Auxetic piezoelectric effect in heterostructures.

Inherent symmetry breaking at the interface has been fundamental to a myriad of physical effects and functionalities, such as efficient spin-charge interconversion, exotic magnetic structures and an emergent bulk photovoltaic effect. It has recently been demonstrated that interface asymmetry can induce sizable piezoelectric effects in heterostructures, even those consisting of centrosymmetric semiconductors, which provides flexibility to develop and optimize electromechanical coupling phenomena. Here, by targeted engineering of the interface symmetry, we achieve piezoelectric phenomena behaving as the electrical analogue of the negative Poisson's ratio.

Photoinduced Negative Differential Resistivity and Gunn Oscillations in SrTiO3.

SrTiO , a perovskite oxide, holds significant potential for application in the field of oxide electronics. Notably, its photoelectric activity in the low temperature regime, which overlaps with the quantum paraelectric state, exhibits remarkable characteristics. In this study, it is demonstrated that when photo-excited with above band gap energy photons, SrTiO exhibits non-linear transport of photocarriers and voltage-controlled negative resistance, resulting from an intervalley transfer of photo-induced electrons.

Acquired benign tracheo‑oesophageal fistula secondary to oesophageal stenting for post lye ingestion stenosis: A case report.

Acquired benign trachea-oesophageal fistula is a rare benign pathological entity with varying aetiologies that most often occurs post-intubation. This case report presents the case of a female patient, 31 years old, admitted to the emergency room with sepsis syndrome following bilateral aspiration pneumonia caused by a large trachea-oesophageal fistula. The fistula was the result of intra-tracheal migration of an oesophageal stent placed for post lye ingestion stenosis.

Bond engineering of molecular ferroelectrics renders soft and high-performance piezoelectric energy harvesting materials.

Piezoelectric materials convert mechanical stress to electrical energy and thus are widely used in energy harvesting and wearable devices. However, in the piezoelectric family, there are two pairs of properties that improving one of them will generally compromises the other, which limits their applications. The first pair is piezoelectric strain and voltage constant, and the second is piezoelectric performance and mechanical softness.

Enhanced Photoconductivity at Dislocations in SrTiO.

Dislocations are 1D crystallographic line defects and are usually seen as detrimental to the functional properties of classic semiconductors. It is shown here that this not necessarily accounts for oxide semiconductors in which dislocations are capable of boosting the photoconductivity. Strontium titanate single crystals are controllably deformed to generate a high density of ordered dislocations of two slip systems possessing different mesoscopic arrangements.

Dual-Ferroelectric-Coupling-Engineered Two-Dimensional Transistors for Multifunctional In-Memory Computing.

In-memory computing featuring a radical departure from the von Neumann architecture is promising to substantially reduce the energy and time consumption for data-intensive computation. With the increasing challenges facing silicon complementary metal-oxide-semiconductor (CMOS) technology, developing in-memory computing hardware would require a different platform to deliver significantly enhanced functionalities at the material and device level. Here, we explore a dual-gate two-dimensional ferroelectric field-effect transistor (2D FeFET) as a basic device to form both nonvolatile logic gates and artificial synapses, addressing in-memory computing simultaneously in digital and analog spaces.

Ferroelectric incommensurate spin crystals.

Ferroics, especially ferromagnets, can form complex topological spin structures such as vortices and skyrmions when subjected to particular electrical and mechanical boundary conditions. Simple vortex-like, electric-dipole-based topological structures have been observed in dedicated ferroelectric systems, especially ferroelectric-insulator superlattices such as PbTiO/SrTiO, which was later shown to be a model system owing to its high depolarizing field. To date, the electric dipole equivalent of ordered magnetic spin lattices driven by the Dzyaloshinskii-Moriya interaction (DMi) has not been experimentally observed.

Fast Photostriction in Ferroelectrics.

Light-induced nonthermal strain, known as the photostrictive effect, offers a potential way to excite mechanical strain and acoustic wave remotely. The anisotropic photostrictive effect induced by the combination of bulk photovoltaic effect (BPVE) and converse piezoelectric effect in ferroelectric materials is known as too small and slow for the applications requiring a high strain rate, such as ultrasound generation and high-speed signal transmission. Here, a strategy to achieve high rate dynamic photostrictive strain by utilizing local fast responses under modulating continuous light excitation in the resonance condition is reported.

Quantitative Local Probing of Polarization with Application on HfO -Based Thin Films.

Owing to their switchable spontaneous polarization, ferroelectric materials have been applied in various fields, such as information technologies, actuators, and sensors. In the last decade, as the characteristic sizes of both devices and materials have decreased significantly below the nanoscale, the development of appropriate characterization tools became essential. Recently, a technique based on conductive atomic force microscopy (AFM), called AFM-positive-up-negative-down (PUND), is employed for the direct measurement of ferroelectric polarization under the AFM tip.

Boosting Piezoelectricity under Illumination via the Bulk Photovoltaic Effect and the Schottky Barrier Effect in BiFeO.

Piezoelectricity is a key functionality induced by conversion between mechanical and electrical energy. Enhancement of piezoelectricity in ferroelectrics often has been realized by complicated synthetical approaches to host unique structural boundaries, so-called morphotropic phase boundaries. While structural approaches are well-known, enhancing piezoelectricity by external stimuli has yet to be clearly explored, despite their advantages of offering not only simple and in situ control without any prior processing requirement, but compatibility with other functionalities.

Comprehensive mineralogical and physicochemical characterization of recent sapropels from Romanian saline lakes for potential use in pelotherapy.

In this study we aimed to compare the mineralogical, thermal, physicochemical, and biological characteristics of recent organic carbon-rich sediments ('sapropels') from three geographically distant Romanian lakes (Tekirghiol and Amara, SE Romania, and Ursu, Central Romania) with distinct hydrogeochemical origins, presently used for pelotherapy. The investigated lakes were classified as inland brackish Na-Cl-sulfated type (Amara), coastal moderately saline and inland hypersaline Na-Cl types (Tekirghiol and Ursu, respectively). The settled organic matter is largely composed of photosynthetic pigments derived from autochthonous phytoplankton.

Real-space observation of ferroelectrically induced magnetic spin crystal in SrRuO.

Unusual features in the Hall Resistivity of thin film systems are frequently associated with whirling spin textures such as Skyrmions. A host of recent investigations of Hall Hysteresis loops in SrRuO heterostructures have provided conflicting evidence for different causes for such features. We have constructed an SrRuO-PbTiO (Ferromagnetic - Ferroelectric) bilayer that exhibits features in the Hall Hysteresis previously attributed to a Topological Hall Effect, and Skyrmions.

Emerging Opportunities for 2D Semiconductor/Ferroelectric Transistor-Structure Devices.

Semiconductor technology, which is rapidly evolving, is poised to enter a new era for which revolutionary innovations are needed to address fundamental limitations on material and working principle level. 2D semiconductors inherently holding novel properties at the atomic limit show great promise to tackle challenges imposed by traditional bulk semiconductor materials. Synergistic combination of 2D semiconductors with functional ferroelectrics further offers new working principles, and is expected to deliver massively enhanced device performance for existing complementary metal-oxide-semiconductor (CMOS) technologies and add unprecedented applications for next-generation electronics.

Anisotropic Ion Migration and Electronic Conduction in van der Waals Ferroelectric CuInPS.

Van der Waals (vdW) thio- and seleno-phosphates have recently gained considerable attention for the use as "active" dielectrics in two-dimensional/quasi-two-dimensional electronic devices. Bulk ionic conductivity in these materials has been identified as a key factor for the control of their electronic properties. However, direct evidence of specific ion species' migration at the nanoscale, particularly under electric fields, and its impact on material properties has been elusive.

Photovoltaic and flexible deep ultraviolet wavelength detector based on novel β-GaO/muscovite heteroepitaxy.

Flexible and self-powered deep ultraviolet (UV) photodetectors are pivotal for next-generation electronic skins to enrich human life quality. The fabrication of epitaxial β-GaO thin films is challenging on flexible substrates due to high-temperature growth requirements. Herein, β-GaO ([Formula: see text] 0 1) films are hetero-epitaxially grown on ultra-thin and environment-friendly muscovite mica which is the first time β-GaO epitaxy growth on any flexible substrate.

Piezoelectric and pyroelectric effects induced by interface polar symmetry.

Interfaces in heterostructures have been a key point of interest in condensed-matter physics for decades owing to a plethora of distinctive phenomena-such as rectification, the photovoltaic effect, the quantum Hall effect and high-temperature superconductivity-and their critical roles in present-day technical devices. However, the symmetry modulation at interfaces and the resultant effects have been largely overlooked. Here we show that a built-in electric field that originates from band bending at heterostructure interfaces induces polar symmetry therein that results in emergent functionalities, including piezoelectricity and pyroelectricity, even though the component materials are centrosymmetric.

Emergent Antipolar Phase in BiFeO-LaSrMnO Superlattice.

Ferroelectric-paraelectric superlattices show emerging new states, such as polar vortices, through the interplay and different energy scales of various thermodynamic constraints. By introducing magnetic coupling at BiFeO-LaSrMnO interfaces epitaxially grown on SrTiO substrate, we find, for the first time in thin films, a sub-nanometer thick lamella-like BiFeO. The emergent phase is characterized by an arrangement of a two unit cell thick lamella-like structure featuring antiparallel polarization, resulting an antiferroelectric-like structure typically associated with a morphotropic phase transition.

Polarization Screening Mechanisms at LaSrMnO-PbTiO Interfaces.

The structural, electronic, and magnetic properties of interfaces between epitaxial LaSrMnO and PbTiO have been explored via atomic resolution transmission electron microscopy of a functional multiferroic tunnel junction. Measurements of the polar displacements and octahedral tilting show the competition between the two distortions at the interface and demonstrate strong dependence on the polarization orientation. The density functional theory provides information on the electronic and magnetic properties, where the interface termination plays a crucial role in the screening mechanisms.

Spatio-temporal insights into microbiology of the freshwater-to-hypersaline, oxic-hypoxic-euxinic waters of Ursu Lake.

Ursu Lake is located in the Middle Miocene salt deposit of Central Romania. It is stratified, and the water column has three distinct water masses: an upper freshwater-to-moderately saline stratum (0-3 m), an intermediate stratum exhibiting a steep halocline (3-3.5 m), and a lower hypersaline stratum (4 m and below) that is euxinic (i.

Artificial Optoelectronic Synapses Based on Ferroelectric Field-Effect Enabled 2D Transition Metal Dichalcogenide Memristive Transistors.

Neuromorphic visual sensory and memory systems, which can perceive, process, and memorize optical information, represent core technology for artificial intelligence and robotics with autonomous navigation. An optoelectronic synapse with an elegant integration of biometric optical sensing and synaptic learning functions can be a fundamental element for the hardware-implementation of such systems. Here, we report a class of ferroelectric field-effect memristive transistors made of a two-dimensional WS semiconductor atop a ferroelectric PbZrTiO (PZT) thin film for optoelectronic synaptic devices.

Non-conventional mechanism of ferroelectric fatigue via cation migration.

The unique properties of ferroelectric materials enable a plethora of applications, which are hindered by the phenomenon known as ferroelectric fatigue that leads to the degradation of ferroelectric properties with polarization cycling. Multiple microscopic models explaining fatigue have been suggested; however, the chemical origins remain poorly understood. Here, we utilize multimodal chemical imaging that combines atomic force microscopy with time-of-flight secondary mass spectrometry to explore the chemical phenomena associated with fatigue in PbZrTiO (PZT) thin films.

Topological domain states and magnetoelectric properties in multiferroic nanostructures.

Multiferroic nanostructures have been attracting tremendous attention over the past decade, due to their rich cross-coupling effects and prospective electronic applications. In particular, the emergence of some exotic phenomena in size-confined multiferroic systems, including topological domain states such as vortices, center domains, and skyrmion bubble domains, has opened a new avenue to a number of intriguing physical properties and functionalities, and thus underpins a wide range of applications in future nanoelectronic devices. It is also highly appreciated that nano-domain engineering provides a pathway to control the magnetoelectric properties, which is promising for future energy-efficient spintronic devices.

Strain-gradient mediated local conduction in strained bismuth ferrite films.

It has been recently shown that the strain gradient is able to separate the light-excited electron-hole pairs in semiconductors, but how it affects the photoelectric properties of the photo-active materials remains an open question. Here, we demonstrate the critical role of the strain gradient in mediating local photoelectric properties in the strained BiFeO thin films by systematically characterizing the local conduction with nanometre lateral resolution in both dark and illuminated conditions. Due to the giant strain gradient manifested at the morphotropic phase boundaries, the associated flexo-photovoltaic effect induces on one side an enhanced photoconduction in the R-phase, and on the other side a negative photoconductivity in the morphotropic [Formula: see text]-phase.

Flexible Memristors Based on Single-Crystalline Ferroelectric Tunnel Junctions.

Ferroelectric tunnel junction (FTJ) based memristors exhibiting continuous electric field controllable resistance states have been considered promising candidates for future high-density memories and advanced neuromorphic computational architectures. However, the use of rigid single crystal substrate and high temperature growth of the epitaxial FTJ thin films constitutes the main obstacles to using this kind of heterostructure in flexible computing devices. Here, we report the integration of centimeter-scale single crystalline FTJs on flexible plastic substrates, by water-etching based epitaxial oxide membrane lift-off and the following transfer.