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in a metallic conductance at the DWs in insulating ferroelectrics. [ 15 ] Such a CDWinduced enhancement of domain wall conductivity has been convinced recently in BaTiO 3 , [ 5 ] LiNbO 3 , [ 16 ] improper ferroelectric ErMnO 3 , [ 13 ] and HoMnO 3 . [ 17 ] Nevertheless, atomic structures of CDWs which are greatly important for understanding the novel DW phenomenon are still inadequate, although aberration-corrected transmission electron microscopy has been applied to several CDWs in tetragonal PbTiO 3 , [ 18 ] PbZr 0.2 Ti 0.8 O 3 , [ 19 ] hexagonal YMnO 3 .[ 20 ] The 90° and 180° CDWs in PbTiO 3 and PbZr 0.2 Ti 0.8 O 3 are in a broadened fashion where the electric dipoles are smaller than the bulk value; [ 18,19 ] reduction of Mn-O distances at CDW were revealed in YMnO 3 .[ 20 ] All these CDWs exhibit novel characters remarkably distinct from the uncharged ones.Rhombohedral multiferroic BiFeO 3 (BFO) possesses various kinds of DWs which feature 109°, 180°, and 71° confi gurations, respectively. Since the fi nding of novel DW conduction in BFO, several emergent phenomena at DWs are confi rmed, such as electrically tunable conductance, enhanced photovoltage and magnetoresistant effect. [ 8,14,21 ] Particularly, CDWs in BFO exhibit electrically controlled photodetection property which implies nonvolatile optoelectronic memory applications. [ 21 ] In addition, these CDWs are also known to exhibit pinning effects on the movement of DWs and thus induce polarization fatigue in BFO memories. Although a charge-accumulation driven T phase was identifi ed at a 71° CDW with "head-to-head" polarizations, [ 22 ] atomic-scale mapping of tail-to-tail CDWs in BFO fi lms is still so incomprehensive that the physical insights of the CDW phenomena are known little.Here, using aberration-corrected scanning transmission electron microscopy (STEM), negatively CDWs in BFO fi lms were systematically investigated, with their structures being directly mapped on the atomic scale. 109°, 180°, and 71° CDWs on (100) plane and a 109° CDW on (110) plane, with tail-to-tail dipole confi gurations, are thus revealed. Unusual 1D structural modulations characterized by alternate lattice expansions and clockwise/counterclockwise lattice rotations along the corresponding DWs are found, which differ remarkably from both uncharged domain walls (UCDWs) and positively CDW with head-to-head polarizations in BFO reported previously. [ 3,[22][23][24][25] These fi ndings are expected to broaden our understanding on DW structures as well as the effect of bound charges on structural stabilities of Charged domain walls (CDWs) show great potentials to mediate the properties of ferroelectrics. Direct mapping of these domain walls at an atomic scale is of critical importance for understanding the domain wall dominated properties. Here, based on aberration-corrected scanning transmission electron microscopy, tail-to-tail CDWs at 71°, 109°, and 180° domains in BiFeO 3 thin fi lms have been identifi ed. 2D mappings demonstrate 1D structural modulations with alternate ...

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Doped BaSnO3 has arisen many interests recently as one of the promising transparent conducting oxides for future applications. Understanding the microstructural characteristics are crucial for the exploration of relevant devices. In this paper, we investigated the microstructural features of 0.001% La doped BaSnO3 thin film using both conventional and aberration corrected transmission electron microscopes. Contrast analysis shows high densities of Ruddlesden-Popper faults in the film, which are on {100} planes with translational displacements of 1/2a < 111 > . Atomic EELS element mappings reveal that the Ruddlesden-Popper faults are Ba-O layer terminated, and two kinds of kink structures at the Ruddlesden-Popper faults with different element distributions are also demonstrated. Quantitative analysis on lattice distortions of the Ruddlesden-Popper faults illustrates that the local lattice spacing poses a huge increment of 36%, indicating that large strains exist around the Ruddlesden-Popper faults in the film.

Functional oxide interfaces have received a great deal of attention owing to their intriguing physical properties induced by the interplay of lattice, orbital, charge, and spin degrees of freedom. Atomic-scale precision growth of the oxide interface opens new corridors to manipulate the correlated features in nanoelectronics devices. Here, we demonstrate that both head-to-head positively charged and tail-to-tail negatively charged BiFeO/PbTiO (BFO/PTO) heterointerfaces were successfully fabricated by designing the BFO/PTO film system deliberately. Aberration-corrected scanning transmission electron microscopic mapping reveals a head-to-head polarization configuration present at the BFO/PTO interface, when the film was deposited directly on a SrTiO (001) substrate. The interfacial atomic structure is reconstructed, and the interfacial width is determined to be 5-6 unit cells. The polarization on both sides of the interface is remarkably enhanced. Atomic-scale structural and chemical element analyses exhibit that the reconstructed interface is rich in oxygen, which effectively compensates for the positive bound charges at the head-to-head polarized BFO/PTO interface. In contrast to the head-to-head polarization configuration, the tail-to-tail BFO/PTO interface exhibits a perfect coherency, when SrRuO was introduced as a buffer layer on the substrates prior to the film growth. The width of this tail-to-tail interface is estimated to be 3-4 unit cells, and oxygen vacancies are supposed to screen the negative polarization bound charge. The formation mechanism of these distinct interfaces was discussed from the perspective of charge redistribution.

In the quest for designing affordable diagnostic devices with high performance, precisely functionalized carbon-based materials with high accuracy and selectivity are required. Every material has its own unique ability to interact with the analyte, and its performance can be enhanced by probing the interaction mechanism. Herein, p-aminophenol (PAP)-functionalized reduced graphene oxide (rGO) nanoscale material is developed by a one-step synthetic route as an all-organic-based sensor. As the PAP molecules are precisely covalently interacted with the rGO at the basal plane and form a wrinkled-paper-like structure, the functionalized material exhibits an outstanding sensing ability (7.5 nM neurotransmitter dopamine (DA) at a wide linear range, 0.01–100 μM) with fast electrical transduction (<3 s) and good recyclability (∼10 cycles) in a real sample. Combining various analytical and density functional theory (DFT) calculation methods, physicochemical properties and the interaction mechanism of analyte–materials transduction are discussed exclusively. Besides, the potential application of the well-dispersed rGO-PAP gravure ink in flexible-printed electronics fields is explored. This study not only provides new insights into the surface/interface chemistry and working principle of this unique anchoring of PAP on rGO but also offers a new pathway for developing other forms of metal-free/organic functionalized biosensors with high efficiency.

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