Surface alloys multilayer

Single-layer surface alloys Multilayer surface alloys... 

Further annealing induces additional Ag overlayer enrichment with Pd atoms, causing a substantial intensity increase of the Pd resonant state, while the intensity at the Fermi level remained very small. This is a clear indication of the localized character of the Pd 4d state. The annealing of the Ag multilayer produces a surface alloy with a composition very close to Ago.sPdo.s which has a DOS at the Fermi level substantially smaller than the pure palladium. The annealing at higher temperature produces a Pd(l 10) surface with very small but very persistent amount of silver, which is in the form of three-dimensional clusters, located most probably below the first Pd(l 1 0) layer. 

The influence of Pt modihcations on the electrochemical and electrocatalytic properties of Ru(OOOl) electrodes has been investigated on structurally well-defined bimetallic PtRu surfaces. Two types of brmetalhc surfaces were considered Ru(OOOl) electrodes covered by monolayer Pt islands and monolayer PtRu/Ru(0001) surface alloys with a highly dispersed and almost random distribution of the respective surface atoms, with different Pt surface contents for both types of structures. The morphology of these surfaces differs significantly from that of brmetaUic PtRu surfaces prepared by electrochemical deposition of Pt on Ru(0001), where Pt predominantly exists in small multilayer islands. The electrochemical and electrocatal5d ic measurements, base CVs, and CO bulk oxidation under continuous electrolyte flow, led to the following conclusions ... 

The term surface alloy is somewhat generic and may refer to a variety of different systems. Here, we apply it to those systems where ultra-thin metal layers (i.e. a few atomic layers thick) are deposited on a bulk metal surface and where the system is subsequently annealed in vacuum in order to obtain alloying in a surface region a few atoms thick. In these conditions it is possible to obtain single atomic layer binary phases, or multilayer surface alloy phases (also termed epitaxial alloys (for a general discussion of these surface alloys, see [5]. Relatively to the subject of the present paper, two Pt-Sn systems have been studied Sn-Pt(l 11) and Sn-Pt(lOO). The behavior and the structural properties of these systems will be discussed in detail in the following. 

The formation of multilayer surface alloys has also been investigated in the Sn-Pt(l 11) system, where Galeotti et al. [37] reported the formation of ordered, epitaxial alloyed Pt-Sn phases. The deposition of amounts of Sn up to 5 mono-layers (ML) at room temperature led to disordered or anyway non-epitaxial tin films. Annealing the deposited films led to interdiffusion and to the formation of various alloy phases (Fig. 17). Alloying was detectable in XPS from the... 

The Al(l 11)—(2 X 2)—Na phase, as described in Sec. 3.1, is a complicated multilayer surface alloy. We regard the successful prediction [58, 86] of the structure of this phase by DFT calculations, as evidenced by the detailed, quantitative agreement with experimental results shown in Table 6, as marking a major advance in the application of DFT theory to surfaces. 

Rb, or Cs, is only possible in part. They can be described in terms of adsorption on a substrate whose first layer contains some fraction of a monolayer of vacancies, just as in the case of the single-layer surface alloys. These vacancies are occupied with a first layer of Na. A second layer of Na (or K, Rb, or Cs in the case of the ternary alloys) is then adsorbed on the A1 vacancy layer. However, in the case of the Al(lll)—(2 x 2) multilayer surface alloys, this second layer of Na is adsorbed in fee sites on the A1 vacancy layer, and the A1 atoms ejected from the vacancy layer are readsorbed in hep sites on the vacancy layer. By contrast, in the Al(l 10)—(4 x 1)—3Na multilayer surface alloy, the second Na layer is adsorbed in sites of low symmetry on the vacancy layer, and the A1 atoms ejected from the vacancy layer do not form a part of the structure, but presumably diffuse to surface steps where they are readsorbed. 

The multilayer surface alloy formed by Li adsorption on Al(lOO) is exceptional in that substitution of 1/2 ML A1 by Li occurs in both the first and third A1 layers. An unexpected feature of this structure is that the registry of Li atoms in the first and third layers is such that they are staggered along the surface normal direction, as in the Al3Ti-type bulk alloy structure, rather than collinear, as in the expected CusAu-type bulk alloy structure known to be adopted by the metastable, AlsLi bulk alloy. DPT calculations for this system lead to the novel prediction that the AlaLi bulk alloy has a stacking fault at the surface, such that it can be described as an AlaTi-type surface on a CuaAu-type bulk. 

An ordered multilayer alloy is a surface alloy containing two (or more) ordered bimetallic layers within the selvedge. Two well characterised examples of ordered multilayer alloy formation have been reported to date. 

The case of Sn-Pt(lll) helps to understand the phenomena that occur in the interplay of the single-layer and the multilayer alloy formation. Other known cases are Au-Cu(lOO) [52] and Al-Ni(lOO) [54]. In other cases, such as Co-Pt(lll) [55], only the multilayer surface alloys have taken known to form. 

Materials science (microelectronics analysis, surface layers, multilayers, PIXE channeling of dopants in crystals, depth profiling, binary alloys, impurities deposited in nuclear fusion devices, magnetic relaxation in nanocrystalline iron, insulating materials, radiation-induced segregation, superconductors, catalysts, and diffusion studies). 

Choi J, Konno T, Matsuno R et al (2008) Surface immobilization of biocompatible phospholipid polymer multilayered hydrogel on titanium alloy. Colloids Surf B Biointerfaces 67 216-223... 

The analysis of several pure metals and binary alloys yields generally at least a duplex and in some cases a multilayer structure of the passive film, as depicted schematically in Fig. 19. These systems have been examined with surface analytical methods, mainly XPS, but also ISS in some cases. The systematic variation of the electrochemical preparation parameters gives insight to the related changes of layer composition and layer development, and support a reliable interpretation of the results. Usually the lower valent species are found in the inner part and the higher valent species in the outer part of the passive layer. It is a consequence of the applied potential which of the species is dominating. Higher valent species are formed at sufficiently positive potentials only and may suppress the contribution of the lower... 

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