Dense networks of amorphous GaSb nanofibers were fabricated by ion irradiation of bulk GaSb, and following formation, they were thermally annealed at a low temperature. Contrary to expectations, annealing of the GaSb fibers at just 50% of their melting temperature resulted in complete chemical decomposition of the nanofibers into core-shell structures consisting of crystalline Sb cores surrounded by amorphous shells. In this study, we investigate the transition of the single-phase nanofibers to their core-shell configuration, and we analyze the unique, temperature-dependent phase decomposition process. Thermodynamic considerations are discussed, and a model is presented to explain the thermally induced decomposition of the GaSb semiconductor fibers into core-shell structures, based upon the singular interaction of several size-dependent material properties.

Based on a ternary Mg75Ni15Gd10 metallic glass former, a new Mg80Ni12Gd4Nd4 bulk metallic glass composite (BMGC) was developed by tailoring the compositions of Mg and rare earth (RE) elements. This BMGC displayed compressive ultimate strength over 900 MPa with a total strain to failure of 4.3% and specific strength of 3.12 × 105 Nm/kg. The improved mechanical properties were attributed to a “dual phases” structure consisting of Mg solid solution flakes and glassy matrix in the Mg80Ni12Gd4Nd4 BMGC. The homogeneously dispersed Mg phases reinforcement in the BMGC were characterized as a long period ordered structure (LPOS) with periodic arrays of six close-packed planes distorted from the ideal hexagonal lattice of 6H-type. The LPOS-Mg in the composite can act as a soft media to trap or interact with the unstable shear bands and contribute to plastic strain. The present study may provide a guideline for designing the Mg–TM–RE-based (TM: transition metals) BMGCs with “dual phases” structures.

The thermoelectric LaFe3CoSb12 nanopowders were synthesized by the hydro/solvo thermal method. The effects of different solvents were investigated by using only the potassium antimony tartrate as Sb source. Also, the effects of the different Sb sources were investigated by using only water as solvent on the morphologies of the resulting nanopowders. The results show that a mixture of nanoparticles and nanorods can be obtained in aqueous solution of cetyltrimethylammonium bromide or ethylenediamine-tetra-acetic disodium salt. In ethylenediamine only nanorods can be obtained, and in ethylene glycol only nanoparticles can be obtained. The other morphologies of the LaFe3CoSb12, such as particle-like, nest-shaped, branch-shaped, or feather-like crystalline, can be synthesized in water by selecting a suitable Sb source.

Epitaxial growth of a NiSi2 layer was observed on S+ ion-implanted Si(100) at a low temperature of 550 °C. Depending on the S+ dose and the Ni thickness, we identified different nickel silicide phases. High quality and uniform epitaxial NiSi2 layers formed at temperatures above 700 °C with a 20-nm Ni on high dose S+ implanted Si(100), whereas no epitaxy was observed for a 36-nm Ni layer. We assume that the presence of sulfur at the silicide/Si(100) interface favors the nucleation of the NiSi2 phase. The S atom distributions showed ultrasteep S depth profiles (3 nm/decade) in the silicon, which results from the snow-plow effect during silicidation and the segregation of S to the interface due to the low solubility of S in both Si and the silicide.

Luminescent silica nanotubes and nanowires were fabricated from cellulose whisker templates by sol-gel processing. The cellulose templates were removed by calcination at 650 °C to generate silica nanotubes with diameters of 15 nm and lengths up to 500 nm. At temperatures of 900 °C the core region previously occupied by the cellulose template was closed yielding silica nanowires. Cathodoluminescence spectra of the silica nanotubes and nanowires were measured in the transmission electron microscope during irradiation with 150 keV electrons. A blue emission at 450 nm was observed for the silica nanowires calcined at 900 °C. This luminescence was found to be related to defects induced by electron irradiation and was investigated in situ as a function of irradiation dose. The as-synthesized and 650 °C calcined nanowires and nanotubes showed a fast decay of the signal. The observed irradiation dose dependent changes in the luminescence spectra will be discussed in terms of defect formation and transformation mechanisms.

A combined experimental/numerical approach was developed to determine the distribution of current density, temperature, and stress arising within the sample during spark plasma sintering (SPS) treatment of zirconium carbide (ZrCx) or oxycarbide (ZrCxOy). Stress distribution was calculated by using a numerical thermomechanical model, assuming that a slip without mechanical friction exists at the interfaces between the sample and the graphite elements. Heating up to 1950 °C at 100 °C min−1 and a constant applied pressure of 100 MPa were retained as process conditions. Simulated temperature distributions were found to be in excellent agreement with those measured experimentally. The numerical model confirms that, during the zirconium oxycarbide sintering, the temperature measured by the pyrometer on the die surface largely underestimates the actual temperature of the sample. This real temperature is in fact near the optimized sintering temperature for hot-pressed zirconium oxycarbide specimens. It is also shown that high stress gradients existing within the sample are much higher than the thermal ones. The amplitude of the stress gradients was found to be correlated with those of temperature even if they are also influenced by the macroscopic sample properties (coefficient of thermal expansion and elastic modulus). At high temperature, the radial and angular stresses, which are much higher than the vertical applied stress, provide the more significant contribution to the stress-related driving force for densification during the SPS treatment. The heat lost by radiation toward the wall chambers controlled both the thermal and stress gradients.

Spark plasma sintering (SPS) of MgAl2O4 powder was investigated at temperatures between 1200 and 1300 °C. A significant grain growth was observed during densification. The densification rate always exhibits at least one strong minimum, and resumes after an incubation period. Transmission electron microscopy investigations performed on sintered samples never revealed extensive dislocation activity in the elemental grains. The densification mechanism involved during SPS was determined by anisothermal (investigation of the heating stage of a SPS run) and isothermal methods (investigation at given soak temperatures). Grain-boundary sliding, accommodated by an in-series {interface-reaction/lattice diffusion of the O2− anions} mechanism controlled by the interface-reaction step, governs densification. The zero-densification-rate period, detected for all soak temperatures, arise from the difficulty of annealing vacancies, necessary for the densification to proceed. The detection of atomic ledges at grain boundaries and the modification of the stoichiometry of spinel during SPS could be related to the difficulty to anneal vacancies at temperature soaks.

A functionalization technique for carbon nanofibers (CNFs) via acid is described. The integrity and chemical nature of the CNFs during the different stages of the applied treatment (oxidation, activation, and functionalization) were examined using different microscopic, chemical, and thermal analysis techniques. The treatment effect on the dispersion ability of the nanofibers in different solvents (tetrahydrofuran, chloroform, and acetone) was also evaluated. Results show that chloroform is the best medium to reach good dispersions and stability of the CNFs in a wide range of concentrations. Using this medium, the functionalization process using 4,4′-diaminodiphenylmethane (DDM) was adopted for the fabrication of reactive CNFs with linker molecules on their surface capable of binding covalently to thermosetting polymers, such as epoxy. The DDM surface derivatized CNFs have been used as reinforcement in epoxy matrix nanocomposites with improved thermomechanical properties in relation to non-treated carbon nanofibers.

Y2O3:Eu3+ nanophosphor was synthesized by flame spray pyrolysis (FSP) from urea added nitrate based liquid precursor. In this study, urea serves as fuel and subsequently provides additional heat in the flame zone during the synthesis of phosphor particles. The end product shows cubic phase Y2O3:Eu3+ nanophosphor successfully prepared by FSP without heat treatment. The influence of synthesis conditions such as different mol of urea and nitrate source materials in aqueous solution, and doping concentration on luminescent properties, were investigated. The characteristics of nanophosphor such as crystallinity and morphology under various experiments of conditions were carried out by x-ray diffraction (XRD) and field emission-scanning electron microscopy (FE-SEM). The particle size of product was found to be in the range of 20–30 nm from transmission electron microscopy (TEM). In photoluminescence (PL) properties, Y2O3:Eu3+ nanophosphor emitted red light with a peak wavelength of 609 nm when excited with 398 nm wavelength photons.

The mechanical response to indentation (including nano- and microindentation) has been investigated in Cu/Au and Cu/Cr multilayers with respective layer thickness ratios of 1:1 and 2:1, and individual layer thickness ranging from nanometer to submicrometer scale. It was found that the Cu/Cr multilayer has higher strength than the Cu/Au multilayer, although both multilayers have close Hall–Petch slope. Examination of indentation-induced deformation behavior shows that the Cu/Cr multilayer exhibits higher resistance to plastic deformation instability than the Cu/Au multilayer. Theoretical analysis indicates that the significant difference in mechanical response originates from the constituent layer configuration and interface structures, which impose distinguishing confining effect on dislocation activity.

A recent report on the “room temperature superplasticity” in the Zr64.13Cu15.75Ni10.12Al10 bulk metallic glass [Y.H. Liu et al., Science315, 1385 (2007)] was ascribed to the distinctive micrometer-sized structural heterogeneity. To verify the microstructure in this alloy, transmission electron microscopy (TEM) and anomalous small-angle x-ray scattering experiments were conducted. The results show that no micrometer-sized or nanometer-sized structural heterogeneities can be found. The micrometer-sized dark and bright regions that were previously reported as the reason for the plasticity are artifacts caused by TEM specimen preparation, rather than the intrinsic structure feature of this alloy. This finding is important for further studying the unique properties of this alloy.

Strontium titanium silicates are possible oxide forms for immobilization of short lived fission products in radioactive waste. Through beta decay, strontium decays to yttrium, and then to zirconium. Therefore, not only the stability of Sr-loaded waste forms, but also that of a potential decay product series with charge-balance in a naturally occurring mineral or a ceramic is of fundamental importance. Strontium titanosilicate (SrTiSiO5) is the Sr-analogue of titanite (CaTiSiO5). To incorporate the reaction 3Sr2+ = 2Y3+ + vacancy in the titanite composition, Y-substituted Sr-analogues of titanite, (Sr1–xY2/3x)TiSiO5 (x = 0, 0.25, 0.5, 0.75) were prepared by high temperature synthesis and were found to form glass upon cooling. The Y-end-member (Y2/3TiSiO5, x = 1) crystallized to a mixture of Y2TiSiO7, TiO2, and SiO2 upon quenching in air. The enthalpies of formation of Y-substituted Sr-titanite glasses were obtained from drop solution calorimetry in a molten lead borate (2PbO·B2O3) solvent at 702 °C. The enthalpies of formation from constituent oxides are exothermic but become less so with increasing Y content. The thermodynamic stability of the Y-substituted Sr-analogue of crystalline titanite may become marginal with increasing yttrium content.

To evaluate mechanical properties by means of nanoindentation, information on the contact area is crucial. However, the contact area is not directly accessible in experiments and is usually calculated according to the Oliver and Pharr procedure, which turned out to be unsatisfying when applied to viscoelastic materials like polymers. In this study, complementary in situ indentation testing and finite element analysis (FEA) were performed on silicone elastomers. Through this combination of techniques, several individual error sources in the conventional contact area determination have been identified and quantified. For shallow penetrations, contact areas after Oliver and Pharr were up to 40% smaller than the in situ testing results; for larger penetrations, the contact size was overestimated by approximately 6%. The deviations of the resulting mechanical properties were approximately 10%. Viscoelastic effects could be captured if dynamic indentation testing was performed.

A major drawback in using bulk metallic glasses (BMGs) as structural materials is their extremely poor fatigue performance. One way to alleviate this problem is through the composite route, in which second phases are introduced into the glass to arrest crack growth. In this paper, the fatigue crack growth behavior of in situ reinforced BMGs with crystalline dendrites, which are tailored to impart significant ductility and toughness to the BMG, was investigated. Three composites, all with equal volume fraction of dendrite phases, were examined to assess the influence of chemical composition on the near-threshold fatigue crack growth characteristics. While the ductility is enhanced at the cost of yield strength vis-à-vis that of the fully amorphous BMG, the threshold stress intensity factor range for fatigue crack initiation in composites was found to be enhanced by more than 100%. Crack blunting and trapping by the dendritic phases and constraining of the shear bands within the interdendritic regions are the micromechanisms responsible for this enhanced fatigue crack growth resistance.

Ferromagnetic Cu-doped GaN film was grown on a GaN-buffered sapphire (0001) substrate by a hybrid physical-chemical-vapor-deposition method (HPCVD). The GaCuN film (Cu: 3.6 at.%) has a highly c-axis-oriented hexagonal wurtzite crystal structure, which is similar to GaN buffer but without any secondary phases such as metallic Cu, CuxNy, and CuxGay compounds. Two weak near-band edge (NBE) emissions at 3.38 eV and donor-acceptor-pair (DAP) transition at 3.2 eV with a typical strong broad yellow emission were observed in photoluminescence spectra for GaN buffer. In contrast, the yellow emission was completely quenched in GaCuN film because Ga vacancies causing the observed yellow emission in undoped GaN were substituted by Cu atoms. In addition, GaCuN film exhibits a blue shift of NBE emission, which could be explained with the +2 oxidation state of Cu ions, replacing +3 Ga ions resulting in band gap increment. The valance sate of Cu in GaCuN film was also confirmed by x-ray photoelectron spectroscopy (XPS) analysis. The GaCuN film shows ferromagnetic ordering and possesses a residual magnetization of 0.12 emu/cm3 and a coercive field of 264 Oe at room temperature. The unpaired spins in Cu2+ ions (d9) are most likely to be responsible for the observed ferromagnetism in GaCuN.

An all-oxide Al2O3-TiO2 ceramic multilayer composed of 10–100 nm thick alternating layers was fabricated using the reactive magnetron sputtering process. Microindentation tests were carried out on the multilayer ceramic followed by microstructural observations of the cross-sections of the indented sites to characterize the indentation response of the system. During the observations, it was noted that an extensive room temperature “deformation” occurred in the multilayer ceramic material. The material shows a thickness reduction of as much as ∼40% under a conical indenter at 300 mN of load without microcracking and dislocation-assisted deformation. The room temperature deformation mechanism is governed by the relative movement and rearrangement of the anisotropic nanoscale columnar grains along the intergranular boundaries containing elongated voids. The relative sliding along the intergranular boundaries, and the subsequent granular rotation under indentation were well captured by finite element simulation.

We used reverse Monte Carlo (RMC) modeling to simulate the atomic structure of a Zr-based bulk metallic glass (BMG), incorporating short-range structural data from the electron diffraction total reduced density function G(r) and medium-range structural data from fluctuation electron microscopy (FEM). Including the FEM data created within the model loosely ordered planar atomic arrangements covering regions ∼1 nm in diameter without degrading the agreement with G(r). RMC refinement against only G(r) produced no agreement with FEM. Improved simulations are needed to create fully realistic BMG structures, but these results show that including FEM in RMC further constrains the structure compared with G(r) data alone and that the FEM signal in real materials is likely to arise from pseudo-planar arrangements of atoms.

High temperature plasma nitriding of yttria-partially-stabilized zirconia in atmospheric pressure microwave plasma was investigated. The morphological, mechanical, and physicochemical characteristics of the resulting nitrided layer were characterized by different methods, such as optical and scanning electron microscopy, microindentation, x-ray diffraction, narrow resonant nuclear reaction profiling, secondary neutral mass spectrometry, and x-ray photoelectron spectroscopy, aiming at investigating the applicability of this highly efficient process for nitriding of ceramics. The structure of the plasma nitrided layer was found to be complex, composed of tetragonal and cubic zirconia, as well as zirconium nitride and oxynitride. The growth rate of the nitrided layer, 4 µm/min, is much higher than that obtained by any other previous nitriding process, whereas a typical 50% increase in Vickers hardness over that of yttria-partially-stabilized zirconia was observed.

New advances toward microstructural improvement of epitaxial CeO2 films grown by chemical solution deposition and their use as buffer layers for YBa2Cu3O7 (YBCO) films are presented. We demonstrate that the degree of epitaxy and the fraction of (001) atomically flat surface area are controlled by the incorporation of tetravalent (Zr4+) or trivalent (Gd3+) cations into the ceria lattice. The degree of epitaxy has been investigated by means of Rutherford backscattering spectroscopy-channeling and reflection high-energy electron diffraction, and a new methodology is also presented to quantify the fraction of (001) atomically flat area from atomic force microscopy images. Results are further correlated with the superconducting properties, microstructure, and texture of YBCO films grown by the trifluoroacetate route. A comparison with pulsed laser deposition and YBCO films grown on the same ceria layers is also presented. This growth procedure has allowed us to obtain all chemical multilayer films with controlled microstructure and critical current densities above 4 MA cm−2 at 77 K.

To understand the mechanism of the coercivity enhancement by a trace addition of Cu in Nd-Fe-B sintered magnets, we investigated the microstructure difference between Cu-doped and Cu-free alloys using high resolution scanning electron microscopy (HRSEM), transmission electron microscopy (TEM), and laser assisted three dimensional atom probe (LA-3DAP). From a serial sectioning back scattered electron (BSE) images of the Nd-rich phase obtained by an integration of the focused ion beam (FIB) and HRSEM technique, it was found that Cu addition leads to a continuous formation of Nd-rich thin layers along the grain boundaries. 3DAP analysis has shown that a thin Cu-rich layer with a thickness of approximately 2 nm is present at the interface between the Nd2Fe14B and Nd-rich phase grains.