Interface Roughness Research Articles

A new method for characterizing the atomic composition distribution and interface structure of ultrathin multilayer films using molecular dynamics simulation assisted ARXPS

Characterizing ultrathin multilayer films' atom distribution and interface structure remains challenging. This paper innovatively characterized the chemical composition and distribution of Pt/Co/W ultrathin multilayer films by ARXPS. Molecular dynamics simulated the growth process of films to correspond to that in experiment. The results show that through ARXPS, the actual structure of Pt (2 nm)/Co (t = 0.5–3 nm)/W (2 nm) film could be obtained. For Pt (2 nm)/Co (2 nm)/W (2 nm) film, the actual structure was Pt/Co (1.73 nm)/W (0.78 nm)/WO3 + WO2 (1.48 nm). W at the top layer significantly diffused to the bottom layers, and oxidized W reduced from the surface to the interior of multilayer films. Molecular dynamics simulation confirmed that the interdiffusion degree of Co and W atoms was improved with the increase of Co atoms. The growth modes of Co and W layers were respectively layer-by-layer and island. As the number of Co atoms increased, the relative surface roughness of Co and W layers and the relative interface roughness of Co/W were increased. The in-plane magnetic anisotropy and coercivity were respectively enhanced and decreased due to the change in the surface/interface structure. This paper provides a new idea for analyzing ultrathin multilayer films' atom distribution and interface structure.

Magnetic coupling in La2/3Sr1/3MnO3/SrRuO3 heterostructures grown on SrTiO3 (111) substrates with abrupt interface

We report on the magnetic coupling behavior in all-ferromagnetic La0.7Sr0.3MnO3/SrRuO3 (LSMO/SRO) heterostructures deposited on the SrTiO3 (111) substrate, where the interface leads to an enhanced exchange field as compared to the one deposited on SrTiO3 (001). Importantly, high-resolution scanning transmission electron microscopy reveals distinct interface structures of the (111) heterostructures depending on the growth sequence. The heterostructure with an SRO bottom layer shows an atomically flat and abrupt interface, while the one with an LSMO bottom layer shows a deformed interface due to the surface roughening of LSMO deposited directly on SrTiO3 (111). As a result, the heterostructure with an abrupt interface exhibits a robust antiferromagnetic coupling between LSMO and SRO, while the one with a rough interface shows negligible magnetic coupling. Our results demonstrate the key role of an abrupt interface in determining the magnetic properties of oxide heterostructures.

Experimental study of the shear behavior of concrete-rock interfaces under static and dynamic loading in the context of low confinement stress

Modified static and dynamic shear tests are introduced to study the shear behavior of concrete-rock interfaces under static and dynamic loading in the context of low confinement stresses. Static and dynamic shear tests of concrete-sandstone and concrete-granite interfaces are performed using these techniques. Three levels of interface roughness are considered: smooth, bush-hammered, and rough rock surfaces. The results of these tests show that in both static and dynamic regimes, the shear evolution of concrete-rock interfaces can be described according to three successive stages: the shear stress accumulation, the shear slip, and the residual shear stress stage. The main parameters driving the shear process are the concrete-rock bonds, the interface roughness, and the residual friction. However, unlike in the static shear evolution, in the dynamic shear evolution, the concrete-rock bonds and the roughness seem active in the shear stress accumulation stage. Furthermore, the correlation between the shear strength and the normal stress is stronger in static than dynamic conditions. The significance of the normal stress on the dynamic shear strength appears more important in rough concrete-granite interfaces than in the other two interfaces. Lastly, the dynamic peak shear strengths of all the interfaces tested are three to four times higher than their static counterparts.

Shear rate and roughness effect on clay-steel interface strength properties in CU and CPD drainage conditions

Based on the concept of the preformed failure plane, this paper conducted a series of clay-interface tests using a modified triaxial apparatus that can directly measure the interface pore pressure, to investigate the shear rate and interface roughness effect on the deviator stress, interface excess pore pressure, interface stress path, and interface friction angle in both consolidated undrained (CU) and consolidated partially drained (CPD) interface drainage conditions. In general, the specimen with the clay-steel interface had a lower shear strength than the pure clay specimen under the same testing conditions. In CU tests, the total and effective interface friction angles increase approximately linearly with the shear rate in the semi-logarithmic scale, while in CPD tests, both the total and effective interface friction angles decrease with increasing shear rate. Moreover, the increased surface roughness is found to enhance the interface shear strength and the maximum interface pore pressure at a given shear rate and confining pressure. In CU tests, both the normalized efficiency parameter E and the corresponding interface friction angle increase with the average roughness (Ra) in a logarithmic relationship, but it is difficult to describe the positive correlation perfectly in CPD tests.

Corrosion effects on axial pile capacity

Increase in surface roughness by corrosion processes has long been neglected as potential factor influencing pile setup. However, recently there has been an increasing number of studies who referred pile setups largely or solely to corrosion and sand incrustation. Only limited research has been conducted to assess the potential impacts of corrosion directly on pile capacity development. Therefore, we sampled steel and crust surfaces from a steel monopile having been aged for ∼four years in sand. Surface roughness measurements and interface direct shear testing were performed to quantify changes for friction angles. The impact of friction angle changes on pile capacity were calculated using ICP-05 and UWA-05 for a large- and small-diameter geometry and referenced by field data. We can show that corrosion can significantly contribute to temporal pile capacity gains. Evidence have been found that the maximum and critical interface friction angles evolve differently considering the same changes in roughness. Also, differences in shearing behavior to literature were observed, being potentially a result of the naturally corroded surfaces sheared in our study. A strong, maybe exaggerated sensitivity of the capacity prediction approaches to pile diameter was observed. Effects causing an increase in surface roughness, should be reconsidered as an important factor influencing pile setup.

Effect of Annealing on Stress, Microstructure, and Interfaces of NiV/B4C Multilayers

The functionality and reliability of nanoscale multilayer devices and components are influenced by changes in stress and microstructure throughout fabrication, processing, and operation. NiV/B4C multilayers with a d-spacing of 3 nm were prepared by magnetron sputtering, and two groups of annealing experiments were performed. The stress, microstructure, and interface changes in NiV/B4C after annealing were investigated by grazing-incidence X-ray reflectometry (GIXR), grazing-incidence X-ray diffraction (GIXRD), X-ray diffuse scattering, and grazing-incidence small-angle X-ray scattering (GISAXS). The temperature dependence experiments revealed a gradual shift in the multilayer stress from compression to tension during annealing from 70 °C to 340 °C, with the stress approaching near-zero levels between 70 °C and 140 °C. The time-dependent experiments indicated that most of the stress changes occurred within the initial 10 min, which showed that prolonged annealing was unnecessary. Combining the X-ray diffraction and X-ray scattering measurements, it was found that the changes in the thickness, interface roughness, and lateral correlation length, primarily due to crystallization, drove the changes in stress and microstructure.

Modal characteristics of blade-disk including rough interfaces and geometric deviations

The inaccurate prediction of vibrations in blade-disk structures leads to frequent occurrences of failures in rotating machinery, such as air-engines. Existing methods often empirically treat the contact parameters of interfaces as globally constant and rarely consider manufacturing and assembly deviations, resulting in a deviation of prediction models from reality. This work presents a model for complex assembly structures that includes non-uniform distributions of normal contact stiffness and tangential friction coefficients at rough interfaces, while also introducing experimentally measured geometric deviations to enhance alignment with real-world conditions. Taking fir-tree blade-disk structure as an example, the accuracy of the proposed method is comprehensively verified by four measurement experiments and one modal experiment. Subsequently, the combined influence of rough interfaces and three experimentally measured geometric deviations on the overall modal characteristics of blade-disk structure are investigated, and their influencing mechanisms are revealed. The results indicate that ignoring the interface roughness and geometric deviations may significantly affect the prediction accuracy of the modal characteristics. The proposed method has great potential in the field of predicting the modal characteristics for complex assembly structures and optimizing the design of their machining and assembly processes.

Exploring the impact of AlGaN barrier thickness and temperature on normally-on GaN HEMT performance

We study varying barrier thicknesses in GaN/AlGaN HEMTs as well as the effect of temperature fluctuation on device functionality theoretically. Structures A, B, C, D, and E are designed each with barrier thickness 16 nm, 19 nm, 22 nm, 25 nm, and 28 nm respectively. The impact of barrier thickness on the surface barrier height, strain relaxation and 2DEG concentration is explained including GaN HEMT’s drain and transfer properties. At elevated temperatures, the polar-optical phonon dispersion is the predominant process. Yet, at lower temperatures, the interface-roughness (IFR) and alloy disorder dispersion both satisfactorily account for the calculated mobilities.

Mechanical Milling – Induced Microstructure Changes in Argyrodite LPSCl Solid‐State Electrolyte Critically Affect Electrochemical Stability

AbstractMicrostructure of argyrodite solid‐state electrolyte (SSE) critically affects lithium metal electrodeposition/dissolution. While the stability of unmodified SSE is mediocre, once optimized state‐of‐the‐art electrochemical performance is achieved (symmetric cells, full cells with NMC811) without secondary interlayers or functionalized current collectors. Planetary mechanical milling in wet media (m‐xylene) is employed to alter commercial Li6PS5Cl (LPSCl) powder. Quantitative stereology demonstrates how milling progressively refines grain and pore size/distribution in the SSE compact, increases its density, and geometrically smoothens the SSE‐Li interface. Mechanical indentation demonstrates that these changes lead to reduced site‐to‐site variation in the compact's hardness. Milled microstructures promote uniform early‐stage electrodeposition on foil collectors and stabilize solid electrolyte interphase (SEI) reactivity. Analysis of half‐cells with bilayer electrolytes demonstrates the importance of microstructure directly contacting current collector, with interface roughness due to pore and grain size distribution being key. For the first time, short‐circuiting Li metal dendrite is directly identified, employing 1.5 mm diameter “mini” symmetrical cell and cryogenic focused ion beam (cryo‐FIB) electron microscopy. The branching sheet‐like dendrite traverses intergranularly, filling the interparticle voids and forming an SEI around it. Mesoscale modeling reveals the relationship between Li‐SSE interface morphology and the onset of electrochemical instability, based on underlying reaction current distribution.

Electron mobility enhancement by electric field engineering of AlN/GaN/AlN quantum-well HEMTs on single-crystal AlN substrates

To enhance the electron mobility in quantum-well high-electron-mobility transistors (QW HEMTs), we investigate the transport properties in AlN/GaN/AlN heterostructures on Al-polar single-crystal AlN substrates. Theoretical modeling combined with experiment shows that interface roughness scattering due to high electric field in the quantum well limits mobility. Increasing the width of the quantum well to its relaxed form reduces the internal electric field and scattering, resulting in a binary QW HEMT with a high two-dimensional electron gas (2DEG) density of 3.68×1013 cm–2, a mobility of 823 cm2/Vs, and a record-low room temperature (RT) sheet resistance of 206 Ω/□. Further reduction of the quantum well electric field yields a 2DEG density of 2.53×1013 cm–2 and RT mobility > 1000 cm2/V s. These findings will enable future developments in high-voltage and high-power microwave applications on the ultrawide bandgap AlN substrate platform.

The effect of shear rate and overconsolidation ratios on undrained clay–suction caisson interface behaviors

The interface resistance during installation is crucial for the stability and safety of suction caisson in offshore geotechnical engineering, which is strongly affected by the penetration rate and soil–structure interface mechanical properties. This research conducts a series of clay–structure interface shear tests using modified direct simple shear device to fully study the mechanical behavior of clay–suction caisson interface. The effect of shear rate, over consolidation ratios (OCRs), interface boundary conditions, stress levels, and interface roughness were considered. Results show that as the OCR increases, the strength of both the clay and interface increase but show distinct patterns under constant volume (CV) and constant normal load (CNL) boundary condition. It was found that the interface strength is positively related to interface roughness and shear rate impact both the clay and corresponding interface strength. Under CNL conditions, the strength of normally consolidated (NC) clay decreases with rising shear rate, while the over consolidated (OC) clay demonstrate a opposite trend. In contrast, the effect of shear rate on interface behavior gets complicated owing to the combination of roughness, stress levels, and OCRs. Under CV conditions, the shear strength of clay and interface exhibits a logarithmic growth relationship with shear rates. The result of this work can provide a basis for interface resistance evaluation for suction caisson installation in clay.

Grain boundary, electrical transport and thermoelectric properties of the ultra-high rGO amount of C12A7-rGO composites

The Ca12Al14O33 ceramic (C12A7) and reduced graphene oxide (rGO) composite which an ultra-high amount (i.e., 40, 50, 60, and 70 wt%) of rGO (ultra-high amount C12A7/rGO composite) were synthesized by a solid-state reaction process. After the hydraulic press, the heat treatment in the temperature range of 773 K under the argon environment had been performed with the composite pellets for 30 min. XRD results of the C12A7 and all the ultra-high amount C12A7/rGO composites indicated a pure phase of C12A7 ceramic. Raman spectra confirmed the existence of rGO content in all the ultra-high amount C12A7/rGO composites. Raman peaks also suggested reduction of the free O22− and O2− ions from the framework of the ultra-high amount C12A7/rGO composites. SEM image presented the homogeneous grain boundary interface after the heat treatment at 773 K of the C12A7 wrapped by the rGO sheet, the agglomerated rGO sheet, and the rough interface stack of rGO sheets. UV-VIS spectroscopy presented the absorption behavior, direct energy gap, and indirect energy gap modifications of the ultra-high amount C12A7/rGO composites. Electrical conductivity of the ultra-high amount C12A7/rGO composites illustrated larger than 108 times improvement with temperature independence. Range of −5 to −17 μV/K , temperature dependence, and increased with rGO content increasing Seebeck coefficient were reported. Thermal conductivity of the ultra-high amount C12A7/rGO composites was increased with the rGO content increasing. Both the Power factor (PF) and the figure of merit (ZT) of the ultra-high amount C12A7/rGO composites were temperature dependent and were increased with the rGO content increasing, within the range of 0.4 μW/m.K2 of PF and the range of 3x10−4 of ZT, respectively. These experimental results verified grain boundary, modified energy band, electrical transport properties and thermoelectric properties of C12A7/rGO composites loading with ultra-high content rGO

The effect of energy of Ar recoil particles on the interfaces and micro-structure in Ni/Ti multilayer fabricated by direct current magnetron sputtering technique

Ni/Ti multilayers have been therefore widely used in neutron optics devices because of their excellent reflective properties for neutrons, which is strongly dependent to their interfaces and microstructure. Hence, there have been many attempts to improve the interfaces and microstructure of Ni/Ti multilayers, for example reactive sputtering, interlayers and so on. In this paper, the influence of energy of Ar recoil particles on the interface and micro-structure of Ni/Ti multilayers were completed, through varying the sputtering pressure. Firstly, the Simulation present that the decreasing of sputtering pressure would enlarge the number recoil particle proportion. Secondly, three Ni/Ti multilayers were fabricated by direct current sputtering technique with variable sputtering pressures (0.080Pa, 0.120Pa, 0.199Pa). Thirdly, the grazing incidence X-ray reflectometry (GIXRR), diffusing scattering, X-Ray Diffraction (XRD), Transmission Electron Microscope (TEM) were used to characterize the interfaces and micro-structure of these films. The measured results present that their interfacial width and roughness were variable as diseasing the sputtering pressure, and the micro-structure of Ni layers transform from (111) only to both (111) and (100). These experimental results could result from the effects of energy of both Ar recoil particles and the Ni, Ti depositing atoms.

Flexural performance of UHPC-filled narrow joints between precast concrete bridge slabs

The deck slabs narrow joints in concrete bridges filled with Ultra-high performance concrete (UHPC) have the potential for wide application and high-efficiency promotion, but there is limited research available on this topic. This paper conducted flexural tests on the new joints. Ten precast concrete deck panels were designed and manufactured for concrete bridges. These panels were connected using UHPC-filled narrow joints. Combined with stress analysis, this study investigates the influence and mechanism of various factors on the mechanical performance of UHPC joints. These factors include the geometric shape of the joint, the roughness of the joint interface, the filling material used in the joint, the width of the joint, and the configuration of joint reinforcement (including the shape and length of lap reinforcement). The test results show that the panel with the UHPC joint filled with steel fibers has excellent flexural and bonding capacity. The jointed panel with a lap length of 140 mm and 120 mm has better flexural performance than the one with a lap length of 90 mm. The straight-jointed panel has a higher flexural capacity compared to the complex triangular-jointed panel. Additionally, reducing the joint width can achieve similar mechanical properties as before. A method has been proposed for calculating the flexural capacity of a jointed panel, utilizing the strut-and-tie model (STM). This method can accurately predict experimental results.

Investigation of stress-wave-induced crack penetration behavior at the rock-Ultra-High-Performance Concrete (UHPC) interface

The propagation behaviour of initial cracks in concrete penetrating the rock-concrete interface is still unclear. This study investigated the behaviour of stress wave-induced crack penetration through the Ultra-High-Performance Concrete (UHPC)-granite interface and crack propagation speed (CPS) using a combination of the crack propagation gauge (CPG) system and a split Hopkinson pressure bar. The influence of loading rate and UHPC strength grade on the dynamic fracture toughness of the penetration crack entire process was analyzed by experimental–numerical method. The results indicate that the Rock-UHPC interface can suppress the crack opening displacement in UHPC, thereby limiting the CPS. The loading rate significantly enhances the dynamic fracture toughness of the penetration crack's entire process. The interface is the boundary point, and the dynamic fracture toughness at the crack tip shows a trend of first increasing and then decreasing. The increase in concrete strength grade can improve the interface dynamic fracture toughness. Compared to the interface roughness, the enhancement effect of concrete grade on the interface dynamic fracture toughness is one order of magnitude higher. For concrete engineering on rock foundations, increasing the concrete strength grade can effectively prevent the inherent crack defects inside the concrete from expanding into the interior of the rock foundation.

PEMFC sealing modeling relating to fractal characteristics of gasket-BPP interface based on micro-contact

The interface leaking of the gasket-BPP sealing structure affects the efficiency, safety, and reliability of PEMFCs. Aiming to reveal the basic cause of interface leaking and predict the leakage rate, the contact behavior at the micro-scale had been researched by FEM with the fractal multi-scale method, which could eliminate the negative influence of a single observation scale on the gasket-BPP rough interface modeling. Furthermore, in order to relate the contacting behavior at the micro-scale to the leakage rate at the macro-scale of PEMFCs, the mapping model had been established to analyze the sealing performance of the entire interface through the self-affine and self-similar characteristics of the fractal multi-scale contacting model of the gasket-BPP. Not only macroscopic properties of gasket rubber materials are considered in this model, but also microscopic morphologies are taken in to investigate the interface leakage rate, which had not been studied in traditional macroscopic research. By comparing the compression curves and interface leakage rates of the flange sealing device in testing and calculating approaches, the accuracy and reliability of the mapping model had been verified, leading to the analysis and the prediction of the PEMFC interface leakage rate rapidly.

Interface Shear Failure Behavior Between Normal Concrete (NC) and Ultra-High Performance Concrete (UHPC)

Ultra-high performance concrete (UHPC) with excellent mechanical properties and durability is a promising material for reinforcement of existing normal concrete (NC) structures. In this paper, the shear failure behavior of the NC–UHPC interface was studied by the slant shear test and the SEM (scanning electron microscope) visualization test, considering influence of the substrate strength and the interface roughed treatment. As the NC substrate and the UHPC overlay are tightly combined at the interface transition zone (ITZ), the interface exhibits good slant shear performance, and the measured interfacial shear strength could reach 19.4 MPa with C40 substrate and 21.8 MPa with C50 substrate. In addition, the microstructure and composition of the ITZ, the possible interfacial failure modes, and the load-carrying mechanism of the interface under compression–shear force are revealed. The high interface roughness and the substrate strength have positive influence on the shear strength, and greatly affect the prone failure mode and the load-slip characteristic.

Bioinspired thermo-responsive membrane with hybrid micro/nanostructure for water gating and emulsion separation

Smart membranes with tunable wettability hold great promise for controllably oil/water mixtures separations, including oil-water mixtures and surfactant stability oil/water emulsions. Herein, a thermo-responsive membrane with bioinspired hybrid micro/nanostructure was constructed on commercial PVDF membrane, which exhibits excellent thermo-responsive performance and antifouling ability. In this process, the thermo-responsive polymer graft to membrane surface via thiol-ene click reaction, preserve the high interfacial roughness and excellent switching wettability between hydrophilicity/underwater oleophobicity at 25 °C and hydrophobicity at 50 °C. The membrane can be applied in various surfactant stability oil-in-water emulsions and water-in-oil emulsions, demonstrating high separation efficiency, recyclability for various kinds of emulsions. The hybrid micro/nanostructures render the membrane with excellent antifouling performance. The membranes show good potentials for smart liquid separation such as on-demand oil-spill cleanup, remote controllable operation of oil/water emulsion separation device.

Combined resonant tunneling and rate equation modeling of terahertz quantum cascade lasers

Terahertz (THz) quantum cascade lasers (QCLs) are technologically important laser sources for the THz range but are complex to model. An efficient extended rate equation model is developed here by incorporating the resonant tunneling mechanism from the density matrix formalism, which permits to simulate THz QCLs with thick carrier injection barriers within the semi-classical formalism. A self-consistent solution is obtained by iteratively solving the Schrödinger–Poisson equation with this transport model. Carrier–light coupling is also included to simulate the current behavior arising from stimulated emission. As a quasi-ab initio model, intermediate parameters, such as pure dephasing time and optical linewidth, are dynamically calculated in the convergence process, and the only fitting parameters are the interface roughness correlation length and height. Good agreement has been achieved by comparing the simulation results of various designs with experiments, and other models such as density matrix Monte Carlo and non-equilibrium Green's function method that, unlike here, require important computational resources. The accuracy, compatibility, and computational efficiency of our model enable many application scenarios, such as design optimization and quantitative insights into THz QCLs. Finally, the source code of the model is also provided in the supplementary material of this article for readers to repeat the results presented here, investigate, and optimize new designs.

Improved mesh stiffness model of spur gear considering spalling defect influenced by surface roughness under EHL condition

Gear tooth spalling is a typical tooth surface defects in gear transmission. The accurate calculation of the time-varying mesh stiffness of the gear pair with spalling defect under mixed elastohydrodynamic lubrication (EHL) plays an important role in tooth damage prediction and fault feature analysis. In this work, an improved time-varying mesh stiffness (TVMS) model of spalling faulty gear in mixed EHL line contact considering the coupled effect of rough surface topography is established. The proposed model considers the combined effect of spalling defect, surface roughness topography, and lubrication on the contact characteristics of the meshing interface to obtain a revised contact stiffness, which is further used to determine the comprehensive TVMS. The cylindrical contact coefficient for curved meshing interface with spalling fault is derived and incorporated into the statistical micro-contact Greenwood and Williamson model (GW model) to obtain the asperity contact stiffness. The revised contact stiffness at the rough faulty gear interface is obtained from the parallel action of the asperity contact stiffness and oil film stiffness under load-sharing concept. The dynamic responses of the gear system are analyzed using the established mesh stiffness model through the six degrees of freedom translational-torsional dynamic model, in which the dynamic meshing force is calculated iteratively using the transit surface topography and geometrical parameters along the line of contact instead of a quasi-static meshing force. Effects of multi-parameters as surface roughness, spalling fault size, and lubricant on the mesh characteristics and dynamic responses of the gear system are further investigated and discussed.