Structure of liquid Al-Cu-Co alloys near the quasicrystal-forming range

A local short-to-intermediate range order in liquid Al_63.9Cu_19.4Co_16.7, Al₇₁Cu₆Co₂₃, and Al_6oCu₂₉Co₁₁ alloys was investigated by X-ray diffraction technique and the reverse Monte Carlo modeling. A prepeak at Q ~ 17 nm^− 1originating from the unique bonding between the TM-TM pair (TM = Co, Cu) is observed in the structure factors of all investigated melts. The Voronoi-Delaunay analysis of RMC models indicates that a medium-range ordering of TM atoms in dense non-crystalline polytetrahedral clusters is associated with a chemical short-range order. The icosahedral short-range order is also closely related to the dense packing polytetrahedral clusters. A decrease of temperature leads to an enhancement of both chemical short-range order and icosahedral short-range order.     

Chess 2001 users' meeting

Diamonds attract enormous interest as gemstones. This rather frivolous “application” is based on their optical properties and contributes about 95 percent of the turnover in the diamond industry. Another area of application, which may now be seen as a crude application, is a diamond-tipped tool for the abrasive and cutting industries. These applications exploit the hardness and wear resistance of diamond, and dominate the demand for synthetic diamond production. These applications do not place the most stringent requirements on the quality of diamond. As has become clear at this workshop, a crucial new role for diamond in an ultra-high technology area is emerging. Diamond devices at synchrotrons require near– theoretical values of perfection of the diamond lattice. This material is vital to the continued increase in beam performance as well as the expansion of the suite of measurement techniques of modern synchrotrons.

An international workshop on “diamond single crystals for 3rd and 4th generation X-ray sources” was held in Grenoble, France, on May 24–25, 2004.     

Low-angle boundary investigation in silicon single crystals

Low-angle boundaries in Si single crystals grown from the melt in [111], [100], [112], [110], [118] and [115] directions were investigated by chemical etching, copper decoration technique and X-ray topography. — LAB of four types were found in planes parallel to the crystal growth axes. Rearrangement of dislocations from slip bands into LAB was observed in heavily-doped Si crystals. The origin of LAB in melt grown Si crystals is discussed. It is shown that these boundaries are well interpreted in terms of dislocation alignment formation in the thermal stress field of the growing crystal.     

Increase in fatigue life of steels by electron-beam processing

Increase in fatigue life (by 3.5 times) of steels of different structural classes has been determined. By methods of transmission diffraction electron microscopy the variation of structure, phase composition and defective substructures parameters of material surface layer at different scale levels (from micro to nano) and the suppression of processes contributing to the formation of regions being the potential site of submicrocracks’ formation has been analyzed.     

Effect of Rhodium on the Properties of Bifunctional M x O y /ZrO2 Catalysts in the Reduction of Nitrogen Oxides by Hydrocarbons

Scanning electron microscopy, TPDA, XPE and IR spectroscopy were used to study the physicochemical indices of rhodium-promoted Rh-M _x O _y /ZrO₂ oxide catalysts (M = Cr, Ce, Co). The enhancement of the redox properties of the oxide catalysts upon the introduction of rhodium does not alter their bifunctional nature in SCR activity; these catalysts have both redox and strong acid B-sites.     

X-ray diffraction study of Al-Si melts

New layered metal-organic coordination polymers [Zn₃(bpdc)₃(DMA)₂]·3DMA (1) (H₂bpdc = 4,4′-biphenyldicaboxylic acid, DMA = N,N′-dimethylacetamide) and [Zn₃(bdc)₃(im)₂]·1.5H₂O (2) (H₂bdc = terephtalic acid, im = imidazole) are synthesized and characterized by X-ray crystallography.     

Formation of Nanoscale T-Shaped Gates Using Directional Angular Deposition of Thin Aluminum Films

Russian Physics Journal - This paper presents the technology of fabrication of T-shaped gates for GaAs transistors using optical lithography and a unique method of directional angular deposition of...     

A Mechanical Testing Capability for Measuring the Microscale Deformation Behavior of Structural Materials

High energy x-ray diffraction can be used to probe the crystal scale mechanical response of polycrystalline alloys. Recently there have been several efforts to create new high energy x-ray experiments. These include the lattice Strain Pole Figure (SPF) technique. By measuring lattice strains in thousands of directions, the lattice strain tensor associated with each orientation can be determined. The focus of this paper is on transforming the SPF technique from a one-off style experiment to a measurement capability. Such a standardization process is of the utmost importance for the field of mechanics of materials and shifts the discovery associated with these experiments from the measurements themselves, to what they reveal about the material. We define a new technique for quantifying how effectively a set of lattice strain measurements (SPFs) probes each crystal orientation. The polycrystal sampling matrix, defined G^*{\boldsymbol\Gamma^*}, represents the mapping between the most likely strain tensor for each orientation and the lattice strain results. The orientation space sampling matrix, defined G (R){\boldsymbol\Gamma ({\bf R})}, represents the set of lattice strain measurements that interrogate each crystal orientation. The rank of G (R){\boldsymbol\Gamma ({\bf R})} can be used to quantitatively compare different experimental configurations and systematically investigate G^*{\boldsymbol\Gamma^*}. The net result is a new tool for selecting experimental conditions to produce optimal sets of SPF data. Results are shown for different experiment configurations and an example of the SPF technique is provided for the Low Solvus High Refractory (LSHR) nickel base superalloy. In addition, we show that for the face centered cubic LSHR, with lattice strains measured for the {111}, {200}, {220}, and the {311} crystallographic families, there are at most 25 lattice strain measurements that interrogate a single orientation.     

Relationship between chemical and icosahedral local orderings in Al-Ni-Fe melts

An X-ray diffraction study and simulation of the structure of ternary Al_81.6Ni_14.9Fe_3.5, Al_71.6Ni₂₃Fe_5.4, and Al_61.1Ni_31.1Fe_7.3 melts by the reverse Monte Carlo method are conducted. An analysis of the structural models of melts is performed by the Voronoi-Delaunay partition. It is shown that the prepeak on the structure factor curves in the diffraction vector range of 13 nm⁻¹ to 22 nm⁻¹ is due to two factors: chemical ordering of atoms and non-crystalline close packing. The origin of the icosahedral short-range order in the melts as one of the variants of ordering of atoms in non-crystalline close packed clusters is discussed.     

Spatial structure of a focused X‐ray beam diffracted from crystals

The spatial structure of a beam focused by a planar refractive lens and Bragg diffracted from perfect silicon crystals was experimentally studied at the focal plane using a knife‐edge scan and a high‐resolution CCD camera. The use of refractive lenses allowed for a detailed comparison with theory. It was shown that diffraction leads to broadening of the focused beam owing to the extinction effect and, for a sufficiently thin crystal, to the appearance of a second peak owing to reflection from the back surface. It was found that the spatial structure of the diffracted beam depends on whether the crystal diffracts strongly (dynamically) or weakly (kinematically). The results help to understand the physical origin of the diffracted intensity recorded in a typical microbeam diffraction experiment.