Diffusion Mobility Research Articles

Phase-field study of elastic effects on precipitate evolution in (Al)0.05CrFeNi

We introduce a new approach to include for high and medium entropy alloys, stress effects in a Phase-field model (PFM). The approach is applied to simulate the evolution of two-phase BCC/FCC microstructures of AlCrFeNi alloys, combining phase-field method with CALPHAD data and DFT (Density Functional Theory) calculations. The composition dependent Gibbs energies and diffusion mobilities of the BCC and FCC phase as a vital input for simulating real alloys into the PFM are calculated from the Thermo-Calc TCHEA2 and MOBHEA2 databases. The special quasirandom structures (SQS) method was used to obtain the complex multicomponent lattice structures and compute with DFT the elastic properties of the BCC and FCC phases. It is found that elastic stresses emerging due to a difference in eigenstrain between the BCC and FCC phases during a phase transformation have a significant effect on the precipitate formation. The effect of the eigenstrain induced elastic stress on the BCC precipitate shape, size and the equilibrium concentrations in the two phases are quantitatively studied. The PFM presented is one of the first attempts to simulate elastic effects on high entropy alloys(HEAs) microstructures. This work contributes to the understanding of the mechanisms of phase transformation and microstructure evolution in HEAs.

Response of one-dimensional ionised layer to oscillatory electric fields

To provide fundamental insights into the response of laminar flames to alternating current (AC) electric fields, a simplified one-dimensional model using an ionised layer model is formulated with the conservation equations for the ion species with ionisation, recombination, and transport due to molecular diffusion and electric mobility. A parametric study is conducted to investigate the response of the ion layer at different voltages and oscillation frequencies, and the results are examined mainly in terms of the net current–voltage (I–V) characteristics. As the oscillation frequency is increased, a nonmonotonic response in the I–V curve is seen such that the current may exceed the saturation condition corresponding to the steady DC condition. In general the current reaches a peak as the unsteady time scale becomes comparable to the ion transport time scale, which is dictated by the mobility, and eventually becomes attenuated at higher frequencies to behave like a low-pass filter. The extent of the peak current rise and the cut-off frequency are found to depend on the characteristic time scales of the ion chemistry and mobility-induced transport. The simplified model serves as a framework to characterise the behaviour of complex flames in terms of the dominant ionisation and transport processes. The current overshoot behaviour may also imply that the overall effect of the electric field may be further magnified under the AC conditions, motivating further studies of multi-dimensional flames for the ionic wind effects.

Exploring the adsorption behavior of molecular hydrogen on CHA-zeolite by comparing the performance of various force field methods.

Molecular hydrogen (H2) adsorption plays a crucial role in numerous applications, including hydrogen storage and purification processes. Understanding the interaction of H2 with porous materials is essential for designing efficient adsorption systems. In this study, we investigate H2 adsorption on CHA-zeolite using a combination of density functional theory (DFT) and force field-based molecular dynamics (MD) simulations. Firstly, we employ DFT calculations to explore the energetic properties and adsorption sites of H2 on the CHA-zeolite framework. The electronic structure and binding energies of H2 in various adsorption configurations are analyzed, providing valuable insights into the nature of the adsorption process. Subsequently, force field methods are employed to perform extensive MD simulations, allowing us to study the dynamic behavior of H2 molecules adsorbed on the CHA-zeolite surface. The trajectory analysis provides information on the diffusion mechanisms and mobility of H2 within the porous structure, shedding light on the transport properties of the adsorbed gas. Furthermore, the combination of DFT and MD results enables us to validate and refine the force field parameters used in simulations, improving the accuracy of the model, and enhancing our understanding of the H2-CHA interactions. Our comprehensive investigation into molecular hydrogen adsorption on CHA-zeolite using density functional theory and molecular dynamics simulations yields valuable insights into the fundamental aspects of the adsorption process. These findings contribute to the development of advanced hydrogen storage and separation technologies, paving the way for efficient and sustainable energy applications.

NMR Methods to Study the Dynamics of SH2 Domain-Phosphopeptide Complexes.

Nuclear magnetic resonance (NMR) spectroscopy is the method of choice for studying the dynamics of biological macromolecules in solution. By exploiting the intricate interplay between the effects of protein motion (both overall rotational diffusion and internal mobility) and nuclear spin relaxation, NMR allows molecular motion to be probed at atomic resolution over a wide range of timescales, including picosecond (bond vibrations and methyl-group rotations), nanosecond (loop motions and rotational diffusion), and microsecond-millisecond (ligand binding, allostery). In this chapter, we describe different NMR pulse schemes (R1, R1ρ, heteronuclear NOE, and CPMG relaxation dispersion) to characterize the dynamics of SH2 domains. As an example, we use the N-SH2 domain of protein tyrosine phosphatase SHP2 in complex with two phosphopeptides derived from immune checkpoint receptor PD-1 (ITIM and ITSM).

Cellulose‐Derived Wearable Carbon Nanoflake Sensors Customized by Semiconductor Laser Photochemistry

AbstractMulti‐functional wearable electrical materials have been regarded as one of the most pivotal cornerstones for the booming internet of things (IoTs), biomimetic robotics/science, and sensory e‐skins. Nevertheless, customizable, high‐throughput, batch‐fabricated, function‐integrated wearable electronics remain technologically challenging to traditional material engineering. Hereby, a cellulose‐converted active amorphous carbon nanomaterial is developed via a transfer‐free, precursor‐free rapid laser synthesis method incorporating deformation‐tolerant waste papers. The lattice fringe spacing of laser‐synthesized carbon nanoflake is ≈0.305 nm topologically distinct from graphene or carbon dots. The nanostructured three‐dimensional (3D) carbon network exhibits desirable mechanical flexibility, high hygroscopicity/electrical conductivity, large ion storing capacity for Zn2+ or Na+, high sensitivity to pressure, and a natural microwave absorbing ratio (> 37 dB at the terahertz range). Abundant percolation pathways inside cellulose/carbon composite networks offered fast electrolyte diffusion and carrier mobility. A series of low‐cost highly‐deformable interdigitated supercapacitors, tactile sensors, electrical circuits, and functional coatings are experimentally fabricated and identified, enabling waste paper as a function‐magnified meta platform for e‐skins, wearable energy devices, or IoTs interfaces.

SPIN-SELECTIVE INTERACTION OF TRIPLET-EXCITED MOLECULES ON THE SURFACE OF A FERROMAGNETIC NANOPARTICLE

Influence of a magnetic field generated by a ferromagnetic nanoparticle on the annihilation of triplet-excited organic molecules or triplet excitons in a near-surface particle layer is studied. A detailed mathematical model is presented that accounts for electron excitation diffusive mobility and geometry of the system. The kinetic operator is given in the complete 9x9 basis of triplet- triplet pair spin states. Time dependencies of the singlet spin state population of the triplet-triplet pair and the dependence of the triplet-triplet annihilation magnetic response profile (magnetic reaction effect) from the magnetic field induction are obtained. It is found that the influence of a magnetic field gradient on the reaction yield dominates over the other known mechanisms of spin-dynamics in triplet- triplet pairs.

A phase-field study of stainless-steel oxidation from high-temperature carbon dioxide exposure

An electrochemical phase-field model has been developed to investigate the oxidation mechanisms of the 21-2N valve stainless steel alloy exposed to carbon dioxide at 973 K. Three oxide phases observed in oxidation experiments are included in the model: Mn3O4, Cr2O3, and MnCr2O4. Local charge neutrality and the conserved current condition are assumed to include the impact of the electric potential on oxidation, though it is found to be negligible when the system is electrically isolated. The sensitivity of the oxidation processes to the values of the diffusion mobilities is examined, and the oxidation rate is calibrated against experimental data by modifying the sensitive mobilities. We find that both inward oxygen and outward metal diffusion are important for oxidation. By investigating the impact of the order of the initial oxide layers, we find that Cr2O3 serves as a barrier to outward Mn diffusion. Moreover, controlling the initial oxide layer order can be used to limit oxidation.

Soil methane emission suppression control using unmanned aircraft vehicle swarm application of biochar mulch - A simulation study

In this paper, we present a soil methane emissions suppression approach using swarms of unmanned aerial vehicles (UAVs), by spreading biochar mulch on top of the detected methane emissions area/source. Soil microorganisms can produce methane and release it into the atmosphere causing climate change such as global warming. However, people lack methods to manage soil methane emissions, especially quantification of methane emissions from the soil. Current measurement and suppression of methane methods are often limited due to the maintenance, installation, and calibration requirements of these sensing systems. To overcome these drawbacks, we present a new method called FADE-MAS2D (Fractional Advection Diffusion Mobile Actuator and Sensor) in which swarming UAVs are applied as optimal coverage control actuators to various methane release scenarios (from single to multi-source disturbances) utilizing an anomalous diffusion model with different time, and space fractional orders subject to wind fields. This strategy is based on the premise that methane diffusion can be modeled as an anomalous diffusion equation, and swarming UAVs can be applied to tackle the optimal coverage control issue. To simulate methane diffusion under the wind, we utilize the fractional calculus to solve the anomalous diffusion equation and define wind force with the drag equation. In addition, we integrated emissions control, UAV control efforts, and UAV location error in our cost function. Finally, we evaluated our approach using simulation experiments with methane diffusion and multiple methane emission sources in the time and space domain, respectively. The results show that when α ​= ​0.8 and β ​= ​1.8, the shape and emissions of methane perform well. Furthermore, our approach resulted in great control performance with multiple methane emission sources and different wind velocities and directions.

Development of a Diffusion Mobility Database for Co-Based Superalloys

To facilitate the development of high-temperature Co-based γ-γ′ superalloys, a Co-Ni based diffusion mobility database is developed for the eight component FCC (Face Centered Cubic) system of Co-Al-W-Ni-Cr-Ti-Ta-Re. A CALPHAD approach is used to represent the temperature and composition dependency of the multicomponent system. The mobility descriptions were based on previous assessment work for the Ni-based superalloys, published experimental and computational data, and established diffusion correlations. The initial mobility descriptions were then refined using additional diffusion couple experimental data, particularly for the Co-Cr, Co-Ta, and Ni-Ta systems. After re-optimizing the descriptions with the new experimental data, the mobility descriptions were validated using a collection of published diffusion couple composition profiles, which were not included in the initial assessment process.

Diffusion and Atomic Mobility for FCC Ni-Si-Ti Alloys: Experiment and Modeling

The Ni-Si-Ti system plays an important role in high temperature structural materials. Accurate atomic mobilities of fcc Ni-Si-Ti system are essential for the microstructure simulation of Ni-based superalloys. In the present work, diffusion couples of fcc Ni-Si-Ti system have been prepared and annealed at 1273, 1373 and 1473 K. By combining solid/solid diffusion couples with the electron probe microanalysis (EPMA) technique, the interdiffusivities in fcc Ni-Si-Ti were calculated via Matano-Kirkaldy method and numerical inverse method. Based on the reliable thermodynamic description and interdiffusion coefficients measured above, two sets of atomic mobilities were optimized by means of the CALTPP (CALculation of ThermoPhysical Properties) program. These atomic mobilities can reasonably describe the diffusion behaviors by comparing model-predicted diffusivities, concentration profiles and diffusion paths with the experimental ones. Besides, based on these atomic mobilities, three-dimensional surfaces for the interdiffusivity at 1273, 1373 and 1473 K were plotted. Furthermore, three-dimensional planes of the activation energy and frequency factor were evaluated using the Arrhenius equation.

Phosphate ions functionalized spinel iron cobaltite derived from metal organic framework gel for high-performance asymmetric supercapacitors

Spinel iron cobaltite (FeCo2O4) with high theoretical capacity is a promising positive electrode material for building high-performance supercapacitors. However, its inherent poor conductivity and deficient electrochemical active sites hinder the improvement of its electrochemical kinetics behavior. Herein, phosphate ions modified FeCo2O4 is obtained in the presence of oxygen vacancies (P-FeCo2O4-x) by a simple metal organic framework gel-derived strategy. Phosphate ions added on the surface of P-FeCo2O4-x greatly enhances its surface activity, thus prompting the faster charge storage kinetics of the electrode material. Due to its ample electrochemical active sites and rapid ion diffusion and electron mobility, the optimized P-FeCo2O4-x electrode delivers a superior specific capacity of 1568.8 F g−1 (784.4 C g−1) at a current density of 1 A/g and has an excellent cycling stability with 93.3 % initial capacity retention ratio after 5000 cycles. More impressively, the assembled asymmetric supercapacitor consisting of P-FeCo2O4-x and activated carbon which act as positive and negative electrode materials, respectively displays a favorable energy density of 60.2 Wh kg−1 at a power density of 800 W kg−1 and has a long cycling lifespan. These results demonstrate the potential importance of modifying the surface of spinel cobaltite with phosphate ions and incorporating oxygen defects in it as a facile strategy for enhancing the electrochemical kinetics of electrode materials.

In Situ Growth Intercalation Structure MXene@Anatase/Rutile TiO2 Ternary Heterojunction with Excellent Phosphoprotein Detection in Sweat.

Abnormal protein phosphorylation may relate to diseases such as Alzheimer’s, schizophrenia, and Parkinson’s. Therefore, the real-time detection of phosphoproteins in sweat was of great significance for the early knowledge, detection, and treatment of neurological diseases. In this work, anatase/rutile TiO2 was in situ grown on the MXene surface to constructing the intercalation structure MXene@anatase/rutile TiO2 ternary heterostructure as a sensing platform for detecting phosphoprotein in sweat. Here, the intercalation structure of MXene acted as electron and diffusion channels for phosphoproteins. The in situ grown anatase/rutile TiO2 with n-n-type heterostructure provided specific adsorption sites for the phosphoproteins. The determination of phosphoprotein covered concentrations in sweat, with linear range from 0.01 to 1 mg/mL, along with a low LOD of 1.52 μM. It is worth noting that, since the macromolecular phosphoprotein was adsorbed on the surface of the material, the electrochemical signal gradually decreased with the increase of phosphoprotein concentration. In addition, the active sites in the MXene@anatase/rutile TiO2 ternary heterojunction and synergistic effect of the heterojunction were verified by first-principle calculations to further realize the response to phosphoproteins. Additionally, the effective diffusion capacity and mobility of phosphoprotein molecules in the ternary heterojunction structure were studied by molecular dynamics simulation. Furthermore, the constructed sensing platform showed high selectivity, repeatability, reproducibility, and stability, and this newly developed sensor can detect for phosphoprotein in actual sweat samples. This satisfactory sensing strategy could be promoted to realize the noninvasive and continuous detection of sweat.

(Invited) Thin-Film Transistor Accumulation-Mode Modeling

Analytical equations are developed for electrostatic assessment of accumulation-mode thin-film transistors (TFTs) so that potential, electric field, and accumulation layer free electron concentration profiles may be generated. Additionally, equations are derived for plotting TFT trap density versus surface potential, based on accurate extraction of the channel mobility as a function of gate voltage. A key factor in formulating these device physics equations is distinguishing between a ‘long-base’ or ‘short-base’ channel thickness. A ‘long-base’ (‘short-base’) channel thickness is defined to occur when the accumulation layer thickness (as calculated in the normal manner) is less than (greater than) the physical thickness of the channel layer. The electrostatic equations derived herein are applied to the analysis of two amorphous oxide semiconductor (AOS) TFTs with differing channel layers, i.e., a 40 nm amorphous indium gallium zinc oxide (a-IGZO) or a 7 nm amorphous indium zinc oxide (a-IZO). Application of these equations suggests that optimal TFT performance is obtained when the channel layer thickness is chosen to be similar to its Debye length. Estimated trap densities of these two AOS TFTs are found to be quite similar. Therefore, the superior mobility performance of the a-IZO TFT compared to the a-IGZO TFT is ascribed to the smaller effective mass of a-IZO, assuming that the maximum (no trapping) drift mobility in the channel is established by the thermally-limited diffusive mobility.

Interactive Evaporation of Neighboring Pendant and Sessile Droplet Pair

Abstract In this article, we experimentally probe the vapor-mediated interaction behavior of evaporating sessile and pendant droplets in an interacting droplet (ID) system. For this purpose, a pendant droplet was introduced in the vapor diffusion domain of a sessile droplet and both were allowed to evaporate simultaneously. The evaporation dynamics were monitored using optical imaging techniques for varied separation (both horizontal and vertical) distances between them. Our observations reveal curtailed mass transfer rate from both the droplets although the evolution of droplet morphology (such as pendant droplet radius, contact radius, and contact angle of sessile droplet) at different stages of evaporation remain similar. The evaporative fluxes from these two droplets interact with one another and thereby reduce the diffusive mobility of vapor molecules in the liquid–vapor interface of both. This condition suppresses the diffusion mechanism and thereby impedes the evaporation rate. We show that the evaporation behavior for two droplets in an interacting droplet system is solely dictated by an effective external vapor concentration depending on the problem geometry. Therefore, to characterize the vapor diffusion domain we hypothesize a vapor front enfolding both the droplets and put forward a theoretical model by applying conservation of mass across it. We also propose a relationship to show the variation of the effective external vapor concentration with the relative separation distance between the droplets. The predictions from theoretical models are found to be in good agreement with our detailed experimental observations.

Intrinsic Channel Mobility Associated with Extended State Transport in IGZO TFTs

There is wide variation in the interpretation of the interaction and/or independence of channel mobility and charge trapping in IGZO TFTs. Electrical measurements reveal temperature-dependent behavior that is not explained by existing TCAD models employed for defect states and carrier mobility. An IGZO TFT device model has been recently developed using Silvaco Atlas, which accounts for the role of donor-like oxygen vacancy defects, acceptor-like BTS, and acceptor-like interface traps, thus properly regulating the amount of free channel charge. The channel mobility is defined as only a function of temperature, and reflects a thermally-activated diffusive mobility with a distinct activation energy Ea = 40 meV. This thermally activated process is clearly intrinsic, as it is constant over all bias conditions and is not dependent on the steady-state trapped charge level. The model demonstrates a remarkable match to transfer characteristics measured at T = 150 K to room temperature.

Effects of lattice dilution on the nonequilibrium phase transition in the stochastic susceptible-infectious-recovered model.

We investigate how site dilution, as would be introduced by immunization, affects the properties of the active-to-absorbing nonequilibrium phase transition in the paradigmatic susceptible-infectious-recovered (SIR) model on regular cubic lattices. According to the Harris criterion, the critical behavior of the SIR model, which is governed by the universal scaling exponents of the dynamic isotropic percolation (DyIP) universality class, should remain unaltered after introducing impurities. However, when the SIR reactions are simulated for immobile agents on two- and three-dimensional lattices subject to quenched disorder, we observe a wide crossover region characterized by varying effective exponents. Only after a sufficient increase of the lattice sizes does it become clear that the SIR system must transition from that crossover regime before the effective critical exponents asymptotically assume the expected DyIP values. We attribute the appearance of this exceedingly long crossover to a time lag in a complete recovery of small disconnected clusters of susceptible sites, which are apt to be generated when the system is prepared with Poisson-distributed quenched disorder. Finally, we demonstrate that this transient region becomes drastically diminished when we significantly increase the value of the recovery rate or enable diffusive agent mobility through short-range hopping.

Trion-phonon interaction in atomically thin semiconductors

Optical and transport properties of doped monolayer semiconductors are dominated by trions, which are three-particle compounds formed by two electrons and one hole or vice versa. In this work, we investigate the trion-phonon interaction on a microscopic footing and apply our model to the exemplary case of a molybdenum diselenide (MoSe2) monolayer. We determine the trion series of states and their internal quantum structure by solving the trion Schr\"odinger equation. Transforming the system into a trion basis and solving equations of motion, including the trion-phonon interaction within the second-order Born-Markov approximation, provides a microscopic access to the trion dynamics. In particular, we investigate trion propagation and compute the diffusion coefficient and mobility. In the low density limit, we find that trions propagate less efficiently than excitons and electrons due to their stronger coupling with phonons and their larger mass. For increasing densities, we predict a drastic enhancement of diffusion caused by the build-up of a large pressure by the degenerate trion gas, which is a direct consequence of the fermionic character of trions. Our work provides microscopic insights into the trion-phonon interaction and its impact on the diffusion behaviour in atomically thin semiconductors.

In situ growth of ZnO nanosheets on Ti3C2Tx MXene for Superior-Performance Zinc-Nickel secondary battery

Although Zn-Ni battery is a potential energy storage system, the anode zinc electrode often faces dendrite, passivation and deformation problems, which tend to be exacerbated at high current densities particularly, and severely hamper its practical applications. Zinc oxide was modified with 2D transition metal carbides/nitride (ZnO@MXene) firstly for the purpose of broadening the application scenarios of zinc alkaline secondary batteries. A variety of characterizations and density functional theory (DFT) calculations certify that highly conductive MXene matrix provides a high-speed electron transfer channel and its low ionic diffusion barrier and excellent ionic diffusion mobility of MXene can quickly reduce the ion concentration gradient at the solid–liquid interface, which weakens the concentration polarization. Also, MXene can tune the diffusion behavior to induce homogeneous deposition of zinc via the zinc-oriented-O groups, forming well-dispersed “seed points” to realize uniform nucleation and inhibiting dendrite growth. Therefore, ZnO@MXene as the anode of a Zn-Ni battery can keep its capacity of 594mAh·g−1 after 1500 cycles at 10C. That reaches 90% of its initial capacity (596mAh·g−1), suggesting superb specific capacity, rate performance, and cycle life span.

Diffusion and ion carrier mobility studies in binary SPEs based on PVA integrated with K+ ion provider salt: structural and electrical insights

Diffusion and ion carrier mobility studies in binary SPEs based on PVA integrated with K+ ion provider salt: structural and electrical insights

Screening confinement of entanglements: Role of a self-propelling end inducing ballistic chain reptation.

Synthetic and natural nanomaterials with self-propelling mechanisms continue to be explored to boost chain mobility beyond normal reptation in the crowded environments of entangled chains. Here we employ scaling theory and numerical simulations to demonstrate that activating one chain end of a singular or isolated chain boosts entanglement-constrained chain reptation from the one-dimensional diffusive mobility as described by the de Gennes-Edwards-Doi model to ballistic motion along the entanglement tube contour. The active chain is effectively screened from the constraint of entanglements on length scales exceeding the tube size.