The role of argon in plasma-assisted deposition of indium nitride

Radiofrequency (RF) nitrogen plasma sources are commonly employed in the growth of group III-nitrides by molecular beam epitaxy and reactive evaporation. These sources produce atomic nitrogen and excited molecules (N₂*). In this work the relative flux of these two species produced by an RF source was studied by emission spectroscopy as a function of power, pressure, and argon dilution. Polycrystalline indium nitride thin films were synthesized under the same conditions. It was found that argon dilution had a strong influence on the production of active nitrogen, with maximum fluxes obtained around ∼40% N₂. Film properties, as measured by X-ray diffraction, atomic force microscopy and Hall effect, were also optimized at this condition. It was observed that the Hall mobility scaled with the sum of N and N₂* emission, suggesting that both species may be beneficial for InN growth.     

Structure and dynamics of levitated liquid aluminates

We used the aerodynamic levitation technique combined with CO₂ laser heating to study the structures of liquid CaAl₂O₄ and MgAl₂O₄ above their melting point with X-ray and neutron diffraction. We determined the structure factors and corresponding pair correlation functions describing the short-range order in the liquids. The combination of the two scattering techniques makes it possible to derive information not accessible with a single measurement. We also obtained information on the dynamics of liquid MgAl₂O₄ with inelastic X-ray scattering. In particular, we determined the sound velocity and the longitudinal viscosity.     

Physico-chemical processes in single crystal growing of calcium aluminates by zone melting

The growing of single crystals of calcium aluminates of compositions 12 CaO · 7 Al₂O₂, CaO · Al₂O₃, and CaO · 2 Al₂O₃ by zone melting under vacuum of 10⁻⁵ mm Hg permitted to establish that some of the Al³⁺ ions in octahedral coordination have been driven back by the moving crystallization front. Energetically, this process can be represented on the basis of the viscous flow model with the activation energy of −45 kcal/mole. The possible mathematical models have been considered for the processes of preparation of single phase crystals of the aluminates mentioned above which take account of incongruent vaporization of the component oxides and refining of the melt from structural impurities by the moving crystallization front.     

Sublimation crystal growth of yttrium nitride

The sublimation–recombination crystal growth of bulk yttrium nitride crystals is reported. The YN source material was prepared by reacting yttrium metal with nitrogen at 1200 °C and 800 Torr total pressure. Crystals were produced by subliming this YN from the source zone, and recondensing it from the vapor as crystals at a lower temperature (by 50 °C). Crystals were grown from 2000 to 2100 °C and with a nitrogen pressure from 125 to 960 Torr. The highest rate was 9.64×10⁻⁵ mol/h (9.92 mg/h). The YN sublimation rate activation energy was 467.1±21.7 kJ/mol. Individual crystals up to 200 μm in dimension were prepared. X-ray diffraction confirmed that the crystals were rock salt YN, with a lattice constant of 4.88 Å. The YN crystals were unstable in air; they spontaneously converted to yttria (Y₂O₃) in 2–4 h. A small fraction of cubic yttria was detected in the XRD of a sample exposed to air for a limited time, while non-cubic yttria was detected in the Raman spectra for a sample exposed to air for more than 1 h.     

Sol-gel synthesis of erbium-doped yttrium silicate glass-ceramics

Yttrium silicate glasses and glass-ceramics were prepared by the sol-gel process. Yttrium nitrate was added to tetraethyl orthosilicate in amounts representing between 0.2 and 20 mol%, as well as amounts corresponding to the disilicate composition. Some samples were doped with erbium acetate. The solutions underwent gellation in 2-7 days and were dried for 2 weeks. Differential thermal analysis was used to design a multi-step heat treatment to 1000 °C to densify samples to transparent or translucent monoliths. Above 1000 °C, samples crystallized to yttrium disilicate and cristobalite. Phase separation before crystallization influenced the formation of the crystal phases.     

Structural fluctuations in argon and gold microclusters

A set of extensive molecular dynamics simulations of clusters of 79 argon and gold atoms is performed to investigate structural fluctuations in microclusters. Within a finite range of total energy, the cluster exhibited structural fluctuations between solid-like and liquid-like states and among different solid-like states. Based on the simulations, it may be concluded that the thermal expansion of the cluster initiates the structural fluctuations. The qualitative features are the same for argon and gold microclusters.     

Short range order in powder of amorphous anodic yttrium oxide

The characteristics of the short-range order in a powder of amorphous yttrium oxide obtained by anodic oxidation are determined by the Finbak-Warren method. It is established that the first coordination number equals seven. Amorphous oxide is built by irregular coordination polyhedra characteristic of the hexagonal and monoclinic modifications of yttrium oxide.     

Crystal structure of an yttrium nitrate complex with tetramethylurea

An X-ray diffraction study of Y(NO₃)₃ · 3TMU crystals is performed (heavy-atom method, difference electron-density maps, H atoms in calculated positions, full-matrix anisotropic-isotropic (H) least-squares refinement). The crystals are monoclinic, a = 9.353(1) Å, b = 15.966(3) Å, c = 18.805(8) Å, β = 95.41(2)°, Z = 4, and space group P2₁/c. The structural units of the crystals are molecular complexes. The coordination number of the Y atom is nine due to three bidentate NO₃ groups and three monodentate tetramethylurea molecules. The mean Y-O bond lengths are 2.464 and 2.274 Å for NO₃ and tetramethylurea, respectively.     

Growth and microscopic studies of yttrium aluminium garnet single crystals

A study has been made to understand the growth history and growth mechanism of flux grown yttrium aluminium garnet (YAG) single crystals. Etching has been done to reveal the growth patterns of flux grown crystals. Optical and scanning electron micrographs are presented. Optical micrographs were taken under polarised light and oblique incident light. The nature and origin of growth hillock is elucidated.     

Luminescence characteristics of Yb, La codoped yttrium oxide nanopowders

Luminescence characteristics of Yb³⁺, La³⁺ codoped yttrium oxide nanopowders were investigated. The grain size and the crystallinity of (Yb_0.05Y_0.90La_0.05)₂O₃ nanopowders increase with the increase of calcination temperature. The average grain size of the nanopowders calcined at 1100 °C is 66 nm and its cooperative up-conversion luminescence centered at 498 nm was detected due to nanometer size effect and perfect crystallinity. However, the cooperative up-conversion luminescence of (Yb_0.05Y_0.90La_0.05)₂O₃ transparent ceramics was not detected.     

Annealing-induced relief of compressive misfit strain in liquid phase epitaxial yttrium iron garnet films

Films of yttrium iron garnet were grown on (111) gadolinium gallium garnet by liquid phase epitaxy from a PbO-B₂O₃ flux. Incorporation of Pb as a substitutional impurity produced an increase in film lattice parameter which resulted in initial compressive misfit strains in the films. The initial strains were relieved by annealing in O₂. The relief process was studied by X-ray double-crystal diffractometry and topography supplemented by optical and scanning electron microscopy. Strain relief was found to be associated with the occurrence of defects which were imaged in both film and substrate topographs. When the initial compressive misfit was sufficiently large, annealing eventually resulted in a tensile strain and the development of cracks which propagated through the films and into the substrates.     

The role of iron ions in laser ruby

Doping possibility of long ruby crystals grown by Czochralski method under reducing protective atmosphere by iron ions in described. Using the admixture of hydrocarbons to the protective atmosphere this dopage may be realized. Iron ions increases damage threshold of the Q-switched laser ruby rods.     

Adjusting valence state of europium in sintered porous glass by adding of aluminum and yttrium

We report on valence state adjusting of europium in porous glass by co-doping with aluminum or yttrium into porous glass. The influence of Al³⁺ and Y³⁺ on the emission intensity of Eu³⁺ and Eu²⁺ in sintered high-silica porous glass has been investigated. It is found that the emission intensity of Eu³⁺ can be increased by adding of Y³⁺ and Al³⁺, and the emission intensity of Eu²⁺ can be decreased by adding of Y³⁺ and increased by Al³⁺. At the same time, the emission peak position of Eu²⁺ can also be changed by adding of Al³⁺ or Y³⁺. It is suggested that the adjusting of valence state and the peak position shift is relative to the optical basicity of glasses or crystal field strength around REs.     

Enhanced glass-forming ability of a Zr-based bulk metallic glass with yttrium doping

A significant enhancement in glass formation in a newly developed Zr₅₁Cu_20.7Ni₁₂Al_16.3 alloy has been achieved by yttrium doping. With just 0.5 at.% yttrium doping, the critical diameter of the as-cast alloys for glass formation has been increased from 3 mm to at least 10 mm. In the undoped, large-sized alloys, massive oxygen stabilized crystalline phases are observed but disappear in yttrium doped alloys. Very small amounts of stable α-Y₂O₃ phases found in the yttrium doped alloys, and their negligible effect on the metallic glasses’ properties, provide a superior solution to achieve metallic glasses with a high glass formability.