110 research outputs found
Influence of strain in Ag on Al(111) and Al on Ag(100) thin film growth
We demonstrate the influence of interfacial strain on the growth modes of Ag films on Al(111), despite the small magnitude of the lattice misfit in this system. The strain is relieved by the formation of stacking fault domains bounded by Shockley partial dislocations. The growth mode and the step roughness appear to be strongly connected. Growth is three-dimensional (3D) as long as the steps are straight, but switches to 2D at higher coverage when the steps become rough. Anisotropic strain relaxation and straight steps seem to be related. We also report related observations for Al deposited on Ag(100)
Pseudomorphic Growth of a Single Element Quasiperiodic Ultrathin Film on a Quasicrystal Substrate
An ultrathin film with a periodic interlayer spacing was grown by the deposition of Cu atoms on thefivefold surface of the icosahedral Al70 Pd21 Mn9 quasicrystal. For coverages from 5 to 25 monolayers, a distinctive quasiperiodic low-energy electron diffraction pattern is observed. Scanning tunneling microscopy images show that the in-plane structure comprises rows having separations of S = 4.5 �0.2 �A and L = 7.3 0.3 A, whose ratio equals � =1.618... within experimental error. The sequences of such row separations form segments of terms of the Fibonacci sequence, indicative of the formation of a pseudomorphic Cu film
Nanodomains due to Phason Defects at a Quasicrystal Surface
Among the three coexisting types of terraces found on the twofold surface of the d-Al-Cu-Co quasicrystal, nanodomains are essentially observed on the transition-metal rich ones, with a coherent interface boundary. Both clean surface and Ag growth analyses, demonstrate that nanodomain surfaces are structurally identical to one of the two other terraces, which contains 85 at. % Al. We provide evidence that the nanodomains are a manifestation of phason defects that extend downward toward the bulk, and state that nanodomains develop because the energetic cost of creating the phason is outweighed by the change in surface energy. Consequently, the formation of nanodomains involves more than just the surface layer, but is driven by surface energetics
The surface science of quasicrystals
The surfaces of quasicrystals have been extensively studied since about 1990. In this paper we review work on the structure and morphology of clean surfaces, and their electronic and phonon structure. We also describe progress in adsorption and epitaxy studies. The paper is illustrated throughout with examples from the literature. We offer some reflections on the wider impact of this body of work and anticipate areas for future development.
(Some figures in this article are in colour only in the electronic version
Surface structure of the Ag-In-(rare earth) complex intermetallics
We present a study of the surface structure of the Ag-In-RE (RE: rare-earth elements Gd, Tb, and Yb) complex intermetallics using scanning tunneling microscopy and low-energy electron diffraction. The surface of the Ag-In-Yb approximant prepared by sputter-annealing methods under ultrahigh-vacuum conditions produces a flat (100) surface with no facets. However, the Ag-In-Gd and Ag-In-Tb 1/1 approximants, which have a surface miscut of about 12∘ relative to the (100) plane, develop surface facets along various crystallographic directions. The structure of each facet can be explained as a truncation of the rhombic triacontahedral clusters, i.e., the main building blocks of these systems. Despite their differences in atomic structure, symmetry, and density, the facets show common features. The facet planes are In rich. The analysis of the nearest-neighbor atom distances suggests that In atoms form bonds with the RE atoms, which we suggest is a key factor that stabilizes even low-density facet planes
A maximum density rule for surfaces of quasicrystals
A rule due to Bravais of wide validity for crystals is that their surfaces
correspond to the densest planes of atoms in the bulk of the material.
Comparing a theoretical model of i-AlPdMn with experimental results, we find
that this correspondence breaks down and that surfaces parallel to the densest
planes in the bulk are not the most stable, i.e. they are not so-called bulk
terminations. The correspondence can be restored by recognizing that there is a
contribution to the surface not just from one geometrical plane but from a
layer of stacked atoms, possibly containing more than one plane. We find that
not only does the stability of high-symmetry surfaces match the density of the
corresponding layer-like bulk terminations but the exact spacings between
surface terraces and their degree of pittedness may be determined by a simple
analysis of the density of layers predicted by the bulk geometric model.Comment: 8 pages of ps-file, 3 Figs (jpg
Twofold surface of the decagonal Al-Cu-Co quasicrystal
We have investigated the atomic structure of the twofold surface of the decagonal Al-Cu-Co quasicrystal using scanning tunneling microscopy and low-energy electron diffraction. We have found that most of the surface features can be interpreted using the bulk-structure model proposed by Deloudi and Steurer (S. Deloudi, Ph.D. thesis, ETH, Zürich, 2008). The surface consists of terraces separated by steps of various heights. Step heights and steps sequences match with the thickness and the stacking sequence of blocks of layers separated by gaps in the model. These blocks of layers define possible surface terminations consisting of periodic atomic rows which are aperiodically stacked. These surface terminations are dense (∼10 at./nm2) and are of three types. The first two types are pure or almost pure Al while the third one contains 30–40 at. % of transition-metal atoms. Experimentally, we observe three different types of fine structures on terraces, which can be interpreted using the three possible types of bulk terminations. Terraces containing transition metals exhibit a strong bias dependency and present a doubling of the basic 0.42 nm periodicity, in agreement with the 0.84 nm superstructure of the bulk. In addition, a high density of interlayer phason defects is observed on this surface that could contribute to the stabilization of this system through configurational entropy associated with phason disorder
Formation of a stable deacagonal quasicrystalline Al-Pd-Mn surface layer
We report the in situ formation of an ordered equilibrium decagonal Al-Pd-Mn
quasicrystal overlayer on the 5-fold symmetric surface of an icosahedral
Al-Pd-Mn monograin. The decagonal structure of the epilayer is evidenced by
x-ray photoelectron diffraction, low-energy electron diffraction and electron
backscatter diffraction. This overlayer is also characterized by a reduced
density of states near the Fermi edge as expected for quasicrystals. This is
the first time that a millimeter-size surface of the stable decagonal Al-Pd-Mn
is obtained, studied and compared to its icosahedral counterpart.Comment: Submitted to Phys. Ref. Lett. (18 July 2001
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