Structural investigation of the (110) surface ofγ-Al4Cu9

Abstract

We present a detailed study of the ͑110͒ surface of the ␥-Al 4 Cu 9 crystal using both experimental methods and first-principles calculations based on density-functional theory. Our experimental approach, using lowenergy electron diffraction, scanning tunneling microscopy ͑STM͒ images, and x-ray photoelectron spectroscopy highlights the presence of two types of surface terminations. Combining experimental results and simulations provides many arguments to match the two observed surfaces with the two puckered terminations built from bulk truncation: ͑i͒ calculations show that these two puckered terminations present lower surface energies compared to another conceivable flat termination obtained also from bulk truncation, ͑ii͒ step height measurements are consistent with calculated interlayer spacings and ͑iii͒ simulated STM images are in reasonable agreement with the experimental ones and mirror the experimental voltage dependence.

Effect of temperature on the initial stages of oxidation of γ-Al4Cu9(110)

“…In addition, similarly to the results obtained for oxidation at room temperature, Cu-O bonds are never formed, even at low coverages (see also Fig. 1), in spite of the fact that the clean (1 1 0) surface of ␥-Al 4 Cu 9 is consisting of 55% copper [13,17]. This suggests a similar oxidation mechanism at 115 K and room temperature.…”

“…4 shows the LEED patterns observed at 60 eV and 115 K following sequential dosing of the ␥-Al 4 Cu 9 (1 1 0) surface with oxygen at 115 K and 2 × 10 −7 mbar. The LEED pattern observed for the clean surface is similar to the one previously reported [13,17] and corresponds to a rectangular surface unit cell having parameters a = 8.7Å and b = 12.4Å. Initial dosing with oxygen does not induce any change in the LEED pattern which remains well contrasted with a low background.…”

“…Preparation of the ␥-Al 4 Cu 9 crystal has been previously described in detail [17]. Briefly, induction melting of the pure elements (Al-99.9% and Cu-99.99%) under an argon atmosphere is followed by homogenisation by annealing at 1323 K for 4 h and slow cooling down to room temperature.…”

“…This value is much smaller than those usually ascribed to the vacancy diffusion mechanism of aluminium in crystalline Al-based intermetallics (∼1.6 eV) [18] or in Cu (1.81 eV) [19] and has been explained by considering that the activation energy of diffusion is composed of a vacancy formation and a vacancy migration contributions to enthalpy, which have close values (0.68 and 0.62 respectively in pure Al [20]). As the ␥-Al 4 Cu 9 phase has a structure based on a 3 × 3 × 3 CsCl superstructure containing two vacancies [17,21] only the vacancy migration enthalpy must be considered in the case of ␥-Al 4 Cu 9 , thus leading to a very low value of the activation energy for Al segregation in this material.…”

Surfaces of Al-based complex metallic alloys: atomic structure, thin film growth and reactivity

“…Bottom row: simulated STM images obtained at V = +0.5 V for the PP (a) and PF (b) models. (c) Representation of the bulk structure along the [110] direction [59]. (Reprinted figure 8(a), (b) with permission from [59].…”