Effect of a gold cover layer on the encapsulation of rhodium by titanium oxides on titanium dioxide(110)

L. Óvári, A. Berkó, Richárd Gubó, Árpád Rácz, Z. Kónya

Research output: Contribution to journalArticle

13 Citations (Scopus)

Abstract

The present study focuses on the thermal behavior of continuous rhodium thin films (̃10 nm) deposited on a TiO2(110) substrate at 300 K and covered by a continuous ultrathin gold film (̃1 nm), applying scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and low-energy ion scattering (LEIS) techniques. This arrangement facilitated a rather clear-cut investigation into the effect of the Au cover layer on the well-known encapsulation/decoration of Rh by TiOx, since the contribution of the titania substrate to the XPS and LEIS spectra could be avoided. Upon annealing a monometallic Rh film, the diffusion of Ti and O from the TiO2(110) substrate on top of the Rh film is essentially complete up to 850 K, leading characteristically to the formation of a "pinwheel" encapsulation layer with a TiO1.2 stoichiometry. The dewetting of the Rh film does not take place up to 950 K. Upon annealing of the Rh film in the presence of a continuous Au cover layer, the diffusion/accumulation of O was completely blocked up to 850 K, but metallic Ti was well detectable by XPS. Since LEIS spectra were dominated by the Au peak, and almost no Ti signal was observable up to this temperature, the metallic Ti is mainly stabilized at subsurface positions, probably either at the Rh-Au interface or within the Au film, in any case in contact with Au. The complete separation of O and Ti diffusion in this temperature range can be attributed to the weak interaction between oxygen and gold. Raising the sample temperature up to 930 K induces substantial changes. The diffusion of O is no longer kinetically hindered, and it reacts with a part of the alloyed Ti to form well-separated TiO2 nanoclusters on top of the Au shell. However, no oxygen is stabilized at subsurface sites in the bimetallic film. The rest of Ti alloyed in the subsurface is detectable by STM as ringlike features. The "pinwheel" TiO1.2 encapsulation layer appearing typically on a pure Rh film did not form on the bimetallic Au-Rh film at any of the temperatures investigated.

Original languageEnglish
Pages (from-to)12340-12352
Number of pages13
JournalJournal of Physical Chemistry C
Volume118
Issue number23
DOIs
Publication statusPublished - Jun 12 2014

Fingerprint

Rhodium
Titanium oxides
rhodium
Encapsulation
titanium oxides
Gold
Titanium dioxide
gold
ion scattering
X ray photoelectron spectroscopy
photoelectron spectroscopy
Scanning tunneling microscopy
Scattering
Ions
scanning tunneling microscopy
Substrates
Annealing
Oxygen
titanium dioxide
Temperature

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Electronic, Optical and Magnetic Materials
  • Surfaces, Coatings and Films
  • Energy(all)

Cite this

Effect of a gold cover layer on the encapsulation of rhodium by titanium oxides on titanium dioxide(110). / Óvári, L.; Berkó, A.; Gubó, Richárd; Rácz, Árpád; Kónya, Z.

In: Journal of Physical Chemistry C, Vol. 118, No. 23, 12.06.2014, p. 12340-12352.

Research output: Contribution to journalArticle

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AU - Kónya, Z.

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