Electrical rectification by selective wave-function coupling in small Ag clusters on Si ( 111 ) − ( 7 × 7 )

A cluster consisting of as few as three Ag atoms deposited on $\text{Si}(111)\text{\ensuremath{-}}(7\ifmmode\times\else\texttimes\fi{}7)$ surface was found to behave as a strong electric rectifier, with a rectification ratio as large as $\ensuremath{\sim}150$. Based on first-principles calculations, we found that the wave functions of electronic states at different energies spread out from the surface to different distances. We demonstrated by theoretical simulations and experiments that the observed rectification is a result of coupling the scanning tunneling microscope tip with selective wave functions of the cluster.