Adatom Interactions Research Articles

Computational investigation of quantum capacitance enhancement in Mg-substituted MgB[formula omitted]-based supercapacitor electrodes

The investigation into surface functionalization’s effect on magnesium diboride (MgB2) presents a captivating research direction, shedding light on the modifications in its electronic structure resulting from functionalization systematically analysed through density functional theory (DFT) calculations. This study systematically investigates the effects of varying functionalization concentrations on MgB2, unveiling a profound influence on its quantum capacitance(CQ). Maximum enhancement is found within an optimal doping range; however, impurity ad-atom interactions may cause quantum capacitance to decrease above this barrier. Notably, these ad-atoms act as magnetic impurities, generating a localized density of states near the Fermi energy, thereby increasing charge carrier density and resulting in a remarkable increase in quantum capacitance. We also emphasize the importance of functionalized MgB2 as an example of a two-dimensional supercapacitor electrode material in the advancement of energy storage technology. These materials promise improved charge storage capacities and tailored electronic properties, which will accelerate the development of effective energy storage technologies. This paper highlights the potential direction of two-dimensional electrode materials in developing supercapacitor technology towards superior energy storage systems by elucidating fundamental mechanisms using quantum capacitance enhancement.

Element-specific cluster growth on the two-dimensional metal–organic network

A porous two-dimensional metal–organic network (2D-MON) on a substrate captures deposited metal atoms and metal clusters growing in the pores of the 2D-MON. We found that the growth mechanisms of Ag, In, and Pd clusters in the 2D-MON synthesized from 1,3,5-tris(4-bromophenyl)benzene molecules on Ag(111) are different from each other, and the difference derives from the interaction of an adatom with the 2D-MON. Ag and Pd clusters grow from the 2D-MON since the interaction of Ag and Pd adatoms with the 2D-MON is attractive. In clusters grow inside of the pores of the 2D-MON since the interaction between an In adatom and the 2D-MON is repulsive. The growth process of metal clusters is determined by the element-specific behavior of metal adatoms in the pores, taking into account interactions with the 2D-MON.

Horizontal lithium growth driven by surface dynamics on single crystal Cu(111) foil

Single-crystal Cu(111) foil promotes the lateral growth of lithium rhombic dodecahedra, preventing dendritic lithium growth during plating. This is achieved through surface migration and the interaction of lithium adatoms with individual grains.

Metal–Organic Chemical Vapor Deposition‐Grown AlScN for Microelectromechanical‐Based Acoustic Filter Applications

AlScN films are produced in a commercial metal–organic chemical vapor deposition (MOCVD) system modified to low‐vapor‐pressure Sc metal–organic precursors. Growth conditions are optimized for surface morphology, film stress, and piezoelectric coefficient across a range of compositions. Epitaxial structures are designed to eliminate internal tensile stresses that develop during the film growth as well as prevent surface adatom interactions unique to the MOCVD process. From these films, wide‐bandwidth resonators and filters are manufactured using a novel microelectromechanical‐based bulk acoustic wave (BAW) transfer process. When tested on‐wafer, resonators exhibit a of 10.5%, and a value of 1400. Ladder‐type RF filters using these resonators are fabricated at 6.2 GHz and show improved performance over filters fabricated using physical vapor deposition‐deposited AlScN.

In situ scanning tunneling microscopy studies of carbonate-induced restructuring of Ag-decorated Cu(100) electrodes.

Ag-decorated Cu electrocatalysts are of great interest for electrochemical CO2 reduction, because of an increased yield of multi-carbon products. Here, we present studies of well-defined AgCu electrodes by in situ scanning tunneling microscopy. These bimetallic model electrocatalysts are prepared by electrodepositing submonolayer Ag coverages on Cu(100) in 0.1 M H2SO4, resulting in monolayer islands with a hexagonal quasi-Ag(111) atomic lattice. Upon exchanging the solution at potentials in the double layer range to 0.1 M KHCO3, pronounced Ag island restructuring towards anisotropic shapes, the nucleation and growth of new islands, and a strong reduction in surface mobility are observed. In addition, high-resolution images reveal a highly disordered molecular adlayer, contrary to the case of Ag-free Cu(100) electrodes. These observations can be explained by interactions of metal adatoms with adsorbed (bi)carbonate and show that Ag redispersion on Cu electrocatalysts may occur even in the absence of CO2 reduction.

Electronic changes at the platinum interface induced by bismuth and tellurium adatom adsorption

Chemical modification of catalytic surfaces by adatoms adsorption is one of the most common methods for designing new (electro)catalytic materials. In this work, the interaction of single bismuth and tellurium adatoms with model platinum basal planes has been investigated using density functional theory to explore changes in the electronic properties of these systems. Calculations indicate that both adatoms are stable, and there is a charge transfer from the adsorbate to the surface in all the systems. As the result, the work function of Pt surfaces lowers and a trend: (100) > (110) > (111) emerges, different from (111) > (100) > (110) seen for the pristine planes. Both Bi and Te cause a noticeable shift in the d-band center of the surfaces, indicating a significant impact of these adatoms on Pt catalytic properties, as experimentally reported. For the Bi/Pt(111), the only system for which similar data has been described, results are in good agreement to previous studies. Results allow to gain insights at atomic-level into adatom-induced changes in electronic properties of Pt, which in turn shed light on key factors that control Pt catalytic activity toward model reactions. In this context, it is found that in contrast to the Bi/Pt(111) system, adatom’s electronegativity cannot be considered as an effective descriptor for the enhanced activity of other Bi/Pt, or Te/Pt systems for the oxidation of organic molecules. Contrarily, calculated data offer a reasonable explanation for the reported inhibition of the hydrogen evolution reaction on Bi/Pt and Te/Pt surfaces in light of the substrate’s adatom-induced strain.

A first-principles and mesoscopic model analysis for pair, trio, and quarto interactions of Au adatoms on Ag(100)

The first-principles density functional theory (DFT) method is used to directly calculate the short- and medium-range pair, trio, and quarto interactions of Au atoms in Ag(100)-supported and freestanding (unsupported) Au dimers, trimers, and tetramers. This allows us to systematically investigate the substrate effects. We find that the interactions for freestanding Au clusters have striking differences from their Ag(100)-supported counterparts, especially for shorter-range interactions. This reflects the strong substrate effects on these pair, trio, and quarto interactions. We also find that, for these Ag(100)-supported two-dimensional Au clusters, the substrate-mediated interactions obtained from an elastic eigenvector approach including a mesoscopic interacting range (called the mesoscopic model) have reasonable agreement with the DFT results.

Interplay of magnetic states and hyperfine fields of iron dimers on MgO(001)

Individual nuclear spin states can have very long lifetimes and could be useful as qubits. Progress in this direction was achieved on MgO/Ag(001) via detection of the hyperfine interaction (HFI) of Fe, Ti and Cu adatoms using scanning tunneling microscopy. Previously, we systematically quantified from first-principles the HFI for the whole series of 3d transition adatoms (Sc-Cu) deposited on various ultra-thin insulators, establishing the trends of the computed HFI with respect to the filling of the magnetic s- and d-orbitals of the adatoms and on the bonding with the substrate. Here we explore the case of dimers by investigating the correlation between the HFI and the magnetic state of free standing Fe dimers, single Fe adatoms and dimers deposited on a bilayer of MgO(001). We find that the magnitude of the HFI can be controlled by switching the magnetic state of the dimers. For short Fe-Fe distances, the antiferromagnetic state enhances the HFI with respect to that of the ferromagnetic state. By increasing the distance between the magnetic atoms, a transition toward the opposite behavior is observed. Furthermore, we demonstrate the ability to substantially modify the HFI by atomic control of the location of the adatoms on the substrate. Our results establish the limits of applicability of the usual hyperfine hamiltonian and we propose an extension based on multiple scattering processes.

DFT study of Sb layers on the Mo(112) surface

Relativistic DFT calculations, performed for Sb layers adsorbed on the Mo (112) surface, have revealed a strong interaction of Sb adatoms with the surface. At low coverages, the layer is predicted to form a c (2 × 2) structure, while for a complete Sb monolayer the most favorable structure is the p (1 × 1), which forms despite a minor one-dimensional compressing of the layer in the direction along the Mo (112) surface furrows. This structure is favorable also for complete bilayer and 3-layer films, so that very thin Sb layers reproduce the furrowed structure of the Mo (112) surface. The adsorbed Sb layers cause a significant redistribution of the densities of states, which, however, does not increase enough at the Fermi level to produce any substantial metallization of the film. The spin-orbit coupling causes only minor changes in the band structure, while Sb layer on one face of the Mo (112) slab destroys the inversion symmetry of the adsorption system thus leading to the appearance of the Rashba-type splitting of the bands.

Cu ion and adatom interaction with stainless steel and silicon

Copper ion-implanted stainless steel possesses antibacterial properties and resistance to corrosion and wear. These properties have been found beneficial in surgical implants where stainless steel has a profound use. Simulations have been performed using SRIM (Stopping and Range of Ions in Matter) software, where copper ions were implanted into stainless steel substrate. The results were obtained in terms of different plots of collision events, ion range, ionization, lateral range distribution of ions, and energy loss to phonons concerning target depth. The morphology of copper deposited on Si by sputtering techniques was observed which is a technologically important system.

Role of transferred graphene on atomic interaction of GaAs for remote epitaxy

Remote epitaxy is a recently discovered type of epitaxy, wherein single-crystalline thin films can be grown on graphene-coated substrates following the crystallinity of the substrate via remote interaction through graphene. Although remote epitaxy provides a pathway to form freestanding membranes by controlled exfoliation of grown film at the graphene interface, implementing remote epitaxy is not straightforward because atomically precise control of interface is required. Here, we unveil the role of the graphene–substrate interface on the remote epitaxy of GaAs by investigating the interface at the atomic scale. By comparing remote epitaxy on wet-transferred and dry-transferred graphene, we show that interfacial oxide layer formed at the graphene–substrate interface hinders remote interaction through graphene when wet-transferred graphene is employed, which is confirmed by an increase of interatomic distance through graphene and also by the formation of polycrystalline films on graphene. On the other hand, when dry-transferred graphene is employed, the interface is free of native oxide, and single-crystalline remote epitaxial films are formed on graphene, with the interatomic distance between the epilayer and the substrate matching with the theoretically predicted value. The first atomic layer of the grown film on graphene is vertically aligned with the top layer of the substrate with these atoms having different polarities, substantiating the remote interaction of adatoms with the substrate through graphene. These results directly show the impact of interface properties formed by different graphene transfer methods on remote epitaxy.

Bayesian Learning of Adatom Interactions from Atomically Resolved Imaging Data.

Atomic structures and adatom geometries of surfaces encode information about the thermodynamics and kinetics of the processes that lead to their formation, and which can be captured by a generative physical model. Here we develop a workflow based on a machine-learning-based analysis of scanning tunneling microscopy images to reconstruct the atomic and adatom positions, and a Bayesian optimization procedure to minimize statistical distance between the chosen physical models and experimental observations. We optimize the parameters of a 2- and 3-parameter Ising model describing surface ordering and use the derived generative model to make predictions across the parameter space. For concentration dependence, we compare the predicted morphologies at different adatom concentrations with the dissimilar regions on the sample surfaces that serendipitously had different adatom concentrations. The proposed workflow can be used to reconstruct the thermodynamic models and associated uncertainties from the experimental observations of materials microstructures. The code used in the manuscript is available at https://github.com/saimani5/Adatom_interactions.

Trends in the hyperfine interactions of magnetic adatoms on thin insulating layers

Nuclear spins are among the potential candidates prospected for quantum information technology. A recent breakthrough enabled to atomically resolve their interaction with the electron spin, the so-called hyperfine interaction, within individual atoms utilizing scanning tunneling microscopy (STM). Intriguingly, this was only realized for a few species put on a two-layers thick MgO. Here, we systematically quantify from first-principles the hyperfine interactions of the whole series of 3d transition adatoms deposited on various thicknesses of MgO, NaF, NaCl, h–BN, and Cu2N films. We identify the adatom-substrate complexes with the largest hyperfine interactions and unveil the main trends and exceptions. We reveal the core mechanisms at play, such as the interplay of the local bonding geometry and the chemical nature of the thin films, which trigger transitions between high- and low-spin states accompanied with subtle internal rearrangements of the magnetic electrons. By providing a general map of hyperfine interactions, our work has immediate implications in future STM investigations aiming at detecting and realizing quantum concepts hinging on nuclear spins.

Impact of 2D-3D Heterointerface on Remote Epitaxial Interaction through Graphene.

Remote epitaxy has drawn attention as it offers epitaxy of functional materials that can be released from the substrates with atomic precision, thus enabling production and heterointegration of flexible, transferrable, and stackable freestanding single-crystalline membranes. In addition, the remote interaction of atoms and adatoms through two-dimensional (2D) materials in remote epitaxy allows investigation and utilization of electrical/chemical/physical coupling of bulk (3D) materials via 2D materials (3D-2D-3D coupling). Here, we unveil the respective roles and impacts of the substrate material, graphene, substrate-graphene interface, and epitaxial material for electrostatic coupling of these materials, which governs cohesive ordering and can lead to single-crystal epitaxy in the overlying film. We show that simply coating a graphene layer on wafers does not guarantee successful implementation of remote epitaxy, since atomically precise control of the graphene-coated interface is required, and provides key considerations for maximizing the remote electrostatic interaction between the substrate and adatoms. This was enabled by exploring various material systems and processing conditions, and we demonstrate that the rules of remote epitaxy vary significantly depending on the ionicity of material systems as well as the graphene-substrate interface and the epitaxy environment. The general rule of thumb discovered here enables expanding 3D material libraries that can be stacked in freestanding form.

Morphology-Controlled Vapor Phase Growth and Characterization of One-Dimensional GaTe Nanowires and Two-Dimensional Nanosheets for Potential Visible-Light Active Photocatalysts.

Gallium telluride (GaTe) one-dimensional (1D) and two-dimensional (2D) materials have drawn much attention for high-performance optoelectronic applications because it possesses a direct bandgap for all thickness. We report the morphology-controlled vapor phase growth of 1D GaTe nanowires and 2D GaTe nanosheets by a simple physical vapor transport (PVT) approach. The surface morphology, crystal structure, phonon vibration modes, and optical property of samples were characterized and studied. The growth temperature is a key synthetic factor to control sample morphology. The 1D GaTe single crystal monoclinic nanowires were synthesized at 550 °C. The strong interlayer interaction and high surface migration of adatoms on c-sapphire enable the assembly of 1D nanowires into 2D nanosheet under 600 °C. Based on the characterization results demonstrated, we propose the van der Waals growth mechanism of 1D nanowires and 2D nanosheets. Moreover, the visible-light photocatalytic activity of 1D nanowires and 2D nanosheets was examined. Both 1D and 2D GaTe nanostructures exhibit visible-light active photocatalytic activity, suggesting that the GaTe nanostructures may be promising materials for visible light photocatalytic applications.

Modelling the size of nitrogen c(2x2) islands on Cu(001) with elastic multisite interactions

An extended elastic eigenvector approach for adatom interactions is applied to model nitrogen c(2x2) atom islands on Cu(001). Oscillating interactions between adatom monomers or dimers are considered. Attractive pair interactions of adatoms are able to describe agglomeration but fail to explain the size of islands. Multisite interactions created by dimers, however, can explain the size of islands if an interaction parameter is adjusted properly. Finite size islands are formed when repulsive monomer interactions are balanced by attractive monomer-dimer interactions.A simple model of nearest neighbor attraction and s−3 repulsion is used as an example for the interaction parameter search.Previous experimental studies have shown that in the low coverage region nitrogen atoms agglomerate to isolated square islands of about 5 nm × 5 nm size with a c(2x2) structure. With increasing coverage those islands form regular patterns but do not touch below about 0.4 monolayers. Previous experiments and calculations have shown that the square island pattern show significant elastic effects.Different adatom structures within the nitrogen islands have been analyzed, a dimer step model is able to reproduce the experimentally found island size. This model requires a molecular bond between nitrogen adatoms forming dimers. The model is also used to compute elastic interactions between islands and to check it against the experimentally found island pattern.Shortcomings and limitations of the model are discussed and open questions are formulated.

Domain formation in the deposition of thin films of two-component mixtures

We perform a kinetic Monte Carlo simulation study of a model of thin film deposition of a two-component mixture in which the activation energy for diffusion of an adatom is additive over its nearest neighbors and in which the interactions between adatoms of the same species are stronger than those between adatoms of different species. The film morphology is investigated for broad ranges of values of the ratios between terrace diffusivity and atomic flux, of the probabilities of detachment from lateral neighbors, and of probabilities of crossing terrace edges. First, we consider a symmetric case in which the interactions of adatoms of the same species are the same for the two components. For low and intermediate temperatures, we show the formation of narrow domains, whose widths are $3$-$30$ lattice constants, which meander in the layers parallel to the substrate, and are connected through very long distances. The domain width depends on the diffusivity-flux ratio of the same species, but it is weakly affected by interactions of different species, so rough estimates of that width can be obtained by using tabulated properties of films with a single component. At high temperatures, the separation of domains is enhanced, but their long distance connectivity is lost, which shows that the formation of the long meandering domains is restricted to a certain range of temperature and flux. Similar morphological features are obtained when the intra-species interactions are different and the adatom diffusion coefficients on terraces of the same species differ up to two orders of magnitude. An approximate scaling relation for the domain width is obtained, but the species with the largest mobility constrains the temperature range in which the long connected domains are found.

Elastic interactions of Fe adatoms on Cu(111) at the mesoscale

An extended elastic eigenvector approach had earlier been developed to interpret ab-initio calculations of adatom interactions. It shows oscillating interactions as well as trio- and quarto (multisite) terms within clusters. It is now applied to the interaction of Fe adatoms on Cu(111).The extended approach differs from previous calculations by using a sharp cutoff - generating oscillating interactions - and by taking into account interacting dimers - generating strong anisotropies and multisite terms. Additional weak anisotropy stems from the substrate and from the surface Brillouin zone shape.This approach has 3 free parameters which have been fitted to first principles interactions of Fe adatoms on Cu(111). Elastic adatom pair interactions and dimer-dimer interactions at mesoscale separations show a reasonable good fit to the first principles interactions. At smaller separations elastic interaction values remain questionable. To enable a comparison with future first principle calculations also dimer-monomer interactions are shown.Some conclusions on initial adatom formation and diffusion are proposed and open questions are formulated.

Phosphorus Adsorption on Fe(110): An ab Initio Comparative Study of Iron Passivation by Different Adsorbates

From corrosion protection to embrittlement and lubrication, the presence of phosphorus at iron surfaces is critical for a range of processes and applications. However, phosphorus adsorption on iron has never been studied experimentally or theoretically. Here P chemisorption on the most stable surface of iron is analyzed by means of density functional theory. The most stable adsorption geometry and coverage are identified, and the changes induced by P adsorption on the structural and electronic properties of the metal are discussed. A systematic comparison among P, S, N, and O uncovers a peculiar behavior of the P and S species: attractive adatom–adatom interactions at high coverage lead to the formation of two-dimensional overlayers that reduce the metal reactivity and work function. This effect is important in iron embrittlement and for the functionality of P- and S-containing additives included in lubricant oils.

Long-range interaction of radiation-generated self-interstitial atoms and adatoms on tungsten surface

ABSTRACTThe morphological modification of the W surface induced by specimen irradiation with 5 keV He atoms was studied at the atomic level using low-temperature field ion microscope techniques. The major impact-induced damage mode on W {110} surface was found to be the formation of adatom sets produced by radiation-generated self-interstitial atoms emerging at the surface. The long-range interaction was revealed by evaluating the experimental probability density of finding two radiation-generated adatoms at a given separation in comparison with the probability density corresponding to a random distribution of adatoms. The statistically significant difference of these distributions consists of the absence or severe reduction of observed adatom pairs with separations in the range 5–11 Å. The experimental distribution was characterised by a relatively open arrangement of adatoms with the closest separation of about 11 Å. Our field ion microscope observations also reveal the self-organisation of radiation-generated W adatoms into atomic chains with the lateral interatomic separation substantially larger than the nearest-neighbor distance. These effects indicate the existence of long-range interactions between radiation-generated adatoms and radiation-generated self-interstitial atoms in the subsurface region.