Scanning force microscopy investigation of the Pb(Zr0.25Ti0.75)O3/Pt interface

Abstract

We report on a novel approach for the investigation of the Pb(ZrxTi1−x)O3/Pt interface applying scanning force microscopy techniques. Ferroelectric samples (PZT film /Pt/SiO2/Si) were polished at a shallow angle (∼6.1°) thereby enlarging the film cross section from a 430 nm film thickness to a width of more than 4 μm. Piezoresponse force microscopy and Kelvin probe force microscopy were applied in order to deduce the dielectric polarization P and local potential distribution over the full cross section. We clearly observe a transition layer with a thickness of ∼240 nm which manifests itself both in a gradual decrease of the piezoresponse signal as a function of film thickness and in a corresponding variation of the surface potential. Furthermore, after polarization reversal due to a dc voltage applied to the tip, a different retention behavior was observed within the transition layer. The results are tentatively attributed to negatively charged defects accumulated at the PZT/Pt interface.

Thickness dependence of structure and piezoelectric properties at nanoscale of polycrystalline lead zirconate titanate thin films

“…39,40 It can be described by the second term on the right-hand side of the electric polarization written as P i ¼ d ijk r jk þ l ijkl ð@e jk =@x l Þ, where d ijk is the third-rank tensor piezoelectric coefficient, r jk is the stress component, l ijkl is the fourth-rank tensor flexoelectric coefficient, and @e jk =@x l is the strain gradient. 38,39 Taking into account the scenario described above, the main mechanisms responsible for the self-polarization effect in highly oriented films can be excluded as the mechanisms responsible for the same effect observed in PZT thin films studied in the present work. The linear increasing at the microstrain observed in Figure 2(a) with the glancing angle h increasing is indicative that gradient strain along the film depth is small and does not increase substantially near the film-electrode interface, differently from that observed for highly oriented films.…”

“…32 To find out the polarization distribution across the film thickness, PFM measurements should be done destructively as previously proposed. 38 As there is no direct method to access the polarization distribution across the thickness, the depletion model requires further justification. On the other hand, a perfect match between lattice parameters of the ferroelectric and of the substrate occurs in epitaxial films, leading to a strain at the interface that decays when the distance into the film bulks.…”

The Importance of Distributed Loading and Cantilever Angle in Piezo-Force Microscopy

“…interactions between the sample and the incorporated cantilever [2], as well as sample mechanics, have been reported [3]. However, several important details have been overlooked by the AFM community, each having profound influences on PFM measurements under certain circumstances as described below.…”

Metal-ferroelectric-metal heterostructures with Schottky contacts. I. Influence of the ferroelectric properties

“…This assumption was suggested by a recent report on the presence of negative charges at the surface of ferroelectric films. 42 7. Contrary to the standard assumption that the polarization charges (or the associated depolarization field) are compensated with free charges from the electrodes, in the present case it is assumed that the surface bound charges associated with the ferroelectric polarization are compensated with trapped charges and with ionized shallow impurities located in the SCR.…”