LEED investigation of the alloying/de-alloying transition in the Cu{100}/Bi system

Abstract

The surface structures formed by deposition of 0.25 ML and 0.50 ML Bi on Cu{100} at room temperature have been determined quantitatively using the symmetrised automated tensor low energy electron diffraction (SATLEED). At y Bi ¼ 0.25 ML, Bi forms a semi-ordered p(2 Â 2) surface alloy with the Bi atoms located at a height of 0.56 AE 0.06 A ˚with respect to centre of gravity of the buckled outermost Cu layer (buckling amplitude ¼ 0.11 A ˚). The interlayer spacings in the first three substrate layers are found to be:The first and the third Cu layers are found to be buckled by 0.11 AE 0.06 A ˚and 0.05 AE 0.06 A ˚, respectively. At higher Bi coverage, de-alloying occurs culminating in formation of a well ordered c(2 Â 2) overlayer at y Bi ¼ 0.50 ML. Bi atoms occupy the four-fold hollow sites with a vertical Bi-Cu interlayer separation of d Bi-Cu ¼ 2.17 AE 0.06 A ˚above a slightly perturbed substrate. The interlayer spacing in the first four substrate layers are found to be:A small buckling of 0.02 AE 0.02 A ˚is detected in the second Cu layer in which Cu atoms below Bi atoms are rippled outwards. The structures obtained by LEED are compared to those evaluated recently for the same system by surface X-ray diffraction.

Investigation of c(2×2) Phase of Pb and Bi Coadsorption on Cu(001) by Low Energy Electron Diffraction

“…We then determined the c(2×2) phases quantitatively. Before the determination of c(2×2) coadsorption, we reconfirm the c(2×2) phases of individual adsorption of Pb and Bi on Cu(001) more accurately than in previous reports [13][14][15] . Our results also show that both types of metal form an overlayer structure.…”

Equivalent ordered-mixed-surface-structures of p(4×4)-p4gm formed on Cu(001) by coadsorptions of Bi+Mg and Sb+Mg

“…Coverage is defined as a ratio of the number density of adatoms to that of Cu atoms in the topmost ideal Cu(0 0 1) layer. Mg atoms are located at substitutional sites [12], while Bi atoms are at the surface hollow sites on Cu(0 0 1) [8,13]. For Sb, a p(2 · 2) structure is formed at a coverage of 0.25 at RT [14].…”

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

“…For the clean Cu{1 0 0} surface, the total R-factor measured in our lab was 0.15 [8] while for the underlayer structure of the Cu{1 0 0}-c(2 · 2)-Pt it was 0.20 [7]. Hence, a slightly higher value is not unexpected for the more complicated structure inves- tigated in this study.…”

“…The sample was cleaned in situ by repeated cycles of argon ion bombardment (4 kV) and annealing to 700 K for 5 min periods. The clean Cu{1 0 0} sample showed no impurities by AES (C and O) and exhibited a sharp well contrasted p(1 · 1) LEED pattern with normal incidence IðV Þ spectra from the ð1; 0Þ beam in excellent visual agreement with previously reported spectra [8]. Platinum was evaporated from ultra-high purity (99.99%) 0.125 mm Pt wire wrapped around a shrouded and collimated 0.3 mm tungsten filament.…”