Surface morphology of heterogeneous nanocrystalline rutile/amorphous anatase TiO2 films grown by reactive pulsed magnetron sputtering

Raúl Gago, Mykola Vinnichenko, Andrés Redondo-Cubero, Zsolt Czigány, Luis Vázquez

Research output: Contribution to journalArticle

12 Citations (Scopus)

Abstract

Titanium dioxide films were grown on unheated substrates by mid-frequency (100 kHz) reactive pulsed magnetron sputtering at different O2 partial pressures in an Ar/O2 atmosphere. X-ray diffraction and absorption measurements reveal a transition from amorphous anatase to nanocrystalline rutile with [O2], with a mixture of both phases at intermediate values. Atomic force microscopy shows that the promotion of rutile is accompanied by surface roughening due to the apparition of hollow structures (holes) on the surface, in contrast with the extremely smooth morphology of amorphous anatase films. The number and size of holes increase with [O 2] and growth time in such a way that they eventually coalesce and percolate to lead to a rough surface for those growth conditions for which a rutile rich film is obtained. Transmission electron microscopy analysis shows the growth evolution of a heterogeneous phase mixture and provides unambiguous correlation between the hole (smooth) morphology and the underlying rutile (anatase) phase. Therefore, the surface morphology results from the slower local growth rate of nanocrystalline rutile compared to that of the surrounding amorphous anatase flat regions as well as from the fast (slow) lateral (vertical) growth rate of the rutile domains. A correlation between the morphology and structural evolution of TiO2 films grown by reactive pulsed magnetron sputtering (PMS) has been established. X-ray absorption near edge structure (XANES) and transmission electron microscopy (TEM) have shown the evolution of a heterogeneous (nanocrystalline) rutile and (amorphous) anatase phase mixture. The rutile phase is favored with the O2 content ([O2]) in the plasma discharge and growth time. This heterogeneity is also imprinted on the surface morphology evolution, where hollow structures (holes) appear over smooth regions due to the underlying rutile and anatase phases. The origin of such morphologic depressions are the result of the slower growth rate of rutile than (amorphous) anatase as well as the faster lateral than vertical growth rate of rutile domains.

Original languageEnglish
Pages (from-to)813-823
Number of pages11
JournalPlasma Processes and Polymers
Volume7
Issue number9-10
DOIs
Publication statusPublished - Oct 14 2010

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Keywords

  • amorphous
  • magnetron
  • oxides
  • pulsed discharges
  • thin films

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Polymers and Plastics

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