Electrostatic force evolution during the tip-induced ferroelectric domain switching

摘要

Different from the signals of amplitude and phase lag in piezoresponse force microscopy (PFM) and piezoresponse force spectroscopy (PFS), the signals of the contact resonance frequency (f(0)) have not been clearly interpreted. Due to the complexity of the tip-sample system at the nanoscale, the relevant models and mechanisms were continuously improved in the past decades. The variation of f(0) has been reported in a few previous studies, but the physical meaning of the unique variation in ferroelectric materials still needs to be investigated. Due to the imperfect tip-sample contact, the existence of a dielectric gap and screening charges causes the discontinuity in the conduction band. The evolution of the electrostatic force during the PFS measurements is significantly affected by the tip-induced ferroelectric domain evolution, resulting in the variation of the effective contact stiffness (k*) and f(0). By involving the screening effect and tunneling effect in this model, the anomalies of the on-field f(0) and off-field f(0) can be well explained, respectively.