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The characterization of ferroelectricity in ultra-thin ferroelectric (FE) films is highly challenging due to enlarged leakage current and resistive switching (RS) effect. In this study, we investigated the polarization switching properties of 1.5-nm thick Hf0.5Zr0.5O2 (HZO) films via direct hysteresis remnant polarization/voltage (P–V) loop measurement. To reduce the leakage current and eliminate the RS effect, positive-up–negative-down (PUND) measurement was implemented on back-to-back connected complementary cells. Rational hysteresis loops, with remnant polarization of approximately $2~\mu \text{C}$ /cm2, were successfully obtained by directly measuring the polarization switching currents. In this study, we provide direct evidence of the stable ferroelectric property in 1.5-nm thick HZO films, and thereby show a potential prospect of ultimate scalability of HZO films.

An epitaxial SmNiO3 thin-film grown on an LaAlO3 (001) substrate using pulsed laser deposition is investigated with spherical-aberration corrected scanning transmission electron microscopy techniques, including high-angle annular dark field, X-ray energy dispersive, and electron energy-loss spectroscopy. High-density Ruddlesden–Popper (RP)-type faults, which generate two types of image contrast due to overlaps along the electron beam direction, are identified with the translational vector of 1/2a⟨111⟩c, corresponding to 1/2a⟨101⟩c displacement of Sm atoms when observed along the [010]c zone axis. These defects originate from Sm-rich non-stoichiometry within the SmNiO3, and their directions depend on the local stress states. Lattice distortion induced by the RP faults reduces the metal-to-insulator transition temperature to around 340 K. The effects of high-density RP faults on the lattice strain, domain size, and strong electronic-lattice correlations indicate that RP faults can provide extra freedom to tailor the physical properties of SmNiO3 thin films for potential electronic device applications. High-density Ruddlesden–Popper-type faults are revealed in an epitaxial SmNiO3 thin film grown on LaAlO3 (001) by pulsed laser deposition, originating from Sm-rich non-stoichiometry, and their directions depend on the local stress states. Lattice distortion induced by the RP faults reduces the metal-to-insulator transition temperature to around 340 K. RP faults provide extra freedom to tailor intriguing properties of SmNiO3 for potential electronic device applications.

Interface structure plays an extremely important role in the charge-transfer and photocatalytic performances in plasmonic metal/semiconductor systems. Defect engineering by introducing an oxygen vacancy (O-vac) is an effective way to modulate the interface structure. Here, a representative photocatalyst system including TiO2, TiO2-x, Au-TiO2 and Au-TiO2-x as designed delicately to reveal the detailed mechanism of the plasmon-resonance-induced charge separation in interfacial defect structure from the nanoscale. The local charge transfer via a conducting amorphous-like interface layer is visualized as the arched valence change from Ti3+ to Ti4+ at the Au-TiO2-x interface after Schottky contact. This phenomenon eventually leads to the enhancement of localized surface plasmon resonance (LSPR) at 2.3 eV, and the introduction of O-vac reduces the Schottky barrier height of Au-TiO2-x by 5 mV compared with that of Au-TiO2. Under visible light, Au-TiO2-x excites the most photogenerated carriers to the surface, which is larger than that of TiO2-x and Au-TiO2. It can be concluded that the changes in electronic structure eventually promote charge transfer in visible light and explain the original reason that the coupling of O-vac and Au could improve the photocatalytic performance.

Two-dimensional ferroelectrics have gained attention because of their unique ferroelectric properties, e.g., giant negative electrostriction, odd/even layer effect, intercorrelation of in-plane and out-of-plane ferroelectricity, ferroelectric metal nature or tunable quadruple-well ferroelectric property. Here, the interplay between ionic kinetics and ferroelectric switching properties is reported in a model system, CuInP2S6, one of the few van der Waals room-temperature ferroelectric crystals. An unconventional out-of-plane domain inversion phenomenon induced by an in-plane electric field has been observed and clarified experimentally. The intralayer hopping motions of Cu-ions can play a role as media of ferroelectric domain inversion. These findings not only provide direct evidence for the microscopic origin of ferroelectric polarization in CuInP2S6, but also establish a new mechanism to reverse ferroelectric dipoles simply and effectively, offering opportunities for both fundamental studies and new device applications in information and energy storage.

Electrochemical activation strategy is very effective to improve the intrinsic catalytic activity of metal phosphate toward the sluggish oxygen evolution reaction (OER) for water electrolysis. However, it is still challenging to operando trace the activated reconstruction and corresponding electrocatalytic dynamic mechanisms. Herein, a constant voltage activation strategy is adopted to in situ activate Ni

Cubic heteroepitaxial (001) SrMnO3-δ (SMO) films were grown on SrTiO3 substrates by atomic alternating layer molecular beam epitaxy. Precise control of cation stoichiometry was achieved by in situ reflection high-energy electron diffraction (RHEED) oscillation. During SMO film growth, a correlation between RHEED oscillation features and the cation stoichiometry/monolayer dose was established. In non-stoichiometric films, there were out-of-plane lattice expansions due to off-stoichiometry-dependent defects, including Ruddlesden–Popper SrO planar faults in Sr-rich films and Sr vacancy defect clusters in Mn-rich films.

A model system of oxygen vacancy modified titanium dioxide (TiO2-x) nanobelts supported Au nanoparticles with different sizes is prepared for methylene blue photodegradation. The Au/TiO2-x heterostructure with the smallest Au size exhibits the best performance than other samples. Based on detailed microstructural investigations, the effect of Au particle size on the photocatalytic performance is revealed in the view points of electron transfer mechanism and interface microstructure. It implicates that although the size effect determines the overall photoelectric properties of samples, it is the number and transport behavior of carriers at the interface that fundamentally affect the photocatalytic performance.