Amorphous-like Structure Research Articles

Surface modification of 5083 Al alloy by electrical discharge alloying processing with a 75 mass% Si–Fe alloy electrode

This study experimentally investigates the surface modification of 5083 Al alloy by the electrical discharge alloying (EDA) process with a Si–Fe alloy as an electrode. Samples were analyzed by transmission electron microscopy (TEM), scanning electron microscopy (SEM), micro-hardness and corrosion resistance tests. The micro-hardness of EDA alloyed layer was evidently higher than that of the base metal (5083 Al alloy). The TEM results show that the matrix of the alloyed layer has an amorphous-like structure; the matrix contains fine needle-like Si particles, block-like Si particles and nano-size Al4.5FeSi and Al13Fe4 particles. The TEM results support experimental results for the high hardness of the alloyed layer. Moreover, the EDA alloyed layer with composite microstructures has good corrosion resistance in NaCl aqueous solution.

Robust ultra-thin RuMo alloy film as a seedless Cu diffusion barrier

This study investigated the properties of 5 nm-thick RuMo film as a Cu diffusion barrier. The sheet resistance variation and X-ray diffraction patterns show that the RuMo alloy film has excellent barrier performance and that it is stable upon annealing at 725 °C against Cu. The transmission electron microscopy micrograph and diffraction patterns show that the RuMo film is an amorphous-like structure, whereas pure Ru film is a nano-crystalline structure. The elements’ depth profiles, analyzed by X-ray photoelectron spectroscopy, indicate no inter-diffusion behavior between the Cu and Si layer, even annealing at 700 °C. Lower leakage current has been achieved from the Cu/barrier/insulator/Si test structure using RuMo film as the barrier layer. A 5 nm ultrathin RuMo film provided two orders of magnitude improvement in leakage current and also exhibited a 175 °C improvement in thermal stability than that of the pure Ru film. It is a potential candidate as a seedless Cu diffusion barrier for advanced Cu interconnects.

Chemical and electrochemical characterization of TiO2/Al2O3 atomic layer depositions on AZ-31 magnesium alloy

In this study, innovative TiO2/Al2O3 mono/multilayers were applied by atomic layer depositions (ALD) on ASTM-AZ-31 magnesium/aluminum alloy to enhance its well-known scarce corrosion resistance. Four different configurations of ALD layers were tested: single TiO2 layer, single Al2O3 layer, Al2O3/TiO2 bilayer and Al2O3/TiO2/Al2O3/TiO2 multilayer deposited using Al[(CH3)]3 (trimethylaluminum, TMA), and TiCl4 and H2O precursors. All depositions were performed at 120°C to obtain an amorphous-like structure of both oxide layers. The four coatings were then investigated using different techniques, such as scanning electron microscope (SEM), stylus profilometer, glow discharge optical emission spectrometry (GDOES) and polarization curves in 0.05-M NaCl solution. The thickness of all the coatings was around 100 nm. The layers compositions were successfully investigated by the GDOES technique, although obtained data seem to be affected by substrate roughness and differences in sputtering rates between ceramic oxides and metallic magnesium alloy. Corrosion resistance showed to be strongly enhanced by the nanometric coatings, giving lower corrosion current densities in 0.05-M NaCl media with respect to the uncoated substrate (from 10−4 to 10−6 A/cm2 for the single layers and from 10−4 to 10−8 A/cm2 for the bi- and multilayers). All polarization curves on coated samples also showed a passive region, wider for the bi-layer (from −0.58 to −0.43 V with respect to Ag/AgCl) and multilayer (from −0.53 to −0.38 V with respect to Ag/AgCl) structures.

Carbon nanotube growth from catalytic nano-clusters formed by hot-ion-implantation into the SiO2/Si interface

We have studied growth of chirality-controlled carbon nanotubes (CNTs) from hot-implantation-formed catalytic nano-clusters in a thermally grown SiO2/Si substrate. This procedure has the advantage of high controllability of the diameter and the number of clusters by optimizing the conditions of the ion implantation. In the present study, Co+ ions with ion dose of 8×1016cm−2 are implanted in the vicinity of the SiO2/Si interface at 300°C temperature. The implanted Co atoms located in the SiO2 layer has an amorphous-like structure with a cluster diameter of several nm. In contrast, implanted Co atoms in the Si substrate are found to take a cobalt silicide structure, confirmed by the high-resolution image of transmission electron microscope. CNTs are grown by microwave-plasma-enhanced chemical vapor deposition. We have confirmed a large amount of vertically-aligned multi-walled CNTs from the Co nano-clusters formed by the hot-ion-implantation near the SiO2/Si interface.

Bandgap reduction responsible for the improved thermoelectric performance of bulk polycrystalline In2–xCuxSe3 (x = 0−0.2)

α-In2Se3 is of large bandgap (∼1.4 eV) semiconductor and its structure is based on two-layer hexagonally packed arrays of selenium atoms with 1/3 of the sites of indium atoms being empty. Here we report a bandgap Eg reduction due mainly to the formation of a Cu2Se slab in the host In2Se3, which is responsible for the remarkable improvement of thermoelectric performance of bulk polycrystalline In2−xCuxSe3 (x = 0.1–0.2). When x = 0.2 the dimensionless figure of merit ZT and power factor were increased by a factor of 2 and 3, respectively, at 846 K if compared to those of Cu-free In2Se3. Interestingly, an incorporation of Cu into the lattice of In2Se3 results in a change in morphology from amorphouslike structure represented by In2Se3 to a visible polycrystalline form attributed to partial crystallization of the structure. This change enhances lattice thermal conductivities κL over the very low values of In2Se3. However, the enhancement is only moderate because of the effective scattering of phonons in the polycrystalline nanostructure.

Structural Transitions and Magnetic Properties of Ni50Mn36.7In13.3 Particles with Amorphous-Like Phase

The high-energy ball-milling method was used for fabricating Ni50Mn36.7In13.3 fine-sized particles. The as-melt polycrystalline Ni50Mn36.7In13.3 alloy exhibits a 14 M modulated martensite structure at room temperature (RT). The atomic pair distribution function analysis together with the differential scanning calorimetry technique proved that the 14 M modulated martensite transformed to a metastable amorphous-like structure after ball milling for 8 hours. Annealing of the ball-milled particles with the amorphous-like phase first led to the crystallization to form a B2 structure at 523 K (250 °C), and then an ordered Heusler L21 structure (with a small tetragonal distortion) at 684 K (411 °C). The annealed particles undergo different structural transitions during cooling, tailored by the atomic arrangements of the high-temperature phase. Low-field thermomagnetization measurements show that the ball-milled particles with the amorphous-like structure or the atomically disordered crystalline structure exhibit a magnetic transition from the paramagnetic-like to the spin-glass state with decreasing temperature, whereas the crystalline particles with the ordered Heusler L21 structure present a ferromagnetic behavior with the Curie temperature T c ≈ 310 K (37 °C).

Control of c-axis orientation of L1-FePd in dual-phase-equilibrium FePd/Fe thin films

This work establishes a method of controlling the c-axis-oriented structure of α-Fe (soft magnetic)/L10-FePd (hard magnetic) thin films in the dual-phase compositional region in thermal equilibrium. Two types of thin films were prepared; one is a single-layered thin film, and the other is a multilayered film, [FePd(x nm)/Fe(5 nm)]n (x: thickness, n: the number of multilayers), both of which are deposited on silica glass substrates. For single-layered films, the ordering process is retarded by phase separation that requires long-range diffusion. In this case, the ⟨111⟩ oriented domains preferentially grow from the film surface, and the c-axis-oriented structure is not obtained. On the contrary, for multilayered films, each FePd layer can undergo ordering without phase separation subject to the constraint of strong biaxial tensile stress resulting from the difference in the thermal contractions between Fe/FePd film and the silica glass substrate. Consequently, the L10 domains with c-axis orientation in the normal direction of the film surface are preferentially formed in the initial amorphouslike structure, eventually leading to the desired c-axis-oriented structure.

Microstructures and mechanical properties of multi-component (AlCrTaTiZr)N xC y nanocomposite coatings

Multi-component (AlCrTaTiZr)N xC y coatings with the incorporation of quinary metallic elements and different N and C contents were deposited by AlCrTaTiZr/C co-sputtering in an N 2/Ar mixed atmosphere under an AlCrTaTiZr-alloy-target power of 150 W and different C-target powers (0–200 W). At a C-target power of 0 W, an (AlCrTaTiZr)N 0.6 coating with a face-centered cubic solid-solution structure was deposited and exhibited a large columnar structure; its hardness and steady-stage creep strain rate were measured as about 20 GPa and 1.5 × 10 −4 1/s, respectively. By applying a C-target power of 100 W, an (AlCrTaTiZr)N 0.6C 0.2 coating was formed with a fine columnar structure. Owing to the incorporated C atoms, the (111) interplanar spacing of the face-centered cubic structure was increased from 0.249 to 0.253 nm. The hardness increased to 32 GPa and the creep strain rate was lowered to 1.1 × 10 −4 1/s attributed to the introduction of covalent-like bonds, grain refinement and the formation of an amorphous-like and nanocomposite structure. Furthermore, under a C-target power of 200 W, excess C atoms agglomerated to form clusters in the deposited (AlCrTaTiZr)N 0.6C 0.4 coating. Consequently, the hardness slightly decreased to 30 GPa and the creep strain rate increased to 2.4 × 10 −4 1/s.

Microstructural and Corrosion Characteristics of Iron-Silicon Alloyed Layer on 5083 Al Alloy by Electrical Discharge Alloying Processing

In the study, the surface modification of 5083 Al alloy by electrical discharge alloying (EDA) with a 75 mass% ferrosilicon electrode was used to examine the effects of machining parameters (discharge current, pulse duration and duty factor) on the thickness, hardness and surface roughness of the alloyed layer. Experiment results reveal that the thickness tends to increase with the increase in the pulse duration and discharge current. In addition, the micro-hardness evidently higher compared to the substrate. The hardness also increases with the increasing discharge current and pulse duration. TEM examinations show that the matrix of the alloyed layer is an amorphous-like structure, whereas the matrix contains fine needle-like Si particles, block-like Si particles and nano-size Al4:5FeSi and Al13Fe4 particles. The results of EPMA compositional analysis indicate that the alloying elements (Si and Fe) contained in the electrode effectively dissolve in the alloyed layer of 5083 Al alloy and the content of the dissolved alloying elements gradually decreases with the increase in the distance from the discharge surface. Furthermore, the surface roughness increases with the increase in the discharge current and pulse duration. It is also found that the alloyed layer with composite microstructures exhibits sufficient corrosion resistance to NaCl aqueous solutions.

Solid state amorphisation of mechanically alloyed Fe-Co-Nb-B alloys

Fe 61 Co 21 Nb 3 B 15 powder mixture was prepared by mechanical alloying process in a high energy planetary ball mill. Structural and thermal changes of the milled powders were followed by X-ray diffraction (XRD), Mossbauer spectrometry and differential scanning calorimetry (DSC). Both XRD and Mossbauer spectrometry results reveal the formation, after 48 h of milling, of a highly disordered amorphous-like structure where nanometer-sized iron borides were embedded. A mechanical recrystallisation process gives rise to the formation of α-Fe and α-FeCo nanograins on further milling. The occurrence of structural disorder in the milled powders might be confirmed by broad exothermic reaction in the DSC scans which consists of several overlapping exothermic peaks. Such behaviour originates from recovery, strain relaxation, grain growth and crystallisation.

The heat treatment effect on the structure and mechanical properties of electrodeposited nano grain size Ni–W alloy coatings

The Ni–W alloy coatings with tungsten content from 32.5 to 61.2 wt.% were prepared in this study by electro-deposition. Experimental results show that the grain size of Ni–W coatings evaluated by XRD decreased with increasing tungsten content in coatings, however, the micro-hardness increased with increasing tungsten content. As-deposited Ni–61.2 wt.%W coating has amorphous-like structure and the grain size is around 1.5 nm, after annealing at 500 °C, the hardness of the coating is promoted to 1293 Hv owing to formation of Ni 4W and NW precipitates. In addition, the heat-treated Ni–W coatings show a better wear resistance than the as-plated Ni–W coatings.

Crystallographic Properties of Ge/Si Heterojunctions Fabricated by Wet Wafer Bonding

Ge/Si heterojunctions formed by wet wafer bonding were observed using transmission electron microscopy and energy-dispersive x-ray spectroscopy. For the samples annealed at 880°C, there was a transition layer at the heterointerface with modified regions in the Si and Ge extending 20 nm to 30 nm from the interface. In these modified regions, crystal defects were observed, and a large amount of Ge was detected on the Si side of the junction. For the samples annealed at 250°C or 350°C, the transition layers had an amorphous-like structure with a thickness of about 10 nm. No modified layer or enlargement of lattice spacing was observed.

Electroless Ni–Mo–P diffusion barriers with Pd-activated self-assembled monolayer on SiO 2

Ternary Ni-based amorphous films can serve as a diffusion barrier layer for Cu interconnects in ultralarge-scale integration (ULSI) applications. In this paper, electroless Ni–Mo–P films deposited on SiO 2 layer without sputtered seed layer were prepared by using Pd-activated self-assembled monolayer (SAM). The solutions and operating conditions for pretreatment and deposition were presented, and the formation of Pd-activated SAM was demonstrated by XPS (X-ray photoelectron spectroscopy) analysis and BSE (back-scattered electron) observation. The effects of the concentration of Na 2MoO 4 added in electrolytes, pH value, and bath temperature on the surface morphology and compositions of Ni–Mo–P films were investigated. The microstructures, diffusion barrier property, electrical resistivity, and adhesion were also examined. Based on the experimental results, the Ni–Mo–P alloys produced by using Pd-activated SAM had an amorphous or amorphous-like structure, and possessed good performance as diffusion barrier layer.

Selective Crystalline Seed Layer Assisted Growth of Vertically Aligned MgZnO Nanowires and Their High-Brightness Field-Emission Behavior

This article reports a new approach for fabricating vertically aligned MgZnO nanowire arrays using selective crystalline seed layers deposited at relatively high temperatures by metalorganic chemical vapor deposition. In the phase-separated MgZnO seed layers, Zn-rich regions with a wurtzite structure allowed the growth of slim MgZnO nanowires, while the Mg-rich seeds with a cubic or amorphous-like structure hindered the formation of nanowires. The photoluminescence of these nanowires showed a remarkable increase in the activation energy of the excitons, ∼100 meV. The field-emission performance showed excellent emission behavior with extremely improved brightness, ∼80 times higher current density than that of the ZnO nanowires grown under the same conditions. Models for the growth evolution of slim nanowires on Si substrates were also proposed, based on microstructural characterization.

Reduction of magnetic grain size of perpendicular recording media with CoCrW seed layer

We report the use of CoCrW seed layer (SL) for making the fine grain granular structure and high crystalline orientation of CoCrPt-oxide magnetic recording layer. It is found that CoCrW SL should be of amorphouslike structure to make fine grain of CoCrPt-oxide magnetic layer. Moreover, the smooth surface of CoCrW SL provides high crystalline orientation of the CoCrPt-oxide magnetic layer.

An investigation on the transition characteristics of the wood cell walls during carbonization

The structural changes of the cell wall and crystalline cellulose of Quercus variabilis wood in a pyrolysis system at several temperatures ranging from 250 to 500°C were investigated to examine the wood carbonization characteristics. The volume of the wood sample was decreased and the weight loss was increased by increasing the carbonization temperature. Vessels collapsed severely in tangential direction during the charring process above 350°C. SEM observation indicated that the layering structure of the walls in wood fibers and parenchyma cells were retained below 300°C. However, the cell walls above 350°C changed to an amorphous-like structure without cell wall layering. X-ray diffraction confirmed that the cellulose crystalline substance was still remained at the carbonization temperature of 300°C but was not detected above 350°C. It can be concluded that the transition from Q. variabilis wood to charcoal might occur at approximately 350°C.

Atomic and electronic structure transformations of silver nanoparticles under rapid coolingconditions

The structural evolution and dynamics of silver nanodropsAg2869 (4.4 nm in diameter) under rapid cooling conditions have been studied by meansof molecular dynamics simulations and electronic density of state calculations.The interaction of silver atoms is modelled by a tight-binding semiempiricalinteratomic potential proposed by Cleri and Rosato. The pair correlation functionsand the pair analysis technique are used to reveal the structural transition inthe process of solidification. It is shown that Ag nanoparticles evolve intodifferent nanostructures under different cooling processes. At a cooling rate of1.5625 × 1013 K s−1 the nanoparticles preserve an amorphous-like structure containing a large amount of 1551and 1541 pairs which correspond to icosahedral symmetry. For a lower cooling rate(1.5625 × 1012 K s−1), the nanoparticles transform into a crystal-like structure consisting mainly of 1421 and1422 pairs which correspond to the face centred cubic and hexagonal close packedstructures, respectively. The variations of the electronic density of states for thedifferently cooled nanoparticles are small, but in correspondence with the structuralchanges.

Grain Boundary Characteristics Evaluation by Atomistic Investigation Methods

AbstractThe grain boundary has been recognized for one of the major defect structures in determining the material strength. It is increasingly important to understand the individual characteristics of various types of grain boundaries due to the recent advances in material miniaturization technique.In the present study three types of grain boundaries of coincidence site lattice (CSL), small angle (SA), and random types are considered as the representative example of grain boundaries. The grain boundary energies and atomic configurations of CSL are first evaluated by first-principle density functional theory (DFT) and the embedded atom method (EAM) calculations. SA and random grain boundaries are subsequently constructed by the same EAM and the fundamental characteristics are investigated by the discrete dislocation mechanics models and the Voronoi polyhedral computational geometric method. As the result, it is found that the local structures are well accorded with the previously reported high resolution-transmission electron microscope (HR-TEM) observations, and that stress distributions of CSL and SA grain boundaries are localized around the grain boundary core. The random grain boundary shows extremely heterogeneous core structures including a lot of pentagon-shaped Voronoi polyhedral resulting from the amorphous-like structure.

Influence of Fiber Surface Structure on Interfacial Structure between Fiber and Matrix in Vapor Grown Carbon Fiber Reinforced Aluminum Matrix Composites

Vapor grown carbon fiber reinforced pure aluminum matrix composites were fabricated by the hot-pressing method below the melting temperature of pure aluminum. The surface structures of the vapor grown carbon fibers and the interfacial structures between the fibers and the matrix in the composite were observed. The precipitation mechanism of crystalline aluminum carbide was also investigated. An interlayer with an amorphous-like structure formed at the interface between the carbon surface structure and the aluminum matrix. This interlayer between the wave or irregular carbon structure and the matrix grew more rapidly than that formed between the linear carbon surface structure and the matrix. The thickness of the interlayer increased with the increased fabrication temperature of the composite. Crystalline aluminum carbide could not easily be precipitated in the composite fabricated below 933 K owing to the thicker interlayer separating the vapor grown carbon fibers and aluminum. By either extending the heat-treatment time to 18 ks or increasing the fabrication temperature to 933 K, we could promote the precipitation of crystalline aluminum carbide in the composite. After heat-treating the composite produced at 933 K, aluminum carbide crystals precipitated from the stacked carbon lamellae at the interface between the fibers and the matrix. [doi:10.2320/matertrans.MRA2008350]

Morphology, structure, chemical composition, and light emitting properties of very thin anodic silicon films fabricated using short single pulses of current

In this work, the morphology, structure, surface chemical composition, and optical properties of very thin (10–70 nm) anodic silicon films grown on a silicon substrate by electrochemical dissolution of bulk crystalline silicon in the transition regime between the porous formation and electropolishing were investigated in detail. Anodization was performed by using short single pulses of anodization current in low and high hydrofluoric acid (HF) concentration electrolytes. A systematic comparison was made between films grown at low and high HF concentration electrolytes. The morphology and structure of the films were investigated by combining atomic force microscopy and transmission electron microscopy (TEM), while x-ray and ultraviolet photoelectron spectroscopies were used to investigate the chemical composition of the films. Photoluminescence was used to investigate the optical properties. It was found that films that formed at low HF concentrations were much thinner than films that formed at high HF concentrations due to surface dissolution of the films during anodization. High resolution TEM images revealed an amorphouslike structure (porous) in all of the films in which discrete Si nanocrystals (NCs) were identified. NC size was, on the average, larger in films fabricated in low HF concentration electrolytes and these films were not luminescent. On the other hand, films fabricated in high HF concentration electrolytes were thicker and contained smaller NCs. A silicon oxide layer covered the internal surface of all films, this oxide being much thinner in films grown at high HF concentrations. This last effect was attributed to self-limiting oxidation of the very small NCs constituting these films.