Search

The formation of a surface metal-metal bond can produce large perturbations in the electronic, chemical, and catalytic properties of a metal. Recent studies indicate that charge transfer is an important component in surface metal-metal bonds that involve dissimilar elements. The larger the charge transfer, the stronger the cohesive energy of the bimetallic bond. On a surface, the formation of a heteronuclear metal-metal bond induces a flow of electron density toward the element with the larger fraction of empty states in its valence band. This behavior is completely contrary to that observed in bulk alloys, indicating that the nature of a heteronuclear metal-metal bond depends strongly on the structural geometry of the bimetallic system., In general, metals are elements characterized by the presence of a large number of valence orbitals that can donate or accept electrons. Isolated metal atoms are unstable, very reactive, and [...]

Author(s): Bogdan Diaconescu [1]; Karsten Pohl (corresponding author) [1]; Luca Vattuone [2]; Letizia Savio [2]; Philip Hofmann [3]; Vyacheslav M. Silkin [4]; Jose M. Pitarke [5]; Eugene V. Chulkov [4]; [...]

Interaction of high-power laser light with materials often causes irreversible damage of the near-surface region. It is shown that copper single-crystal surfaces can be patterned by laser light. Irradiation with green light produced adatoms and vacancies, which self-organized into nanoscale pyramids. This restructuring can be removed by annealing. In contrast to green light, infrared laser irradiation at equivalent absorbed energy density did not produce any structural change. This, for metallic systems, unforeseen spectral difference in laser light action points to a concerted process as the source for structural modification, which involves long-lived primary excitation of localized d-electrons through interband transition together with phonon excitation., The creation and dissipation of electronic excitation are fundamental for a variety of physical and chemical processes. Lasers, as a source of primary excitation, play an expanding role in material [...]

Time-resolved two-photon photoemission in combination with the coherent excitation of several quantum states was used to study the ultrafast electron dynamics of image-potential states on metal surfaces. For a (100) surface of copper, the spectroscopy of quantum beats made previously unresolved high-order states (quantum number n [is greater than or equal to] 4) experimentally accessible. By exciting electrons close to the vacuum level, electron wave packets could be created and detected that described the quasi-classical periodic motion of weakly bound electrons. They traveled more than 200 A away from the surface and oscillated back and forth with a period of 800 femtoseconds., Photoelectron spectroscopy has developed into one of the most versatile and successful tools for surface studies. Particularly attractive features of this technique are the high surface sensitivity associated with the [...]

Many processes at surfaces, from chemical reactions to electron transfer, involve the creation and decay of electronically excited states. At metal surfaces, the density of electrons is high, leading to [...]

A flick of a switch lights up the room, powers up the television, and turns on a host of other gadgets large and small. Now a group of chemists and [...]

The interaction of water with solid surfaces plays a crucial role in catalysis and weathering. The structure and properties of the first water layers on well-defined metal surfaces have been [...]

Atomic Arrangements at Metal Surfaces THE TERMINATION OF A SOLID CREATES A SURFACE. THIS statement is so obvious that many of its consequences are often overlooked. For example, the corrosion [...]

NMR Studies of Simple Molecules on Metal Surfaces ONE OF THE MOST ACTIVE AREAS OF RESEARCH TODAY IS the study of metal surfaces. While a broad range of scientific questions [...]

Until only a few years ago, the idea that a traditional organic or metal-organic substance could exhibit the electrical, optical, and magnetic properties of a metal seemed a complete contradiction [...]

Small metal clusters and related molecules have been the focus of increasing attention in recent years. This interest stems, in part, from the broader interest in catalysis and from the [...]

Electrons are normally not supposed to wander very far from metal surfaces. Yet on page 1480 of this issue, Hofer et al.[1] report an interdisciplinary investigation that catches surface electrons [...]

A recently designed single-crystal surface calorimeter has been deployed to measure the energy difference between two solid surface structures. The clean Pt{100) surface is reconstructed to a stable phase in which the surface layer of platinum atoms has a quasi-hexagonal structure. By comparison of the heats of adsorption of CO and of [C.sub.2][H.sub.4] on this stable Pt{100}-hex phase with those on a metastable Pt{100}-(1x1) surface, the energy difference between the two clean phases was measured as 20 ± 3 and 25 ± 3 kilojoules per mole of surface platinum atoms., Phase transitions in bulk systems can be readily characterized by their enthalpy change by using calorimetric measurements. Although surface phase transitions are well known, their energetics have been inferred indirectly, [...]