Surface alloys as interfacial layers between quasicrystalline and periodic materials

Abstract

Low adhesion with normal metals is an intrinsic property of many quasicrystalline surfaces. Although this property could be useful to develop low friction or non-stick coatings, it is also responsible for the poor adhesion of quasicrystalline coatings on metal substrates. Here we investigate the possibility of using complex metallic surface alloys as interface layers to enhance the adhesion between quasicrystals and simple metal substrates. We first review some examples where such complex phases are formed as an overlayer. Then we study the formation of such surface alloys in a controlled way by annealing a thin film deposited on a quasicrystalline substrate. We demonstrate that a coherent buffer layer consisting of the γ-Al4Cu9 approximant can be grown between pure Al and the i-Al–Cu–Fe quasicrystal. The interfacial relationships between the different layers are defined by .

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

“…It has been shown using STM and LEED techniques that Cu adatoms deposited on the fivefold and twofold i -AlPdMn surface yields quasiperiodic structures [86, 87]. However, five-rotational domains of (110)-orientated β -Al(Cu, Fe) phase are obtained for 8 ML Cu atoms adsorbed on the fivefold i -Al-Cu-Fe surface [88]. Annealing a 20 ML thick film leads to the formation of five domains of γ -AlCu exposing the (110) surface.…”

Structurally complex metallic coatings in the Al-Cu system and their orientation relationships with an icosahedral quasicrystal

“…Note that due to the fivefold symmetry of the substrate, rotational epitaxy of either the b-CsCl or the g-Al 4 Cu 9 phase implies that only two out of three crystallographic axes are aligned with a dense axis of the substrate. 16,34,[43][44][45] Hence, the film should not appear as completely dark in these images. Also, grains of the film appearing with a bright contrast can nevertheless have ORs with the substrate, albeit with another substrate axis, different from the zone axis considered.…”

“…One possibility to circumvent this problem is to develop an interfacial layer such as obtaining a gradient of properties between the substrate and the surface. 16 This interface layer should be an intermetallic compound presenting electronic and crystallographic characteristics that are intermediate between those of a simple metal and a quasicrystal. This condition is usually met by the so-called approximant phases, which have a periodic structure with giant unit cells and a local order similar to that of the quasicrystalline phase.…”

“…They thus represent an intermediate complexity between simple metals and quasicrystals. In addition, recent ultra high vacuum studies have shown that the g-Al 4 Cu 9 phase can be grown on the fivefold surface of either Al-Cu-Fe or Al-Pd-Mn icosahedral quasicrystals, 16,34 with clear rotational epitaxy with the substrates. This supports the idea that such compounds could be used as a buffer layer to accommodate the interface between a quasicrystalline coating and a simple metal substrate.…”

Structural investigation of the (110) surface ofγ-Al4Cu9

“…In addition, it can be formed as a surface alloy in orientational relationship on quasicrystalline substrates. [35][36][37] The paper is organized as follows. Section II describes the single-crystal growth along with experimental and computational details.…”