4fphotoemission from Ce clusters and disordered reaction products at Ce/Si and Ce/GaAs interfaces

Abstract

Synchrotron radiation photoemission has been used to study the 4f emission from 4f electrons in Ce clusters and disordered reaction products at Ce/GaAs(110) and Ce/Si(111) interfaces. For low Ce coverages on GaAs(110), the reacted interface forms Ce-As local configurations with two 4f-derived features similar to those of bulk CeAs. The shallower 4f peak is located \ensuremath{\sim}1 eV below ${E}_{F}$, indicating that it is not due to fully relaxed 4f holes, consistent with the As p\ensuremath{\rightarrow}Ce 4f charge-transfer screening mechanism. For the Ce/Si interface, small Ce clusters formed at low coverage have only a single 4f peak at -3.3 eV, with no evidence of a second peak nearer ${E}_{F}$. This is attributed to the reduced number of neighboring Ce 5d orbitals for the clusters, apparent stability of the \ensuremath{\gamma} phase relative to the \ensuremath{\alpha} phase (in the ground state), and reducted 5d\ensuremath{\rightarrow}4f charge-transfer screening probability in the photoemission final state. At high coverages, Ce overlayers cover the reacted interfaces, but our results show that the 4f emission near ${E}_{F}$ is not established until \ensuremath{\theta}\ensuremath{\simeq}20 monolayers, suggesting that the 4f-5d hybridization in metallic Ce is long ranged compared with the short-range Ce-4f/As-p hybridization.