Purified rhodium edge states: undercoordination-induced quantum entrapment and polarization

Artificial undercoordination of Rh atoms at a surface is indeed fascinating. It not only generates unusual energy states, but also differentiates the processes of catalytic reaction and growth nucleation at such atomic sites from those proceeding at a flat surface. Recent findings have stimulated the need a better understanding of the mechanism behind these observations. An X-ray photoelectron differential spectroscopy (XPDS) study reported herein reveals that the undercoordinated Rh atoms at step edges and the nearby missing-row vacancies generate two extra states in the 3d(5/2) band. These findings confirm theoretical [C. Q. Sun, Prog. Solid State Chem., 2007, 35, 1] expectations that the shorter and stronger bonds between undercoordinated atoms cause the local quantum entrapment of the core charge and the polarization of the otherwise conducting s-electrons by the densely and deeply trapped core electrons. Therefore, the XPDS resolved low-energy component arises from quantum entrapment, while the high-energy one arises from potential screening by polarization.