Binary Alloy Surfaces Research Articles

Interpreting chemisorption strength with AutoML-based feature deletion experiments

The chemisorption energy of reactants on a catalyst surface, [Formula: see text], is among the most informative characteristics of understanding and pinpointing the optimal catalyst. The intrinsic complexity of catalyst surfaces and chemisorption reactions presents significant difficulties in identifying the pivotal physical quantities determining [Formula: see text]. In response to this, the study proposes a methodology, the feature deletion experiment, based on Automatic Machine Learning (AutoML) for knowledge extraction from a high-throughput density functional theory (DFT) database. The study reveals that, for binary alloy surfaces, the local adsorption site geometric information is the primary physical quantity determining [Formula: see text], compared to the electronic and physiochemical properties of the catalyst alloys. By integrating the feature deletion experiment with instance-wise variable selection (INVASE), a neural network-based explainable AI (XAI) tool, we established the best-performing feature set containing 21 intrinsic, non-DFT computed properties, achieving an MAE of 0.23 eV across a periodic table-wide chemical space involving more than 1,600 types of alloys surfaces and 8,400 chemisorption reactions. This study demonstrates the stability, consistency, and potential of AutoML-based feature deletion experiment in developing concise, predictive, and theoretically meaningful models for complex chemical problems with minimal human intervention.

Decreasing the O2‐to‐H2O2 Kinetic Energy Barrier on Dilute Binary Alloy Surfaces with Controlled Configurations of Isolated Active Atoms

AbstractShifting from the typical 4e– pathway to H2O in electrochemical oxygen reduction to the 2e– pathway to H2O2 is increasingly recognized as an environmentally friendly approach for producing H2O2. However, the competitive 4e− pathway is a significant obstacle to the production of H2O2 since H2O is the thermodynamically favored product. Here, a series of Pt, Pd, and Rh active atoms diluted within inert‐Au matrices with precisely controlled atomic arrangements and coordination environments are synthesized via facet engineering for O2‐to‐H2O2 production. Surprisingly, individually dispersed Pt atoms within the Au surface enclosed by the square atomic arrangements exhibit superior H2O2 selectivity and achieve a maximum selectivity of 90% at 0.36 V versus the reversible hydrogen electrode. Operando synchrotron ambient pressure X‐ray photoelectron spectroscopy identifies the presence of *OOH key intermediates on these isolated Pt active sites. Grand canonical density‐functional theory also reveals that the kinetic energy barrier for the 2e− pathway (0.08 eV; OOH* + H+ + e− → H2O2) on the isolated Pt sites is significantly lower than the 4e− pathway (0.29 eV; OOH* + H+ + e− → O* + H2O). This work enables atomic‐scale control in dilute binary alloy surfaces with specific configurations of isolated active atoms and provides essential guidance for catalyst design to boost O2‐to‐H2O2 production.

Corrosion behavior of anodized Ti-Ta binary surface alloys in various physiological fluids for implant applications

In this study, corrosion-resistant surface-modified biometals were developed by coating titanium-tantalum alloy thin films onto titanium substrates, followed by anodization. These films were systematically investigated for their crystal structure, morphology, and microstructure. Electrochemical studies were carried out in 0.9% NaCl, PBS, and SBF. EIS data was evaluated using equivalent circuit models and a physical model is proposed to describe the corrosion process. The polarization resistance values suggest that the anodized Ti-Ta thin film alloy possesses favorable corrosion resistance properties, thereby indicating its potential for use in orthopedic applications.

Atomistic Mechanisms of Binary Alloy Surface Segregation from Nanoseconds to Seconds Using Accelerated Dynamics.

Although the equilibrium composition of many alloy surfaces is well understood, the rate of transient surface segregation during annealing is not known, despite its crucial effect on alloy corrosion and catalytic reactions occurring on overlapping timescales. In this work, CuNi bimetallic alloys representing (100) surface facets are annealed in vacuum using atomistic simulations to observe the effect of vacancy diffusion on surface separation. We employ multi-timescale methods to sample the early transient, intermediate, and equilibrium states of slab surfaces during the separation process, including standard MD as well as three methods to perform atomistic, long-time dynamics: parallel trajectory splicing (ParSplice), adaptive kinetic Monte Carlo (AKMC), and kinetic Monte Carlo (KMC). From nanosecond (ns) to second timescales, our multiscale computational methodology can observe rare stochastic events not typically seen with standard MD, closing the gap between computational and experimental timescales for surface segregation. Rapid diffusion of a vacancy to the slab is resolved by all four methods in tens of nanoseconds. Stochastic re-entry of vacancies into the subsurface, however, is only seen on the microsecond timescale in the two KMC methods. Kinetic vacancy trapping on the surface and its effect on the segregation rate are discussed. The equilibrium composition profile of CuNi after segregation during annealing is estimated to occur on a timescale of seconds as determined by KMC, a result directly comparable to nanoscale experiments.

Theoretical insight into adsorption and dissociation of water on NiCr binary alloy surfaces: Early-stage oxidation mechanism

The effects of alloy surface composition and pre-adsorbed oxygen on the behaviors of H2O over Ni–Cr binary alloy surfaces were investigated by using the first-principles method. The surface energies and work functions for a series of Ni–Cr (111) alloy surfaces with different Cr concentrations were addressed to track the surface reactivities. An enhancement effect on the surface reactivity from Cr doping in the top-surface layer (TSL) of nickel substrates was identified. The locations of Cr in the TSL dramatically promoted exothermic adsorption of H2O and its decomposed products, including OH, O, and H. The calculated potential dissociation pathways further demonstrated that the successive dissociation of H2O molecules was substantially triggered in the presence of Cr doping in the TSL. By contrast, the Cr doping in the sub-surface layer hindered the dehydrogenation of H2O with a relatively higher energy barrier for OH dissociation. Moreover, with pre-adsorbed oxygen atoms closer to Cr, the first elementary step of H2O dissociation was easily fostered, whereas the OH dissociation was hindered. The Cr doping and O pre-adsorption accelerated the dissociation of H2O, which plays a critical role in the initial oxidation of nickel-based alloys in water- or oxygen-bearing environments.

Erratum: Directed long-range transport of a nearly pure component atom clusters by the electromigration of a binary surface alloy [Phys. Rev. Materials 5 , 024001 (2021)

Erratum: Directed long-range transport of a nearly pure component atom clusters by the electromigration of a binary surface alloy [Phys. Rev. Materials <b>5</b> , 024001 (2021)

The oxidation of Fe/Ni alloy surface with supercritical water: A ReaxFF molecular dynamics simulation

A ReaxFF force field for Fe/Ni/H/O is developed to describe the interactions between Fe/Ni binary alloy surface and supercritical water (SCW). The energies and charge distributions of surface binding are compared with DFT calculations to validate the developed force field. ReaxFF molecular dynamics (MD) simulations are performed to investigate the oxidation mechanism of Fe/Ni alloy surface in SCW. Simulation results show that SCW selectively oxidizes Fe on the alloy surface. Fe atoms dissolve into SCW, leading to the dealloying of the alloy surface. Bond order analysis and energy calculation reveal that the selective oxidation is because Fe has stronger bonding with O and higher mobility in alloy than Ni. Disordered Fe/Ni alloy has a faster oxidation rate than ordered Fe/Ni alloy. This result is explained by the lower migration energy cost of the O atom in a local Fe-rich structure on the alloy surface. The anti-oxidant mechanism of Ni is due to its role in stabilizing the alloy lattice structure and increasing the migration energy barrier of oxygen through the alloy surface layer. Adjusting the content and distribution of nickel atoms in the alloy might improve the oxidation resistance of iron-nickel alloys.

Directed long-range transport of a nearly pure component atom clusters by the electromigration of a binary surface alloy

Assuming a vacancy-mediated diffusion, a continuum model for electromigration-driven transport of an embedded atom cluster across a surface terrace of a phase-separating A$_x$B$_{1-x}$ surface alloy, such as fcc AgPt(111), is presented. Computations show that the electron wind carries the cluster over hundreds of lattice spacings and in the set direction, while the cluster grows and its purity improves during the drift. Impacts of the current density, the diffusion anisotropy, the magnitude and sign of the ratio of the effective charges $q_A/q_B$, and the jump frequencies ratio $\Gamma_A/\Gamma_B$ on the cluster's drift speed, drift direction, purity and shape are demonstrated.

Atomistic Mechanisms of Binary Alloy Surface Segregation From Nanoseconds to Seconds Using Accelerated Dynamics

Although the equilibrium composition of many alloy surfaces is well understood, the rate of transient surface segregation during annealing is not known, despite its crucial effect on alloy corrosion and catalytic reactions occurring on overlapping timescales. In this work, CuNi bimetallic alloys representing (100) surface facets are annealed in vacuum using atomistic simulations to observe the effect of vacancy diffusion on surface separation. We employ multi-timescale methods to sample the early transient, intermediate, and equilibrium states of slab surfaces during the separation process, including standard MD as well as three methods to perform atomistic, long-time dynamics: parallel trajectory splicing (ParSplice), adaptive kinetic Monte Carlo (AKMC), and kinetic Monte Carlo (KMC). From nanosecond (ns) to second timescales, our multiscale computational methodology can observe rare stochastic events not typically seen with standard MD, closing the gap between computational and experimental timescales for surface segregation. Rapid diffusion of a vacancy to the slab is resolved by all four methods in tens of ns. Stochastic re-entry of vacancies into the subsurface, however, is only seen on the microsecond timescale in the two KMC methods. Kinetic vacancy trapping on the surface and its effect on the segregation rate are discussed. The equilibrium composition profile of CuNi after segregation during annealing is estimated to occur on a timescale of seconds as determined by KMC, a result directly comparable to nanoscale experiments.

Modeling evolution of composition patterns in a binary surface alloy

Evolution of composition patterns in the annealed, single-crystal surface alloy film is considered in the presence of the spinodal decomposition, the compositional stress and the diffusion anisotropy. While the former two effects contribute to overall phase separation, the anisotropy, correlated with the surface crystallographic orientation, guides the in-plane formation and orientation of a pattern. The impacts of the anisotropy parameters on patterns are systematically computed for [110], [100], and [111]-oriented fcc cubic alloy surfaces.

Species distribution in laser-induced plasma on the surface of binary miscible alloy

The spatiotemporal species distribution and dynamics of plasma play a crucially important role in improving the quality of the deposited film fabricated by pulsed laser deposition (PLD) and optimizing the spectral acquisition to enhance the quantitative performance of spatial-resolved laser-induced breakdown spectroscopy (LIBS). In this work, the monochrome imaging is used to analyze the plasmas induced from binary miscible alloys and explore the dependence of species distribution in plasma on laser-supported combustion (LSC) and laser-supported detonation (LSD) wave propagation regimes. This paper includes three conclusions: 1) the species distribution in LSC-wave dominated plasma induced from immiscible alloy is heavily influenced by the melting points of constituted elements, while in LSC-wave dominated plasma induced from miscible alloy, it is related to the boiling points; 2) whether the alloy is miscible or immiscible, the species distribution in LSD-wave dominated plasma is only related to the atomic masses; 3) to a great extent, the reduction rate of species in LSC-wave dominated plasma is associated with the transition probability, while that in LSD-wave dominated plasma is associated with the number density of species in the upper energy level.

The corrosion behavior of Mg–Nd binary alloys in the harsh marine environment

Abstract The corrosion behavior of Mg-Nd binary alloys in the harsh South China Sea environment was researched by scanning electron microscopy, energy-dispersive spectrometry and X-ray diffraction analysis. In order to explain the corrosion mechanism, corrosion resistance was analyzed by weight loss rate and electrochemical measurement in the laboratory. With a continuous enlargement of Nd-content, Mg12Nd phases increased and multiplied. The weight loss rate of Mg-0.5Nd alloy was 0.0436 mg•cm−2•y−1 (0.0837 mm•y−1), whereas that of Mg-1.5Nd alloy was 0.0294 mg•cm−2•y−1 (0.0517 mm•y−1) during the exposure corrosion in the South China Sea site. The mechanical strength of Mg-1.5Nd alloy was 148 MPa before the exposure in the harsh marine environment, while the residual mechanical strength was merely about 94 MPa after the exposure test. Both Mg-1.5Nd alloy and Mg-1.0Nd alloy occurred the brittle fracture, which resulted that the elongation was nearly equal to zero. The self-corrosion current density demonstrated that degradation rate of Mg-Nd binary alloys was as follows : Mg-0.5Nd>Mg-1.0Nd>Mg-1.5Nd. For the South China Sea corrosion site, a large amount of sea salts exited in the atmospheric environment. Due to the heavy rainfall and high humidity, sodium chloride in the atmospheric environment dissolved, more serious electrochemical corrosion occurred on the surface of Mg-Nd binary alloys.

Machine-learning adsorption on binary alloy surfaces for catalyst screening

Over the last few years, machine learning is gradually becoming an essential approach for the investigation of heterogeneous catalysis. As one of the important catalysts, binary alloys have attracted extensive attention for the screening of bifunctional catalysts. Here we present a holistic framework for machine learning approach to rapidly predict adsorption energies on the surfaces of metals and binary alloys. We evaluate different machine-learning methods to understand their applicability to the problem and combine a tree-ensemble method with a compressed-sensing method to construct decision trees for about 60000 adsorption data. Compared to linear scaling relations, our approach enables to make more accurate predictions lowering predictive root-mean-square error by a factor of two and more general to predict adsorption energies of various adsorbates on thousands of binary alloys surfaces, thus paving the way for the discovery of novel bimetallic catalysts.

Species distribution in laser-induced plasma on the surface of binary immiscible alloy

Investigation on species distribution of vapor plasma is of great significance for understanding the laser-target interaction, the plasma dynamics and verifying theoretical models. It is also helpful for optimizing the spectral acquisition to improve the quantitative performance of spatial-resolved laser-induced breakdown spectroscopy (LIBS). In this work, the laser-induced plasma on the surface of binary alloy is analyzed by using spectrally, spatially and temporally resolved dual-wavelength differential imaging to explore the dependence of species distribution in plasma on laser-supported absorption (LSA) wave regime and sample composition. The laser-supported combustion (LSC) and laser-supported detonation (LSD) wave dominated plasmas with different elemental mass ratios are induced from a series of binary immiscible alloys by using low and high irradiance laser pulses, respectively. By comparing the spatial-temporal emissivity images of species, the following conclusions are drawn: 1) laser irradiance can change the species distribution of plasma, while the sample composition cannot; 2) for LSC-wave dominated plasma, the species distribution mainly depends on the melting points of constituted elements in the sample, while for LSD-wave dominated plasma, it mainly depends on the atomic masses of elements. The above behaviours on species distribution in plasma produced from binary immiscible alloys are expected to be suitable for other elements or even multi-element plasmas.

First-principles study of crystal-face specificity in surface properties of Fe-rich Fe-Cr alloys

A density-functional theory investigation of the (100) and (110) surfaces of the body-centered cubic (bcc) Fe1-xbCrxb binary alloys, x(b) <= 15 at.%, is reported. The energies and segregation en ...

Analysis of dynamic decomposition for barium dimethyl-naphthalene-sulfonate on an Al3Mg (0 0 1) surface from ab-initio molecular dynamics

One important dynamic decomposition pathway for a surface corrosion-inhibitor: barium dimethyl- naphthalene-sulfonate, is investigated on a clean Al3Mg (0 0 1) binary-alloy surface using ab-initio molecular dynamics based upon density functional theory. Each inhibitor molecule is oriented its functional groups of sulfonic-oxygen bases toward the surface, starting at an initial impact velocity. The dynamic decomposition pathway occurs upon molecular collision with the surface, leading to the decomposed fragments that may clearly represent the initial formation stage of additive thin-film on the surface during a plastic substrate deformation. In addition, three important factors: initial impact speed acting on molecule (kinetic effect), substrate temperature (thermal effect) and initial molecular orientation (geometric effect) etc, are employed to analyze their influences on molecular decomposition. An approach of design-of-experiment (DOE) is applied to an analysis of relative importance for each factor and all factor interactions in above, so as to figure out the best way of surface protection. Final DOE analysis indicates that the most significant factor for promoting molecular decomposition on surface is the substrate temperature, i.e., the higher the substrate temperature, the more rapid decomposition of molecule on surface. While initial impact velocity plays a smaller role, and initial molecular orientation performs less importance to molecular decomposition.

Thermodynamic, Structural, Surface and Transport Properties of In-Tl Liquid Alloy at Different Temperatures

The thermodynamic, structural, surface and transport properties of In-Tl binary liquid alloy are studied on the basis of theoretical analysis using the regular solution model at different temperatures. The properties of the alloy at 723 K have been computed by estimating the best fit value of order energy parameter (ω) in the entire range of concentration to match their observed and theoretical values. The values of order energy parameter at different temperatures have been calculated using the value of order energy parameter at 723 K which played key role to study different properties of the alloy using optimization method. The theoretical analysis gives the positive energy parameter (ω), which is found to be temperature dependent.

Galvanic exchange-formed ultra-low Pt loading on synthesized unique porous Ag-Pd nanotubes for increased active sites toward oxygen reduction reaction

Development of an inexpensive high performance catalyst with low Pt loading remains a great challenge. Herein galvanic exchange-formed ultra-low Pt loaded porous Ag-Pd binary alloy nanotubes (Pt/Ag-Pd) was prepared as a catalyst toward oxygen reduction reaction (ORR). With highly dispersed active but ultra-low Pt atoms (Pt: about 5.8 wt%) on the porous binary alloy surface, the Pt/Ag-Pd catalyst increases mass activity toward ORR by 1.82 times than commercial Pt/C while possessing excellent operation stability. The performance enhancement is mainly attributed to the unique porous Pt shell/Ag-Pd core tubular structure for increased active sites and facilitated interfacial electron transfer rate by a unique Ag-Pd jointly modified electronic structure. This catalyst holds great promise for practical applications in low temperature fuel cells.

On the Ni-Ion release rate from surfaces of binary NiTi shape memory alloys

Abstract The study is focused on Ni-ion release rates from NiTi surfaces exposed in the cell culture media and human vascular endothelial cell (HUVEC) culture environments. The NiTi surface layers situated in the depth of 70 μm below a NiTi oxide scale are affected by interactions between the NiTi alloys and the bio-environments. The finding was proved with use of inductively coupled plasma mass spectrometry and electron microscopy experiments. As the exclusive factor controlling the Ni-ion release rates was not only thicknesses of the oxide scale, but also the passivation depth, which was two-fold larger. Our experimental data strongly suggested that some other factors, in addition to the Ni concentration in the oxide scale, admittedly hydrogen soaking deep below the oxide scale, must be taken into account in order to rationalize the concentrations of Ni-ions released into the bio-environments. The suggested role of hydrogen as the surface passivation agent is also in line with the fact that the Ni-ion release rates considerably decrease in NiTi samples that were annealed in controlled hydrogen atmospheres prior to bio-environmental exposures.

Experimental studies of an In/Pb binary surface alloy on Ge(111)

In this study, we present a binary In/Pb surface alloy on Ge(111) formed by evaporating In on the Pb/Ge(111)3×3 β phase. A well-defined 3×3 periodicity is formed after annealing, as verified by both low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). Overview STM images show a clear 3×3 periodicity. Detailed STM images reveal protrusions corresponding to atomic sized features with a local hexagonal arrangement. Each 3×3 unit cell contains nine such features indicating a structure with 9 atoms per 3×3 cell in the topmost layer. Based on angle resolved photoelectron spectroscopy (ARPES) data, we have identified five surface bands within the bulk band gap. Four of them cross the Fermi level leading to a metallic character of the surface. The dispersions of these bands have been mapped in detail along two high symmetry directions of the surface Brillouin zone. Constant energy contours, mapped in two dimensional k-space, show interesting features. In particular, the occurrence of two differently rotated hexagon-like contours is presented.