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Intermetallic compounds are promising materials in numerous fields, especially those involving surface interactions, such as catalysis. A key factor to investigate their surface properties lies in adsorption energy maps, typically built using first-principles approaches. However, exploring the adsorption energy landscapes of intermetallic compounds can be cumbersome, usually requiring huge computational resources. In this work, we propose an efficient method to predict adsorption energies, based on a Machine Learning (ML) scheme fed by a few Density Functional Theory (DFT) estimates performed on n sites selected through the Farthest Point Sampling (FPS) process. We detail its application on the Al 13 Co 4 (100) quasicrystalline approximant surface for several atomic adsorbates (H, O, and Pb). On this specific example, our approach is shown to outperform both simple interpolation strategies and the recent ML force field MACE [arXiv.2206.07697], especially when the number n is small, i.e., below 36 sites. The ground-truth DFT adsorption energies are much more correlated with the predicted FPS-ML estimates (Pearson R-factor of 0.71, 0.73, and 0.90 for H, O and Pb, respectively, when n = 36) than with interpolation-based or MACE-ML ones (Pearson R-factors of 0.43, 0.39, and 0.56 for H, O, and Pb, in the former case and 0.22, 0.35, and 0.63 in the latter case). The unbiased root-mean-square error (ubRMSE) is lower for FPS-ML than for interpolation-based and MACE-ML predictions (0.15, 0.17, and 0.17 eV, respectively, for hydrogen and 0.17, 0.25, and 0.22 eV for lead), except for oxygen (0.55, 0.47, and 0.46 eV) due to large surface relaxations in this case. We believe that these findings and the corresponding methodology can be extended to a wide range of systems, which will motivate the discovery of novel functional materials.

The field of intermetallic catalysts, alloying a p-block and a transition metal to form a pM-TM bimetallic alloy, is experiencing robust growth, emerging as a vibrant frontier in catalysis research. Although such materials are increasingly used in the form of nanoparticles, a precise description of their atomic arrangements at the nanoscale remains scarce. Based on the In-Pd binary as a typical pM-TM system, we performed density functional theory calculations to investigate the morphologies, relative stabilities and electronic properties of 24 Å and 36 Å nanoparticles built from the In 3 Pd 2 , InPd and InPd 3 compounds. Wulff equilibrium structures are compared to other ordered and disordered structures. Surface energies are computed to discuss their thermodynamic stability, while work functions are calculated to examine their electronic structures. For any compound, increasing the size leads to the stabilisation of Wulff polyhedra, which are found to offer smaller surface energies than non-crystalline and chemically disordered structures. Disordered In 3 Pd 2 and InPd nanoparticles show a tendency towards amorphisation, owing to repulsive short In-In bonds. Tuning nanoparticles' work functions can be achieved through the control of the surface structure and composition, by virtue of the roughly linear correlation found between the surface composition and the work function which nevertheless includes a certain number of outliers. This work paves the way to rationalisation of both structural and electronic properties of pM-TM nanoparticles.

Steel is the most commonly manufactured material in the world. Its performances can be improved by hot-dip coating with the low weight aluminum metal. The structure of the Al∥Fe interface, which is known to contain a buffer layer made of complex intermetallic compounds such as Al 5 Fe 2 and Al 13 Fe 4 , is crucial for the properties. On the basis of surface X-ray diffraction, combined with theoretical calculations, we derive in this work a consistent model at the atomic scale for the complex Al 13 Fe 4 (010)∥Al 5 Fe 2 (001) interface. The epitaxial relationships are found to be [130] Al 5 Fe 2 ∥[010] Al 13 Fe 4 and [1 1̅0] Al 5 Fe 2 ∥[100] Al 13 Fe 4 . Interfacial and constrained energies, as well as works of adhesion, calculated for several structural models based on density functional theory, identify the lattice mismatch and the interfacial chemical composition as main factors for the stability of the interface. Molecular dynamics simulations suggest a mechanism of Al diffusion to explain the formation of the complex Al 13 Fe 4 and Al 5 Fe 2 phases at the Al∥Fe interface.

Recently, the discovery of the quasiperiodic order in ultra-thin perovskite films reinvigorated the field of 2-dimensional oxides on metals, and raised the question of the reasons behind the emergence of the quasiperiodic order in these systems. The effect of size-mismatch between the two separate systems has been widely reported as a key factor governing the formation of new oxide structures on metals. Herein, we show that electronic effects can play an important role as well. To this end, the structural, thermodynamic, electronic and magnetic properties of freestanding two-dimensional oxide quasicrystalline approximants and their characteristics when deposited over metallic substrates are systematically investigated to unveil the structure-property relationships within the series. Our thermodynamic approach suggests that the formation of these aperiodic systems is likely for a wide range of compositions. In addition, the magnetic properties and work functions of the thin films can be controlled by tuning their chemical composition. This work provides well-founded general insights into the driving forces behind the emergence of the quasiperiodic order in ternary oxides grown on elemental metals and offers guidelines for the discovery of new oxide quasicrystalline ultra-thin films with interesting physical properties.

The tunability offered by alloying different elements is useful to design catalysts with greater activity, selectivity, and stability than single metals. By comparing the Pd(111) and PdZn(111) model catalysts for CO 2 hydrogenation to methanol, we show that intermetallic alloying is a possible strategy to control the reaction pathway from the tuning of adsorbate binding energies. In comparison to Pd, the strong electron-donor character of PdZn weakens the adsorption of carbon-bound species and strengthens the binding of oxygen-bound species. As a consequence, the first step of CO 2 hydrogenation more likely leads to the formate intermediate on PdZn, while the carboxyl intermediate is preferentially formed on Pd. This results in the opening of a pathway from carbon dioxide to methanol on PdZn similar to that previously proposed on Cu. These findings rationalize the superiority of PdZn over Pd for CO 2 conversion into methanol and suggest guidance for designing more efficient catalysts by promoting the proper reaction intermediates.

A few low-order approximants to decagonal quasicrystals have been shown to provide excellent activity and selectivity for the hydrogenation of alkenes and alkynes. It is the case for the Al 13 Co 4 compound, for which the catalytic properties of the pseudo-2-fold orientation have been revealed to be among the best. A combination of surface science studies, including surface X-ray diffraction, and calculations based on density functional theory is used here to derive an atomistic model for the pseudo-2-fold o -Al 13 Co 4 surface, whose faceted and columnar structure is found very similar to the one of the 2-fold surface of the d -Al-Ni-Co quasicrystal. Facets substantially stabilize the system, with energies in the range 1.19-1.31 J/m 2 , i.e., much smaller than the ones of the pseudo-10-fold (1.49-1.68 J/m 2 ) and pseudo-2-fold (1.66 J/m 2 ) surfaces. Faceting is also a main factor at the origin of the Al 13 Co 4 catalytic performances, as illustrated by the comparison of the pseudo-10-fold, pseudo-2-fold and facet potential energy maps for hydrogen adsorption. This work gives insights toward the design of complex intermetallic catalysts through surface nanostructuration for optimized catalytic performances.

Good wetting is generally observed for liquid metals on metallic substrates, while poor wetting usually occurs for metals on insulating oxides. In this work, we report unexpected large contact angles for lead on two metallic approximants to decagonal quasicrystals, namely, Al 5 Co 2 and Al 13 Co 4 . Intrinsic surface wettability is predicted from first principles, using a thermodynamic model based on the Young equation, and validated by the good agreement with experimental measurements performed under ultra-high vacuum by scanning electron microscopy. The atomistic details of the atomic and electronic structures at the Pb-substrate interface, and the comparison with Pb(111)/Al(111), underline the influence of the specific electronic structures of quasicrystalline approximants on wetting. Our work suggests a possible correlation of the contact angles with the density of states at the Fermi energy and paves the way for a better fundamental understanding of wettability on intermetallic substrates, which has potential consequences in several applications such as supported catalysts, protective coatings, or crystal growth.

A new ternary phase with a composition Al 1+ x V 2 Sn 2- x ( x = 0.19) has been found during investigation of the Al-V-Sn ternary system. Single-crystal X-ray diffraction measurements reveal that this ternary phase crystallizes with an orthorhombic structure with a = 5.5931(1) Å, b = 18.8017(5) Å, and c = 6.7005(2) Å (space group Cmce ). This compound is thus isostructural to the GaV 2 Sn 2 structure type, showing a layered structure composed of vanadium cluster bands formed with pentagonal faces intercalated by Sn atom layers. High-resolution transmission electron microscopy measurements confirm the orthorhombic structure. Regarding lattice perfection, no dislocation could be identified within the probed Al 1.19 V 2 Sn 1.81 single-crystal lamella. Ab initio calculations reveal a reduction of the density of states at the Fermi level, which could be attributed to both a Hume-Rothery effect combined with strong spd hybridization.

Clusters, i.e. polyhedral geometric entities, are widely used to describe the structure of complex intermetallic compounds. However, little is generally known about their physical significance. The atomic and electronic structures of the Al 13 TM 4 complex intermetallic compounds (TM = Fe, Co, Ru, Rh) have been investigated using a wide range of ab initio tools in order to examine the influence of the chemical composition on the pertinence of the bulk structure description based on 3D clusters. In addition, since surface studies were found to be a relevant approach to address the question of cluster stability in complex phases, the interplay of the cluster substructure with the 2D surface is addressed in the case of the Al 13 Co 4 (100) and Al 13 Fe 4 (010) surfaces., (open access.)

Point island models (PIMs) are presented for the formation of supported nanoclusters (or islands) during deposition on flat crystalline substrates at lower submonolayer coverages. These models treat islands as occupying a single adsorption site, although carrying a label to track their size (i.e., they suppress island structure). However, they are particularly effective in describing the island size and spatial distributions. In fact, these PIMs provide fundamental insight into the key features for homogeneous nucleation and growth processes on surfaces. PIMs are also versatile being readily adapted to treat both diffusion-limited and attachment-limited growth and also a variety of other nucleation processes with modified mechanisms. Their behavior is readily and precisely assessed by kinetic Monte Carlo simulation.

A new ternary phase with a composition of Al3AuIr has been found in the Al-rich area of the Al-Au-Ir system. Differential thermal analysis indicates a melting point of 990 °C, and single-crystal X-ray diffraction measurements reveal that this ternary phase adopts a Ni2Al3 structure type (space group P3̅m1) with a = 4.2584(5) Å and c = 5.1991(7) Å. This compound is isostructural to the Al3Cu1.5Co0.5 phase also found in the Al-rich part of the Al-Cu-Co ternary diagram. Experimental evidence combined with ab initio calculations point toward an Al3AuIr phase stabilized by a Hume-Rothery mechanism. Quantum chemical calculations indicate two-center and multicenter interactions in the Al3AuIr phase. Layered distribution of two-center interactions separated by regions with four- and five-center bonds suggests a preferential cleavage of the material at puckered planes perpendicular to the [001] direction.

We present a review on recent work performed on periodic complex metallic alloy (CMA) surfaces. The electronic and crystallographic structures of clean pseudo-tenfold, pseudo-twofold, sixfold surfaces will be presented along with the recent findings on CMA of lower structural complexity, i.e. with a smaller unit cell. The use of CMA surfaces as templates for thin film growth and the formation of surface alloy will also be introduced. The reactivity of these complex surfaces and their impact in the field of heterogeneous catalysis will be discussed. Finally, common trends among these systems will be highlighted when possible and future challenges will be examined.

Self-organized molecular films with long-range quasiperiodic order have been grown by using the complex potential energy landscape of quasicrystalline surfaces as templates. The long-range order arises from a specific subset of quasilattice sites acting as preferred adsorption sites for the molecules, thus enforcing a quasiperiodic structure in the film. These adsorption sites exhibit a local 5-fold symmetry resulting from the cut by the surface plane through the cluster units identified in the bulk solid. Symmetry matching between the C60 fullerene and the substrate leads to a preferred adsorption configuration of the molecules with a pentagonal face down, a feature unique to quasicrystalline surfaces, enabling efficient chemical bonding at the molecule-substrate interface. This finding offers opportunities to investigate the physical properties of model 2D quasiperiodic systems, as the molecules can be functionalized to yield architectures with tailor-made properties.