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Graphical abstract The band structures of Ag(1 1 1) slabs of various thicknesses. Highlights • Splitting of surface bands of clean films depends on the thickness of slabs. • The splitting stems from the interaction between the surfaces. • For clean Cu(1 1 1), Ag(1 1 1), and Au(1 1 1) films, spin-splitting is absent. • Existence of a surface itself does not destroy inversion symmetry of the system. • Hydrogen monolayer on one face of the films leads to Rashba splitting. Abstract The splitting of the surface bands of Cu(1 1 1), Ag(1 1 1), and Au(1 1 1) films is studied by means of relativistic density-functional theory (DFT) calculations. It is found that the splitting of the bands of clean films obtained in semirelativistic approximation, in agreement with previous studies, stems from the interaction between the surfaces and hence depends on the thickness of the slabs. Since the Kramers' degeneracy is not broken by the presence of the surface, the spin-orbit coupling does not lead to the spin-splitting of the bands. An H monolayer, deposited on one face of the film, breaks the inversion symmetry and results in the appearance of the Rashba-type splitting of the bands. [ABSTRACT FROM AUTHOR]

As a kind of gas insulation medium, SF 6 is widely used in the power industry. Due to its high global warming potential value, the degradation and recycle of SF 6 has become a research hotspot in recent years. At present, there have been some achievements in the experimental study on the degradation of SF 6 , but there is little research on the catalytic degradation of SF 6 by metal catalysts. Based on the first-principle, this paper investigated the interaction between SF 6 and Ag(1 1 1) and evaluated the possibility of using Ag as a catalyst in SF 6 degradation. It is found that SF 6 can interact with Ag(1 1 1) surface with eight initial configurations. After the interaction, the distance between the F atom in the SF 6 molecule and the Ag surface is significantly shortened and the S F bond is elongated. There is a strong charge exchange process between the Ag metal interfaces and SF 6 molecule. Ag (1 1 1) transfers electrons of about 1.1e− to the SF 6 molecule and the dissociation of SF 6 by Ag metal shows a catalytic effect. The related research results provide a theoretical reference for the silver-catalyzed degradation of SF 6 . [ABSTRACT FROM AUTHOR]

Abstract First-principles density functional study has been performed to systematically investigate the adsorption of CH 3 I on Ag(1 1 1) and Ag 2 O(1 1 1) surfaces at different coverages. It is found that the adsorption energy of CH 3 I on two surfaces at all sites is coverage-dependent, and the adsorption is thermodynamic favorable. The interaction between CH 3 I and two surfaces can be mainly attributed to the hybridization of I(p) state and Ag(d) state. For the adsorption of CH 3 I on Ag(1 1 1) surface, fcc site is the most stable site whether at lower or higher coverage. For Ag 2 O(1 1 1) surface, Ag CUS site and Ag CUS (Ag CSA) site is more favorable at lower and higher coverage, respectively. The large adsorption energy occurred on the adsorption of CH 3 I on Ag CUS (Ag CSA) site is due to the strong interaction between I atom and Ag CUS atom and the formation of H O bond according to the LDOS and CDD calculations. [ABSTRACT FROM AUTHOR]

Synchrotron-radiation core-level photoemission spectroscopy has been utilized to explore the growth and annealing processes of silicon growth on the Ag(1 1 1) surface. Above 230 °C, adsorbed silicon atoms start to evaporate from the surface. No evidence of Si in-diffusion or formation of Si–Ag alloy was observed. Two components are visually discernible in the Si 2 p spectra for all coverages and various growth temperatures. This observation and the analysis of the Ag 3 d line shapes indicate the Si–Ag interface has similar bonding properties regardless of the reconstructions and thickness. The results are consistent with the growth scenarios that the top surface is terminated by some amounts of segregated silver atoms and has a similar structure to the Ag/Si(1 1 1)-( 3 × 3 ) R 30° surface. [ABSTRACT FROM AUTHOR]

The growth of Cu on Ag(1 1 1) under varied growth conditions was investigated with angle-resolved photoemission spectra. The evolution of Cu/Ag(1 1 1) during annealing was characterized on monitoring its surface states. The surface morphology of a Cu film on Ag(1 1 1) depends on the temperature and the Cu coverage. Islands or crystalline films develop when Cu is deposited at ∼300 K. Defects in the Cu films penetrate deeply into the Ag(1 1 1) substrate and expose the Ag(1 1 1) surface. The deposition of Cu at a low temperature results in disordered films. On annealing, the films become ordered with defects. Our results show the segregation of Ag on the Cu surface, which occurs at 300 K and becomes accelerated significantly at ∼380 K. After being annealed above 430 K, all islands and films of Cu are fully covered with Ag, showing a (9 × 9) reconstruction. Our results indicate also that the segregation of Ag on the Cu surface occurs only after the Ag(1 1 1) surface is exposed, indicating that Ag atoms migrate to the Cu(1 1 1) surface, not through bulk Cu, but along the walls of the islands and the defects in the films. [ABSTRACT FROM AUTHOR]

Low-temperature scanning tunneling microscopy (LT-STM) and ab initio density functional theory (DFT) calculations have been utilized to explore the growth processes and atomic structure of silicene on the Ag(1 1 1) surface. STM images reveal an etching growth mode in the sub-monolayer range. The results confirm the existence of various overlayer structures reported previously and that the lattice parameters of several overlayer structures at sub-monolayer coverages are close to the corresponding substrate supercells. However, detailed analysis of domain boundaries and Moiré-like superstructure in the STM images strongly suggest that the overlayer structures and the substrate lattices have no coincident relationships. Preliminary results of DFT calculations show that the changes in total energy upon translational displacement of the (3 × 3) Si silicene supercells with respect to the Ag(1 1 1) lattice is within a few tens of meV/Si atom. [ABSTRACT FROM AUTHOR]

Single and binary two-dimensional (2D) films of Pb and Sn on Ag(1 1 1) prepared at room temperature have been investigated using low-energy electron diffraction (LEED) and scanning tunneling microscopy. (√28 × √28)-Pb is observed in addition to (√3 × √3)-Pb at coverages higher than 0.35 ML. The nominal coverages for the (√28 × √28)-Pb and (√3 × √3)-Pb structures are determined to be 0.68 and 1/3 ML, respectively. The (1 × 1)-Sn structure is formed at coverages less than 1 ML. Both Pb and Sn films form a hexagonal close-packed structure on Ag(1 1 1). When the Sn coverage increases to more than 1 ML, excess Sn atoms form a (√3 × √3) structure on the (1 × 1)-Sn surface. The 2D binary films exhibit an incommensurate structure close to (√13 × √13) at Pb and Sn coverages of 0.5 and 0.25 ML, respectively. Atomic-resolution STM images exhibit a hexagonal close-packed structure. From the DFT total energy calculations, it is concluded that the Pb and Sn atoms of the (“√13 × √13″) structure do not form an ordered alloy but, rather, form a solid solution alloy. From these results, it is concluded that the binary 2D films also follow the Hume-Rothery rule. [ABSTRACT FROM AUTHOR]

Silicene, a two-dimensional honeycomb sheet consisting of Si atoms, has attracted much attention as a new low-dimensional material because it gains various fascinating characteristics originating from the combination of Dirac fermion features with spin–orbit coupling. The novel properties such as the quantum spin Hall effect and the compatibility with the current Si device technologies have fueled competition to realize the silicene. This review article focuses on the geometric and electronic structures of silicene grown on Ag(1 1 1) investigated by scanning tunneling microcopy (STM), low energy electron diffraction (LEED) and density functional theory (DFT) calculations. The silicene on Ag(1 1 1) takes locally-buckled structure in which the Si atoms are displaced perpendicularly to the basal plane. As a result, several superstructures such as 4 × 4 , 13 × 13 R 13.9 ° , 4 / 3 × 4 / 3 , and etc. emerge. The atomic arrangement of the 4 × 4 silicene has been determined by STM, DFT calculations and LEED dynamical analysis, while the other superstructures remain to be fully-resolved. In the 4 × 4 silicene, Si atoms are arranged to form a buckled honeycomb structure where six Si atoms of 18 Si atoms in the unit cell are displaced vertically. The displacements lead to the vertical shift of the substrate Ag atoms, indicating the non-negligible coupling at the interface between the silicene layer and the substrate. The interface coupling significantly modifies the electronic structure of the 4 × 4 silicene. No Landau level sequences were observed by scanning tunneling spectroscopy (STS) with magnetic fields applied perpendicularly to the sample surface. The DFT calculations showed that the π and π ∗ bands derived from the Si 3p z are hybridized with the Ag electronic states, leading to the drastic modification in the band structure and then the absence of Dirac fermion features together with the two-dimensionality in the electronic states. These findings demonstrate that the strong coupling at the interface causes the symmetry breaking for the 4 × 4 silicene and as a result the disappearance of Dirac fermion features. The geometric and electronic structures of other superstructures are also discussed. [ABSTRACT FROM AUTHOR]

The selectivity of PO decreased with the increase of oxygen coverage, which was mainly due to the influence of the primary reaction while the secondary reaction had little influence (defined ΔE a(primary) = E a(AHS) - E a(OMMP) , ΔE a(secondary) = E a(AC) - E a(PO)). [Display omitted] • The stepwise absorption energy is adopted to investigate the saturated coverage of oxygen on Ag(1 1 1). • The elementary reaction of two competing paths for propylene epoxidation at different oxygen coverage is studied. • The potential energy of key species involved in elementary reaction is obtained. • The selectivity of PO formation is analyzed based on the competitive results of the two reaction pathways. The direct epoxidation of propylene on Ag(1 1 1) under different oxygen coverage conditions was systemically studied on the basis of density functional theory calculation and the general trends of oxygen coverage on the two parallel competitive reaction paths in propylene oxide (PO) formation: α -H stripping versus epoxidation and the generation of PO versus acetone (AC) were explored. Then, the PO formation selectivity was investigated. Results showed that increase in oxygen coverage enhanced the adsorption strength of adsorbed species, except the O* species. In the primary reaction of propylene epoxidation, high oxygen coverage facilitates the first α -H stripping process, and opposite trend was observed in epoxidation process. As for the secondary chemistry in propylene epoxidation, increase in oxygen coverage benefits PO and AC formation. The coverage of O* has considerable influences on the primary reaction but small influence on the secondary reaction. Although a high oxygen coverage benefits the first α -H stripping, the second α -H stripping has higher barrier than that in secondary chemistry, and thus the PO formation would be better than that of acrolein formation at higher oxygen coverage. [ABSTRACT FROM AUTHOR]