Silver Single Crystal Surfaces Research Articles

Understanding the Electrochemical Carbon Dioxide Reduction Reaction Mechanism of Lattice Tuning of Copper by Silver Single-Crystal Surface.

Intermolecular interactions and adsorbate coverage on a metal electrode's surface/interface play an important role in CO2 reduction reaction (CO2RR). Herein, the activity and selectivity of CO2RR on bimetallic electrode, where a full monoatomic Cu layer covers on Ag surface (CuML/Ag) are investigated by using density functional theory calculations. The surface geometric and electronic structure results indicate that there is high electrocatalytic activity for CO2RR on the CuML/Ag electrode. Specifically, the CuML/Ag surface can accelerate the H2O and CO2 adsorption and hydrogenation while lowering the reaction energy of the rate-determining step. The structure parameters of chemisorbed CO2 with and without H2O demonstrate that activated H2O not only promotes the C-O dissociation but also provides the protons required for CO2RR on the CuML/Ag electrode surface. Furthermore, the various reaction mechanism diagrams indicate that the CuML/Ag electrode has high selectivity for CO2RR, and the efficiency of products can be regulated by modulating the reaction's electric potential.

On‐Surface Isomerization of Indigo within 1D Coordination Polymers

AbstractNatural products are attractive components to tailor environmentally friendly advanced new materials. We present surface‐confined metallosupramolecular engineering of coordination polymers using natural dyes as molecular building blocks: indigo and the related Tyrian purple. Both building blocks yield identical, well‐defined coordination polymers composed of (1 dehydroindigo : 1 Fe) repeat units on two different silver single crystal surfaces. These polymers are characterized atomically by submolecular resolution scanning tunnelling microscopy, bond‐resolving atomic force microscopy and X‐ray photoelectron spectroscopy. On Ag(100) and on Ag(111), the trans configuration of dehydroindigo results in N,O‐chelation in the polymer chains. On the more inert Ag(111) surface, the molecules additionally undergo thermally induced isomerization from the trans to the cis configuration and afford N,N‐ plus O,O‐chelation. Density functional theory calculations confirm that the coordination polymers of the cis‐isomers on Ag(111) and of the trans‐isomers on Ag(100) are energetically favoured. Our results demonstrate post‐synthetic linker isomerization in interfacial metal‐organic nanosystems.

On-Surface Isomerization of Indigo within 1D Coordination Polymers.

Natural products are attractive components to tailor environmentally friendly advanced new materials. We present surface-confined metallosupramolecular engineering of coordination polymers using natural dyes as molecular building blocks: indigo and the related Tyrian purple. Both building blocks yield identical, well-defined coordination polymers composed of (1 dehydroindigo : 1 Fe) repeat units on two different silver single crystal surfaces. These polymers are characterized atomically by submolecular resolution scanning tunnelling microscopy, bond-resolving atomic force microscopy and X-ray photoelectron spectroscopy. On Ag(100) and on Ag(111), the trans configuration of dehydroindigo results in N,O-chelation in the polymer chains. On the more inert Ag(111) surface, the molecules additionally undergo thermally induced isomerization from the trans to the cis configuration and afford N,N- plus O,O-chelation. Density functional theory calculations confirm that the coordination polymers of the cis-isomers on Ag(111) and of the trans-isomers on Ag(100) are energetically favoured. Our results demonstrate post-synthetic linker isomerization in interfacial metal-organic nanosystems.

Chiral Kagome Lattices from On‐Surface Synthesized Molecules

Kagome lattices have attracted much attention owing to their potential applications in spin-frustrated magnetism and host-guest chemistry. Examples toward the fabrication of 2D Kagome lattices reported previously have in common that the precursor molecules were typically deposited on the surface structurally intact with no chemical reactions accompanied. Herein, by using a combination of synchrotron radiation photoelectron spectroscopy (SRPES) and scanning tunneling microscopy (STM), we demonstrated the fabrication of two types of chiral Kagome lattices from on-surface synthesized organometallic compounds, which are known as intermediates of Glaser coupling on silver single crystal surfaces. These Kagome lattices are stabilized by the interplay of various intermolecular interactions, including Br⋅⋅⋅Br bonds, C-Br⋅⋅⋅π bonds and π-π stacking. The chiral transference and host-guest supramolecular structure in the novel Kagome lattices were also studied. Our studies may pave a new way to engineer complex supramolecular networks through on-surface reactions.

Desorption kinetics from a surface derived from direct imaging of the adsorbate layer.

There are numerous indications that adsorbed particles on a surface do not desorb statistically, but that their spatial distribution is important. Evidence almost exclusively comes from temperature-programmed desorption, the standard method for measuring desorption rates. However, this method, as a kinetics experiment, cannot uniquely prove an atomic mechanism. Here we report a low-energy electron microscopy investigation in which a surface is microscopically imaged while simultaneously temperature-programmed desorption is recorded. The data show that during desorption of oxygen molecules from a silver single crystal surface, islands of oxygen atoms are present. By correlating the microscopy and the kinetics data, a model is derived that includes the shapes of the islands and assumes that the oxygen molecules desorb from the island edges. The model quantitatively reproduces the complex desorption kinetics, confirming that desorption is affected by islands and that the often used mean-field treatment is inappropriate.

Formation of metal–organic interface states studied with 2PPE

Experimental and theoretical investigations on the formation mechanism of interface-specific electronic states at metal–organic interfaces are reviewed. Model systems discussed are thin films of 3,4,9,10-perylene-tetracarboxylic acid dianhydride (PTCDA) and 1,4,5,8-naphthalene-tetracarboxylic acid dianhydride (NTCDA) on the silver single crystal surfaces Ag(111) and Ag(100). Time and angle-resolved two-photon photoemission (2PPE) reveals the occurrence of unoccupied electronic states that have no counterpart in the bulk metal or the organic overlayer. The interface states resemble Shockley-surface states of clean metals. They are strongly dispersive and show an ultra-short lifetime in the range of tens to hundred femtoseconds. The energy position of the interface states is to a large extent determined by the adsorption height of the molecules and their local surface density while the wave function experiences a strong influence from the adsorption geometry of the molecules.

Characterisation of chloride and bromide specific adsorption process on silver single crystal surfaces by impedance spectroscopy: Part I. An extended model to obtain the charge density from impedance spectra applied to Ag(1 1 1) at low concentrations of halides

The adsorption processes of chloride and bromide are investigated by means of impedance spectroscopy. A physical model is proposed to obtain different kinetic and mass transport parameters at low concentrations of halides. Differential capacitance curves are determined by employing different equivalent circuits depending on the concentration of halides. The excess surface charge densities were calculated by integration of the total capacitance obtained from impedance spectroscopy.

Strong electron-phonon coupling at a metal/organic interface: PTCDA/Ag(111)

We analyze the electronic interaction of PTCDA, a ribbon-shaped functionalized polycyclic molecule commonly used as model system, with various silver single crystal surfaces, using high resolution electron energy loss spectroscopy as a probe. Special emphasis is placed on the coupling of hybrid electronic states to intramolecular vibrations. Under certain circumstances, this coupling leads to an extremely strong activation of otherwise forbidden vibrational modes. Apart from a strong intramolecular electron-phonon interaction, the formation of a metallic (i.e., partially filled) molecular band is a prerequisite for this effect, which is reported here both for the PTCDA/Ag(111) interface and for ultrathin potassium-doped PTCDA films on Ag(110) while undoped PTCDA/Ag(110) does not show this behavior. In the second part of the paper, we formulate and apply a theoretical model for the interfacial electron-phonon coupling, with the goal to understand the observed Fano line shapes in the case of PTCDA/Ag(111). This model allows us to accurately describe the observed line shape and trace it back to a nonadiabatic interaction between electronic states and molecular vibrations, secondly to rationalize why the K/PTCDA/Ag(110) system exhibits adiabatic behavior, and thirdly to extract values for the intramolecular electron-phonon coupling in PTCDA which are in good agreement with other data. The implications of our experimental observations and the theoretical analysis are discussed.

Distinct Demonstration of Methylene Insertion into the Metal−Carbon Bond on Ag(111)

We provide a clear demonstration of the migratory insertion of methylene into the metal−carbon bond on a silver single-crystal surface. The insertion reaction is characterized by the interaction between methylene and perfluoromethyl groups coadsorbed on Ag(111). The CH2 insertion into the Ag−CF3 bond followed by β-fluoride elimination produces CH2CF2, which is our experimental evidence for the insertion mechanism. Our observations confirm the step concerning the propagation of the carbon chain in the Fischer−Tropsch processes.

Coadsorption of hydrogen and potassium on silver single crystal surfaces

Adsorption and coadsorption of H 2 (D 2) and potassium on the single crystal silver surfaces (111) and (110) have been studied using TPD, angle-resolved TPD, work function measurements and LEED. Atomic hydrogen was used to cover the silver surfaces, since a very high activation barrier for molecular adsorption exists. From the Ag(111) surface hydrogen desorbs in a single peak with a close to second order reaction and a desorption energy of 7 kcal/mol. Hydrogen desorption from Ag(110) is characterized by two overlapping desorption peaks which are very sensitive to small amounts of water coadsorption. Angular distributions of the desorption probability following a cos 2.5Θ and a cos 3.5Θ function for Ag(111) and Ag(110) were observed, respectively. Upon hydrogen saturation (0.65 ML) on Ag(111) the work function increases by 240 meV. Coadsorbed potassium shifts the desorption temperature for H 2 dramatically by 250 K to higher temperature on both surfaces. Simultaneous desorption of hydrogen and potassium on both silver surfaces with a ratio of 1 K-atom to 4 H 2 molecules indicates a strong potassium-hydrogen interaction in the coadsorbate.

Electronic excitations on silver single crystal surfaces

Abstract Recent results are presented of surface electronic excitations on Ag single crystals. For small q ∥ the data show a linear and positive dispersion of the surface plasmon for all faces, whose slope depends on crystallographic face, and a strong azimuthal anisotropy in case of Ag(110). This demonstrates that the centroid of the induced charge for frequencies equal to the surface plasmon frequency is placed inside the surface. Different mechanisms determine surface plasmon damping. Face dependence is caused by the presence of face specific surface states. The dependence on crystal temperature is discussed.

Electronic excitations on silver single crystal surfaces

Recent results are presented of surface electronic excitations on Ag single crystals. For small q ∥ the data show a linear and positive dispersion of the surface plasmon for all faces, whose slope depends on crystallographic face, and a strong azimuthal anisotropy in case of Ag(110). This demonstrates that the centroid of the induced charge for frequencies equal to the surface plasmon frequency is placed inside the surface. Different mechanisms determine surface plasmon damping. Face dependence is caused by the presence of face specific surface states. The dependence on crystal temperature is discussed.

STM studies of real and quasi-perfect silver single crystal surfaces used in electrochemical experiments

STM studies of real and quasi-perfect silver single crystal surfaces used in electrochemical experiments

STM studies of real and quasi-perfect silver single crystal surfaces used in electrochemical experiments

Real and quasi-perfect silver single crystal surfaces, which have been used intensively in different electrochemical investigations, are studied by STM to determine the surface profile on an atomic level. The measurements were carried out on chemically polished macroelectrodes and electrolytically grown microelectrodes in contact with air as well as under potentially controlled electrochemical conditions. The real macroelectrodes show a much higher surface corrugation than the quasi-perfect microelectrodes which have large atomically flat terraces separated by monoatomic steps. The possibility to observe the dynamics of monoatomic steps under anodic and cathodic polarization conditions on quasi-perfect single crystal surfaces is demonstrated. Nucleation and crystal growth processes are observed by means of in situ STM investigations of lead electrodeposition on Ag(111) macroelectrodes. The results demonstrate the possibility to study fundamentally the initial steps of electrocrystallization by in situ STM under electrochemical well-defined conditions.

Electronic structure of clean and oxygen covered silver (110) surface

We use angle-resolved photoelectron spectroscopy to investigate the electronic structure of the clean and atomic oxygen covered Ag(110) surface. A comparison is made to results of surface band-structure calculations using a tight-binding method in a recursive layer-by-layer scheme. For the clean surface, where angle-resolved inverse photoemission data are also available, w obtain good agreement for all (except image potential) surface states. For the Ag(110)-p(2 × 1)-O surface, the electronic structure is calculated for a “buckled-row” and a “missing-row” reconstruction model. All occupied surface states are reproduced by both models where alternate silver 〈001〉 rows are displaced outward by 0.2 ± 0.2Å from the first layer and the oxygens are located 0.2± 0.2 Å above these. Angle-resolved inverse photoemission however would distinguish between the two reconstruction models since the unoccupied surface states are quite different. We also discuss the electronic structure of some other possible forms of oxygen adsorption on and absorption in silver single-crystal surfaces in relation to photoelectron spectroscopy.

The influence of solution composition on lead, cadmium and thallium underpotential deposition on (111) oriented silver single crystal surfaces

The influence of solution composition on the process of lead, cadmium and thallium UPD on (111) oriented silver single crystal surfaces has been investigated by using linear sweep voltammetry and differential capacity measurements. It is shown that the Y'-E curves can be used qualitatively as a criterion for the occurrence of partial charge transfer reactions in the double layer region and the commencement of the faradaic reaction of UPD. The C-E curves obtained in the presence and in the absence of depositing metal cations can give useful information about the nature of species present in the solution and adsorbed onto the substrate surface. It is also demonstrated that the presence of different complexes of cations investigated and the kinetics of their reduction can be responsible for a change in the UPD voltammograms.

Photoemission studies of KCl migration on Ag(110)

The migration of KCl molecules on the silver (110) single crystal surface is investigated by photoemission measurements. The behaviour of the quantum yield distribution curves is examined at different substrate temperatures. The analysis of Fowler's theoretical photoemission curves is made and compared with the experimental curves. This shows the process of the nucleation of KCl molecules as a result of their migration on the silver surface in a defined temperature range, which allows the activation energy of migration to be determined.

ChemInform Abstract: Influence of Adsorbing Substances on the UPD of Lead onto the (111)‐Oriented Silver Single Crystal Surface. Part 2.

AbstractThe kinetics of UPD (underpotential deposition) of Pb on an Ag single crystal were investigated in the presence of Cl04‐ , AcO′ and the citrate anion by potential step measurements rendering Current ‐ time transients.

The influence of adsorbing substances on the UPD of lead onto the (111)-oriented silver single crystal surface—II

Detailed analysis of the kinetics of UPD of lead on the (111) surface of a silver single crystal in the presence of perchlorate, acetate and citrate anions, has been made on the basis of potentiostatic current—time transients. It was established that while at concentrations of Pb 2+ ions in solution below 10 −2 M the process is diffusion controlled and hence independent of anions present, at higher concentrations nucleation phenomena take over the control. Anions affect the kinetics in line with their adsorbability discussed in Part I [V.D. Jović, Electrochim. Acta 28, 1625–1638 (1984), ie nucleation and growth are fastest in perchlorate and slowest in citrate solutions. During a potentiostatic pulse, driving the electrode from potential positive with respect to the “reversible” potential of UPD to a certain “cathodic overvoltage”, after some time the current response assumes a course obeying the equation derived for deposition controlled by 2-D growth with overlap of growing centres created by instantaneous nucleation. At shorter times however, an excess of current indicates a charge-transfer controlled adsorption of lead with formation of a low density superstructure (2√3 × 2√3) R30°, before the growth of the compact phase becomes dominant. Adsorption of anions does not seem to hamper the formation of this superstructure. Quantitative estimates of kinetics of all the processes, as well as of the properties of the obtained phases were derived.

Spectroscopic and electrochemical studies of transition-metal tetrasulfonated phthalocyanines: Part VI. The adsorption of iron tetrasulfonated phthalocyanine on single crystal silver electrodes

Abstract : Adsorbed layers of iron tetrasulfonated phthalocyanine have been examined using cyclic voltammetry on the silver single crystal low index surface: (100), (110), and (111). The peak potentials and charge under the voltammetry peaks show some dependence on the crystal planes. The effects of the underpotential deposition of lead on the adsorbed macrocycle have also been examined on the silver single crystal electrode. The lead can be underpotential deposited on the silver directly through a pre-adsorbed macrocycle layer without desorbing the macrocycle. The data are explained in terms of a model for the adsorbed macrocycle which has the plane of the ligand perpendicular to the electrode surface.