LEED crystallographic studies for the chemisorption of oxygen on the (100) surface of copper

Abstract

. Can. J. Chem. 66, 2054Chem. 66, (1988. Intensity analyses with low-energy electron diffraction (LEED) are reported for surface structures obtained by adsorbing submonolayer amounts of oxygen on the (100) surface of copper. It is found for chemisorption on the four-coordinate hollow sites that the correspondence between experimental and calculated intensity-versus-energy curves, for 10 diffracted beams, is slightly better for coplanar adsorption than for adsorption about 0.75 A above the surface (the latter model is essentially as proposed previously by both SEXAFS and photoelectron diffraction). Nevertheless, in neither of these contrasting situations is the agreement sufficient to conclude that the structural analysis is complete. Evidence is presented that nearly coplanar chemisorption, in combination with a missing row model, can accommodate a number of structural features for this system, including the existence of the ( 2 d 2 x d2)45"-0 phase, beam splittings resulting from antiphase domain boundaries, and the structural analogy noted in other studies between the ( 2 d 2 x d2)45"-0 phase and the stepped nature of the (410) copper surface which can form by faceting in oxygen. Considerations of 0-Cu surface bond lengths, guided by those in bulk Cu20, suggest that additional lateral relaxations are likely in the topmost copper layer. This study provides no support for the 0 chemisorption occumng in tetrahedral-type sites. On a effectut les analyses d'intensitt de diffractions ilectronique de basse Cnergie (DEBE) pour des structures de surface obtenues par l'adsorption de quantitts ne correspondant pas a des monocouches d'oxygtne sur la surface (100) du cuivre. Pour la chemisorption sur les sites vides de coordination-4, examinte a l'aide de 10 faisceaux de diffraction, on a trouvt que la correspondance entre les courbes expirimentales et les courbes calcultes de l'intensitt vs 1'Cnergie est ltgtrement meilleure pour I'adsorption coplanaire que pour l'adsorption environ 0,75 A au-dessus de la surface (ce dernier modtle est essentiellement celui qui avait it6 proposC anttrieurement tant par SEXAFS que par diffraction Clectronique). Toutefois, ni I'une ni l'autre de ces situations pourtant trts difftrentes ne conduit une concordance suffisante pour conclure que l'analyse de structure est complete. On prtsente des donntes suggtrant que de la chemisorption coplanaire, combinCe avec un modkle impliquant une couche manquante peut accommoder un certain nombre de caractCristiques de structure de ce systkme, y compris l'existence de la phase ( 2 d 2 x d2)45"-0 ainsi que la nature en escalier de la surface (410) du cuivre qui peut se former lorsqu'elle est facettie dans de l'oxygtne. Des considtrations concernant les longueurs des liaisons Cu-0 de surface, basCes sur celles que l'on retrouve dans du Cu20, suggtrent que les relaxations lattrales additionnelles sont probables dans la couche supCrieure du cuivre. Cette ttude ne fournit accun support pour l'hypothtse selon laquelle la chemisorption des 0 se fait sur des ...

STM and LEED: Atomic Valences and Bond Geometry

“…Both are the numerical solutions to the same system. An inverse operation by rotating the O-Cu-O chain 180°around its axis and followed by offsetting the O-Cu-O chain in the vertical direction switches between the two cases [8][9][10]. The exchange in the vertical position of O and Cu (0.59/0.16 = 3.68) seems to approach the ratio of atomic numbers Z Cu /Z O = 58/16 = 3.63.…”

“…For each pair of values of (D 12 , D O ) that fit the diffraction data, there must be a counterpart that also fit. For example, the value at point [8] couples with the value at point [10]. Both are the numerical solutions to the same system.…”

“…[46]. The data and references are given in 3.2 O-Cu(001), (110), (111)Therefore, all the solutions along the line from [8] to [10] can find a counterpart that could fit the diffraction data. The vertical change of positions for both the partners should satisfy the numerical relation between D 0 and D 12 .…”

“…The Ni(100)-4H2(1 9 1)R45°-16 N -3 STM image exhibits two orientations of the depressions. With slight deviation, one is along the [10] direction and the other closes to the [01] direction. This provides the opportunity for one to identify the atomic valences of N at the surface.…”

The structure of oxygen-induced reconstruction on Cu{100}-c(2×2)–Pt surface alloy: the Pt/Cu{100}-(2×2)–O

“…The existence of such reconstructions on fcc{1 0 0} surfaces, where reconstruction of this type lowers the surface symmetry (this symmetry lowering does not happen in the fcc{1 1 0} case), sounds less presumable. One example of adsorbateinduced reconstruction on fcc{1 0 0} is the missingrow Cu{1 0 0}-(2 p 2Â p 2)R45°-2O reconstruction, first proposed by Zeng and Mitchell [1]. The Cu{1 0 0}/O system has received much attention, especially the Cu{1 0 0}-c(2 · 2)-O phase [2], which is now known not to exist or at least not to be very stable.…”