Search

Variations from equilibrium Young's angle, known as contact angle hysteresis (CAH), are frequently observed upon droplet deposition on a solid surface. This ubiquitous phenomenon indicates the presence of multiple local surface energy minima for the sessile droplet. Previous research primarily explains CAH via considering macroscopic roughness, such as topographical defects, which alter the effective interfacial energy between the fluid phase and the solid phase, thereby shifting the global surface energy minimum. One typical example is the classic Cassie–Baxter–Wenzel theory. Here, we propose an alternative microscopic mechanism that emphasizes the complexity of molecular rearrangements at the fluid–solid interface, treating their interfacial tensions as variables, which results in multiple local surface energy minima. Our theoretical framework demonstrates that CAH can occur even on chemically homogeneous and mechanically smooth-flat substrates, aligning with previously unexplained experimental observations. In addition, we explore the interplay between macroscopic and microscopic roughness in influencing CAH and clarify the contrasting wetting behaviors—the lotus effect and the rose petal effect—on hierarchical roughness from a thermodynamic perspective. This work provides valuable insights into surface tension determination by restoring the natural physical properties of interfaces and illuminates the multifaceted mechanisms underlying the everyday occurrences of CAH. [ABSTRACT FROM AUTHOR]

Structural disorder in mesoporous solids gives rise to complex phase behavior for materials confined within their pore spaces. As a result, a wide spectrum of possible phase configurations associated with spatial distributions of thermodynamic phases throughout the pore networks can be realized in experiments. Despite their importance, quantifying these states remains largely unaddressed. By considering solid–liquid equilibria as a representative example and using a simple random network model, we investigate the spectrum of such states accessible in real experiments and relate this spectrum to the structural characteristics of porous solids. We classify these states by their free energies and demonstrate how network effects break degeneracies for specific phase compositions and temperatures. Furthermore, we identify the experimental conditions that delineate boundary free energy states, differentiating accessible from inaccessible states. The insights from this study on solid–liquid equilibria are also equally applicable to gas–liquid equilibria in confined spaces and contribute to a deeper understanding of relaxation dynamics associated with hysteresis. [ABSTRACT FROM AUTHOR]

Marine foundation species are critical for the structure and functioning of ecosystems and constitute the pillar of trophic chains while also providing a variety of ecosystem services. In recent decades, many foundation species have declined in abundance, sometimes threatening their current geographical distribution. Kelps (Laminariales) are the primary foundation species in temperate coastal systems worldwide. Kelp ecosystems are notoriously variable, challenging the identification of key factors controlling their dynamics. Identification of these drivers is key to predicting the fate of kelp ecosystems under climatic change and to informing management and conservation decisions such as restoration. Here, we used in situ data from long-term monitoring programs across 1350 km of coast spanning multiple biogeographic regions in the state of California (USA) to identify the major regional drivers of density of two dominant canopy-forming kelp species and to elucidate the spatial and temporal scales over which they operate. We used generalized additive mixed models to identify the key drivers of density of two dominant kelp species (Nereocystis luetkeana and Macrocystis pyrifera) across four ecological regions of the state of California (north, central, southwest, and southeast) and for the past two decades (2004-2021). The dominant drivers of kelp density varied among regions and species but always included some combination of nitrate availability, wave energy and exposure, density of purple sea urchins, and temperature as the most important predictors. These variables explained 63% of the variability of bull kelp in the northern and central regions, and 45% and 51.4% of the variability in giant kelp for the central/southwest and southeast regions, respectively. These large-scale analyses infer that a combination of lower nutrient availability, changes in wave energy and exposure, and increases in temperature and purple sea urchin counts have contributed to the decline of kelp observed in the last decade. Understanding the drivers of kelp dynamics can be used to identify regional patterns of historical stability and periods of significant change, ultimately informing resource management and conservation decisions such as site selection for kelp protection and restoration.

The generation of above-bandgap photovoltage, referred to as the anomalous photovoltaic effect (APV), is an extraordinary characteristic sought after property in bulk ferroelectric photovoltaic devices. Despite the fact that the relatively narrow bandgap of BiFeO3 (BFO) (2.7 eV) induces a comparatively larger generation of photocurrent than other ferroelectric photovoltaic, it falls short in producing an anomalous photovoltage (Eg ≪ Voc) and exhibits leaky ferroelectric hysteresis due to unavoidable oxygen vacancies. This work revealed a reduction in oxygen vacancies through the substitution of Ba(Fe1/2Nb1/2)O3 in BFO, leading to improved structural, morphological, synchrotron XPS, and electrical properties. This reduction in oxygen vacancies has resulted in an impressive above-bandgap photovoltage (APV) of 4.41 V for 80BFO–20BFN with greater ferroelectric polarization (Pr = 20.45 μC/cm2) observed at the co-existence of polar and non-polar phases. Moreover, both theoretical and experimental optical analyses have demonstrated a significant decrease in the bandgap to 1.92 eV, effectively extending the visible region close to 653 nm. As a result, a larger population of photoexcited charge carriers is generated, enabling the attainment of a high current density (Jsc) of 0.75 μA/cm2 under 100 mW/cm2 light irradiation. [ABSTRACT FROM AUTHOR]

This paper investigates wake-up and imprint in ferroelectric Al0.70Sc0.30N films. The study employs a series of electrical measurements with varying field amplitudes and waveforms to understand the origin and underlying principle of wake-up and imprint as well as their relation. It is shown that the material can be considered wake-up free. However, inherent imprint and imprint variation of the polarization-electric field hysteresis in combination with minor loops result in a wake-up like effect. This effect is most likely related to the formation of persistent inversion domain nuclei—a mechanism that is discussed in detail and compared with alternative explanations based on charged defects. Investigations using unipolar fields are conducted to explore the reversibility of imprint and ways to program it, while partial switching is applied to investigate domain propagation and support the aforementioned explanation for the evolution of the polarization-electric field hysteresis. It is concluded that after an energetically more demanding domain nucleation, domain wall motion can switch the majority of polarization in Al1−xScxN. As a consequence, the presence of initial domains reduces the coercive field with respect to unipolar films. [ABSTRACT FROM AUTHOR]

The time-dependent quantum transportation through a metal/polymer/metal system is theoretically investigated on the basis of a Su–Schrieffer–Heeger model combined with the hierarchical equations of motion formalism. Using a non-adiabatic dynamical method, the evolution of the electron subspace and lattice atoms with time can be obtained. It is found that the calculated transient currents vary with time and reach stable values after a response time under the bias voltages. However, the stable current as the system reaches its dynamical steady state exhibits a discrepancy between two sweep directions of the bias voltage, which results in pronounced electrical hysteresis loops in the current–voltage curve. By analyzing the evolution of instantaneous energy eigenstates, the occupation number of the instantaneous eigenstates, and the lattice of the polymer, we show that the formation of excitons and the delay of their annihilation are responsible for the hysteretic current–voltage characteristics, where electron–phonon interactions play the key factor. Furthermore, the hysteresis width and amplitude can also be modulated by the strength of the electron–phonon coupling, level-width broadening function, and temperature. We hope these results about past condition-dependent switching performance at a sweep voltage can provide further insight into some of the basic issues of interest in hysteresis processes in conducting polymers. [ABSTRACT FROM AUTHOR]

The thermal hysteresis exhibited in plastic crystal compounds greatly reduces their cyclic efficiency, limiting their potential for replacing current environmentally harmful refrigerants. A mechanistic understanding of the origins of this hysteresis has yet to be established. Here, we systematically investigate the transformation kinetics of the model plastic crystal, neopentyl glycol (NPG), through microscopic and calorimetric techniques. We reveal an asymmetry between the forward (heating) and reverse (cooling) transitions. We also demonstrate that the forward transformation is rate-limited by the rate of growth of rotationally disordered domains. In contrast, the reverse transformation is rate-limited by the nucleation of the ordered crystal domain, demonstrated by the sharp exothermic peaks in calorimetry and rapid self-nucleation phenomena observed optically. This nucleation limitation is largely responsible for the large thermal hysteresis in NPG, which we observe to be as large as 16.7 °C for an approximately 10 mg sample cooled at 0.5 °C min−1. These findings demonstrate the underlying origin of the thermal hysteresis and introduce a direction to mitigate hysteresis in plastic crystal transformations. [ABSTRACT FROM AUTHOR]

In this work, three atomic layer deposition (ALD) approaches are used to deposit an Al2O3 gate insulator on n-GaN for application in vertical GaN power switches: thermal ALD (ThALD), plasma-enhanced ALD (PEALD), and their stacked combination. The latter is a novel method to yield the most ideal insulating layer. Also, the influence of an in situ NH3 or H2 plasma pre-treatment is studied. Planar MIS capacitors are used to investigate the electrical properties and robustness of the gate insulators. In vacuo x-ray photoelectron spectroscopy (XPS) is used to study the changes in chemical composition after every surface treatment. XPS shows that all plasma pre-treatments efficiently remove all carbon contamination from the surface, but only NH3 plasma is observed to additionally remove the native oxide from the n-GaN surface. The water precursor step in the ThALD process does not completely remove the CH3 ligands of the trimethylaluminum precursor step, which might electrically be associated with a reduced forward bias robustness. The O2 plasma step in the PEALD process is associated with the removal of carbon and a tremendous increase of the O content in the GaN surface region. Electrically, this strongly correlates to an enhanced forward bias robustness and an increased forward bias hysteresis, respectively. The ThALD/PEALD stack method mitigates the shortcomings of both ALD processes while maintaining its advantages. Electrical measurements indicate that the stack method alongside NH3 plasma pretreatment provides the best characteristics in terms of hysteresis, threshold voltage, forward bias robustness, and interface trap density of states. [ABSTRACT FROM AUTHOR]

The advancement of magnetic materials with coupled magneto-structural phase transition (MST) to fulfill the ultimate objectives of practical solid-state cooling applications requires a better understanding of the hysteresis phenomenon linked across the phase transition region along with the large magnetocaloric parameters. For the present sample Mn0.65Ni0.65Fe0.70Si, the MST is associated with a sharp jump in magnetization along with a small thermal hysteresis of ∼13 K. A giant isothermal magnetic entropy change (| Δ S M max |) of ∼37.6 J kg−1 K−1 at 299 K and effective refrigerant capacity (R C effe ) of ∼214.3 J kg−1 under ΔH = 30 kOe is obtained with excellent compatibility between the martensite and austenite phases. The geometrical compatibility condition, i.e., very small (∼0.55%) deviation of the middle eigenvalue (λ 2) from unity justifies the observation of small hysteresis in the present material. The investigation of hysteresis behavior under different extents of the driving forces (temperature or magnetic field) reveals that both the driving forces trigger equally the phase transition and are responsible equivalently for the hysteresis phenomenon. The present study provides a pathway to understand the complexity of the hysteresis behavior, its impact on the reversibility of magnetocaloric effect, and its minimization by optimizing the geometrical compatibility condition between the austenite and martensite phases. [ABSTRACT FROM AUTHOR]

Nanowires (NWs) composed of 2,4-bis[(4-diethylamino)-2-hydroxyphenyl] squaraine were prepared by evaporation-induced self-assembly (EISA). NWs were ∼560 nm wide (aspect ratios: 10–90). X-ray diffraction analysis indicated polymorphism (monoclinic/triclinic). Optical data reported the triclinic phase with energetic disorder. Given the favorable alignment of the Au work function and squaraine HOMO energy, symmetric, unipolar metal–insulator–metal devices were formed by the EISA of NW meshes on inter-digitated Au electrodes. Room temperature DC I–V characteristics displayed hysteretic I–V loops, indicating memristive behavior. At low bias, data indicated Ohmic transport with carrier extraction facilitated by thermionic emission. At high biases, devices exhibited space-charge-limited conduction in the presence of shallow traps. At 77 K, data indicated Ohmic transport at low bias with carrier extraction by thermionic emission while, at high biases, trap-limited space-charge-limited conduction in the presence of traps distributed in energy, with carrier extraction by Fowler–Nordheim tunneling, was observed. The I–V hysteresis was eliminated at 77 K and attenuated by fast scan rates at room temperature, suggesting that carrier trapping/de-trapping underpinned the hysteresis. In impedance measurements, the device response fitted a Randles equivalent circuit indicating purely electronic conduction. By applying voltage waveforms, I–V hysteresis and analog resistive switching (memristive) functionality were observed. Device conductance could be increased sweep by sweep, giving conductance tuning through distinct states, with wait time- or voltage-erase options, consistent with trap filling/emptying effects. Repeated erase–write–read of multiple distinct states over many voltage cycles during continuous use in air was demonstrated. Finally, synaptic functions, e.g., pulse-dependent plasticity, and short- to long-term memory transition, were successfully emulated. [ABSTRACT FROM AUTHOR]

In the fight for legitimacy, understanding the rules of status games is critical. This idea holds true in the wedding marketplace. However, when legalization of marriage for same-sex couples disrupted the binary wedding script, the rules of the game became less clear to consumers. Couples sometimes found their gendered bodies, roles, and expressions were out of sync with the evolving script of a destabilized wedding field, thus raising legitimacy questions. This situation is defined as hysteresis—meaning delays in the realignment between habitus and the field. Hysteresis results in consumers' disorientation about what forms of capital are valued as well as perceived absences of materials or recognition from the market. This study investigates consumers' attempts to mobilize gendered capital to resolve hysteresis through realignment of habitus and the script. Grounded in a Bourdieuian field-level analysis of depth interviews with 30 same-sex couples and ethnographic observation in the wedding field, four consumption alignment strategies are identified that consumers leverage to address hysteresis: confronting, masking, collaborating, and experimenting. Consumers' variations in gendered capital explain which consumption alignment strategies they use, with different possibilities for updating habitus and expanding the script. Throughout this process, consumers' moral judgments hinder this pursuit. [ABSTRACT FROM AUTHOR]

As one of the promising room temperature nuclear radiation detection materials, the all-inorganic perovskite CsPbBr3 single crystal has been receiving much attention in recent years. Even though the performance of the CsPbBr3 detector is improving continuously, the disadvantages of detection instability have not been solved fundamentally, and this instability is mainly caused by ionic migration in the CsPbBr3 single crystal itself. In this paper, a reasonable ionic migration model is proposed based on an in-depth study of the current hysteresis phenomenon and ionic migration mechanism in the Ti/CsPbBr3/Ti detector. The model shows that the ions migrate to the anode or cathode under an external electric field, and the accumulated ions subsequently form an inverted internal electric field inside the crystal and carrier transport barriers at the metal–semiconductor interface simultaneously. The photoelectric characteristic and ionic migration activation energy (E a i o n) fitting results also prove the rationality of the ionic migration model. Furthermore, the ionic migration model can also be used to explain the left-shift of the energy response peak and the decrease in the normalized charge collection efficiency in the Ti/CsPbBr3/Ti detector. This paper systematically investigates the intrinsic origin of migrated ions and the influence of ionic migration on detection stability, which will provide a potential solution to improve detection stability by suppressing ionic migration in the near future. [ABSTRACT FROM AUTHOR]

In this paper, we report an analysis of reverse current mechanisms observed in GaN Schottky barrier diodes leading to hysteretic behavior of the I–V curves at low temperature. By means of DC measurements from 33 to 475 K, we demonstrate the presence of two leakage mechanisms when comparing the experiments with the results obtained using a unified model to predict the ideal reverse current of the diode. Poole–Frenkel emission is the dominant mechanism for temperatures above 200 K, while trap-assisted tunneling prevails for lower temperatures, where also, hysteresis cycles are revealed by means of DC dual-sweep voltage measurements. The energy of the corresponding traps has also been determined, being around 0.2 and 0.45 eV, respectively. The hysteresis phenomenon is attributed to the bias-induced occupancy of the energy states originating the leakage-current processes, which leads to the reduction of the reverse current after a high negative voltage is applied to the diode. [ABSTRACT FROM AUTHOR]

In a sequential posture selection task, we reuse former motor plans to reduce cognitive planning cost. The resulting persistence in the former posture, termed motor hysteresis, can serve as a proxy for the percentage of motor plan reuse (PoR). A recent study showed a significant drop in PoR if participants were asked to skip every second drawer in a sequential drawer opening task. In the current study, we sought to disentangle four confounded factors that were potentially responsible for this drop in PoR: a change of (1) spatial distance, (2) digit distance, (3) number of drawers, or (4) context (presence of skipped drawers). To this end, two groups of participants were tested in a series of sequential drawer tasks, where each of the four potential influencing factors was varied independently. PoR was calculated as the dependent variable. Participants displayed a hysteresis effect in all ordered tasks, but the PoR was only reduced by an increase in spatial distance. The three remaining factors had no significant effect. This finding indicates that motor planning is only affected by local (spatial) parameters of the task, but not by context factors (digits, skipped drawers) or global parameters such as the number of drawers. [ABSTRACT FROM AUTHOR]