Modelling of bond structure and potential barrier of O-Cu(001) surface characterised by STM/S and VLEED

The O-Cu(00I) surface has been studied extensively for several decades. The existing static-structure models have contributed greatly to the advance of this regime but disputes still remain concerning the nature and formation of the O­Cu bond. Scanning Tunnelling Microscopy/Spectroscopy (STM/S) has provided dynamic visions of the reconstruction but quantitative information and a detailed description of the reaction dynamics is still lacking. The analysis of a variety of STM/S O-metal outcomes and VLEED spectra of the O-Cu(00l) surface leads to a new model of the bond structure and suggests that a non-uniform surface potential barrier (SPB) for O-metal surfaces is required. It is taken into account that the O possesses two bonding and two nonbonding orbitals and that the atomic radii vary with the alternation of their atomic states and their coordination surroundings. It is proposed that the O­metal reaction is a result of the hybridisation of the O generating two Goldschmidt-contraction ionic bonds and two nonbonding lone pairs and that the lone-pair-induced metal dipoles reinforce the SPB and reduce the local work function ØL(x, y). These models support Lang's Tunnelling theory regarding O-chemisorbed metal systems and explain the big protrusions on O­metal surfaces and the reduction of work function as arising from the metal dipoles. The formation of the lone-pair-zigzagged O-M chains and the presence/absence of missing rows is a consequence of the surface-bond formation. The generality of the bond model is shown by proposing four kinds of O-metal chains to explain the STM images of orderly reconstructed O-metal surfaces. The ability of the model to provide a quantitative description of the reaction dynamics is demonstrated by simulating the O-increasing VLEED spectra of the Cu(00l) surface with individual variation of only three bond-structure variables. It is found that the VLEED is as useful as STM/S in revealing information of the spatial electron distribution and the variation of the density of states in the shared energy window. This work therefore demonstrates the combination of STM/S and VLEED techniques as powerful complementary tools for revealing the processes of surface reconstruction