Interfacial Adhesion Energy Research Articles

Adhesion Properties of Thin Film Multilayers: Comparison of Nanoindentation and Four-Point-Bending Techniques

In this study, we investigated the adhesion strength of SiO2/SiN/TiW/Cu film stacks on silicon by the use of cross-sectional nanoindentation (CSN) technique. The delamination occurred along the SiN/TiW interface as determined by means of SEM and EDX analysis. The critical energy release rate was determined as a quantitative measure of the adhesion strength by application of analytical models as well as Finite Element Method (FEM). Comparative measurements on samples of the same layer composition using the well-established four-point bending (4PB) technique were performed to validate the results of the CSN measurements. FEM was performed to calculate the loading conditions and stress distribution in the samples. The calculations also allowed separating the contribution of plastic and elastic energy in the metallization layers during delamination testing and thereby estimating the value of the interfacial adhesion energy. The experimental results show the good applicability of both the 4PB and CSN method for determining quantitative values of the fracture toughness of thin-film interfaces found in microelectronic components and indicate a good agreement between the two methods.

Edge effect and interface confinement modulated strain distribution and interface adhesion energy in graphene/Si system

In order to clarify the edge and interface effect on the adhesion energy between graphene (Gr) and its substrate, a theoretical model is proposed to study the interaction and strain distribution of Gr/Si system in terms of continuum medium mechanics and nanothermodynamics. We find that the interface separation and adhesion energy are determined by the thickness of Gr and substrate. The disturbed interaction and redistributed strain in the Gr/Si system induced by the effect of surface and interface can make the interface adhesion energy decrease with increasing thickness of Gr and diminishing thickness of Si. Moreover, our results show that the smaller area of Gr is more likely to adhere to the substrate since the edge effect improves the active energy and strain energy. Our predictions can be expected to be a guide for designing high performance of Gr-based electronic devices.

Effects of Ar/N 2 Two-step Plasma Treatment on the Quantitative Interfacial Adhesion Energy of Low-Temperature Cu-Cu Bonding Interface

Effects of Ar/N 2 Two-step Plasma Treatment on the Quantitative Interfacial Adhesion Energy of Low-Temperature Cu-Cu Bonding Interface

In situ SEM observation and interface adhesion strength analysis of a serpentine interconnect on a flexible electronic composite film

The buckling deformation of a serpentine interconnect on a flexible electronic composite film is analyzed by a scanning electron microscope miniature tensile stage in situ observation workstation. The buckle formed at the junction of the interconnect pattern under a tensile load is observed. Combined with the buckle size and a theoretical model, the interface adhesion energy and shear stress are derived. The relationship between thickness of the interconnect Cu layer and interface performance is further analyzed. Results show that within the thickness range of 25–500 nm, a 75 nm thick serpentine interconnect has the best adhesion performance on a flexible substrate (about 10.09 J m–2).

A study on the interfacial adhesion energy between capping layer and dielectric for cu interconnects

Recently, Cu interconnect and low-k materials have been applied to reduce the interconnect resistive-capacitive delay issue. However, as the process node size is reduced to a few nanometers, high leakage currents appear through the dielectric under high electric fields. Therefore, issues of Cu diffusion at the interface between the dielectric and the capping layer have been reported. This study investigated interfacial adhesion energy change at the film level between dielectric (low-k, tetraethyl orthosilicate (TEOS)) and capping layer (SiCN, SiN) taking into account the correlation between interfacial adhesion energy and interconnect reliability. In the capping layer/low-k interface, when low-k is applied to the top layer, it shows high interfacial adhesion energy (> 34.31 ± 3.49 J/m2) due to the presence of an O-rich thin layer. But when low-k is applied to the bottom layer, due to the SiC bond, it shows low interfacial adhesion energy (< 5.60 ± 2.46 J/m2). The interface between TEOS and SiN has high interfacial adhesion energy (> 32.54 ± 1.97 J/m2) regardless of the stacking order and CMP process. It clearly shows that low-k dielectrics will affect the deterioration of the interfacial adhesion energy and O-rich layer will greatly improve the interfacial adhesion energy in dielectric/capping layers.

Direct measurements of interfacial adhesion in 2D materials and van der Waals heterostructures in ambient air

Interfacial adhesion energy is a fundamental property of two-dimensional (2D) layered materials and van der Waals heterostructures due to their intrinsic ultrahigh surface to volume ratio, making adhesion forces very strong in many processes related to fabrication, integration and performance of devices incorporating 2D crystals. However, direct quantitative characterization of adhesion behavior of fresh and aged homo/heterointerfaces at nanoscale has remained elusive. Here, we use an atomic force microscopy technique to report precise adhesion measurements in ambient air through well-defined interactions of tip-attached 2D crystal nanomesas with 2D crystal and SiOx substrates. We quantify how different levels of short-range dispersive and long-range electrostatic interactions respond to airborne contaminants and humidity upon thermal annealing. We show that a simple but very effective precooling treatment can protect 2D crystal substrates against the airborne contaminants and thus boost the adhesion level at the interface of similar and dissimilar van der Waals heterostructures. Our combined experimental and computational analysis also reveals a distinctive interfacial behavior in transition metal dichalcogenides and graphite/SiOx heterostructures beyond the widely accepted van der Waals interaction.

Layer-dependent interface adhesion energy of graphene in a curved substrate

In order to clarify the interface adhesion properties between graphene (Gr) membrane and curved substrate, we investigate three kinds of systems, including Gr/Si nanowire, Gr/Si nanotube and Gr/silicene in terms of continuum medium mechanics and nanothermodynamics. We find that the interface adhesion energy is determined by the thickness of the Gr and curvature of the substrate. The coupling role of the surface effect and interface confinement affects the strain energy and induces the strain redistribution in the Gr and curved substrate, resulting in the interface adhesion energy increasing with diminishing thickness of Gr and increasing curvature of the substrate. Our findings can be expected to be applied to the design of Gr-based electronic devices.

Investigation of zero-degree peeling behavior of visco-hyperelastic highly stretchable adhesive tape on rigid substrate

The zero-degree peeling behavior of the highly stretchable adhesive tape on a rigid substrate was investigated. To explicitly consider the influences from the viscoelasticity, hyperelasticity and visco-hyperelasticity of the tape on the peeling performance, the analytical formulae were proposed based on a simple and effective energy approach. Assuming the interface adhesion energy to be constant, the debonding phase diagram was established accordingly and then experimentally validated. It was found that, (1) the instant peeling force of viscoelastic tape can be greatly improved through a rate-dependent coefficient from the tape’s viscoelasticity; (2) the Neo-Hookean type of hyperelasticity significantly enhances the interfacial stability; (3) despite delivering decent instant peeling force and interfacial stability, the visco-hyperelasticity of the bulk tape may bring great risk of delayed debonding if the tape is subjected to a constant stretching force. The guidance to help the innovative designs of the visco-hyperelastic tape bonding system were also discussed.

Investigation of the Effects of Adsorbed Water on Adhesion Energy and Nanostructure of Asphalt and Aggregate Surfaces Based on Molecular Dynamics Simulation.

The purpose of this study was to investigate the effect of aggregate surface adsorbed water on the adhesive capacity and nanostructure of asphalt-aggregate interfaces at the atomic scale. Molecular dynamics (MD) simulation was performed to measure and analyze the molecular interactions of asphalt binder with calcite and silica. Radial distribution function (RDF) and relative concentration (RC) were applied to characterizing the concentrations and distributions of asphalt components on aggregate surfaces. In addition, debonding energy and adhesion energy were employed to calculate the variations of interface adhesion energy of the asphalt-aggregate system under different conditions. The obtained results illustrated that the water molecules adsorbed onto the surface of weakly alkaline aggregates inhibited the concentration and distribution of asphalt components near the aggregate surface, decreased adhesion energy between asphalt and aggregates, and changed asphalt nanostructure. Especially, when external free water intruded into the interface of the asphalt-calcite system, the adsorbed water interacted with free water and seriously declined the water damage resistance of the asphalt mixture with limestone as an aggregate and decreased the durability of the mixtures. The water adsorbed onto the surface of the acid aggregate negatively affected the asphalt-silica interface system and slightly reduced the water damage resistance of the asphalt mixture.

Humidity effect on peeling of monolayer graphene and hexagonal boron nitride

Ambient humidity introduces water adsorption and intercalation at the surfaces and interfaces of low-dimensional materials. Our extensive molecular dynamics (MD) simulations reveal the completely opposite contributions of interfacial water to the peeling of monolayer graphene and hexagonal boron nitride (h-BN) sheets from graphite and BN substrates. For graphene, interfacial water decreases the peeling force, due to lower adhesion at the graphene/water interface. The peeling force of h-BN increases with an increase in the thickness of interfacial water, owing to stronger adhesion at the h-BN/water interface and the detachment of the water layer from the substrates. In this work, a theoretical model considering graphene/water and water/substrate interfacial adhesion energies is established, to predict the peeling forces of graphene and h-BN, which coincides well with the peeling forces predicted by the MD simulations. Our results should provide a deeper insight into the effect of interfacial water, induced by ambient humidity, on mechanical exfoliation and the transfer of two-dimensional van der Waals crystals.

The spatially oriented redistribute of photogenerated carriers and photocatalytic hydrogen evolution mechanism research on polymeric carbon nitride Van der Waals homojunction

The weaker interlayer Van der Waals force of polymeric carbon nitride (PCN) increases the potential barrier of electron transfer between layers, which greatly inhibits the carrier separation efficiency of PCN. Herein, we designed and prepared Van der Waals homojunction of PCN (VHPCN), which the interlayer Van der Waals force forces were instead by Coulomb force. DFT calculated reveals that the equilibrium distance and the interface adhesion energy of VHPCN were significantly decreased and enhanced, respectively, under the function of Coulomb force. The equilibrium distance decreased from 3.27 Å to 2.49 Å and the interface adhesion energy enhanced from −0.35 eV to −1.78 eV. This structure not only the transfer distance of electrons at the interface is effectively decreased, but also the transfer barrier of electrons at the interface is reduced. Thus, the electrons/holes pairs in the VHPCN photocatalyst present the phenomenon of oriented interlayer transfer and ultrahigh carrier separation efficiency under the synergistic effect between the built-in electric field and the interlayer Coulomb force of the Van der Waals homojunction. The optimal VHPCN exhibited the photocatalytic H2 evolution rate and apparent quantum yield (AQY), which are 7.9 mmol·g−1·h−1 and 32.4% (>420 nm), respectively. This work put forward a promising strategy to construct novel Van der Waals homojunction within 2D materials for the desirable photogeneration carrier spatially distribution controlling, which could be generalized to other 2D materials for photocatalytic applications in the advanced energy and environmental field.

Well-Adhered Copper Nanocubes on Electrospun Polymeric Fibers.

Electrospun polymer fibers can be used as templates for the stabilization of metallic nanostructures, but metallic species and polymer macromolecules generally exhibit weak interfacial adhesion. We have investigated the adhesion of model copper nanocubes on chemically treated aligned electrospun polyacrylonitrile (PAN) fibers based on the introduction of interfacial shear strains through mechanical deformation. The composite structures were subjected to distinct macroscopic tensile strain levels of 7%, 11%, and 14%. The fibers exhibited peculiar deformation behaviors that underscored their disparate strain transfer mechanisms depending on fiber size; nanofibers exhibited multiple necking phenomena, while microfiber deformation proceeded through localized dilatation that resulted in craze (and microcrack) formation. The copper nanocubes exhibited strong adhesion on both fibrous structures at all strain levels tested. Raman spectroscopy suggests chemisorption as the main adhesion mechanism. The interfacial adhesion energy of Cu on these treated PAN nanofibers was estimated using the Gibbs–Wulff–Kaischew shape theory giving a first order approximation of about 1 J/m2. A lower bound for the system’s adhesion strength, based on limited measurements of interfacial separation between PAN and Cu using mechanically applied strain, is 0.48 J/m2.

A theoretical study on three long-range interactions between two nanoparticles under the humid condition

At the micro/nanoscale under the humid condition, the competition among three long-range interactions of the electrostatic, cohesive, and capillary forces dominates the adhesive behavior between two nanoparticles. In this study, explicit solutions of the interfacial adhesive energy between two nanoparticles are obtained through continuum modeling by considering the three long-range interactions between them, where the Coulomb theorem, the Lennard–Jones potential, and the Young–Laplace equation are taken into consideration. The present theoretical results show that the interfacial adhesive forces strongly depend on the three interactions, where the cohesive force and capillary force play more important roles in the competition for a smaller distance h between two nanoparticles, while the electrostatic force dominates the interactions for a larger distance h. Checking against present molecular dynamics simulations shows that the present continuum solution has high accuracy. This study should be of great help for deeply understanding the aggregation and separation of nanoparticles under the humid condition.

Insights into the interfacial strengthening mechanism of waste rubber/cement paste using polyvinyl alcohol: Experimental and molecular dynamics study

Recycling of waste rubber into concrete is one of the most efficacious and environmentally-friendly methods to solve the so-called black pollution. However, the incorporation of waste rubber particles reduces the mechanical properties of concrete, resulting from the low stiffness of the rubber particles as well as the insufficient adhesion energy between waste rubber and hardened cement paste. To solve the latter issue, an innovative surface treatment method for hydrophilicity improvement of waste rubber using polyvinyl alcohol (PVA) is proposed in this paper. The interfacial strengthening mechanism of waste rubber/cement paste using PVA is systematically studied from the aspects of macro-scopic mechanical properties, micro-structure characteristics and molecular-scale modifications. The addition of 0.1% PVA solution can significantly enhance the compressive and flexural strength of rubber-cement composites by 7–14% and 20–38% at the age of 28 days, respectively. SEM observation and EDS results verify the bridging effect of PVA at the waste rubber/cement paste interface, which eliminates the gap caused by the hydrophobicity of rubber. The molecular dynamics simulation shows that the interfacial adhesion energy between rubber hydrocarbon (RH) and PVA is 52% higher than that between RH and calcium-silicate-hydrate (C–S–H), resulting in the accumulation of PVA molecules on rubber surface by van der Waals force and electrostatic interaction. The RH/PVA/C–S–H model has better mechanical properties than the RH/C–S–H model, verifying the bridging role of PVA at the molecular scale.

Novel antibacterial silver coating on PET fabric assisted with hollow‐cathode glow discharge

The silver‐coated fabrics are of much importance because of their outstanding antibacterial features and are useable in several medical and hygienic applications. The silver deposition on fabrics by conventional techniques is not feasible because of their high processing cost, long processing duration, complex equipment, and multiple steps processing (nanoparticle synthesis and subsequent deposition on fabrics). In this novel study, the antibacterial silver coating is deposited by using a hollow cathode discharge (HCD) capable of generating high‐density plasma, and thus it exhibits high‐efficiency processing. The silver is deposited on woven and non‐woven PET fabrics for various treatment times (10‐60 minutes), and their antibacterial performance against E. coli and S. aureus bacterial is tested. The XRD results verified the deposition of silver with (111) preferred orientation, while SEM analysis depicted the uniform/ homogeneous deposition of silver particles. The interfacial free energy of adhesion depicts that after the silver deposition on both fabrics, the surface is actively unfavorable for bacterial adhesion. The antibacterial test revealed that the silver‐coated woven and non‐woven PET fabrics exhibit exceptional antibacterial activity against E. coli and S. aureus bacteria. As the HCD technique is relatively cost‐effective, no need for specific sputtering targets, eco‐friendly, and require single‐step processing for silver deposition. Thus the results are expected to be of remarkable importance to prepare silver‐coated antibacterial fabrics useable in hospitals and other appropriate applications.

Red algae-derived k-carrageenan-based proton-conducting electrolytes for the wearable electrical devices

Proton-conducting non-porous nature of k-carrageenan-based flexible solid electrolytes was prepared by facile solution casting technique. Altering the composition of NH4COOH, free ion percentage (%) was improved significantly and contributed vital role on the proton conductivity to an utmost level of 8.54 × 10−4 Scm−1. Especially, increasing the composition of protonic carrier, electrochemical stability window was tuned tremendously and topmost value of 6.3 V was captured for the 0.4 (M wt%) NH4COOH added electrolyte. Also, interfacial adhesion energy of the electrolytes was enhanced to the maximum level of 96.27 Jm−2, inferred from contact angle measurements. The obtained significant electrochemical performance of k-carrageenan-based samples is an excellent substitute direction towards the cost-effective and eco-friendly wearable electrical applications.

Assessment of non-uniform residual stress field of the thermal sprayed stainless steel coatings on aluminium substrates by the integral hole drilling method

Thermal spray is one of the most used techniques to produce coatings on structural materials. Such coatings are used as protection against high temperatures, corrosion, erosion and wear. The combined action of high pressures, temperatures and spraying conditions give rise to non-uniform residual stresses. The latter plays an important role in coating design and process parameters optimization. The present work highlights the influence of coatings thickness on the evolution of residual stresses in layered materials. Therefore, thick stainless steel coatings (ASTM 301) of different thicknesses are manufactured by wire arc spraying on aluminium alloy substrates (ASTM 2017A). For a better bond strength, a Ni–Al bond coat is first deposited. Furthermore, a numerically supported hole drilling strain gage method for residual stress field evaluation is proposed. Required calibration coefficients, for the strain–stress transformation formalism based on the integral method, are computed through finite element calculations using Abaqus software. The results indicate that the maximum residual stresses, for all thicknesses, are tensile and range from 140 to 275 MPa. The bond coat does not seem to affect the stress field. Also, it was found that the mean equivalent Von-Mises stress decreases with increasing coating thickness; hence reducing the interfacial adhesion energy of the sprayed materials.

Effects of Post-annealing and Co Interlayer Between SiNx and Cu on the Interfacial Adhesion Energy for Advanced Cu Interconnections

Effects of Co interlayer and 200 °C post-annealing treatment on interfacial adhesion energy of SiNx/Cu structure were systematically investigated. Initial interfacial adhesion energy of SiNx/Cu structure measured by double cantilever beam test was 0.92 J/m2. The interfacial adhesion energy increased to 2.94 J/m2 with Co interlayer between SiNx and Cu films. After post-annealing treatment at 200 °C for 500 h, the interfacial adhesion energy of SiNx/Co/Cu structure decreased to 0.95 J/m2. X-ray photoelectron spectroscopy analysis revealed that the interfacial adhesion energy increased for SiNx/Co/Cu thin films due to CoSi2 reaction layer at SiNx/Co interface, but sharply decreased during post-annealing treatment by SiO2 formation at SiNx/Co interface.

Strengthening of Wood-Like Materials via Densification and Nanoparticle Intercalation.

Recently, several chemical and physical treatments were developed to improve different properties of wood. Such treatments are applicable to many types of cellulose-based materials. Densification leads the group in terms of mechanical results and comprises a chemical treatment followed by a thermo-compression stage. First, chemicals selectively etch the matrix of lignin and hemicellulose. Then, thermo-compression increases the packing density of cellulose microfibrils boosting mechanical performance. In this paper, in comparison with the state-of-the-art for wood treatments we introduce an additional nano-reinforcemeent on densified giant reed to further improve the mechanical performance. The modified nanocomposite materials are stiffer, stronger, tougher and show higher fire resistance. After the addition of nanoparticles, no relevant structural modification is induced as they are located in the gaps between cellulose microfibrils. Their peculiar positioning could increase the interfacial adhesion energy and improve the stress transfer between cellulose microfibrils. The presented process stands as a viable solution to introduce nanoparticles as new functionalities into cellulose-based natural materials.

Chitosan interphase around nanodiamond: Insight from equilibrium molecular dynamics

In the context of nanodiamond/chitosan (ND/CS) nanocomposites and utilizing atomistic molecular dynamics, the interaction mechanism of adsorbed CS layer around a model ND has been investigated at three level of hydration: in bulk of water, water as a droplet, and completely dry condition. The effect of amination and carboxylation of ND has been studied. To ensure that the comparison of these model systems is meaningful (energetically and geometrically), the CS interphases around NDs were characterized through holistic concentration profiles and density distribution maps. Our results revealed that in a completely dry condition or hydrated by a molecularly small droplet, both of the functionalized NDs are having much stronger adhesion interactions compared with the non-functionalized ND with the dominance of electrostatic mechanism. However, hydrated by large amount of water with implication to solutions, interfacial adhesion energies between ND and CS are the same through van der Waals mechanism.