Narrow Results

Nowadays, researchers are extremely fascinated with the study of the doping effects of nanostructures of different materials, sizes and concentrations in high $T_c$ superconductors. This paper presents the presence of nanorods (N) structures, which have not previously been observed in the bulk HTSCs materials, and the influence of Iron doping in Bi-2223 superconductor using composition Bi₂Sr₂Ca${}_{n-1}$(Cu${}_{1-x}$Fe_x)_nO${}_{10+\delta }$, ($n=3$) for ($x=0.00$ and 0.01). The composition is prepared through a solid state route (SSR). The obtained samples are characterized with XRD, FESEM with EDX, HR-TEM and FTIR, and categorized into two samples ($\alpha$) and ($\beta$) Bi₂Sr₂Ca₂Cu₃O${}_{10+\delta }$, and Bi₂Sr₂Ca₂(Cu${}_{0.99}$Fe${}_{0.01}$)₃O${}_{10+\delta }$, respectively, which show Lattice dimensions $a=5.3912$Å, $b=5.4075$Å, $c=6.7961$Å and $a=5.4031$Å, $b=5.4170$Å, $c=36.7944$Å with Orthorhombic crystal structure, respectively. The FE-SEM micrographs show plate-like layered structures and (N) in the samples, which are uniformly distributed. The obtained size of crystallite nanoparticles is 2nm–100nm, calculated by the Scherrer method, and verified with HR-TEM data. The HR-TEM study also confirmed the layered form in the orthorhombic phase. The FESEM-EDX energy peaks in the spectrum confirm the presence of the elements in both samples ($\alpha$) and ($\beta$). The HRTEM-EDX confirms the extant iron in the sample in the form of (N). The FTIR bond stretching 1630.89cm${}^{-1}$ and 1629.657cm${}^{-1}$ of the samples ($\alpha$) and ($\beta$), respectively, confirms the superconductor bismuth-based 2223 phase, respectively. The electrical resistivity study of ($\alpha$) and ($\beta$) samples shows the critical temperature ($T_c$) of 63.083K and 22.8195K, respectively. The onset temperature for both samples is measured at 115.1785K and 68.314K, which represent the Bi-2223 phase. The magnetoresistance is obtained at low temperatures by a physical properties measurement system (PPMS) and with the increasing order of applied magnetic field from 0 to 12 Tesla, an increase in the resistivity in the pure sample ($\alpha$) and also a decrease in transition temperature are observed. These results are as similar to those obtained in the Bi-2223 Superconductor. The results show the growth of nanoparticles in the iron-doped Bisco superconductors.

Novel structure light emitting diodes (LEDs) made of InN/GaN multiple quantum wells (MQWs) are proposed and demonstrated. The MQWs consisted of very fine and narrow 1 monolayer (ML)-thick InN wells embedded in GaN matrix, which were successfully fabricated by radio-frequency molecular beam epitaxy. The thickness of InN wells can be fractional ML and/or two MLs depending on the growth conditions, resulting in different wavelength light emissions from deep violet to blue. Epitaxy processes for the MQWs fabrication are very unique on the basis of the self-ordering and coherent growth mode for atomically flat ~1 ML InN well deposition on GaN template. It is shown that the epitaxy temperature for 1 ML InN wells can be much higher than the highest epitaxy temperature of thick InN layer due to the effects of GaN matrix. Bright electroluminescence (EL) emission is observed at 418 nm at room temperature in LEDs fabricated by the MQWs. Further it is confirmed that the quantum confined Stark effect (QCSE) in InN wells is remarkably reduced due to the effects with using ultimately thin InN wells as active layers, resulting an extremely small blue shift in the EL peak wavelengths for two orders different injection current levels.

We investigate using molecular dynamics, the tensile failure of single-crystal and nanocrystalline Lennard-Jones solids under uniaxial strain. Stresses are relaxed by plasticity and tensile failure, which are induced via stacking faults, twin planes, void nucleation and growth, and their interactions. Stacking faults and twin planes as well as multiple nanovoids are nucleated at grain boundaries in a nanocrystalline solid. Void formation is characterized by under-coordinated atoms with coordination number ≤ 7, and the critical void size is comparable to a vacancy. For a single crystal, the number of stacking faults and twin planes decreases during failure mostly due to the absorption by nanovoids. In contrast, it increases with strain monotonically for a nanocrystalline solid, where abundant grain boundaries help the nucleation and deter the propagation and absorption of the stacking faults and twin planes, inducing effective dislocation pile-ups at grain boundaries even in the presence of nanovoids.

Nearly monodisperse silica spheres with a diameter of ~90 nm containing NiFe₂O₄ nanoparticles were successfully prepared by hydrolysis of TEOS in the presence of NiFe₂O₄ nanoparticles, synthesized through a hydrothermal method. The colloid particles were characterized by XRD, TEM and VSM. The results indicate that the particles possess better magnetic properties at room temperature, compared with paramagnetic colloids with magnetic core by co-precipitation method. The colloid particles assembled under additional magnetic fields could have potential application in biomedical systems.

Advanced turbine engines require the application of thermal barrier coatings (TBCs) to provide still higher reliability, thermal insulation effect and longer lifetime under harsh operating conditions. TBCs with nanostructure proved to be promising to deliver the desired property and performance. To exploit full potentials of the current widely used yttria-partially-stabilized zirconia (YSZ), nano-sized YSZ powders were developed and used as the ceramic source material. By controlling the deposition processes, novel TBCs with outstanding nanostructure such as nano-sized grains and pores were produced by atmospheric plasma spray (APS) and electron beam physical vapor deposition (EB-PVD), respectively. The incorporated nanostructure in TBCs resulted in substantial increase in thermal barrier effect and their lifetime. The long-term microstructure stability of the nanocoating was also investigated.

The microstructural evolution and powder particle morphology change in the process used to synthesize bulk nanostructured γ-TiAl intermetallic based binary Ti-47Al (in at%) alloy (TA-1) and complex Ti-45Al-2Cr-2Nb-1B-0.5Ta (in at%) alloy (TA-2) have been studied. This process combines high energy mechanical milling of elemental powder mixtures, thermal treatment and HIP. The bulk alloys consist of predominantly TiAl phase and a small fraction of Ti₃Al phase, with the average grain sizes of the TiAl and Ti₃Al phases being approximately 45nm and 40nm respectively in the bulk TA-1 alloy and being 37nm and 35nm respectively in the bulk TA-2 alloy. The study also shows that addition of a small fraction of hard powder particles such as Nb, Cr, B and Ta powder particles to the starting powder mixture has a significant effect in maintaining a small average particle size during high energy mechanical milling without using PCA and thus significantly enhances the mechanical alloying effect of the milling process.

Many rare-earth metals can react with Si atoms to form rare-earth metal silicides, which have a high conductivity and a low Schottky barrier on the n-type Si substrate. The investigations of the rare-earth metal silicide nanostructures self-assembled on the Si(001) surface are reviewed in this paper. The growth behaviors of Er silicide nanostructures are studied as the functions of annealing temperature, annealing time and Er coverage. The crystalline structures of the nanowires and nanoislands, the influence of substrate surface on the formation of nanostructures, and the shape transitions occuring during growth are analyzed comprehensively, which make contributions to the silicide nanostructure growth with the controlled structures and size-distributions. Furthermore, recent study progresses have been reported for the electrical and electronic properties of the rare-earth metal silicide nanowires.

Composites of polyaniline with synthesized nanostructured titania (TiO₂) and polyaniline with commercial TiO₂ have been in situ synthesized by oxidative chemical polymerization method. Sulfuric acid was used as dopant during the polymerization process. Sol-gel precipitates of nanostructured titania were synthesized by hydrolyzing the mixture of titanium chloride (TiCl₃) and colloidal transparent solution of starch. Composite materials were subjected for comparison to spectroscopic and X-ray diffraction analysis. Strong coupling/interaction of titania with the imine nitrogen in polyaniline confirmed by FTIR spectral analysis. XRD shows the composite of synthesized titania with polyaniline have broaden peak as compared to that of commercial titania with polyaniline indicating particle size in the range of nanometer scale which is supported by 40 nm particle size of the synthesized titania from TEM picture. Increase in conductivity with increasing temperature was observed in both the composite materials.

Large-scale replication of the natural process of photosynthesis is a crucial subject of storing solar energy and saving our environment. Here, we report femtosecond laser induced self-assembled metal nanostructure arrays, which are easily mass producible on earth-abundant metals, can directly synthesize liquid and solid hydrocarbon compounds from carbon dioxide, water, and sunlight at a production rate of more than 1 × 10⁵ μL/(gh) that is significantly (10³–10⁶ times) higher than those in previous studies.^1,2 The efficiency for storing solar energy of the photosynthesis is about 10% in the present simple experimental setup which can be further improved. Moreover, different from previous artificial photosynthesis works, this phenomenon presents a new mechanism that, through a surface-enhanced photodissociation process, nature-like photosynthesis can be performed artificially.

Nanostructured alumina ceramic templates have been fabricated by anodizing annealed high-purity aluminium foil. Pore diameter, pore separation and thickness in these alumina ceramics can be controlled using a range of acid electrolytes and anodizing voltage profiles. Thermal development of the structure of these robust and optically clear templates have been compared using XRD, thermal analysis and ²⁷Al MAS NMR techniques, showing that species substituted in the alumina lattice from decomposition of the acid electrolyte play a major role in determining the chemical and physical stability of the ceramic template at elevated temperatures. Deposition of ultrathin palladium films on the surface of these alumina templates creates robust membranes that enable hydrogen separation from mixed gas streams at elevated temperatures. Gas permeability measurements through these membranes as a function of temperature have demonstrated their very high selectivity for hydrogen.

In this study, the (FePt)_100-xCu_x (x=0, 4.6, 6.7, 8.8, 10.9) (FePtCu) alloy films were prepared by co-sputtering. The effects of Cu addition content and heat treatment on the nanostructure and magnetic properties of the polycrystalline (FePt)_100-xCu_x films are reported. The experimental results show that the ordering temperature of the (FePt)_100-xCu_x (x=6.7) films reduced to 320°C, which is much lower than that of the FePt alloy. After heat treatment at 600°C for 1 hour, the (FePt)_100-xCu_x (x=6.7) film shows a coercive force of 15 kOe and the magnetization of 576 emu/cc. The magnetic properties of the FePtCu films can be adjusted by varying the Cu content in the films. The enhancement of the magnetic properties of the FePtCu films mainly resulted from the formation of the order L1₀ phase. DSC traces of as-deposited disorder films at different heating rates, to evaluate the crystallization of the order phase, showed that the addition of Cu atoms reduced the activation energy of ordering from 217 kJ/mol to 87 kJ/mol for the (FePt)_100-xCu_x films (x= 0 and 6.7, respectively). The reduction of the ordering temperature and corresponding activation energy might due to the solid solution of the Cu atoms in the FePt films.

Cu-(5-10)vol.%Al₂O₃ nanocomposite powders were produced from a mixture of Cu powder and Al₂O₃ nanopowder using a high energy mechanical milling (HEMM) route consisting of two stages. The microstructural evolution of the Cu–Al₂O₃ nanocomposite powder particles (or granules) produced after first and the second stages of milling was studied using scanning electron microscopy (SEM), transmission electron microcopy (TEM), scanning transmission electron microscopy (STEM) and energy dispersive X-ray (EDX) mapping. The study confirmed that homogenous dispersion of Al₂O₃ nanoparticles in the Cu matrix was achieved after the first stage of milling and the relatively large Al₂O₃ particles were further broken into smaller nanoparticles after the second stage of milling. The milled nanocomposite powders were also heat treated at 150, 300, 400 and 500°C for 1 hour, respectively, to determine the microstructural changes of the powder particles as a function of annealing temperature. It was found that after heat treatment at 150°C, the Cu grain sizes decreased due to recrystallisation, and increasing the annealing temperature to 300°C causes slight coarsening of the Cu grains. Further increasing the annealing temperature to 500°C caused significant coarsening of the Cu grains and the Al₂O₃ nanoparticles. It also appeared that the coarsening of Cu grains in the composite powder particles after annealing at 500°C become less severe with increasing the volume fraction of Al₂O₃ particles.

Al₂O₃-20vol%Fe₇₀Co₃₀ composite powders have been prepared by high energy ball milling a mixture of Al₂O₃ powder and Fe₇₀Co₃₀ alloy powder. The Fe₇₀Co₃₀ alloy powder was also prepared by mechanical alloying of Fe and Co powders using the same process. The effects of milling duration from 8 to 48 hours on microstructure and magnetic properties of the nanostructured composite powders have been studied by means of X-ray Diffractometry (XRD), scanning electron microscopy (SEM) and vibrating sample magnetometry (VSM). It was found that the nanostructured composite powder particles with irregular shapes and Fe₇₀Co₃₀ alloy particles being embedded in them formed after 8 hours of milling. The average grain size of the Al₂O₃ matrix reduced drastically to less than 18nm after 16 hours of milling. On the other hand, the embedded alloy particles demonstrated almost unchanged average grain size in the range of 14-15nm. Magnetic properties of the powder compacts at room temperature were measured from hysteresis curves, and show strong dependence of the milling time, with the coercivity increasing from 67.1 up to 127.9kOe with increasing the milling time from 8 to 48 hours. The possible microstructural reasons for this dependence are discussed.

Styrene-doped ZrLaO_y nanostructures were obtained by sol–gel method low-temperature synthesis. The nanostructures were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), atomic force microscope (AFM) and transmission electron microscopy (TEM) techniques. The observation using SEM and TEM revealed that the ring-shaped nanostructures were very uniform. Further characterization using XRD disclosed that the cohesion of the samples was controllable with annealing temperatures in the range of 800–1500°C. Cohesion property was investigated for the samples. The cohesion increased when increasing the annealing temperature. This was linked to the reinforcement of the oxygen bound on the ZrLaO_y nanostructures The shape of nanostructures showed a transformation from a ring-shaped growth mode to a hole-surfaced growth mode with increasing annealing temperature. The styrene-doped ZrLaO_y nanostructures with controllable crystallinity will have great potential for various applications in fuel, cells, batteries, electronics devices and chemical sensors.

Tris(8-hydroxyquinoline) aluminum $({\mathrm{\text{Alq}}}_3)$ nanostructures are promising materials for nanooptoelectronic devices and molecular spintronics. In this paper, we report ${\mathrm{\text{Alq}}}_3$ nanocrystals prepared by both physical vapor deposition (PVD) and facile solution method. The transmission electron microscopy (TEM) and high resolution scanning electron microscope (SEM) measurements show that the ${\mathrm{\text{Alq}}}_3$ nanomaterials prepared by PVD technique are $\epsilon$-${\mathrm{\text{Alq}}}_3$ nanoflowers, while the ${\mathrm{\text{Alq}}}_3$ nanostructures prepared by solution method are $\alpha$-${\mathrm{\text{Alq}}}_3$ nanorods. Our experiments indicate that the $\alpha$-${\mathrm{\text{Alq}}}_3$ nanomaterials prepared by using solution method are more suitable for the fabrication of molecular spintronic devices than that of PVD method.

Effects of current density on nanostructure and light emitting properties of porous silicon (PS) samples were investigated by field emission scanning electron microscope (FE-SEM), gravimetric method, Raman and photoluminescence (PL) spectroscopy. FE-SEM images have shown that below 60 mA/cm², macropore and mesopore arrays, exhibiting rough morphology, are formed together, whose pore diameter, pore depth and porosity are about 265–760 nm, 58–63 μ m and 44–61%, respectively. However, PS samples prepared above 60 mA/cm² display smooth and straight macropore arrays, with pore diameter ranging from 900–1250 nm, porosity of 61–80% and pore depth between 63–69 μm. Raman analyses have shown that when the current density is increased from 10 mA/cm² to 100 mA/cm², Raman peaks of PS samples shift to lower wavenumbers by comparison to crystalline silicon (c-Si). The highest Raman peak shift is found to be 3.2 cm^-1 for PS sample, prepared at 90 mA/cm², which has the smallest nanocrystallite size, about 5.2 nm. This sample also shows a pronounced PL, with the highest blue shifting, of about 12 nm. Nanocrystalline silicon, with the smallest nanocrystallite size, confirmed by our Raman analyses using microcrystal model (MCM), should be responsible for both the highest Raman peak shift and PL blue shift due to quantum confinement effect (QCE).

This work reports the influence of sintering temperature on structure, microstructure and piezoelectric properties of 0.48 Ba(Zr${}_{0.2}$Ti${}_{0.8}$)O₃–0.52 (Ba${}_{0.7}$Ca${}_{0.3}$)TiO₃(BZT–BCT) doped with ZnO nanoparticle ceramics manufactured by a conventional solid state reaction method. By increasing sintering temperature, the piezoelectric behaviors were improved and rose up to the best parameters at a sintering temperature of 1450${}^{\circ }$C ($d_{33}=576$ pC/N and $k_p=0.55$). The corresponding properties of undoped BZT–BCT ceramics were investigated as a comparison. The received results show that the sintering behavior and piezo-parameters of doped BZT–BCT samples are better than the undoped BZT–BCT samples at each sintering temperature.

A group of ABO₃ perovskite-type oxides is currently under intensive studies for their potential as chemical sensing, ferroelectric memories, gas separation and computer devices. This group includes La${}_x$Sr${}_{1-x}$CoO₃ (LSCO). In the present work, we have synthesized LSCO samples by using the sol–gel method and studied their nano structural and electrical properties with using the scanning electron microscopy (SEM), energy dispersive X-ray (EDX), Current density–voltage ($J$–$V$) and Fourier transform infrared spectroscopy (FTIR) techniques. We synthesized nanoparticles with diameters between 50 and 100 nm by calcination of the pulverized gel powders, and then studied its structure. The band gap characteristics of the La${}_{0.5}$Sr${}_{0.5}$CoO₃ structure were also analyzed. The obtained results show that La${}_{0.5}$Sr${}_{0.5}$CoO₃ with favorable carrier mobility ($\sim 1.7\times 10^{-2}$ cm²v${}^{-2}$s${}^{-1}$) and dielectric constant (16) exhibits a variety of interesting physical properties which include ferroelectric, dielectric, pyroelectric and piezoelectric behavior.

The Cd${}_x$Zn${}_{1-x}$O thin films have been deposited on glass and Si substrates at room-temperature with different Cd contents (x = 0, 2%, 4% and 6 wt.%) by pulsed laser deposition (PLD) technique. X-ray diffraction (XRD) analyses evidenced that the films possess polycrystalline and a hexagonal ZnO crystal structure for x = 0, 2% and 4% with a preferred orientation in the a-axis (101) direction, while films with a mixed hexagonal and cubic structure was revealed for x = 6 wt.%. Electrical measurement presented that the resistivity decreased with increased temperature and concentration of Cd. The deliberated activation energy was reduced was from 0.224 to 0.113 eV with increase doping concentration. Current–voltage (I–V) and capacitance–voltage (C–V) characteristics of the fabricated Cd${}_x$Zn${}_{1-x}$O/p-Si heterojunction varied with the applied bias and the Cd concentration. The results of the values of built-in potential (V${}_{\mathrm{\text{bi}}}$) and the ideality factor (n) increased with raising Cd concentration.

Periodic nanostructures along the polarization direction of light are observed inside silica glasses and tellurium dioxide single crystal after irradiation by a focused single femtosecond laser beam. Backscattering electron images of the irradiated spot inside silica glass reveal a periodic structure of stripe-like regions of ~20 nm width with a low oxygen concentration. In the case of the tellurium dioxide single crystal, secondary electron images within the focal spot show the formation of a periodic structure of voids with ~30 nm width. Oxygen defects in a silica glass and voids in a tellurium dioxide single crystal are aligned perpendicular to the laser polarization direction. These are the smallest nanostructures below the diffraction limit of light, which are formed inside transparent materials. The phenomenon is interpreted in terms of interference between the incident light field and the electric field of electron plasma wave generated in the bulk of material.