Electronic charge transfer during metal/SiO₂contact: Insight from density functional theory

Contact charging of hydroxylated SiO2/metal interfaces is studied using density functional theory calculations. Atomic scale models are generated for hydroxylated α-cristobalite interfaced with three different fcc metals: Al, Pt, and Au. Regions of electron accumulation and depletion are highest in magnitude near the SiO2/Pt and SiO2/Au interfaces and lower at the SiO2/Al interface. One key finding of this work is that the presence of a metal surface near the hydroxylated SiO2 induces electronic states at the SiO2 surface within the apparent insulating bandgap. The magnitude of these states is highest for Pt and Au contacts and lowest for Al, indicating that the amount of charge transfer at the interface trends with the density of electronic defect states. Such electronic defect states reside near the fermi level of the system and it is proposed that these states from surface oxygen atoms are at least partly responsible for the electronic charge transfer mechanism between a metal and an insulator.