The formation and stability of Rh nanostructures on TiO 2 (1 1 0) surface and TiO x encapsulation layers

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Abstract

Rh overlayers formed on slightly oxygen deficient TiO 2 (1 1 0) single crystals, as well as on ultrathin encapsulation titania layers prepared on Rh multilayers were characterized by AES, LEIS, XPS, TPD and work function (WF) measurements. Rh deposition on TiO 2 (1 1 0) below 0.1 monolayer (ML) Rh coverage led to electron transfer from the metal toward the TiO 2 (1 1 0) surface. Annealing of Rh multilayers up to 950 K in UHV resulted in the surface diffusion of titanium and oxygen ions into a TiO x encapsulation layer of definite stoichiometry and a thickness of a few atomic layers. The accompanying 0.3-0.6 eV WF enhancement at Θ Rh = 2-6 ML can be attributed to the smoothing of the Rh overlayer and the formation of a continuous TiO x dipole layer consisting of positively charged titanium ions at the metal-oxide interface and negative oxygen ions in the topmost layer. De-encapsulation of Rh particles was observed on a TiO 2 sample less reduced in its bulk, revealing the roles of bulk and surface substrate stoichiometry on the decoration process. Increasing the thickness of Rh multilayers supported on the TiO 2 (1 1 0) single crystal hampered ion diffusion and consequently, it led to an increase in the temperature characteristic of the completion of the encapsulation. Deposition of additional Rh on the TiO x encapsulation layers covering Rh multilayers resulted in the growth of Rh particles having a similar height up to 1 ML. LEIS data indicated that the decoration of the second metal layer by titania was hindered. It occurred at a temperature more than 100 K higher than that characteristic of the TiO 2 (1 1 0) surface at the same Rh coverage. Aspects of the produced structures in relation to the formation of protective oxide layers, modification of surface work function, catalysis and metal-insulator-metal (MIM) devices are considered.

Original languageEnglish
Pages (from-to)60-66
Number of pages7
JournalApplied Surface Science
Volume280
DOIs
Publication statusPublished - Sep 1 2013

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Keywords

  • Charge transfer
  • Encapsulation
  • MIM device
  • Protecting oxide layer
  • Rhodium film
  • Self-limited growth
  • Titanium dioxide template

ASJC Scopus subject areas

  • Chemistry(all)
  • Condensed Matter Physics
  • Physics and Astronomy(all)
  • Surfaces and Interfaces
  • Surfaces, Coatings and Films

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