Surface structures of In-Pd intermetallic compounds. I. Experimental study of In thin films on Pd(111) and alloy formation

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...

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Bibliographic Details
Published in:	The Journal of chemical physics 2014-08, Vol.141 (8), p.084702-084702
Main Authors:	McGuirk, G M, Ledieu, J, Gaudry, É, de Weerd, M-C, Fournée, V
Format:	Article
Language:	eng
Subjects:	ANNEALING BCC LATTICES Chemical Sciences CHEMICAL SHIFT Condensed Matter Copper DENSITY DEPOSITS Diffraction patterns Domains ELECTRON DIFFRACTION ELECTRONIC STRUCTURE INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY INTERMETALLIC COMPOUNDS Intermetallic phases Low energy electron diffraction Material chemistry Materials Science Monolayers Multilayers Organic chemistry Palladium PALLADIUM 111 Physics SCANNING TUNNELING MICROSCOPY SPECTRA Spectrum analysis SUBSTRATES Superstructures Surface alloying THIN FILMS Valence band X ray photoelectron spectroscopy X ray spectra
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Summary:	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.
ISSN:	0021-9606 1089-7690