Quasicrystalline Films Research Articles

Single-phase quasicrystalline Al–Cu–Fe thin film prepared by direct current magnetron sputtering on stainless steel

It is generally difficult to obtain single-phase quasicrystalline thin films due to the stringent requirement for composition and working parameter controls. In this paper, the magnetron sputtering preparation of a single-phase quasicrystalline film is described in detail. Three key issues are particularly addressed: target composition, process parameters, and subsequent heat treatment scheme. Firstly, an alloy ingot of composition Al63Cu25Fe12(at.%) is melted as the raw material for the target. Then thin film depositions were made in a magnetron sputtering system with 196 W and 1 h, subsequently annealed at 650 °C for 15 min to obtain single-phase quasicrystalline films. The dense and uniform film is well attached to the 304 stainless steel substrate, with a bonding force between film and substrate being 42.5±0.6 N. Such a high-quality film allows reliable characterizations on properties such as hardness (13.4±0.3 GPa), elastic modulus (218±6 GPa), hardness-over-modulus ratio (0.062±0.004), non-stick (water contact angle reaching 102±2°), corrosion resistance (self-corrosion potential −653.19 mV and self-corrosion current density 4.19 μA⋅cm−2 in 3.5 wt.% NaCl electrolyte), coefficient of friction (0.16, using 304 stainless steel ball), all falling close to those of bulk quasicrystals. The root mean square roughness of the quasicrystalline film was found to be 2.12 nm.

Peculiarities of quasicrystalline films formation processes on crystal surface under irradiation with proton-ion flows

Quasicrystalline film with densest package of atoms can be formed on a crystal surface under irradiating crystal surface with protonion flows at a certain ratio of atoms diameters of irradiated crystal and the ions of irradiating flow. Atom-free area of 1 Å order is formed. These are traps for protons from the irradiation stream, thus a quantum dot appears. Atomic package of quasicrystalline film is a package of equilateral Penrose rhombs and there are centers of atoms mass at the vertices. A mathematical relation is obtained that allows predicting radii of irradiation flux ions to form quasicrystalline film and select atomic composition of the obtained film with predetermined properties. Nanostructuring of materials is an entire family of physicochemical processes associated with proton transfer and their localization in crystal lattice and these include ion exchange, diffusion, and ion implantation. Ion and proton exchange can be considered an established universal method of surface modification technology [24– 26]. The case of implantation of protons into the structure of cluster systems formed on the surface of crystals is described in this paper. In this case, a quantum dot is formed in the cluster structure, which is a potential hole with quantized proton motion, wherein the radiation of quantum dot is in IR area of electromagnetic spectrum.

Research of the wear resistance of multi-component bronze in the conditions of the hydraulic oil processed by the power field

The object of research is the process of changing the wear resistance of bronze under the conditions of electrostatic treatment of hydraulic oil. The wear resistance of the bronze elements of the friction pairs determines the life of the axial-plunger pumps and affects their feed – pressure main characteristics. The studies were based on the theory of experimental design and statistical methods for processing test results. The research methodology provided for modeling the process of sliding friction using a – friction pair on the SMC-2 friction machine (the country is the manufacturer of the USSR, modernization in Ukraine). This type of friction takes place in the plunger – cylinder distribution disk – cylinder block tribosystem. Also, the method was supposed to pre-treat the hydraulic oil with an electrostatic field in the device, followed by feeding it into the tank with a roller using a pump station. Two independent factors varied: electrostatic field strength and hydraulic oil operating time. The constant factors were the hydraulic oil flow rate in the device, hydraulic oil temperature, contact pressure, linear roller sliding speed and time of each test. The obtained experimental data made it possible to establish a regularity characterizing the sliding friction process when a force field is applied to hydraulic oil. This pattern reveals the effect of electrostatic field strength and hydraulic oil operation on the wear resistance of a bronze block, which was tested on a friction machine SMC-2. This made it possible to determine the rational values of the parameters of the electrostatic field, at which the maximum wear resistance of the bronze is achieved depending on the operating time of the hydraulic oil, ranging from 1 • 106 V/m to 1.25 • 106 V/m. Thus, the effect of the field on oil helps to increase the wear resistance of bronze up to 5 times in the conditions of hydraulic oil in the delivery state and up to 3 times in oil with an operating time of 2000 hours. The influence of the field leads to polarization effects in the oil, which contribute to the formation of quasicrystalline films on the friction surface, increasing the tribojunction wear resistance.

Unique growth mode observed in a Pb thin film on the threefold surface of an i-Ag-In-Yb quasicrystal

Novel epitaxial quasicrystalline films can be grown using the surfaces of intermetallic quasicrystals as templates. Here, we present a study of Pb adsorption on the threefold i-Ag-In-Yb surface, where Pb grows in a manner contrasting with conventional thin-film growth modes. Pb atoms are found to adsorb at sites over a range of heights, which are explained by bulk atomic positions left vacant by surface truncation, producing three-dimensional, isolated quasicrystalline Pb structures. This finding is contrasted with the growth of Pb on the more commonly used fivefold surface of the same quasicrystal, where smooth epitaxial layers result. We suggest that this unique structure originates due to the lower atomic density of the threefold surface, compared to the fivefold surface. Similar atomic density can be found in lower symmetry planes of periodic systems, but these planes are often unstable and become facetted. This stable low-density quasicrystalline substrate provides a facile route to achieve this type of templated growth.

Structure and Phase Formation Features of Ti-Zr-Ni Quasicrystalline Films under Heating

Structure and Phase Formation Features of Ti-Zr-Ni Quasicrystalline Films under Heating

The quasicrystal model of cluster systems in condensed matter

The paper proposes a quasicrystal model of the structure of clusters. The model is based on the similarity of the structure of clusters and macroscopic structure of quasicrystals. It offers a formula to calculate the radii of successive coordination spheres in quasicrystalline films. The formula is based on the properties of Fibonacci sequence and characteristics of the power potential of interaction between particles.

Templated three-dimensional growth of quasicrystalline lead

Quasicrystals, materials with aperiodic long-range order, have been found in intermetallics, soft materials such as colloids and supermolecules, and also in two-dimensional monolayer films. Here we present the first example of three-dimensional growth of a single-element quasicrystalline film. Using a hitherto unexplored template, the icosahedral Ag-In-Yb quasicrystal, and various experimental techniques combined with theoretical calculations of adsorption energies, we find that lead atoms deposited on the surface occupy the positions of atoms in the rhombic triacontahedral cluster, the building block of the substrate, and thus grow in layers with different heights and adsorption energies. We show that the adlayer-adlayer interaction is crucial for stabilizing this epitaxial quasicrystalline structure. The finding opens an avenue for further investigation of the impact of the aperiodic atomic order over periodic order on the physical and chemical properties of materials.

Synthesis of quasicrystalline film of Al–Ga–Pd–Mn alloy

Present work describes the synthesis of Al (Ga)–Pd–Mn quasicrystalline films via flash evaporation followed by annealing. The icosahedral quasicrystal of Al65Ga5Pd17Mn13 alloy has been used as a precursor material. An amorphous phase with very fine icosahedral grain was found in the as-deposited films of ~1.5μm thickness. After annealing at 300°C for 120h, the film completely transformed into an icosahedral phase showing micron size islands, these are precipitated on the surface of film. The X-ray diffraction and transmission electron microscopy confirms the formation of icosahedral phase. The energy dispersive X-ray analysis reveals that the final stoichiometry is maintained in the film. The formation of icosahedral Al–Ga–Pd–Mn film provides opportunities to investigate the useful properties of quasicrystals including the surface characteristics, which may well enhance the scientific interest in applied aspect of quasicrystals.

Shift and broadening of surface polaritons of sapphire upon deposition of a quasicrystalline film

The influence of a quasicrystalline Al-Pd-Re film on the shift and broadening of surface polaritons of a substrate (sapphire) has been studied. Measurements have been performed both on a sample containing only the quasicrystalline phase and on a sample which, in addition to the quasicrystalline phase, contains the crystalline (metallic) phase. The complex dielectric function of the films in the mid-IR region (650–800 cm−1) has been estimated.

Residual stress in as-deposited Al–Cu–Fe–B quasicrystalline thin films

Abstract

Electronic properties of stable decagonal quasicrystals

AbstractSelected topics of electronic properties of stable decagonal quasicrystals are reviewed. Phonon localization and enhanced electron–phonon interaction may play important roles in the transport properties of these materials. The electronic specific heat measurements support the picture that the Hume–Rothery instability is responsible for the formation of the phase. On the other hand, careful examination of the magnetoresistance on highly oriented quasicrystalline films does not support the applicability of the quantum interference effect to the phenomenon.

Copper underpotential deposition on Ru quasi-single-crystal films

Ru quasi-single-crystal electrodes, prepared by resistive heating of Ru deposited on Pt single-crystal surfaces in a nitrogen atmosphere, have been used to study copper underpotential deposition (Cu-UPD), Bulk and surface Cu stripping experiments were performed on the low-index Ru/Pt(1 0 0), Ru/Pt(1 1 0) and Ru/Pt(1 1 1) quasi-crystalline film electrodes and also stepped Ru/Pt(S)[ n(1 0 0) × (1 1 1)] and Ru/Pt(S)[4(1 1 1) × (1 0 0)] electrodes vicinal to the (1 0 0) and (1 1 1) planes respectively. Upon performing Cu-UPD experiments in the potential range from 0 to 500 mV vs. Cu/Cu 2+ on the Ru/Pt(1 0 0) quasi-single-crystal film electrode, a single peak for Cu-UPD was observed at a potential of about 200 mV vs. Cu/Cu 2+. Its charge density was close to that for copper on the clean Pt(1 0 0) single-crystal substrate consistent with a coverage of one monolayer (1.3 × 10 15 atoms cm −2). In contrast, on Ru/Pt(1 1 0) and Ru/Pt(1 1 1), no significant amounts of Cu could be deposited – possibly due to competitive adsorption by adsorbed oxygen-species. For Cu-UPD on stepped Ru/Pt(S)[ n(1 0 0) × (1 1 1)] film electrodes vicinal to the (1 0 0) plane, a peak was also found in the same potential range as observed for Ru/Pt(1 0 0). From the linear variation of the charge densities of this Cu-UPD peak with the step density, we conclude that Cu-UPD is related to the adsorption of Cu on (1 0 0) terrace sites. Hence Cu-UPD is a structural probe of (1 0 0) terrace sites on quasi-crystalline Ru films supported on platinum. In order to reduce the amount of oxygen-species blocking the Ru/Pt(1 1 1) and vicinal surfaces, diffusion controlled progressive over-potential deposition (OPD) of Cu (in the sub-monolayer regime but at very negative potentials) from very dilute Cu 2+(aq) containing solutions was performed. For the Ru/Pt(1 1 1) film electrode, a desorption peak in the UPD range around 300 mV vs. Cu/Cu 2+ for Cu desorption from the (1 1 1) sites was then observed, while for experiments on the Ru/Pt(3 1 1), Ru/Pt(5 1 1) and Ru/Pt(5 3 3) electrodes, we could also observe a peak at around 200 mV, which we ascribe to the desorption of Cu from the (1 0 0) oriented sites. From these experimental results, we conclude that after preparation of the Ru-film electrodes, the terrace and step sites of the underlying Pt single-crystal substrate are preserved on the Ru film. These results for Cu-UPD on the Ru-film electrodes also demonstrate that free Pt domains do not exist on the Ru-film electrodes.

Chirality-selective synthesis of carbon nanotubes by catalytic-chemical vapor deposition using quasicrystal alloys as catalysts

Abstract We study ultrathin quasicrystalline (QC) films as catalysts for the synthesis of carbon nanotubes (CNTs). To optimize the conditions for the synthesis of CNTs with single chirality, it is important to understand the effects of the catalyst on the chirality-selectivity. Among QC alloys found so far, an icosahedral Al–Cu–Fe alloy system with fivefold symmetry was tested for a catalyst in the synthesis of CNTs by alcohol catalytic-chemical vapor deposition (CCVD). Cross-sectional scanning electron microscopic images of the samples revealed that vertically-aligned CNTs were synthesized reproducibly. It implies that QC films have a significant catalytic activity for the synthesis of CNTs. Moreover, preliminary results of chirality-selectivity are obtained by means of resonance Raman scattering. It is suggested that Al–Cu–Fe ultrathin films are useful for the preferential synthesis of armchair-type CNTs, that is, QC nanoclusters play an important role as catalyst in alcohol CCVD.

Growth of Bi thin films on quasicrystal surfaces

We present a comprehensive study of Bi thin-film growth on quasicrystal surfaces. The substrates used for the growth are the fivefold surface of icosahedral $(i)$-Al-Cu-Fe and $i$-Al-Pd-Mn and the tenfold surface of decagonal $(d)$-Al-Ni-Co quasicrystals. The growth is investigated at 300 and 525 K substrate temperatures and at different coverage $(\ensuremath{\theta})$ ranging from submonolayer to ten monolayers. The film is characterized by scanning tunneling microscopy, reflection high-energy electron diffraction, and x-ray photoelectron spectroscopy. At 300 K, the deposited Bi yields a quasicrystalline film for $\ensuremath{\theta}\ensuremath{\le}1$. For $1l\ensuremath{\theta}l5$, it forms nanocrystallites with (100) surface orientation. The islands have magic heights, which correspond to the stacking of four atomic layers (predominantly). The selection of magic heights is interpreted in terms of quantum size effects arising from the electron confinement within the film thickness. The islands establish rotational epitaxial relationship with the substrate. For higher coverage, the film grows with monatomic height, not with magic heights, and reflects the symmetry of the bulk Bi. When deposition is performed at 525 K, terrace diffusion is more effective, resulting in the aggregation of Bi adatoms developing into a smooth monolayer with quasiperiodic order. At this temperature, multilayers do not adsorb.

IR reflectance spectra and optical constants of Al-Cu-Fe quasicrystalline thin films

The optical properties of Al-Cu-Fe quasicrystalline films and, for comparison, crystalline films of similar composition are studied using middle-and far-IR reflectance spectroscopy. Measurements are performed with 0.1-to 0.3-μm-thick films on sapphire substrates. The complex dielectric function of the films is calculated from experimental data. It is found that the real part of the dielectric function is negative for the crystalline films but positive and weakly frequency dependent, except in the range near 245 cm−1, for the quasicrystalline films. The optical conductivity of the quasicrystalline films does not feature the Drude peak observed for crystalline films and exhibits a peak at 245 cm−1, which can be assigned to optical phonon excitations and is absent for crystalline films.

In situ control of AlCuFe thin film crystallization using optical pyrometry

Al 62Cu 25.5Fe 12.5 quasicrystalline films are formed by annealing of successive and simultaneous deposition of the three elements. In situ pyrometrical control during temperature increase of annealing treatment points to a break in the radiative transfer only during the heating of films obtained by successive deposition. This discrepancy between the two processes is interpreted as being linked to the differing crystallization paths of the two initial mixtures. The discontinuity which appears at 730 K is attributed to the appearance of β and ω-AlCuFe ternary phases in the mixture. In situ pyrometrical control is used to optimize the annealing treatment of this kind of thin deposit and to access a value of heat capacity equal to 710 J/kg K for T > 720 K. This pyrometrical measurement can thus be regarded as a simple way to perform non-destructive differential thermal analysis measurements on ultra thin deposits.

Observations on the growth of Al–Ni–Co decagonal thin films by atomic force microscopy and transmission electron microscopy

Thin films of Al–Ni–Co alloy were produced by vacuum deposition technique using a substrate material of amorphous carbon thin-foil. Attempts were made to obtain a homogeneous decagonal quasicrystalline film, where the preparation technique was based on the direct evaporation of pre-alloyed ingot of Al 72Ni 15Co 13 onto the heated substrates. In order to explore early stages of the decagonal film growth, the Al–Ni–Co films with different thicknesses ranging from 2 nm to 30 nm were deposited on either substrates heated at 500 °C or non-heated substrates. The film samples so obtained were examined mainly by atomic force microscopy in combination with transmission electron diffraction and imaging techniques. On the basis of these observations, deposition conditions necessary for the growth of decagonal phase in the resulting films as well as the growth mechanism of the decagonal film will be discussed.

Preparation of AlCuFe quasicrystalline film by pulsed laser-arc deposition

Formation of stable AlCuFe quasicrystalline thin films by pulsed laser-arc deposition technique is reported in this paper. Using a single-source bulk AlCuFe quasicrystal as target material, AlCuFe film with ideal composition of quasicrystalline phase formation was deposited by suitably controlling the deposition parameters. The as-deposited film was basically in amorphous form. Icosahedral phase appeared after the films were annealed at elevated temperature. AlCuFe film was also deposited by pulsed laser ablation. Comparison of the quality of the films prepared using the two methods indicates that pulsed laser-arc deposition has greater ability in forming AlCuFe quasicrystalline structure.

Steam and Water Lubrication of Quasicrystalline Films

The present work reports on the comparison of tribological properties between quasicrystalline and approximant films under steam and water lubrication. These films have nearly the same stoichiometry, which allows evaluation of the quasicrystalline structure as compared with the crystalline structure of the approximant. The goal of this study is to determine the effects crystal structure has on tribological properties and to study the general tribological behavior of quasicrystals in a steam and water environment. AlCuFe quasicrystals coatings were deposited by unbalanced magnetron sputtering. The test films were 10 μm thick deposited on a 1inch diameter Al2O3 disk and a 1/4inch diameter Al2O3 ball. Data were collected under water and steam lubricated conditions. Friction coefficients and wear rates of quasicrystals and approximants were nearly indistinguishable. During water lubrication, quasicrystals act similar to ceramics where surface smoothing and hydrodynamic lift control the friction and wear properties. With steam-lubricated conditions, the friction and wear process is controlled by brittle fracture and third body abrasion. Generally, less than 5% difference in the friction and wear properties were observed between the icosahedral quasicrystal phase and the approximant phase.

Swelling Behavior of Self-Assembled Monolayers of Alkanethiol-Terminated Poly(ethylene glycol): A Neutron Reflectometry Study

The swelling behavior of alkanethiol-terminated poly(ethylene glycol) with an average molecular weight of 2180 Da (i.e., approximately 45 ethylene glycol, EG, units) in contact with water was investigated by neutron reflectometry as a function of the morphology of the PEG-SH layer. Amorphous films at a low grafting density show significant swelling with an increase of the film thickness from approximately 25 A in the dry state to approximately 70 A in contact with D2O, which corresponds to a total water uptake of approximately 38 mass %. In contrast, quasi-crystalline monolayers exhibit only a small amount of water penetrating into the film (approximately 8 mass %) with a corresponding change of the layer thickness from approximately 110 to approximately 125 A. The water uptake per EG unit corresponds to the literature value of 1.5 for the amorphous layer and to only 0.25 in the case of the quasi-crystalline film.