Adsorbate-induced Reconstruction Research Articles

Probing the nanoscale driving forces for adsorbate-induced Rh50Pd50 nanoparticle reconstruction via mean-field models of multi-faceted nanoparticles

Adsorbate-induced bimetallic nanoparticle reconstruction via mean-field models.

In-situ adaptive evolution of rhodium oxide clusters into single atoms via mobile rhodium-adsorbate intermediates

It is a common phenomenon for supported metal catalysts to undergo thermally-induced or adsorbate-induced reconstruction. Great efforts have been devoted to making these reconstruction adaptive to the reaction environment instead of deactivation. Herein, we reported the evolution of initially inactive RhOx clusters on Al2O3 into the formation of catalytically active oxygen vacancies and Rh single atoms via mobile Rh-CO intermediates during hydroformylation of propene. The activated catalyst exhibited a high specific activity of 3.0 × 104 mol molRh–1 h–1 towards hydroformylation reaction. Mechanistic studies revealed the evolution paths. Specially, RhOx clusters were reduced by CO to form oxygen vacancy where the surrounding unsaturated Rh atoms enabled the chemisorption of CO*. Rh atoms that were ejected from RhOx clusters diffused on Al2O3 supports to generate Rh single atom via the formation of carbonyl or geminal dicarbonyl species. Meanwhile, the Rh atoms on clusters were also leached to the solution by the adsorbed CO molecules, followed by partial re-adsorption on the support. This work not only offers an efficient catalyst for propene hydroformylation, but also advances the understandings of dynamic evolution of catalysts.

(2×1) Reconstruction Mechanism of Rutile TiO2(011) Surface.

Understanding the reconstruction kinetics of solid surfaces involving an ensemble of atomic movements is practically important but challenging due to the complexity of high-dimensional potential energy surfaces. Herein, we develop a step-deciding technique incorporated with the nudged elastic band method, which enables multidirection pathway sampling and ensures the capture of a minimum energy path (MEP). Using this approach, the (2×1) reconstruction mechanism of a rutile-TiO2(011) surface, a classic and long-standing open problem in the fields of surface science and heterogeneous catalysis, is quantified, and the MEP is explicitly identified and explained. Following the least-bond-breaking rule, it gives a stepwise Ti-O bond cleavage mechanism with a collection of decoupled local structural relaxation modes at an overall barrier of 1.25 eV critically affected by initial Ti-O bond opening, which is much lower than the common synergy mechanism. Moreover, the adsorption-induced reconstruction is rationalized considering practical reaction conditions, where H atom adsorbate is shown to effectively stabilize the labile one-fold O1c intermediate and promote the reconstruction kinetics. This work reveals the reconstruction mechanism regarding multiatom movements and provides a general method for the structural exploration of other complicated systems.

Identification of stable adsorption sites and diffusion paths on nanocluster surfaces: an automated scanning algorithm

The diverse coordination environments on the surfaces of discrete, three-dimensional (3D) nanoclusters contribute significantly to their unique catalytic properties. Identifying the numerous adsorption sites and diffusion paths on these clusters is however tedious and time-consuming, especially for large, asymmetric nanoclusters. Here, we present a simple, automated method for constructing approximate 2D potential energy surfaces for the adsorption of atomic species on the surfaces of 3D nanoclusters with minimal human intervention. These potential energy surfaces fully characterize the important adsorption sites and diffusion paths on the nanocluster surfaces with accuracies similar to current approaches and at comparable computational cost. Our method can treat complex nanoclusters, such as alloy nanoclusters, and accounts for cluster relaxation and adsorbate-induced reconstruction, important for obtaining accurate energetics. Moreover, its highly parallelizable nature is ideal for modern supercomputer architectures. We showcase our method using two clusters: Au18 and Pt55. For Au18, diffusion of atomic hydrogen between the most stable sites occurs via non-intuitive paths, underlining the necessity of exploring the complete potential energy surface. By enabling the rapid and unbiased assessment of adsorption and diffusion on large, complex nanoclusters, which are particularly difficult to handle manually, our method will help advance materials discovery and the rational design of catalysts.

Quantitative and Atomic-Scale View of CO-Induced Pt Nanoparticle Surface Reconstruction at Saturation Coverage via DFT Calculations Coupled with in Situ TEM and IR.

Atomic-scale insights into how supported metal nanoparticles catalyze chemical reactions are critical for the optimization of chemical conversion processes. It is well-known that different geometric configurations of surface atoms on supported metal nanoparticles have different catalytic reactivity and that the adsorption of reactive species can cause reconstruction of metal surfaces. Thus, characterizing metallic surface structures under reaction conditions at atomic scale is critical for understanding reactivity. Elucidation of such insights on high surface area oxide supported metal nanoparticles has been limited by less than atomic resolution typically achieved by environmental transmission electron microscopy (TEM) when operated under realistic conditions and a lack of correlated experimental measurements providing quantitative information about the distribution of exposed surface atoms under relevant reaction conditions. We overcome these limitations by correlating density functional theory predictions of adsorbate-induced surface reconstruction visually with atom-resolved imaging by in situ TEM and quantitatively with sample-averaged measurements of surface atom configurations by in situ infrared spectroscopy all at identical saturation adsorbate coverage. This is demonstrated for platinum (Pt) nanoparticle surface reconstruction induced by CO adsorption at saturation coverage and elevated (>400 K) temperature, which is relevant for the CO oxidation reaction under cold-start conditions in the catalytic convertor. Through our correlated approach, it is observed that the truncated octahedron shape adopted by bare Pt nanoparticles undergoes a reversible, facet selective reconstruction due to saturation CO coverage, where {100} facets roughen into vicinal stepped high Miller index facets, while {111} facets remain intact.

Shell-isolated nanoparticle-enhanced Raman spectroscopy study of the adsorption behaviour of DNA bases on Au(111) electrode surfaces.

For the first time, we used the electrochemical shell-isolated nanoparticle-enhanced Raman spectroscopy (EC-SHINERS) technique to in situ characterize the adsorption behaviour of four DNA bases (adenine, guanine, thymine, and cytosine) on atomically flat Au(111) electrode surfaces. The spectroscopic results of the various molecules reveal similar features, such as the adsorption-induced reconstruction of the Au(111) surface and the drastic Raman intensity reduction of the ring breathing modes after the lifting reconstruction. As a preliminary study of the photo-induced charge transfer (PICT) mechanism, the in situ spectroscopic results obtained on single crystal surfaces are excellently illustrated with electrochemical data.

ChemInform Abstract: Adsorption of NO and CO and Specific Features of Their Interaction on the Pt(100) Surface

AbstractReview: 127 refs.

Adsorbate-induced surface stress, surface strain and surface reconstruction: CH3S on Cu(100) and Cu(111)

Adsorbate-induced surface stress, surface strain and surface reconstruction: CH3S on Cu(100) and Cu(111)

Pd–Rh Nanocrystals with Tunable Morphologies and Compositions as Efficient Catalysts toward Suzuki Cross-Coupling Reactions

Delicate elaboration of the nanostructures of multimetal catalytic materials with well-defined shapes and compositions to reveal their potential use as heterogeneous nanocatalysts for organic synthetic reactions with the combined merits of heterogeneous and homogeneous catalysis is both scientifically and technologically important, but this type of investigation has remained rarely pursued. In this work, we demonstrated a facile hydrothermal approach toward the one-pot shape-selective syntheses of Pd–Rh nanocrystals with tunable compositions and morphologies, including hollow nanocubes (NCs), nanoicosahedrons (NIs), and nanotruncated octahedrons (NTOs), using poly(vinylpyrrolidone) as both reductant and capping agent and halide anions (Br–/I–) as shape control agents. The formation of Pd–Rh hollow NCs was induced by an iodine adsorbate-induced reconstruction mechanism with KI, whereas the formation of Pd–Rh NIs and NTOs were realized by controlling the selective nucleation of twinned seeds or single crystal seeds and their relative growth rates along different facets (e.g., (111) and (100) facets) through finely adjusting the Pd/Rh ratio and the amount of KBr added in the absence of KI. Due to the great significance of Pd-catalyzed organic reactions, the catalytic performances of Pd–Rh nanocrystals for Suzuki cross-coupling reactions with different reactants were evaluated. The measured turnover frequencies (TOFs) suggested that Pd–Rh hollow NCs held considerably enhanced catalytic activities (at least 3 times) than other Pd-based solid nanocrystals including Pd–Rh NIs, Pd–Rh NTOs, Pd–Rh NCs, Pd NCs, and commercial Pd/C, with iodobenzene as the reactant. In addition, even for more inert reactants such as bromobenzene or 4-bromotoluene, the catalytic activities of Pd–Rh hollow NCs were still impressive (showing similar TOFs to those of other shapes for reactions with iodobenzene as the reactant), indicating the promising application of Pd-based nanocatalysts for other powerful Pd-catalyzed organic synthesis reactions. Meanwhile, Pd-based solid NCs, enclosed with (100) facets only, showed better catalytic performance than NIs as well as NTOs, which had a larger fraction of (111) facets other than (100) ones, further suggesting that morphology differences were vitally significant to tune the catalytic performances of bimetallic nanocatalysts.

The Flexible Surface Revisited: Adsorbate-Induced Reconstruction, Homocoupling, and Sonogashira Cross-Coupling on the Au(100) Surface

Phenylacetylene (PA) and iodobenzene (IB) are prototypical reactants in Sonogashira cross-coupling. Their adsorption behavior and reactivity on the Au(100) surface were studied by STM, temperature-programmed desorption and reaction, and DFT calculations that included the effect of dispersion forces. The two species exhibited very different behavior. Thus, even at 200 K, PA rearranged Au surface atoms so as to lift the hex reconstruction and adsorb in 4-fold-symmetric islands on the unreconstructed 100 surface. On the other hand, IB adsorbed on the reconstructed hex surface, again as islands, forming three different coexisting close-packed structures. The DFT results are in good accord with these findings, demonstrating the strong preference of PA and IB for the (100) and hex surfaces, respectively. Moreover, the calculated adsorption energies were in satisfactory agreement with values estimated from the desorption data. Adsorbed separately, both PA and IB underwent homocoupling, yielding diphenyl diacetyl...

Adsorption of NO and CO and specific features of their interaction on the Pt(100) surface

This article presents an analytical review of the author’s results and the literature concerning the nature of species resulting from NO and CO adsorption on the unreconstructed (1 × 1) and reconstructed hexagonal (hex) Pt(100) surfaces, including specific features of the reactions between these species. At 300 K, both surfaces adsorb NO and CO mainly in their molecular states. When adsorbed on Pt(100)-1 × 1, the NOads and COads molecules are uniformly distributed on the surface. Under the same conditions, the hexagonal surface undergoes adsorption-induced reconstruction with the formation of NOads/1 × 1 and COads/1 × 1 islands, which are areas of the unreconstructed phase saturated with adsorbed molecules and surrounded with the adsorbate-free hex phase. In adsorption on structurally heterogeneous surfaces containing both hex and 1 × 1 areas, the 1 × 1 and hex phases are occupied in succession, the latter undergoing reconstruction into the 1 × 1 phase. The reaction between NO and CO on the unreconstructed surfaces occurs even at room temperature and results in the formation of N2 and CO2 in quantitative yield. On the hexagonal surface, a stable layer of adsorbed molecules as (NOads + COads)/1 × 1 mixed islands forms under these conditions. Above 350 K, the reaction in the mixed islands is initiated by the desorption of small amounts of the initial compounds, and this is followed by rapid self-acceleration leading to a surface explosion yielding N2, CO2, and N2O (minor product). These products show themselves as very narrow desorption peaks in the temperature-programmed reaction spectrum.

Large perpendicular magnetic anisotropy at Fe/MgO interface

A large perpendicular magnetic anisotropy (PMA) of 1.4 MJ/m3 was observed from ultrathin Fe/MgO(001) bilayers grown on Cr-buffered MgO(001). The PMA strongly depends on the surface state of Fe prior to the MgO deposition. A large PMA energy density of 1.4 MJ/m3 was achieved for a 0.7 nm thick Fe layer having adsorbate-induced surface reconstruction, which is likely to originate from oxygen atoms floating up from the Cr buffer layer. This large magnitude of PMA satisfies the criterion that is required for thermal stability of magnetization in a few tens nanometer-sized magnetic memory elements.

Scanning Tunneling Microscopy and Density Functional Theory Studies of Adatom-Involved Adsorption of Methylnitrene on Copper(110) Surface

In this study, we used scanning tunneling microscopy (STM) and density functional theory (DFT) to examine the bonding structure of CH3N adsorbed on the Cu(110) surface. A previous study [Chin. J. Phys.2005, 43, 212–218] shows the adsorbed CH3N aggregate to form a zigzag structure with a p(2 × 3) unit cell, without considering the possibility of adsorbate-induced surface reconstruction. Here, we propose a revised adsorption structure, with the key feature of bonding each CH3N with two Cu adatoms in a tetrahedral manner. Three structure models (double-row, dimer, and alternative-dimer) are examined by ab initio calculations. We find that the most energetically favorable model is the double-row model with CH3N bonding alternatingly along either side of double added rows from Cu adatoms.

Adsorbate-induced surface stress, surface strain and surface reconstruction: S on Cu(100) and Ni(100)

Density functional theory (DFT) calculations have been applied to investigate the known difference in behaviour of S adsorption on Cu(100) and Ni(100). Both surfaces form a 0.25ML (2×2) adsorption phase, but while at higher coverage a 0.5ML c(2×2) phase forms on Ni(100), on Cu(100) only a reconstructed 0.47ML (√17×√17)R14° structure occurs. Calculations of the energy, structure, and surface stress of (2×2) and c(2×2) phases on both substrates show there is an energy advantage on both surfaces to form the higher coverage phase, but that both surfaces show local surface strain around the S atoms in the (2×2) phase, a phenomenon previously investigated only on Cu(100). More than forty different structural models of the Cu(100)(√17×√17)R14°-S phase have been investigated. The pseudo-(100)c(2×2) structure previously proposed, containing 16 Cu adatoms per unit mesh in the reconstructed layer, is found to be less energetically favourable than many other possible structures, even after taking account of local structural relaxations. Significantly more favourable is a structure with 12 Cu adatoms per (√17×√17)R14° unit mesh, previously proposed on the basis of scanning tunnelling microscopy (STM), and found to yield simulated STM images in good agreement with experiment. This model has all S atoms in local 4-fold coordinated hollows relative to the Cu atoms below, half being located above Cu adatoms with the remainder lying above the underlying outermost substrate layer. However, an alternative model with only 4 Cu adatoms and with half the S atoms at 3-fold coordinated sites on the periphery of the Cu adatom cluster, has an even lower energy and gives simulated STM images in excellent agreement with experiment.

Atomic imaging of the monolayer nucleation and unpinning of a compound semiconductor surface during atomic layer deposition

The reaction of trimethyl aluminum on the group III rich reconstructions of InAs(0 0 1) and In(0.53)Ga(0.47)As(0 0 1) is observed with scanning tunneling microscopy/spectroscopy. At high coverage, a self-terminated ordered overlayer is observed that provides the monolayer nucleation density required for subnanometer thick transistor gate oxide scaling and removes the surface Fermi level pinning that is present on the clean InGaAs surface. Density functional theory simulations confirm that an adsorbate-induced reconstruction is the basis of the monolayer nucleation density and passivation.

Interplay between adsorbate-induced reconstruction and local strain: Formation of phases on theCu(110)−(2×1):Osurface

We present an STM study on the interplay between adsorbate-induced reconstruction and local strain on the oxygen adsorbed Cu(110) surface. Thermal annealing of the surface resulted in surface terrace ripening revealing larger terraces, uniformly covered by the $(2\ifmmode\times\else\texttimes\fi{}1)\text{-O}$ reconstructed phase, separated by step bunches. The largest terrace was found to be partially splitted by emerging dislocations inducing strong inhomogeneous strain in their close vicinity. This extra strain caused local conversion of the dominating $(2\ifmmode\times\else\texttimes\fi{}1)\text{-O}$ phase into oxygen chemisorbed phases drastically different from the dominating phase. A meaningful correlation between lateral evolution of the extra strain and structure of these phases has been found. The symmetry of the discovered phases has been determined and their structural models have been elaborated.

Adsorbate-induced reconstruction of an array of atomic wires: Indium on the Si(553)-Au surface

The In-induced surface reconstruction of the Si(553)-Au surface has been studied using the combined experiment of low-energy-electron diffraction, scanning tunneling microscopy, and angle-resolved photoemission spectroscopy. Low-energy-electron diffraction revealed that In adsorbates interact actively with the surface above $150\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$, widening the terraces uniformly and forming a new atomic wire array. This wire structure has a $\ifmmode\times\else\texttimes\fi{}2$ period along the wires, where the phase coherence across the wires was much better than that of the pristine Si(553)-Au surface. The In-induced uniform terrace widening was confirmed by scanning tunneling microscopy. More interestingly, the In adsorbates alter the metallic atomic wires of the Si(553)-Au surface with highly dispersive one-dimensional bands into insulating ones with still large dispersion.

The interface structure of n-alkylthiolate self-assembled monolayers on coinage metal surfaces

The current state of understanding of the structure of the metal/thiolate interface of n-alkylthiolate 'self-assembled monolayers' (SAMs) on Cu(111), Ag(111) and Au(111) is reviewed. On Cu(111) and Ag(111) there is now clear evidence that adsorbate-induced reconstruction of the outermost metal layer occurs to a less atomically-dense structure, with the S head-group atom bonded to four-fold and three-fold coordinated hollow sites, respectively, and that intermolecular interaction plays some role in the periodicity of the resulting SAMs. On the far more heavily-studied Au(111) surface, the detailed interface structure remains controversial, but there is growing evidence for the role of Au-adatom-thiolate moieties in the layer ordering.

4×1to7×3transition in theIn∕GexSi1−x(111)system induced by varying the substrate lattice constant

Taking $\mathrm{Si}(111)4\ifmmode\times\else\texttimes\fi{}1\text{\ensuremath{-}}\mathrm{In}$ as a prototype reconstruction, we have examined the possibility of modifying an adsorbate-induced reconstruction by varying the averaged lattice constant of the substrate. In the experiment, the lattice constant of Si(111) substrate has been increased by forming a thin alloying ${\mathrm{Ge}}_{x}{\mathrm{Si}}_{1\ensuremath{-}x}$ layer on Si(111). It has been found that this action results in removing the $4\ifmmode\times\else\texttimes\fi{}1$ reconstruction and developing a $7\ifmmode\times\else\texttimes\fi{}3$ reconstruction, the transformation being completed when more than 0.3 ML (monolayer) of Ge has been incorporated into the substrate. The $7\ifmmode\times\else\texttimes\fi{}3$ reconstruction has a striped-shaped structure built of double rows and plausibly contains 0.1 ML of In and $0.65\ifmmode\pm\else\textpm\fi{}0.04$ ML of Si(Ge) atoms and, like the $4\ifmmode\times\else\texttimes\fi{}1$, demonstrates metallic properties. The $7\ifmmode\times\else\texttimes\fi{}3$ reconstruction is not observed in ``pure'' $\mathrm{In}∕\mathrm{Si}(111)$ and $\mathrm{In}∕\mathrm{Ge}(111)$ systems. We believe that the artificial variation of substrate lattice constant not only provides a possibility of examining the role of surface stress in reconstructions but also opens a degree of freedom for engineering other types of reconstructions.

Structure of the Pentylthiolate Self-Assembled Monolayer on Ag(111)

A combination of scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), and normal incidence X-ray standing waves (NIXSW) has been used to investigate the structure of the self-assembled monolayer (SAM) formed by pentylthiolate on Ag(111) in ultrahigh vacuum through interaction with pentanethiol. NIXSW data are closely similar to those for methythiolate on Ag(111) in the commensurate (root 7x root 7)R19 degrees phase and consistent with a similar adsorbate-induced reconstruction of the outermost Ag layer comprising only 3/7 ML of Ag atoms. However, both STM and LEED show that the local lateral periodicity is similar to 5% larger in the pentylthiolate phase and that the resulting SAM is not commensurate with the substrate. The results are discussed in the context of previously published results for other alkylthiolate SAMs on Ag(111).