Surface Science Reports最新文献

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, on Ge(001)-Au and of 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.

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