Strain-induced incomplete wetting at CuAu(001) surfaces

Abstract

X-ray reflectivity measurements, modeled on atomic scale by a dynamic approach, reveal a smooth Au top layer and subsequent Cu/ Au layering at the (001) surface of CuAu crystals at high temperatures, enforced by a large surface field h 1. Approaching the first order bulk transition the ordered near surface film grows but does not completely wet its disordered bulk phase as predicted. In contrast to earlier wetting experiments on heterogeneous systems which were dominated by surface roughness, we found strong lattice relaxations and incomplete wetting due to strain.

In Situ High-Resolution Transmission Electron Microscopy in the Study of Nanomaterials and Properties

“…The maximum and minimum interphase boundary thicknesses observed were 3.3 and 0.8 nm, respectively, which represent variations in thickness on the order of 100%. The average interphase boundary thickness measured from Figure 7b is comparable to recent studies on straininduced incomplete wetting above the critical temperature T c , where the alloy becomes disordered, at AuCu-I (001) surfaces, 27 and is also similar to previous calculations for a Au-Cu alloy 31 and recent atomistic calculations performed on Al-Li and Al-Ag alloys slightly below T c using embedded atom potentials and Monte Carlo methods. 32,33 In the Albased alloys, which behave similar to Au-Cu alloy, the calculations indicate that the diffuse interphase boundary should extend over 4-6 unit cells (i.e., L 1.6-2.4 nm), and the strain-induced incomplete wetting phenomenon leads to order in AuCu (001) surfaces that extends 5-7 planes (i.e., L~ 1.0-1.4 nm) into the crystal at temperatures much greater than T c .…”

“…The different interphase boundary behaviors observed in Figure 7a are likely due to a combination of several factors occurring at the interphase boundary, namely: (1) the tetragonality of the AuCu-I structure, which leads to an energetically stable (001) plane that tends to keep the ordered side of the interphase boundary parallel to this plane, (2) a lower average diffusivity in the AuCu-I phase as compared to the disordered α phase at 305°C, (3) a related longer atomic jump-distance (0.357 nm) for diffusion perpendicular to the ordered (001) planes in the AuCu-I ordered phase, and (4) the fact that the interphase boundary must move this same distance between Au-rich planes on the ordered side. 27,28 A combination of these effects leads to a significantly higher activation energy for movement of the ordered side of the interphase boundary, causing the experimentally observed interphase boundary behavior in Figure 7a. In fact, if one performs an approximate calculation for the average diffusivities and corresponding jump frequencies of the atoms in the ordered and disordered phases, respectively, using the equation Γ = 6D/λ 2 , where Γ is the jump frequency (s −1 ), D is the diffusivity at 305˚C of 1.7 × 10 −15 m 2 /s for the α phase and 7.0 × 10 −16 m 2 /s for the AuCu-I phase, 28 and λ is the jump distance (3.7 × 10 −10 m in AuCu-I), one finds that the jump frequency in the disordered phase is approximately 3 × 10 5 s −1 , as compared to 3 × 10 4 s −1 in the ordered phase, consistent with the considerations mentioned above.…”

Surface premelting and melting of colloidal glasses

“…The hyperbolic tangent profile commonly exists on vapor-liquid interfaces ( 47 ), liquid-solid interfaces ( 48 , 49 ), vapor-solid interfaces ( 50 ), and solid-solid interfaces ( 51 ). In addition, error function (erf), the prediction of Landau theory for crystal premelting ( 45 ), and the Fisk-Widom (FW) function for the interface between fluid phases can fit normalρfalse~false(yfalse).1emand.1emsfalse~2false(yfalse) equally well (Fig.…”

Surface segregation at the binary alloy CuAu (100) studied by low-energy ion scattering

“…Most studies refer to the Cu 3 Au phase [11], much less to CuAu 3 [12]. For CuAu only few experimental results are published in the literature [13][14][15]. Recent theoretical studies deal with density functional calculations of corresponding surface alloys [16] and with the structure of CuAu bimtetallic clusters [17].…”