ALKALI METAL GAAS(110) INTERFACES - CORRELATION-EFFECTS AND SUBGAP ELECTRON-ENERGY-LOSS SPECTRA/

The sub-gap high-resolution electron energy loss spectra (HREELS) of t he interfaces between Rb, Cs, K,Na and GaAs(110) are presented. The sp ectra of the Rb/GaAs(110) interface show that this interface is insula ting up to half-monolayer coverage when two strong loss peaks appear a t 0.6 and 1.3 eV, in analogy to that already found for Cs and K and co nfirmed here. By comparing the energies of these two losses in the dif ferent interfaces, interesting regularities are found as well as a pos sible connection with the corresponding bulk metal surface plasmon. Th is comparison also suggests that the formerly proposed link between th e two peaks and the presence of correlation effects is not as direct. The two loss features could be associated with coupled collective exci tations of the small clusters originated from the decay, at above half a monolayer, of the multi-row atomic chains formed by Cs, K and presu mably also by Rb atoms on the GaAs(110) surface. In the case of the Na /GaAs(110) interface, on the contrary, the formation of bi-polarons se ems to prevent the build-up of multi-rows chains and their decay into small bi-dimensional clusters. Accordingly, no sub-gap features are fo und in the corresponding spectra. (C) 1998 Elsevier Science B.V. All r ights reserved.