Ag Surface Research Articles

Highly Selective Production of C2+ Oxygenates from CO2 in Strongly Acidic Condition by Rough Ag-Cu Electrocatalyst.

The acidic electrocatalytic conversion of CO2 to multi-carbon (C2+) oxygenates is of great importance in view of enhancing carbon utilization efficiency and generating products with high energy densities, but suffering from low selectivity and activity. Herein, we synthesized Ag-Cu alloy catalyst with highly rough surface, by which the selectivity to C2+ oxygenates can be greatly improved. In a strongly acidic condition (pH=0.75), the maximum C2+ products Faradaic efficiency (FE) and C2+ oxygenates FE reach 80.4 % and 56.5 % at -1.9 V versus reversible hydrogen electrode, respectively, with a ratio of FEC2+ oxygenates to FEethylene up to 2.36. At this condition, the C2+ oxygenates partial current density is as high as 480 mA cm-2. The in situ spectra, control experiments and theoretical calculations indicate that the high generation of C2+ oxygenates over the catalyst originates from its large surface roughness and Ag alloying.

Surface Plasmon Resonance Modulation by Complexation of Platinum on the Surface of Silver Nanocubes.

The use of plasmonic particles, specifically, localized surface plasmonic resonance (LSPR), may lead to a significant improvement in the electrical, electrochemical, and optical properties of materials. Chemical modification of the dielectric constant near the plasmonic surface should lead to a shift of the optical resonance and, therefore, the basis for color tuning and sensing. In this research, we investigated the variation of the LSPR by modifying the chemical environment of Ag nanoparticles (NPs) through the complexation of Pt(IV) metal cations near the plasmonic surface. This study is carried out by measuring the shift of the plasmon dipole resonance of Ag nanocubes (NCs) and nanowires (NWs) of differing sizes upon coating the Ag surface with a layer of polydopamine (PDA) as a coordinating matrix for Pt(IV) complexes. The red shift of up to 45 nm depends linearly on the thickness of the PDA/Pt(IV) layer and the Pt(IV) content. Additionally, we calculated the dielectric constant of the surrounding medium using a numerical method.

Probing charge redistribution at the interface of self-assembled cyclo-P5 pentamers on Ag(111)

Phosphorus pentamers (cyclo-P5) are unstable in nature but can be synthesized at the Ag(111) surface. Unlike monolayer black phosphorous, little is known about their electronic properties when in contact with metal electrodes, although this is crucial for future applications. Here, we characterize the atomic structure of cyclo-P5 assembled on Ag(111) using atomic force microscopy with functionalized tips and density functional theory. Combining force and tunneling spectroscopy, we find that a strong charge transfer induces an inward dipole moment at the cyclo-P5/Ag interface as well as the formation of an interface state. We probe the image potential states by field-effect resonant tunneling and quantify the increase of the local change of work function of 0.46 eV at the cyclo-P5 assembly. Our experimental approach suggest that the cyclo-P5/Ag interface has the characteristic ingredients of a p-type semiconductor-metal Schottky junction with potential applications in field-effect transistors, diodes, or solar cells.

Metal-water interface formation: Thermodynamics from abinitio molecular dynamics simulations.

Metal-water interfaces are central to many electrochemical, (electro)catalytic, and materials science processes and systems. However, our current understanding of their thermodynamic properties is limited by the scarcity of accurate experimental and computational data and procedures. In this work, thermodynamic quantities for metal-water interface formation are computed for a range of FCC(111) surfaces (Pd, Pt, Au, Ag, Rh, and PdAu) through extensive density functional theory based molecular dynamics and the two-phase entropy model. We show that metal-water interface formation is thermodynamically favorable and that most metal surfaces studied in this work are completely wettable, i.e., have contact angles of zero. Interfacial water has higher entropy than bulk water due to the increased population of low-frequency translational modes. The entropic contributions also correlate with the orientational water density, and the highest solvation entropies are observed for interfaces with a moderately ordered first water layer; the entropic contributions account for up to ∼25% of the formation free energy. Water adsorption energy correlates with the water orientation and structure and is found to be a good descriptor of the internal energy part of the interface formation free energy, but it alone cannot satisfactorily explain the interfacial thermodynamics; the interface formation is driven by the competition between energetic and entropic contributions. The obtained results and insight can be used to develop, parameterize, and benchmark theoretical and computational methods for studying metal-water interfaces. Overall, our study yields benchmark-quality data and fundamental insight into the thermodynamic forces driving metal-water interface formation.

A quantum sensor for atomic-scale electric and magnetic fields

The detection of faint magnetic fields from single-electron and nuclear spins at the atomic scale is a long-standing challenge in physics. While current mobile quantum sensors achieve single-electron spin sensitivity, atomic spatial resolution remains elusive for existing techniques. Here we fabricate a single-molecule quantum sensor at the apex of the metallic tip of a scanning tunnelling microscope by attaching Fe atoms and a PTCDA (3,4,9,10-perylenetetracarboxylic-dianhydride) molecule to the tip apex. We address the molecular spin by electron spin resonance and achieve ~100 neV resolution in energy. In a proof-of-principle experiment, we measure the magnetic and electric dipole fields emanating from a single Fe atom and an Ag dimer on an Ag(111) surface with sub-angstrom spatial resolution. Our method enables atomic-scale quantum sensing experiments of electric and magnetic fields on conducting surfaces and may find applications in the sensing of spin-labelled biomolecules and of spin textures in quantum materials.

Transmetalation in Surface-Confined Single-Layer Organometallic Networks with Alkynyl-Metal-Alkynyl Linkages.

Transmetalation represents an appealing strategy toward fabricating and tuning functional metal-organic polymers and frameworks for diverse applications. In particular, building two-dimensional metal-organic and organometallic networks affords versatile nanoarchitectures of potential interest for nanodevices and quantum technology. The controlled replacement of embedded metal centers holds promise for exploring versatile material varieties by serial modification and different functionalization. Herein, we introduce a protocol for the modification of a single-layer carbon-metal-based organometallic network via transmetalation. By integrating external Cu atoms into the alkynyl-Ag organometallic network constructed with 1,3,5-triethynylbenzene precursors, we successfully realized in situ its highly regular alkynyl-Cu counterpart on the Ag(111) surface. While maintaining a similar lattice periodicity and pore morphology to the original alkynyl-Ag sheet, the Cu-based network exhibits increased thermal stability, guaranteeing improved robustness for practical implementation.

Advancing on ametrine pesticide detection through surface‐enhanced Raman spectroscopy and Ag colloid: Understanding the pH effect and the adsorption mechanism supported by theoretical calculation

AbstractThe excessive use of pesticides has detrimental effects on the ecosystem, leading to soil contamination and the spread of pollution beyond the targeted areas. Concerns arise regarding the permissible limits of pesticides, typically around 10−8 mol/L. In this study, we employed surface‐enhanced Raman spectroscopy (SERS), a highly sensitive and selective technique, to investigate the behavior of the pesticide ametrine (AMT) on silver colloids. The Ag nanoparticles (AgNPs) exhibited an average size of (26 ± 2) nm and a zeta potential of (−30 ± 1) mV in the absence of AMT, which decreased to (−24 ± 1) mV in the presence of AMT, resulting in mild AgNPs aggregation, with the average diameter of AgNPs increasing to approximately 300 nm. This aggregation is advantageous, as they provide active sites for pesticide detection. Besides, the purification method employed ensured that AMT remained undegraded, and various conformations of AMT were simulated using Ag clusters to study the SERS effect. Comparison with the experimental spectra indicated that the SERS‐4 conformer closely resembled the experimental spectrum, suggesting simultaneous interaction between the Ag surface and the sulfur (S) and nitrogen (N) atoms of the AMT triazine ring. Notably, changes in the AMT molecule were observed with pH variations: at pH below 5, hydroxylation occurred, resulting in an Ag–Cl stretching at 241 cm−1 in the SERS spectra. Conversely, at pH above 5 (pH 6–13), the presence of bands at 230 and 219 cm−1 in the SERS spectra indicate the formation of Ag–N and Ag–S bonds, respectively, between the AMT and the AgNPs. Furthermore, the study successfully detected AMT at pH 7, establishing a limit of detection (LOD) of 1.36 × 10−8 mol/L (3 ppb) based on the SERS spectra. These findings underscore the applicability of the SERS technique in the sensitive and selective detection of AMT, offering a promising approach for monitoring the presence of this pesticide in environmental samples.

Structure Determination of F4TCNQ on Ag(111): A Systematic Trend in Metal Adatom Incorporation.

A structure determination of the commensurate phase formed by 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (F4TCNQ) absorbed on Ag(111) is reported. Initial characterization was performed using low-energy electron diffraction and synchrotron radiation photoelectron spectroscopy, with quantitative structural data being provided by normal incident X-ray standing waves (NIXSW) and surface X-ray diffraction (SXRD). NIXSW data show the F4TCNQ molecule to adopt a "twisted" conformation on the surface, previously found to be associated with metal adatom incorporation into a 2d-metal-organic framework for F4TCNQ on Au(111), Ag(100), and Cu(111). SXRD results provide direct evidence of the presence of Ag adatoms that are found to occupy near-bridge or fcc hollow sites with respect to the underlying surface, at an adsorption height of 2.69 ± 0.10 Å. The results show a consistent pattern of behavior for F4TCNQ adsorption on the (111) surfaces of Cu, Ag, and Au.

Study on the self-assembly process of 2,7-dibromopyrene molecules

The first-principle technique has been utilized to investigate the self-assembly process of 2,7-dibromopyrene (Br2Py) molecules in forming monolayers. Based on Br-H adsorption and Br-Br repulsion, Br2Py molecules form two molecular chains and one molecular cluster, which then lead to the formation of four possible monolayers. CASTEP calculation demonstrates that both the molecular chains and monolayers are all the self-assembly system, with the structural parameters of the monolayers being consistent with existing literature. Electron density analysis on these molecular chains and monolayers validates the Br-H adsorption and Br-Br repulsion. Furthermore, the probability for formation of monolayers is presented. It is evident that while the atomic structure of a Br2Py monolayer is primarily influenced by intermolecular interactions, there exists a certain selectivity for film-forming on Au(111), Ag(111) and Cu(111) surfaces.

Influence of lateral configurations on the charge transfer between H− ions and Na/Ag(1 1 1) surfaces

This study investigates the electron transfer during lateral collisions between H− projectiles and Ag(111) surfaces with Na adsorbates. These interactions aim to probe the nearside region of the adsorbate. Compared to the on-top configuration, the lateral projected density of states reveals strong local effects such as perturbations of energy levels, adsorbate-induced states not identifiable from on-top, and image states enhancement. A study of dynamics reveals that, in addition to the projectile’s distance of closest approach and interaction time with surface, the projectile’s survival is influenced by the balance between electron capture and loss at the start of the exit trajectory.

Efficient Fabrication of Plasmonic Nanostructures Using Chloroform‐Mediated Heterogeneous Bonding

AbstractPlasmonic nanostructures (PNs) have transformed nanophotonics by offering control over electromagnetic waves. Although innovative structural designs have demonstrated PNs' potential, significant fabrication challenges, including the precise alignment of heterogeneous materials, remain. Using chloroform and pre‐UV exposure (PUVE) to enhance adhesion at the metal‐dielectric interface (MDI) addresses these challenges. PUVE preserves plasmon resonance in the MDI, ensuring high performance without compromising structural integrity. Through an annealing process, PUVE strengthens van der Waals bonds, ensuring chloroform molecules remain on the Ag surface during chloroform residue removal, allowing: i) stable preservation of the Ag thin film on the PNs during stripping; and ii) the formation of chloroform‐mediated heterogeneous bonding (CMHB) using energy supplied by UV‐nanoimprint lithography (UV‐NIL). This approach enables PNs' scalable fabrication with enhanced adhesion properties, while CMHB increases adhesion between the UV‐curable resin and Ag, offering scalability to large‐area applications with UV‐NIL. The structural morphology and chemical properties of the fabricated PNs are analyzed using scanning electron microscopy, atomic force microscopy, energy‐dispersive spectroscopy, and X‐ray photoelectron spectroscopy. These PNs demonstrate potential in CCD filters, enhancing optical signal amplification for real‐time imaging at the 785 nm band. This robust fabrication method advances PNs' performance and scalability, advancing nanophotonics and related applications.

Theoretical study of the compatibility between environmentally friendly insulation gas CF3SO2F and silver, zinc, and zinc oxide materials in gas-insulated equipment

Exploring the gas-solid compatibility between insulating gas and solids materials used in electrical equipment is of great significance for determining the long-term behavior of insulating gas trifluoromethanesulonyl fluoride (CF3SO2F). The gas-solid compatibility of CF3SO2F and its decomposition products with Ag, Zn, and ZnO common surfaces has been assessed based on first-principles calculations, with SF6 as the control group. CF3SO2F has excellent gas-solid compatibility with the solid surfaces by analyzing the adsorption configurations, adsorption energies, charge transfer, adsorption height, density of states, and ab initio molecular dynamics (AIMD) results. The external electric fields do not affect the excellent compatibility between CF3SO2F and the solid surfaces. Besides, the Ag(111) surface exhibits fine gas-solid compatibility with all decomposition products benefitting from its low surface energy. Originating in the existence of the three-center-four-electron (3c4e) π bond and F atoms with strong electronegativity in SO2F2, SO2F2 has poor compatibility with the Ag(110), (100), and Zn(001) surface. SO2, COF2, and HF gases may accelerate equipment failure due to the strong adsorption strength and poor compatibility with ZnO(100) and (110) surfaces. The results provide the theoretical guidance for the engineering application and long-term performance evaluation of CF3SO2F.

L -gap surface resonance at Pt(111): Influence of atomic structure, d bands, and spin-orbit interaction

Pt(111) hosts a surface resonance with peculiar properties concerning energy vs momentum dispersion and spin texture. At variance with the free-electron-like behavior of the L-gap Shockley-type surface states on the fcc(111) surfaces of Au, Ag, and Cu, it splits into several branches with distinct spin polarization around the center of the surface Brillouin zone Γ¯. Theoretical predictions based on density-functional theory vary depending on the particular functionals used. To clarify this issue, we investigate the atomic structure of Pt(111) by low-energy electron diffraction and the unoccupied electronic structure by spin- and angle-resolved inverse photoemission. The experimental results are backed by theoretical studies using different functionals, which show that the characteristics of the surface band depend critically on the lattice constant. From the analysis of the energy-dependent low-energy electron diffraction intensities, we derive structural parameters of the Pt(111) surface relaxation with high accuracy. In addition, we give an unambiguous definition of the nonequivalent mirror-plane directions Γ¯M¯ and Γ¯M¯′ at fcc(111) surfaces, which is consistent with band-structure calculations and inverse-photoemission data. Concerning the surface resonance at the bottom of the L gap, we identified a delicate interplay of several contributions. Lattice constant, hybridization with d bands, and the influence of spin-orbit interaction are critical ingredients for understanding the peculiar energy dispersion and spin character of the unoccupied surface resonance. Published by the American Physical Society 2024

Evidence for double resonant Raman decay from a Ag surface

We have investigated the electron pair emission from a Ag(100) surface upon photon absorption which leads to the emission of a 4p photoelectron. The subsequent Auger decay proceeds in a single-step process as shown previously. Key finding was the emergence of a diagonal intensity feature in a two-dimensional kinetic energy distribution of the electron pair whose width reveals a characteristic time of 30 as for the dynamics of the core-hole decay process. We utilize this observation as a tool to identify an unexpected pathway of electron pair emission. Once the photon energy is at the threshold of a double 4p core hole creation we notice a sizeable broadening of the energy sharing distribution. We associate this process to the excitation of two 4p electrons between the Fermi and vacuum level followed by radiation less double electron excitation. This feature is characterized by an energy sum of the pair which disperses linearly with the photon energy. Therefore, we regard it as a double resonant Raman decay. Published by the American Physical Society 2024

The Selectivity Origins in Ag-Catalyzed CO2 Electroreduction.

Ag exhibits high selectivity of electrochemical CO2 reduction (CO2R) toward C1 products, while the hydrogenation involving the concerted proton-electron transfer (CPET) or sequential electron-proton transfer (SEPT) mechanism is still in debate. Toward a better understanding of the Ag-catalyzed electrochemical CO2R, we employed a microkinetic model based on the Marcus electron transfer theory to thoroughly investigate the selectivity of C1 products of electrochemical CO2R over the Ag(111) surface. We found that at an acidic condition of pH = 1.94, formate is the main product when U < -0.94 V via the CPET mechanism, whereas CO becomes the primary product when U > -0.94 V via the SEPT mechanism. Conversely, at an alkaline condition of pH = 13.95, formate is the main product following the SEPT mechanism. Our findings provide novel insights into the influence of external factors (applied potential and pH) on the product selectivity and hydrogenation mechanism of electrochemical CO2R.

Surface modification of XSe (X = Cu and Ag) monolayers by grope 1 elements: A metal to semiconductor transition by a first-principles perspective

Two-dimensional (2D) materials can be effectively functionalized by chemically modified using doping. Very recently, a flat AgSe monolayer was successfully prepared through direct selenization of the Ag(111) surface. Besides, the results indicate that the AgSe monolayer like CuSe, has a honeycomb lattice. Motivated by the experimental outcomes, in this work, employing first-principles calculations, we systematically investigate the electronic and optical properties of AgSe and CuSe monolayers, as well as the impact of alkali metals (Li, Na and K). Without functionalization, both the CuSe and AgSe monolayers exhibit metallic characteristics. The Li (Na)-CuSe and Na (K)-AgSe systems are dynamically stable while, the K- and Li-CuSe and Li-AgSe are dynamically unstable. Interestingly, the functionalized CuSe system with Li and Na atom as well as AgSe with K and Na atom, can open the band gaps, leading to the actualization of metal to semiconductor transitions. Our results show that, the electronic characteristics of the Na-CuSe/AgSe system can be modulated by adjusting the adsorption heights, which gives rise to the change in the electronic properties and the band gap may be controlled. Furthermore, from the optical properties we can find that the K-AgSe system is the best candidate monolayer to absorb infrared radiation and visible light. Consequently, our findings shed light on the functionalization of 2D materials based CuSe and AgSe monolayers and can potentially enhance and motivate studies in producing these monolayers for current nanodevices and future applications.

Integration of conventional surface science techniques with surface-sensitive azimuthal and polarization dependent femtosecond-resolved sum frequency generation spectroscopy.

Experimental insight into the elementary processes underlying charge transfer across interfaces has blossomed with the wide-spread availability of ultra-high vacuum (UHV) setups that allow the preparation and characterization of solid surfaces with well-defined molecular adsorbates over a wide range of temperatures. Within the last 15 years, such insights have extended to charge transfer heterostructures containing solids overlain by one or more atomically thin two dimensional materials. Such systems are of wide potential interest both because they appear to offer a path to separate surface reactivity from bulk chemical properties and because some offer completely novel physics, unrealizable in bulk three dimensional solids. Thick layers of molecular adsorbates or heterostructures of 2D materials generally preclude the use of electrons or atoms as probes. However, with linear photon-in/photon-out techniques, it is often challenging to assign the observed optical response to a particular portion of the interface. We and prior workers have demonstrated that by full characterization of the symmetry of the second order nonlinear optical susceptibility, i.e., the χ(2), in sum frequency generation (SFG) spectroscopy, this problem can be overcome. Here, we describe an UHV system built to allow conventional UHV sample preparation and characterization, femtosecond and polarization resolved SFG spectroscopy, the azimuthal sample rotation necessary to fully describe χ(2) symmetry, and sufficient stability to allow scanning SFG microscopy. We demonstrate these capabilities in proof-of-principle measurements on CO adsorbed on Pt(111) and on the clean Ag(111) surface. Because this setup allows both full characterization of the nonlinear susceptibility and the temperature control and sample preparation/characterization of conventional UHV setups, we expect it to be of great utility in the investigation of both the basic physics and applications of solid, 2D material heterostructures.

Temperature and thickness-dependent silver hillock generation mechanism and surface morphology nature of direct plated silver layers onto copper substrates

This study delves into the formation of hillocks on Ag surfaces, particularly those resulting from heat-induced processes. We investigate the Ag hillock generation mechanisms in direct Ag plating layers on copper (Cu) substrates, employing a combination of experimental and numerical approaches for comprehensive quantification. In the Ag layer system directly plated on Cu, the strain inside the grain system significantly increases as the temperature increases, but the energy level of the system drops due to the relaxation of the internal strain starting from a certain critical temperature. Namely, the Ag hillock growth mechanisms on Ag plated Cu substrate originated from the microstructural development with thermomechanical behaviors. Nevertheless, the Ag layer directly plated on Cu suffered Ag-Cu diffusion through the grain boundary due to heat, which contaminated the Ag plating surface. Hillock formation is possible even in an Ag layer directly plated on a Cu substrate, but Ag-Cu diffusion may be a factor that inhibits the development and growth of Ag hillocks. In this study, the major feature of the Ag hillock formation on the direct Ag layer plated on Cu substrate was systematically clarified in terms of the microstructures and mechanics of materials.

Dissociative Adsorption of O2 on Ag3Au(111) Surface: A Density Functional Theory Study

The catalytic efficiency of oxygen reduction catalysts is notably influenced by the dissociative adsorption of O2. We conducted a systematic investigation into the dissociative adsorption of O2 on the Ag3Au(111) surface using ab initio density functional theory (DFT) calculations. Our computational findings indicate that adsorption the configuration designated t-b-t exhibits favorable energetics on the Ag3Au(111) surface. Regarding the dissociation of O2, we identified a reasonable dissociation pathway, which proceeds from the initial t-b-t state to the creation of two oxygen atoms that occupy a set of neighboring fcc sites. Furthermore, our analysis indicates that the adsorption of O2 on the Ag3Au(111) surface is less favored thermodynamically and more difficult to dissociate than that on the Ag(111) surface. This study furnishes a theoretical framework elucidating the prospective utilization of Ag-Au alloy in the capacity of oxygen reduction catalysts.

Directed growth of quinacridone chains on the vicinal Ag(35 1 1) surface.

The formation of self-assembled domains and chains of monomolecular width of quinacridone (QA) on the vicinal Ag(35 1 1) surface was investigated by scanning tunneling microscopy and low-energy electron diffraction. The focus was on the influence of the steps on the QA structures and their preferential azimuthal orientations with the aim of achieving a selective orientation. After deposition at a sample temperature of 300 K, QA forms the same kind of molecular chains as on the nominally flat Ag(100) surface because of strong intermolecular hydrogen bonds, which we reported in a previous publication [Humberg, N.; Bretel, R.; Eslam, A.; Le Moal, E.; Sokolowski, M. J. Phys. Chem. C 2020, 124, 24861-24873]. The vicinal surface leads to one additional chain orientation, which is parallel to the Ag step edges. However, most chains nucleate on the Ag terraces between steps with four distinct azimuthal orientations that are identical to those on Ag(100), and which are determined by the interactions with the (100) surface. At 300 K, the chains grow across the Ag steps, which do not break the azimuthal chain orientations. In contrast, during the deposition at sample temperatures of 400 and 500 K, the nucleation of the chains takes place at the Ag step edges. Hence, these have a strong influence on the azimuthal orientation of the molecules, resulting in a preferential growth of the chains in two of the four azimuthal orientations. We explain this by the adaptation of favorable adsorption sites, which involve the replacement of Ag atoms by QA molecules with specific azimuthal orientations at the step edges.