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Abstract:
The crystalline to vitreous phase transformation of a SiO2 bilayer supported on Ru(0001) was studied by means of time‐dependent LEED, local XPS and DFT calculations. The silica bilayer system constitutes a model system that has interesting parallels to 3D silica glass and can be used to understand the mechanism of the disorder transition. An Arrhenius analysis of the time constant for the phase transformation in the 2D hexagonal network of crystalline silica at variable temperature gives apparent activation energy values (Eaapp) of (4.2 ± 0.6) and (4.1 ± 0.2) eV for the transformation in UHV and O2 atmosphere, respectively. The differences observed in the Eaapp values lie within the experimental accuracy of the determination. DFT simulations show that the formation of a Stone‐Wales type of defect follows a complex mechanism, where the two layers show decoupled behavior in terms of chemical bond rearrangements. The calculated activation energy of the rate determining step for the formation of a Stone‐Wales type of defect of 4.3 eV is in a very good agreement with the experimental value. Charge transfer between SiO2 bilayer and Ru(0001) support is shown to lower the activation energy for breaking the Si‐O bond compared to the unsupported film. The pre‐exponential factors obtained under both atmospheres differ significantly, thus suggesting that the interfacial ORu underneath the SiO2 bilayer plays a role on how the disordering propagates within the film.
