Comparative theoretical study of the structure and bonding of propyne on the Pt(1 1 1) and Pd(1 1 1) surfaces

The interaction of propyne with the Pt(1 1 1) and Pd(1 1 1) surfaces has been studied by means of the generalised gradient approach of density functional theory using periodic slab models. For both surfaces, the most stable adsorption mode of propyne is di-σ/π mode where the hydrocarbon is σ-bonded to two metal atoms with some additional π bonding to a third adjacent surface atom. The adsorption geometry is a highly distorted propyne with the C₁ and C₂ in a nearly sp² hybridisation. Two equivalent surface structures have been found on Pt and Pd. These correspond to the adsorption on the fcc or hcp hollow sites. The adsorption energies on Pt(1 1 1) and Pd(1 1 1) are predicted to be ∼−197 and −161 kJ mol⁻¹, respectively. The electronic factors that control the chemisorption have been analysed by means of the projected density of states.     

Static investigation of adsorption and hetero‐diffusion of copper,silver, and gold adatoms on the (111) surface

In this work, we have used the static molecular simulations combined with an interatomic potential derived from the embedded‐atom method to study the adsorption and hetero‐diffusion on the (111) surface of Cu, Ag, and Au adatoms by using LAMMPS code. The investigation is performed for six heterogeneous systems such as Ag/Au(111), Ag/Cu(111), Au/Ag(111), Au/Cu(111), Cu/Ag(111), and Cu/Au(111). First, we have investigated the relaxation trends and the bond lengths of the atoms in the systems. The calculation results show that, the top layer spacing between the first and second layers of the Au(111), Ag(111), and Cu(111) substrates is contracted. This contraction is found to be more important in the Au(111) substrate. On the other hand, the strong reduction of the binding length is found in Au/Cu(111) for the different adsorption sites. In addition, the binding, adsorption, and static activation energies for all studied systems were examined. The results indicated that the binding and adsorption energies reached their maximum values in the Au/Cu(111) and Au/Ag(111) systems, respectively. Moreover, the static activation barriers for hopping diffusion on the (111) surfaces are found to be low compared with those found in the (100) and (110) surfaces. Therefore, our calculations showed that the difference in energy between the hcp and fcc sites on the (111) surfaces is very small. Copyright © 2017 John Wiley & Sons, Ltd.     

In situ and real-time surface differential diffraction (SDD) study of Cd underpotential deposition on Au(1 1 1)

In situ and real-time surface differential diffraction (SDD) has been used to study the underpotential deposition (UPD) of Cd on Au(1 1 1) in sulfuric acid media. Comparison of SDD results in sulfate electrolytes with and without the presence of Cd²⁺ ions reveals that the surface reconstruction associated with the sulfate adsorption and desorption dominates the structural effect. It is also found that the reconstructed gold surface is stable upon Cd UPD process. In the initial stages of UPD, Cd atoms bind to the surface in bridge sites. This is followed by an adlayer structure with Cd adsorption in threefold hollow sites before Au/Cd intermixing takes place.     

密度泛函理论研究十二烷硫醇在Au(111)面上的吸附

采用第一性原理方法研究了十二烷硫醇(C₁₂H₂₅SH)分子在Au(111)面上未解离和解离吸附的结构、能量和吸附性质,在此基础上分析判断长链硫醇分子在Au(111)面吸附时S―H键的解离, 以及分子链长度对吸附结构和能量的影响. 计算了S原子在不同位置以不同方式吸附的系列构型, 结果表明在S―H键解离前和解离后,均存在两种可能的表面结构, 直立吸附构型和平铺吸附构型; 未解离的C₁₂H₂₅SH分子倾向于吸附在top位, 吸附能为0.35-0.38 eV; H原子解离后C₁₂H₂₅S基团倾向于吸附在bri-fcc位, 吸附能量为2.01-2.09 eV. 比较分析未解离吸附和解离吸附, 发现C₁₂H₂₅SH分子未解离吸附相较于解离吸附要稳定, 未解离吸附属于弱化学吸附.局域电子态密度和差分电荷密度分析进一步验证了S―H解离后S原子与表面之间成键的数目增加, 而且键合更强. 同时我们发现长链硫醇的吸附能量较短链硫醇的吸附能量略大, S原子与表面Au原子之间的距离略小.     

First-principles study of hydrogen adsorption on Mo(1 1 0)

First-principles calculations based on density functional theory-generalized gradient approximation method have been performed for hydrogen (H) adsorption on Mo(1 1 0) surface. For various coverages, the hollow (hol) site was found to be the most stable binding site. The adsorption energy of this site was slightly increased as the increasing of hydrogen coverage. Subsurface (sub) occupation at low and medium coverages was ruled out while it became to be stable at the coverage of 1 ML. This is also supported by the potential energy surface (PES) study for hydrogen diffusing from hol to sub site. It’s interesting to find a surface reconstruction at the coverage of 1 ML, which is characterized by the lateral shift of the topmost layer for the sub adsorption. At higher coverage, the local density of states (LDOS) analysis showed that a new peak was clearly visible which was ascribed to a surface state induced by hydrogen adsorption. This surface state was mostly localized on the hydrogen atom and the first Mo layer, implying the hybridization of the hydrogen 1s states and the Mo metal states.     

Metals (Cu,Ag, Au) encapsulated gallium nitride nanotubes (GaNNTs) as sensors for hexabromodiphenyl ether (HBDE) emerging organic pollutant: A computational study

This study is aimed at investigating the potential of transition metals (Cu, Ag, Au) doped gallium nitride nanotubes (GaNNTs) as sensor materials for the enhanced detection of hexabromodiphenyl ether (HBDE) an emerging organic pollutant that has been linked to several health problems, including developmental and neurological disorders, hormonal imbalances, and cancer. Using the density functional theory (DFT) method at the B3LYP-D3(BJ)/def2SVP level of theory, the potential of pristine and metal (Ag, Au, and Cu) doped gallium nitride (GaNNT) nanotube to sense and detect HBDE was evaluated. The interaction of HBDE on the surface was evaluated at two sites, the bromine (Br) and oxygen (O) sites to evaluate the best conformation adsorption. The results showed that the Br site was the preferred sites of adsorption with binding energies of −43.926 kcal/mol, −43.926 kcal/mol, −43.926 kcal/mol and −31.376 kcal/mol for HBDE_Br_Ag@GaNNT, HBDE_Br_Au@GaNNT, HBDE_Br_Cu@GaNNT and HBDE_Br_@GaNNT respectively. The mechanism of surface adsorption was found to be chemisorption and doping of GaNNT surface with metals was found to enhance the conductivity and sensitivity of the surface towards the adsorbent. The result of the thermodynamic assay also affirmed the spontaneous and favorable nature of the surface and adsorbent. Overall, the various analysis considered so far, points that pristine and metal functionalized GaNNT could be used as potential materials to sense HBDE.     

Surface structure for Au on (0 0 1) SrTiO3

First-principle calculations are performed to study the crystal structure, formation energies, and electronic structures of (0 0 1) SrTiO₃ surfaces with/without Au covered. The initiative Au additive layer is crystallized in a fcc structure with (0 0 1) face on SrO-terminated surface. The bimodal growth trend of Au on TiO₂-terminated surface is qualitatively consistent with the experimental observations. The defect structure of Au occupying the oxygen (O) vacancies of TiO₂-terminated surface is energetically favorable under oxygen-poor conditions, and a feature corresponding to gap states appear and the occupied Ti 3d states disappear.     

Modelling of benzene-1,4-dithiol on a Au(1 1 1) surface

The bonding of benzene-1,4-dithiol to a Au(1 1 1) surface is studied using a Au₂₅–SC₆H₄SH model. We find that the most favorable structure has the S directly above an Au atom, i.e., an on-top site. If the molecule is constrained to be perpendicular to the surface, the on-top site is the least favorable site and the threefold hollow is the most favorable one.     

Interaction of Hg Atom with Bare Si（111） Surface

1INTRODUCTION In the past decades,mercury has been a very use-ful electrode material in the fabrication and electrical measurement of molecule modified metal-metal and metal-semiconductor junctions.Majda et al.[1,2]constructed a symmetric Hg-SCn-CnS-Hg junction to study the electron tunneling properties of alkanethio-late bilayers.Whitesides et al.[3～5]fabricated Hg-SAM/SAM-Metal(Ag,Au,Cu)junctions to investi-gate the electrical breakdown voltage of self-assem-bled monolayers(SAMs…     

Spontaneous deposition of Sn on Au(1 1 1). An in situ STM study

The tin adlayer formed by spontaneous deposition on Au(1 1 1) was characterized by cyclic voltammetry and in situ scanning tunneling microscopy (STM) in sulphuric acid solution. Cyclic voltammetry measurements showed oxidation peaks in the potential range −0.60 ⩽ E/V vs SSE ⩽ 0, which can be ascribed to the dissolution of the Sn adsorbed layer. STM images of the Au(1 1 1)/Sn modified surface showed that tin nucleated both on step edges and on the flat terraces forming two-dimensional islands. The anodic polarization of this modified surface produced the gradual dissolution of the Sn adlayer which was evidenced by the formation of some holes and the reduction of the initial terraces to many small islands. STM images with atomic resolution obtained on these islands displayed an hexagonal expanded atomic structure. After the anodic stripping of this Sn adsorbed layer the images exhibited the typical Au(1 1 1) terraces with a (1 × 1) atomic structure. However, at more anodic potentials another dissolution process was observed producing noticeable changes on the surface morphology which could be ascribed to the dissolution of a Au–Sn surface alloy.     

The influence of chloride on the initial anodic dissolution of Cu3Au(1 1 1)

We report a detailed in situ X-ray diffraction study of the influence of chloride on the atomic structure evolution at the solid-electrolyte interface during the selective dissolution of Cu from a Cu₃Au(1 1 1) surface immersed in 0.1 M H₂SO₄. We disclose that the formation of the initial ultrathin Au-rich (1 1 1) with an inverted stacking sequence, as recently observed at Cu₃Au(1 1 1) in contact with pure 0.1 M H₂SO₄, is strongly influenced by adding 5 mM HCl. The main finding is a negative shift of about 150 mV of the critical potential at which the ultra-thin Au-rich layer transforms into thicker Au islands. The presented results support the view that it is not a thermodynamic driving force, but rather the rate of surface diffusion that dominates the formation of the structures of the metallic layer.     

Adsorption of alkali metals on Ge(0 0 1)(2 × 1) surface

Ab initio total energy calculations have been performed for Na, K and Rb adsorption on Ge(0 0 1)(2 × 1) surface. It was found that the adsorption site of AM is AM size dependent. Structural analysis showed that the Ge–Ge dimer bond becomes stronger with increasing AM size. As the coverage increases from 0.5 to 1 ML it turns out that no depolarization effect occurs upon Na adsorption, while this effect becomes more important with increasing AM size. We also found that for all adsorption systems investigated the germanium surface is metallic and semiconducting for the coverage of 0.5 and 1 ML, respectively.     

Structures and thermodynamic phase transitions for oxygen and silver oxide phases on Ag{1 1 1}

With density functional theory, we have examined oxygen adsorption at surface and subsurface sites of Ag{1 1 1}. The microscopic structure of Ag oxide epitaxed to Ag{1 1 1} has also been determined. In agreement with a recent scanning tunneling microscopy study, non-stoichiometric oxide growth is favoured over the previously assumed stoichiometric growth. An ab initio phase diagram for O on Ag{1 1 1} has been constructed from the adsorption free energy of the various O and Ag oxide phases. The key finding is that under real conditions for ethylene epoxidation the active catalyst is likely to be non-stoichiometric Ag oxide.     

Density-functional study for the NOx (x = 1, 2) dissociation mechanism on the Cu(1 1 1) surface

Spin-polarized density functional theory calculation is employed to study the adsorption and dissociation of NO₂ molecule on Cu(1 1 1) surface. It is shown that the most favorable adsorption structure is the NO₂ (T,T-O-,O′-nitrito) configuration which has an adsorption energy of −1.49 eV. The barriers for step-wise NO₂ dissociation reaction, NO_2(g) → N_(a) + 2O_(a), are 1.05 (for O–N–O bond activation), and 2.08 eV (for N–O bond activation), respectively, and the entire process is 0.6 eV exothermic. The energetics of single N–O dissociation with and without the presence of N atom or O atom on the surface are also calculated. The results indicate that in the presence of O atom on Cu(1 1 1) surface would raise the N–O dissociation barrier, whereas in the presence of N atom decrease it. The interaction nature between adsorbates and substrate is analyzed by the local density of states (LDOS) calculation.     

CO在M55（M=Cu,Ag,Au）团簇上吸附的密度泛函研究

在全电子相对论BVP86/DNP水平下对CO在Au55,Ag55和Cu55团簇上的吸附进行了比较研究,并考察了电荷对吸附的影响.计算结果表明,CO在Au55团簇上吸附能最大,其次为Cu55团簇,最弱的为Ag55团簇.团簇电荷对C—O键活化和CO与团簇表面原子成键影响较小.金团簇的电荷对吸附能影响较大,而银和铜团簇的电荷对吸附能影响较小.CO吸附到团簇上导致团簇上电子向CO转移.C—O键活化强度与吸附位置密切相关,其中孔位吸附导致C—O键活化程度最大,最弱的为顶位吸附.CO在金团簇上吸附具有较好选择性,而在银和铜团簇上吸附无选择性.     

NEXAFS study of a Pt-containing rod-like organometallic polymer (Pt-DEBP): molecular orientation onto HOPG, Au/Si(1 1 1), Cr/Si(1 1 1) and Si(1 1 1) surfaces

The influence of different substrates on the molecular orientation of organometallic polymer Pt-DEBP, [Pt(PBu₃)₂CCC₁₂H₈CC]_n, has been investigated by NEXAFS spectroscopy. Thin films were deposited on HOPG, Au/Si(1 1 1), Cr/Si(1 1 1), Si(1 1 1) and stainless steel. The assignment of the spectral features has been carried out on the basis of previous STEX calculations performed on phenylacetylene model molecule in gas phase and adsorbed on Pt(1 1 1) and Cu(1 0 0). Angular dependent analysis of the π* resonance occurring at 285.50 eV photon energy deriving by the benzene carbon orbitals showed a polarisation effect for all substrates. A preferential molecular orientation at nearly 40° to the surface normal was observed. This result might be explained by the strong interaction between sp and sp² carbons of the organic diethynylbiphenyl DEBP moiety contained in close chains, leading to polymer self-assembling.     

缺陷石墨烯吸附Au、Ag、Cu的第一性原理计算

采用基于密度泛函理论的投影缀加波方法研究了Au、Ag、Cu吸附在缺陷石墨烯单侧和双侧的体系,对吸附体系的吸附能、磁性、电荷转移和电子结构进行了计算和分析. 缺陷石墨烯吸附Au、Ag、Cu体系的吸附能比本征石墨烯增加2 eV以上,说明三种金属原子更容易吸附在缺陷位置;吸附体系的电荷密度差分和电子结构的结果表明,Au、Ag、Cu与缺陷石墨烯之间均为化学吸附. 计算吸附体系的磁性发现,单侧吸附时三种吸附体系均有磁性,磁矩大约为1μ_B;双侧吸附时,三种吸附体系磁矩大约为2μ_B.     

The interfacial chemistry and energy level structure of a liquid crystalline perylene derivative on Au(1 1 1) and graphite surfaces

We compare the energy level structure of ordered monolayers of N,N′-ditridecyl-3,4,9,10-perylenetetracarboxylic diimide (PTCDI-C13) on Au(1 1 1) and highly oriented pyrolytic graphite (HOPG). Both ultraviolet photoemission spectroscopy and scanning tunneling spectroscopy measurements show the formation of an occupied interface state for PTCDI-C13 on Au(1 1 1), whereas no such state is observed for PTCDI-C13 on HOPG. Comparative density functional theory calculations for various isolated perylene derivatives in the neutral and anionic states are unable to explain differences in observed interface state formation, which suggests that the interface state for PTCDI-C13/Au(1 1 1) is a consequence of a weak chemical interaction of this molecule and the Au substrate.     

Stability of underpotentially deposited Ag layers on a Au(1 1 1) surface studied by surface X-ray scattering

Stability of underpotentially deposited (upd) Ag layers on Au(1 1 1) surface was investigated by surface X-ray scattering (SXS). While the complete pseudomorphic Ag bilayer on Au(1 1 1) surface obtained by upd at 10 mV (vs. Ag/Ag⁺) was maintained its structure even after the circuit was disconnected and the surface was exposed to ambient atmosphere, the pseudomorphic Ag monolayer obtained by upd at 50 mV was converted to a partial bilayer with the coverage of 0.66 and 0.46 ML for the 1st and 2nd layer, respectively. These results show that Ag bilayer is structurally more stable than Ag monolayer on Au(1 1 1) and Ag atoms of the upd monolayer move around on the Au(1 1 1) surface without potential control.