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.