Alloys single-crystal surface

Potter HC, Blakeley JM (1975) LEED, Auger spectroscopy, and contact potential studies of copper-gold alloy single crystal surfaces. J Vac Sci Technol 12 635-642... 

Bimetallic alloy surfaces are also of great importance. Most metallic materials used commercially, and in particular metal-based, heterogenous catalysts, have multicomponent alloy phases. Despite their obvious importance, alloy single-crystal surfaces have not been studied so extensively in the past. A first step in understanding the chemistry of these surfaces is a thorough characterization of the structure of such surfaces. These attempts are part of efforts to overcome the material gap between commercial catalysts and surface-science studies. 

X-ray Photoelectron Spectroscopy and Scanning Tunneling Microscopy Studies of Thin Anodic Oxide Overlayers on Metal and Alloy Single-Crystal Surfaces... 

AR-XPS has been extensively used to investigate the chemical composition, the chemical states and the thickness of thin anodic oxide overlayers (passive films) formed on well-defined metal and alloy single crystal surfaces. More recently direct imaging of the surface structure by STM with atomic resolution provided new data on the crystallinity, the epitaxy and the nature of the structural defects existing in the thin oxide layers. Such data are useful... 

Adsorption-induced reconstruction, surface metal atom, 245 Adsorption isotherms, development, 4/,5 Alcohols, role in photooxidation reaction of water on n-Ti02 electrode, 297-308 Alloy single-crystal surface, thin anodic oxide overlayers, 236-244 Alloy surfaces, chemical reconstruction, 246-247... 

An alternative type of tip-induced nanostructuring has recently been proposed. In this method, a single-crystal surface covered by an underpotential-deposited mono-layer is scanned at a close tip-substrate distance in a certain surface area. This appears to lead to the incorporation of UPD atoms into the substrate lattice, yielding a localized alloy. This procedure works for Cu clusters on Pt(l 11), Pt(lOO), Au(l 11), and for some other systems, but a model for this type of nanostructuring has not been available until now. (Xiao et al., 2003). 

In a series of pubhcations, the results of anodic dissolution and passivation of well-defined single-crystal surfaces of Ni (and other metals) and its alloys were presented by Marcus et al. [19-24]. Their approach aimed at a better understanding... 

Is it known that the rate of hydrogenolysis reactions are extremely sensitive to effects of alloying, surface contamination, poisoning, etc. Consequently, in all cases where supported metals are used there must be concern as to whether apparent particle size effects are due to structure sensitivity or to some minor contamination effect. In the few cases where clean single crystal surfaces have been used there is evidence of a structure effect.338 However, the maximum change in activity between different crystal faces seems to be about a factor of 10. For Ni single crystals the (100) surface is more active than the (111) surface. A similar conclusion has been reached for oriented Ni powder samples.339... 

Noble metal deposition on single crystal surfaces, i.e., underpotential deposition (UPD), is one method to prodnce bimetallic snrfaces and alloys, and UPD sometimes remarkably... 

Electrocatalysis is manifested when it is found that the electrochemical rate constant, for an electrode process, standardized with respect to some reference potential (often the thermodynamic reversible potential for the same process) depends on the chemical nature of the electrode metal, the physical state of the electrode surface, the crystal orientation of single-crystal surfaces, or, for example, alloying effects. Also, the reaction mechanism and selectivity 4) may be found to be dependent on the above factors in special cases, for a given reactant, even the reaction pathway [4), for instance, in electrochemical reduction of ketones or alkyl halides, or electrochemical oxidation of aliphatic acids (the Kolbe and Hofer-Moest reactions), may depend on those factors. 

Summary of Pb surface alloy and overlayer structures on single-crystal surfaces of Cu... 

The aim of this chapter is to review our understanding of the fundamental processes that yield improved electrocatalytic properties of bimetallic systems. Three classes of bimetallic systems will be discussed bulk alloys, surface alloys, and overlayer(s) of one metal deposited on the surface of another. First, we describe PtjM (M=Ni, Co, Fe, Cr, V, and Ti) bulk alloys, where a detailed and rather complete analysis of surface structure and composition has been determined by ex situ and in situ surface-sensitive probes. Central to our approach to establish chemisorption and electrocatalytic trends on well-characterized surfaces are concepts of surface segregation, relaxation, and reconstruction of near-surface atoms. For the discussion on surface alloys, the emphasis is on Pd-Au, a system that highlights the importance of surface segregation in controlling surface composition and surface activity. For exploring adsorption and catalytic properties of submonolayer and overlayer structures of one metal on the surface of another, we summarize the results for Pd thin metal films deposited on Pt single-crystal surfaces. For all three systems, we discuss electrocatalytic reactions related to the development of materials... 

Studies of single-crystal surfaces under UHV conditions have allowed us to quantify fundamental interactions at surfaces, and the majority of surface-science studies have been conducted in this manner. Utilization of XPD and LEIS techniques require the studies to be conducted under high vacuum, and studies of clean surfaces or precisely controlled adsorbate layers require UHV conditions. Here we discuss a few examples of the use of these two techniques in studies of single-crystal surfaces, illustrating their power and limitations. The surfaces discussed are metal surfaces that contain controlled amounts of adsorbates, ultrathin metal films, two-component metal alloy surfaces, and oxide surfaces. 

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