WAVES ON A METAL-SURFACE AND QUANTUM CORRALS

Electrons occupying surface states on the close-packed faces of noble metals form a two-dimensional (2-d) nearly free electron gas. Because this system is accessible to the scanning tunneling microscope (STM), it provides a unique opportunity to study the local properties of low- dimensional electrons. On Cu(111) we have observed standing wave patte rns in the surface local density of states due to the quantum mechanic al interference of surface state electrons scattering off of step edge s and adsorbates. We find that Fe adatoms strongly scatter the surface state and, as a result, are good building blocks for constructing ato mic-scale barriers (''quantum corrals'') to confine the surface state electrons. The barriers are constructed by individually positioning Fe adatoms using the tip of a cold (4 K) STM. Tunneling spectroscopy per formed inside of the corrals reveals discrete resonances, consistent w ith sire quantization. A more quantitative understanding is obtained b y accounting for the multiple scattering of surface state electrons wi th the corrals' constituent adatoms. This scattering is characterized by a complex phase shift which can be extracted from the electronic de nsity pattern inside a quantum corral.