title: Surface structures of In-Pd intermetallic compounds. I. Experimental study of In thin films on Pd(111) and alloy formation.
abstract: A combination of experimental methods was used to study the structure of In thin films deposited on the Pd(111) surface and the alloying behavior. X-ray photoelectron spectroscopy (XPS), low-energy electron diffraction (LEED), and scanning tunneling microscopy results indicate that surface alloying takes place at room temperature. Below 2 monolayer equivalents (MLEs), the LEED patterns show the formation of three rotational domains of InPd(110) of poor structural quality on top of the Pd(111) substrate. Both core-levels and valence band XPS spectra show that the surface alloy does not yet exhibit the electronic structure characteristic of the 1:1 intermetallic compound under these conditions. Annealing the 1 MLE thin film up to 690 K yields to a transition from a multilayer InPd near-surface intermetallic phase to a monolayer-like surface alloy exhibiting a well ordered (√3×√3) R30(∘) superstructure and an estimated composition close to In2Pd3. Annealing above 690 K leads to further In depletion and a (1 × 1) pattern is recovered. The (√3×√3) R30(∘) superstructure is not observed for thicker films. Successive annealing of the 2 MLE thin film leads the progressive disappearance of the InPd diffraction spots till a sharp (1 × 1) pattern is recovered above 690 K. In the high coverage regime (from 4 to 35 MLE), the formation of three rotational domains of a bcc-In7Pd3 compound with (110) orientation is observed. This In-rich phase probably grows on top of interfacial InPd(110) domains and is metastable. It transforms into a pure InPd(110) near-surface intermetallic phase in a temperature range between 500 and 600 K depending on the initial coverage. At this stage, the surface alloy exhibits core-level chemical shifts and valence band (VB) spectra identical to those of the 1:1 InPd intermetallic compound and resembling Cu-like density of states. Annealing at higher temperatures yields to a decrease of the In concentration in the near-surface region to about 20 at.% and a (1 × 1) LEED pattern is recovered.
authors.affiliation: Institut Jean Lamour (UMR7198 CNRS-Nancy-Université de Lorraine), Parc de Saurupt, 54011 Nancy Cedex, France.
authors.forename: G M
authors.initials: GM
authors.lastname: McGuirk
authors.affiliation: Institut Jean Lamour (UMR7198 CNRS-Nancy-Université de Lorraine), Parc de Saurupt, 54011 Nancy Cedex, France.
authors.forename: J
authors.initials: J
authors.lastname: Ledieu
authors.affiliation: Institut Jean Lamour (UMR7198 CNRS-Nancy-Université de Lorraine), Parc de Saurupt, 54011 Nancy Cedex, France.
authors.forename: É
authors.initials: É
authors.lastname: Gaudry
authors.affiliation: Institut Jean Lamour (UMR7198 CNRS-Nancy-Université de Lorraine), Parc de Saurupt, 54011 Nancy Cedex, France.
authors.forename: M-C
authors.initials: MC
authors.lastname: de Weerd
authors.affiliation: Institut Jean Lamour (UMR7198 CNRS-Nancy-Université de Lorraine), Parc de Saurupt, 54011 Nancy Cedex, France.
authors.forename: V
authors.initials: V
authors.lastname: Fournée