Efficient determiniation of multilayer relaxation in the Pt(210) stepped and densely kinked surface

Abstract

The multilayer relaxation of the Ft(210) stepped and kinked surface is analyzed by low-energyelectron diffraction. This is the first appUcation of the new real-space multiple-scattering theory of LEED, designed specifically for such open surfaces where conventional theories fail. Combined with an automated tensor LEED method, it efficiently detects nonalternating atomic relaxations which are oriented primarily perpendicular to the surface. These relaxations are in qualitative agreement with new embedded-atom-method results.PACS numbers: 61.14. Hg, 68.35.Bs, 82.65.Jv Few structures of stepped surfaces have been determined on the sub-A scale, despite their great importance in fields as diverse as catalysis, crystal grow^th, crack propagation, and tribology [ll. In particular, multilayer relaxations and adsorption geometries are expected to be crucial in the understanding of many phenomena involving stepped surfaces.The step structures which have so far been analyzed mainly concern relatively low-Miller-index metal surfaces, in which the terraces between steps are very narrow [2]. A rare exception is Cu{410), studied by low-energy ion scattering [3] [the fee (410) surface dififers from (210) only in that the (100)-oriented terraces are 3 times wider]. While this Cu(410) study does not provide much reliable detail, relaxations of step edge atoms are proposed on the scale of 0.18 A, such that the surface is made smoother. It is now generally accepted that relaxations of the atomic positions occur particularly at steps, including multilayer relaxations deeper into the surface.The primary technique used to analyze steps has been low-energy-electron diffraction (LEED) [4]. Progress with LEED has, however, been hampered by diflftculties in dealing with small interlayer spacings due to the stepped nature of the surface. Small spacings result from wide terraces and from kinks in the steps (kinks are nonalignments of step atoms, giving jagged step edges).The Al(210) surface structure, very similar to that of Pt(210), was analyzed some years ago with LEED by Adams et al. [5] using the relatively robust layerdoubling method [4]. This was, however, only possible because of the unusually weak multiple scattering of electrons in aluminum, which permitted layer doubling to converge better than in almost any other metal. By contrast, platinum causes particularly strong multiple scattering and thus serves as a severe test case for a LEED theory. Several approaches [6-10] have been proposed in order to overcome these difliiculties in LEED theory; the most recent ones [9,10] are based on the new real-space multiple-scattering theory (RSMST) [10]. Using RSMST, LEED intensities can be calculated under conditions where conventional methods fail. For instance, in the case of Ft(210), the layer-doubling method failed to converge suflficiently well for us to determine the surface structure. The structure could, however, be solved by applying the new method, coupled with an automated tensor LEED search [11,12] for the many unknown structu...

Adsorbate‐induced reconstructions and nanostructures on high‐index copper surfaces

“…Both MEAM and ECT predict contractions in the first two interlayers and expansion in the third interlayer for Cu(210). The results are also consistent with experiment and theory for Al(210) 24 and Pt(210), 25 which all point to significant inward surface relaxation resulting in smoothening of the corrugated (210) surface for fcc metals. The atoms on the rough surface change their bulk equilibrium positions, thereby minimizing the surface free energy, maximizing coordination number within the surface layer and thus bringing about a smoother surface.…”

Hydrogen adsorption on an open metal surface:H2/Pd(210)

“…This becomes evident when the experimental Pd͑210͒ results are compared to the interlayer relaxations measured for Pt͑210͒. 24 One would expect similar relaxations for Pd and Pt since they have the same number of valence electrons and an almost identical lattice constant. Still the measured Pd͑210͒ results are considerably smaller than the Pt͑210͒ results.…”

Bridging the structure gap: Chemistry of nanostructured surfaces at well-defined defects

“…Algorithms were developed eventually to handle the problem and determine the strong interlayer relaxation taking place. The latter is oriented primarily perpendicular to the surface, as found for Pt (210) [65] and more recently for Cu (210) [66]. The measured value compares well with those determined by computing the energetics of the system by Density Functional Theory (DFT).…”