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An electric field improves the stability against humidity of a two-dimensional halide perovskite, BA2MA2Pb3I10. With a suitable range of the electric field, BA2MA2Pb3I10 could be used as a stable photocatalyst for HI splitting.

Charge ordering (CO), periodic modulation of electron density and lattice distortion, has been the fundamental subject in condensed matter physics, as well as a potential platform to induce novel functional properties. The charge-ordered phase is known to occur in a doped system of high d-electron occupancy but not of low occupancy. Here, we report that the charge-ordered phase is realized in electron-doped (100) SrTiO3 epitaxial thin films that have the lowest d-electron occupancy i.e., d1-d0. Theoretical calculation predicts the presence of a metastable CO state at the bulk state of electron-doped SrTiO3. Atomic scale analysis reveals that (100) surface distortion prefers the electron-lattice coupling for the charge-ordered state and triggers the stabilization for the CO phase from correlated metal, which extends up to six unit cells from the top surface to the interior. Our approach will provide an insight on the way to stabilize a new phase of matter that extends CO phase to the lowest electron occupancy, covering a whole range of 3d transition metal oxide.

Formamidinium lead iodide (FAPbI3)-based perovskites possess high light absorption and long diffusion lengths, making them strong candidates for highly efficient solar cells. However, despite these properties, primary intrinsic defects in FAPbI3 (i.e. iodine vacancy) induce strong electron localisation and become deep traps and recombination centres upon photoexcitation. Consequently, the carrier lifetime is significantly reduced and the superior properties are not fully utilised. Therefore, the manipulation of intrinsic defects has become a critical issue for realising highly efficient solar cells. Herein, formamidine disulfide dihydrochloride (FASCl) is used because the FAS2+ ion is a strong oxidant or electron scavenger. Substitution of the FAS2+ ion for the FA+ ion makes the iodine vacancy lose the strongly localised electrons and removes the deep traps. The incorporation of FASCl induces the formation of intermediate phases with a perovskite precursor, which can effectively stabilise the black α-phase FAPbI3 and retard the crystallisation rate, leading to compact full-coverage perovskite layers with high crystallinity and a large grain size. As a result, the optimal unit device (0.14 cm2) exhibits a remarkable power conversion efficiency (PCE) of 23.11%, a stabilised power output (SPO) of 22.83%, a low voltage deficit of 0.343 V, and a notable fill factor of 83.4%. Without encapsulation, the device retains ∼92.5% and ∼91.7% of its initial efficiency after 1000 h of either heating at 85 °C (thermal) or 50% relative humidity atmospheric testing, respectively. Moreover, the perovskite solar modules (PSMs) achieve PCE values of 20.75% (with a notable fill factor of 78.5%) and 17.44% for the active areas of 23.27 and 59.33 cm2, respectively.

Herein, the direct growth of polar orthorhombic phase in Hf0.5Zr0.5O2 (HZO) thin films is reported using Pulsed Laser Deposition (PLD). The growth of HZO onto a preheated (700 °C) silicon substrate mimics the rapid thermal annealing, which allows the formation of smaller crystallites (~9.7 nm) with large surface energy leading to the stabilization of metastable orthorhombic phase. Unlike atomic layer deposition (ALD) of HZO, PLD is more advantageous for depositing highly crystalline thin films through optimized parameters, such as laser fluence and background gas pressure. Further, the PLD-HZO is integrated with HfO2 dielectric and the resulting gate stacks have been used in the bottom gate FET architecture-‘Si//PLD-HZO/HfO2/MoS2//Ti/Au’. The NCFETs have yielded a sub-thermionic subthreshold swing (SSfor = 33.03 ± 8.7 mV/dec. and SSrev = 36.4 ± 7.7 mV/dec.) and a negligible hysteresis (~28 mV), which is capable in realizing low power integrated digital/analog circuits.

It is 100 years when we think about the history of ferroelectricity. We, who study ferroelectricity, are honored and pleased to share the 100-year anniversary of ferroelectricity and recall its history. At this great moment, we look back to the brief history on the verge of ferroelectricity. Our hope is that ferroelectricity studied as an early collective phenomenon will be coupled with quantum behavior, the essence of modern science, to become a new age in the history of science and technology.

The metal-insulator transition in correlated materials is usually coupled to a symmetry-lowering structural phase transition. This coupling not only complicates the understanding of the basic mechanism of this phenomenon but also limits the speed and endurance of prospective electronic devices. We demonstrate an isostructural, purely electronically driven metal-insulator transition in epitaxial heterostructures of an archetypal correlated material, vanadium dioxide. A combination of thin-film synthesis, structural and electrical characterizations, and theoretical modeling reveals that an interface interaction suppresses the electronic correlations without changing the crystal structure in this otherwise correlated insulator. This interaction stabilizes a nonequilibrium metallic phase and leads to an isostructural metal-insulator transition. This discovery will provide insights into phase transitions of correlated materials and may aid the design of device functionalities.

In correlated materials including transition metal oxides, electronic properties and functionalities are modulated and enriched by couplings between the electron and lattice degrees of freedom. These couplings are controlled by external parameters such as chemical doping, pressure, magnetic and electric fields, and light irradiation. However, the electron–lattice coupling relies on orbital characters, i.e., symmetry and occupancy, of t2g and eg orbitals, so that a large electron–lattice coupling is limited to eg electron system, whereas t2g electron system exhibits an inherently weak coupling. Here, we design and demonstrate a strongly enhanced electron–lattice coupling in electron-doped SrTiO3, that is, the t2g electron system. In ultrathin films of electron-doped SrTiO3 [i.e., (La0.25Sr0.75)TiO3], we reveal the strong electron–lattice–orbital coupling, which is manifested by extremely increased tetragonality and the corresponding metal-to-insulator transition. Our findings open the way of an active tuni...

Phase transitions in correlated materials can be manipulated at the nanoscale to yield emergent functional properties, promising new paradigms for nanoelectronics and nanophotonics. Vanadium dioxide (VO2), an archetypal correlated material, exhibits a metal–insulator transition (MIT) above room temperature. At the thicknesses required for heterostructure applications, such as an optical modulator discussed here, the strain state of VO2 largely determines the MIT dynamics critical to the device performance. We develop an approach to control the MIT dynamics in epitaxial VO2 films by employing an intermediate template layer with large lattice mismatch to relieve the interfacial lattice constraints, contrary to conventional thin film epitaxy that favors lattice match between the substrate and the growing film. A combination of phase-field simulation, in situ real-time nanoscale imaging, and electrical measurements reveals robust undisturbed MIT dynamics even at preexisting structural domain boundaries and si...

The dissociation process of methane on Ni and Ni alloys are investigated by density functional theory (DFT) in terms of catalytic efficiency and carbon deposition. Examining the dissociation to CH3, CH2, CH, C, and H is not sufficient to properly predict the catalytic efficiency and carbon deposition, and further investigation of the CO gas-evolving reaction is required to completely understand methane dissociation in steam. The location of alloying element in Ni alloy needed be addressed from the results of ab-inito molecular dynamics (MD). The reaction pathway of methane dissociation associated with CO gas evolution is traced by performing first-principles calculations of the adsorption and activation energies of each dissociation step. During the dissociation process, two alternative reaction steps producing adsorbed C and H or adsorbed CO are critically important in determining coking inhibition as well as H2 gas evolution (i.e., the catalytic efficiency). The theoretical calculations presented here suggest that alloying Ni with Ru is an effective way to reduce carbon deposition and enhance the catalytic efficiency of H2 fueling in solid oxide fuel cells (SOFCs).

The ac electrical conduction of Cr-doped SrTiO3 thin films with an oxygen-deficient interface layer was investigated as a function of temperature and frequency. The Cr-doped SrTiO3 (Cr-STO) thin films with an ultra-thin (∼2 nm) oxygen-deficient layer inserted between the top electrode and the Cr-STO layer exhibited two ac conduction mechanisms, i.e., variable-range hopping and small-polaron hopping conduction, accompanied by a relaxation process. Since high oxygen deficiency induces large lattice distortion in the depletion layer, the first relaxation process occurs at low frequencies in the thin oxygen depletion layer Cr-SrTiO3−δ , and the corresponding conduction behavior follows the small-polaron tunneling model. In the high frequency range, an additional relaxation process is involved and is associated with the variable-range hopping between the localized states in the band gap of the thick Cr-SrTiO3 layer.

Piezoelectric actuators, exhibiting large displacement and torque, are attractive for use in a broad range of actuator applications. One of the important applications is a tactile device, e.g., refreshable Braille display. Piezoelectric actuation in the Braille module requires large torque and large displacement for the tactile sensing of the human finger. In this study, we design piezoelectric actuators for the tactile interface including a Braille cell by finite element method (FEM) simulations. FEM simulations allow us to capture the entire device physics and solve the coupled piezoelectricity/solid mechanics problem. We investigated the effect of the structure, geometric variation, and physical properties of the materials used on the displacement and torque force. The studied structure includes a trilayer bimorph consisting of piezoelectric and supporting layers, and a multilayer with multiple bimorphs. The simulation result provides a useful guide toward piezoelectric actuators of tactile function.

Flexible magnetoelectric (ME) materials have been studied for new applications such as memory, energy harvesters, and magnetic field sensors. Herein, with the widely studied and progressive advantages of ME phenomena in the multiferroic field, we demonstrate a new approach for utilizing flexible ME materials as gate dielectric layers in ME organic field-effect transistors (ME-OFET) that can be used for sensing a magnetic field and extracting the ME properties of the gate dielectric itself. The magnetoelectric nanohybrid gate dielectric layer comprises sandwiched stacks of magnetostrictive CoFe2O4 nanoparticles and a highly piezoelectric poly(vinylidene fluoride-co-trifluoroethylene) layer. While varying the magnetic field applied to the ME gate dielectric, the ME effect in the functional gate dielectric modulates the channel conductance of the ME-OFET owing to a change in the effective gate field. The clear separation of the ME responses in the gate dielectric layer of ME-OFET from those of the other parameters was demonstrated using the AC gate biasing method and enabled the extraction of the ME coefficient of ME materials. Additionally, the device shows high stability after cyclic bending of 10,000 cycles at a banding radius of 1.2 cm. The device has significant potential for not only the extraction of the intrinsic characterization of ME materials but also the sensing of a magnetic field in integrated flexible electronic systems.

Reversible resistive switching of Cr2O3 films was studied by use of conductive atomic force microscopy. Resistive switching in Cr2O3 films occurs as a result of Ag filament paths formed during electrochemical redox reactions. A large memory density of 100 Tbit/sq. inch was achieved with a small filament diameter of 2.9 nm under the action of a compliance current of 10 nA. A fast switching speed of 10 ns, high scalability, and low set/reset currents suggest that Cr2O3-based resistive memory is suitable for nanoscale devices.

Phase transitions in correlated materials can be manipulated at the nanoscale to yield emergent functional properties, promising new paradigms for nanoelectronics and nanophotonics. Vanadium dioxide (VO

Oxygen vacancies have been implicitly assumed isolated ones, and understanding oxide materials possibly containing oxygen vacancies remains elusive within the scheme of the isolated vacancies, although the oxygen vacancies have been playing a decisive role in oxide materials. Here, we report the presence of oxygen vacancy linear clusters and their orientation along a specific crystallographic direction in SrTiO3, a representative of a perovskite oxide. The presence of the linear clusters and associated electron localization was revealed by an electronic structure represented in the increase in the Ti2+ valence state or corresponding Ti 3d2 electronic configuration along with divacancy cluster model analysis and transport measurement. The orientation of the linear clusters along the [001] direction in perovskite SrTiO3 was verified by further X-ray diffuse scattering analysis. Because SrTiO3 is an archetypical perovskite oxide, the vacancy linear clustering with the specific aligned direction and electron ...

We have grown Sr0.75La0.25TiO3 (SLTO) thin films using pulsed laser deposition (PLD) with various laser energy fluences. We investigated the effect of energy fluence on the compositions of SLTO films. The stoichiometry of SLTO films was controlled by adjusting the laser energy density. At low energy densities below 1.0 J/cm2, SLTO films become non-stoichiometric with Ti deficiency. The Ti deficiency increases with decreasing the laser energy fluence. We have also investigated the effect of laser energy fluence on the electrical properties of the thin films. The electrical resistivity and carrier density intimately depend on the laser energy fluence as a result of the non-stoichiometry. After eliminating the effect of oxygen vacancies by post-annealing, the electrical properties are dependent on the cation stoichiometry in the oxide films.

Recently, piezoelectricity has been observed in 2D atomically thin materials, such as hexagonal-boron nitride, graphene, and transition metal dichalcogenides (TMDs). Specifically, exfoliated monolayer MoS

We report the kinetics of nanoscale domain growth in ferroelectric PbZrO3/PbTiO3 artificial superlattices. Ferroelectric superlattices behave as single ferroelectric materials with only 180° domain structure (monodomain). Domain size increases linearly with the pulse voltage, and is linearly dependent on the logarithmic value of the pulse duration. It was found that ferroelectric superlattices have a relatively high activation field for domain growth and enhanced domain stability, resulting in a long-term retention behavior of more than one month.

We investigated resistance switching behavior of the Ag/ZnO/Ti structures for random access memory devices. These films were prepared on glass substrate by dc sputtering technique at room temperature. The resistance switching follows unipolar switching mode with small switching voltages (0.4 V – 0.6 V). Our results figured out that the Ag/ZnO/Ti/Glass structure is a candidate structure for nonvolatile data storage applications.

This study examined the electrical conduction of Cr-doped SrTiO3 thin films in a metal (Pt)–insulator–metal (La0.5Sr0.5CoO3) structure. Two DC transport mechanisms, variable range hopping and the trap-controlled space-charge-limited current conduction, were found to be responsible for the conduction behavior. Resistance switching mechanism involved the trapping/detrapping of injected carriers at the weakly localized states.

High-performance, flexible all graphene-based thin film transistor (TFT) was fabricated on plastic substrates using a graphene active layer, graphene oxide (GO) dielectrics, and graphene electrodes. The GO dielectrics exhibit a dielectric constant (3.1 at 77 K), low leakage current (17 mA/cm(2)), breakdown bias (1.5 × 10(6) V/cm), and good mechanical flexibility. Graphene-based TFTs showed a hole and electron mobility of 300 and 250 cm(2)/(V·s), respectively, at a drain bias of -0.1 V. Moreover, graphene TFTs on the plastic substrates exhibited remarkably good mechanical flexibility and optical transmittance. This method explores a significant step for the application of graphene toward flexible and stretchable electronics.

The resistance switching mechanism and the electrical conduction of thick Cu/ZnO/Cu/ZnO/Cu structures were investigated for various ZnO thicknesses (40, 80, 160, and 320 nm) when the thickness of the middle Cu layer was 2 nm. The ZnO films had a microstructure with columnar grains normal to the substrate. The switching voltages (VSET and VRESET) varied with the thickness of the ZnO layer. A symmetric electrode structure exhibited a unipolar resistance switching. The electrical transport of both high-resistance state (HRS) and low-resistance state (LRS) was Ohmic conduction, and the resistance switching mechanism was driven by the formation and the rupture of Cu conducting paths.

Epitaxial thin films of a heterostructure with Bi 4 Ti 3 O 12 (BIT)/SrTiO 3 (ST) were successfully grown with a bottom electrode consisting of La 0.5 Sr 0.5 CoO 3 (LSCO) on MgO(001) substrates using pulsed laser deposition. The grown BIT and ST (001) planes were parallel to the growth surface with the orientation relationship of BIT //ST . In the as-deposited film, the BIT (001) plane appeared to expand to relieve a lattice mismatch with the ST (001) plane. However, annealing for 20–40 min induced the BIT (001) plane to contract horizontally with its c -axis expanding, which was associated with a local perturbation in the layer stacking of the BIT structure. This structural distortion was reduced in the film annealed for 1 h, with restoration of the periodicity of the layer stacking. Correspondingly, the dielectric constant of the as-deposited film was increased from 292 to 411 by annealing for 1 h. In parallel, the film was paraelectric but became more ferroelectric, with the remanent polarization and the coercive field changing from 0.1 μC/cm 2 and 14 kV/cm to 1.7 μC/cm 2 and 69 kV/cm, respectively.

The displacement performance of piezoelectrically actuated inkjet print head in a bending mode was investigated with the numerical and experimental analysis. The bending actuator membrane with a multi-layered structure, including piezoelectric, elastic and support layers was fabricated by MEMS processing. The displacement of the actuator membrane reaches a maximum at a relative width ratio of PZT to support layer in the range from 0.6 to 0.8, depending on their thickness ratio. The fabricated actuator membrane exhibited its maximum displacement of 0.098 um/V, which agreed well with simulation results, i.e., 0.089 μ m/V.

The electrical conduction properties of 0.2% Cr-doped SrTiO3 thin film in metal–insulator–metal (MIM) structure was investigated by using dc and impedance spectroscopic measurements at room temperature. The dc measurement shows that the electronic conduction is the trap-controlled space-charge-limited current (SCLC) conduction. The impedance study shows that the electrical conduction is bulk-limited conduction. The behavior of the bulk resistance obtained in the equivalent circuit model from the impedance analysis is also consistent with the trap-controlled space-charge-limited conduction with exponential trap distribution.

The resistive switching of 0.2% Cr-doped SrTiO3 (Cr-STO) thin films grown on (La0.5, Sr0.5)CoO3/SrTiO3 (LSCO/STO) substrate have been investigated. The structure in a metal-insulator-metal (MIM) i.e., Pt/Cr-STO/LSCO, shows hysteretic and asymmetric behaviors in current-voltage (I-V) characteristics. The current-voltage characteristics are attributed to the resistive switching of Cr-STO thin films between high resistance state (HRS) and low resistance state (LRS) by applying pulsed or dc bias voltage stress. The current and voltage ramp sweeps in the I-V measurement reveal that threshold current is required to induce the resistive switching from HRS to LRS in the negative voltage region.

We have successfully fabricated SrTiO 3 /(Sr 1− x ,La x )TiO 3 (STO/SLTO) superlattices on step-terrace structured SrTiO 3 , in which La defect is distributed in a regular manner of one dimension. The superlattices contain one unit cell thick SLTO layer with various stacking sequences. The charge carrier density of the superlattices was in the range of 1.7 × 10 19 –2 × 10 16 cm − 3 . In addition, the mobility and resistivity of STO/SLTO superlattice were 11 cm 2 /Vs and 0.18 Ω cm at the STO 1 /SLTO 1 stacking sequence, respectively. The charge carrier density of STO/SLTO superlattices increased significantly with the change in a stacking sequence, while the mobility is relatively insensitive to the change in the stacking sequence. The resulting resistivity of the superlattics changed significantly with the change in the stacking sequence due to mainly the change of the charge carrier density. The oxide superlattice approach provides an useful way of nonlinear control of charge carrier density and electrical resistivity.

We have grown Sr0.75La0.25TiO3 (SLTO) thin films using pulsed laser deposition (PLD) with various laser energy fluences. We investigated the effect of energy fluence on the compositions of SLTO films. The stoichiometry of SLTO films was controlled by adjusting the laser energy density. At low energy densities below 1.0 J/cm2, SLTO films become non-stoichiometric with Ti deficiency. The Ti deficiency increases with decreasing the laser energy fluence. We have also investigated the effect of laser energy fluence on the electrical properties of the thin films. The electrical resistivity and carrier density intimately depend on the laser energy fluence as a result of the non-stoichiometry. After eliminating the effect of oxygen vacancies by post-annealing, the electrical properties are dependent on the cation stoichiometry in the oxide films.

The electronic structure of oxygen deficient BaTiO3 has been investigated by the first principles calculation. The oxygen vacancy doping in the form of isolated single vacancies does not create the localized state (i.e. trap level) in the band gap, as reported in many experimental studies. Electrons associated with the oxygen vacancy are occupied in the defect level with mainly Ti 3d e g character in significant hybridization with O 2p state, which leads to the lowering of the defect energy level to the minimum edge of the conduction band. The resulting occupied energy band has a little dispersion indicating that BaTiO3 becomes electrically conducting with low electron mobility. It is suggested that oxygen vacancy clustering may lead to further lowering of the defect level into the band gap.

Various types of piezoelectrically driven microtransducers which have a similar physical dimension, i.e., microcantilever, microdiaphragm and microbridge, were fabricated by micro electromechanical system (MEMS) technique and are compared on the mass sensing behavior. The diol based sol-gel derived Pb(Zr0.52,Ti0.48)O3 (PZT) thin film capacitors were integrated for the piezoelectric actuation. We have used the resonant frequency change of microtransducer upon mass increase as a sensing mechanism. The resonant frequency of the microtransducer was measured by analysis of electrical signals from microtransducer such as impedance, capacitance, phase and dielectric loss. The fundamental resonant frequencies of the microcantilever, microbridge and microdiaphragm with similar dimension (∼300 μm) were about 26 kHz, 260 kHz and 290 kHz, respectively. The mass sensitivities of bare microtransducers were measured by metallic thin film deposition and analysis of spectral responses from microtransducers. When ...