Interface Width Research Articles

Growth dynamics and its correlation with plasmonic properties of silver nanoparticles grown by solid state dewetting

Surface morphology and growth dynamics of silver nanoparticles grown by solid-state dewetting of sputtered precursor silver films are studied using atomic force microscopy (AFM) with advanced statistical analysis. Height-height correlation function (HHCF) and power spectral density function (PSDF) were extracted from AFM data, and scaling exponents αlocal,β,1/z and α were determined using analysis. HHCF analysis reveals that interface width w follows power law dependence with precursor film thickness (t) as ∼t0.48±0.01 for as-deposited films and ∼t1.27±0.08 for annealed films. Similarly, lateral correlation length ξ is observed to scale with precursor film thickness as ∼t0.58±0.08 for as-deposited films and ∼t0.65±0.05 for annealed films. The HHCF and PSDF analysis confirmed mound-like growth of the nanoparticles for the higher thickness of the precursor films. A direct correlation between morphology and the localized surface plasmon resonance (LSPR) properties of the silver nanoparticles is also observed.

From Self-Affine Ag to Mounded Ag@Ag2O Core–Shell Nanoplasmonic Surfaces By Sonochemistry

A controllable ultrasound-assisted synthetic approach has been developed that allows deposition of elemental silver and core–shell Ag@Ag2O nanoparticles, close-packed in thin-film form on glass substrates, suitable for a wide range of applications. Ultrasonic irradiation modifies the reaction mechanism, allowing precise control over the composition of the nanoparticles and their packing in the form of thin films. The crystal radii of the synthesized materials fall within the nano range (∼9 nm in the case of bare Ag, 5 nm for the Ag core, and 9 nm for the Ag2O shell in the case of Ag@Ag2O films). Nanostructured Ag films exhibit self-affine, while the films built up by Ag@Ag2O core–shell nanocrystals exhibit a mounded morphology. The interface width and the mean roughness are significantly smaller for sonochemically synthesized surfaces. The observed trends in the localized surface plasmon resonance (LSPR) absorptions in the case of bare Ag plasmonic surfaces are dominated by the particle size, inhomogeneous broadening induced by the size dispersion of the nanoparticles, interparticle plasmon coupling, and nanocrystal–substrate interaction. The notable red shift of the LSPR absorption maximum in the case of films built up by Ag@Ag2O core–shell nanoparticles is governed by the influence of the dielectric shell.

An Electrochemical Perspective on the Interfacial Width between Two Immiscible Liquid Phases.

Molecular dynamics simulations and vibrational sum-frequency spectroscopy are historically the main techniques applied to the description of the molecular structure and dynamics of the immiscible liquid/liquid interface. A molecular sharpness is estimated for oil/water interfaces, with an interfacial width that extends from hundreds of Å to 1 nm. However, electrochemical studies have elucidated a deeper liquid/liquid interface on the order of several micrometers. The breaking down of single-entity electrochemistry to simpler systems and the combination of high-resolution microscopies is confirming a larger extension of the interface. What can be the role of the electrochemist in clarifying this fundamental question? We try to give a suggestion at the end of a brief historical overview of the liquid/liquid interface studies.

Research on dynamic coupling characteristics of magnetic fluid and gas medium interface in sealing devices

The widths and shapes of sealing interfaces are key indicators for characterizing the sealing stability of dynamic and static magnetic fluid seals. In this study, the interface of a magnetic fluid seal was numerically simulated and changes in the interfacial shape and width were tested and verified using a magnetic fluid seal device. The results showed that the pressure resistance decreased with an increase in seal clearance, and the magnetic fluid seal interface generated a small leakage channel. Following the complete formation of the leakage channel, the static seal gradually failed. During failure, the interface width of the magnetic fluid became narrow. At a certain pressure, the maximum pressure resistance decreased as a function of the rotational speed. Compared with a static seal, more small leakage channels and bubbles were generated. In constant conditions, such as fixed sealing clearance speed during dynamic and static sealing, the change in the width of the magnetic fluid interface of the dynamic seal was 5–7 times that of the static seal.

Interface and electromagnetic effects in the valley splitting of Si quantum dots

The performance and scalability of silicon spin qubits depend directly on the value of the conduction band valley splitting (VS). In this work, we investigate the influence of electromagnetic fields and the interface width on the VS of a quantum dot in a Si/SiGe heterostructure. We propose a new three-dimensional theoretical model within the effective mass theory for the calculation of the VS in such heterostructures that takes into account the concentration fluctuation at the interfaces and the lateral confinement. With this model, we predict that the electric field is an important parameter for VS engineering, since it can shift the probability distribution away from small VSs for some interface widths. We also obtain a critical softness of the interfaces in the heterostructure, above which the best option for spin qubits is to consider an interface as wide as possible.

Proximity to criticality predicts surface properties of biomolecular condensates

It has recently become appreciated that cells self-organize their interiors through the formation of biomolecular condensates. These condensates, typically formed through liquid-liquid phase separation of proteins, nucleic acids, and other biopolymers, exhibit reversible assembly/disassembly in response to changing conditions. Condensates play many functional roles, aiding in biochemical reactions, signal transduction, and sequestration of certain components. Ultimately, these functions depend on the physical properties of condensates, which are encoded in the microscopic features of the constituent biomolecules. In general, the mapping from microscopic features to macroscopic properties is complex, but it is known that near a critical point, macroscopic properties follow power laws with only a small number of parameters, making it easier to identify underlying principles. How far does this critical region extend for biomolecular condensates and what principles govern condensate properties in the critical regime? Using coarse-grained molecular-dynamics simulations of a representative class of biomolecular condensates, we found that the critical regime can be wide enough to cover the full physiological range of temperatures. Within this critical regime, we identified that polymer sequence influences surface tension predominately via shifting the critical temperature. Finally, we show that condensate surface tension over a wide range of temperatures can be calculated from the critical temperature and a single measurement of the interface width.

Laser powder bed fusion of bimetallic stainless steel/Nickel-based superalloy: Interface and mechanical properties

Potential applications of steel/nickel bimetals in corrosive environments are of increasing interest. In this study, bimetallic 316L/Hastelloy X was processed via laser powder bed fusion (L-PBF) using different parameters. Results indicated that the rapid cooling of L-PBF reduced the element segregation and carbide formation, thus leading to an interface free of cracks. However, also due to rapid solidification, the constituent elements of dissimilar materials at the interface were not mixed properly. With the increasing laser energy density, the interfacial width increased from dozens to hundreds of microns. The epitaxial grain growth from 316L to Hastelloy X was observed under the optimal processing parameters. The microhardness first declined at the front of the 316L side and then continuously increased in the interfacial region with the addition of Hastelloy X. During the tensile tests, the optimally built samples failed at the 316L side, implying the formation of solid bonding between the two metals.

Study on the mechanical properties and microstructure of a rich-watered grouting material

The effective method of mine gas control and efficient development is gas extraction technology. The sealing effect of grouting material on borehole directly affects the efficiency of gas extraction. The new type of rich-watered sealing material with suitable mechanical strength and significant plastic characteristics was developed based on the addition of accelererant, alkali activator, expansion agent and reinforcing agent to Portland cement for mining. The effect of reinforcing agent on the mechanical properties of materials under different w/c ratios was tested by RMT. By means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and other test methods, the microstructure evolution of grouting materials and its influence mechanism on macroscopic mechanics were revealed. The results show that the crystal structures of hydration products AFt, Ca(OH)2 and C-A-H regulate the development of mechanical strength of materials. The uniaxial compressive strength of rich-watered grouting materials can reach 3.5–5.6 MPa and the residual strength is greater than 3 MPa in the range of rich-watered ratio of 0.9–1.3. The new rich-watered grouting material developed has significant plastic deformation characteristics under high rich-watered ratio conditions, which can greatly adapt to borehole deformation and reduce the gap width of slurry-coal interface, and can meet the technical requirements of long-term sealing of gas extraction boreholes.

Spin-torque generation using a compositional gradient at the interface between titanium and tungsten thin films

We experimentally demonstrate spin-torque generation using a compositional gradient at the interface between titanium and tungsten thin films. The width of the compositional gradient interface (CGI) between films is varied from 1.4 to 2.0 nm via sputtering. Spin-torque ferromagnetic resonance is observed in the ferromagnetic ${\mathrm{Ni}}_{95}{\mathrm{Cu}}_{5}$ alloy fabricated on a Ti/W bilayer with the CGI. The positive spin torque increases with decreasing CGI width, but a negative spin torque is superimposed owing to the negative spin Hall effect in bulk tungsten. A structural undulation in the CGI eliminates this variation in positive spin torque. The CGI width dependence of the spin torque is associated with the generation of spin and/or orbital angular momentum flow at the CGI. Spin-torque generation using a CGI expands the range of material choice for magnetic nonvolatile memory applications.

Particle-based mesoscopic model for phase separation in a binary fluid mixture.

A mesoscopic simulation model to study the phase separation in a binary fluid mixture in three dimensions (3D) is presented here by augmenting the existing particle-based multiparticle collision dynamics (MPCD) algorithm. The approach describes the nonideal equationof the fluid state by incorporating the excluded-volume interaction between the two components within the framework of stochastic collision, which depends on the local fluid composition and velocity. Calculating the nonideal contribution to the pressure both from simulation and analytics shows the model to be thermodynamically consistent. A phase diagram to explore the range of parameters that give rise to phase separation in the model is investigated. The interfacial width and phase growth obtained from the model agree with the literature for a wide range of temperatures and parameters.

Morphology control in Ni/Ti multilayer neutron mirrors by ion-assisted interface engineering and B4C incorporation

The optical contrast and minimum layer thickness of Ni/Ti broadband neutron multilayer supermirrors is usually hampered by an interface width, typically 0.7 nm, caused by nanocrystallites, interdiffusion, and/or intermixing. We explore the elimination of nanocrystallites in combination with interface smoothening by modulation of ion assistance during magnetron sputter deposition of 0.8 to 6.4 nm thick Ni and Ti layers. The amorphization is achieved through incorporation of natural B4C where B and C preferably bond to Ti. A two-stage substrate bias was applied to each layer; -30 V for the initial 1 nm followed by -100 V for the remaining part, generating multilayer mirrors with interface widths of 0.40-0.45 nm. The results predict that high performance supermirrors with m-values as high as 10 are feasible by using 11B isotope-enriched B4C combined with temporal control of the ion assistance.

Atomistic-informed kinetic phase-field modeling of non-equilibrium crystal growth during rapid solidification

A novel method based on molecular dynamics (MD) is developed to make the kinetic phase-field (PF) model quantitative in predicting non-equilibrium crystal growth during rapid solidification. MD-calculated variations of the diffuse solid-liquid (SL) interface width versus interface velocity are used to parameterize the kinetic PF model. Two approaches are adopted to study temperature independent and temperature dependent interfacial properties on the accuracy of predictions. MD simulations of slow and rapid solidification regimes for an fcc metal (Ni) show that the SL interface width decreases by increasing the solidification velocity. Fitting the dynamic response of the interface width to the traveling wave solution of hyperbolic PF equation determines the target SL interfacial properties, namely propagation velocity and diffusion coefficient. Independently, the MD calculations of nonlinearity in velocity versus undercooling is used to validate the atomistic-informed kinetic PF model. Both parabolic and kinetic PF models parameterized by temperature-independent material properties can accurately simulate the linear portion of near-equilibrium crystal growth during solidification. However, they both fail to predict the crystal growth kinetics during rapid solidification. The kinetic PF model parameterized with the temperature-dependent SL interfacial properties can accurately predict both the equilibrium and non-equilibrium crystal growth during slow and rapid solidification. MD simulation results on Ni along with some analytical analysis on the variation of interface width versus interface velocity show that for fcc metals, in general, {110} interface has a smaller propagation velocity in comparison to {100} interface, resulting in a larger non-linear behavior at smaller undercooling.

Mechanical theory of nonequilibrium coexistence and motility-induced phase separation

Nonequilibrium phase transitions are routinely observed in both natural and synthetic systems. The ubiquity of these transitions highlights the conspicuous absence of a general theory of phase coexistence that is broadly applicable to both nonequilibrium and equilibrium systems. Here, we present a general mechanical theory for phase separation rooted in ideas explored nearly a half-century ago in the study of inhomogeneous fluids. The core idea is that the mechanical forces within the interface separating two coexisting phases uniquely determine coexistence criteria, regardless of whether a system is in equilibrium or not. We demonstrate the power and utility of this theory by applying it to active Brownian particles, predicting a quantitative phase diagram for motility-induced phase separation in both two and three dimensions. This formulation additionally allows for the prediction of novel interfacial phenomena, such as an increasing interface width while moving deeper into the two-phase region, a uniquely nonequilibrium effect confirmed by computer simulations. The self-consistent determination of bulk phase behavior and interfacial phenomena offered by this mechanical perspective provide a concrete path forward toward a general theory for nonequilibrium phase transitions.

Diffuse-Interface Blended Method for Imposing Physical Boundaries in Two-Fluid Flows.

Multiphase flows are commonly found in chemical engineering processes such as distillation columns, bubble columns, fluidized beds and heat exchangers. The physical boundaries of domains in numerical simulations of multiphase flows are generally defined by a conformal unstructured mesh which, depending on the complexity of the physical system, results in time-consuming mesh generation which frequently requires user-intervention. Furthermore, the resulting conformal unstructured mesh could potentially contain a large number of skewed elements, which is undesirable for numerical stability and accuracy. The diffuse-interface approach allows for the use of a simple structured meshes to be used while still capturing the desired physical (e.g., solid-fluid) boundaries. In this work, a novel diffuse-interface method for the imposition of physical boundaries is developed for the incompressible two-fluid multiphase flow model. This model is appropriate for dispersed multiphase flows which are pervasive in chemical engineering processes, in that this flow regime results in high levels of mass and energy transfer between phases. A diffuse interface is used to define the physical boundaries and boundary conditions are imposed by blending the conservation equations from the two-fluid model with that of the nondeformable solid. The results from the diffuse-interface method are compared with results from a conformal unstructured mesh for different interface functions and widths. For small interface widths, the accuracy of the flow profile is unaffected by the choice of interface function and the phase fraction distribution and flow behavior are within 3% compared to those from a conformal mesh. As the interface width increases, the diffuse-interface solution deviates from the conformal mesh solution in both the localized gas fraction and the overall gas hold-up, resulting in a difference up to 30%. In the case of flow past a cylinder, where the solid interacts with the flow, the presence of the diffuse interface extends the thickness of the solid boundary and results in a deviation from the conformal mesh solution as time increases.

Robust a posteriori estimates for the stochastic Cahn-Hilliard equation

We derive a posteriori error estimates for a fully discrete finite element approximation of the stochastic Cahn-Hilliard equation. The a posteriori bound is obtained by a splitting of the equation into a linear stochastic partial differential equation and a nonlinear random partial differential equation. The resulting estimate is robust with respect to the interfacial width parameter and is computable since it involves the discrete principal eigenvalue of a linearized (stochastic) Cahn-Hilliard operator. Furthermore, the estimate is robust with respect to topological changes as well as the intensity of the stochastic noise. We provide numerical simulations to demonstrate the practicability of the proposed adaptive algorithm.

Fracture behaviour of Zr(Fe,Cr)2 Laves phase precipitates in Zircaloy-4 subjected to β forging

Fractured C14 (hexagonal close-packed) Laves phase Zr(Fe,Cr)2 precipitates were found in β forged Zircaloy-4. Transmission electron microscopy observations showed that the precipitates were initially a single entity and, during hot forging, underwent fracture along the planes where Peierls stress possibly exceeded fracture stress. Narrow interfacial width of a few nanometres and small misorientation angle in case of each fractured precipitate also implied that the precipitate retained brittle nature at high temperature. The fracture mainly occurred along the c-axes of Laves phase precipitates.

Interfacial properties of square-well chains from molecular dynamics simulation

ABSTRACT Square-well (SW) potential is likely the simplest potential describing attractive and repulsive interactions. However, its discontinuous functional form makes it difficult to be used in Molecular Dynamics (MD) simulation, particularly with commercial MD packages. Recently, Zerón and collaborators [Mol. Phys. 116, 3355 (2018)] have presented a parameterisation of the SW potential that allows its use for simulation packages since the intermolecular potential and force are described by continuous mathematical functions. It was validated for SW spheres. In this work, we use this reported continuous SW potential to describe for the first time the equilibrium and interfacial properties of SW chains, with potential ranges of and 1.75. Simulations for tetramers interacting with are compared with available computational data in the literature, which has allowed to validate the method for molecular chain systems. Besides, a systematic study for the potential range of has not been addressed so far, which represents valuable information for instance to discern whether different microscopic theories are capable of describing this type of system. In particular, we assess the effect of temperature, chain length, and potential range on the calculated properties, namely density profiles, coexistence densities, vapour pressures, surface tensions and critical points. Overall, with increasing the chain length, the width of the envelope of the coexistence phase increases, which results in an increase of the surface tension as well as the critical temperature at the same time that the vapour pressure and the interfacial width decrease.

A quantitative variational phase field framework

The finite solid–liquid interface width in phase field models results in non-equilibrium effects, including solute trapping. Prior phase field modeling has shown that this extra degree of freedom, when compared to sharp-interface models, results in solute trapping that is well captured when realistic parameters, such as interface width, are employed. However, increasing the interface width, which is desirable for computational reasons, leads to artificially enhanced trapping thus making it difficult to model departure from equilibrium quantitatively. In the present work, we develop a variational phase field model that guarantees a temporal decrease in the free energy with independent kinetic equations for the solid and liquid phases. Separate kinetic equations for the phase concentrations obviate the assumption of point wise equality of diffusion potentials, as is done in previous works. Non-equilibrium effects such as solute trapping, drag and interface kinetics can be introduced in a controlled manner in the present model. In addition, the model parameters can be tuned to obtain “experimentally-relevant” trapping while using significantly larger interface widths than prior efforts. A comparison with these other phase field models suggests that interface width of about three to twenty-five times larger than current best-in-class models can be employed depending upon the material system at hand leading to a speed-up by a factor of W(d+2), where W and d denote the interface width and spatial dimension, respectively. Finally the capacity to model non-equilibrium phenomena is demonstrated by simulating oscillatory instability leading to the formation of solute bands.

Study of the peritectic phase transformation kinetics with elastic effect in the Fe–C system by quantitative phase-field modeling

A quantitative phase-field model developed for two-phase growth process (Folch and Plapp, 2005) is applied to the simulation of peritectic phase transformation in a Fe–C binary alloy system with elastic effects due to the misfit on the solid/solid interface. The model includes the anti-trapping current, elastic effect, and the quantitative model parameters estimated based on the thin-interface limit. The diffusion of carbon in the solid phases (i.e. δ and γ phases) has not been neglected and an appropriate free-energy functional has been developed such that there is no presence of any extra phase in the interface. The model’s behavior over a wide range of interface width has been studied and the effect of anti-trapping current and elastic effect on the phase transformation has been closely analyzed.

Synthesis and characterization of 11B4C containing Ni/Ti multilayers using combined neutron and X-ray reflectometry

The performance of multilayers in optical components, such as those used in neutron scattering instruments, is crucially dependent on the achievable interface width. We have shown how the interface width of Ni/Ti multilayers can be improved using the incorporation of B4C to inhibit the formation of nanocrystals and limit interdiffusion and intermetallic reactions at the interfaces. A modulated ion-assistance scheme was used to prevent intermixing and roughness accumulation throughout the layer stack. In this work we investigate the incorporation of low-neutron-absorbing 11B4C for Ni/Ti neutron multilayers. Combined fitting of neutron reflectivity and X-ray reflectivity measurements shows an elimination of accumulated roughness for the 11B4C containing multilayers with a mean interface width of 4.5 Å, resulting in an increase in reflectivity at the first Bragg peak by a factor of 2.3 and 1.5 for neutron and X-ray measurements, respectively.