Quasicrystal Films Research Articles

On the interfacial behavior of two-dimensional decagonal quasicrystal films with an adhesive layer due to thermal misfit

The interfacial behavior of a thin two-dimensional decagonal quasicrystal (QC) film bonded to a half plane with an adhesive layer is analyzed under thermal misfit. Under a perfect non-slipping contact condition at interface, a theoretical model is established based on the membrane assumption, with the governing integral–differential equations being constructed in terms of phonon interfacial shear stresses in one single and multiple films. Then, these governing equations are numerically solved by Chebyshev polynomials, obtaining the phonon interfacial shear and internal normal stresses as well as the longitudinal displacement in the QC film. Finally, the effects of neighboring films, material mismatch, adhesive layer, the geometry of QC film, and temperature variation are briefly discussed on the interfacial response. It is found that the adhesive layer plays as a softening medium which can greatly reduce the value of normal and shear stresses and weaken the singularity of shear stresses near the ends of films. These findings will be instructive to the accurate measurement and safety monitoring of QC films.

On the Thermally Induced Interfacial Behavior of Thin Two-Dimensional Hexagonal Quasicrystal Films with an Adhesive Layer

The mechanical response of a quasicrystal thin film is strongly affected by an adhesive layer along the interface. In this paper, a theoretical model is proposed to study a thin two-dimensional hexagonal quasicrystal film attached to a half-plane substrate with an adhesive layer, which undergoes a thermally induced deformation. A perfect non-slipping contact condition is assumed at the interface by adopting the membrane assumption. An analytical solution to the problem is obtained by constructing governing integral–differential equations for both single and multiple films in terms of interfacial shear stresses that are reduced to a linear algebraic system via the series expansion of Chebyshev polynomials. The solution is compared to that without adhesive layers, and the effects of the aspect ratio of films, material mismatch, and the adhesive layer, as well as the interaction between films, are discussed in detail. It is found that the adhesive layer can soften the localized stress concentration. This study is instructive to the accurate safety assessment and functional design of a quasicrystal film system.

The thermally induced interfacial behavior of a thin two-dimensional decagonal quasicrystal film

The thermally induced interfacial behavior of a thin two-dimensional decagonal quasicrystal film

Thermal-induced interfacial behavior of a thin one-dimensional hexagonal quasicrystal film

Thermal-induced interfacial behavior of a thin one-dimensional hexagonal quasicrystal film

Growth of Ba–O ultrathin films on Pt(1 1 1) followed by Ti incorporation to prepare oxide crystalline approximants and quasicrystals

In this study, three different precursor Ba–O films on Pt(111) are characterized and the oxide crystalline approximant (OCA) and oxide quasicrystal (OQC) films are prepared by annealing after Ti deposition on the films. The prepared Ba–O ultra-thin films are BaO(100)–(√2×√2)R3°:Pt(111), Ba–O:Pt(111)–(2 × 2) and Ba–O:Pt(111)–(√13×√13)R13.9°, as determined using scanning tunneling microscopy, low-energy electron diffraction, and X-ray photoelectron spectroscopy. The phase transformation from an OCA film to an OQC film likely follows the mechanism where Ti is reduced and its surface atomic density decreased, while Ba is oxidized. The schematic structural models of the OCA film as Ba4Ti4O10 and the OQC film as Ba12Ti5O12, where the Ba atoms form a cluster tiling, are proposed.

Growth and composition of an ultrathin Ba-Ti-O quasicrystal film and its crystalline approximant on Pt(111)

As a new family of quasicrystals, oxide quasicrystals (OQCs) were recently discovered in Ba-Ti-O films on Pt(111). Here we report on the growth and composition of an ultrathin Ba-Ti-O OQC film and its crystalline approximant, studied by scanning tunneling microscopy (STM), low-energy electron diffraction, Auger electron spectroscopy, x-ray photoelectron spectroscopy, and Rutherford backscattering spectroscopy. STM images reveal a wide-scale ultrathin OQC film without BaO islands, and magnified STM images display typical OQC clusters. The ultrathin OQC film has been prepared by annealing an oxide crystalline approximant with decreasing Ti concentration. We also found that the ultrathin Ba-Ti-O film forms a $(2\ifmmode\times\else\texttimes\fi{}2)$ superstructure on annealing the ultrathin OQC film. For quantitative analysis, the XPS peak intensity was measured as a function of elemental atomic density. The elemental atomic densities for the ultrathin OQC film were determined to be $8\ifmmode\times\else\texttimes\fi{}{10}^{14}$, $4\ifmmode\times\else\texttimes\fi{}{10}^{14}$, and $3\ifmmode\times\else\texttimes\fi{}{10}^{14}\phantom{\rule{0.16em}{0ex}}\mathrm{atoms}/{\mathrm{cm}}^{2}$ for Ba, Ti, and O, respectively.

TiZrNi quasicrystal film prepared by magnetron sputtering

Neutron generators, as an important neutron source, have been widely used in various fields. In order to improve their storage and service lifetime, the preparation of TiZrNi quasicrystal tritium target film with magnetron sputtering technology is explored in this paper. The nano-quasicrystal phase is found and confirmed for the first time in the film fabricated with the alloy target of Ti34Zr49Ni17 and substrate deposition temperature of 450 °C. At a given composition of the TiZrNi alloy target, the formation of quasicrystal phase is very sensitive to the substrate temperature. Amorphous and fcc-(Ti,Zr)2Ni phase predominate in the TiZrNi films when the substrate temperatures are in the range of 100–400 °C and 500–600 °C, respectively. The compositions of the TiZrNi films prepared under different substrate temperatures are very close to each other and the values are about Ti40Zr40Ni20. The surface and cross-section morphologies show that the TiZrNi films are compact and dense with good adhesion between films and substrates. The TiZrNi quasicrystal film obtained in this work is hopeful to be applied to tritium target film of neutron generators.

2D quasicrystals from perovskites

Perovskite oxides represent a versatile class of materials with a simple cubic or pseudo-cubic crystal structure. The family of perovskite oxides contains insulators, metals, semiconductors, and superconductors with nearly identical lattice parameters. This structural equivalence additionally allows to combine perovskites with different properties in multilayer systems to produce functional materials with unique properties. We report here on the formation of a quasicrystal (QC) thin film on a threefold Pt(111) surface. This QC film is derived from the classical perovskite oxide BaTiO3 which is the most intensely studied ferroelectric perovskite oxide. An easily accessible ferroelectric to paraelectric phase transition at 400 K makes the material so interesting for basic and applied research. Due to matching lattice conditions BaTiO3 can be grown epitaxially on selected metal substrates. Periodic thin films of either BaTiO3(100) or BaTiO3(111) have been grown depending on substrate orientation and preparation conditions on Pt(001) and on Pt(111) [1, 2]. As we demonstrate here, astonishingly also a two-dimensional dodecagonal quasicrystalline structure can be formed by annealing an initially 1.4 nm thick BaTiO3 film on Pt(111) [3]. It develops at a temperature of 1250 K from a wetting layer spreading between a few thicker BaTiO3(111) islands. Surface sensitive electron diffraction (LEED) shows a bright and sharp pattern with dodecagonal symmetry. High-resolution scanning tunneling microscopy (STM) images reveal an arrangement of quadratic, triangular, and rhombic elements which compares well to a Gähler tiling. The development of higher-order self-similar structures is widely suppressed by a linear phason strain. This is supported by the fine structure of the diffraction data.

Formation and Characterization of the Quasicrystal Films

Al-Cu-Fe quasicrystals powder was used to prepare the thin films on the surface of the A3 steel by the means of DMD-450 vacuum evaporation equipment. The thin films with different characterization were obtained through different parameters. The microstructures of the thin films were analyzed by Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD). Additionally, the nano-hardness and the modulus of the films are tested by MTS and Neophot micro-hardness meter. The results showed that the modulus of the films was about 160GPa. Nano hardness of the films was about 7.5 Gpa. The films consisted of CuAl2, AlCu3. The thickness and the micro-hardness of the films are improved. In same way, with the increase of the electric current, the thickness and the hardness of the films are also improved. Along with increase of the time and the electric current, the wear behavior of the films was improved. To some extent, the microstructure of films contained the quasicrystal phase of Al65Cu20Fe15.

Structure and reflective properties of Al-Cu-Fe quasicrystalline thin film prepared by laser induced arc method

Al-Cu-Fe thin films were prepared by laser induced arc (laser-arc) method from a single source—Al63Cu25Fe12 alloy, which was proved to consist of quasicrystalline phase together with approximant phase. The composition of the deposited films meets the requirement for formation of icosahedral symmetry phase. Quasicrystalline phase was obtained after annealing the amorphous as-deposit film samples. The optical properties of the samples were investigated. Thin film samples of Al, Cu and Fe deposited under the same condition were employed for comparison. The results showed specific reflective properties of Al-Cu-Fe quasicrystal thin film in some wavelength range. The optical conductivity of the films exhibited a negative peak, centered about 440 nm in range of 190 to 800 nm. The Al-Cu-Fe quasicrystal thin films could absorb almost all the ray in the wavelength range from 420nm to 450 nm. The ratio of absorption was greater than 99%.

Investigation of quaternary Al-based quasicrystal thin films for corrosion protection

Recent work has shown that thin film quasicrystal coatings have unique properties such as very high electrical and thermal resistivities and very low surface energy. Aluminum-based quasicrystals are insulator alloys composed of approximately 70% of aluminum. The corrosion related properties of aluminum-based quasicrystal thin film coatings have been studied on quasicrystal-coated AA-2024 substrates. The thin film deposition parameters are discussed. Results of microstructural and surface chemistry analyses of the quasicrystal films are presented. The corrosion protection properties of the films have been studied by potentiodynamic scan and electrochemical impedance spectroscopy. Analysis of the electrochemical data indicates that nanostructured quasicrystal films significantly resist corrosion of AA2024-T3 substrates in constant immersion environment. Morphology studies and electrochemical analysis of quasicrystal films have shown that quaternary Al-based quasicrystal thin films possess unique corrosion control properties. Superior resistance to electrolyte attack makes these coatings strong candidates for corrosion-resistant surface treatment of Al alloys. These films can be utilized as conversion coatings for Al substrates or incorporated into a full coating system containing an organic primer and a topcoat.

Investigation of nanostructured Al-based quasicrystal thin films for corrosion protection

Quasicrystals belong to a particular type of solids, which consist of highly symmetric atom clusters. The structure is neither periodically ordered, as in crystalline materials, nor amorphous, as in a glass. Recent work has shown that thin film quasicrystal coatings can have unique properties such as very high electrical and thermal resistivities and very low surface energy, which may result in interesting corrosion properties. For example, aluminum alloy based quasicrystals are insulator alloys containing about 70% of aluminum. Other interesting properties involving, for instance, adhesion, corrosion, friction, and hardness suggest that quasicrystal coatings are promising materials for a variety of industrial applications. The corrosion related properties of aluminum alloy based quasicrystal thin film coatings have been studied on coated AA2024 substrates. The thin film deposition parameters are briefly discussed. Results of the microstructural, surface chemistry, and surface energy analysis of the quasicrystal films are presented. The corrosion protection properties of the films have been studied by potentiodynamic scan and electrochemical impedance spectroscopy. Analysis of the electrochemical data indicates that nanostructured quasicrystal films significantly resist corrosion of AA2024-T3 substrates in a constant immersion environment.

Fabrication and transport properties of thin films of quasicrystals

We present a brief overview of the preparation of quasicrystalline thin films, emphasising the constraints and methods used to prepare stable ternary quasicrystal films. As an example, we present the preparation of thin i-Al–Cu–Fe and i-Al–Pd–Re films and the study of dimensionality effects in the electrical conductivity.

Quasicrystal films: numerical optimization as a solar selective absorber

Selective absorbers for solar thermal energy applications have to show high solar absorptance α s and low thermal emittance ϵ h. Stability against oxidation and diffusion is indispensable, especially at high absorber temperatures. The new class of quasicrystalline materials seems to have favourable properties regarding stability. With a genetic algorithm a thin film stack based on dielectric and quasicrystal films was optimized as a selective absorber. A sandwich system dielectric/quasicrystal/dielectric on copper has highly selective properties: α s = 0.86 and ϵ h (400 ° C) = 0.051. Even better results can be achieved, at least in theory, by the use of a cermet. The optical constants of cermets with the quasicrystalline material as the metal were calculated with the Bruggeman theory. A system of a cermet film and an additional antireflective coating on copper shows α s = 0.92 and ϵ h (400 ° C) = 0.048.

Layering transitions in quasicrystal films.

Adsorbed quasicrystal films are predicted to have first-order layering transitions. The critical end point for large film thickness h tends to infinity like ${\mathit{T}}_{\mathit{c}}$(h)\ensuremath{\simeq}J(h/a${)}^{(\mathrm{\ensuremath{\alpha}}+2)/2}$/${\mathrm{ln}}^{1/2}$(h/a) for perfect-tiling models and like ${\mathit{T}}_{\mathit{c}}$(h)\ensuremath{\simeq}J ${\mathrm{ln}}^{2/3}$(h/a) for models with phason Debye-Waller disorder, where J is the microscopic interaction energy, a is the atomic scale, and the exponent \ensuremath{\alpha} describes the falloff of the film-surface--substrate interaction.

Growth of Al-Mn, Al-Cu-Fe and Al-Fe quasicrystalline films prepared by vacuum deposition

Thin films of Al-Mn, Al-Fe and Al-Cu-Fe quasicrystalline films are prepared by a successive deposition technique in a vacuum onto air-cleaved sodium chloride surfaces at substrate temperatures of 220–350°C. The growth of the quasicrystals is found as grains of 20–50 nm in size, the five-fold axis being perpendicular to the film surface and the two-fold axis of the quasicrystal parallel to [110] directions of the (111) orientated aluminum film. For the Al-Fe and Al-Cu-Fe system, the rotation of the five-fold axis around the two-fold axes by around 10° can be recognized. Below about 10 at % of manganese or iron content, a coexistence of aluminum and the quasicrystalline grains is observed. High resolution electron microscopy is applied to the quasicrystal films, by which the vertex model with a decoration in Penrose tiling is suggested.

Growth of Al-Mn quasi-crystals by vacuum deposition

Thin films of Al-Mn quasi-crystals are prepared by a successive deposition technique in vacuum onto air-cleaved sodium chloride surfaces. At a substrate temperature of 280 to 330°C, the growth of the quasi-crystals is found to produce polycrystalline films with a grain size of 20 to 50 nm, the composition ratio of aluminium and manganese being about 5:1. No structure change can be found after a heat treatment of the film at 280°C for 8 h, though a trend of grain growth is detected. For a specimen with a composition ratio above 8:1 grown at 280°C, a diffraction pattern due to aluminium with (111) orientation is recognized in addition to that of quasi-crystals, the lattice relation being that the [110] direction of aluminium is parallel to the two-fold axis of the quasi-crystal. A heat treatment at 330°C for a few hours brings about a transformation from quasi-crystalline films to an alloy phase, Al 6Mn. High resolution electron microscopy is applied to the quasi-crystal films and the edge length of the fundamental hexahedron of the Penrose tiling has been determined to be 0.47 nm from the structure images.

Growth of AlMn quasicrystals by vacuum deposition

Thin films of AlMn quasicrystals are prepared by a successive deposition technique in a vacuum onto air-cleaved sodium chloride surfaces at a substrate temperature of 280–330°C. The growth of the quasicrystals is found as random orientated films with a grain size of 20–50 nm for Al-21 at.% Mn. For a specimen of Al-5at.% Mn grown at 280°C, quasicrystals and aluminum with (111) orientation are recognized, the lattice relation being that the [110] direction of the aluminum is parallel to the twofold axis of the quasicrystal. Heat treatment at 330°C for a few hours brings about a transformation from quasicrystalline films to an equilibrium phase Al 6Mn. High resolution electron microscopy is applied to the quasicrystal films, by which the edge length of the fundamental hexahedron of the Penrose tiling is determined to be 0.47 nm from the structural images.

Formation of Al–Cr Quasicrystal Films by RF-Sputtering

La formation de quasi-cristaux par pulverisation est possible lorsque les supports utilises sont des couches de polymere (imide). Aucun quasi-cristal n'est visible sur un substrat en quartz. Etude de la structure et de la composition chimique par diffraction electronique et par spectrometrie dispersive de rayons X