TY  - JOUR
AU  - Bauer, O.
AU  - Schmitz, C. H.
AU  - Ikonomov, J.
AU  - Willenbockel, M.
AU  - Soubatch, S.
AU  - Tautz, F. S.
AU  - Sokolowski, M.
TI  - Au enrichment and vertical relaxation of the Cu$_{3}$ Au ( 111 ) surface studied by normal-incidence x-ray standing waves
JO  - Physical review / B
VL  - 93
IS  - 23
SN  - 2469-9950
CY  - Woodbury, NY
PB  - Inst.
M1  - FZJ-2017-00328
SP  - 235429
PY  - 2016
AB  - We have investigated the Cu3Au(111) surface, prepared under ultrahigh vacuum conditions by sputtering and annealing, by low energy electron diffraction (LEED), scanning tunneling microscopy (STM), x-ray photoelectron spectroscopy, and normal incidence x-ray standing waves (NIXSW). We find the surface to be depleted with Cu and enriched with Au at the same time, yielding a nominal Cu:Au ratio of 0.61:0.39 in the topmost layer. The STM images reveal that the first layer is nearly closely filled with atoms and contains a small amount of vacancies with an area concentration of about 5%. Together with the Au enrichment, these cause local short-range disorder of the Au p(2×2) reconstruction. From this data, the average stoichiometry of the p(2×2) surface unit cell is estimated at Cu2.22Au1.44□0.20 (instead of Cu3.00Au1.00□0.00 of the ideal surface; □ denotes an atomic vacancy site). From NIXSW we find a significant outward relaxation of both the Cu and Au atoms of the topmost layer by 0.28 Å and 0.33 Å, which corresponds to 13% and 15% of the (111) bulk layer spacing of Cu3Au. We suggest that this originates from a widening of the first/second layer spacing, by 6.8% and 8.8% for the Cu and Au atoms, respectively, plus an additional rigid increase in the second/third layer spacing by 6.2%. We explain this by steric repulsions between Au atoms of the topmost layer, replacing smaller Cu atoms, and Au atoms in the second layer in combination with disorder. Finally, a lateral reconstruction, similar to that on the Au(111) surface, but with a much larger periodicity of 290 Å, is identified from LEED.
LB  - PUB:(DE-HGF)16
UR  - <Go to ISI:>//WOS:000378050600006
DO  - DOI:10.1103/PhysRevB.93.235429
UR  - https://juser.fz-juelich.de/record/826068
ER  -