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Luminescence properties of the transition-metal chromium-doped gallium nitride (GaCrN) epitaxial layers on sapphire substrates have been extensively studied by varying the doping level, excitation intensity, and temperature of study. Photoluminescence spectra of the doped films were found to be dominated by an excitonic peak around 3.25–3.29 eV in accordance with the doping level, due to the transition of neutral-donor bound excitions of GaCrN cubic modification. It is attributed that Cr, which is an acceptor in GaN matrix, acts as a surfactant and modifies the growth kinetics to induce phase modification from wurtzite to zinc blende of GaN. Moreover, Cr doping induced a blue band centered around 2.9 eV, which is a donor-acceptor pair, and also two bound excitonic lines at 3.36 and 3.31 eV at some locations of the sample: the expected origin of these is due to the transitions of excitons bound at the stacking faults which are formed due to the co-existence of hexagon and cubic modifications of GaN. The Raman-scattering spectra have also showed both the wurtzite GaN characteristic phonon signal E2 (high) at 568 cm-1 and cubic GaN (TO)-phonon signal at 553 cm-1, and confirmed the existence of polymorphism in the doped films. High-resolution transmission electron microscopy and selected area electron-diffraction patterns give a visual comparison and authenticate the doping-induced polymorphism in the GaCrN films. [ABSTRACT FROM AUTHOR]

Finely dispersed hard magnetic L1o-FePtCu nanoparticles with 〈100〉 orientation were directly synthesized by RF-sputtering on NaCl substrate at a temperature of 613 K. The maximum coercivity of the particles was 1.4 kOe (at RT). Degrees of atomic long-range order (LRO) for the L1o-FePtCu nanoparticles with different sizes were obtained using nanobeam electron diffraction technique. The decrease of LRO parameter became remarkable when the size became below 8 nm. The coercivity value also decreased with decreasing the particle size. The relation between the LRO parameter decrease and the coercivity decrease with particle size was discussed. [ABSTRACT FROM AUTHOR]

Thermal annealing-induced recrystallisation in Fe ion-implanted Si was investigated by transmission electron microscopy. Single crystals of Si(111) were implanted with 120 keV Fe ions to a fluence of 1.0×1017 cm-2 at cryogenic temperature. A buried amorphous Fe-Si layer in an amorphous Si matrix was formed in the as-implanted sample. Nanobeam electron diffraction revealed that metastable α-FeSi2 precipitates embedded in the amorphous Si matrix were formed after annealing at 350 °C for 8 h. The formation of this α-FeSi2-derived phase was unusual, because it has been observed only in epitaxially grown thin films. Based on the Fe1-xSi (02 in the amorphous matrix. [ABSTRACT FROM AUTHOR]

The atomistic structure of a high-strength Cu42.5Ti41.5Ni7.5Zr2.5Hf5Si1 bulk metallic glass prepared by copper-mould casting has been characterized by transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). High-resolution TEM and high-angle annular dark-field observations revealed that crystalline nanoparticles with sizes less than 10?nm are embedded in an amorphous matrix. It was confirmed by energy-dispersive X-ray spectroscopy in combination with STEM that these nanoparticles possess higher copper content than the amorphous matrix. Nanobeam electron diffraction experiments indicated that their crystalline structure is basically face-centred cubic with ordered atomic arrangements. [ABSTRACT FROM AUTHOR]

Thin films of FePt nanoparticles were prepared by co-deposition of Fe and Pt on to amorphous C films kept at 350°C. As-prepared films were composed of disordered Fe-Pt nanoparticles with a fcc structure, where twinned and multiply twinned Fe-Pt nanoparticles could be identified by transmission electron microscopy (TEM) and electron diffraction. Atomic ordering from fcc to L1 0 structure was followed by in-situ TEM observation during heating up to 750°C. Multiply twinned (fivefold) nanoparticles of the L1 0 FePt were observed for the first time by high-resolution TEM observation. In these nanoparticles the crystallographic c axes of L1 0 structure is oriented parallel to the film plane in each segment. The stability of the fivefold FePt nanoparticles is briefly discussed. [ABSTRACT FROM AUTHOR]

Martensitic transformations in nanometre-sized particles of Au-Cd alloys of near-equiatomic compositions were studied by means of transmission electron microscopy and electron diffraction. The alloy particles with an average size of several nanometres were prepared by high-vacuum electron-beam deposition. In the as-deposited state the particles were crystalline and possessed a B2-type structure at room temperature, similar to that of the β[sub 2] phase in the corresponding bulk. The β[sub 2]-phase particles with an average composition of Au-44.5 at.% Cd were transformed at 76 K into an orthorhombic structure similar to that of the γ′[sub 2] phase in the bulk, while those with an average composition of Au-50.2 at.% Cd were transformed at 60 K into a trigonal structure similar to that of the ζ ′[sub 2] phase in bulk. The temperature parameter in the Debye-Waller factor measured at room temperature for the β[sub 2]-phase particles was roughly four times that for Au in the bulk. It was thus found that the M[sub s] temperatures for the β[sub 2] → γ ′[sub 2] and β[sub 2] → ζ ′ transformations in the nanometre-sized particles were lowered far below room temperature despite the increasing surface area and the enhanced lattice softening. Their reverse transformations, however, took place on heating to room temperature. It was thus seen that the lowering of the transformation temperatures was due to the decrease in the thermodynamic equilibrium temperatures T[sub 0] between the β[sub 2] and γ ′[sub 2] and between the β[sub 2] and ζ ′ phases. The decrease in T[sub 0] indicated that the free energies of the β[sub 2], γ ′[sub 2] and ζ ′[sub 2] phases of the alloys in the small-particle state are definitely different from those in the bulk state. [ABSTRACT FROM AUTHOR]

Two different eosinophil chemotactic factors (delayed ECF-a and ECF-b) were isolated from the delayed phase (24 hr old) of eosinophil-rich inflammatory reaction sites induced by DNP-ascaris extract, which could be separated by DEAE- Sephadex. Both the factors were thermolabile (56°, 30 min) and had a mol. wt of about 70,000, whereas they were clearly different in antigenicity. Delayed tissue eosinophilia was shown to be mediated by peritoneal exudate cells (PEC) and serum from immunized donors to recipients. A chemotactic factor, closely resembling a delayed ECF-a, was isolated from the skin lesions of recipients transferred by sensitized PEC and challenged. Another factor, closely resembling a delayed ECF-b, was isolated from those of recipients transferred by immune serum and challenged. Furthermore, we have shown that delayed ECF-b, but not delayed ECF-a, shared a common antigenicity with some guinea-pig serum component. Thus we concluded that delayed tissue eosinophilia was mediated by the combined actions of two different factors, delayed ECF-a and ECF-b. [ABSTRACT FROM AUTHOR]

An eosinophil chemotactic factor (ECF) was produced in the cell-free culture supernatants (CFS) of peritoneal exudate cells (PEC) from guinea-pigs immunized with dinitrophenyl derivatives of ascaris extract (DNP-As), when stimulated by the antigen in vitro without activation by immune complexes. A 2 or 6 hr pulse of the antigen was sufficient for ECF production, whereas long time incubation (48 hr) was required for the production of a sufficient amount of the factor. Treatment of PEC by cycloheximide resulted in the reduction of ECF production, suggesting that protein synthesis is essential. Its generation appeared carrier-specific and the source of the factor is presumed to be lymphocytes, probably T lymphocytes. The factor with a molecular weight of 70,000 shared a common antigenicity with delayed eosinophil chemotactic factor-a (delayed ECF-a), which was isolated from the skin lesions showing delayed tissue eosinophilia in vivo. [ABSTRACT FROM AUTHOR]

Tissue eosinophilia in active cutaneous anaphylaxis reactions is biphasic: the early phase (6 hr) is induced by a low molecular (mol. wt. 300) factor (early ECF), and the delayed phase (24 hr) is mediated by synergy of two different factors (delayed ECF-a and -b). In this study, we report the mediation of tissue eosinophilia in passive cutaneous anaphylactic (PCA) reaction sites. Tissue eosinophilia in systemic PCA showed two phases with peaks at 6 hr and 24 hr, while that in local PCA was monophasic and peaked at 12 hr. A dialysable eosinophil chemotactic factor was isolated from the early stage (0-6 hr) of local PCA skin sites, and another chemotactic factor (mol. wt. 15,000), sharing a common antigenicity with guinea- pig serum C5, from 12-hr-old local PCA skin sites. On the other hand, a different chemotactic factor with a mol. wt. of about 70,000, sharing a common antigenicity with delayed ECF-b isolated from active cutaneous anaphylactic skin lesions, was isolated from 24-hr-old systemic PCA skin lesions. Although the dialysable factor was also isolated from systemic PCA skin sites, the factor from systemic PCA delayed skin sites may not contribute to delayed tissue eosinophilia, since the activity paralleled the intensity of basophil accumulation but not to that of eosinophils. It is thus suggested that tissue eosinophilia in systemic and local PCA reactions is mediated by different chemotactic factors. [ABSTRACT FROM AUTHOR]

GaN nanorod films have been grown on Si(001) substrates with native silicon oxides by radio-frequency plasma-enhanced molecular beam epitaxy. GaN nanorod films are made up of single-crystalline nanorods with a so-called (0001) fiber-like texture. Each nanorod is elongated along c axis in perpendicular to the substrate surface and has no preferential axis in film plane. Excellent electron field emission characteristics were observed for the fabricated GaN nanorod films with a field emission threshold as low as 1.25 V/μm at a current density of 0.1 μA/cm2 and a field emission current density as high as 2.5 mA/cm2 at an applied field of 2.5 V/μm. These excellent characteristics are attributed to the geometrical configuration of nanorods and their good crystalline quality as well as the low electron affinity of GaN. [ABSTRACT FROM AUTHOR]

Extended abstract of a paper presented at Microscopy and Microanalysis 2009 in Richmond, Virginia, USA, July 26 – July 30, 2009 [ABSTRACT FROM PUBLISHER]

Extended abstract of a paper presented at Microscopy and Microanalysis 2009 in Richmond, Virginia, USA, July 26 – July 30, 2009 [ABSTRACT FROM PUBLISHER]

The structures of melt-spun, and subsequently annealed, Zr[sub 70]Pd[sub 30] alloys, which form a nanosized icosahedral quasicrystalline phase during the primary crystallization of the amorphous phase, have been investigated by means of electron-diffraction pair-distribution-function (PDF) analysis. The PDF analysis for this alloy was performed by precise measurements of elastic halo-electron-diffraction intensities. Possible structure models for as-quenched and annealed amorphous structures were constructed with the help of reverse Monte Carlo simulations. In order to obtain the local atomic structures, the Voronoi-polyhedra analysis was performed. A considerable number of icosahedral clusters with Zr atoms in the center are present in the simulated structure of the as-quenched state, and the number of the clusters increases by annealing. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]