Shear-induced chemical segregation in a Fe-based bulk metallic glass at room temperature

Shear-induced segregation, by particle size, is known in the flow of colloids and granular media, but is unexpected at the atomic level in the deformation of solid materials, especially at room temperature. In nanoscale wear tests of an Fe-based bulk metallic glass at room temperature, without significant surface heating, we find that intense shear localization under a scanned indenter tip can induce strong segregation of a dilute large-atom solute (Y) to planar regions that then crystallize as a Y-rich solid solution. There is stiffening of the material, and the underlying chemical and structural effects are characterized by transmission electron microscopy. The key influence of the soft Fe–Y interatomic interaction is investigated by ab-initio calculation. The driving force for the induced segregation, and its mechanisms, are considered by comparison with effects in other sheared media.

Investigation on the Origin of Magnetization in Plastically Deformed NI51TI49 Alloy

The article deals with the investigation of structure and magnetic properties of plastically deformed Ni51Ti49 alloy. The magnetic hysteresis loops confirm the presence of ferromagnetic properties in the alloy. The transmission electron microscopy (TEM) detects the appearance of lenticular crystals with bending contours which indicate the large distortion of the crystal lattice. The crystal lattice curvature occurs due to the large atom displacement. As a result, icosahedral clusters with the Frank-Kasper (FK) structure can be formed. The spin-polarized density of electron states and the magnetic moments for both non-deformed (near-spherical structure) and deformed (elongated by 5% along the Z-axis) Ni7Ti5 (FK-12), Ni8Ti5 (FK-13), and Ni10Ti6 (FK-16) clusters are calculated for the explanation of possibility of magnetization appearance in Ni51Ti49 alloy. The calculations show the increase in the magnetic moments for the deformed clusters. The calculated spectra demonstrate the high density of electron states near the Fermi level which is a characteristic feature of ferromagnetic alloys.

Atomic structure and phason modes of the Sc–Zn icosahedral quasicrystal

The detailed atomic structure of the binary icosahedral (i) ScZn7.33quasicrystal has been investigated by means of high-resolution synchrotron single-crystal X-ray diffraction and absolute scale measurements of diffuse scattering. The average atomic structure has been solved using the measured Bragg intensity data based on a six-dimensional model that is isostructural to the i-YbCd5.7one. The structure is described with a quasiperiodic packing of large Tsai-type rhombic triacontahedron clusters and double Friauf polyhedra (DFP), both resulting from a close-packing of a large (Sc) and a small (Zn) atom. The difference in chemical composition between i-ScZn7.33and i-YbCd5.7was found to lie in the icosahedron shell and the DFP where in i-ScZn7.33chemical disorder occurs on the large atom sites, which induces a significant distortion to the structure units. The intensity in reciprocal space displays a substantial amount of diffuse scattering with anisotropic distribution, located around the strong Bragg peaks, that can be fully interpreted as resulting from phason fluctuations, with a ratio of the phason elastic constantsK2/K1= −0.53,i.e.close to a threefold instability limit. This induces a relatively large perpendicular (or phason) Debye–Waller factor, which explains the vanishing of `high-Qperp' reflections.

The local structure of skutterudites: A view from inside the unit cell

The skutterudites form a large class of compounds with many unusual properties, attributed in part to the novel crystal structure. The unit cell is cubic and is composed of eight sub-cubes formed by transition metal atoms. Six of the sub-cubes contain rings of atoms; the other two sub-cubes can be empty but are usually filled with rare earth or alkali earth atoms. These “filler” atoms can vibrate at low energies and hence are called “rattler” atoms. Here, the dynamics of various atom pairs are reviewed with a focus on the rattler atoms. Most of the work is based on extended X-ray absorption fine structure (EXAFS) studies but results obtained using other techniques, such as inelastic scattering experiments or atomic displacement parameters in diffraction, are also included. Although the main framework of the unit cell is often considered quite stiff, the stiffest springs in the system are only factors of 3–5 larger than the springs connecting the rattler to its neighbors. In addition, the environment about the atoms in the ring structures (e.g. Sb4 in CeFe4Sb[Formula: see text]) has a low symmetry and our recent EXAFS experiments suggest that the rings can be considered to be quasi-rigid units, and treated as a large atom. The restoring forces on the rings are asymmetric, with large forces perpendicular to the ring and weak forces in the direction toward a rattler. This suggests that some low energy modes that have been observed in these systems may be a correlated motion of the rattler atoms and the rings. In addition, the unusual result that the second neighbor effective spring constants are stiffer than the nearest neighbor bonds has been observed for several oxy-skutterudites. A simple one-dimensional (1D) model, of a chain of rattlers and rings, weakly coupled to the rest of the lattice has been developed which can explain these unusual results. These calculations also indicate that the thermal conductivity might be further suppressed using a composite formed of several types of nanoparticles rather than just multiple filling on the rattler sites.

Stability and Microstructure Characterization of Barrierless Cu (Sn, C) Films

Thermal stability, adhesion and electronic resistivity of the Cu alloy films with diffusion barrier elements (large atom Sn and small atom C) have been studied. Ternary Cu (0.6 at.% Sn, 2 at.% C) films were prepared by magnetron co-sputtering in this work. The microstructure and resistivity analysis on the films showed that the Cu (0.6 at.% Sn, 2 at.% C) film had better adhesion with the substrate and lower resistivity (2.8 μΩ·cm, after annealing at 600 °C for 1 h). Therefore, the doping of carbon atoms makes less effect to the resistivity by decreasing the amount of the doped large atoms, which results in the decreasing of the whole resistivity of the barrierless structure. After annealing, the doped elements in the film diffused to the interface to form self-passivated amorphous layer, which could further hinder the diffusion between Cu and Si. So thus ternary Cu (0.6 at.% Sn, 2 at.% C) film had better diffusion barrier effect. Co-doping of large atoms and small atoms in the Cu film is a promising way to improve the barrierless structure.

Coupling a Single Trapped Atom to a Nanoscale Optical Cavity

Hybrid quantum devices, in which dissimilar quantum systems are combined in order to attain qualities not available with either system alone, may enable far-reaching control in quantum measurement, sensing, and information processing. A paradigmatic example is trapped ultracold atoms, which offer excellent quantum coherent properties, coupled to nanoscale solid-state systems, which allow for strong interactions. We demonstrate a deterministic interface between a single trapped rubidium atom and a nanoscale photonic crystal cavity. Precise control over the atom's position allows us to probe the cavity near-field with a resolution below the diffraction limit and to observe large atom-photon coupling. This approach may enable the realization of integrated, strongly coupled quantum nano-optical circuits.