Surface Science Reports最新文献

The interest in understanding and controlling the properties of two-dimensional materials (2DMs) has fostered in the last years a significant and multidisciplinary research effort involving condensed matter physics and materials science. Although 2DMs have been investigated with a wide set of different experimental and theoretical methodologies, experiments carried out with surface-science based techniques were essential to elucidate many aspects of the properties of this family of materials. In particular, synchrotron-based X-ray photoelectron spectroscopy (XPS) has been playing a central role in casting light on the properties of 2DMs, providing an in-depth and precise characterization of these materials and helping to elucidate many elusive and intricate aspects related to them. XPS was crucial, for example, in understanding the mechanism of growth of several 2DMs at surfaces and in identifying the parameters governing it. Moreover, the chemical sensitivity of this technique is crucial in obtaining knowledge about functionalized 2DMs and in testing their behavior in several model chemical reactions. The achievements accomplished so far in this field have reached a maturity point for which a recap of the milestones is desirable. In this review, we will showcase relevant examples of studies on 2DMs for which synchrotron-based XPS, in combination with other techniques and state-of-the-art theoretical modeling of the electronic structure and of the growth mechanisms, was essential to unravel many aspects connected to the synthesis and properties of 2DMs at surfaces. The results highlighted herein and the methodologies followed to achieve them will serve as a guidance to researchers in testing and comparing their research outcomes and in stimulating further investigations to expand the knowledge of the broad and versatile 2DMs family.

The review describes electrochemical applications of tip-enhanced Raman spectroscopy (TERS). These applications combine the merits of both scanning probe microscopy (SPM) and Raman spectroscopy, which enables us to simultaneously obtain high-resolution images of surface morphology and chemical information under the electrochemical environment. This review, first summarizes the pioneering work done on the TERS systems that operate in liquid and electrochemical environments, and then gives an overview of the typical instrumentation of electrochemical TERS (EC-TERS) based on electrochemical scanning tunneling microscopy (EC-STM). Furthermore, this review summarizes the advancements in EC-TERS studies of events that occur at the interfaces. These include potential dependent structural changes and electrochemical reactions. Finally, we discuss the current issues and future prospects of EC-TERS for microscopic studies of electrochemical interfaces.

The property of a variable charge state makes ions unique to other types of radiation a material surface can be exposed to. As a consequence of charge exchange between ions and surfaces, energy is transferred to the surface and material damage may be triggered. Furthermore, a changing charge state of the ion alters its slowing down process in solids and has important implications when back-scattered ions are to be measured for material analysis purposes. Over the last decades extensive research was devoted to the understanding of ion charge exchange with solids. Here I review recent progress in this field with special emphasize on slow ions in high charge states. This class of ions allows a detailed analysis of charge exchange in experiments, which employ also ultra-thin solid targets and therefore give experimental access to electronic processes on the femtosecond timescale. In this review I will discuss general properties of charge exchange and present typical experimental techniques. I will also discuss current developments in the modelling and simulation of ion-surface interaction. Recent findings using freestanding 2D materials are discussed as well as results from spectroscopy of emitted secondary particles. The paper concludes with a unified picture of ion charge exchange at surfaces and presents possible applications based on the understanding of the underlying physics.

The interest in graphene (a carbon monolayer) adsorbed on metal surfaces goes back to the 60's, long before isolated graphene was produced in the laboratory. Owing to the carbon-metal interaction and the lattice mismatch between the carbon monolayer and the metal surface, graphene usually adopts a rippled structure, known as moiré, that confers it interesting electronic properties not present in isolated graphene. These moiré structures can be used as versatile templates where to adsorb, isolate and assemble organic-molecule structures with some desired geometric and electronic properties. In this review, we first describe the main experimental techniques and the theoretical methods currently available to produce and characterize these complex systems. Then, we review the diversity of moiré structures that have been reported in the literature and the consequences for the electronic properties of graphene, attending to the magnitude of the lattice mismatch and the type of interaction, chemical or physical, between graphene and the metal surface. Subsequently, we address the problem of the adsorption of single organic molecules and then of several ones, from dimers to complete monolayers, describing both the different arrangements that these molecules can adopt as well as their physical and chemical properties. We pay a special attention to graphene/Ru(0001) due to its exceptional electronic properties, which have been used to induce long-range magnetic order in tetracyanoquinodimethane (TCNQ) monolayers, to catalyze the (reversible) reaction between acetonitrile and TCNQ molecules and to efficiently photogenerate large acenes.

Molybdenum Disulfide (MoS₂) is a well-known transition metal dichalcogenide with a hexagonal structure arrangement analogous to graphene. Two dimensional (2D) MoS₂ has attracted wide attention in various applications such as energy storage, catalysis, sensing, energy conversion and optoelectronics due to its unique properties including tunable bandgap, substantial carrier mobility, outstanding mechanical strength and dangling-bond free basal surface. Moreover, MoS₂ has shown an excellent capability to be a host for foreign atoms which tune its physicochemical properties. Herein, currently known structural changes in the MoS₂ crystals introduced by various single atom dopants coming from all over the chemical table of elements are reviewed. Accompanying electrical, optical and magnetic properties of such structures are discussed in detail. Potential applications of the doped MoS₂ are introduced briefly as well. The review concentrates on the recent state-of-the-art results obtained mostly by the high resolution scanning transmission electron microscopy (STEM), such as high angle annular dark field (HAADF) imaging as well as scanning probe microscopy (SPM) such as scanning tunneling microscopy (STM). These techniques have been used to decipher dopant positions and other sub-atomic structural changes introduced to the MoS₂ structure by isolated dopants.

An atomic projectile colliding with a surface at kinetic energies in the thermal or hyperthermal range interacts with and is reflected by the electronic density well in front of the first layer of target atoms, and it is generally accepted that the repulsive interaction potential is proportional to the density of electrons extending outside the surface. This review develops a complete treatment of the elastic and inelastic scattering of atoms from a conducting surface in which the interaction with the electron density and its vibrations is treated using electron-phonon coupling theory. Starting from the basic principles of formal scattering theory, the elastic and inelastic scattering intensities are developed in a manner that identifies the small overlap region in the surface electron density where the projectile atom is repelled. The effective vibrational displacements of the electron gas, which lead to energy transfer through excitation of phonons, are directly related to the vibrational displacements of the atomic cores in the target crystal via electron-phonon coupling. The effective Debye-Waller factor for atom-surface scattering is developed and related to the mean square displacements of the atomic cores. The complex dependence of the Debye-Waller factor on momentum and energy of the projectile, including the effects of the attractive adsorption well in the interaction potential, are clearly defined. Applying the standard approximations of electron-phonon coupling theory for metals to the distorted wave Born approximation leads to expressions which relate the elastic and inelastic scattering intensities, as well as the Debye-Waller factor, to the well known electron-phonon coupling constant λ. This treatment reproduces the previously obtained result that the intensities for single phonon inelastic peaks in the scattered spectra are proportional to the mode specific mass correction components λ_Q,ν defined by the relationship λ = 〈λ_Q,ν〉. The intensities of elastic diffraction peaks are shown to be a weighted sum over the λ_Q,ν, and the Debye-Waller factor can also be expressed in terms of a similar weighted summation. In the simplest case the Debye-Waller exponent is shown to be proportional to λ and for simple metals, metal overlayers, and other kinds of conducting surfaces values of λ are extracted from available experimental data. This dependence of the elastic and inelastic scattering, and that of the Debye-Waller factor, on the electron-phonon coupling constant λ shows that measurements of elastic and inelastic spectra of atomic scattering are capable of revealing detailed information about the electron-phonon coupling mechanism in the surface electron density.

Water-solid interfaces play important roles across a broad range of scientific and application fields. In the past decades, atomic force microscopy (AFM) has significantly deepened our understanding of water-solid interfaces at molecular scale. In this review, we describe the recent progresses on probing water-solid interfaces by noncontact AFM, highlighting the imaging of interfacial water with ultrahigh spatial resolution. In particular, the recent development of qPlus-based AFM with functionalized tips has made it possible to directly image the H-bonding skeleton of interfacial water under UHV environment. Based on high-order electrostatic forces, such a technique even enables submolecular-level imaging of weakly bonded water structures with negligible disturbance. In addition, the three-dimensional (3D) AFM using low-noise cantilever deflection sensors can achieve atomic resolution imaging at liquid/solid interfaces, which opens up the possibility of probing the hydration layer structures under realistic conditions. We then discuss the application of those AFM techniques to various interfacial water systems, including water clusters, ion hydrates, water chains, water monolayers/multilayers and bulk water/ice on different surfaces under UHV or ambient environments. Some important issues will be addressed, including the H-bonding topology, ice nucleation and growth, ion hydration and transport, dielectric properties of water, etc. In the end, we present an outlook on the directions of future AFM studies of water at interfaces and the challenges faced by this field, as well as the development of new AFM techniques.

Metallic two-dimensional (2D) materials such as transition-metal dichalcogenides (TMDCs) and MXenes exhibit intriguing properties, including superconductivity, magnetism and electrocatalysis. Studies on the correlation between their nanoscale structures and properties can facilitate the development of photodetectors, supercapacitors, nanocatalysts, etc., but this topic has not been reviewed systematically. Here, we provide a comprehensive overview on the key factors that dictate the structures and properties of these 2D metals. We examine their phase transitions induced by structural or electronic modifications based on microscopic imaging, spectral characterization, and electrical measurements. From the perspective of surface and interface engineering, we elucidate the influences of lattice defects, dopants, and intercalated species between adjacent layers. Moreover, heterostructures involving highly conductive 2D component(s) are discussed, which may enable the observation of fascinating phenomena and/or synergistic effects due to the interlayer interactions. Finally, we provide insights into opportunities for new applications, e.g., radio-frequency antennas and electromagnetic interference shields. Feasible routes are also proposed to overcome the current challenges.

Catalytic reactions involve the direct interaction of reactants, intermediates and products with the catalyst surface. We not only need to control the atomic structure and electronic properties of the active site, but also explore the multiple molecular interactions that occur beyond the active site; they play an essential role in altering the binding and reactivity of surface species. In liquid-phase catalysis, solvents provide additional degrees of freedom in the design of the catalytic process for desirable activity and selectivity. The multi-faceted effects of solvents have a profound impact on the catalyst performance by restricting the mass transfer to the site, tuning the chemical potential of the surface species, competing for active sites, stabilizing the initial and transition states, and causing mechanistic changes by participating in the kinetically relevant elementary steps. This review addresses the different aspects of solvent effects, using a few prototype solid-liquid interfaces to illustrate these fundamental features. Recent experimental and computational studies that provide new insight at the molecular level are examined. Solvent structures in the proximity of the catalyst surface are discussed along with their influence in molecular binding and reaction at the solid-liquid interfaces. Furthermore, opportunities to alter such a solid-liquid interaction by tuning the wettability of the catalyst surfaces are explored.