QUANTUM CORRALS

Electrons occupying surface states on the close-packed faces of the noble metals form a two-dimensional (2D) nearly-free electron gas that can be imaged with a scanning tunneling microscope (STM). We find that Fe adatoms strongly scatter metallic surface state electrons, acid so are good building blocks for constructing atomic-scale barriers to confine these electrons. The barriers (''quantum corrals'') are constructed by individually positioning Fe adatoms using the tip of a cold (4K) STM. Tunneling spectroscopy performed inside of the corrals reveals discrete resonances, consistent with size quantization. A more quantitative understanding is obtained by accounting for the multiple-scattering of the surface state electrons with the corrals' constituent adatoms. This scattering is characterized by a complex phase shift which can be extracted from the electronic density pattern inside a quantum corral.