Synthesis and optoelectrical properties of SnO2 nanospheres derived by microwave-assisted hydrothermal method

SnO₂ nanospheres have been synthesized by microwave-assisted hydrothermal method from the starting materials of citric acid and tin metallic particles. From the results of SEM and TEM images, it can be found that the SnO₂ nanospheres are uniform with diameter of ~100 nm and aggregated by SnO₂ nanocrystals with size of 8–10 nm. The photoluminescence spectrum of the nanospheres shows a peak at ~330 nm and a cutoff wavelength of around 400 nm. The pronounced photocurrent was recoded from the as-prepared SnO₂ nanospheres assembled on a Mo thin sheet under the UV illumination, which is suggested for the potential application of UV photodetector.     

Facile template-free one-pot fabrication of ZnCo<Subscript>2</Subscript>O<Subscript>4</Subscript> nanospheres for advanced lithium storage capability

Large-scale ZnCo₂O₄ nanospheres with an average diameter of 350 nm were developed via a hydrothermal method. By adjusting the molar ratio of polyvinyl pyrrolidone (PVP), the ZnCo₂O₄ nanospheres can be facilely designed. Meanwhile, controlled experiment factors, namely the concentration of reagents, play important roles in the formation of the nanospheres. The possible mechanism for the nanostructures formation was discussed. In addition, when tested as anode materials for lithium-ion batteries, these ZnCo₂O₄ nanospheres have exhibited excellent lithium-storage performance.     

Angular reflectance of suspended gold, aluminum and silver nanospheres on a gold film: Effects of concentration and size distribution

In this article, we describe a parametric study of the effects of the size distribution (SD) and the concentration of nanospheres in ethanol on the angular reflectance. Calculations are based on an effective medium approach in which the effective dielectric constant of the mixture is obtained using the Maxwell–Garnett formula. The detectable size limits of gold, aluminum, and silver nanospheres on a 50-nm-thick gold film are calculated to investigate the sensitivity of the reflectance to the SD and the concentration of the nanospheres. The following assumptions are made: (1) the total number of particles in the unit volume of suspension is constant, (2) the nanospheres in the suspension on a gold film have a SD with three different concentrations, and (3) there is no agglomeration and the particles have a log-normal SD, where the effective diameter, d _eff and the effective variance, ν _eff are given. The dependence of the reflectance on the d _eff, ν _eff, and the width of the SD are also investigated numerically. The angular variation of the reflectance as a function of the incident angle shows a strong dependence on the effective size of the metallic nanospheres. The results confirm that the size of the nanospheres (d _eff <100 nm) can be detected by reflected light from the bottom surface of a gold film with a reasonable sensitivity if a proper angle of incidence is chosen based on the type of metallic particles on a gold thin film at λ = 632 nm. We show that the optimum incident angle to characterize the size of nanospheres on a gold film is between 70° and 75° for a given concentration with a particular SD.     

Honeycomb-like manganese oxide nanospheres for redox supercapacitors

Honeycomb-like MnO₂ nanospheres were synthesized using stainless steel substrates by a facile chemical bath deposition method. The obtained nanospheres were about 200–400 nm in diameter and consisted of porous ultrathin nanosheets. Honeycomb-like MnO₂ nanospheres exhibited a high specific capacitance of 240 F g^?1 and 87.1% capacitance retention after 1000 cycles at a current density of 0.5 A g^?1. These remarkable electrochemical results imply great potential for applications of the honeycomb-like MnO₂ nanospheres in supercapacitors.     

Decoration of carbon nanotube with size-controlled L10-FePt nanoparticles for storage media

In this work, first multi-wall carbon nanotubes (MWCNTs) with outer diameter about 20–30 nm are synthesized by a CVD method; they have been purified and functionalized with a two-step process. The approach consists of thermal oxidation and subsequent chemical oxidation. Then, monosize FePt nanoparticles along carbon nanotubes surface are synthesized by a Polyol process. The synthesized FePt nanoparticles are about 2.5 nm in size and they have superparamagnetic behavior with fcc structure. The CNTs surfaces as a substrate prevent the coalescence of particles during thermal annealing. Annealing at the temperature higher than 600 ^°C for 2 h under a reducing atmosphere (90 % Ar + 10 % H₂) leads to phase transition from fcc to fct-L1₀ structure. So, the magnetic behavior changes from the superparamagnetic to the ferromagnetic. Furthermore, after the phase transition, the FePt nanoparticles have finite size with an average of about 3.5 nm and the coercivity of particles reaches 5.1 kOe.     

Surface topography of ultrashort laser-irradiated CaF2

A single-crystal CaF₂ (111) was irradiated with single and multiple laser (Ti:sapphire, 800 nm, 25 fs) shots at fluences ranging from 0.25 to 1.5 J cm^?2. In this fluence regime, a single laser pulse usually leads to typical bump-like features ranging from 200 nm to 1.5 μm in diameter and 10–50 nm in height. These bumps are related to compressive stresses due to a pressure build-up induced by fast laser heating and their subsequent relaxation. When CaF₂ is irradiated with successive (in our case 20) shots at a laser fluence of 1.5 J cm^?2, nanocavities at the top of the microbumps are observed. The formation of these nanocavities is regarded as an explosion and is attributed to the explosive expansion generated by shock waves due to laser-induced plasma after the nonlinear absorption of the laser energy by the material. Such kinds of surface structures at the nanometre scale could be attractive for nanolithography.     

Gold nanosphere propulsion by using femtosecond laser-excited enhanced near field

We propose nanosphere propulsion by using femtosecond laser-excited enhanced near field based on the theoretical calculations and experimental study. The optical intensity distribution and enhancement around a gold nanosphere on a silicon substrate was simulated by a 3D finite-difference time-domain method. The sphere velocities and propelled angles were calculated based on the optical intensity distribution. In our simulation, we calculated the optical intensity for the gold nanospheres with a diameter ranging from 100 to 600 nm. Calculation results show that the sphere velocity was fairly constant for the diameters ranging from 100 to 250 nm, while the velocity decreased for diameters larger than 250 nm. The propelled angle could be controlled up to only 4.6° by varying the incident angles of p-polarized waves. We have demonstrated the gold nanosphere propulsion in experiment. The gold nanospheres with a diameter of 200 nm were used in our experiments. The propelled gold particles have been melted by laser irradiation and deposited on the receiver substrate. The size and spatial distributions of gold particles have been investigated. The decrease in the laser spot size and the gap distance between the donor and receiver substrate would realize the reduction in the existence region of gold particles on the receiver substrate.     

Synthesis of Ni<Subscript>80</Subscript>Fe<Subscript>20</Subscript> and Co nanodot arrays by self-assembling of polystyrene nanospheres: magnetic and microstructural properties

Array of dots have been designed by assembling a monolayer of polystyrene nanospheres (PN) on sputtered thin films having Ni₈₀Fe₂₀ and Co composition with different thickness, ranging in the interval 20 ÷ 80 nm. Subsequently the films are nanopatterned using the nanospheres as a mask during sputter etching with Ar⁺ ions. A Reactive Ion Etching (RIE) process before sputter etching is used to control the final diameter of the magnetic dots that thus can be tailored as desired (typically ranging in the interval 250 ÷ 400 nm depending on the PN starting diameter). In addition, electron beam lithography has been exploited to obtain arrays of dots in Ni₈₀Fe₂₀ thin films having approximately the same mean size and dot distance as in self-assembled samples. All films have been routinely characterized by SEM and AFM microscopy to evaluate the microstructure. Magnetic domain patterns at magnetic remanence and in the demagnetised state have been imaged by MFM microscopy technique. Room-temperature hysteresis properties have been measured by an alternating gradient force magnetometer. In general, the magnetization process in all patterned films has been observed to have features typical of a vortex whose nucleation field depends on sample thickness and mean dot dimension. A comparison between magnetic arrays of Ni₈₀Fe₂₀ dots prepared by self-assembling of polystyrene nanospheres and electron beam lithography is presented to rule out the role of microstructure (i.e., order, size, and mutual distance of the magnetic dots) on magnetic properties.     

Atmospheric pressure chemical vapour synthesis of silicon–carbon nanoceramics from hexamethyldisilane in high temperature aerosol reactor

Silicon–carbon nanoceramics have been synthesised from hexamethyldisilane (HMDS) by the atmospheric pressure chemical vapour synthesis (APCVS). Direct aerosol phase synthesis enables continuous production of high purity materials in one-stage process. The particle formation is based on the decomposition of the precursor in a high temperature reactor. Reaction of the gas phase species leads to homogeneous nucleation and formation of the nanoparticles with a narrow size distribution (geometric mean diameter range of particle number size distribution 160–200 nm with 1.5–1.6 geometric standard deviation at reaction temperatures 800–1200 °C). A systematic investigation of the influence of the process temperature on the powder characteristics, including the particle size, crystallinity, chemical structure, surface and bulk composition and surface morphology, was carried out. At the reactor temperature of 800 °C, the synthesised nanoparticles were amorphous preceramics containing mostly SiC₄, Si–CH₂–Si and Si–H units. The composition of the powder turned towards nanocrystalline 3C–SiC (crystal size under 2 nm) when the reaction temperature was increased to 1200 °C. The reaction temperature appeared to be a key parameter controlling the structure and properties of the synthesised powders.     

A study of oleic acid-based hydrothermal preparation of CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles

Nearly monodisperse, well crystalline, superparamagnetic CoFe₂O₄ nanoparticles with diameter of 6 nm were synthesized in oleic acid–water–pentanol system at 180 °C. Hydrothermal procedure, as an efficient and environment friendly alternative to organic decomposition methods, was investigated by variation of reaction conditions, and the particle formation mechanism was finally proposed (i.e., hydrolysis of metal oleates in organic phase, with size of the particles (5–8 nm) controlled by polarity-driven precipitation into water phase). As-prepared particles were hydrophobic due to coating by oleic acid. Further modification with dimercaptosuccinic acid led to water-dispersible particles with hydrodynamic diameter of 20 nm. Prepared particles were investigated by TEM, XRD, ICP-AES, light scattering, SQUID magnetometry, and Mössbauer spectroscopy.     

Synthesis of Au-functionalized SnO2 nanotubes using TeO2 nanowires as templates and their enhanced gas sensing properties

Au-functionalized SnO₂ nanotubes were prepared for use as gas sensors using TeO₂ nanowires as templates. Transmission electron microscopy revealed tube diameters, tube lengths and tube wall thicknesses ranging from 50 to 200 nm, 5 to 50 μm, and 13 to 18 nm, respectively. The Au-functionalized SnO₂ nanotube sensors showed responses of 179–473 % to 1–5 ppm NO₂ at 300 ^°C. These values are much higher than those obtained using bare SnO₂ nanotubes synthesized in this study and most other SnO₂ one-dimensional nanostructure-based sensors reported in the literature. The NO₂ gas sensing mechanism of the Au-functionalized SnO₂ nanotube sensors is also discussed.     

Preparation of novel magnetic fluorescent nanospheres by sonochemical method

This study focuses on the preparation and characterization of magnetic fluorescent nanospheres (MFNs). MFNs are prepared using a sonochemical method in the presence of hydrophobic Fe₃O₄ nanopaticles, and then the nanospheres are modified with Rhodamine B through an electrostatic interaction. The properties of MFNs are characterized using transmission electron microscopy, Fourier-transform infrared, thermogravimetric analysis, vibration sample magnetometry, and fluorescence emission spectrum. The results indicate that the superparamagnetic nanospheres have a particle size of 160 nm, high saturation magnetization of 54 emu/g, and significant fluorescence. MFNs possess potential in medical imaging, drug targeting, and catalysis. The possible formation mechanism of MFNs is discussed.     

Fabrication and characterization of MoO3 clusters-coated TiO2 nanotubes showing charge-transferred photoluminescence

MoO₃ clusters-coated TiO₂ nanotubes were synthesized wet-chemically and characterized by measuring photoluminescence spectra and kinetic profiles as well as extinction spectra and electron microscope images. TiO₂ nanotubes having an average outer diameter of 30 nm and an average thickness of 8 nm are surrounded by MoO₃ clusters with an average thickness of 4 nm. The excitation of both the TiO₂ cores and the MoO₃ shells of the type-II nanocomposites suspended in water yields charge-transferred junction photoluminescence having a long lifetime of 2.3 ns at 460 nm.     

Effect of the particle size on the electrochemical performance of nano-Li2FeSiO4/C composites

Nano-Li₂FeSiO₄/C composites were prepared from three kinds of nano-SiO₂ (their particle sizes are 15?±?5, 30?±?5, and 50?±?5 nm, respectively) by a traditional solid-state reaction method. The as-prepared materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), elementary analyzer, Brunauer–Emmett–Teller (BET) analysis, galvanostatic charge–discharge test, and electrochemical impedance spectroscopy. XRD results reveal that nano-Li₂FeSiO₄ composites fabricated from nano-SiO₂ (smaller than 30 nm) have less impurity. SEM results indicate that the particle size of nano-Li₂FeSiO₄ composites is nearly accord with the particle size of nano-SiO₂. BET analysis indicates that the specific surface areas of LFS15, LFS30, and LFS50 are 35.10, 35.27, and 26.68 m² g, respectively, and the main pore size distribution of LFS15, LFS30, and LFS50 are 1.5, 5.5, and 10 nm, respectively. Electrochemical measurements indicate that nano-Li₂FeSiO₄ composites prepared from nano-SiO₂ of 30?±?5 nm have the best electrochemical performance among the three samples.     

Formation of metallic NbSe2 nanotubes and nanofibers

We succeed in synthesizing NbSe₂ nanotubes along with nanofibers by chemical vapor transportation. They are stable crystalline systems and can be synthesized reproducibly in a nearly equilibrium reacting process. We have investigated these nanosize structures of NbSe₂ by transmission electron microscopy and electron diffraction. Both of the structures have a similar size of 100–200 nm in diameter. While nanotubes consist of rolled-up NbSe₂ layers, nanofibers are a pile of thin flat layers. We propose a mechanism of the formation of NbSe₂ nanotubes and nanofibers on the basis of deseleniditive transition from a NbSe₃ fiber-shaped crystal. We also measured electrical resistance of the nanofibers with conductive atomic force microscopy and demonstrated that the material show metallic behavior at room temperature.     

Sn and SnO2-graphene composites as anode materials for lithium-ion batteries

Sn and SnO₂-graphene composites were synthesized using hydrothermal process, followed by annealing in Ar/H₂ atmosphere, and characterized using x-ray diffraction, scanning electron microscopy, and transition electron microscopy. The results indicated that the polycrystalline metallic Sn forms nanospheres with a diameter of 100?～?300 nm, while the SnO₂ nanoparticles are much smaller with a size below 15 nm, which adsorb tightly on the surface of graphene sheets. The Sn and SnO₂-gaphene composites showed good electrochemical performance. After 55 charging/discharging cycles, the capacity remains above 440 mAh/g at a cycling rate of 400 mA/g and the coulombic efficiency is 99.1 %. The good electrochemical properties of the composites are partially contributed to the graphene component with good mechanical flexibility and electrical conductivity, which is an excellent carbon matrix for dispersing the Sn and SnO₂ nanostructures and provides the electron transport pathways as well.     

Effect of particle size on the photochromic response of PWA/SiO2 nanocomposite

A series of photochromic phosphotungstic acid (PWA)/SiO₂ composites were synthesized using the sol-gel method. Depending on the feeding schedule of PWA during synthesis, the size of the formed PWA/SiO₂ particles varied considerably from as small as 1.2 nm to ca. 10 nm. With decreasing silica particle size, the total contact area/interaction between SiO₂ and PWA increases, as revealed by FT-IR and solid-state ²⁹Si-NMR analyses. Particularly, when the size of PWA/SiO₂ is ~1 nm, crystallization of PWA is inhibited, and PWA presents as amorphous molecular entities distributing uniformly in the SiO₂ host, which is in evidence in the XRD spectroscopy and HR-TEM imaging. In contrast, substantial crystallization of PWA takes place when PWA/SiO₂ particles are as large as 10 nm, in which case less amount of surface free Si-OH is available for PWA to make bonds with. Photochromism occurs activated by ultraviolet light irradiation. The rate of coloration/bleaching is found to depend strongly on the particle size of PWA/SiO₂; specifically, the rate increases twice when the particle size is reduced from 10 nm to 1.2 nm.     

Morphological and optical properties of soft-landed supported nanoclusters: effect of rapid thermal annealing

We report the formation of large islands of bi-modal lateral size distributions having one peak at lateral size ～100 nm (height ～70 nm) and another at ～160 nm (height ～110 nm) by soft-landing of size-selected copper nanoclusters (3 nm in diameter) at room temperature (26 °C). Si(100) wafer containing native oxide is used as substrate. Transmission electron microscopy (TEM), scanning electron microscopy (SEM) and atomic force microscopy (AFM) are employed to study the morphological aspects and for optical aspect cathodoluminescence measurement is used. Rapid thermal annealing (RTA) (200 °C, dry N₂, 120 s) induced effects on the morphology shows that individual islands are morphologically stable. A careful qualitative study of the optical property using cathodoluminescence in a SEM before and after the thermal treatment, using RTA, reveals very low diffusion of the cluster material into the substrate.     

Disordered chromite in the Martian meteorite Allan Hills 84001

The magnetic structure of NiFe₂O₄ nanoparticles has been investigated by means of Mössbauer spectra at T?=?4.2 K in applied fields up to 12 T. Four samples were studied, with mean particle diameters ranging from 4.3 to 8.9 nm. All spectra could be decomposed into three sextets, two corresponding to the ferrimagnetic sublattices of Fe ions in the spinel structure (core) and the third one to randomly frozen spins near the particle surface (shell). The shell thickness, calculated from the fraction of disordered spins, was found to be about one-third of the particle radius at H _app?=?0 and to decrease with the applied field toward a common limit of ~0.4 nm. The mean canting angle relative to the field was also found to decrease for increasing fields, at a rate inversely correlated to the particle size.