Papers by Keyword: Surface Segregation

Abstract: The effect of B, Si, P, Cr, Ni, Zr and Mg on cohesive properties of Al and the special grain boundary (GB) Σ5 (210)[100], as well as their segregation behavior at the GB and the (210) surface are studied by first principles method. The analysis of these parameters allows us to single out Ni as the best and phosphorus as the worst interatomic bond strengthening alloying elements.

Abstract: Laboratory metal dusting test of several Ni binary alloys containing the representative element was conducted in a simulated syngas atmosphere at 650°C for 100h. The Ni alloys containing element belonging to Group 14 and 15 in the periodic series exhibited excellent metal dusting resistance, while those containing Group 13 did not. This behavior was able to be reasonably interpreted from the Blyholder mechanism and the concept of Pauling’s electronegativity.

Abstract: Methods for the analysis of the oxide-silicon interface were compared for their ability to reveal metal segregation at the interface and organic contamination. The impact of these contaminations on surface recombination velocity measurements, on capacitance vs. voltage, conductance vs. voltage and capacitance vs. time measurements and on MOS-DLTS spectra was studied. Niobium-contaminated wafers were used as an example of metal surface segregation, because it was previously shown that niobium is prone to surface segregation. Interface state density measurements obtained by the conductance method showed a limited impact of niobium implantation. Vice versa significant effects were found in MOS-DLTS spectra. For what concerns organic contamination, MOS-DLTS showed the most significant effects from the point-of-view of the intrinsic properties of the silicon oxide - silicon interface, and GOI tests demonstrate a clear impact of the organic contamination on MOS capacitors oxide breakdown events.

Abstract: Surface segregation in transition metals can be analysed within a generalised Ising model,derived from Tight-Binding electronic structure calculations, which identifies three driving forces:the difference in surface energy and atomic volume between the two components and their tendencyto order or phase separate in the bulk. Using this ”three effects” rule, we present here general mapswhich predict the tendency of the solute metal element to segregate (or not) at the surface of a metalmatrix, for the 702 solute/matrix systems that can be formed with transition metal elements. Ourpredictions compare fairly well to the existing ab initio calculations and experimental data availableon these systems. The few exceptions, which mainly concern given matrix elements are discussed indetails.

Abstract: By molecular dynamics simulation it is shown that interdiffusion in the initial f.c.c. Ag-core ( 28 at. %) – Ni-shell ( 72 at. %) and Ni-core ( 34 at. %) – Pd-shell ( 66 at. %) nanoparticles can lead to surface–sandwich segregation. It is observed that there is a separation of the initial Ag-Ni core-shell structure into Ag-core – Ni-intermediate shell – Ag-disperse surface monolayer. The initial crystal Ni-Pd core-shell structure transforms to the core of a non-crystalline Pd-rich solid solution with quite strongly developed icosahedral short-range order, which is covered by a surface–sandwich shell, where Ni atoms are located in the centres of interpenetrating icosahedra of a subsurface Kagomé net layer while the Pd atoms occupy the vertices of the icosahedra and cover this Ni layer from inside and outside. We demonstrate that under certain conditions a surface–sandwich segregation phenomenon at the nanoscale can be observed in systems with completely different phase diagrams in the bulk states: in systems displaying the extremely low mutual solubility as in the Ag-Ni system, or in systems exhibiting a continuous mutual solid solubility like the Pd-Ni system.

Abstract: Long term service of the materials under stresses and at attacking environments causes material damages, leading to fractures. Among a lot of the material damages, creep cavity and fatigue crack are principal targets to be self healed autonomously during actual service of materials. Since the creep cavity and the fatigue crack are generally too fine to be detected during actual service and difficult to be repaired at the service sites. Recently self healing of creep cavity and fatigue crack has been developed. In the developed methods, segregation and precipitation of solute atoms were applied to self healing of the damages. The self healing methods are comparatively simple and low cost, which may make it easy to be applied to many materials.

Abstract: Long–time scale molecular dynamics simulation in combination with the embedded atom method is used to investigate the effect of surface segregation phenomena at 1000 K on the structure of Pd alloy nanoparticles (of diameter of ∼ 4.5 nm) containing ∼ 30 at. % Ni. A core–shell f.c.c. structure was chosen as the initial state wherein a core of Ni atoms is surrounded by shell of Pd atoms. It is found that such nanoparticles form a surface–sandwich structure by interdiffusion. In this structure, the Ni atoms, which mostly accumulate in a layer just below the surface and at the same time are located in the centres of interpenetrating icosahedra to generate a subsurface shell as a Kagomé net. Meanwhile, the Pd atoms occupy the vertices of the icosahedra and cover this Ni layer from inside and outside as well as being located in the core of the nanoparticle forming (according to alloy composition) a Pd–rich solid solution with the remaining Ni atoms. The total atomic fraction involved in building up the shell of the nanoparticle in the form of the Ni Kagomé net layer covered on both side by Pd atoms can be estimated at ∼ 70 %.

Abstract: Grazing-Incidence Small Angle X-ray Scattering (GISAXS) and X-Ray Photon Correlation Spectroscopy (XPCS) studies of island growth in two different systems are presented: 5 ML of iron on MgO(001) and 10 ML of iron on Au(001). Due to a missing conducting surface Fe/MgO thinner than approximately 20 ML could not be studied previously by common methods like STM. Fe/Au(001) is interesting as atoms of gold diffuse easily through iron layers and form precipitates. The coarsening dynamics of these precipitates is investigated by XPCS in GISAXS geometry. Their growth depends on the crystallographic directions of the substrate and correlates with the morphology measured by STM microscopy. Measurements were performed at the ESRF in Grenoble.

Abstract: The wetting phenomena and adhesion between Ag-Cu-Zr molten alloys (where Zr is an active brazing element) and ZrB2-ceramic substrate have been investigated from theoretical and experimental point of view. The wetting phenomena of molten alloy/ceramic substrate depend on the bonding characteristics of liquid alloys and ceramics as well as the magnitude of interactive forces at the interface. Accordingly, the first step of this investigation is to determine the surface properties of Ag-Cu, Ag-Zr and Cu-Zr liquid alloys. The energetics of the bulk and the surface of liquid alloys have been analysed in the framework of statistical mechanical theory in conjunction with Quasi-Lattice Theory (QLT), through the study of the concentration dependence of various properties such as surface tension, surface composition, concentration fluctuations in the long wavelength limit and Warren-Cowley chemical short-range order parameter. Combining the Young and the Dupré equations, the obtained values of surface tension together with contact angle data have been used to calculate the work of adhesion.