Surface Strain Effects Research Articles

Strain Dependence of Metal Anode Surface Properties.

Dendrite growth poses a significant problem in the design of modern batteries as it can lead to capacity loss and short‐circuiting. Recently, it has been proposed that self‐diffusion barriers might be used as a descriptor for the occurrence of dendrite growth in batteries. As surface strain effects can modify dendritic growth, we present first‐principles DFT calculations of the dependence of metal self‐diffusion barriers on applied surface strain for a number of metals that are used as charge carriers in batteries. Overall, we find a rather small strain dependence of the barriers. We mainly attribute this to cancellation effects in the strain dependence of the initial and the transition states in diffusion.

On critical surface strain during hot forging of lubricated aluminum alloy

Abstract We present a new concept of critical surface strain to evaluate the lubrication-effective limit for process design in metal forming. Finite-element predictions obtained at various fixed Coulomb friction coefficients were compared in hot-forging experiments of a passenger car piston fabricated from short cylindrical aluminum alloy specimens well-lubricated with a solid film of water-dispersed lubricant. The Coulomb friction coefficient was formulated as a function of temperature, pressure, and material strain, and optimized by minimizing the difference between the predicted and experimental results. We established that the effect of surface strain dominated the metal-forming process, and that the optimized Coulomb friction coefficient changed abruptly at the critical surface strain at which the solid lubricating film used in the process is suddenly disrupted.

Probing the Effect of Surface Strain on CO Binding to Pd Thin Films

We report measurements to investigate the effects of mechanical strain on the binding energy of carbon monoxide (CO) on the (111) surface of a 16 nm thin film of palladium (Pd) grown on rutile titanium dioxide (r-TiO2). The lattice mismatch between Pd and the r-TiO2 leads to a tensile mechanical in-plane stress in the Pd layer of approximately 0.38 GPa. We observe an increase of (40 ± 10) kJ mol–1 in the CO binding energy for the 16 nm sample compared to a bulk Pd(111) crystal, which is in qualitative agreement with expectations based on the d-band model.

Superlinear Photoluminescence by Ultrafast Laser Pulses in Dielectric Matrices with Metal Nanoclusters

An intense photoluminescence emission was observed from noble metal nanoclusters (Pt, Ag or Au) embedded in sapphire plates, nucleated by MeV ion-implantation and assisted by an annealing process. In particular, the spectral photoluminescence characteristics, such as range and peak emission, were compared to the behavior observed from Pt nanoclusters embedded in a silica matrix and excited by UV irradiation. Correlation between emission energy, nanoclusters size and metal composition were analyzed by using the scaling energy relation EFermi/N1/3 from the spherical Jellium model. The metal nanocluster luminescent spectra were numerically simulated and correctly fitted using the bulk Fermi energy for each metal and a Gaussian nanoclusters size distribution for the samples. Our results suggest protoplasmonics photoluminescence from metal nanoclusters free of surface state or strain effects at the nanoclusters-matrix interface that can influence over their optical properties. These metal nanoclusters present very promising optical features such as bright visible photoluminescence and photostability under strong picosecond laser excitations. Besides superlinear photoluminescence from metal nanoclusters were also observed under UV high power excitation showing a quadratic dependence on the pump power fluence.

Competitive adsorption of CO and H<sub>2</sub> on strained Fe(110) surface

In this work, the competitive adsorption behavior of H<sub>2</sub> and CO on strained Fe(110) are investigated by the first-principles method based on the spin-polarized density functional theory to study the hydrogen embrittlement of steels. The results show that the most stable adsorption site for CO is top site, and the orbital of CO molecule hybridizing with Fe 3p and 4s states illustrates a strong electronic interaction between them. The adsorption energy values of CO at the four calculated adsorption sites are more negative than those of H<sub>2</sub>, which favors the binding with Fe(110) surface. The potential energy variations for CO and H<sub>2</sub> molecules close to the surface are calculated. The attractive force of the Fe(110) surface acting on CO in 1.5–3 Å is greater than that acting on H<sub>2</sub>. The pre-adsorbed CO increases the dissociation energy barrier of H<sub>2</sub> from 0.08 eV to 0.13 eV but reduces the force between H<sub>2</sub> and surface. The surface tensile strain enhances the interaction between hydrogen and Fe(110), which, however, is reduced by the compressive strain. The opposite tendency is found in the adsorption of CO. The binding strength of CO is stronger than that of H<sub>2</sub> on the strained Fe(110) surface. The difference in adsorption energy between CO and H<sub>2</sub> decreases with tensile strain increasing. The effect of surface strain and partial pressure of CO gas phase on the surface coverage ratio of H atom are also calculated quantitatively based on thermodynamics at 298 K, with the partial pressure of H<sub>2</sub> set to be 10 MPa. The surface ratio of the H atom decreases with partial pressure of CO increasing. The hydrogen coverage drops nearly to zero when the partial pressure of CO reaches a certain value. This result reveals that CO can inhibit hydrogen adsorption on Fe surface. In the case where the surface ratio of hydrogen decreases to 1%, the corresponding CO partial pressures are 105 Pa, 1.1 × 10<sup>3</sup> Pa, 2.4 × 10<sup>5</sup> Pa on –2%, 0, 2% strained Fe(110) surface, respectively. High CO partial pressure is needed to suppress the hydrogen adsorption since the binding strength of CO is close to that of H<sub>2</sub> on the expanded surface.

Influence of Surface Strain on Passive Film Formation of Duplex Stainless Steel and Its Degradation in Corrosive Environment

The effect of surface strain on the passive film evolution of SAF 2507 super duplex stainless steel exposed to ambient air and 0.1 M NaCl solution with varying anodic polarization at room temperature has been investigated using in-situ grazing incidence X-ray diffraction (GIXRD) in combination with electrochemical measurements. Surface strain affected the crystallinity of the passive film as such that the surface oxides/hydroxides were predominantly amorphous, with some minor crystalline CrOOH and FeOOH present in the film. Crystalline CrOOH was seen to diminish in volume upon immersion in the NaCl solution, well-possibly becoming amorphous during anodic polarization, whereas crystalline FeOOH was seen to increase in volume during polarization to the passive potential regime. Strain relaxation, associated with metal dissolution, occurred in both austenitic and ferritic grains during immersion in the electrolyte. Anodic polarization to the transpassive regime led to maximum strain relaxation, occurring more on the austenite than the ferrite. The selective transpassive dissolution nature of the ferrite was significantly reduced due to large strains in the austenite. Passive film breakdown was reflected by enhanced dissolution of Fe, Cr, Mo and Ni occurring simultaneously around 1300 mV vs. Ag/AgCl.

Surface Strain Effects on the Adsorption of Au Adatoms on MgO(001) Surfaces with Surface O Vacancies

By employing ab-initio total-energy and electronic-structure calculations based on the density-functional theory, we studied the effects of surface strain es on the adsorption properties of a Au adatom on defective MgO(001) surfaces with surface oxygen vacancies (Fs centers). The formation energy of the Fs center on MgO(001) varied very slightly in the region of es from −6% to −4% and monotonically decreased with the increase in es, from −4% to +6%. As es increased, the adsorption energy ( $$E_{ads}^{{F_S}}$$ ) of Au on the es center of strained MgO(001) monotonically decreased and, in particular, showed a much larger decrease in $$E_{ads}^{{F_S}}$$ for a tensile surface strain of es > +4%. The surface strain dependence on the physical properties, such as the charge states, the spatial charge rearrangement, for Au on the Fs center of strained MgO(001) surfaces was also analyzed. These results provide important physical information on the effects of surface strain on the adsorption of Au on MgO(001) surfaces with Fs centers.

Influence of surface strain on activity and selectivity of Pd-based catalysts for the hydrogenation of acetylene: A DFT study

The effects of surface strain and subsurface promoters, which are both important factors in heterogeneous catalysis, on catalytic selectivity and activity of Pd are examined in this study by considering the selective hydrogenation of acetylene as an example. Combined density functional theory calculations and microkinetic modeling reveal that the selectivity and activity of the Pd catalyst for acetylene hydrogenation can both be substantially influenced by the effects of Pd lattice strain variation and subsurface carbon species formation on the adsorption properties of the reactants and products. It is found that the adsorption energies of the reactants and products are, in general, linearly scaled with the lattice strain for both pristine and subsurface carbon atom-modified Pd(111) surfaces, except for the adsorption of C2H2 over Pd(111)-C. The activity for ethylene formation typically corresponds to the region of strong reactants adsorption in the volcano curve; such an effect of lattice strain and the presence of subsurface promoters can improve the activity of the catalyst through the weakening of the adsorption of reactants. The activity and selectivity for Pd(111)-C are always higher than those for the pristine Pd(111) surfaces with respect to ethylene formation. Based on the results obtained, Pd-based catalysts with shrinking lattice constants are suggested as good candidates for the selective hydrogenation of acetylene. A similar approach can be used to facilitate the future design of novel heterogeneous catalysts.

Contact involving a functionally graded elastic thin film and considering surface effects

This paper reported a size-dependent semi-analytical model (SAM) on the contact involving a functionally graded elastic film indented by a rigid frictionless cylinder, where Chen-Yao's surface elastic theory is employed to account for the effects of surface energy and surface strain. The model assumes that the film is perfectly bonded to a rigid substrate, and that the shear modulus of the film varies along the thickness direction following a simple exponential form. The core fundamental solutions of the elastic displacements and stresses for such an elastic thin film with respect to the unit applied force are derived firstly, incorporating the surface effects by means of Chen-Yao's surface elastic theory. Then the frequency response functions (FRFs) and their conversion into the corresponding influence coefficients (ICs), are analytical obtained. Efficient numerical techniques, supported by the conjugate gradient method (CGM) and the fast Fourier transform (FFT), are applied to obtain the unknown pressure and stress distributions. The combined effects of shear modulus ratio, film thickness, and surface energy on the contact behavior of the thin film are explored, and a schematic map is constructed to reveal the influences of film thickness and material characteristic length, which correlates the geometric configuration (i.e. a film or a half-space) and surface behaviors (i.e. with or without considering the surface effects).

Dealloyed Pt3Co nanoparticles with higher geometric strain for superior hydrogen evolution reaction

In the present work, the effect of surface strain in the carbon supported Pt3Co dealloy catalyst towards hydrogen evolution reaction (HER) has been reported. Dealloying process is adopted to generate the geometric strain in Pt3Co/C alloy by preferential dissolution of non-noble metal (Co) from the alloy. The developed geometric strain has been estimated by different microstructural characterization techniques. Electrochemical studies showed that the highest current density for HER was obtained for Pt3Co/C dealloy catalyst and it was nearly 2 and 5 times higher than Pt3Co/C alloy and Pt/C respectively. Tafel slope for HER was improved from 49 (Pt/C) to 34 mV dec−1 (Pt3Co/C dealloy), indicating that the surface strain plays important role in the improvement of the catalytic activity of Pt3Co catalyst. The chronoamperometry data, LSV curves and ECSA values before and after chronoamperometry confirmed that Pt3Co/C dealloy catalyst was a stable as well as a durable electrocatalyst for HER.

Designing Efficient Catalysts through Bimetallic Architecture: Rh@Pt Nanocubes as a Case Study

AbstractBimetallic nanocatalysts often have increased activities and stabilities over their monometallic counterparts due to surface strain effects and electron transfer between the two metals. Here, we demonstrate that the performance of a nanocatalyst can be precisely manipulated in shape‐controlled nanocrystals through a bimetallic core@shell architecture. This ability is achieved in a model core@shell Rh@Pt nanocube system through control of shell thickness. The enhanced performance with thin‐shelled nanocrystals is correlated with the weakening of surface–adsorbate interactions. In these thin‐shelled Rh@Pt nanocubes, the maximum current density achieved during formic acid oxidation was over 2 times greater than that achieved with similarly sized Pt nanocubes, with a decreased CO poisoning ratio as well. The strategy employed here should also enhance the performance of many other bimetallic nanomaterials composed of more cost‐effective metals too.

The effect of surface strain on the CO-poisoned surface of Pt electrode for hydrogen adsorption

The impact of mechanical strain is studied at CO-poisoned Pt(111) surface for hydrogen adsorption. Our experiment first investigates a coupling parameter of interest, ζH, which quantifies the variation of hydrogen adsorption potential in response to surface strain. The result exhibits a bigger ζH at CO-poisoned surface than the value measured at clean surface. Since adsorption potential is linked to adsorption energy, it indicates significantly the larger effect of tensile strain on decreasing hydrogen adsorption energy at CO-poisoned surface, comparing to the clean surface. DFT calculations at an atomic level support the experimental observation and explain this behavior can be attributed to the strain-induced reduction in CO-poisoning effect on hydrogen adsorption energy.

Strain engineering of H/transition metal systems

The effects of both compressive and tensile surface strain on the hydrogenated low-index faces of Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Os, Ir, Pt and Au has been investigated using density functional theory (DFT). Changes in the preferred H binding site have been observed on the Pd, Ir and Pt surfaces when the surface lattice constant is strained by up to 2%, and on Fe, Rh, Ag and Os surfaces for larger strains of up to 5%. A complete discussion of the variance of the hydrogen binding energy, charge, density of states and local geometry with strain is presented. The exchange-correlation, electrostatic and kinetic contributions to the binding energy are delineated and their respective contributions are discussed. The mechanism which determines the preferred binding site for each system under strain is shown to be complex.

Surface Strain Effect Engineers the Catalytic Performance of Pd Nanocrystals in CO<sub>2</sub> Electrochemical Reduction

Surface Strain Effect Engineers the Catalytic Performance of Pd Nanocrystals in CO<sub>2</sub> Electrochemical Reduction

Surface strain effects on the adsorption and the diffusion of Au atoms on MgO(001) surfaces

The effects of surface strain on the adsorption and the diffusion properties of a Au adatom on MgO(001) surfaces are studied using first-principles electronic-structure calculations based on the density functional theory. The adsorption of Au on MgO(001) is found to become stronger with increasing surface strain. In addition, the adsorption site of Au changes from a site on top of a surface O atom of MgO(001) to a site near a surface O atom for tensile surface strains over +4 %. In the case of a tensile surface strain of +7 %, the adsorption energy changes from −0.87 eV for unstrained MgO(001) to −1.17 eV. The variation in the charge states of Au on MgO(001) with surface strain, based on a Bader charge analysis, is also presented. The Bader charges of Au are found to become more negative as the surface strain increases. For a tensile surface strain of +7 %, the Bader charge is −0.38 |e|, more negative than the value of −0.29 |e| for unstrained MgO(001). Contrary to the adsorption energies and the charge states of Au, the variation in the surface diffusion barriers of Au on MgO(001) is found to be very small, less than 0.03 eV.

Incorporation of silicone oil into elastomers enhances barnacle detachment by active surface strain

Silicone-oil additives are often used in fouling-release silicone coatings to reduce the adhesion strength of barnacles and other biofouling organisms. This study follows on from a recently reported active approach to detach barnacles, which was based on the surface strain of elastomeric materials, by investigating a new, dual-action approach to barnacle detachment using Ecoflex®-based elastomers incorporated with poly(dimethylsiloxane)-based oil additives. The experimental results support the hypothesis that silicone-oil additives reduce the amount of substratum strain required to detach barnacles. The study also de-coupled the two effects of silicone oils (ie surface-activity and alteration of the bulk modulus) and examined their contributions in reducing barnacle adhesion strength. Further, a finite element model based on fracture mechanics was employed to qualitatively understand the effects of surface strain and substratum modulus on barnacle adhesion strength. The study demonstrates that dynamic substratum deformation of elastomers with silicone-oil additives provides a bifunctional approach towards management of biofouling by barnacles.

Uniaxial-Strain Effects in the Paclitaxel Drug Molecule Adsorption on Nitrogen-Doped Graphene

It has been recently investigated [A. Azizi and S. Ebrahimi, Nano 9, 1450088 (2004).] the Paclitaxel (PTX) anticancer drug molecule adsorption on nitrogen doped graphene (NG). However, the surface strain effect on adsorption is not considered in the literature. In this study, using molecular dynamics (MD) simulation, we show that the PTX molecule adsorption can be tuned by exploiting the rippling effect of the strained NG. The dependence of the nitrogen concentration in the presence of ripples on the surface, arising due to thermal fluctuations, is examined. We have also considered the connection between the average distance of PTX from NG surface and the maximum induced deformation on the surface structure. It is demonstrated that the average distance of PTX from NG is increased with increasing the strain until a critical value is reached, and then it has remained almost constant. To this end, the dependence of the degree of ripple-type distortion of the surface on the PTX adsorption is investigated.

Maximum catalytic activity of Pt3M in Li-O2 batteries: M=group V transition metals

Li-O2 batteries are considered as promising power sources for electric vehicles due to their remarkably high energy density. However, low rate capability and short cycle life caused by sluggish oxygen reduction/evolution reaction (ORR/OER) kinetics limit their practical applications. Here, we investigate the catalytic activities of Pt3M bimetallic alloys (M=3d, 4d, and 5d transition metals) for improving the ORR and OER kinetics using first-principles calculations. We found that the group 5 elements (V, Nb, and Ta in 3d, 4d, and 5d periods, respectively) are the most effective alloy components for high catalytic activity. Pt3V, Pt3Nb, and Pt3Ta alloys exhibit considerably lower ORR and OER overpotentials (by 71–77% and 57–59%, respectively) than those of Pt. The catalytic activities are successfully described by the adsorption strengths of reaction intermediate species (Li and LiO2) on the alloy surface rather than the d-band center of the alloy surface and are fundamentally controlled by the amount of surface charge. The superior catalytic activities of Pt3M alloys with the group 5 elements originate from their electron-rich surfaces and can also be interpreted in terms of the integration of mechanical interplay and chemical interplay of Pt and M, i.e., an appropriate trade-off between surface strain and ligand effects.

Atomistic Mechanism of Pt Extraction at Oxidized Surfaces: Insights from DFT

In this article, we propose a novel mechanism for the atomic-level processes that lead to oxide formation and eventually Pt dissolution at an oxidized Pt(111) surface. The mechanism involves a Pt extraction step followed by the substitution of chemisorbed oxygen to the subsurface. The energy diagrams of these processes have been generated using density functional theory and were analyzed to determine the critical coverages of chemisorbed oxygen for the Pt extraction and Oads substitution steps. The Pt extraction process depends on two essential conditions: (1) the local coordination of a Pt surface atom by three chemisorbed oxygen atoms at nearest-neighboring fcc adsorption sites; (2) the interaction of the buckled Pt atom with surface water molecules. Results are discussed in terms of surface charging effects caused by oxygen coverage, surface strain effects, as well the contribution from electronic interaction effects. The utility of the proposed mechanism for the understanding of Pt stability at bimetallic surfaces will be demonstrated by evaluating the energy diagram of a CuML/Pt(111) near-surface alloy.

Electronic and magnetic properties of germanene: Surface functionalization and strain effects

The surface functionalization and strain effects on the structural, electronic, and magnetic properties of full-/half-passivated germanenes are investigated systematically by the first-principle calculations within density functional theory. It is found that the germanenes with full-passivation have different band structures. i.e., the band-gap of GeH is larger than that of GeF and GeCl. Interestingly, when surface passivation and strain are utilized, germanenes go through a transformation from semiconductor to semi-metal. Moreover, germanenes with half-passivation present different magnetic characters, i.e,. Ge2H is a ferromagnetic semiconductor, while Ge2F and Ge2Cl are anti-ferromagnetic semiconductors. The stability of magnetic coupling of Ge2Xs can be modulated by external strain. Our calculations indicate that the electronic and magnetic properties of passivated-germanenes strongly depend on their surface functionalization and strain effects.