Structural and electronic properties of ultrathin films of In, Sn and Sb grow on Pd (111), studied by PED and XPS

Nesse trabalho nos propomos a estudar a estrutura eletrônica e geométrica de ligas de superfície à partir de filmes ultra finos, da ordem de monocamada atômica , crescidos por MBE sobre substratos monocristalinos. Os filmes finos foram crescidos in situ e analizados por XPS (X-Ray Photoelectron Spectroscopy), PED (Photoelectron Diffraction), LEED (Low Energy Electron Diffraction) e UPS (Ultra Violet Photoelectron Spectroscopy). As ligas de superfície estudas foram InPd, SnPd e SbPd sempre sobre um substrato de Pd(111). Os resultados das medidas PED dos sistemas InPd e SnPd foram interpretadas usando programas tipo MSCD[1]. Foi mostrado que Sn e In em baixa cobertura formam uma estrutura (raiz2 3 x raiz2 3) R 30o ( e o In mostrou uma estrutura (1x1) para filmes com mais de 2 monocamadas, provavelmente na forma de ilhas sobre a superfície do Pd. Estudos anteriores mostraram que Sb sobre Pd(111) também apresenta a fase (raiz2 3 x raiz2 3)R 30o para baixas coberturas[2]. Os modelos que melhor se adequaram aos dados sugerem fortemente que os metais sp(In, Sn,e Sb) não difundem além da segunda monocamada. Durante estes estudos foi observado que a intensidade do satélite de shake-up do Pd tendia a zero para os átomos em contato direto com os metais spThe purpose of this report is to present a study of the electronic and geometric structure of surface alloys grown by MBE (Molecular Beam Epitaxy) on single crystal substrates in the sub monolayer regime. The films were grown "in-situ" in the analysis chamber and analyzed by XPS (X-Ray Photoelectron Spectroscopy), PED (Photoelectron Diffraction), LEED (Low Energy Electron Diffraction) and UPS (Ultra Violet Photoelectron Spectroscopy). The alloys studied were InPd, SnPd e SbPd, all grown on the (111) face of a Pd crystal. The PED measurements for InPd and SnPd were analyzed using the MSCD code[3]. It was possible to show that for low coverages both metals formed a (raiz2 3 x raiz2 3) R 30o ( reconstruction and the first inter-planar distances were determined. For films with over two monolayers the In grew with a (1x1) structure probably in the form of islands separated by clean Pd. Previous studies showed that Sb[4] at low coverage also forms a (raiz2 3 x raiz2 3) R 30o ( structure. Our simulations suggest that In, Sn and Sb for the coverages studied do not diffuse beyond the second atomic layer. We also observed that the intensity of the Pd shake up satellite tends to zero for the Pd atoms in contact with these sp metal