoms on a copper (III) surface. The iron atoms, being less conductive, can confine some of the copper's surface electrons within the ring. The 48 iron atoms, adsorbed on the copper (III) surface, were moved into position with the tip of a low temperature scanning tunneling microscope (STM), to make a corral ring with a radius of 7.13x10-9 m. The ripples in the corral ring represent the density distribution of a particular set of quantum states of copper's surface electrons. The image is also obtained by using STM. Colours of the photo above were added artificially. The quantum corral also verifies the existence of electrons and the wave-particle duality.
An animation showing how a Scanning Tunneling Microscope works can be found here, namely, 

http://ktgss.edu.hk/academic/physics/phyindex/image/stm_animated.gif