Quasicrystalline nature of quasicrystal surfaces: A photoemission study

Differently prepared surfaces of quasicrystalline i-Al-Pd-Mn are analyzed using angle-resolved photoemission in the x-ray andultraviolet range of photon energies. Depending on the preparation, we find both surfaces with crystalline structure and metallic character, and surfaces with quasicrystalline structural fingerprints and a suppressed density of states at the Fermi level, compatible with a pseudogap

Morphological evolution of the fivefold surface of i-AlPdMn quasicrystals

Morphology of the fivefold symmetric quasicrystal surface of AlPdMn was investigated by x-ray reflectivity and by x-ray diffraction. X-ray experiments revealed two different morphologies depending on the surface preparation. Sputtering and annealing up to 900 K, under UHV conditions, produced a rough and facetted quasicrystal surface. These features were confirmed by atomic force microscopy and scanning tunnel microscopy measurements. We also observed that an annealing above 900 K induces a rapid and irreversible transition toward a flat surface

Characterization And Properties Of The AIPdMn 5 Surface

The surface of the AlPdMn quasicrystal perpendicular to a fivefold axis has been probed by LEED, XPS, Auger spectroscopy and surface EXAFS.This article is from MRS Proceedings 553 (1998): 243–250, doi:10.1557/PROC-553-243.</p

Processing Of Al-Cu-Fe Single Grains

The phase equilibria of the Al-Cu-Fe quasicrystalline phase (y phase) is complex and conventional crystal growth techniques like the Bridgman and Czochralski methods are not applicable in preparation of large crystals. Large single grains of the y phase been have prepared by either slow cooling or isothermal anneals. In the later technique, arc melted ingots were subjected to either single or multiple heat treatments between 825 and 840°C to encourage grain growth. Following heat treatment, grains of the icosahedral phase are found either as isolated pentagonal-faceted crystals within the ingot or within clusters of intergrown grains. The growth of the large grains is independent of the sample processing history of the sample, is facilitated by the presence of liquid at the growth temperatures and is constrained by the physical dimension of the ingot. The microstructure of both grain types is similar containing a minor quantity (on the order of 5–10 %) of a second phase and a high degree of porosity in the as-grown state. The second phase is usually present as a thin layer between adjacent grains or associated with a pore within a single grain. The grain porosity is distributed throughout the ingot. These defects can be removed through post-growth hot isostatic pressing and anneal treatments.This article is from MRS Proceedings 553 (1998): 3–12, doi:10.1557/PROC-553-3.</p

Lattice-dynamical study of the premartensitic state of the Cu-Al-Be alloys

Neutron-scattering techniques have been used to study the premartensitic state of a family of Cu-Al-Be alloys, which transform from the bcc phase to an 18R martensitic structure. We find that the phonon modes of the TA2[110] branch have very low energies with anomalous temperature dependence. A slight anomaly at q=2/3 was observed; this anomaly, however, does not change significantly with temperature. No elastic peaks, related to the martensite structure, were found in the premartensitic state of these alloys. The results are compared with measurements, performed under the same instrumental conditions, on two Cu-Al-Ni and a Cu-Zn-Al martensitic alloy.This article is from Physical Review B 48 (1993): 15708–15711, doi:10.1103/PhysRevB.48.15708.</p

Quasicrystalline nature of quasicrystal surfaces: A photoemission study

Differently prepared surfaces of quasicrystalline i-Al-Pd-Mn are analyzed using angle-resolved photoemission in the x-ray andultraviolet range of photon energies. Depending on the preparation, we find both surfaces with crystalline structure and metallic character, and surfaces with quasicrystalline structural fingerprints and a suppressed density of states at the Fermi level, compatible with a pseudogap.This article is from Physical Review B 60 (1999): R16330, doi:10.1103/PhysRevB.60.R16330.</p

Clustered, Terraced And Mixed Surface Phases Of The Al70Pd21Mn9 Quasicrystal

The five-fold surface of the Al70 Pd21 Mn9 quasicrystal has been studied using STM, LEED and AES. STM images from surfaces which have been sputtered and annealed to 875 K reveal 20-30 Å protrusions that have been identified by others as Mackay-type clusters. Higher-resolution images reveal substructures in these clusters having dimensions 2-3 Å. Longer annealing times at 875 K produced large areas having flat terraces which were imaged with atomic resolution. The LEED pattern from this surface has sharp spots on a low background, and AES indicates that the surface is deficient in Mn relative to the bulk. For surfaces annealed to 1050 K for less than 2 hours, STM images indicate that cluster and terrace phases coexist, and a third phase having aligned arrays of clusters is identified which appears to be intermediate between the cluster and terrace phases.This article appeared in MRS Proceedings 553 (1998): 237–244, doi:10.1557/PROC-553-237.</p

Dynamical x-ray diffraction from an icosahedral quasicrystal

We present direct evidence of dynamical diffraction of x rays from a quasicrystal. High-resolution x-ray-diffraction measurements of the Al-Pd-Mn face-centered icosahedral quasicrystal were performed, revealing a mosaic full width at half maximum of less than 0.001°. In a second experiment, the anomalous transmission of x rays (the Borrmann effect) was observed. These measurements show that nearly perfect quasicrystals may be grown to centimeter-size dimensions allowing x-ray techniques based upon dynamical diffraction to be brought to bear on the analysis of icosahedral structures.This article is from Physical Review B 48 (1993): 3544–3547, doi:10.1103/PhysRevB.48.3544.</p

Characterization And Properties Of The AIPdMn 5 Surface

The surface of the AlPdMn quasicrystal perpendicular to a fivefold axis has been probed by LEED, XPS, Auger spectroscopy and surface EXAFS.This article is from MRS Proceedings 553 (1998): 243–250, doi:10.1557/PROC-553-243.</p

Morphological evolution of the fivefold surface of i-AlPdMn quasicrystals

Morphology of the fivefold symmetric quasicrystal surface of AlPdMn was investigated by x-ray reflectivity and by x-ray diffraction. X-ray experiments revealed two different morphologies depending on the surface preparation. Sputtering and annealing up to 900 K, under UHV conditions, produced a rough and facetted quasicrystal surface. These features were confirmed by atomic force microscopy and scanning tunnel microscopy measurements. We also observed that an annealing above 900 K induces a rapid and irreversible transition toward a flat surface.This article is from Physical Review B 65 (2002): 245405, doi:10.1103/PhysRevB.65.245405.</p