Surface Atoms Research Articles

Isostructural Nanocluster Manipulation Reveals Pivotal Role of One Surface Atom in Click Chemistry.

Elucidating single-atom effects on the fundamental properties of nanoparticles is challenging because single-atom modifications are typically accompanied by appreciable changes to the overall particle's structure. Herein, we report the synthesis of a [Cu58 H20 PET36 (PPh3 )4 ]2+ (Cu58 ; PET: phenylethanethiolate; PPh3 : triphenylphosphine) nanocluster-an atomically precise nanoparticle-that can be transformed into the surface-defective analog [Cu57 H20 PET36 (PPh3 )4 ]+ (Cu57 ). Both nanoclusters are virtually identical, with five concentric metal shells, save for one missing surface copper atom in Cu57 . Remarkably, the loss of this single surface atom drastically alters the reactivity of the nanocluster. In contrast to Cu58 , Cu57 shows promising activity for click chemistry, particularly photoinduced [3+2] azide-alkyne cycloaddition (AAC), which is attributed to the active catalytic site in Cu57 after the removal of one surface copper atom. Our study not only presents a unique system for uncovering the effect of a single-surface atom modification on nanoparticle properties but also showcases single-atom surface modification as a powerful means for designing nanoparticle catalysts.

Fractal Design of Hierarchical PtPd with Enhanced Exposed Surface Atoms for Highly Catalytic Activity and Stability.

Hierarchical assembly of arc-like fractal nanostructures not only has its unique self-similarity feature for stability enhancement but also possesses the structural advantages of highly exposed surface-active sites for activity enhancement, remaining a great challenge for high-performance metallic nanocatalyst design. Herein, we report a facile strategy to synthesize a novel arc-like hierarchical fractal structure of PtPd bimetallic nanoparticles (h-PtPd) by using pyridinium-type ionic liquids as the structure-directing agent. Growth mechanisms of the arc-like nanostructured PtPd nanoparticles have been fully studied, and precise control of the particle sizes and pore sizes has been achieved. Due to the structural features, such as size control by self-similarity growth of subunits, structural stability by nanofusion of subunits, and increased numbers of exposed active atoms by the curved homoepitaxial growth, h-PtPd displays outstanding electrocatalytic activity toward oxygen reduction reaction and excellent stability during hydrothermal treatment and catalytic process.

Isostructural Nanocluster Manipulation Reveals Pivotal Role of One Surface Atom in Click Chemistry

AbstractElucidating single‐atom effects on the fundamental properties of nanoparticles is challenging because single‐atom modifications are typically accompanied by appreciable changes to the overall particle's structure. Herein, we report the synthesis of a [Cu58H20PET36(PPh3)4]2+ (Cu58; PET: phenylethanethiolate; PPh3: triphenylphosphine) nanocluster—an atomically precise nanoparticle—that can be transformed into the surface‐defective analog [Cu57H20PET36(PPh3)4]+ (Cu57). Both nanoclusters are virtually identical, with five concentric metal shells, save for one missing surface copper atom in Cu57. Remarkably, the loss of this single surface atom drastically alters the reactivity of the nanocluster. In contrast to Cu58, Cu57 shows promising activity for click chemistry, particularly photoinduced [3+2] azide‐alkyne cycloaddition (AAC), which is attributed to the active catalytic site in Cu57 after the removal of one surface copper atom. Our study not only presents a unique system for uncovering the effect of a single‐surface atom modification on nanoparticle properties but also showcases single‐atom surface modification as a powerful means for designing nanoparticle catalysts.

Nanothermodynamics on the Example of Metallic Nanoparticles

After analyzing the problem of extending the Gibbs surface excess method to nanoscale objects, two different approaches to the application of the Gibbs method for finding the specific surface energy of metal nanoparticles are being considered. The first approach involves the use of the local coordination approximation to estimate the specific surface energy of icosahedral FCC metal nanoparticles (magic nanoclusters). For the first time, we have drawn attention to the fact that for such a nanocluster, it is possible to accurately calculate both the fraction of surface atoms and the values of the first coordination number in the inner region of the nanoparticle and on its surface (faces, edges, and vertices). The second approach implemented by us earlier for spherical Au nanoparticles and here for FCC Pt nanoparticles, involves the complex application of the Gibbs method adapted for nanoparticles and the results of molecular dynamics simulation. Estimates using both approaches agree with the experimental values of the surface energy corresponding to the flat surface of the bulk phases of the corresponding metals. In the final section of the work, the limits of applicability of thermodynamics to nanosystems are discussed.

A Chemist's View on Electronic and Steric Effects of Surface Ligands on Plasmonic Metal Nanostructures.

ConspectusPlasmonic metal nanostructures have been extensively developed over the past few decades because of their ability to confine light within the surfaces and manipulate strong light-matter interactions. The light energy stored by plasmonic nanomaterials in the form of surface plasmons can be utilized to initiate chemical reactions, so-called plasmon-induced catalysis, which stresses the importance of understanding the surface chemistry of the plasmonic materials. Nevertheless, only physical interpretation of plasmonic behaviors has been a dominant theme, largely excluding chemical intuitions that facilitate understanding of plasmonic systems from molecular perspectives. To overcome and address the lack of this complementary understanding based on molecular viewpoints, in this Account we provide a new concept encompassing the well-developed physics of plasmonics and the corresponding surface chemistry while reviewing and discussing related references. Inspired by Roald Hoffmann's descriptions of solid-state surfaces based on the molecular orbital picture, we treat molecular interfaces of plasmonic metal nanostructures as a series of metal-ligand complexes. Accordingly, the effects of the surface ligands can be described by bisecting them into electronic and steric contributions to the systems. By exploration of the quality of orbital overlaps and the symmetry of the plasmonic systems, electronic effects of surface ligands on localized surface plasmon resonances (LSPRs), surface diffusion rates, and hot-carrier transfer mechanisms are investigated. Specifically, the propensity of ligands to donate electrons in a σ-bonding manner can change the LSPR by shifting the density of states near the Fermi level, whereas other types of ligands donating or accepting electrons in a π-bonding manner modulate surface diffusion rates by affecting the metal-metal bond strength. In addition, the formation of metal-ligand bonds facilitates direct hot-carrier transfer by forming a sort of molecular orbital between a plasmonic structure and ligands. Furthermore, effects of steric environments are discussed in terms of ligand-ligand and ligand-surface nonbonding interactions. The steric hindrance allows for controlling the accessibility of the surrounding chemical species toward the metal surface by modulating the packing density of ligands and generating repulsive interactions with the surface atoms. This unconventional approach of considering the plasmonic system as a delocalized molecular entity could establish a basis for integrating chemical intuition with physical phenomena. Our chemist's outlook on a molecular interface of the plasmonic surface can provide insights and avenues for the design and development of more exquisite plasmonic catalysts with regio- and enantioselectivities as well as advanced sensors with unprecedented chemical controllability and specificity.

ZIF-67 derived Co nanoparticles on ZIF-Derived carbon for hydrogen spillover and storage

Hydrogen spillover involves the dissociation of H2 on transition metal nanoparticles and further atomic hydrogen surface migration on catalyst supports. Hence, the spillover phenomenon has been reported in applications of heterogeneous catalysis in hydrogenation and room-temperature hydrogen storage. However, a proper catalyst design is requisite to initiate hydrogen spillover, considering the transition metal particle dispersion, sorbent surface modification, porosity, etc. In this report, we pyrolyzed the zeolitic imidazolate framework ZIF-67 for residual Co metal nanoparticles and N-dopant on ZIF-derived carbon (ZDC) for hydrogen adsorption via spillover effect. Catalyst optimization by proper ZIF carbonization process regarding manipulated pyrolytic temperatures, atmospheres, and ramping rates, results in different properties in ZDCs. Well-distributed Co nanoparticles can be obtained on N-rich graphitic sorbent ZDCs with retained high specific surface area. The Co on ZDC exhibits improved room-temperature hydrogen capacity of 0.77 wt% than neat ZIF-67 of 0.09 wt% at 30 bar, 300 K. The adsorption sites were examined experimentally by nitrogen hydrogenation, and possible atomic hydrogen diffusion was evaluated theoretically showing energy barrier reduced by over 0.1 eV. It demonstrates that cobalt nanoparticles can successfully initiate hydrogen spillover on ZIF-derived carbon with nitrogen functionality, even without noble metals.

Oxidation and corrosion investigation on Ti2AlV (110) surface using first principle approach

Ti-Al-V alloys are frequently used as structural materials in metallurgy, electronics, and other industrial sectors due to their exceptional qualities. However, the inherent limitations of the material include porosity, surface roughness, and a strong affinity for oxygen. The adsorption of oxygen and chlorine on metal surfaces is crucial, especially for catalysis and corrosion applications. In this study, the adsorption mechanism of oxygen and chlorine on the surface of Ti2AlV (110) is investigated using density functional theory. Surface oxidation and corrosion were compared using adsorption strength, work function, density of states, and charge density redistribution. The findings revealed that the adsorption behaviour of oxygen and chlorine is an exothermic and spontaneous reaction. Furthermore, the adsorption of oxygen has a negative adsorption energy higher than that of chlorine. Subsequently, various adsorption sites were examined on the surface, with the bridge sites being identified as the most stable adsorption configuration. In addition, a linear relationship was discovered between the adsorption energy strength and charge density redistribution. Electron depletion was observed on surface atoms, as well as charge accumulation on adsorbates. Moreover, adsorption was also discovered to alter the surface work function.

Nitrogen flow rate dependent atomic coordination, phonon vibration and surface analysis of DC magnetron sputtered nitrogen rich-AlN thin films

In this work, the effect on crystallite orientation, surface morphology, fractal geometry, structural coordination and electronic environment of DC magnetron sputtered AlN films were investigated. X-ray diffraction results disclosed that the c-axis orientation of AlN films increased with the preferred wurtzite hexagonal structure above 17% N2 flow. X-ray reflectivity data confirmed AlN film density increased with increasing N2 flow and was found to be 3.18 g/cm3 for 40% N2. The transition of electrons from N 1s to 2p states hybridized with Al 3p states because of π* resonance was obtained from X-ray absorption spectroscopy of the N K-edge. The semi-empirical coordination geometry of nitrogen atoms has been studied by deconvolution of N K-edge. The surface composition of AlN films at 40% N2 consists of 32.08, 51.94 and 15.97 at.% Al, N and O respectively. Blue-shifting of A1(LO) and E1(LO) modes in the Raman spectra at phonon energies 800 and 1051 cm−1 respectively was most likely due to the presence of oxygen bonds in the AlN films.

The Structures of Small (< 3 nm), Solubilized Platinum Nanocrystals are Composed of an Ordered Core Surrounded by Mobile Surface Atoms.

The Structures of Small (< 3 nm), Solubilized Platinum Nanocrystals are Composed of an Ordered Core Surrounded by Mobile Surface Atoms.

Dispersion-Corrected DFT-D4 Study of the Adsorption of Halobenzenes and 1,3,5-Trihalobenzenes on the Cu(111) Surface─Effect of Sigma Hole Properties.

Halogen bonds, characterized by directionality, tunability, hydrophobicity, and variable sizes, are ideal noncovalent interactions to design and control the formation of self-assembled nanostructures. The specific self-assembly cases formed by the halogen-bonding interaction have been well studied by scanning tunneling microscopy (STM) experiments and density functional theory (DFT) calculations. However, there is a lack of systematic theoretical adsorption studies on halogenated molecules. In this work, the adsorption of halobenzenes and 1,3,5-trihalobenzenes on the Cu(111) surface was examined by dispersion-corrected DFT methods. The adsorption geometries, noncovalent molecule-surface interactions, electronic densities, and electrostatic potential maps were examined for their most stable adsorption sites using the DFT-D4 method. Our calculations revealed that the iodo compounds favor a different adsorption geometry from aryl chlorides and bromides. Down the halogen group (Cl to I), the adsorption energy increases and the distance between the halogen atom and Cu surface decreases, which indicates stronger molecule-surface interactions. This is supported by the changes in the density of states upon adsorption. Noncovalent interaction analysis was also employed to further understand the nature and relative strength of the molecule-surface interactions. Electrostatic potential maps revealed that the positive character of the halogen sigma hole becomes stronger upon adsorption. Thus, surface adsorption of the halogenated molecule will enhance the formation of intermolecular halogen bonds. The present theoretical findings are expected to contribute toward a more comprehensive understanding of halogen bonding on the Cu(111) surface.

Oriented lateral growth of two-dimensional materials on c-plane sapphire.

Two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs) represent the ultimate thickness for scaling down channel materials. They provide a tantalizing solution to push the limit of semiconductor technology nodes in the sub-1 nm range. One key challenge with 2D semiconducting TMD channel materials is to achieve large-scale batch growth on insulating substrates of single crystals with spatial homogeneity and compelling electrical properties. Recent studies have claimed the epitaxy growth of wafer-scale, single-crystal 2D TMDs on a c-plane sapphire substrate with deliberately engineered off-cut angles. It has been postulated that exposed step edges break the energy degeneracy of nucleation and thus drive the seamless stitching of mono-oriented flakes. Here we show that a more dominant factor should be considered: in particular, the interaction of 2D TMD grains with the exposed oxygen-aluminium atomic plane establishes an energy-minimized 2D TMD-sapphire configuration. Reconstructing the surfaces of c-plane sapphire substrates to only a single type of atomic plane (plane symmetry) already guarantees the single-crystal epitaxy of monolayer TMDs without the aid of step edges. Electrical results evidence the structural uniformity of the monolayers. Our findings elucidate a long-standing question that curbs the wafer-scale batch epitaxy of 2D TMD single crystals-an important step towards using 2D materials for future electronics. Experiments extended to perovskite materials also support the argument that the interaction with sapphire atomic surfaces is more dominant than step-edge docking.

Electronic Structure and Mechanical Properties of Solvated Montmorillonite Clay Using Large-Scale DFT Method

Montmorillonite clay (MMT) has been widely used in engineering and environmental applications as a landfill barrier and toxic waste repository due to its unique property as an expandable clay mineral that can absorb water easily. This absorption process rendered MMT to be highly exothermic due to electrostatic interactions among molecules and hydrogen bonds between surface atoms. A detailed study of a large supercell model of structural clay enables us to predict long-term nuclear waste storage. Herein, a large solvent MMT model with 4071 atoms is studied using ab initio density functional theory. The DFT calculation and analysis clarify the important issues, such as bond strength, solvation effect, elasticity, and seismic wave velocities. These results are compared to our previous study on crystalline MMT (dry). The solvated MMT has reduced shear modulus (G), bulk modulus (K), and Young’s modulus (E). We observe that the conduction band (CB) in the density of states (DOS) of solvated MMT model has a single, conspicuous peak at −8.5 eV. Moreover, the atom-resolved partial density of states (PDOS) summarizes the roles played by each atom in the DOS. These findings illuminate numerous potential sophisticated applications of MMT clay.

Plasma-Induced Formation of Pt Nanoparticles with Optimized Surface Oxidation States for Methanol Oxidation and Oxygen Reduction Reactions to Achieve High-Performance DMFCs.

Plasma treatment and reduction are used to synthesize Pt nanoparticles (NPs) on nitrogen-doped carbon nanotubes (p-Pt/p-NCNT) with a low Pt content. In particular, the plasma treatment is used to treat the NCNT to give it with more surface defects, facilitating a better growth of the Pt NPs, while the plasma reduction produces the Pt NPs with a reduced fraction of the surface atoms at the high oxidation states, increasing the catalytic activities of the p-Pt@p-NCNT. Even at the low Pt content (7.8wt.%), the p-Pt@p-NCNT shows superior catalytic activities and good stabilities for methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR). The density functional theory (DFT) calculations indicate that the defects generated in the plasma treatment can help the growth of the Pt NPs on the NCNTs, leading to the stronger electronic coupling between Pt and NCNT and the increased stability of the catalyst. The plasma reduction can give the Pt NPs with optimized surface oxidation states, decreasing the energy barriers of the rate-determining steps for MOR and ORR. When used as the anode and cathode catalysts for the direct methanol fuel cells (DMFCs), the p-Pt@p-NCNT exhibits a higher maximum power density of 81.9 mW cm-2 at 80 °C and shows good durability.

Atomic surface of fused silica and polishing mechanism interpreted by molecular dynamics and density functional theory

For fused silica, it is difficult to obtain an atomic surface with a high material removal rate (MRR), and the polishing mechanism is still a challenge. Chemical mechanical polishing (CMP) has historically used toxic and polluted ingredients. To meet these demanding constraints, it is extremely difficult to produce green CMP for fused silica. In this work, we report on the development of a novel green CMP slurry containing ceria, nicotinic acid, sodium alginate, and deionized water. After CMP, an atomic surface is achieved with a surface roughness Sa of 0.098 nm using a scanning area of 20 × 20 μm2, and the MRR is 7.65 μm/h. According to density functional theory and molecular dynamics simulations, nicotinic acid and fused silica generated a novel complex during CMP that could be peeled by active ceria by creating coordinating bonds. These findings offer an intuitive understanding of the CMP mechanism and suggest a novel method for fabricating fused silica atomic surfaces for possible usage in high-performance optical devices.

Fitting the charged-optimized many-body potential for the Al-O-Se-Zn system

A charge-optimized many-body (COMB3) potential has been developed for the Al-O-Se-Zn system using first-principles data. This work updates COMB3 for zinc and extends it to include selenium as well as other pairwise and three-body interactions that were not developed previously. We tested the empirical potential for known crystalline phases and find reasonable agreement between the calculated structural, elastic, and vibrational properties and experimental data. We use the anisotropic coefficients of the thermal expansion method to calculate the temperature-dependent properties of a few selected materials. We then compare the total energy of the system and its first- and second-order positional derivatives, as well as the second-order strain derivative with respect to the atomic potential energy surface to thermal properties obtained from molecular dynamics simulations using the fitted COMB3 potential. The results of our temperature-dependent calculations show reasonable agreement with previous work for temperatures below the system’s melting point. With this fitting, we could utilize a versatile, charge-dependent empirical potential to model the interface between ZnSe and Al2O3 by molecular dynamics simulations.

Assessing the stability of Kagome D019-Mn3Ga (0001) surfaces: A first-principles study

Using non-collinear spin-polarized first-principles calculations, we have investigated the properties of the hexagonal D019 (0001) Mn3Ga surface. Two different surface terminations were considered: type-1 and type-2, with opposite chiralities. In the case of pristine surfaces, the Kagome triangular AFM character remains on the surface and in inner layers, with a slight increase in the surface magnetic moments due to the low coordination of the surface atoms. An increase in the remnant out-of-plane FM character compared to the bulk is also noticed. The effect of Ga or Mn vacancies on both surfaces was also investigated. Ga vacancies in the 2nd monolayer are more stable than in other layers. Such vacancies distort the triangular AFM configuration of the neighboring layers. Despite this, the AFM layer-by-layer nature remains. Conversely, Mn vacancies stabilize in the most exposed layer. In this case, the neighboring layers completely lose the triangular alignment. However, Mn atoms rearrange to preserve the AFM layer-by-layer character. Upon evaluating the thermodynamic stability of these surfaces, we observe that the pristine Kagome AFM magnetic surfaces are the most stable. Ga vacancies are the least stable configurations because they break down the super-exchange interaction that holds the Kagome magnetic arrangement. Finally, our calculations show that the Kagome magnetic arrangement at the surface is stabilized by both the magnetic (Mn) and non-magnetic (Ga) atoms. Therefore, it is expected that D019-Mn3Ga will not present low-index reconstructions induced by vacancies.

Vacancy-induced magnetic states in TiO2 surfaces

We present a combined experimental and theoretical study of surface-related magnetic states in TiO2. Our experiments on nano-sized thin films of pure TiO2 have suggested that the observed room-temperature magnetism originates from defects, in particular, from the surface of thin films as well as from point defects, such as oxygen vacancies located mainly at the surface. Clarifying this phenomenon is very important for harnessing magnetic properties of pristine TiO2 films in future spintronic applications but a detailed experimental investigation is very demanding. Therefore, quantum-mechanical density functional theory calculations were performed for (i) bulk anatase TiO2, (ii) bulk-like TiO2-terminated vacancy-free (001) surfaces, (iii) vacancy-containing TiO-terminated (001) surfaces, (iv) TiO0.75-terminated (001) surfaces with additional 25% surface oxygen vacancies, as well as (v) oxygen-terminated (001)-surfaces. Our fixed-spin-moment calculations identified both the bulk and the bulk-like terminated vacancy-free TiO2-terminated (001) surfaces as non-magnetic. In contrast, oxygen vacancies in the case of TiO-terminated and TiO0.75-terminated (001) surfaces lead to ferromagnetic and rather complex ferrimagnetic states, respectively. The spin-polarized atoms are the Ti atoms (due to the d-states) located in the surface and sub-surface atomic planes. Last, the O-terminated surfaces are also magnetic due to the surface and sub-surface oxygen atoms and sub-surface Ti atoms (but their surface energy is high).

Ceria–Zirconia Supported Platinum Catalysts for Water Gas Shift Reaction: Influence of Support Composition

The study is presented on the influence of the composition of a ceria-zirconia support on the structure and the activity in water gas shift reaction of platinum catalysts (Pt/Ce0.75Zr0.25O2 и Pt/Ce0.4Zr0.5Y0.05La0.05O2). The structure diagnostics of the samples were performed using high-resolution transmission electron microscopy, powder X-ray diffraction, CO chemisorption and X-ray atomic pair distribution function method. It was shown that the catalysts contain highly dispersed platinum particles not exceeding 2 nm in size. Platinum particles supported on Ce0.75Zr0.25O2 are smaller due to the higher specific surface area of the support. The catalysts Pt/Ce0.75Zr0.25O2 and Pt/Ce0.4Zr0.5Y0.05La0.05O2 proved to have similar efficiency while having the same platinum content. It was assumed that the catalysts supported on Ce0.4Zr0.5Y0.05La0.05O2 demonstrate a slightly higher turnover frequency per platinum surface atom, but it is likely compensated by the difference in the supported metal particle size.

DFT study of the formation of the Sb-Ag(1 1 1) (√3×√3) – R30° surface alloy

According to performed DFT calculations, the (√3×√3) – R30° structure, in which Sb atoms occupy hcp sites on Ag(111), is more energetically favorable than the related substitutional SbAg2 surface alloy. The difference in energies is significant, 0.66 eV per unit cell, and can be attributed to a larger size of Sb atoms compared to Ag. The obtained results of modeling the substitutional process explain the formation of adsorbed Sb layer on the Ag(111) surface by means of Sb deposition instead of the formation of the substitutional surface alloy. In turn, Ag deposition onto the alloy surface will cause a floating up (segregation to the surface) of Sb atoms thus restoring the alloy surface, which may serve as a surfactant in the process of the growth of Ag crystal.

Investigating the Inhibitory Properties of Cupressus sempervirens Extract against Copper Corrosion in 0.5 M H2SO4: Combining Quantum (Density Functional Theory Calculation-Monte Carlo Simulation) and Electrochemical-Surface Studies.

The study investigates the potential of Cupressus sempervirens (EO) as a sustainable and eco-friendly inhibitor of copper corrosion in a 0.5 M sulfuric acid medium. The electrochemical impedance spectroscopy analysis shows that the effectiveness of corrosion inhibition rises with increasing inhibitor concentrations, reaching 94% with the application of 2 g/L of EO, and potentiodynamic polarization (PDP) studies reveal that EO functions as a mixed-type corrosion inhibitor. In addition, the Langmuir adsorption isotherm is an effective descriptor of its adsorption. Scanning electron microscopy/energy-dispersive X-ray spectroscopy, atomic force microscopy surface examination, and contact angle measurement indicate that EO may form a barrier layer on the metal surface. Density functional theory calculations, Monte Carlo simulation models, and the radial distribution function were also used to provide a more detailed understanding of the corrosion protection mechanism. Overall, the findings suggest that Cupressus sempervirens (EO) has the potential to serve as an effective and sustainable corrosion inhibitor for copper in a sulfuric acid medium, contributing to the development of green corrosion inhibitors for environmentally friendly industrial processes.