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Hierarchical polydomain nanostructures, usually formed in epitaxial films, serve to fully relax the misfits between the film and substrate, as well as the strains between the poly-twin variants of the film material. The minimization of the elastic energy endows this type of structure superior stability over other domain architectures. However, the existence of energetically degenerate polytwin variants and their intersecting domain boundaries often led to undesirable functional properties in non-engineered films. Here we show that such nanostructures in epitaxial perovskite ferroelectric films can be crystallographically engineered to eliminate intersecting domain boundaries, thereby achieving an improved ferroelectric performance. In addition to a reduced coercive field and increased dielectric and piezoelectric responses, this type of ferroelectric polydomain nanostructure shows an enhanced ferroelectric polarization with a substantially improved fatigue resistance, as opposed to non-engineered nanostructures with intersecting domain boundaries. These findings suggest an alternative route for the fabrication of highly-reliable nonvolatile ferroelectric memory devices, and may find broader applications in piezoelectrics and energy storage.

Transparent flexible electronics have captured tremendous attention as the next-generation of electronic devices. Recently, flexible devices for wearing are in high demand in practical applications under special circumstances, such as aeronautics and astronautics, which require highly-transparent and large-scale flexibility, as well as stability at elevated temperature. Here, highly transparent, epitaxial Pb(Zr0.1Ti0.9)O3 (PZT) ferroelectric thin films were fabricated on Sn-doped In2O3 (ITO) transparent electrodes on yttria-stabilized zirconia (YSZ) bufferred mica substrate using pulsed laser deposition. The structural, optical, mechanical, and electrical properties of these all-oxide heterostructures of the PZT/ITO/YSZ/mica were studied. The heteroepitaxy exhibit a high transmittance and an excellent remarkable mechanical properties with robust operation in bending cycle tests. Moreover, the electrical properties are examined to show the preservation of the primitive properties of PZT. Various bending tests are performed to show the tunability of functionalities and to confirm that the heterostructures retain the physical properties under repeated cycles at high temperature. These results demonstrated that these high-performance transparent flexible capacitors would open a route for the applications in transparent flexible devices under harsh conditions.

The ability to electrically write magnetic bits is highly desirable for future magnetic memories and spintronic devices, though fully deterministic, reversible, and nonvolatile switching of magnetic moments by electric field remains elusive despite extensive research. In this work, we develop a concept to electrically switch magnetization via polarization modulated oxygen vacancies, and we demonstrate the idea in a multiferroic epitaxial heterostructure of BaTiO3/Fe3O4 fabricated by pulsed laser deposition. The piezoelectricity and ferroelectricity of BaTiO3 have been confirmed by macro- and microscale measurements, for which Fe3O4 serves as the top electrode for switching the polarization. X-ray absorption spectroscopy and X-ray magnetic circular dichroism spectra indicate a mixture of Fe2+ and Fe3+ at O h sites and Fe3+ at T d sites in Fe3O4, while the room-temperature magnetic domains of Fe3O4 are revealed by microscopic magnetic force microscopy measurements. It is demonstrated that the magnetic domains of Fe3O4 can be switched by not only magnetic fields but also electric fields in a deterministic, reversible, and nonvolatile manner, wherein polarization reversal by electric field modulates the oxygen vacancy distribution in Fe3O4, and thus its magnetic state, making it attractive for electrically written magnetic memories.

Ferroelectric films epitaxially grown on vicinal substrates have been widely researched in recent decades for their unprecedented performance tuned by the surface-step-terrace (SST) induced strains of substrates. Here, BaTiO3 films are epitaxially grown on miscut (001) SrTiO3 substrates with different miscut angles of 0°, 0.2°, 1°, and 2°, and the impacts of SST-induced strains on the second-order nonlinear optical coefficients are discussed by fitting the measured second harmonic generation (SHG) signals from the films. The results show that different miscut angles of the substrates can bring about different SST strain states in the BTO films, which make different contributions on the second-order nonlinear optical coefficients. These results disclose that the second-order nonlinear optical coefficients can be effectively controlled by SST induced strains, which provides a new way to tune the optical properties of functional oxide thin films.

Ferroelectric semiconductors splitting water reactions have presented a new paradigm in improving conversion efficient of solar energy into electricity or fuel. Here, we show the switchable photoelectrochemical response controlled by ferroelectric polarization in (101)-oriented Pb(Zr0.2Ti0.8)O3 (PZT) epitaxial films prepared on the (110) SrTiO3 substrate with SrRuO3 as bottom electrodes. Photoelectrochemical (PEC) measurements exhibit that the switchable photocurrent response can be observed in the PZT/SRO heterostructures photo-electrode. Moreover, under illumination, the switchable photocurrents of the PZT/SRO electrode present high repeatability and non-volatility, which only depend in the ferroelectric polarization direction of the PZT film. The result indicates that the PZT/SRO electrode may be as a photoanode or photocathode only through poling treatment with the external electric field. We suggest that the internal electric field and depletion region by ferroelectric polarization at the PZT film is mainly responsible for the switchable PEC effect. The study indicates that this ferroelectric photo-electrode material may have potential applications in solar water splitting, and specially in the PEC sensing and any other smart photo-responsive systems. Keywords: Switchable PEC effect, Ferroelectric polarization, Poling treatment, PZT thin film, Photo-electrode, Water splitting

Due to their excellent carrier mobility, high absorption coefficient and narrow bandgap, most 2D IVA metal chalcogenide semiconductors (GIVMCs, metal = Ge, Sn, Pb; chalcogen = S, Se) are regarded as promising candidates for realizing high-performance photodetectors. We synthesized high-quality two-dimensional (2D) tin sulfide (SnS) nanosheets using the physical vapor deposition (PVD) method and fabricated a 2D SnS visible-light photodetector. The photodetector exhibits a high photoresponsivity of 161 A⋅W−1 and possesses an external quantum efficiency of 4.45 × 104%, as well as a detectivity of 1.15 × 109 Jones under 450 nm blue light illumination. Moreover, under poor illumination at optical densities down to 2 mW⋅cm−2, the responsivity of the device is higher than that at stronger optical densities. We suggest that a photogating effect in the 2D SnS photodetector is mainly responsible for its low-light responsivity. Defects and impurities in 2D SnS can trap carriers and form localized electric fields, which can delay the recombination process of electron-hole pairs, prolong carrier lifetimes, and thus improve the low-light responsivity. This work provides design strategies for detecting low levels of light using photodetectors made of 2D materials.

Multilevel data ferroelectric storage memory is a breakthrough for addressing low density in ferroelectric random access memories. However, the application of the multilevel data ferroelectric storage memory is limited by high cost and difficulty to prepare high quality epitaxial films. Herein, we create a multilevel data ferroelectric storage memory with a non-epitaxial ferroelectric ultrathin film to overcome these issues. Through controlling the polarization switching and oxygen vacancy migration with the voltage pulses, we demonstrated that voltage-controlled barrier heights yield a memristive behavior with resistance variations. Moreover, we achieved eight logic states, which are written and read easily. Our results suggest new opportunities for ferroelectrics as high density non-volatile memories.

5-inch diameter Bi 3.15 Nd 0.85 Ti 3 O 12 (BNT) ferroelectric thin films were prepared on Si wafers by a modified pulsed laser deposition method, in which two laser scanning rates and 6-inch diameter target were used. The investigation on the distribution of the film thickness reveals that the laser scanning technique used in conjunction with the large-diameter target can improve the uniformity of film thickness. Especially the reasonable setup of the laser scanning rate ablating the fringe area of the large target has a prominent effect on weakening the edge deviation of thickness distribution. Such phenomenon was fundamentally explained by the simulation results on the ablation tracks of the laser beam on target. Through optimizing the laser scanning rates, BNT thin film with uniform thickness was obtained on 5-inch diameter Si wafer and the maximum variation in film thickness was found to be less than ± 2.5%. The results of X-ray photoelectron spectroscopy and X-ray diffraction show that the prepared 5-inch BNT thin film has great uniformity in stoichiometry and crystallinity. In addition, the measurements of electrical properties indicated that the prepared BNT thin film exhibits good ferroelectric property and I – V characteristic.

Ferroelectric-gate thin-film transistors (FGTs) with a stacked oxide structure of ZnO/Bi3.15Nd0.85Ti3O12 (BNT)/LaNiO3 (LNO) on Si substrates have been prepared and characterized. The FGT devices show good electrical properties, such as a large “on” current of 2.5 × 10−4 A and low threshold voltage of 1.1 V. These are mainly attributed to the coupling enhancement of the gate electric field to the channel layer due to a-axis preferential orientation of BNT ferroelectric-gate insulator thin films obtained by using the LNO buffer layer and the relatively good interface properties. The results suggest that ZnO/BNT/LNO/Si structures are well suited for thin-film transistors for future nonvolatile memory applications.

Lanthanide ions-doped NaLuF4 hexagonal-prismatic microtubes have been successfully synthesized via a facile hydrothermal approach for the first time. The as-grown microtubes are determined to be pure hexagonal (β-) NaLuF4 phase with an outermost diameter of about 3 μm and a length of approximately 40 μm. The Yb3+/Er3+(Tm3+)-codoped NaLuF4 microtubes emit bright three-primary-color (red, green, and blue) light under 980 nm laser diode excitation undergoing an upconversion. Mechanisms for the excitation and emission were analyzed based on the emission spectra, the plot of luminescence intensity to pump power and a simplified energy level diagram.

Both the linear and nonlinear optical properties of Bi3.15Nd0.85Ti3O12 (BNT0.85) ferroelectric thin films deposited on quartz substrates were investigated. The fundamental optical constants were determined as a function of light wavelength by optical transmittance measurements. By performing single-beam Z-scan experiments with femtosecond laser pulses at a wavelength of 800 nm, the two-photon absorption (TPA) coefficient β and third-order nonlinear refraction index γ were measured to be 1.15 × 102 cm/GW and −8.15 × 10−3 cm2/GW, respectively. The large TPA is attributed to an indirect transition process via the intermediate energy levels and the large refractive nonlinearity is the result of the electronic polarization and ferroelectric polarization arisen from the femtosecond midinfrared radiation. The results indicate that the BNT0.85 thin film is a promising candidate for applications in nonlinear photonic devices.

Thin films of Nd3+∕Zr4+ cosubstituted Bi4Ti3O12 (BIT), i.e., Bi3.15Nd0.85Ti2.8Zr0.2O12 (BNTZ), were fabricated on Pt∕Ti∕SiO2∕Si(100) substrates by chemical solution deposition and annealed at different temperatures of 600, 650, 700, and 800°C. The effects of annealing temperature on the microstructure, leakage current, ferroelectric, and dielectric properties of the BNTZ films were investigated in detail. Significantly, compared with the Bi3.15Nd0.85Ti3O12 film, the BNTZ thin film has a lower coercive field (2Ec) and leakage current density and a slightly larger remnant polarization (2Pr). It shows that Nd3+∕Zr4+ cosubstitution in BIT film might be an effective way to improve ferroelectric properties of BIT.