Formation and characterisation of CeO2 and Gd:CeO2 nanowires/rods for fuel cell applications

Ceria and gadolinium (Gd) doped ceria nanowires have been synthesised by hydrothermal technique with mild reaction conditions. The structure and morphology of as-prepared nanowires were studied by X-ray diffraction and field emission scanning electron microscopy (FE-SEM) techniques. The FE-SEM analysis revealed the formation of nanowires with an average diameter of 10–15 nm. Atomic force microscopy (AFM) analysis for the annealed samples confirms the existence of well defined nanorods of 120–150 nm diameter and 1–1.3 μm length. Fluorescence and diffuse reflectance spectroscopy techniques have been used to study the optical properties of the prepared nanowires. The observed red shift in the ultraviolet–visible absorption spectra confirmed the promoted electron–phonon interaction in CeO₂ and Gd:CeO₂ nanowires compared to bulk structures. The prepared nanowires/rods were thermally stable at up to 350?°C, as revealed by thermogravimetric analysis. The electrical properties were studied by cyclic voltammetry (CV) and impedance spectroscopy. The CV results demonstrated that Gd:CeO₂ exhibited a higher electro-oxidation than CeO₂ nanowires.     

Thermal and ion-induced dissociation of NiSi and NiSi2 in contact with nickel

The interaction of nickel with NiSi and NiSi₂ was investigated using backscattering spectrometry and glancing angle X-ray diffraction. With nickel films deposited onto NiSi or NiSi₂, Ni₂Si was formed at the original compound-nickel interface by the dissociation of the compounds on annealing at temperatures of about 300 °C. The dissociation of NiSi and NiSi₂ into Ni₂Si has also been observed when the samples were irradiated with argon ions. We attribute similarities in the two processes to the presence of thermodynamic forces in ion-induced reactions and the dependence of the radiation-enhanced migration on the intrinsic diffusion properties in the system.     

Growth of vertically aligned carbon nanofibers from nickel nanodot arrays produced from diblock copolymer thin film templates

Diblock copolymers of polystyrene and poly(methyl methacrylate) are utilized in a thin film to create a nanoscale template, which is used to deposit a nanoscale array of nickel nanodots. Systematic experiments show that this process must be optimized to successfully transfer the order of the diblock copolymer template to the resultant nickel nanodot array. It is found that the amount of nickel deposited dramatically impacts the fidelity of the final nanodot array, with a thickness ratio for copolymer:metal of 8:1 found to be optimal. The results also indicate that the method by which the surface is neutralized for the diblock domain alignment impacts the amount of nickel nanodots that remain on the surface after template removal. Finally, the nanoscale array of nickel nanodots is utilized to successfully grow vertically aligned carbon nanofibers from 18 nm and 40 nm diameter nickel dots.     

Interconnect and contact for nanoelectronics: Metallic TaSi2 nanowires

TaSi₂ nanowires have been synthesized on Si substrate by annealing FeSi₂ thin film and NiSi₂ films at 950 °C in an ambient containing Ta vapor whose length would be grown up to 13 μm. The metallic TaSi₂ nanowires exhibit excellent electrical properties with remarkable high failure current density of 3 × 10⁸ A cm^− 2. In addition, the growth mechanism is addressed in detail, The TaSi₂ nanowires are formed in three steps: segregation of Si atoms from the FeSi₂ thin film and NiSi₂ films underlayer to form Si base, growth of TaSi₂ nanodots on Si base, and elongation of TaSi₂ nanowire along the growth direction. This simple approach promises future applications in nanoelectronics and nano-optoelectronics.     

N-channel narrow gap charge-coupled devices using electron-beam lithography

Electron-beam lithography has been applied to 1 μm gap electrodes for charge-coupled devices. The damage to A1/phosphosilicate glass-SiO₂/Si structures irradiated by 15 keV electrons was annealed out in hydrogen at 400°–450°C, but latent damage was observed by interface state measurements in irradiated Al₂O₃-SiO₂ capacitors.     

The annealing of misfit dislocations in the (111) Cu/(111) Cu2O system

Recent work on the early stages of the epitaxial oxidation of (111) Cu at 350 °C and in oxygen pressures between 10^-7 and 10^-4 Torr has resulted in the determination of the growth modes that occur and the accompanying elastic strains. Initially a hexagonal 3 × 3 oxide superlattice is formed which continues to grow by a layer growth mechanism up to a theoretically estimated thickness of approximately five monomolecular layers. Subsequent oxidation occurs by the formation of lamellar islands containing misfit dislocations which reduce the coincidence lattice misfit strain. In the present work these (111) Cu/(111) Cu₂O bilayers were annealed and examined in situ in the transmission electron microscope in the temperature range 25–350 °C. The misfit dislocation density decreased as the temperature was increased. The annealing effects are complex and interdiffusion phenomena can be observed even at 60 °C.     

Novel method to synthesize SiC nanowires and effect of SiC nanowires on flexural strength of Cf/SiC composite

The graphite fiber toughened silicon carbide (C_f/SiC) composite was annealed at 1500, 1600, 1700, 1750, 1800 and 1850 °C for 30 min and the flexural strength increased first and then decreased as annealing temperature increased. The maximum flexural strength was obtained for the sample annealed at 1750 °C. The microstructure observation indicated that the amount and length of in situ formed SiC nanowires increased as the annealing treatment time increased, which was very favorable to the improvement of flexural strength. The formation of SiC nanowires was attributed to the presence of the metal La and Al. The vapor–liquid–solid growth mechanism of the SiC nanowires along 〈1 1 1〉 direction is proposed. Furthermore, the purpose of this paper is to report novel method to synthesize SiC nanowires.     

Red-emitting alkaline-earth rare-earth pentaoxometallates powders prepared by metal carboxylates solution

Moisture-insensitive metal carboxylates that are mostly liquids at room temperature have been first applied to the preparation of strontium europium aluminate (Sr₂EuAlO₅) powders for red-emitting phosphor under near ultraviolet radiation. Strontium naphthenate, aluminium-2-ethylhexanoate and europium-2-ethylhexanoate were dissolved with toluene to prepare starting solution. Precursor pyrolyzed at 500 °C for 240 min was finally annealed at 900–1200 °C for 240 min in Ar. X-ray diffraction analysis, field emission–scanning electron microscope and fluorescent spectrophotometer were used to evaluate structural and optical properties. For the 1000 °C-annealed powders with regular shape and narrow size distribution confirmed by FE–SEM observation, strong red emission at 615 nm under the excitation of 395 nm maximum was reached, then the higher annealed samples at above 1100 °C gave the lower emission intensities.     

Alloying behavior of gold,Au-Ge and Au-Ge-Ni on GaAs

The alloying behavior of gold, Au-Ge and Au-Ge-Ni films on GaAs has been studied after furnace annealing at 350 °C, 425 °C and 450 °C for 15 min, 0.5 min and 15 min respectively. Rutherford backscattering reveals that gold from Au-Ge films diffuses into the GaAs at a much lower temperature than that from gold and Au-Ge-Ni films. Transmission electron microscopy analysis reveals the presence of β-Ga₂O₃ in the 450 °C annealed specimens. In addition to this, the presence of Au₇Ga₂ and metastable γ-(Au-Ge) phases was identified in annealed Au-Ge films. Scanning electron micrographs of annealed samples show black patches which were found to be gold deficient compared with the light-gray areas. The surface morphology of Au-Ge-Ni films after alloying is more uniform than that of Au-Ge films.     

SO<Subscript>2</Subscript> chemisorption on SnO<Subscript>2</Subscript>〈Sb〉

We have studied SO₂ chemisorption on antimony-doped SnO₂ samples annealed at 200 and 600°C. Increasing the annealing temperature from 200 to 600°C makes the sample surface more homogeneous. In the range 100–200°C, the electrical conductivity of the samples air-annealed at 600°C increases in proportion with the amount of absorbed SO₂. Doping with 0.2 at % Sb ensures the largest increase in conductivity upon chemisorption.     

Simultaneous growth mechanisms for Cu-seeded InP nanowires

We report on epitaxial growth of InP nanowires (NWs) from Cu seed particles by metal-organic vapor phase epitaxy (MOVPE). Vertically-aligned straight nanowires can be achieved in a limited temperature range between 340 °C and 370 °C as reported earlier. In this paper we present the effect of the V/III ratio on nanowire morphology, growth rate, and particle configuration at a growth temperature of 350 °C. Two regimes can be observed in the investigated range of molar fractions. At high V/III ratios nanowires grow from a solid Cu₂In particle. At low V/III ratios, nanowire growth from two particle types occurs simultaneously: Growth from solid Cu₂In particles, and significantly faster growth from In-rich particles. We discuss a possible growth mechanism relying on a dynamic interplay between vapor-liquid-solid (VLS) and vapor-solid-solid (VSS) growth. Our results bring us one step closer to the replacement of Au as seed particle material as well as towards a deeper understanding of particle-assisted nanowire growth.      

Growth and properties of well-oriented In2Te3 thin films

Well-oriented thin films of In₂Te₃ were grown on sapphire substrates by thermal evaporation at 350°C and were then annealed in an argon atmosphere at 400°C for 2 h. Studies of the d.c. conductivity and Hall effect for these films were carried out in the temperature range 77–295 K. The variation in the Hall mobility with temperature indicated that there is a considerable contribution from lattice scattering above 220 K.     

Microstructure and mechanical properties of spark plasma sintered austenitic ODS steel

In this work, austenitic oxide dispersion strengthened (AODS) steel of composition Fe–16Cr–16Ni–1.5 W–0.21Ti–0.3Y₂O₃ (wt. %) was fabricated using two–stage ball milling followed by consolidation through spark plasma sintering (SPS). In the first–stage, mechanical alloying (MA) of ferritic powder and nano sized Y₂O₃ was carried out. This was followed by the addition of Ni in second–stage milling. SPS of the milled powder was carried out at 900, 950, 1000 and 1050 °C to explore the role of SPS temperature on density, microstructure as well as mechanical properties of the consolidated samples. A relative density of ～ 99% was obtained for samples sintered at 950 and 1000 °C. The as–sintered samples were subsequently solution annealed at 1075 °C for 2 h and water quenched. X–ray diffraction studies confirmed the presence of austenite in the consolidated and solution annealed samples. Electron back scatter diffraction analysis of solution annealed samples sintered at all the temperatures revealed a bimodal microstructure. The average grain size of 1.07 ± 0.72 µm was obtained for solution annealed samples sintered at 1000 °C. Yield strength and elongation of the same was measured as 851 MPa and 18%, respectively at room temperature. These values are the best combination of strength to elongation achieved on AODS alloys processed using MA and SPS, which makes this AODS steel much promising for high temperature applications.     

Growth mechanism of TiN reaction layers produced on AlN via active metal bonding

Interfacial reactions related to the TiN layer growth process between nanocrystalline epitaxial layers of AlN deposited on c-plane sapphire and a Ti-containing metal brazing or sintering layer using Ag–Cu–TiH₂, Ag–TiH₂ and Cu–TiH₂ pastes have been investigated. The brazed/sintered samples were heated in vacuum at 850 °C for 30 min. The TiN layer produced at the metal/AlN interfaces consists of TiN particles?<?50 nm in size and grain boundary phases including Al-containing Ag and Al-containing Cu. The Al concentration within the TiN layer decreases as the distance increases from the AlN epitaxial layer. These experimental observations all suggest that when AlN is used as a starting material in the active metal bonding method, interfacial reaction processes take place with the generation of a local Al-based eutectic liquid phase and elemental transport through this eutectic liquid phase.

     

Optimized Sol–Gel Chemical Route Using Vacuum Suction for Fabrication of Densely Packed NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript> Nanowires

Highly ordered nanowire arrays of NiFe₂O₄ spinel with a high aspect ratio were fabricated by sol–gel method associated with anodic aluminum oxide (AAO) templates. The preparation of nanowires was carried out by sol–gel method using nickel nitrate, ferric nitrate and citric acid. The molar proportion of nickel nitrate to ferric nitrate and citric acid was 1:2:3. The suction with 0.1 mbar vacuum was used to draw the gel into the AAO nanochannels. The results showed that the lowest annealing temperature is around 600?°C to obtain the single-phase nanostructured NiFe₂O₄. The NiFe₂O₄ nanowires were also uniform and parallel. TEM pictures determined the diameter size of the nanowires of about 100 nm. The magnetic results also showed that the wires have an easy axis of magnetization along their length and they are fully saturated in a field of 7 kOe. It seems that this material could be a good candidate for high perpendicular magnetic storage devices.     

Thermal stability of gold-PS nanocomposites thin films

Low-temperature transmission electron microscopy (TEM) studies were performed on polystyrene (PS, M _w = 234 K) — Au nanoparticle composite thin films that were annealed up to 350°C under reduced pressure conditions. The composite thin films were prepared by wet chemical approach and the samples were then subsequently spin-coated on a carbon-coated copper grid for TEM measurements. TEM measurements were performed at liquid nitrogen temperatures to reduce the electron-beam-induced radiation damage. The results showed a marginal increase in Au nanoparticle diameter (2.3 nm–3.6 nm) and more importantly, an improved thermal stability of the polystyrene (PS) composite film much above its glass transition temperature.     

Epitaxial growth of the nickel disilicide phase

The nickel disilicide (NiSi₂) phase which forms epitaxially on silicon single-crystal substrates in many ways exhibits an interesting behavior. A regular network of the silicon-rich phase was observed to originate at or near the Si-silicide interface using the Berg-Barrett X-ray topographic technique. The regularity, the thickness and the density of the network increase as the epitaxial layer increases in thickness. For (100)-oriented silicon substrates the network runs along two perpendicular 〈110〉 directions; for (111)-oriented silicon substrates the network runs along 〈112〉 directions. Large voids on the surface of the epitaxial layer and fracturing of the layer along the edges of the network for thick epitaxial layers were also observed. The results are explained in terms of the corrugated morphology of the NiSi₂-Si structure.     

Synthesis of SiO2 covered SiC nanowires with milled Si,C nanopowders

SiO₂ covered β-SiC nanowires were directly synthesized with a novel method, annealing the milled Si,C nanopowders at 900–1100 °C on Si wafer or Al₂O₃ substrate, and there is no any metal catalysts used. The diameters of the nanowires are range of 20 to 50 nm, and the lengths of the nanowires are up to several hundreds of microns. There is a uniform SiO₂ amorphous layer on the surface of SiC nanowires. The axial direction of SiC nanowires is < 111>, and there are stacking faults and twin lamellae in the SiC nanowires. The synthetic mechanism of SiC nanowires includes two solid–solid reactions and one gas–solid reaction between SiO, Si, C and CO.     

Incorporation of cobalt and nickel metal nano-particles in nano-grain zirconia film matrix by solution route

Precursor solutions of cobalt/nickel incorporated nano-grain zirconia films were prepared from aquo-organic solutions of zirconium oxychloride octahydrate and corresponding transition metal nitrate. The films were deposited onto silica glass substrate by the dipping technique. Annealing was made at different temperatures from 450°C to 1200°C ± 5°C in air atmosphere. The range of thickness of the films baked at 450°C was 1800–1870 å. For cobalt system Co₃O₄ was formed initially at 450°C which gradually transformed to alpha cobalt and next to cubic cobalt along with a non-stoichiometric compound (Zr_0.71Co_0.23O_0.06) with increasing annealing temperature. On the other hand, for nickel system nickel metal of nano-size was observed in the nano-grain zirconia film matrix at 450°C. By increasing annealing temperature to 1200°C, a compound, ZrNi₄O, was formed which was found to be stable for ～ 30 days.     

Synthesis of SiOF nanoporous ultra low-k thin film

In this work, we have investigated the effect of annealing temperature on physical, chemical and electrical properties of Fluorine (F) incorporated porous SiO₂ xerogel low-k films. The SiO₂ xerogel thin films were prepared by sol–gel spin-on method using tetraethylorthosilicate as a source of Si. The hydrofluoric acid was used as a catalyst for the incorporation of F ion in the film matrix. The thickness and refractive index (RI) of the films were observed to be decreasing with increase in annealing temperature with minimum value 156 nm and 1.31 respectively for film annealed at 400 °C. Based on measured RI value, the 34 % porosity and 1.53 gm/cm³ density of the film annealed at 400 °C have been determined. The roughness of the films as a function of annealing temperature measured through AFM was found to be increased from 0.9 to 1.95 nm. The Electrical properties such as dielectric constant and leakage current density were evaluated with capacitance–voltage (C–V) and leakage current density–voltage (J–V) measurements of fabricated Al/SiO₂ xerogel/P–Si metal–insulator-semiconductor (MIS) structure. Film annealed at 400 °C, was observed to be with the lowest dielectric constant value (k = 2) and with the lowest leakage current (3.4 × 10^?8 A/cm²) with high dielectric breakdown.