Origin of surface potential change during ferroelectric switching in epitaxial PbTiO3 thin films studied by scanning force microscopy

Abstract

We investigated the surface potential of the ferroelectric domains of the epitaxial PbTiO3 (PTO) films using both Kelvin probe and piezoresponse force microscopy. The surface potential changes as a function of applied biases suggested that the amount and sign of surface potentials depend on the correlation between polarization and screen charges. It also suggested that the trapped negative charges exist on the as-deposited PTO surfaces. Injected charges and their resultant surface potentials are investigated by grounded tip scans. The results unveiled the origin of surface potential changes during ferroelectric switching in the epitaxial PTO films.

Charge gradient microscopy

“…2D. This is in agreement with the surface potential evolution as a function of number of scans using grounded tip on prewritten domains reported by Kim et al (27). It should be noted that CGM does not work for the case where the screening mainly takes place through internal screening as supported by the CGM images of Significance Polarization charges of ferroelectric materials are screened by an equal amount of surface charges with opposite polarity in ambient condition.…”

Non-piezoelectric effects in piezoresponse force microscopy

“…Such local and non-local electrostatic effects can arise from the various electrical interactions between the AFM tip/cantilever and sample surface, such as the capacitive interaction, [80,81] the CPD, [79,82] the application of an external voltage to the entire sample, and the corresponding injected charges on the sample surface. [83][84][85] Hong et al reported a significant influence of the electrostatic effect on piezoresponse hysteresis loop measurements. [81] A piezoresponse hysteresis loop is generally measured using a triangular waveform, which can be of two kinds, referred to as continuous and pulsed dc modes, as shown in Figs.…”

Surface charge dynamics on ferroelectric PbZr0.48Ti0.52O3 films responding to the switching bias of electric force microscope

“…10 The comparative study of KFM and PFM on surface potential of PbTiO 3 thin films also showed the role of surface charges in the observation of switched ferroelectric domains. 19 The amount of the surface charges can be evaluated from the Schottky current J = AT 2 exp͑−q⌽ B / k B T͒ ϫexp͓1 / k B T͑q 3 E / 4 ͒ 1/2 ͔, where A is the Richardson constant, q⌽ B is the energy barrier to access the empty conduction-band states of the PZT thin film from the gold tip, E is the applied electric field, and is the dielectric constant of PZT. 20 The electric field between the EFM tip and the surface can be written as E =−͑Q / 2 ͒͐ 0 ϱ kJ 0 ͑kr͒ ϫ͓exp͑−kz͒ + exp͑kz −2d −2a͔͒ / ͓1 + exp͑−2kd͔͒dk, where J 0 ͑kr͒ is the zeroth-order Bessel function, d is the thickness of the film, and a is the tip radius.…”