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2016-05-08 - Colloque/Présentation - poster - Anglais - 1 page(s)

Raza Mohsin, Cornil David , Cornil Jérôme , Lucas Stéphane, Thomann A.L., Caillard Amaël, El Mokh M., Pierson Jean-François, Boulet Pascal, Snyders Rony , Konstantinidis Stéphanos , "Phase formation and stability of reactive sputtered zirconium dioxide thin films" in Plasma-Surface Interaction IAP workshop , Nancy, France, 2106

  • Codes CREF : Physique de l'état solide (DI1261), Physique des surfaces (DI1265), Chimie des solides (DI1316), Physique des plasmas (DI1233), Sciences exactes et naturelles (DI1000)
  • Unités de recherche UMONS : Chimie des interactions plasma-surface (S882)
  • Instituts UMONS : Institut de Recherche en Science et Ingénierie des Matériaux (Matériaux)
  • Centres UMONS : Centre d’Innovation et de Recherche en Matériaux Polymères (CIRMAP)

Abstract(s) :

(Anglais) Since materials properties are greatly influenced by their phase constitution, therefore it’s of high importance to understand and address those mechanisms which drive their phase formation and stability. In this respect, Zirconia (ZrO2) is one of the most important technological ceramic who has been enjoying a special attention since last couple of decades to understand its cubic (c)-phase formation and stabilization at room temperature without any doping. In the present study, we investigate the role of film chemistry i.e. of oxygen vacancies and of energy deposited during the film growth on c-phase formation. To this purpose, 100 nm thick films of zirconium oxide are grown in the poisoned mode as well as in the transition zone with the help of voltage feedback control unit (Speedflo mini from Gencoa UK). By systematically varying the working parameters, it is observed that for films grown at 200 mA, 10 mTorr in the poisoned mode (i.e. ZrO2 films), the XRD diffractograms only exhibits reflections from the low-temperature stable monoclinic (m)-phase. On the other hand, while working inside the transition zone i.e. by growing under-stoichiometric zirconium oxide (ZrO2-x) thin films as demonstrated by careful elemental characterization, the film phase is dramatically modified and only the c reflections are observed. Theoretical calculations at the Density Functional Theory (DFT) level are in remarkable agreement with the experimental data, hence highlighting that the incorporation of oxygen vacancies is the sole responsible mechanism for the stabilization of the c-phase. It is also observed that any deviation from the optimized working conditions leads to the change in film phase constitution, as an example, if the film thickness (and obviously the duration of the deposition process) is increased, the XRD spectrum is modified. A clear modification of the XRD spectrum is also witnessed if the discharge current is increased (400 mA) or if the working pressure is decreased (5 mTorr). Thermal annealing analysis performed in air and N2 shows the oxygen vacancy stabilized zirconia (ZrO2-x) films are stable up-to 750 C. Above 750 C, the mechanical stress, generated in the film due to the mismatch of the thermal expansion coefficients of both the zirconia film and the substrate, apparently surpasses a critical value and leads to the appearance of m-phase. In conclusion, c-phase of zirconia can be stabilized at room temperature (up to 750°C) by solely incorporating the oxygen vacancies in the zirconia lattice. However, increasing the energy flux during film growth or the mechanical stress may induce the transformation of the oxygen vacancy stabilized cubic phase of zirconia into the m-phase.