Time-resolved photoemission spectroscopy on a metal/ferroelectric heterostructure

In thin-film ferroelectric (FE) capacitors the chemical and electronic structure of the electrode/FE interface can play a crucial role in determining the kinetics of polarization switching. We investigate the electronic structure of a Pt/BaTiO₃/SrTiO₃:Nb capacitor using time-resolved photoemission spectroscopy. The chemical, electronic, and depth sensitivity of core-level photoemission are used to probe the transient response of different parts of the upper electrode/ferroelectric interface to voltage-pulse-induced polarization reversal. The linear response of the electronic structure agrees quantitatively with a simple RC circuit model. The nonlinear response due to the polarization switch is demonstrated by the time-resolved response of the characteristic core levels of the electrode and the ferroelectric. Adjustment of the RC circuit model allows an estimation of the Pt/BaTiO₃ (BTO) interface capacitance. The experiment shows that the interface capacitance is at least 100 times higher than the bulk capacitance of the BTO film, in qualitative agreement with theoretical predictions from the literature.