Switching Kinetics Research Articles

Probing of Polarization Reversal in Ferroelectric (Al,Sc)N Films Using Single‐ and Tri‐Layered Structures With Different Sc/(Al+Sc) Ratio

AbstractWurtzite‐(Al,Sc)N films are promising candidates for ferroelectric memory devices owing to their outstanding properties. However, there are many challenges on the way to practical applications, including lowering an electric field required for polarization switching. Understanding the switching kinetics, especially the starting point of polarization reversal, is key to designing materials with desired properties. Here, the impact of Sc concentration and segregation on the switching kinetics for (Al,Sc)N capacitors is investigated by evaluating time‐ and field‐dependences of the switching polarization for the tri‐layered (Al,Sc)N films with various Sc/(Al+Sc) ratios. The remanent polarization of stacked films slightly decreased compared to those of the single‐layered films with the same average Sc/(Al+Sc) ratio, while their coercive fields depended on the average Sc content in (Al,Sc)N. The ferroelectric switching behavior suggests the possibility of nucleation originating from the Sc‐rich region and the sequential switching mechanism for individual layers, which is unique to multilayered films. This shows a possibility that nucleations of the polarization switching start not from the interface between the (Al,Sc)N films and the electrodes. The unique switching kinetics in tri‐layered (Al,Sc)N films have provided new insights into the field of ferroelectric switching in wurtzite‐nitrides.

Intrinsically Stable Charged Domain Walls in Molecular Ferroelectric Thin Films

AbstractCharged domain walls in ferroelectrics hold great promise for applications in ferroelectric random‐access memory (FeRAM), with advantages such as low energy consumption, high density, and non‐destructive operation. Due to the mechanical compatibility condition, the neutral domain walls are dominant in traditional ferroelectric thin films. Herein, using phase‐field simulations, the formation of intrinsically stable charged domain walls (CDWs) in the molecular ferroelectric films is demonstrated, which can be mainly attributed to the small mechanical stiffness. The switching kinetics are further investigated for the CDWs, showing a lower switching barrier as compared to the neutral counterparts. Moreover, it is indicated that increasing the compressive misfit strain can lead to prolonged switching time, with a significantly increased switching energy barrier. These findings pave the way for the potential applications of metal‐free organic ferroelectric materials in FeRAM devices.

Characterizing polarization switching kinetics of ferroelectric Hf0.5Zr0.5O2 at cryogenic temperature

We have characterized polarization switching kinetics of Hf0.5Zr0.5O2 (HZO) at cryogenic temperature (T) down to 100 K. By the nucleation-limited-switching model with Lorentzian distribution fittings, the dependences of the average switching time (log τ1) and switching time distribution (ω) on T are extracted. As T decreases from 300 to 100 K, log τ1 first rapidly decreases and then gradually stabilizes. Meanwhile, ω exhibits different trends under different external electric fields (Eext), decreasing under low Eext while increasing under high Eext, eventually stabilizing at non-zero constants. With the further decrease in T (<100 K), log τ1 and ω exhibited by HZO are almost unchanged, indicating the intrinsic properties of ferroelectric multiple domains, which are different from the prediction in previous literature studies that log τ1 and ω will linearly decrease as T decreases.

Robust Dual-Color Electrochromism of Vanadium Oxide Nanorods Embedded on Reduced Graphene Oxide: Unraveling the Mechanism

Vanadium pentoxide (V2O5), associated with both cathodic and anodic coloration, is considered as one of the best electrochromic (EC) materials for energy-saving smart electronics. Here we present the fabrication and detailed mechanism analysis for improving the electrochromic properties of V2O5 incorporated in a reduced graphene oxide (rGO) matrix using a facile wet chemical method. The microstructural study disclosed the formation of prominent V2O5 nanorods embedded in the rGO matrix. The optimized electrochromic film resulted in coloration (tc) and bleaching time (tb) of ∼6.2 and ∼4.8 s, respectively, much faster than the color switching kinetics of the pristine V2O5 sample (tc ∼ 19.4 s, tb ∼ 15.3 s). The more dispersed structure also ensured an approximate 400% enhancement in the optical modulation of EC film and reflected a noticeable improvement in the coloration efficiency (∼347 cm2/C) of V2O5 film. Modification with rGO resulted in an outstanding improvement in the electrochemical redox stability of V2O5 up to 5000 CV cycles with minimum deterioration in the curve area. The formation of nanorod structure was the prime factor for better ion diffusion and thereby facilitating enhanced performance.

Sodium alginate grafted phase-changing electrolyte for energy-efficient thermochromic and electrochromic synergy with uniquely tunable optical states and simultaneous Vis-NIR modulation

Conventional smart windows, limited by their single-stimulus response, often fail to meet diverse practical needs, and cannot achieve zero transmission across the Visible-NIR spectrum. Integrating thermochromic, electrochromic, and synergetic-responsiveness into a single device is both challenging and essential for effective light modulation and energy efficiency. Herein, we present a novel green phase-changing electrolyte integrated with a versatile chromogen, to create an “all-in-one” smart window. This device autonomously switches functions and can also simultaneously respond to dual-stimuli, achieving an absolute private state. The device’s tunable performance in optical contrast, switching kinetics, coloration efficiency, and cyclic stability, influenced by lattice water concentration is also meticulously assessed. Our comprehensive study highlights the device’s robust multifunctional properties, including thermal insulation, lifestyle interventions, and environmental remediation. These features make the smart window a highly energy-efficient solution with exceptional climate adaptability, such as shutting down light transmission with environmentally-benign operations and on-demand color changes. This innovative approach transforms smart windows from mere energy savers to versatile, energy-efficient systems for modern buildings. By bridging the gap between advanced materials and practical applications, our “all-in-one” smart window represents a significant advancement, paving the way for broader adoption in various environmental and energy-saving contexts.

(Invited) Engineering the Switching Kinetics of Valence Change-Based Memristive Devices for Neuromorphic Computing

Memristive devices based on the valence mechanism are highly interesting candidates for the use as hardware representation of synapses in neuromorphic computing. The memristive model system SrTiO3 exhibit gradual switching and can be tuned between short-term and long-term plasticity. We will discuss the impact of the switching kinetics on the gradual switching mode and provide general guidelines for the design of gradual switching systems. Moreover, we present an approach to accelerate the switching kinetics of SrTiO3 by up to 103 times, or reduce the operating voltage by ≈ 30% to maintain the switching speed.Our approach is to introduce a low thermal conductivity layer inside the active electrode of the active electrode of the devices, which blocks the heat dissipation caused by Joule heating during switching. Our method leaves the switching layer and its interfaces with the electrodes intact, while the use of HfO2 and TaOx as the heat blocking layers ensures ease of fabrication and CMOS compatibility. We will demonstrate that this approach is transferable to other more common material systems.

Trajectory Analysis in Single-Particle Tracking: From Mean Squared Displacement to Machine Learning Approaches.

Single-particle tracking is a powerful technique to investigate the motion of molecules or particles. Here, we review the methods for analyzing the reconstructed trajectories, a fundamental step for deciphering the underlying mechanisms driving the motion. First, we review the traditional analysis based on the mean squared displacement (MSD), highlighting the sometimes-neglected factors potentially affecting the accuracy of the results. We then report methods that exploit the distribution of parameters other than displacements, e.g., angles, velocities, and times and probabilities of reaching a target, discussing how they are more sensitive in characterizing heterogeneities and transient behaviors masked in the MSD analysis. Hidden Markov Models are also used for this purpose, and these allow for the identification of different states, their populations and the switching kinetics. Finally, we discuss a rapidly expanding field-trajectory analysis based on machine learning. Various approaches, from random forest to deep learning, are used to classify trajectory motions, which can be identified by motion models or by model-free sets of trajectory features, either previously defined or automatically identified by the algorithms. We also review free software available for some of the analysis methods. We emphasize that approaches based on a combination of the different methods, including classical statistics and machine learning, may be the way to obtain the most informative and accurate results.

Influence of the concentration of KOH-based aqueous electrolyte on the electrochemical behavior of NiO thin film

In this research, we explored the influence of varying concentrations of KOH electrolyte (0.5, 1, and 2 M) on the electrochemical characteristics of Nickel Oxide (NiO) thin film. The deposition of NiO material onto glass and Fluor Tin Oxide (FTO) coated glass substrates was achieved through the chemical spray pyrolysis method. Subsequent examinations encompassed structural, morphological, optical, and electrochemical assessments, employing X-ray diffraction (XRD), Raman spectroscopy, Scanning Electron Microscopy coupled with Energy Dispersive X-ray Spectroscopy (SEM-EDS), UV-VIS-NIR spectrophotometry, and cyclic voltammetry (CV), respectively. XRD analysis unveiled a polycrystalline cubic structure of NiO with a preference for orientation along the (111) plane. Raman spectroscopy confirmed the presence of the NiO phase, whereas SEM images depicted the emergence of interconnected nanograins with occasional minor cracks. EDS examination and elemental mapping further substantiated a homogeneous dispersion of elements. Optical analysis disclosed a band gap energy of 3.54 eV and an average transmittance of 71 % in the visible range. Electrochemical analysis indicated that the specific capacitance reached its peak at [1 M] (70 F. g−1). The [2 M] electrolyte exhibited the highest optical modulation (29 %), the most substantial charge density (Qi = 9.5 mC/cm2), and the most favorable switching kinetics. However, the coloration efficiency slightly decreased from 30.94 cm2/C in [1 M] to 30.47 cm2/C in the [2 M] solution, despite these improvements.

Electrochemically controlled blinking of fluorophores for quantitative STORM imaging

Stochastic optical reconstruction microscopy (STORM) allows wide-field imaging with single-molecule resolution by calculating the coordinates of individual fluorophores from the separation of fluorophore emission in both time and space. Such separation is achieved by photoswitching the fluorophores between a long-lived OFF state and an emissive ON state. Although STORM can image single molecules, molecular counting remains challenging due to undercounting errors from photobleached or overlapping dyes and overcounting artefacts from the repetitive random blinking of dyes. Here we show that fluorophores can be electrochemically switched for STORM imaging (EC-STORM), with excellent control over the switching kinetics, duty cycle and recovery yield. Using EC-STORM, we demonstrate molecular counting by using electrochemical potential to control the photophysics of dyes. The random blinking of dyes is suppressed by a negative potential but the switching-ON event can be activated by a short positive-potential pulse, such that the frequency of ON events scales linearly with the number of underlying dyes. We also demonstrate EC-STORM of tubulin in fixed cells with a spatial resolution as low as ~28 nm and counting of single Alexa 647 fluorophores on various DNA nanoruler structures. This control over fluorophore switching will enable EC-STORM to be broadly applicable in super-resolution imaging and molecular counting.

Dual-frequency-addressable photochromic cholesteric mixture with photo- and electro-switchable optical properties

Cholesteric liquid crystalline mixture with photo-, electro-controllable optical properties was prepared and the features of its switching behavior were demonstrated. The working principle of the obtained switchable cell is based on using dual-frequency-addressable nematic mixture that enables effective control of selectively reflected planar and scattered focal conics texture by applied field frequency modulation. The nematic mixture was doped with the chiral substance in order to induce a cholesteric structure formation with selective light reflection in visible spectral range. Azobenzene-containing photochrome was also introduced into this mixture in order to stimulate photo-optical response. An application of low-frequency electric field as well as UV irradiation induces short-wavelength shift of the selective light reflection. Under action of an electric field, a transition to scattered focal conics texture takes place. Amplitude of the light-induced shift is ca. 50 nm, while the electric field leads to a shift ca. 120 nm. On the contrary, high-frequency electric field induces fast (less than 1 s) restoration of perfect highly reflected planar texture. UV irradiation leads to not only shift of the selective light reflection band, but alters the electrooptic response by increase of frequency necessary for the restoration of the planar state and considerably changes the switching kinetics. The possibility of photopatterning of the obtained electrooptic cells by UV irradiation through a mask is demonstrated. It is shown, that application of electric field of different strength and frequencies enables smart control of the photorecorded image contrast.

Tuning the Electro‐Optic Properties of BaTiO3 Epitaxial Thin Films via Buffer Layer‐Controlled Polarization Rotation Paths

AbstractBaTiO3 thin films emerge as a highly promising material platform for integrated photonics due to their outstanding electro‐optic properties and diverse functionalities. Despite extensive studies, there remains a notable gap in the understanding of the intricate relationship between the phase structure, domain switching kinetics and electro‐optic performance of these materials. By controlling the structural phase evolution, it is possible to gain deep insights into the physical mechanisms underlying the electro‐optic performance. Here, the phase constitution of BaTiO3 epitaxial thin films is successfully tuned by the insertion of a GdScO3 buffer layer. Continuous polarization rotation paths are observed from an out‐of‐plane tetragonal‐like phase, to an intermediate rhombohedral‐like phase, and finally an in‐plane tetragonal‐like phase, achieving an enhanced effective electro‐optic coefficient of 175 pm V−1 compared to unbuffered films. Furthermore, by in situ second harmonic generation microscopy and electro‐optic measurements, the domain switching behaviors in both statistical and spatially resolved manners are examined, resulting in a clear delineation of the key domain nucleation processes. The in‐depth explorations of these structural mechanisms and kinetics inform the rational design of strong electro‐optic thin films and help in the realization of high‐performance integrated photonic devices such as electro‐optic modulators and multilevel phase shifters.

Ferroelectric Thin Films and Composites Based on Polyvinylidene Fluoride and Graphene Layers: Molecular Dynamics Study

This work is devoted to the study of nanosized polymer polyvinylidene fluoride (PVDF) thin ferroelectric films (two-dimensional ferroelectrics) and their composites with graphene layers, using molecular dynamics methods to (1) study and calculate the polarization switching time depending on the electric field and film thickness, (2) study and calculate the polarization switching time depending on changes of the PVDF in PVDF-TrFE film, and (3) study the polarization switching time in PVDF under the influence of graphene layers. All calculations at each MD run step were carried out using the semi-empirical quantum method PM3. A comparison and analysis of the results of these calculations and the kinetics of polarization switching within the framework of the Landau–Ginzburg–Devonshire theory for homogeneous switching in ferroelectric polymer films is carried out. The study of the composite heterostructures of the “graphene-PVDF” type, and calculations of their polarization switching times, are presented. It is shown that replacing PVDF with PVDF-TrFE significantly changes the polarization switching times in these thin polymer films, and that introducing various graphene layers into the PVDF layered structure leads to both an increase and a decrease in the polarization switching time. It is shown that everything here depends on the position and displacement of the coercive field depending on the damping parameters of the system. These phenomena are very important for various ferroelectric coatings.

Long-lived electrochromic device with protonated viologen and Poly(ethylenedioxythiophene-carbazole)/Prussian blue composite for smart windows

A complementary electrochromic device (ECD) configuration featuring a protonated viologen (VNH2+) as the cathodically coloring electrochrome and a composite of poly(ethylenedioxythiophene-carbazole) (i.e. poly(EDOT-Cz)) and Prussian blue (PB) as the anodically coloring electrochrome marks the first implementation of this innovative high contrast device. A comparative analysis of VNH2+//poly(EDOT-Cz) and VNH2+//poly(EDOT-Cz)/PB ECDs demonstrates a superior integrated visible light transmission modulation (ΔT) of 50.4%, versus 76.7%, higher diffusion coefficient of 4.4 × 10−11versus 3.9 × 10−10 cm2 s−1, higher coloration efficiency (CE) of 424 versus 562 cm2 C−1 (at 550 nm), faster color-bleach switching times of (7.0 and 4.0 s) versus (1.2 and 1.0 s) and a CIE chromaticity coordinate corresponding an intense deep blue state (y: 0.058 versus 0.218) achieved with the composite relative to the pure polymer. The VNH2+//PB ECD also shows lower CE (69 cm2 C−1) and slower coloration-bleaching kinetics (20 and 2 s) compared to the composite based ECD. In addition, long-term cycling stability attained for the VNH2+//poly(EDOT-Cz)/PB ECD, whereby it endures 5000+ color-bleach cycles without showing any major deterioration in optical modulation or switching kinetics underscores the suitability of the composite based ECD for practical smart window applications.

Complete Selective Switching of Ferroelastic Domain Stripes in Multiferroic Thin Films by Tip Scanning

AbstractBiFeO3 is a rare single‐phase multiferroic which shows coupled ferroelectricity, ferroelasticity and antiferromagnetism at room temperature. Many fantastic properties of BiFeO3 are regulated by its domain structure. While (001) rhombohedral BiFeO3 thin films can possibly develop up‐to eight degenerate states of two‐variant 71° ferroelastic domain stripes, complete selective control of all possible switching paths between these states has not yet been achieved. Here, combining phase field simulations and scanning probe microscopy experiments, we demonstrated such a complete selective control. The tip bias and the built‐in field were shown to affect the volume fraction of the 71°, 109° and 180° switched domains in rhombohedral BiFeO3 thin films under single‐point loading. Meanwhile, tip scanning further broke the symmetry of the nucleated domains, leading to different switched domain patterns. We then grew BiFeO3 thin films with a specific two‐variant 71° ferroelastic domain state and showed that such a state could be deterministically switched into the other seven two‐variant domain states by collaborative controlling tip scanning and tip bias in scanning probe microscopy experiments. These results should deepen our current understanding on the domain switching kinetics in BiFeO3 thin films and indicate they are promising platforms for developing configurable electronic and spintronic devices.

Electrodeposited Tungsten Trioxide (WO3) Thin Films for Electrochromic Applications

The need of smart and innovative technology with energy saving approach is the main and serious concern while dealing with fastest growing urbanization and civilization. The smart technologies like electrochromic supercapacitors are beneficial in multifunctional way by providing energy storage systems with visual and reversible colour changes in many applications such as smart windows, electrochromic goggles, automotive mirrors, sunroofs, displays and so on. Herein, nanoporous WO3 thin film is prepared by using cathodic electrodeposition technique and used to study electrochromic as well as electrochemical properties. The bi-functionality of the electrode was confirmed by electrochemical tests including CV, GCD, EIS and chrono methods. The film shows greater coloration efficiency up to 52.61 cm2/C with an aerial capacitance 2.8 mF /cm2. Also, film shows faster switching kinetics as faster coloration and bleaching times like 1.88 and 2.6 s respectively. Hence, electrodeposited WO3 can be a good candidate for bi-functional electrochromic supercapacitors.

Resistive switching kinetics of electrolyte-gated polyaniline-based memristive devices

Memristive devices have a multitude of potential applications, ranging from neuromorphic computing systems and chips to bioprosthetic, each demanding distinct characteristics and features. Among these attributes, the time of resistive switching stands out as one of the most important items. Achieving synchronization between switching rates of memristive devices and existing systems that they complement, either CMOS or biological, is of crucial importance. Moreover, switching time defines energy consumption. Organic memristive devices, particularly those built upon semiconductive polymer polyaniline (PANI), exhibit promising attributes. The primary parameter of a PANI-based memristor is the thickness of the active polymer film. This study provides an insight into the dependency of switching time of PANI–based memristive devices on the thickness of the film and a comprehensive analysis of a switching process itself. Throughout the investigation, it is found that the switching time to conductive state decreases with diminishing PANI film thickness, until reaching a threshold, beyond that the trend reverses. In contrast, devices featuring PANI film thicknesses ranging from 10 to 20 nm exhibit the swiftest switching behavior and are thus considered as an optimal choice for further applications.

A novel deep eutectic solvent/switchable-hydrophilicity solvent/H2O system with enhanced CO2 switchability for integrated extraction of phenolics, flavonoids and essential oil from Flos Chrysanthemi Indici flower

Despite the considerable attention received by switchable solvents in natural product extraction and biorefinery, their CO2 switching kinetic properties and extraction ability still present significant challenges. To tackle this issue, the present study has the following innovative endeavors: (1) Proposing a novel approach to enhance the performance of switchable-hydrophilicity solvent (SHS) by incorporating deep eutectic solvent (DES), leading to the successful design of a DES/SHS/H2O system. (2) Developing an innovative high-speed homogenization assisted extraction method using the DES/SHS/H2O system and applying it to the integrated extraction of phenolics, flavonoids, and essential oil from Flos Chrysanthemi Indici. The switching process was characterized using 1H-NMR, the extraction process was optimized employing response surface methodology, the components of extracted essential oils were analyzed by GC-MS, and the cytotoxicity and anti-inflammatory activity of essential oils were determined through MTT and ELISA. Our findings demonstrate that the incorporation of DES can significantly augment the CO2 switching kinetics of SHS, resulting in a 32.7% reduction in switching time and a remarkable decrease of 73.7% residual content within the aqueous phase. The innovative DES/SHS/H2O based extraction method exhibited substantial enhancements in phenolics, flavonoids, and essential oil extraction efficiency compared to conventional approaches, yielding extracts with superior chemical profiles and enhanced anti-inflammatory activity. Therefore, the proposed strategy of enhancing the CO2 switching kinetic properties and extraction ability of SHS by incorporating DES is feasible, providing valuable guidance for the rational design of innovative smart solvent systems. The developed DES/SHS/H2O system, exhibiting improved performance, holds significant application and research prospects.

Quantifying Dynamic Phenotypic Heterogeneity in Resistant Escherichia coli under Translation-Inhibiting Antibiotics.

Understanding the phenotypic heterogeneity of antibiotic-resistant bacteria following treatment and the transitions between different phenotypes is crucial for developing effective infection control strategies. The study expands upon previous work by explicating chloramphenicol-induced phenotypic heterogeneities in growth rate, gene expression, and morphology of resistant Escherichia coli using time-lapse microscopy. Correlating the bacterial growth rate and cspC expression, four interchangeable phenotypic subpopulations across varying antibiotic concentrations are identified, surpassing the previously described growth rate bistability. Notably, bacterial cells exhibiting either fast or slow growth rates can concurrently harbor subpopulations characterized by high and low gene expression levels, respectively. To elucidate the mechanisms behind this enhanced heterogeneity, a concise gene expression network model is proposed and the biological significance of the four phenotypes is further explored. Additionally, by employing Hidden Markov Model fitting and integrating the non-equilibrium landscape and flux theory, the real-time data encompassing diverse bacterial traits are analyzed. This approach reveals dynamic changes and switching kinetics in different cell fates, facilitating the quantification of observable behaviors and the non-equilibrium dynamics and thermodynamics at play. The results highlight the multi-dimensional heterogeneous behaviors of antibiotic-resistant bacteria under antibiotic stress, providing new insights into the compromised antibiotic efficacy, microbial response, and associated evolution processes.

Heat accumulation and phase transition induction in a VO2 thin film by a femtosecond pulse-periodic radiation.

The kinetics of optical switching due to the insulator-metal phase transition in a VO2 thin film is studied experimentally at different laser pulse repetition frequencies (PRFs) in the NIR range and compared with temperature kinetics obtained through the thermal conductance calculations. Two switching processes have been found with characteristic times <2 ms and <15 ms depending on the PRF; the former is explained by the accumulation of metallic domains remaining after a single-pulse phase transition, and the latter is referred to the heat accumulation in the film. Consequently, the dynamics of the microscopic domains is leading in the initiation of phase transition under pulse-periodic conditions compared to the macroscopic heat transfer. The reverse transition at the radiation turn-off depends on the PRF with a time coefficient of 17.5 µs/kHz and is determined by the metallic domains' decay in the film. The results are important for understanding the nature of the insulator-metal transition in thin films of VO2 as well as using them in all-optical switches of pulse-periodic laser radiation.

A hydrophobic alloy-coated Zn anode for durable electrochromic devices.

To mitigate Zn corrosion, dendrite growth and hydrogen evolution reactions (HER) in Zn-anode based electrochromic devices, hydrophobic CuZn5 alloy was coated on Zn@CuZn with lower nucleation potential, high coulombic efficiency, inhibited HER, and prolonged reversibility, enabling improved switching kinetics and cycling stability in an electrochromic Zn@CuZn||Prussian Blue (PB) device.