| AVS 60th International Symposium and Exhibition | |
| Advanced Surface Engineering | Thursday Sessions |
| Session SE+NS+TF-ThA |
| Session: | Nanostructured Thin Films and Coatings |
| Presenter: | X. Noirfalise, University of Mons, Belgium |
| Authors: | X. Noirfalise, University of Mons, Belgium D. Cossement, Materia Nova J.-F. Paul, Université Lille, France F. Renaux, Materia Nova R. Snyders, University of Mons, Belgium |
| Correspondent: | Click to Email |
Recently, TiO2 surfaces supporting metals, used in numerous fields of application, have generated a lot of works because of the relationship between the morphology of the deposit and the electronic interactions at the TiO2/metal interface. As an example, oxygen deficient MoOx compound supported on TiO2 substrates demonstrate interesting catalytic properties. Accordingly, the growth of ordered MoOx nanostructures (nano-particles or ultrathin films) on TiO2 is of particular importance. Until now, the influence of the chemistry of the support on the deposit morphology is mainly studied. No systematic studies of the impact of the crystallographic constitution of the TiO2 substrates on the morphology of ultrathin (< 5 nm) Mo films have been reported yet. The objective of this work is to address this question.
We grew, by non-reactive DC sputtering of a metallic Mo target, MoOx films on home-made (reactive sputtering) and standard TiO2 supports. The TiO2 supports differ by their crystallographic constitution (amorphous, anatase and rutile). Aparticular attention is made on the influence of the TiO2 properties on the diffusion mechanism and oxidation process at the interface TiO2/MoOx using XPS and Tof-SIMS measurement. Periodic DFT calculations have been performed to support the experimental data.
XPS measurements showed that the interfacial reaction between the TiO2 surface and the deposited Mo is affected by the crystalline properties of the TiO2 support. The strong oxidation of the first monolayer of the deposited Mo is evidenced. Differences were found in the electronic exchange and, as a consequence, in the growth mode for the three TiO2 substrates. The emphasis is made with the Cabrera-Mott theory, namely the dependence of the interface reaction on the bulk electronic structure of the three phases.
The data are supported by Tof-SIMS depth profile measurements revealing the substrate-dependent diffusion of oxygen at the interface with appearance of a more or less important oxygen depleted zone at the surface of the TiO2 support. Additional measurements performed with Ti18O2 substrates as well as DFT calculations support the initial conclusion.
The growth mechanisms were estimated from the analysis of the peak and background shapes of the XPS signal by using the “QUASES” software. Due to the differences of the electronic exchange at the interface, a layer-by-layer growth mode is observed for Mo deposited on the (110)-rutile substrate, a Volmer-Weber growth mode is observed on the (101)-anatase substrate and a Stranki-Krastanov growth on the amorphous one.