Search

An analytical transmission electron microscopy study was performed on the nature of nanosize secondary phase precipitates that form in standard heat-treated commercial nickel base superalloy IN 738. In addition to M5B3 borides and M23C6 carbides, the precipitates were found to also consist of particles of M2B-type boride phase, which is previously unreported in the alloy and rarely reported in nickel base superalloys. The M2B borides exhibited a dual crystallographic structure: body centered tetragonal and face centered orthorhombic. Analyses of electron diffraction patterns and high-resolution transmission electron microscopy images indicated that both crystal structures can co-exist in a single M2B particle as an intergrowth with the formation of planar defects. Crystallographic relationship between microconstituent phases in the heat-treated alloy were elucidated and the influence of the borides on resistance to grain boundary liquation cracking during high-temperature material processing, such as lase...

Microstructural study of laser-beam-welded IN 738 superalloy was carefully performed to better understand the causes of heat-affected zone (HAZ) cracking and to determine an improved approach of alleviating the weldability problem. The HAZ cracks in the alloy were intergranular liquation cracks that resulted from the liquation reaction of both secondary solidification products (MC carbides and γ-γ′ eutectic) and solid-state reaction products (γ′ particles) present in the preweld material. In contrast to the expectation based on Chadwick’s equation, a reduction of grain boundary liquid film thickness did not produce a decrease in HAZ cracking owing to increased base alloy hardness that accompanied a preweld heat treatment designed to reduce the intergranular liquation. Moreover, a major factor limiting the effectiveness of an existing preweld heat treatment with low base alloy hardness in reducing HAZ cracking was found to be the formation of intergranular M5B3 boride particles during the heat treatment. These borides can widen the HAZ brittle temperature range (BTR) during weld cooling and increase the propensity for cracking. Based on the results, a new preweld heat treatment that induces a moderate hardness and precludes grain boundary boride formation was found and was shown to produce a significant reduction in HAZ cracking in the welded alloy compared to the most effective pre-existing preweld heat treatment.

Analytical transmission electron microscopy study of intergranular regions in directionally solidified (DS) RENE 80 superalloy was performed. In addition to the generally reported M3B2-type boride particles that form in the alloy during ingot solidification, considerable presence of a different type of boride particles, M5B3, which has not been generally reported in the alloy, was observed. Extensive formation of these particles along the grain boundaries in the DS alloy is pertinent to high-temperature performance of the material.

Rene 80 is a precipitation hardened nickel-based superalloy, which is widely used to manufacture components of gas turbine engines for aerospace and power generation applications. It is designed to withstand service temperatures of up to 980 C [1] and possesses remarkable hot corrosion resistance, long-term microstructural stability, and hightemperature strength produced primarily by precipitation hardening by ordered intermetallic Ni3(Al,Ti) c0 precipitates. Directional solidification (DS) processing of the alloy results in further improvement of its elevated temperature properties and permits the use of a higher service temperature, which improves the thermal efficiency of gas turbines [2–5]. It has been reported that in DS Rene 80, the tensile strength is increased by about 10–15% and the creep rupture life is extended by 2–4 times relative to conventionally cast material [5]. Boron is an essential minor elemental addition to these heat resistant materials primarily to improve their creep rupture properties [3, 4]. Nevertheless, it has been recognized that the mode in which boron exists on grain boundary regions, either in austenitic solid solution form or selectively partitioned into second phase particles, can significantly influence the creep properties of superalloys [6, 7]. Experimental study is crucial in establishing the presence and nature of intergranular borides in multi-component superalloys due to the influence of interfacial elemental segregation that is not generally considered during thermodynamic equilibrium calculations of theoretical models [8]. The objective of this investigation was to perform transmission electron microscopy (TEM) study of heat-treated DS Rene 80 superalloy to understand the nature of boron rich second phase particles present along its grain boundary regions. The composition of the DS Rene 80 material used in this study was (wt%) 0.2C, 14.1Cr, 9.52Co, 4.0W, 3.98Mo, 0.02Nb, 0.18Fe, 2.9Al, 4.98Ti, 0.028Zr, 0.013B balance nickel. The alloy was subjected to standard solution heat treatment for 2 h at 1200 C and was subsequently aged at 1025 C for 16 h. Thin foils from the aged material for TEM study were prepared by mechanical polishing and dimpling to a thickness of less than 10 lm followed by ion milling in a Gatan precision ion polishing system (PIPS). TEM microchemical and crystal-structure analyses were performed in a field emission gun JEOL 2100F scanning transmission electron microscope equipped with Oxford energy dispersive spectrometer (EDS), Gatan imaging filter (GIF) system, and electron energy-loss spectrometer (EELS). High-resolution TEM micrographs were filtered using an inverse fourier fast transform (FFT) program in Gatan Digital Micrography software. A TEM boron post-edge electron energy loss image of the heat-treated alloy consisting of c0 precipitates and particles of a different phase along the grain boundary and inside the grain identified with arrows is shown in Fig. 1a. Microchemical analysis by X-ray energy dispersive spectroscopy indicated that the particles are rich in Cr, Mo, W, and B (Fig. 1b), and have much different composition from the adjoining regions (Fig. 1c). The presence of boron in the particles was further confirmed by EELS analysis (Fig. 1d) and EELS-based energy filtered transmission electron microscopy (EFTEM) elemental mapping (Fig. 1e). TEM Electron diffraction pattern (EDP) analysis was performed by systematic titling of particle of this phase along certain crystallographic directions to determine its crystal structure. Figure 2a is a [001] zone-axis EDP showing a fourfold symmetry of the phase. Figure 2b and c were obtained by H. R. Zhang O. A. Ojo (&) Department of Mechanical and Manufacturing Engineering, University of Manitoba, Winnipeg, MB, Canada R3T 5V6 e-mail: ojo@cc.umanitoba.ca

Grain boundary microconstituents in aged nickel-based superalloys were studied by transmission electron microscopy techniques. A nanosized M 5 B 3 boride phase, possibly formed by intergranular solute desegregation-induced precipitation, was positively identified. The presence of these intergranular nanoborides provides reasonable clarification of a previously reported reduction of grain boundary liquation temperature during the weld heat affected zone thermal cycle.

Large-area single-crystalline vanadium dioxide nanoflakes were first fabricated via a thermal reduction method in a tube furnace. The sample was characterized by x-ray diffraction, x-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy. The results show that VO2 nanoflakes are single-crystalline with a monoclinic structure. The VO2 nanoflakes have a width of 200–300 nm, a thickness of 50–100 nm, and a length up to 1–2 μm. It is found that single-crystalline VO2 nanoflakes show a novel and complicated 5–7-step Li-storage behavior for an insertion amount of 2.

Researchers have demonstrated that BiFeO3 exhibits ferroelectric hysteresis but none have shown a strong ferromagnetic response in either bulk or thin film without significant structural or compositional modification. When remanent magnetisations are observed in BiFeO3 based thin films, iron oxide second phases are often detected. Using aberration-corrected scanning transmission electron microscopy, atomic resolution electron energy loss spectrum-mapping and quantitative energy dispersive X-ray spectroscopy analysis, we reveal the existence of a new Fe2O3-rich perovskite nanophase, with an approximate formula (Fe0.6Bi0.25Nd0.15)3+ Fe3+O3, formed within epitaxial Ti and Nd doped BiFeO3 perovskite films grown by pulsed laser deposition. The incorporation of Nd and Bi ions on the A-site and coherent growth with the matrix stabilise the Fe2O3-rich perovskite phase and preliminary density functional theory calculations suggest that it should have a ferrimagnetic response. Perovskite-structured Fe2O3 has been reported previously but never conclusively proven when fabricated at high-pressure high-temperature. This work suggests the incorporation of large A-site species may help stabilise perovskite-structured Fe2O3. This finding is therefore significant not only to the thin film but also to the high-pressure community.

Sr0.95Ce0.05CoO3-δ (I) and Sr0.9Ce0.1CoO3-δ (II) are prepared by sol-gel reaction of Sr(NO3)2, Co(NO3)2, and Ce(NO3)3 in citric acid and ethylene glycol (353 K, 10 h) followed by gel drying and calcination in air (1373 K, 5 h).

The interaction of grain boundaries with ferroelectric domain walls strongly influences the extrinsic contribution to piezoelectric activity in Pb(Zr,Ti)O3 (PZT), ubiquitous in modern transducers and actuators. However, the fundamental understanding of these phenomena has been limited by complex mechanisms originating from the interplay of atomic-level domain wall pinning, collective domain wall dynamics, and emergent mesoscopic behavior. This contribution utilizes engineered grain boundaries created by depositing epitaxial PZT films with various Zr:Ti ratio onto 24o SrTiO3 tilt bicrystals. The nonlinear piezoelectric response and surface domain structure across the boundary are investigated using piezoresponse force microscopy whilst cross section domain structure is studied using transmission electron microscopy. The grain boundary reduces domain wall motion over a width of 800±70 nm for PZT 45:55 and 450±30 nm for PZT 52:48. Phase field modeling provides an understanding of the elastic and electric fields associated with the grain boundary and local domain configurations. In conclusion, this study demonstrates that complex mesoscopic behaviors can be explored to complement atomic-level pictures of the material system.

A new perovskite cathode, Sr0.95Ce0.05CoO3-δ, performs well for oxygen-reduction reactions in solid oxide fuel cells (SOFCs). We gain insight into the crystal structure of Sr1-xCexCoO3-δ (x = 0.05, 0.1) and temperature-dependent structural evolution of Sr0.95Ce0.05CoO3-δ by X-ray diffraction, neutron powder diffraction, and scanning transmission electron microscopy experiments. Sr0.9Ce0.1CoO3-δ shows a perfectly cubic structure (a = a0), with a large oxygen deficiency in a single oxygen site; however, Sr0.95Ce0.05CoO3-δ exhibits a tetragonal perovskite superstructure with a double c axis, defined in the P4/mmm space group, that contains two crystallographically different cobalt positions, with distinct oxygen environments. The structural evolution of Sr0.95Ce0.05CoO3-δ at high temperatures was further studied by in situ temperature-dependent NPD experiments. At 1100 K, the oxygen atoms in Sr0.95Ce0.05CoO3-δ show large and highly anisotropic displacement factors, suggesting a significant ionic mobility. The test cell with a La0.8Sr0.2Ga0.83Mg0.17O3-δ-electrolyte-supported (∼300 μ thickness) configuration yields peak power densities of 0.25 and 0.48 W cm-2 at temperatures of 1023 and 1073 K, respectively, with pure H2 as the fuel and ambient air as the oxidant. The electrochemical impedance spectra evolution with time of the symmetric cathode fuel cell measured at 1073 K shows that the Sr0.95Ce0.05CoO3-δ cathode possesses superior ORR catalytic activity and long-term stability. Mixed ionic-electronic conduction properties of Sr0.95Ce0.05CoO3-δ account for its good performance as an oxygen-reduction catalyst., We are grateful to the Spanish Ministry of Economy and Competitivity for granting Project MAT2013-41099-R and ILL and PSI for making all facilities available for the neutron diffraction experiments. C.S. gratefully acknowledges financial support by the National Science Foundation of China (Grants 51172275 and 51372271) and the National Key Basic Research Program of China (Grant 2012CB215402).

Nearly monodisperse flowerlike CeO2 microspheres were synthesized via a simultaneous polymerization-precipitate reaction, metamorphic reconstruction, and mineralization under hydrothermal condition as well as subsequent calcination. The obtained CeO2 microsphere consists of 20-30 nm thick nanosheets as petals. It has an open three-dimensional (3D) porous and hollow structure and possesses high surface area, large pore volume, and marked hydrothermal stability. It can be doped easily after synthesis, and the initial 3D texture is maintained. The controlling factors and a possible formation mechanism are discussed in detail. This novel material can be used as a support for catalysts with various purposes. With CuO loaded on flowerlike CeO2, the catalytic activities and hydrothermal stability of Cu/CeO2 for ethanol stream reforming were examined. At 300 degrees C, the H2 selectivity reached a maximum value of 74.9 mol %, while CO was not detected within the precision of the gas chromatogram. It produced a hydrogen-rich gas mixture in the wide temperature range (300-500 degrees C) and showed excellent hydrothermal stability at high temperature (550 degrees C), which is a good choice for ethanol processors for hydrogen fuel cell applications.

In this paper, hollow and porous Cu2O nanoparticles were prepared by adjusting the cationic surfactant cetyltrimethylammonium (CTAB) concentration in the solution-phase reaction. Structural investigations reveal that Cu2O nanoparticles can be either well-defined hollow nanoboxes or porous nanocubes depending on the synthesis conditions. The transmission electron microscopy (TEM) observations demonstrated that the nanoparticles in general are composed of small grains coherently growing along certain preferred orientations.

Monodisperse Fe3O4 nanoparticles (NPs) with narrow size distribution are synthesized by a high-temperature solution-phase method. The diameter of the as-synthesized NPs is tuned from 2 to 14 nm by varying the reaction conditions. Highly ordered superlattice structures of the Fe3O4 NPs with areas extending over 0.8 microm x 0.7 microm have been successfully obtained. The magnetic properties are investigated in their different states, such as in the solid state and diluted in wax with different concentrations. Some magnetic properties enhanced by increasing interparticle distances, such as the remanent magnetization and coercive field at low temperature, were noticed. Furthermore, we also observed that the saturation magnetization changed with temperature as expected. The preliminary explanation for the properties mentioned above is proposed.

Uniform-sized gold nanoparticles were synthesized by a facile method, which is comprised of three steps: the first step to prepare Au colloid in aqueous, the second to transfer the particles into organic solvent and the third to reflux organic solution. The 2D/3D superlattices of as-prepared gold nanoparticles were fabricated by evaporating solvent from colloid solution at optimal concentration.

Transmission electron microscopy (TEM) observations reveal the presence of complex superstructures and remarkable phase separation in association with Na-ordering phenomenon in gamma-Na0.5CoO2. Resistivity and magnetization measurements indicate that three phase transitions at the temperatures of 25, 53 and 90 K, respectively, appear commonly in gamma-Na0.5CoO2 samples. Under a high pressure up to 10 kbar, the low-temperature transport properties show certain changes below the charge order transition; under an applied magnetic field of 7 T, phase transitions at around 25 and 53 K, proposed fundamentally in connection with alternations of magnetic structure and charge ordering maintain almost unchanged. (c) 2005 Elsevier B.V. All rights reserved.

The electronic structure of Sr0.35CoO2, structurally analogous to the layered NaxCoO2, has been evaluated using the local spin density approximation (LSDA). We find that evident c-dispersions appear in both the e(g)' and a(1g) Co-derived bands, demonstrating the existence of a notable interplanar interaction in Sr0.35CoO2. The LSDA + U calculation reveals that the electronic structure, in particular the band splitting between the spin-up and spin-down electrons, changes evidently along with the increase of the effective on-site Coulomb interaction U. Analysis of theoretical and experimental electron energy-loss spectra (EELS) for the oxygen K-edge and the Co L-23-edge suggests that the on-site interaction (U) in Sr0.35CoO2 is less than 3 eV which is noticeably weaker than the estimated value (from 5 to 8 eV) in the NaxCoO2 materials. (C) 2005 Elsevier Ltd. All rights reserved.

Pvramid-like Fe3O4 nanostructures (see Figure) are formed over large areas on alpha-Fe2O3(0001) substrates using a plasma-sputtering technique. No catalysts or templates are used in the reaction process. This nanostructure resembles Egyptian pyramids, possessing many layers and standing perpendicular to the substrate surface. These structures may have potential applications in constructing nanoscale magnetic and high-density storage devices.

Pure phase CeO2 nanorods (about 40?50?nm in diameter and 0.3?2??m in length) were synthesized through a solvothermal synthesis method. The addition of ethylenediamine is critical to obtain CeO2 nanorods. Other experimental conditions, such as the solvent composition, surfactant and the cerium source precursor were of importance in the final product morphology. The reaction temperature and reaction time also had significant influence on the yield of CeO2 nanorods. A possible formation mechanism of CeO2 nanorods was discussed mainly based on the dependences of controlling parameters on the final morphologies. In addition, the optical properties of CeO2 nanorods were investigated. The UV?visible adsorption spectrum and photoluminescence spectrum of the CeO2 nanorods showed unusual red-shift and enhanced light emission, respectively.

Carbon nanotube (CNT) bundles are synthesized on rough polycrystalline ceramic wafers by pyrolyzing ferrocene/melamine mixtures through a three-step process in a single stage furnace in an Ar atmosphere. The CNTs are multi-walled and have outer diameters from 10 to 90 nm and lengths from 20 to 100 microns. These CNTs display a bamboo-like structure with open graphite layers and defects at the outer surfaces. Field electron emission (FEE) measurements show that the turn-on electrical field is 2.9 V/μm and the field enhancement factor is 2700.

Without catalyst and at a low temperature (550 °C), well-aligned ZnO nanorods and nanowires were prepared on porous silicon substrates using a simple method. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results confirm that both the nanorods and the nanowires are perfect single crystals with the wurtzite structure. The diameters range from 40 to 100 nm. The growth directions are along the [0 0 0 1] axis. Photoluminescence (PL) spectra show that the UV emission shifts slightly to low frequency and the intensity of green emission decreases with the improvement of ZnO crystallization.

Hard carbon spherules (HCS) were used as support of Pt nanoparticles as electrocatalyst for direct methanol fuel cells (DMFCs). Scanning electron microscopy (SEM) images show that the size of the Pt particles on HCS by reduction of K2PtCl6 with ethylene glycol is 4-5 nm. High-resolution transmission electron microscopy (HRTEM) study reveals that the Pt particles on the HCS surface have faceted crystalline structures. The size and aggregation of the Pt particles depend on the surface properties of the carbon support and the medium of the reduction reaction. Cyclic voltammetry and galvanostatic polarization experiments show that the Pt/ HCS catalyst exhibits a higher catalytic activity in the electrooxidation of methanol than either the Pt/MCMB or the commercial Pt/Vulcan XC-72 catalyst does. (C) 2004 Elsevier Ltd. All rights reserved.

The microstructures of a single-crystal nickel-base superalloy were observed by transmission electron microscopy (TEM) before and after thermo-mechanical fatigue. Both dislocation configurations and γ′ precipitate morphologies under in-phase (IP) testing were found to be clearly different from those under out-of-phase (OP) testing. Under IP testing, dense hexagonal dislocation networks were found on the horizontal interfaces, and irregular dislocation networks on the vertical interfaces. With decreasing mechanical strain amplitude, rafting of γ′ precipitates was more pronounced. Under OP testing, no dislocation networks were found on the γ/γ′ interfaces; also, γ′ precipitates were sheared by superlattice stacking faults, and were not clearly rafted. The characteristic dislocation networks and partials of the stacking fault are analysed and the rafting mechanism of the γ′ precipitates is discussed.

We report on the controlled growth of novel self-assembled nanostructures (nanoaeroplanes, nanocombs, and tetrapod-like networks of zinc oxide) by a simple thermal evaporation technique in a single-stage furnace. Scanning electron microscopy and transmission electron microscopy are used to investigate their morphologies and structures. Shapes are regular and unit sizes vary from 80 nm to 5 µm. The relationship between the preparation conditions and the nanomorphologies in the experiments is helpful for controlling the physical properties of the nanosystems and, hence, is described in some detail. A possible growth mechanism is discussed.

WO3� x nanorods were grown on the tips of electrochemical etched W filaments by in-situ heating under different growth conditions. This kind of nanorods has the average diameter of 20 nm and the length of 1–2 lm. Transmission-electron microscopy investigations indicate that the sub-stoichiometric WO3 nanorods, prepared at about 830 C under the atmosphere of H2 and Ar mixture, could grow along the either h 00 1i or h 11 0i direction with evident stacking faults and textural structure. Nanorods prepared without H2 atmosphere are found to be respectively W18O49 grown at around 900 C and WO2:9 grown at 800 C. 2004 Elsevier B.V. All rights reserved.

Hollow polyhedra and cubes of nanostructured Cu(2)O particles have been synthesized by reduction of CuSO(4) with ascorbate acid in the solution phase. The nanostructures were obtained when the cetyltrimethylammonium (CTAB) concentration ranged from 0 to 0.03 M in the presence of NaOH. Structural characterizations, by means of x-ray photoelectron spectroscopy (XPS) for measuring Cu valence states and by electron microscopy for microstructure and chemical analyses, suggest that most Cu(2)O nanoparticles are covered with a thin CuO shell arising possibly from reaction of the adsorbed oxygen on the Cu(2)O particle surface. The blue shift is observed as microstructures of Cu(2)O nanoparticles changed from cubic to hollow in ultraviolet and visible (UV-visible) absorption spectra. Both the Cu(2)O hollow and cubic nanostructures show certain quantum-confined effects. A cationic CTAB template mechanism is proposed to interpret the formation of the Cu(2)O nanoparticles.

Transmission electron microscopy study of brazed joint microstructure in a Ni3Al-based intermetallic alloy IC 6 was performed. A continuously distributed microconstituents consisting of γ solid-solution, M 3B2-type and M23B6-type borides, which were likely formed by eutectic-type reaction(s) from residual liquated insert during cooling from brazing temperature, were observed along the joint centreline. Consideration of possible incipient melting due to eutectic-type transformation reaction of these phases is pertinent to development of post braze heat treatment for modifying the brazement microstructure. © 2010 Springer Science+Business Media, LLC.

The structural properties of Ni(2)FeGa Heusler alloy synthesized by melt-spinning technique have been systematically studied by means of in situ heating and cooling transmission electron microscopy. It was found that the Ni(2)FeGa alloy was annealed into a well-defined L2(1) structure at around 980 K, and complex microstructural domains appeared along with lowering temperature. At room temperature (293 K), a rich variety of micromodulated domains were observed. The domain structures were aligned along the or directions resulting to complex tweed structures. Below martensitic transformation (MT) temperature (M(s),similar to 142 K), the cubic parent phase transformed into unmodulated martensitic variants and modulated martensitic variants. The variants were alternated along the direction with various arrangements and steplike incommensurate boundaries. The modulated martensitic variants were composed of lamellar structures that have predominately a 5M modulation structure along the directions. The electron energy-loss spectroscopy analysis of the low-loss region and the electron energy-loss near-edge fine structure revealed a visible change of the electronic structure along with MT, which can be well interpreted by means of intra-atomic or intraband charge redistribution due to spd orbital hybridization among the Ni-Fe-Ga atoms.

Electron energy-loss spectroscopy (EELS) is routinely used to estimate local specimen thickness in a TEM. The relative specimen thickness is conveniently estimated from the low-loss spectrum using log-ratio method with a formula t/λ = ln(Iₜ /I₀). Here λ is an inelastic mean free path (IMFP) for the material in question, I₀ is the area under zero-loss peak (ZLP) and Iₜ the total area under the whole spectrum. An absolute thickness t measurement requires knowledge of the IMFP, which depends on the specimen material, electron energy and collection semiangle. The most commonly used IMFP formula, incorporated into Gatan Digital Micrograph software, was developed by Malis et al. and exhibits a smooth dependence on atomic number Z., Proceedings of Microscopy & Microanalysis 2011, August 7-11, 2011, Nashville, Tennessee

Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010.

Guided propagation of neutrons in thin films was directly observed in a ${\mathrm{TiO}}_{2}$/Ti/Si waveguide by exciting one of its discrete guided modes from an external neutron beam. The condition found experimentally for exciting this particular mode agrees well with theory. The measured intensity of the guided neutrons was also in good agreement with a calculation based on a previous coupling theory.

Mn-doped 3C-SiC nanoparticles have been fabricated by a sol-gel and carbothermal reduction method. The average particle size of the nanoparticles is about 126 nm. Raman scattering studies indicate that the transverse optical and the longitudinal optical modes shift to low wave number and the full widths at half-maximum of Raman peaks increase after Mn was doped. Extended x-ray absorption fine structure reveals that the doped-Mn atoms substitute for the C sites in the 3C-SiC lattice. Magnetic measurement results show that the room temperature intrinsic ferromagnetism (FM) order is established. The origin of the FM has been discussed in detail.

A seed-mediated method was employed here for CTAB-assisted gold nanoparticle growth. 3–4 nm silver aqueous colloid was stabilized by sodium citrate and used as seed solution to initial gold particle growth. The concentration of seed solution was calculated based on its relationship with silver atom concentration and seed particle statistical mean volume. It was found that there is a maximum seed concentration of 8.57 × 10 −12 M( ∼25 μ l0 .343 × 10 −8 M seed solution added) in 10 ml 2.5 × 10 −4 M HAuCl4 growth solution for growth of rodlike particles. Below this seed amount, the aspect ratio of nanorods could be controlled by varying the silver seed amount, i.e. nanorods with aspect ratio ∼18.9 were obtained when the seed concentration in the growth solution was 0.343 × 10 −12 M by adding 1 μ l0 .343 × 10 −8 M silver seed solution and nanorods with aspect ratio ∼9.69 were obtained when the seed concentration in the growth solution was 1.715 × 10 −12 M by adding 5 μ l0 .343 × 10 −8 M silver seed solution. As the seed concentration in the growth solution was more than 8.58 × 10 −12 M( 25μ l0 .343 × 10 −8 M silver seed solution was added), there were no rodlike particles formed but spherical ones instead. These spheres were further studied by TEM and found to all be hollow structures. It was suggested that there were probably two different nucleation processes for growth of nanorods and spheres. For hollow spheres, the reaction between Ag seeds and Au ions formed hollow structures based on the Ag particle template effect. Then further growth of Au on these hollow structures produced hollow gold nanospheres. For nanorods, due to the very low concentration of silver seed (molar ratio of Ag seed: Au = 3.426 × 10 −8 ), the growth process here probably was started by silver-induced Au nucleation, in which reduction of gold ions by silver resulted in small gold clusters. These gold clusters further grew up into nanoparticles and nanorods in the presence of CTAB. S Supplementary data are available from stacks.iop.org/Nano/18/115608

Visible and infrared photoluminescence was observed from AlN:Er films grown by reactive radio-frequency magnetron sputtering under different powers. X-ray diffraction indicates that the films have a c-axis oriented hexagonal wurtzite structure with an average crystallite size of about 59-83 nm and a strain of about (1.12-1.69) x 10(-3). Green emissions (similar to 540 and 558 nm) from the AlN: Er films are due to the intra-4f(n) transition of Er3+ from H-2(11/2) and S-4(3/2) to I-4(15/2), and infrared (similar to 1535 nm) emissions correspond to I-4(13/2) to I-4(15/2) transitions. Increasing the sputtering power results in larger grain size, lower strain, and enhancement of the luminescence intensity. (c) 2006 American Institute of Physics.

Strong photoluminescence (PL) is observed in nanostructured crystalline tungsten oxide thin films that are prepared by thermal evaporation. Two kinds of films are investigated—one made of nanoparticles and another of nanowires. At room temperature, strong PL emissions at ultraviolet-visible and blue regions are found in both of the films. Compared with the complete absence of emission of bulk phase tungsten oxide powder under the same excitation conditions, our results clearly demonstrate the quantum-confinement-effect-induced photoluminescence in nanostructured tungsten oxides.