Time-dependent polarization relaxation behaviors induced by a depolarization field E d were investigated on high-quality ultrathin SrRuO3/BaTiO3/SrRuO3 capacitors. The E d values were determined experimentally from an applied external field to stop the net polarization relaxation. These values agree with those from the electrostatic calculations, demonstrating that a large E d inside the ultrathin ferroelectric layer could cause severe polarization relaxation. For numerous ferroelectric devices of capacitor configuration, this effect will set a stricter size limit than the critical thickness issue.PACS numbers: 77.22. Ej, 77.22.Gm, 77.80.Dj, 77.55.+f With recent breakthroughs in fabricating high-quality oxide films [1,2,3], ultrathin ferroelectric (FE) films have attracted much attention from the scientific as well as application points of view. As the FE film thickness d approaches tens of unit cell length, the FE films often show significantly different physical properties from those of bulk FE materials. Some extrinsic effects, especially coming from FE film surfaces and/or interfaces with other materials, could be very important [4]. For some other cases, intrinsic physical quantities could play vital roles in determining the unique properties of ultrathin films.Many FE-based electronic devices have the capacitor configuration, where a FE layer is inserted between two conducting electrodes. Then, polarization bound charges will be induced at the surfaces of the FE layer, but compensated by free charge carriers in the conducting electrodes. In real conducting electrodes, however, the compensating charges will be induced with a finite extent, called the screening length λ. This will result in an incomplete compensation of the polarization charges. Such an incomplete charge compensation should induce a depolarization field E d inside the FE layer, with a direction opposite to that of the FE polarization P [5]. Therefore, E d will appear in every FE capacitor, and its effects will becomes larger with the decrease of d [5]. (For a FE film without electrodes, there is no compensation for the polarization bound charge, so the value of E d will become even larger than that of the FE capacitor case.) E d has been known to be important in determining the critical thickness [6] and domain structure of ultrathin FE films [7,8,9], and reliability problems of numerous FE devices [10,11].Recently, using a first principles calculation, Junquera and Ghosez investigated the critical thickness of BaTiO 3 (BTO) layers in SrRuO 3 (SRO)/BTO/SRO capacitor [6]. For calculations, they assumed that all of the BTO and SRO layers were fully strained with the SrTiO 3 substrate. By taking the real SRO/BTO interfaces into account properly, they showed that E d could make the ferroelectricity vanish for the BTO films thinner than 6 unit cells, i.e. 2.4 nm [6]. More recently, using pulsed laser deposition with a reflection high energy electron diffraction monitoring system, we fabricated high-quality fully-strained SRO/BTO/SRO capacitors...

Articles you may be interested inTemperature-dependent polarization back-switching and dielectric nonlinearity in PbZr0.4Ti0.6O3 ferroelectric thin films J. Appl. Phys. 116, 034109 (2014); 10.1063/1.4890340 Direct observation of fatigue in epitaxially grown Pb(Zr,Ti)O3 thin films using second harmonic piezoresponse force microscopy Appl. Phys. Lett. 99, 052904 (2011); 10.1063/1.3619839 Microstructure and ferroelectric properties of low-fatigue epitaxial, all (001)-oriented ( Bi , La ) 4 Ti 3 O 12 ∕ Pb ( Zr 0.4 Ti 0.6 ) O 3 ∕ ( Bi , La ) 4 Ti 3 O 12 trilayered thin films on (001) Sr Ti O 3 substrates J. Appl. Phys. 98, 014101 (2005); 10.1063/1.1946913 Growth, structure, and properties of all-epitaxial ferroelectric ( Bi , La ) 4 Ti 3 O 12 ∕ Pb ( Zr 0.4 Ti 0.6 ) O 3 ∕ ( Bi , La ) 4 Ti 3 O 12 trilayered thin films on Sr Ru O 3 -covered Sr Ti O 3 ( 011 ) substrates Appl. Phys. Lett. 86, 082906 (2005); 10.1063/1.1864248 Effect of oxygen stoichiometry on the ferroelectric property of epitaxial all-oxide La 0.7 Sr 0.3 MnO 3 /Pb(Zr 0.52 Ti 0.48 )O 3 /La 0.7 Sr 0.3 MnO 3 thin-film capacitors

A long standing problem of domain switching process -how domains nucleate -is examined in ultrathin ferroelectric films. We demonstrate that the large depolarization fields in ultrathin films could significantly lower the nucleation energy barrier (U *) to a level comparable to thermal energy (kBT ), resulting in power-law like polarization decay behaviors. The "Landauer's paradox": U * is thermally insurmountable is not a critical issue in the polarization switching of ultrathin ferroelectric films. We empirically find a universal relation between the polarization decay behavior and U */kB T .PACS numbers: 77.22. Ej, 77.80.Fm Recent advances in complex oxide thin film synthesis and in first-principles calculations have intensified the basic research on ferroelectricity at nanoscale dimension [1,2]. The cooperative nature of ferroelectricity is expected to induce different polarization states at nanoscale due to low-dimensional boundary conditions and the strong interactions of polarization with strain, charge, and other electromechanical parameters [1,2,3,4,5,6,7]. Many workers have reported intriguing physical phenomena occurring in ultrathin ferroelectric (FE) films and other nanostructures, such as intrinsic size effects [1, 2, 3], strain-enhanced FE properties [4], unusual low-dimensional phases [5], and domain patterns [6,7]. On the other hand, the mechanism and domain dynamics of FE switching in ultrathin films have rarely been investigated in spite of their scientific and technological importance [8,9,10].Historically, the mechanism of polarization switching dynamics in ferroelectrics has been the subject of a great deal of research. It is now believed that the polarization switching takes place not by coherent switching, but by the nucleation and growth of new domains [8,9,10]. However, there still remains an unsolved issue: How do the domains nucleate? In the late 1950s, Landauer emphasized that a thermodynamic nucleation process cannot play a role in FE domain switching [11]. For a nucleus with reversed polarization to be created by a thermodynamic process, an energy barrier for nucleation U * should be thermally overcome, as shown in Fig. 1(a). However, Landauer's and later estimates showed that U * is practically insurmountable by the thermal activation process: U * > 10 8 k B T at an electric field E ∼ 1 kV/cm (a typical value of the coercive field for bulk ferroelectrics) [11] and U ∼ 10 3 k B T at E ∼ 100 kV/cm (a typical value of the coercive field for most FE thin films) [10,13], where k B is Plank's constant and T is temperature. According to these estimates, it is difficult to understand the observed domain nucleation in ferroelectrics. This problem has been known as the "Landauer's paradox". To overcome this difficulty, numerous workers have assumed that the nuclei could be formed inhomogeneously due to external effects, such as defects [12], long-range interaction between nuclei [13] and FE-electrode coupling [14]. However, in this Letter, we will demonstrate that U * could be thermally ...

thicknesses of between 5 nm and 30 nm, show well-defined interfaces between ferroelectric BaTiO 3 and electrode SrRuO 3 layers. In these capacitors, we cannot observe any extrinsic electrical effects due to either the formation of an insulating interfacial passive layer or passive-layer-induced charge injection. Such high quality interfaces result in very good fatigue endurance, even for the 5 nm thick BaTiO 3 capacitor.

Chemotherapy is often futile in systemic listeriosis, translating to being a peril to public health. There is, thus, an imperative need for novel antilisterial compounds, possibly acting through mechanisms dissimilar to those of existing drugs. The present study describes one such agent-the non-steroidal anti-inflammatory drug (NSAID) diclofenac sodium (Dc). The National Committee for Clinical Laboratory Standards (NCCLS) minimum inhibitory concentration (MIC), mode of action, and two mechanisms of action, i.e., on bacterial DNA and membrane, have been characterized with respect to Dc. The drug showed noteworthy inhibitory action (MIC90 = 50 microg/ml) against Listeria strains, demonstrated cidal (minimum bactericidal concentration [MBC]=100 microg/ml) activity, inhibited listerial DNA synthesis (45.48%; incorporation of [methyl-3H] thymidine), and possessed bacterial membrane-damaging activity (37.33%; BacLight assay). Dc could be used as a lead compound for the synthesis of new, more active agents perhaps devoid of side effects. Further, quantitative structure-activity relationship (QSAR) studies will contribute to a new generation of promising adjuvants to existing antilisterial drugs.