In situhard x-ray photoemission spectroscopy of barrier-height control at metal/PMN-PT interfaces

Ferroelectrics exhibit switchable spontaneous polarization, a functionality that can be harnessed in nonvolatile memory devices. The main characteristics of these devices are governed by the electronic band alignment at the interfaces, particularly at the metallic contacts. Here, the authors study such an interface using state-of-the-art high-energy x-ray photoelectron spectroscopy, with in situ polarization reversal achieved by applying poling voltage. They confirm a result central to the physics of ferroelectric devices: an electrode-dependent potential drop at the interface that is linear in the spontaneous polarization. They also reveal a novel effect: electric-field-dependent increase of the energy offset due to the field-induced strain in the ferroelectric material.