Alloy films bulk structure

The literature on the oxidation of nickel-copper alloys is not extensive and emphasis tends to be placed on the copper-rich materials. The nickel-rich alloys oxidise according to a parabolic law and at a rate similar to that for nickel Corronil (Ni-30Cu) exhibited a parabolic rate behaviour below 850°C but a more complex behaviour involving two parabolic stages above 900°C. Electron diffraction examination of the oxide films formed on a range of nickel-copper alloys showed the structures of the films to be the same as for the bulk oxides of the component metals and on all the alloys examined only copper oxide was formed below 500°C and only nickel oxide above 700°C . 

Table VIII records the Arrhenius parameters and the activity of four alloy films and the two pure metals the results are insufficient to provide a neat correlation with bulk electronic structure such as observed for CO oxidation over Pd-Au wires 129), but the familiar pattern is discernible. The rate of CO oxidation is approximately constant for Ag and Ag-rich films but decreases by a factor of 104 over pure Pd and a Pd-rich film.

Fig. 1 Side view of slab models of various bimetallic structures often used in computational studies. In each case, the bottom layers of the material are defined using the structure of a specified bulk material. The number of surface and bulk layers varies in different studies, (a) In the sandwich structure the surface is one component, often the same component as the bulk material and the second layer is another component. This structure is often used to determine ligand effects, (b) The pseudomorphic monolayer structure combines strain and ligand effects in one structure by placing a second component on top of a bulk material, (c) The near surface alloy combines strain, ligand and ensemble effects in one structure by considering an alloy film defined by just a few atomic layers on top of an ordered bulk material.

In electrochemical multicomponent systems", i.e., using electrolytes containing different Me , mixed UPD and OPD deposition of different metals can be used for a sequential deposition of different Me, monolayers forming sandwich-structured ultrathin metal films, S/Mei/Me2/...Me . The formation of 2D Me-S and Me,-Mey surface alloys and 3D Me-S bulk alloys can be utilized to form ultrathin surface alloy films such as S/Me-S, S/Me,-Mey, and S/Me, -S/Me/-Mey. Ultrathin sandwich-structured films and surface alloys will be denoted as heterostructures. 

The coating chamber was equipped with a set of independently controlled stainless steel boats and a shutter system to enable the fabrication of multilayer structures. Pure selenium pellets were loaded into one boat and As Sei alloys into another. The two sources were evaporated sequentially (without breaking the vacuum) at boat temperatures of about 450 K. Typical coating rates were l j,m/min. After evaporation, they were allowed to anneal over several weeks in the dark at room temperature. During this period, due to structural bulk relaxation, most physical properties of the photoconductor film become stabilized. The compositions of the deposited films were determined by electron probe microanalysis, and the compositions quoted (0 < X < 0.20) are accurate to within 0.5 at.%. By shuttering the beginning and the end of the evaporation, a uniform arsenic composition across the film thickness can be obtained. In all experiments, a transparent gold electrode ( 300 jm thick) was used as the top contact. 

There are four types of fundamental subjects involved in the process represented by Eq. (1.1) (1) metal-solution interface as the locus of the deposition process, (2) kinetics and mechanism of the deposition process, (3) nucleation and growth processes of the metal lattice (M a[tice), and (4) structure and properties of the deposits. The material in this book is arranged according to these four fundamental issues. We start by considering the basic components of an electrochemical cell for deposition in the first three chapters. Chapter 2 treats water and ionic solutions Chapter 3, metal and metal surfaces and Chapter 4, the metal-solution interface. In Chapter 5 we discuss the potential difference across an interface. Chapter 6 contains presentation of the kinetics and mechanisms of electrodeposition. Nucleation and growth of thin films and formation of the bulk phase are treated in Chapter 7. Electroless deposition and deposition by displacement are the subject of Chapters 8 and 9, respectively. Chapter 10 contains discussion on the effects of additives in the deposition and nucleation and growth processes. Simultaneous deposition of two or more metals, alloy deposition, is discussed in Chapter 11. The manner in which... 

Clusters and alloys are molecular species that may show different catalytic activity, selectivity and stability than bulk metals and alloys. Small metal clusters and alloy clusters have been studied reeendy for potential use as catalysts, ceramic precursors, and as thin films. Several fundamental questions regarding such clusters are apparent. How many atoms are needed before metallic properties are observed How are steric and electronic properties related to the number, type and structure of such clusters Do mixed metal clusters behave like bulk alloy phases ... 

C.2.1. PdlAl20s Preparation and Structural Properties. To prepare a thin well-ordered AI2O3 model support, a NiAl(l 10) alloy single crystal was oxidized in 10 mbar of O2 at 523 K (290). The structure of the alumina film was examined by a variety of techniques (see Reference (101) and references cited therein), and recently it was even possible to image its atomic structure by STM at 4K (Fig. 19) (215). The alumina film was only approximately 0.5 nm thick and hydroxyl-free, and one should also keep in mind that its exact structure may deviate from those of bulk aluminas (101,215,292,293). Its properties are certainly influenced by the observed line defects (antiphase domain boundaries and reflection domain boundaries). 

In presence of significant Me-S lattice misfit, the epitaxy of isolated 3D Me crystallites or compact 3D Me films is strongly determined by the structure of internally strained 2D Meads overlayer and/or 2D Me-S surface alloy formed in the UPD range at high F or low AEi. The misfit between the lattice parameters of the 2D Meads phase and/or 2D Me-S surface alloy phase and the 3D Me bulk phase is mainly removed by misfit dislocations. The initial strain disappears after depositing a certain thickness of the 3D Me bulk phase. Usually, a thickness of n Me monolayers where 2 < < 20 is necessary to adjust the 3D Me bulk lattice parameters [4.58, 4.59]. If an incommensurate structure of a 2D Meads overlayer is formed in the UPD range, this structure will also be reflected epitaxially in 3D Me crystallites and ultrathin 3D Me films. 

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... 

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