Surface screening of written ferroelectric domains in ambient conditions

Abstract

We have combined Piezoresponse Force Microscopy and Kelvin Probe Force Microscopy (KPFM) to study screening charge dynamics in written domains on PbZr0.2Ti0.8O3 (PZT) thin film surfaces under a controlled environment and at variable temperature. The screening dynamics decayed exponentially on a timescale of tens of minutes, consistently with what we expected for water-mediated surface diffusion of ionic species. Variable-temperature KPFM measurements showed variations in surface potential due to temporary unbalanced surface screening charges. Low humidity experiments revealed gradual incorporation of positive charges onto the surface, even in a non-reactive environment (N2), as well as deceleration of the screening dynamics upon reversal of the temperature variation. Our work may serve as a guide for future studies on the dynamics and nature of adsorbates on polarized PZT thin films.

Surface charged species and electrochemistry of ferroelectric thin films

“…Key aspects of their fundamental properties and performance in devices, such as the structure, stability, and switching dynamics of polarization domains, are driven by electrostatic boundary conditions and determined by the bound charges and associated depolarizing fields at the surfaces orthogonal to the polar axes, as well as by internal screening effects such as band bending. [1][2][3][4][5] In this respect, adsorbed water from the environment has long been recognized as playing a crucial role in electrostatic screening under atmospheric conditions due to its polar nature and ionic conductivity, and the associated screening dynamics have been studied as a function of humidity 6,7 and temperature, [8][9][10] leading to the development of a full thermodynamic theory of the screening mechanisms. 11 However, few studies and ab initio modeling have considered the capacity of water molecules to dissociate and participate in redox chemical reactions at ferroelectric surfaces, [12][13][14][15][16] which would be expected to provide a large additional screening contribution, 17,18 in particular on highly reactive perovskite oxides.…”

“…28 Exploring the coupling between electrochemistry and ferroelectricity is made particularly challenging by not only the spatial but also chemical resolution required, lacking in any one single technique. 29 Scanning probe microscopy (SPM) studies allowing nanoscale resolution and long-duration tracking of ferroelectric domains have demonstrated a difference in surface potential between oppositely polarized domains, 30 which moreover evolves with increasing humidity, 6 as well as significant changes in polarization switching dynamics under high humidity (60-70% RH) 22 or liquid immersion. 31,32 These observations point to a dual effect of adsorbed water: it both modifies the spatial distribution of the electric fields generated by a biased SPM tip and plays a key role in polarization screening.…”

Preface to Special Topic: Selected Papers from the Piezoresponse Force Microscopy Workshop Series: Part of the Joint ISAF-ECAPD-PFM 2012 Conference

“…Guo et al 67 report the detailed studies of temperatureinduced evolution of structure and electromechanical response in ferroelectric polymer, and Shur et al 68 and Rodrigiez et al communicate their findings of light-induced photochemical reactivity on the ferroelectric LiNbO 3 surfaces, 69 providing new insight into physics and electrochemistry of ferroelectric-semiconductors. [33][34][35] The role of surface humidity of surface potential was explored by Verdaguer, 70 complementing earlier data on BaTiO 3 surfaces. [36][37][38][39][40] Several studies combine PFM and other localized characterizations, such as atomic force acoustic microscopy (AFAM) 41,42 by Zhou and Li et al, 71 and confocal Raman microscopy 72 and Raman spectroscopy.…”

A new non-destructive readout by using photo-recovered surface potential contrast

“…The difference of imaging contrast reflects the SP difference of patterned domains. Normally the quantitative value of SP is difficult to be determined 16 . However, the difference of SP between the nearest oppositely polarized domains, i.e., DSP, can be quantitatively measured through the line profile of KPFM image.…”