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Single-layer ZrTeSe4 is a novel 2D semiconductor as well as a promising candidate for 2D thermoelectric materials.

Quantum confinements, especially quantum in narrow wells, have been investigated because of their controllability over electrical parameters. For example, quantum dots can emit a variety of photon wavelengths even for the same material depending on their particle size. More recently, the research into two-dimensional (2D) materials has shown the availability of several quantum mechanical phenomenon confined within a sheet of materials. Starting with the gapless semimetal properties of graphene, current research has begun into the excitons and their properties within 2D materials. Even for simple 2D systems, experimental results often offer surprising results, unexpected from traditional studies. We investigated a coupled quantum well system using 2D hexagonal boron nitride (hBN) barrier as well as 2D tungsten disulfide (WS2) semiconductor arranged in stacked structures to study the various 2D to 2D interactions. We determined that for hexagonal boron nitride-tungsten disulfide (hBN/WS2) quantum well stacks, the interaction between successive wells resulted in decreasing bandgap, and the effect was pronounced even over a large distance of up to four stacks. Additionally, we observed that a single layer of isolating hBN barriers significantly reduces interlayer interaction between WS2 layers, while still preserving the interwell interactions in the alternative hBN/WS2 structure. The methods we used for the study of coupled quantum wells here show a method for determining the respective exciton energy levels and trion energy levels within 2D materials and 2D materials-based structures. Renormalization energy levels are the key in understanding conductive and photonic properties of stacked 2D materials.

This study is on the degradation phenomenon of oxide semiconductor thin-film transistor under dynamic stress applied to the drain. The current reduction that occurs during the rise and fall of the pulse was clearly observed through electrical measurements and the cause of the current drop was investigated via a two-dimensional device simulation. The results confirmed that while the instantaneous rise of the pulse provides high energy to the electrons ejected to the drain, the rapid drop of the pulse only produces impact ionization rates in very small areas with an electronic backflow to the drain. Furthermore, a model based on these relationships is proposed for asymmetric local degradation by high energy ( hot ) electrons.

Above-bandgap femtosecond optical excitation of a ferroelectric/dielectric BaTiO3/CaTiO3 superlattice leads to structural responses that are a consequence of the screening of the strong electrostatic coupling between the component layers. Time-resolved x-ray free-electron laser diffraction shows that the structural response to optical excitation includes a net lattice expansion of the superlattice consistent with depolarization-field screening driven by the photoexcited charge carriers. The depolarization-field-screening-driven expansion is separate from a photoacoustic pulse launched from the bottom electrode on which the superlattice was epitaxially grown. The distribution of diffracted intensity of superlattice x-ray reflections indicates that the depolarization-field-screening-induced strain includes a photoinduced expansion in the ferroelectric BaTiO3 and a contraction in CaTiO3. The magnitude of expansion in BaTiO3 layers is larger than the contraction in CaTiO3. The difference in the magnitude of depolarization-field-screening-driven strain in the BaTiO3 and CaTiO3 components can arise from the contribution of the oxygen octahedral rotation patterns at the BaTiO3/CaTiO3 interfaces to the polarization of CaTiO3. The depolarization-field-screening-driven polarization reduction in the CaTiO3 layers points to a new direction for the manipulation of polarization in the component layers of a strongly coupled ferroelectric/dielectric superlattice.

IEEE Energy Conversion Congress and Exposition, ECCE (14th. 2022. Detroit, USA), This work was supported in part by the Research, Technological, Development and Innovation Programs of the Spanish Ministry of Science and Innovation, under grant PID2019-106057RB-I00.

IEEE Energy Conversion Congress and Exposition, ECCE (13th. 2021. Virtual), This work was supported in part by the Research, Technological Development and Innovation Programs of the Spanish Ministry of Science and Innovation, under grant PID2019-106057RB-I00.

Superlattice comprising of ferroelectric (FE) and non-ferroelectric (non-FE) material has been developed to induce a ferroelectric response in the non-ferroelectric layer. In this study, a superlattice thin film comprising of BiFeO3 (BFO) as FE oxide and La0.85Ce0.15MnO3 (LCMO) as semiconducting non-FE oxide is fabricated and investigated the FE and piezoelectric responses in LCMO. We observed the piezoelectric response of individual layers using time-resolved X-ray microdiffraction experiment under an external electric field. Piezoelectric response of individual layers was resolved by comparing it with the values obtained from kinematic diffraction calculation. Piezoelectric coefficient (d33) of LCMO monolayer is found to be approximately 27 pm/V, which is a similar value as that of the BFO layer.

The reduction in current ability accompanied by the hump phenomenon in oxide semiconductor thin-film transistors to which high DC voltages and AC drive voltages are applied has not been studied extensively, although it is a significant bottleneck in the manufacture of integrated circuits. Here, we report on the origin of the hump and current drop in reliability tests caused by the degradation in the oxide semiconductor during a circuit driving test. The hump phenomenon and current drop according to two different driving stresses were verified. Through a numerical computational simulation, we confirmed that this issue can be caused by an additional “needle”, a shallow (~0.2 eV) and narrow (

독자의 읽기 목적에 따라 독자가 활용하는 텍스트 정보에 차이가 있다. 이 연구는 읽기 목적에 따라 활용 가능한 텍스트 정보의 차이를 시각적으로 제시하는 방안을 제안한다. 읽기 행동은 진공상태에서 이루어지는 것이 아닌 특별한 목적에서 수행된다. 그러나 지금까지의 텍스트 분석 연구가 맥락이 배제된 일반적인 읽기 상황을 가정한 연구에 한정되어 있었다. 같은 텍스트를 활용하더라도 목적에 따라 독자에게 필요한 정보의 종류, 분포, 연결 관계 등이 달라진다. 특히 읽기 부진에 처해있는 학습자들을 지원할 수 있는 읽기 교수·학습 내용을 현시적 지도 방안으로 구성하는 것을 목적으로 하였다. 독자의 읽기 목적에 따라 달라지는 텍스트의 정보를 시각적으로 비교할 수 있도록 의미망 연결, 토픽 분석 등을 활용하여 텍스트 분석 결과를 제시하였다. 변화하는 매체 환경에서는 독자가 읽은 텍스트의 내용 전체를 기억하는 것보다는 필요한 정보가 어디에 있는지를 회상하고 빠르게 재탐색할 수 있는 능력이 보장되어야 한다. 따라서 독자의 문제 해결에 필요한 텍스트 정보에 대한 단서를 시각적으로 제시하여 스스로 학습할 수 있는 수단을 제공함으로써 읽기 능력의 향상을 도모할 수 있을 것이다.

이 연구는 비정형 데이터인 텍스트에 대해 컴퓨터를 활용하여 글의 수준을 판별하기 위해 활용할 수 있는 변인 탐색을 목적으로 하였다. 이를 위해 텍스트 분석과 유사한 분야인 미술 작품에 대한 신경미학을 검토하고 미술분야에서 활용한 인공지능 알고리즘을 검토하였다. 또한 자동 채점에서 활용할 수 있는 텍스트 요인과 분석 방법을 탐구하고자 자연언어처리를 활용한 텍스트 분석 연구의 여러 분야를 비교하였다. 각 연구 분야별로 활용하고 있는 텍스트 분석 요인과 분석 방법을 살펴봄으로써 자동 채점과의 유사점과 차이점을 도출하고자 하였다. 무엇보다 잘 쓴 글, 또는 좋은 글에 대한 명확하고 합의된 정의가 요구된다. 이를 통해 글의 수준을 설명할 수 있는 수량화, 정량화 가능한 요인을 추출할 수 있다. 또한 텍스트를 구성하고 있는 기본 요소인 단어(형태소)가 텍스트 분석의 기본 요인이지만 단어가 가진 어떤 속성을 활용할 것인지는 연구 분야마다 차이를 보인다. 텍스트는 단어의 집합으로 구성되지만 텍스트의 의미는 단어의 단순 총합 이상이다. 따라서 텍스트의 특성을 설명할 수 있는 단어 이외의 변인을 선정할 수 있어야 하며 각 변인은 텍스트의 특성을 정확하고 변별적으로 측정할 수 있어야 한다.

Ferroelectric polymer blend film with non-polar relaxor polymer shows composition dependency of switching behaviors. Studies of ferroelectric properties in polymer blend films with increase volume fraction of relaxor polymer revealed inversely decrease both remnant polarization and coercive voltage, simultaneously. The reduced coercive voltage of the blend with films with higher volume fraction of realxor polymer relative to that of pure ferroelectric film is consistent with the high frequency of applied voltage. Nanoscale ferroelectric polarization switching of blend film was also faster than that of pure ferroelectric film.

Weakly coupled ferroelectric/dielectric superlattice thin-film heterostructures exhibit complex nanoscale polarization configurations that arise from a balance of competing electrostatic, elastic, and domain-wall contributions to the free energy. A key feature of these configurations is that the polarization can locally have a significant component that is along the thin-film surface normal direction with an overall configuration maintaining zero net in-plane polarization. PbTiO_{3}/SrTiO_{3} thin-film superlattice heterostructures on a conducting SrRuO_{3} bottom electrode on SrTiO_{3} have a room-temperature stripe nanodomain pattern with a nanometer-scale lateral period. Ultrafast time-resolved x-ray free electron laser diffraction and scattering experiments reveal that above-bandgap optical pulses induce propagating acoustic pulses and a perturbation of the domain diffuse scattering intensity arising from the nanoscale stripe domain configuration. With 400-nm optical excitation, two separate acoustic pulses are observed: a high-amplitude pulse resulting from strong optical absorption in the bottom electrode and a weaker pulse arising from the depolarization-field-screening effect due to absorption directly within the superlattice. The picosecond scale variation of the nanodomain diffuse scattering intensity is consistent with a larger polarization change than would be expected due to the polarization-tetragonality coupling of uniformly polarized ferroelectrics. The polarization change is consistent, instead, with polarization rotation facilitated by the reorientation of the in-plane component of the polarization at the domain boundaries of the striped polarization structure. The complex steady-state configuration within these ferroelectric heterostructures leads to ultrafast polarization rotation phenomena that have previously been available only through the selection of bulk crystal composition.

Heavy metals have adverse effects on microalgae metabolism and growth. Photosynthesis and lipid profile are quite sensitive to heavy metal toxicity. The impact of hexavalent chromium—Cr(VI) on photosynthesis and lipid accumulation in Mucidosphaerium pulchellum and Micractinium pusillum exposed to different concentrations (0–500 μg L−1) was investigated for 11 days. A significant (p &lt, 0.05) increase in lipid content was observed with increasing Cr(VI) concentration. However, growth was suppressed at higher concentrations exceeding 100 μg L−1. Addition of Cr(VI) in the cell culture medium showed a negative effect on quantum yield (Fv/Fm), and a photosynthetic inhibition of &gt, 65% was noted in both species at 500 μg L−1. However, the lipid gravimetric analysis presented inner cell lipid content up to 36% and 30% of dry weight biomass for M. pulchellum and M. pusillum, respectively. The fatty acids profiles of both microalgae species showed higher levels of hexadecenoic acid as well as ω3, ω6, and ω7 fatty acids. The effect of Cr(VI) on photosynthesis and lipid accumulation in both microalgae species was concentration and exposure time dependent. This shows that an appropriate concentration of Cr(VI) in culture medium could be beneficial for higher lipid accumulation in freshwater eukaryotic microalgae species.

As novel applications of oxide semiconductors are realized, various structural devices and integrated circuits are being proposed, and the gate-overlay defect phenomenon is becoming more diverse in its effects. Herein, the electrical properties of the transistor that depend on the geometry between the gate and the semiconductor layer are analyzed, and the specific phenomena associated with the degree of overlap are reproduced. In the semiconductor layer, where the gate electrode is not overlapped, it is experimentally shown that a dual current is generated, and the results of 3D simulations confirm that the magnitude of the current increases as the parasitic current moves away from the gate electrode. The generation and path of the parasitic current are then represented visually through laser-enhanced 2D transport measurements, consequently, the flow of the dual current in the transistor is verified to be induced by the electrical potential imbalance in the semiconductor active layer, where the gate electrodes do not overlap.

The collective dynamics of topological structures1-6 are of interest from both fundamental and applied perspectives. For example, studies of dynamical properties of magnetic vortices and skyrmions3,4 have not only deepened our understanding of many-body physics but also offered potential applications in data processing and storage7. Topological structures constructed from electrical polarization, rather than electron spin, have recently been realized in ferroelectric superlattices5,6, and these are promising for ultrafast electric-field control of topological orders. However, little is known about the dynamics underlying the functionality of such complex extended nanostructures. Here, using terahertz-field excitation and femtosecond X-ray diffraction measurements, we observe ultrafast collective polarization dynamics that are unique to polar vortices, with orders-of-magnitude higher frequencies and smaller lateral size than those of experimentally realized magnetic vortices3. A previously unseen tunable mode, hereafter referred to as a vortexon, emerges in the form of transient arrays of nanoscale circular patterns of atomic displacements, which reverse their vorticity on picosecond timescales. Its frequency is considerably reduced (softened) at a critical strain, indicating a condensation (freezing) of structural dynamics. We use first-principles-based atomistic calculations and phase-field modelling to reveal the microscopic atomic arrangements and corroborate the frequencies of the vortex modes. The discovery of subterahertz collective dynamics in polar vortices opens opportunities for electric-field-driven data processing in topological structures with ultrahigh speed and density.

Quantum confinements, especially quantum in narrow wells, have been investigated because of their controllability over electrical parameters. For example, quantum dots can emit a variety of photon wavelengths even for the same material depending on their particle size. More recently, the research into two-dimensional (2D) materials has shown the availability of several quantum mechanical phenomenon confined within a sheet of materials. Starting with the gapless semimetal properties of graphene, current research has begun into the excitons and their properties within 2D materials. Even for simple 2D systems, experimental results often offer surprising results, unexpected from traditional studies. We investigated a coupled quantum well system using 2D hexagonal boron nitride (hBN) barrier as well as 2D tungsten disulfide (WS

Transition metal oxide-based memristors have widely been proposed for applications toward artificial synapses. In general, memristors have two or more electrically switchable stable resistance states that device researchers see as an analogue to the ion channels found in biological synapses. The mechanism behind resistive switching in metal oxides has been divided into electrochemical metallization models and valence change models. The stability of the resistance states in the memristor vary widely depending on: oxide material, electrode material, deposition conditions, film thickness, and programming conditions. So far, it has been extremely challenging to obtain reliable memristors with more than two stable multivalued states along with endurances greater than ∼1000 cycles for each of those states. Using an oxygen plasma-assisted sputter deposition method of noble metal electrodes, we found that the metal-oxide interface could be deposited with substantially lower interface roughness observable at the n...

Expandability of organic electronics has stimulated ongoing research for the development of a variety of flexible and/or large-area optoelectronic applications. Among these electronic devices, organic non-volatile memories are emerging as suitable components for solid-state data storage because of their low-cost fabrication, large storage capacity, light weight, and conformable mechanical properties. To fully integrate organic memories with wearable and flexible/stretchable electronic systems, it is important to develop a device in which the properties such as threshold voltage and operating regime are controllable. This leads to improvement in the adaptability of the device to peripheral circuitry and encourages the development of multi-functional organic electronic components. Here, we investigate the tunable electrical properties of charge-trap (electret) memory devices based on organic field-effect transistors, obtained by the doping of an ambipolar polymer semiconductor. The electret memory devices using the doped semiconductor showed a remarkable enhancement in the charge-storage capacity, an excellent charge retention time of more than 107 s, and four-fold increase in charge carrier mobility. The improved memory characteristics associated with the controllable molecular doping could pave the way for the development of next-generation memory devices that are compatible with flexible and printed electronic technology.

Atomic movement under application of external stimuli (i.e., electric field or mechanical stress) in oxide materials has not been observed due to a lack of experimental methods but has been well known to determine the electric polarization. Here, we investigated atomic movement arising from the ferroelectric response of BiFeO3 thin films under the effect of an electric field and stress in real time using a combination of switching spectroscopy, time-resolved X-ray microdiffraction, and in situ stress engineering. Under an electric field applied to a BiFeO3 film, the hysteresis loop of the reflected X-ray intensity was found to result from the opposing directions of displaced atoms between the up and down polarization states. An additional shift of atoms arising from the linearly increased dielectric component of the polarization in BiFeO3 was confirmed through gradual reduction of the diffracted X-ray intensity. The electric-field-induced displacement of oxygen atoms was found to be larger than that of Fe atom for both ferroelectric switching and increase of the polarization. The effect of external stress on the BiFeO3 thin film, which was controlled by applying an electric field to the highly piezoelectric substrate, showed smaller atomic shifts than for the case of applying an electric field to the film, despite the similar tetragonality.

The in-plane magnetic field pulse driven domain wall motion on a perpendicularly magnetized nanowire is numerically investigated by performing micromagnetic simulations and magnetic domain wall dynamics are evaluated analytically with one-dimensional collective coordinate models including the interfacial Dzyaloshinskii-Moriya interaction. With the action of the precession torque, the chirality and the magnetic field direction dependent displacements of the magnetic domain walls are clearly observed. In order to move Bloch type and Neel type domain walls, a longitudinal and a transverse in-plane magnetic field pulse are required, respectively. The domain wall type (Bloch or Neel) can easily be determined by the dynamic motion of the domain walls under the applied pulse fields. By applying a temporally asymmetric in-plane field pulse and successive notches in the perpendicularly magnetized nanowire strip line with a proper interval, the concept of racetrack memory based on the synchronous displacements of the chirality dependent multiple domain walls is verified to be feasible. Requirement of multiple domain walls with homogeneous chirality is achieved with the help of Dzyaloshinskii-Moriya interaction.

Asymmetric sized single oxide diode (InZnOx/CuOx) with single resistor (Ti-doped NiO) device (1D-1R) was integrated into a crossbar array at room temperature to provide high current through the diode while keeping resistance switching localized in a small area. The Ti (0.1 wt %) doped NiO layer was fabricated inside an inverted cone-structure to localize switching and improve general device performance. We were able observe resistance switching up to around 100 cycles in the 1D-1R structure. In addition, the addition of the diode to the structure acted as an external resistance suppressing overflow current during Ti-doped NiO switching from a high resistance state to a low resistance state, thus improving switching distribution in both low (average = 3.2×10-5 Ω, standard deviation = 1.3×10-6) and high (average = 2.8×10-6 Ω, standard deviation = 6.7×10-7) resistance states.

Asymmetrical electrical properties induced by local acceptor-like defect states in oxide semiconductor thin-film transistors are investigated. In addition, we report on the origin of asymmetrical transport characteristics depending on the drain voltage level. In particular, we observe that these asymmetrical properties depend strongly on this level. Numerical calculations demonstrate that potential barrier lowering in the local area occurs at the drain electrode's edge.

Hf 0.5 Zr 0.5 O 2 (HZO) thin films were deposited on Si substrates with and without TiN seed layers using a simple and cost-effective solution synthesis. The crystalline quality of the as-deposited HZO films were improved through a post deposition annealing process. Cross-sectional transmission electron microscope analyses of HZO/TiN/Si structure revealed a clear and clean interface formation between HZO and TiN layers. X-ray diffraction and Raman analyses confirm that, after the post annealing process, HZO films deposited on bare Si substrate crystallized in monoclinic phase while the HZO films deposited on TiN/Si substrates tend to crystallize in tetragonal or orthorhombic crystal structure. Varying crystal structure through controlling the post deposition annealing temperature is a promising technique to manipulate the electrical properties of solution processed HZO thin films.

Epitaxial oxide ferroelectric films exhibit emerging phenomena arising from complex domain configurations even at pseudoequilibrium, including the creation of domain states unfavored in nature and abrupt piezoelectric coefficients around morphotropic phase boundaries. The nanometer-sized domain configurations and their domain switching dynamics under external stimuli are directly linked to the ultrafast manipulation of ferroelectric thin films; however, complex domain switching dynamics under homogeneous electric fields has not been fully explored, especially at the nanosecond timescale. This Letter reports the nanosecond dynamics of ferroelastic-domain switching from the 90\ifmmode^\circ\else\textdegree\fi{} to 180\ifmmode^\circ\else\textdegree\fi{} direction using time-resolved x-ray microdiffraction under homogeneous electric fields onto an epitaxial $\mathrm{Pb}({\mathrm{Zr}}_{0.35},{\mathrm{Ti}}_{0.65}){\mathrm{O}}_{3}$ film capacitor. It is found that the application of electric fields induces spatially heterogeneous domain switching processes via intermediate domain structures with rotated polarization vectors. In addition, the domain switching time is shown to be inversely proportional to the magnitude of the applied electric field, and electric fields higher than $480\text{ }\text{ }\mathrm{kV}/\mathrm{cm}$ are found to complete the ferroelastic switching within nanoseconds.

Epitaxial oxide ferroelectric films exhibit emerging phenomena arising from complex domain configurations even at pseudoequilibrium, including the creation of domain states unfavored in nature and abrupt piezoelectric coefficients around morphotropic phase boundaries. The nanometer-sized domain configurations and their domain switching dynamics under external stimuli are directly linked to the ultrafast manipulation of ferroelectric thin films; however, complex domain switching dynamics under homogeneous electric fields has not been fully explored, especially at the nanosecond timescale. This Letter reports the nanosecond dynamics of ferroelastic-domain switching from the 90° to 180° direction using time-resolved x-ray microdiffraction under homogeneous electric fields onto an epitaxial Pb(Zr_{0.35},Ti_{0.65})O_{3} film capacitor. It is found that the application of electric fields induces spatially heterogeneous domain switching processes via intermediate domain structures with rotated polarization vectors. In addition, the domain switching time is shown to be inversely proportional to the magnitude of the applied electric field, and electric fields higher than 480 kV/cm are found to complete the ferroelastic switching within nanoseconds.

We demonstrate the catalytic performance of perovskite-based oxygen reduction reaction (ORR) catalyst based on LaMnO 3+δ nanoparticles (LMO NPs) prepared using the laser ablation synthesis in solution method. The ORR catalytic activity of the post-annealed LMO NPs was similar to that of commercial Pt/C catalysts due to the increased surface area as well as the perovskite crystalline structure of the LMO NPs. The mass and specific activities of the LMO NP catalyst annealed at 800 °C were 20 and 2.2 times higher than those of the bulk LMO, respectively. In a chronoamperometric stability test, our LMO NP catalyst (annealed at 800 °C) outperformed the Pt/C catalyst.

Solar cells based on organic-inorganic perovskite materials have dramatically developed in just a short period of time because of efficient light absorption and their unique semiconducting nature. The best power conversion efficiency is continuously recorded via various approaches; devices from sensitized mesoporous structures to planar structures, modified composition of perovskite, and fabrication methods. Despite the amazing improvement, many groups have encountered low reproducibility and lower device efficiency than reported results because of the perovskite’s own instability and sensitivity under ambient conditions; thus, we need a realistic and experimental investigation. In this study, we compare solution processing representative fabrication methods, which influence the growth, crystal orientation, and the electronic properties of CH 3 NH 3 PbI 3 , device reproducibility, and efficiency in planar perovskite solar. This comparative study gives a realistic overview of the fabrication methods for planar perovskite solar cells.

In this study, humidity control ceramics with good adsorption/desorption capabilities and high strength were fabricated from drinking-water treatment sludge (DWTS) and Onggi soil. The DWTS powder heat-treated at 800°C and Onggi soil were mixed at weight ratios of 40:60, 50:50, 60:40, and 70:30 and fired at 800–1000°C. With increasing DWTS content, density and flexural strength increased. For the sample with a DWTS:Onggi soil weight ratio of 70:30, porosity and specific surface area decreased with increasing firing temperature, attributed to densification and grain growth at high firing temperatures. From the results obtained, a firing temperature of 800°C is the optimum condition for fabricating humidity control ceramics with good adsorption/desorption capabilities and strength. The maximum adsorbed amount for the sample fired at 800°C was 439 g/㎡.

Non-equilibrium domain wall dynamics on a perpendicularly magnetized nanowire manipulated by the transverse magnetic field pulse are numerically investigated. We systematically observe the large displacements of the chiral domain wall and the domain wall tilting angles generated by Dzyaloshinskii–Moriya interaction during the competition between the precession torque and the magnetic damping process. The magnetic-property-dependent domain wall displacements exhibit that the lower magnetic damping constants and Dzyaloshinskii–Moriya energy densities generate the longer transition times and the significant larger domain wall displacements for the non-equilibrium magnetization dynamics. Compare with the spin-polarized-current-driven domain wall dynamics, the transverse magnetic field pulses guarantee faster domain wall movements without Walker breakdown and lower energy consumptions because it is free from the serious Joule heating issue. Finally, we demonstrate successive chiral domain wall displacements, which are necessary to develop multilevel resistive memristors for next-generation artificial intelligent devices based on magnetic domain wall motions.

Electric-field-driven phase transformation phenomena in multiferroic BiFeO3 are directly linked to the functionalities of electronic devices based on multiferroic materials. Understanding how the transformation evolves at the nanoscale under the influence of an electric field will provide fascinating insights into key parameters that utilize the transformation features. Here, we report both the electric-field-driven transient and permanent phase transformations in highly strained BiFeO3 thin films and their transformation dynamics at the nanoscale. We found that two distinct transient and permanent phase transformations were triggered below and above a coercive voltage of the polymorphic phase, indicating that ferroelectric polarization switching could promote permanent phase transformations. We also found that the transient transformations evolve via complex phase boundary motions between the coexisting phases, whereas permanent transformations occurred via nucleation of the other phases.

The spontaneously formed striped polarization nanodomain configuration of a PbTiO${_3}$/SrTiO${_3}$ superlattice transforms to a uniform polarization state under above-bandgap illumination with a time dependence varying with the intensity of optical illumination and a well-defined threshold intensity. Recovery after the end of illumination occurs over a temperature-dependent period of tens of seconds at room temperature and shorter times at elevated temperatures. A model in which the screening of the depolarization field depends on the population of trapped electrons correctly predicts the observed temperature and optical intensity dependence., Comment: This article has been accepted by Applied Physics Letter

Transition metal oxide-based memristors have widely been proposed for applications toward artificial synapses. In general, memristors have two or more electrically switchable stable resistance states that device researchers see as an analogue to the ion channels found in biological synapses. The mechanism behind resistive switching in metal oxides has been divided into electrochemical metallization models and valence change models. The stability of the resistance states in the memristor vary widely depending on: oxide material, electrode material, deposition conditions, film thickness, and programming conditions. So far, it has been extremely challenging to obtain reliable memristors with more than two stable multivalued states along with endurances greater than ∼1000 cycles for each of those states. Using an oxygen plasma-assisted sputter deposition method of noble metal electrodes, we found that the metal-oxide interface could be deposited with substantially lower interface roughness observable at the nanometer scale. This markedly improved device reliability and function, allowing for a demonstration of memristors with four completely distinct levels from ∼6 × 10

A layer-by-layer deposition of two conducting polymers, each layer of which is a few tenths of nanometer thick, has been successfully performed to enhance the thermoelectric power factor of organic thin films, which are critical components of flexible thermoelectric energy harvesting devices. The multilayer films were deposited via multiple solution processes, which exhibit enhanced electrical conductivity without any significant degradation of the Seebeck coefficient, in contrast to a coupling behavior between the electrical conductivity and the Seebeck coefficient in bulk materials. The electrical conductivity and power factor—proportional to the electrical conductivity—of 5(PEDOT:PSS/PANI–CSA) multilayer films are 1.3 and 2 times higher than those of a single PEDOT:PSS layer. Transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) reveal distinct interfaces through which an enhanced electrical conductivity and power factor have been achieved in our multilayer films. From the TEM, EELS, and Raman analyses, a model for the enhancement of the electrical conductivity has been proposed. The enhancement of electrical conductivity occurs via stretching of PEDOT and PANI chains and hole diffusion from the PANI–CSA layer to the PEDOT:PSS layer. The band alignment in the multilayer structure not only enhances electrical conductivity but also maintains the Seebeck coefficient at an optimum value. Our study suggests that the layer-by-layer deposition of polymer thin films is a promising technique for manipulating the thermoelectric properties of each polymer component to enhance thermoelectric performance.

For transparent solar cells, Sn:In 2 O 3 /Pb(Zr, Ti)TiO 3 /Pt(⩽5 nm)/Sn:In 2 O 3 capacitor structures were fabricated using a cost-effective solution process. The insertion of ultra-thin Pt layer between the bottom Sn:In 2 O 3 electrode and Pb(Zr, Ti)TiO 3 plays a critical role in the photovoltaic characteristics of the capacitors. The Pb(Zr,Ti)O 3 capacitors with a 5 nm thick Pt layer showed excellent polarization–voltage curves with reduced leakage current due to both partial (1 1 1) orientation of Pb(Zr,Ti)O 3 and alloy formation between Pt and the Sn:In 2 O 3 bottom electrode, as confirmed using X-ray photoelectron spectra analysis. The capacitors with a 5 nm thick Pt layer exhibit transmittance of 45–50% in the visible light region. The current density–voltage characteristics under light illumination (AM1.5G) exhibit an open circuit voltage value of −0.62 V and short circuit current density of 0.6 μA/cm 2 after negative poling, with a maximum power conversion efficiency of 1.7 × 10 −4 %. The open circuit voltage of the capacitors with a 5 nm thick Pt layer is larger with negative poling due to the higher net internal bias arising from the Schottky barrier.

Bio-compatible actuators are required to exhibit a large actuation displacement and force at a low voltage for various applications in liquid environments, including swimming robots, biomedical catheters, biomimetic sensory-actuators, and drug delivery micro-pumps. Recently, ionic polymer metal nanocomposites (IPMNCs) based on Nafion have been widely used for bio-compatible actuators; however, they have been demonstrated to operate only at high voltages in the range of 2 to 5 V, resulting in water hydrolysis problems which are accompanied by a degradation of actuation performance. Here, we show that IPMNC actuators based on a poly(vinylidenefluoride-co-trifluoroethylene) [P(VDF-TrFE)]/polyvinylpyrrolidone (PVP)/polystyrene sulfonic acid (PSSA) polymer blend membrane can exhibit a large actuation displacement and force at a low voltage of 1 V. Due to the ferroelectric nature of P(VDF-TrFE), the large dipole moment of P(VDF-TrFE) can cause strong intermolecular bonding, causing the P(VDF-TrFE)/PVP/PSSA blend membrane to be miscible. We found that the P(VDF-TrFE)/PVP/PSSA blend membrane with a blending ratio of 30/15/55 can produce the highest proton conductivity (0.0065 S cm−1) and ion exchange capacity (2.95 meq g−1) as compared to those of the commercial Nafion membrane, due to its miscible nature. Our IPMNC exhibits both an enhanced actuation displacement and force by up to 2 times in comparison with those of the IPMNC based on the commercial Nafion-based ionic membrane. Our P(VDF-TrFE)/PVP/PSSA IPMNC shows a stable actuation performance for up to 2200 cycles in hydrated conditions.

Defect generation in oxide semiconductor thin-film transistors under high-voltage driving has not been studied in depth despite being a crucial bottleneck in the making of the integrated circuit utilized in an oxide semiconductor. Here we report on the origin of the asymmetrical transport characteristics caused by the degradation in the oxide semiconductor during integrated circuit driving. The variation of the current profiles based on test conditions is related to the generation of local defect states in the oxide material; this generation could be caused by the structural change of the material. The numerical calculations show that the flow of the electron is blocked by the “electrical pocket” formed by the electric-field distortion due to the local defect states near the edge of the electrode.

Reliability issues associated with driving metal-oxide semiconductor thin film transistors (TFTs), which may arise from various sequential drain/gate pulse voltage stresses and/or certain environmental parameters, have not received much attention due to the competing desire to characterise the shift in the transistor characteristics caused by gate charging. In this paper, we report on the reliability of these devices under AC bias stress conditions because this is one of the major sources of failure. In our analysis, we investigate the effects of the driving frequency, pulse shape, strength of the applied electric field, and channel current, and the results are compared with those from a general reliability test in which the devices were subjected to negative/positive bias, temperature, and illumination stresses, which are known to cause the most stress to oxide semiconductor TFTs. We also report on the key factors that affect the sub-gap defect states, and suggest a possible origin of the current degradation observed with an AC drive. Circuit designers should apply a similar discovery and analysis method to ensure the reliable design of integrated circuits with oxide semiconductor devices, such as the gate driver circuits used in display devices.

For next-generation energy harvesting thermoelectric (TE) devices based on organic/inorganic composites, the barrier energy at interfaces of components is critical in determining the TE performances, because the barrier energy can directly enhance Seebeck coefficient (S). We have succeeded in precisely tuning the barrier energy in poly (3,4-ethylene dioxythiophene) polystyrene sulfonate (PEDOT:PSS)/Bi2Te3 nanowires (NWs) based organic/inorganic nanocomposite films through polar solvent vapor annealing (PSVA). Controlling the PSS/PEDOT ratio as a function of PSVA duration, the work function of PEDOT:PSS was tuned, which eventually varied the barrier energy of nanocomposite thin films. Through optimization of Bi2Te3/PEDOT:PSS barrier energy, the S was maximized up to 47 μV/K. The electrical conductivity was also maximized simultaneously, because of the PSVA-induced π-π stacking among PEDOT chains and templating effect. Density functional theory calculated an optimal barrier energy (0.12 eV), which showed an excellent agreement with our experimentally determined optimal barrier energy (0.11 eV), at which we also maximized the power factor—an efficiency indicator of TE performance. Our feasible strategy on the manipulation of barrier energy in PEDOT:PSS/Bi2Te3 NWs through the PSVA can be extended to other organic/inorganic based TE composites, toward the realization of highly efficient TE devices.

Effects of surface roughness as well as crystallinity onto functionalities of crystalline copolymer films were studied using a dipping method to inject the crystalline grains into voids among crystalline nano-rods. Differently from a widely-used fabrication method such as spin-coating of solution, we achieved a smooth surface and high crystallinity in ferroelectric P(VDF-TrFE) films, simultaneously. Varying dipping temperature and time, remnant polarization and relative dielectric constant values increased by 20% and 75% with a decrease of surface roughness from 20 nm to 7 nm in root mean square value, respectively. The ferroelectric stabilities of P(VDF-TrFE) film capacitors were found to be strongly dependent on the crystallinity.

Intense hard x-ray pulses from a free-electron laser induce irreversible structural damage in a perovskite oxide epitaxial heterostructure when pulse fluences exceed a threshold value. The intensity of x-ray diffraction from a 25-nm thick epitaxial BiFeO$_{3}$ layer on a SrTiO$_{3}$ substrate measured using a series of pulses decreases abruptly with a per-pulse fluence of 2.7 x 10$^{6}$ photons ${\mu}$m$^{-2}$ at 9.7 keV photon energy, but remains constant for 1.3 x 10$^{6}$ photons ${\mu}$m$^{-2}$ or less. The damage resulted in the destruction of the BiFeO$_{3}$ thin film within the focal spot area and the formation of a deep cavity penetrating into the STO substrate via the removal of tens of nanometers of material per pulse. The damage threshold occurs at a fluence that is insufficient to heat the absorption volume to the melting point. The morphology of the ablated sample is consistent with fracture rather than melting. Together these results indicate that the damage occurs via a non-thermal process consistent with ultrafast ionization of the absorption volume., Comment: The following article has been accepted by Applied Physics Letters