Orientation relationship between metallic thin films and quasicrystalline substrates.
- PDF / 1,272,229 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 52 Downloads / 221 Views
LL8.3.1
Orientation relationship between metallic thin films and quasicrystalline substrates. V. Fournée 1, A.R. Ross 2, 3, T.A. Lograsso 2, 3 and P.A. Thiel 2, 4. 1
LSG2M, CNRS-UMR7584, Ecole des Mines, Parc de Saurupt, 54042 Nancy, France. Ames Laboratory, 3 Department of Materials Science and engineering, 4 Department of Chemistry, Iowa State University, Ames, Iowa 50011, USA.
2
ABSTRACT We present experimental results on the structure of Ag thin films grown on high-symmetry surfaces of both quasicrystals and approximants. For coverages above ten monolayers, Ag form fcc nanocrystals with (111) plane parallel to the surface plane. Depending on the substrate surface symmetry, the Ag nanocrystals exist in one, two or five different orientations, rotated by a multiple of 2π/30. The orientation relationship between crystalline films and substrates appears to be determined by the following principles : high atomic density rows of the adsorbate are aligned along high atomic density rows of the substrate. INTRODUCTION The orientation relationship between crystalline thin films and quasicrystalline substrates has been investigated in two different situations. In a first case, the crystalline overlayer is artificially produced by sputtering and annealing the surface [1]. Variations of the sputtering yield across the different elemental constituents result in a shift of the composition from the quasicrystalline phase to a cubic phase with CsCl structure. If the annealing temperature is sufficiently low, the quasicrystalline structure is not recovered and the cubic phase can be observed experimentally as an overlayer. In the second situation, the thin crystalline film is formed by adsorption of extrinsic atoms from the vapor phase through nucleation and growth. This has been realized for a number of systems, where a metal (like Al, Ag, Au or Cu) was deposited onto a high symmetry surface of an icosahedral (AlPdMn or AlCuFe) or decagonal (AlNiCo) substrate [2-4]. When the film becomes thick enough, it usually recovers its crystalline structure, with specific orientation relationship relative to the substrate. Here we present our results for Ag thin films deposited on the 2-fold and 5-fold surfaces of the icosahedral AlPdMn QC, the pseudo-10-fold surface of the ξ’-AlPdMn orthorhombic approximant and the 10-fold surface of the AlNiCo decagonal QC. The orientation relationship between crystalline films and substrates are interpreted using arguments based on alignment of high atomic density rows within the interface plane rather than alignment of symmetry axes. EXPERIMENTAL DESCRIPTION Single grains from the Al72Pd19.5Mn8.5 icosahedral quasicrystalline (IQC) phase and from the ξ’Al77.5Pd19Mn3.5 approximant were grown by the Bridgman method. The Al72Ni11Co17 decagonal quasicrystalline (DQC) sample were grown by a flux method (slow cooling). High symmetry surfaces were extracted from the single grains after orientation within ±0.2° by back-Laue scattering and polished down to a final roughness of 0.25 µm, which leads to a mirro
