Abstract
A combined study of local structural, electric and ferroelectric properties of SrTiO_{3}/La_{0.7}Sr_{0.3}MnO_{3}/BaTiO_{3} heterostructures was performed by Piezoresponse Force Microscopy, tunneling Atomic Force Microscopy and Scanning Tunneling Microscopy in the temperature range 30–295 K. The direct correlation of film structure (epitaxial, nanocrystalline or polycrystalline) with local electric and ferroelectric properties was observed. For polycrystalline ferroelectric films the predominant polarization state is defined by the peculiarity of screening the built-in field by positively charged point defects. Based on Scanning Tunneling Spectroscopy results, it was found that a sequent voltage application provokes the modification of local resistive properties related to the redistribution of point defects in thin ferroelectric films. A qualitative analysis of acquired Piezoresponse Force Microscopy, tunneling Atomic Force Microscopy and Scanning Tunneling Microscopy images together with Scanning Tunneling Spectroscopy measurements enabled us to conclude that in the presence of structural defects the competing processes of electron injection, trap filling and the drift of positively charged point defects drives the change of resistive properties of thin films under applied electric field. In this paper, we propose a new approach based on Scanning Tunneling Microscopy/Spectroscopy under ultrahigh vacuum conditions to clarify the influence of point defects on local resistive properties of nanometer-thick ferroelectric films.
Highlights
Since the first experimental observations of resistive switching effect in ultrathin ferroelectric (FE) layers[1,2] were allowed by advances in FE films technology, a research interest in the respective structures has been rising rapidly owing to their potential electronic applications
FE film thickness d in the FE tunnel junctions (FTJs) structures reported in some works, e.g., 4.6 nm[7], assumes that besides an elastic tunneling, a dominant transport mechanism in FTJs, there should be another contribution to the electron current across the s tructure[8]
We propose an approach, which includes scanning tunneling microscopy/spectroscopy (STM/STS) measurements under ultrahigh vacuum (UHV) conditions
Summary
Since the first experimental observations of resistive switching effect in ultrathin ferroelectric (FE) layers[1,2] were allowed by advances in FE films technology, a research interest in the respective structures has been rising rapidly owing to their potential electronic applications. Note that the epitaxial and the nanocrystalline films require higher Vs than the polycrystalline ones for scanning at the same level of It. To find a relation between the structural and the electric properties of FE films, we firstly analyze I–V characteristics measured with conductive AFM tip over the gold TEs, see Fig. 4a.
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