Monolayered metal oxides (MMOs), typically differing from their bulk counterparts, have attracted extensive research interest due to their unique properties for heterogeneous catalysis. MMOs routinely undergo structural relaxation and form strong interactions with their underlying substrates, giving rise to distinctive energetic and electronic characteristics that dictate their formation and catalytic behavior. In contrast to metals, metal oxides possess a low surface free energy, which endows MMOs with a higher stability than their bulk counterparts, making it relatively easy to obtain MMOs rather than multilayers through either molecular beam epitaxy growth or direct oxidation. For MMOs grown on metal substrates, their electronic structures are remarkably affected by the underlying metal supports. Specifically, the augmented chemical potentials of MMOs by the underlying metal substrates typically facilitate effective dispersion of supported single metal atoms or clusters. Moreover, the interfaces established between MMOs and metal substrates can provide abundant coordinatively unsaturated sites that are widely recognized as critical catalytic active zones for catalytical performance. Therefore, this review primarily focuses on recent research advances of MMOs, covering their stability in synthesis strategies, dispersibility in supporting single-atoms/clusters and activity in model catalysis. Our goal aims at exploiting the great potential of MMOs in advancing our exploration and understanding of practical heterogeneous catalysis.
Research in the field of biointerfaces is currently expanding because of continuous scientific demands stemming from different areas of biology and biomedicine. The most challenging questions require new technological advancements, often emerging from apparently distant disciplines, such as vacuum science and technology (VST). If living systems are characterized by their molecular diversity and scaled hierarchical structure, VST provides a palette of bioanalytical techniques designed to disentangle emerging complex biointerface structures. We review crucial developments in bioanalytical systems concentrating on those based on kinetic electrons and ions. Developments in these techniques are closing the vacuum gap between the conditions required for a sensitive analysis and the natural environment of the sample (near ambient pressure analysis). The biomedical field has been the focus of most of the reviewed developments, with an emphasis on recent research related to microbiological analysis. Additional examples from environmental applications, zoology or agriculture (among others) are also presented.
The advent of atomically thin two-dimensional (2D) materials provides a versatile platform to transcend the fundamental limitations of silicon-based electronics and continue the miniaturization of field-effect transistors, yet the epitaxial growth of wafer-scale, single-crystalline structure remains a formidable challenge. In recent years, the vigorous development of machine learning (ML) techniques has contributed to a revolutionary shift in materials synthesis, characterization and application, offering unprecedented opportunities for scientific and technological innovations that are inaccessible through traditional experimental and computational methods. This review aims to outline recent progress of ML-assisted 2D materials growth, including optimizing synthesis conditions, automating real-time characterizations and unveiling growth mechanisms. Current challenges and future prospects in this frontier research field are also discussed. Overall, this review highlights the synergy between advanced ML techniques and surface growth approaches for accelerated materials synthesis and intelligent design of next-generation functional devices.
Metal–organic frameworks (MOFs) are crystalline materials renowned for their high porosity, chemical tunability, and modular design. The development of surface-anchored and oriented MOF thin films—particularly those fabricated by layer-by-layer or epitaxial growth—has shifted MOF research from powder studies to investigations of well-defined, surface-confined architectures. This review examines MOF thin films from a surface-science perspective, emphasizing how controlled growth at well-defined interfaces enables quantitative studies of structure–property relationships, interfacial charge and energy transfer, polarization-dependent optical responses, and dynamic guest–host interactions. The long-range crystallographic order achievable in these oriented films gives rise to band-structure effects and anisotropic transport phenomena that cannot be observed in MOF thin films prepared from powder-derived particles. Their monolithic and defect-controlled nature allows detailed characterization by advanced surface-sensitive techniques such as IRRAS, XPS, NEXAFS, UPS, nanoindentation, ellipsometry, and AFM, providing direct links between microscopic structure and macroscopic functionality. Beyond serving as model systems, oriented MOF films represent versatile platforms for adsorption, catalysis, and electronic coupling at hybrid organic–inorganic interfaces. The review also highlights how computational modeling, machine learning, and AI-guided synthesis accelerate the rational design of interface-engineered MOF architectures with tailored properties.
Cooperativity and non-additive interactions play central roles in the unusual and surprising behavior of water. A host of reactive oxygen species (ROS) including the hydroxyl radical •OH, superoxide radical anion (O2−•), hydroperoxide radical (HO2•), singlet oxygen (1O2), and also the more recently discussed water radical cation/anion pair (H2O+•/H2O−•) all add to the more familiar acid/base chemical pathways tread by hydronium (H3O+) and hydroxide (OH−). This is amplified in surface science because interfacial water – whether found at the gas/liquid, gas/solid, or liquid/solid interface – poses yet more unique behavior. This review explores the unexpected chemistry associated with ambient temperature aqueous interfaces much of which is mediated not only by ions and neutrals as expected, but also radical species. Water microdroplets catalyze numerous reactions and can also support simultaneous oxidation and reduction reactions through the production of reactive intermediates that owe their existence to the unique influence of the air/water or oil/water interface. Interfacial water influences and is influenced by the ubiquitous phenomenon of contact electrification, a manifestation of spontaneous symmetry breaking. The mechanisms of chemistry not only on and in microdroplets but also at the gas/solid and liquid/solid interfaces rely on a broad set of chemical transformations mediated by radicals. Furthermore, because aqueous macro- and micro-interfaces are ubiquitous on Earth, we find that water radical-mediated chemistry has applications to atmospheric chemistry, geochemistry, mineral weathering, pre-biotic chemistry, enhanced enzyme performance, wastewater remediation, public health, mechanochemistry, and potentially novel routes to pharmaceuticals.
Two-dimensional (2D) organic topological insulators (OTIs) have garnered increasing interest due to their SOC-induced band gaps and topological boundary states that connect the valence and conduction bands. Experimental efforts utilizing substrate-mediated self-assembly have successfully fabricated 2D organic frameworks with various lattice symmetries. The vast diversity of organic molecules and the wide range of possible coordination interactions between organic ligands and metal atoms have led to significant attention toward these frameworks. However, the experimental realization of large-scale, ordered 2D OTIs remains challenging. In particular, the synthesis of monolayer 2D OTIs featuring nearly flat bands due to destructive quantum interference near the Fermi level has been elusive. With advancements in synthetic chemistry and on-surface synthesis techniques, the number of theoretically-predicted 2D OTIs has been gradually experimentally realized. This review provides a comprehensive summary of recent advances in the synthesis and characterization of 2D OTIs, with a particular focus on the experimental identification of nontrivial flat bands. Finally, we discuss future research directions and the challenges associated with characterizing these novel quantum materials.
In this review, the initial oxidation process of low-index surfaces of single-crystalline platinum group metals (PGMs: Ru, Rh, Pd, Ir, and Pt) is discussed in detail at the atomic level, involving several types of oxygen species: chemisorbed O, subsurface O, dissolved O, oxidic O. The oxidation of PGMs begins only when the surface of the PGM is saturated with chemisorbed O. Oxygen penetration into the metal is a critical next step in surface oxide formation, which can occur either through the step edge or directly through the terrace, depending on the oxidants chosen (O2, NO2, atomic O, and ozone O3). However, subsurface oxygen (oxygen directly below the top metal layer) does not form a separate phase in PGM. Instead, a surface oxide consisting of a single O-Me-O trilayer nucleates and grows (heterogeneous growth mode). The oxidation process is a nonlinear process with self-acceleration and passivation behavior, where many processes occur in parallel and in sequence, so that patterning can occur on different length scales. For this reason, oxidation studies must be performed at both the atomic and mesoscale using powerful combinations of surface science techniques such as scanning tunneling microscopy (STM) and low-energy electron microscopy (LEEM).
Infrared (IR)-visible (Vis) sum frequency generation (SFG) is a second-order nonlinear optical process which is forbidden in centrosymmetric bulk media or isotropic phases, but allowed at (open) surfaces or (buried) interfaces where the inversion symmetry is broken. SFG spectroscopy is thus inherently surface- or interface-specific, providing information about the structure, orientation, surface number density, chirality, and dynamics of molecules, provided the system of interest is accessible by light. This review illustrates basic SFG concepts, theory, operation modes (e.g., frequency-domain, broadband, homodyne/heterodyne, time-resolved), and recent extensions and developments of SFG (e.g., doubly resonant, plasmon-enhanced, chiral, microscopy). To illustrate the wide range of SFG applications, selected case studies discuss the characterization of molecular structure and bond orientation at solid-gas (air, UHV), solid-liquid, liquid-air, liquid-liquid, and solid-solid interfaces.
The synthesis and characterization of two dimensional materials are in the focus of nanomaterial and surface science, heterogeneous catalytic and nanoelectronic research laying the basis for various technological applications. Hexagonal boron nitride (h-BN) is an important member of 3D and reduced dimensional materials. Atomically clean sp2-hybridized 2D nano-layers can be grown on various metal supports by different chemical and physical vapor deposition techniques. In case of a significant lattice mismatch and a strong interaction at the h-BN/metal interface, a periodically undulating monolayer - a so-called “moirè structure” - is formed. In the present review, we address some important characteristics of h-BN prepared on several metal surfaces, and we focus on its application as a template for individual atoms, metal clusters and molecules. Moreover, several experimental findings are collected about the features and applications of monolayer h-BN nanosheets as supporting materials. We highlight the results of recent surface science studies, which emphasize the unique role of h-BN including nanomeshes in characteristic adsorption properties, stability and catalytic activity. The characterization of few layer and defective h-BN involving their catalytic applications are also the subject of the present review. We present a comprehensive overview on the electronic and vibrational states of nanoparticles (covered by adsorbates, as well) monitored by surface spectroscopy tools, e.g. XPS, ARPES, UPS, LEIS, AES, STS and HREELS. We also elaborate on the structural and morphological information of h-BN nanoobjects obtained by scanning probe microscopy (SPM). It is also highlighted that density functional theory (DFT) is considered as a very important complementary technique contributing to the better understanding of experimental results. Beside updated recollection of key findings, we outline the present and future research directions of 2D materials and their heterostructures including h-BN-based systems.
X-ray photoelectron spectroscopy is a powerful experimental technique that yields invaluable information on a range of phenomena that occur in solids, liquids, and gasses. The binding energy and shape of a photoemission peak is sensitive not only to the atomic number, valence and orbital from which the electron is ejected, but also to complex many-body effects that accompany photoemission. Provided the influences of these different drivers of spectral line shapes can be disentangled, a great deal can be learned about the electronic structure of materials of interest. In addition to these largely local effects, the long-range electrostatic environment and resulting electric potential at the emitting atom also have a direct effect on the measured binding energies. This fact opens the door to extracting information about the dependence of the valence and conduction band minima on depth below the surface, which in turn allows both vertical and lateral electrical transport data to be better understood. One purpose of this Report is to summarize how the different physical forces described above impact the spectral properties of complex oxide epitaxial films. This class of materials typically incorporates transition metal cations in different valences and such ions exhibit the most complex core-level spectra of any on the periodic chart. A second purpose is to show how a comprehensive understanding of local physical effects in x-ray photoemission allows one to model spectra and extract from core-level line shapes and binding energies detailed information on built-in potentials and band edge discontinuities in heterostructures involving complex oxides.
Wires having a width of one or two atoms are the smallest possible physical objects that may exhibit one-dimensional properties. In order to be experimentally accessible at finite temperatures, such wires must stabilized by interactions in two and even three dimensions. These interactions modify and partly destroy their one-dimensional properties, but introduce new phenomena of coupling and correlation that entangle both charge and spin. We explore this fascinating field by first giving an overview of the present status of theoretical knowledge on 1D physics, including coupling between chains and to the substrate, before we set out for experimental results on ordered arrays of atomic wires on both flat and vicinal Si(111) surfaces comprising Si(111)-In, Si(hhk)-Au, Si(557)-Pb, Si(557)-Ag, Ge(001)-Au and rare earth silicide wires. While for these systems structural, spectroscopic and (magneto-)conductive properties are in the focus, including temperature- and concentration-induced phase transitions, explicit dynamics on the femto- and picosecond time scales were explored for the modified Peierls transition in indium chains on Si(111). All these systems are characterized by strong correlations, including spin, that are extended over whole terraces and partly beyond, so that small geometric changes lead to large modifications of their electronic properties. Thus this coupling in one (1D), two (2D) (and even three) dimensions results in a wealth of phase transitions and transient quasi-1D conductance. As extremes, modified quasi-1D properties survive, as in the Si(111)-In system, whereas strong Fermi nesting results in entanglement of spin and charge between terraces for Si(557)-Pb, so that spin orbit density waves across the steps are formed.
Over the past decade, experimental microscopy and spectroscopy have made significant progress in the study of the morphological, optical, electronic and transport properties of materials. These developments include higher spatial resolution, shorter acquisition times, more efficient monochromators and electron analysers, improved contrast imaging and advancements in sample preparation techniques. These advances have driven the need for more accurate theoretical descriptions and predictions of material properties. Computer simulations based on first principles and Monte Carlo methods have emerged as a rapidly growing field for modeling the interaction of charged particles, such as electron, proton and ion beams, with various systems, such as slabs, nanostructures and crystals. This report delves into the theoretical and computational approaches to modeling the physico-chemical mechanisms that occur when charged beams interact with a medium. These mechanisms encompass single and collective electronic excitation, ionization of the target atoms and the generation of a secondary electron cascade that deposits energy into the irradiated material. We show that the combined application of ab initio methods, which are able to model the dynamics of interacting many-fermion systems, and Monte Carlo methods, which capture statistical fluctuations in energy loss mechanisms by random sampling, proves to be an optimal strategy for the accurate description of charge transport in solids. This joint quantitative approach enables the theoretical interpretation of excitation, loss and secondary electron spectra, the analysis of the chemical composition and dielectric properties of solids and contributes to our understanding of irradiation-induced damage in materials, including those of biological significance.
The oxides of copper have attracted the attention of scientists already for more than hundred years. This fascination is fueled by many outstanding properties of the material, for example, a semiconducting behavior that led to the first diode fabricated in electronics, a pronounced excitonic response that stimulated an intense search for Bose-Einstein condensation, and a pivotal role in unconventional superconductivity. Despite this central position in past and present research activities, many aspects of copper oxides are not sufficiently understood to date. This applies in particular to their surface characteristics, where even fundamental questions, such as the energetically favored termination of low-index Cu2O and CuO planes, are still subject of debates. This review aims at addressing these deficiencies by compiling state-of-the-art knowledge of the surface science of copper oxides, and especially of cuprous oxide.A first focus of the article lies in the oxidation characteristic of copper as a means to prepare well-defined oxide surfaces. It demonstrates that low-pressure oxidation only results in the formation of ultrathin precursor oxides, with properties deviating substantially from those of the bulk material. Consequently, reliable pathways to produce high-quality and bulk-compatible surfaces, either of Cu2O thin films or bulk crystals, are presented. The following chapter provides a comprehensive introduction into the atomic structure of the most relevant Cu2O surfaces, i.e., the (111), (100) and (110) planes. It gives an overview of important diffraction and microscopy experiments on the most accessible Cu2O terminations, and complements this with state-of-the-art theoretical studies to develop corresponding atomistic models. The chapter closes by presenting the atomic configurations of the most relevant Cu2O surfaces at given thermodynamic conditions.Chapter four develops a surface-science view onto the unique optical response of cuprous oxide. After introducing the well-known bulk behavior, it highlights how optical properties can be probed on surfaces with high spectral and spatial resolution. The chapter discusses how optical near-field techniques are employed to analyze oxide excitons and their trapping at lattice defects in real-space experiments. The last chapter summarizes efforts to alter intrinsic Cu2O properties, e.g., the p-type conductivity, the width of the band gap and the exciton trapping and recombination behavior, via doping. It illuminates this topic from an experimental and theoretical viewpoint and highlights several unsolved questions related to the topic.Despite considerable efforts, this review can only present the current state of knowledge on Cu2O surfaces, a subject that continuously advances due to new scientific findings and innovations. We nonetheless hope that it provides a comprehensive and topical overview of the unusual properties of this fascinating oxide system.
Recently there has been an explosion of research related to the Dzyaloshinskii-Moriya interaction (DMI) in magnetic and multiferroic materials. This article reviews the key themes in this research and provides insight into the consequences of the DMI through simple theoretical models. The topics covered include new magnetic structures such as skyrmions and changes in domain wall structures along with their motion under a variety of driving fields. In addition, the influence of DMI on linear and nonlinear spin wave behavior is discussed. Multiferroic materials and new two-dimensional materials with DMI are briefly discussed. Finally, we also present an overview of different DMI materials and their characteristic parameters and potential applications.
Mineral/aqueous interfaces are ubiquitous in geochemistry and are employed for applications spanning catalysis to CO2 sequestration. Small changes in interface morphology have been shown to induce large changes in ion mobility, surface charge, and solvent orientation, which affect the function of these geochemical interfaces. While our ability to probe buried interfaces has been advanced by surface specific and sensitive vibrational spectroscopies, the overlapping response of surface groups and water has made complete structural interpretations of these systems difficult. We believe that by highlighting recent experimental and computational works further progress can be made. This review follows the evolution and current understanding of solvent and surface structure near SiO2, Al2O3, CaF2, and TiO2/aqueous interfaces generated by modern spectroscopic and computational techniques. By comparing information gathered from a range of vibrational spectroscopies and simulations progress can be made in the following fields including and not limited to; geochemistry, industrial/petroleum chemistry, interface science, vibrational spectroscopy, computational chemistry, and materials science.
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.
Molecular switching has established itself as a key functionality of building blocks developed for addressable materials and surfaces over the last two decades. Many challenges in their use and characterisation have been presented by the wide variation in interfaces studied, these ranging from truly single-molecule devices to two-dimensional self-assembled monolayers and thin films that bridge the gap between surface and macroscopically bulk materials (polymers, MOFs, COFs), and further still to other interfaces (solid–liquid, liquid–air, etc.). The low number density of molecules on monolayer-coated interfaces as well as in thin films, for example, presents substantial challenges in the characterisation of the composition of modified interfaces. The switching of molecular structure with external stimuli such as light and electrode potential adds a further layer of complexity in the characterisation of function. Such characterisation “in action” is necessary to correlate macroscopic phenomena with changes in molecular structure. In this review, key classes of molecular switches that have been applied frequently to interfaces will be discussed in the context of the techniques and approaches used for their operando characterisation. In particular, we will address issues surrounding the non-innocence of otherwise information-rich techniques and show how model – non-switching – compounds are often helpful in confirming and understanding the limitations and quirks of specific techniques.
Volcano plots and scaling relations are commonly used to design catalysts and understand catalytic behavior. These plots are a useful tool due to their robust and simple analysis of catalysis; however, catalysts that follow the volcano plot paradigm have an inherent limit to their performance. Scaling and Brønsted-Evans-Polanyi (BEP) relations, which are linear correlations in reaction energetics, force tradeoffs when optimizing catalysts, which leads to this limit on performance. Therefore, materials and design strategies that are not limited by volcano plots and scaling relations are of high interest, and this is the focus of this Report. We first give an overview of volcano plots and scaling relations. Deviations from scaling relations and the volcano plot and their causes are discussed in more detail. Finally, design strategies that do not rely on the volcano plot paradigm are reviewed.
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.
