Commonly used ferroelectric perovskites are also wide-band-gap semiconductors. In such materials, the polarization and the space-charge distribution are intimately coupled, and this Letter studies them simultaneously with no a priori ansatz on either. In particular, we study the structure of domain walls and the depletion layers that form at the metal-ferroelectric interfaces. We find the coupling between polarization and space charges leads to the formation of charge double layers at the 90 domain walls, which, like the depletion layers, are also decorated by defects like oxygen vacancies. In contrast, the 180 domain walls do not interact with the defects or space charges. Implications of these results to domain switching and fatigue in ferroelectric devices are discussed. DOI: 10.1103/PhysRevLett.95.247603 PACS numbers: 77.80.Dj, 73.40.ÿc, 75.60.Ch Ferroelectric perovskites that are widely used as actuators, sensors, and memories have classically been modeled as insulators following the Devonshire-Ginsburg-Landau (DGL) theory [1]. These materials, however, are also wideband-gap semiconductors [2]. Consequently, one has bandbending and depletion layers at electrodes and charge layer formation at domain walls, which in turn affect the polarization distribution. These in turn contribute to fatigue and domain-wall pinning.Recent efforts have sought to augment the DGL theory for these effects [3]. However, they assume a priori the depletion layer and space-charge distribution and calculate the resulting polarization distribution, or vice versa. There have also been ab initio studies of the electronic band structure and atomistic studies of defects [4 -6]. However, they provide limited information at the device scale due to enormous computational effort required to handle realistic length scales and geometries. This Letter provides a comprehensive presentation of a semiconducting ferroelectric at the device scale with no a priori assumptions on the polarization or space charge.We focus on the [001]-polarized tetragonal phase of BaTiO 3 to be specific, though many of our findings are generic. This well-studied material displays both 180 and 90 domain walls. Oxygen vacancies are a common defect and they act as donors [6,7]. We focus on the parallel-plate capacitor geometry (electrode-ferroelectric-electrode), which is the building block of many devices. Our results show the formation of depletion layers and the alteration of the polarization near electrodes, reveal some essential differences between 180 and 90 domain walls, show the redistribution of oxygen vacancies to electrodes and across 90 domain walls during annealing, and provide a concrete mechanism for imprinting a 90 domain wall. These results shed new light on various experimental observations.The state of the semiconducting ferroelectric crystal is determined by the polarization density p, the strain , the space-charge density , and the defect density N d , each of which we treat as field quantities. We assume here that all defects are donors motivated...

Recently, RBC membrane coated nanoparticles have attracted much attention because of their excellent immune escape ability; meanwhile, Au nanocages (AuNs) have been extensively used for cancer therapy due to its photothermal effect and drug delivery capability. The combination of RBC membrane coating and Au nanocages may provide an effective approach for targeted cancer therapy. However, few reports have shown the utilization of combining these two technologies. Here, we present the development of Erythrocyte membrane-coated Gold nanocages for targeted cancer photothermal and chemical therapy. First, anti-EpCam antibodies are used to modify RBC membranes to target 4T1 cancer cells. Second, the antitumor drug paclitaxel is encapsulated into AuNs. Then, the AuNs are coated with the modified RBC membranes. This new nanoparticles are termed EpCam-RPAuNs. We characterize the capability of EpCam-RPAuNs for selective tumor targeting via exposure to the near-infrared irradiation. Experimental results demonstrate that EpCam-RPAuNs can effectively generate hyperthermia and precisely deliver the antitumor drug PTX to targeted cells. We also validate the biocompatibility of our EpCam-RPAuNs in vitro. By combining the targeting moleculars modified RBC membrane and AuNs, our approach provides a new way to design biomimetic nanoparticles to enhance the surface functionality of nanoparticles. We believe that EpCam-RPAuNs can be potentially applied for cancer diagnoses and therapies.

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A new generation of surface-enhanced Raman scattering encoded-nanoparticles has been designed by combining aryl diazonium salt chemistry and gold nanoparticles.

We report the colossal negative electroresistance (ER) in the p-n heterostructure of La0.67Ca0.33MnO3−δ (LCMO) and Nb-doped SrTiO3. For a vacuum-annealed sample, a maximum ER of 4×104% can be reached by 1 mA current and magnetic field has remarkable influence on the ER of the sample. It is interesting that the magnetoresistance of the heterostructure can also be tuned by electric current. The results were explained by the current shunting model. In this scenario, the current shunting is determined by the resistance of LCMO and the junction resistance. On the other hand, the resistance of LCMO and the junction resistance are also affected by current. The interaction of these factors can tune the electrical transport of the heterostructure dramatically. This work shows that manganites combined with other materials can result in some interesting properties that may have potential applications.

We report the fabrication of La0.67Ca0.33MnO3−δ∕SrTiO3∕Nb–SrTiO3 p-i-n junction by pulsed laser deposition. This p-i-n junction shows good rectifying property. The most interesting phenomena observed in this p-i-n junction are the backward diodelike behavior above 210K and the transition to the normal diodelike behavior at low temperatures. The backward diodelike behavior, which has not been reported for the manganite based p-n or p-i-n junctions, can be understood by the nearly degenerate model. The coexistence of the ferromagnetic phase and charge ordering phase in the ultrathin La0.67Ca0.33MnO3−δ thin film can account for the behavior of this p-i-n junction at low temperatures. It is also shown that the electric current in this p-i-n junction is dominated by tunneling process at small bias voltages and diffusion process at high bias voltages. This work implies that manganite based diodes can show various properties displayed by the conventional semiconductor diodes.

This paper proposes a theory to describe the polarization and switching behavior of ferroelectrics that are also wide-gap semiconductors. The salient feature of our theory is that it does not make any a priori assumption about either the space charge distribution or the polarization profile. The theory is used to study a metal-ferroelectric-metal capacitor configuration, where the ferroelectric is n-type doped. The main result of our work is a phase diagram as a function of doping level and thickness that shows different phases, namely, films with polarization profiles that resemble that of undoped classical ferroelectrics, paraelectric, and a new head-to-tail domain structure. We have identified a critical doping level, which depends on the energy barrier in the Landau energy and the built-in potential, which is decided by the electronic structures of both the film and the electrodes. When the doping level is below this critical value, the behavior of the films is almost classical. We see a depleted region, which extends through the film when the film thickness is very small, but is confined to two boundary layers near the electrodes for large film thickness. When the doping level is higher than the critical value, the behavior is classical for only very thin films. Thicker films at this doping level are forced into a tail-to-tail configuration with three depletion layers, lose their ferroelectricity, and may thus be described as nonlinear dielectric or paraelectric. For films which are doped below the critical level, we show that the field required for switching starts out at the classical coercive field for very thin films, but gradually decreases.

La 0.67 Ca 0.33 Mn O 3 − δ ∕ Nb – Sr Ti O 3  p-n junction was fabricated by pulsed laser deposition. The I-V curves of this junction show rectifying behavior. Negative differential resistance (NDR) was observed at low temperatures under large bias voltages and NDR becomes more remarkable with decreasing temperature. In addition to NDR, the I-V curves also show remarkable hysteresis. The results were explained in terms of the effect of local Joule heating on the phase separation in the strained ultrathin La0.67Ca0.33MnO3−δ thin film.