Direct structural determination in ultrathin ferroelectric films by analysis of synchrotron x-ray scattering measurements

Abstract

In order to better understand ferroelectricity in thin films, it is important to explore the atomic-scale structure and the spatial distribution of polarization near the interfaces. We present sub-Ångstrom-resolution electron density maps of three ultrathin PbTiO 3 films grown epitaxially on SrTiO 3 ͑001͒ substrates. The maps were obtained by analysis of synchrotron x-ray scattering measurements of Bragg rod intensities using the recently developed coherent Bragg rod analysis method. A four-and a nine-unit-cell-thick film were studied at room temperature, and a nine-unit-cell-thick film was studied at 181°C. The results show that at room temperature, the PbTiO 3 films are polar, monodomain, and have their polarization oriented away from the substrate. The four-unit-cell film may be the thinnest monodomain perovskite film found to be in the polar phase. At 181°C, the electron density map of the nine-unit-cell film is consistent with the presence of 180°stripe domains. In the monodomain samples, details of the atomic-scale structure of the PbTiO 3 / SrTiO 3 interface are observed, which may provide evidence for the nature of the positive charge layer required to stabilize polarization in monodomain films.

Electroresistance effects in ferroelectric tunnel barriers

“…26 Substantially different to the above-mentioned screening mechanism is the ionic screening. 22,27 In this scenario, part of the polarization charges penetrate into the electrode, which is feasible by the ionic structure of oxide electrodes, and is then screened in situ. 22 That means the screening charges and polarization charges are at the same place yielding no depolarization field.…”

Ultrafast Photovoltaic Response in Ferroelectric Nanolayers

“…In contrast to the expected thermally induced responses, we observe significantly more complex dynamics. Time-dependent rocking curves of photoexcited, monodomain PTO on STO, with polarization pointing out of the film [33], taken at room temperature [ Fig. 1(a) and Fig.…”

Study of the Interface Structure of Epitaxial Ultra-Thin Film by an X-Ray Holographic Imaging Method

“…It should be mentioned that a number of studies have been done to solve the surface structure using various kinds of direct methods [17][18][19][20][21][22][23][24][25][26][27], but most of them are underway. At the present stage we think that such direct methods are much helpful to distinguish the most probable model from others.…”