Tailoring optical properties of TiO2 nanowires coated with Ag nanoparticles by plasmon coupling of Ag nanoparticles

TiO₂ nanowires were grown on titanium foil by an alkali hydrothermal growth method. The as-synthesized nanowires are structurally uniform with diameters of 50-100 nm and lengths of up to a few micrometers. The as-prepared TiO₂ nanowires were coated with Ag nanoparticles by reducing AgNO₃ in solution. The experimental results indicate that the Ag nanoparticles can aggregate together on the surfaces of TiO₂ nanowires by interconnection between nanoparticles. The degree of aggregation of Ag nanostructures can be controlled by changing the concentrations of Ag nanoparticles. The as-prepared nanostructures exhibit a wide optical absorption from 387 to 580 nm that can be easily tuned by controlling the degree of aggregation of Ag nanostructures. The results reveal that optical properties of the Ag-coated TiO₂ nanowires can be enhanced by plasmon coupling of Ag nanoparticles. The as-prepared nanostructures may find potential applications in the field of solar cells.     

Ease of control and switching between ordered free-standing arrays of ZnO nanotubes and nanorods on conductive transparent substrates

Free-standing arrays of ZnO nanotubes and nanorods have selectively been synthesized on indium tin oxide substrates using a template-based electrodeposition method for the first time. The effect of deposition voltage on the growth pattern of Zn in the alumina template has been investigated, providing a tailored ability to reliably produce either nanotubes or nanorods. An annular tungsten base electrode, derived from the anodization of the alumina template, has been found to be crucial to the growth of nanotubes. This method may be adapted for the fabrication of free-standing arrays of other metal and metal oxide nanotubes and nanorods on conducting substrates.     

Real-time measurements of sliding friction and elastic properties of ZnO nanowires inside a scanning electron microscope

A real-time nanomanipulation technique inside a scanning electron microscope (SEM) has been used to investigate the elastic and frictional (tribological) properties of zinc oxide nanowires (NWs). A NW was translated over a surface of an oxidised silicon wafer using a nanomanipulator with a glued atomic-force microscopic tip. The shape of the NW elastically deformed during the translation was used to determine the distributed kinetic friction force. The same NW was then positioned half-suspended on edges of trenches cut by a focused ion beam through a silicon wafer. In order to measure Young’s modulus, the NW was bent by pushing it at the free end with the tip, and the interaction force corresponding to the visually observed bending angle was measured with a quartz tuning fork force sensor.     

Effect of growth temperature on the ZnO nanowires prepared by thermal heating of Zn powders

ZnO nanowires have been synthesized by heating Zn powders under nitrogen (N₂) gas atmosphere. The influence of the growth temperature on the morphology, structure, and photoluminescence (PL) properties of ZnO nanowires has been investigated. At the higher-temperature growth process, thinner nanowires have been obtained. Interestingly, it is observed that the variation of growth temperature has significantly affected the photoluminescence spectra of the ZnO nanowires, showing an enhancement in the relative intensity of the green to UV emission bands with the increase of the growth temperature. In addition, the oxygen sensing properties of the as-synthesized ZnO nanowires were tested.     

Pyrolysis synthesis of magnetic - and -MnO2 nanostructures and the polymorph discrimination

The concentration of the Mn(NO₃)₂ solution has significant influence on the morphologies and the phases of the MnO₂ products. A large number of ε- MnO₂ nanowires were prepared via a simple pyrolysis under lower reaction concentration. The nanowires have lengths up to tens of micrometers and diameters in the range of 20–100 nm. The β- MnO₂ nanobundles and nanoflowers were prepared by increasing the concentration of Mn(NO₃)₂ solution. The superparamagnetism of ε- MnO₂ nanowires and paramagnetism of β- MnO₂ nanoflowers indicate their potential applications in magnetic materials.     

Characterisation of porous doped ZnO thin films deposited by spray pyrolysis technique

Al or Sn doped ZnO films were deposited by spray pyrolysis using aqueous solutions. The films were deposited on either indium tin oxide coated or bare glass substrates. ZnCl₂, AlCl₃ and SnCl₂ were used as precursors. The effect of ZnCl₂ molar concentration (0.1-0.3 M) and doping percentage (2-4% AlCl₃ or SnCl₂) have been investigated. The main goal of this work being to grow porous ZnO thin films, small temperature substrates (200-300 °C) have been used during the spray pyrolysis deposition. It is shown that, if the X-ray diffraction patterns correspond to ZnO, the films deposited onto bare glass substrate are only partly crystallized while those deposited onto ITO coated glass substrate exhibit better crystallization. The homogeneity of the films decreases when the molar concentration of the precursor increases, while the grain size and the porosity decrease when the Al doping increases. The optical study shows that band tails are present in the absorption spectrum of the films deposited onto bare glass substrate, which is typical of disordered materials. Even after annealing 4 h at 400 °C, the longitudinal resistivity of the films is quite high. This result is attributed to the grain boundary effect and the porosity of the films. Effectively, the presence of an important reflection in the IR region in samples annealed testifies of a high free-carriers density in the ZnO crystallites. Finally it is shown that when deposited in the same electrochemical conditions, the transmission of a polymer film onto the rough sprayed ZnO is smaller than that onto smooth sputtered ZnO.     

Catalyst-free synthesis of GeO2 nanowires using the thermal heating of Ge powders

Germanium dioxide (GeO₂) nanowires have been synthesized by means of the simple evaporation of solid Ge powders, without using metal catalysts. The nanowires, with a diameter of about 90–200 nm, were characterized using scanning electron microscopy (SEM), X-ray diffractometry (XRD), and transmission electron microscopy (TEM). The obtained GeO₂ nanowires were crystalline with a hexagonal structure. The growth mechanism was discussed with respect to the vapor–solid process. The photoluminescence measurement revealed two emission peaks at about 2.45 eV and 2.91 eV at room temperature, opening up a route to potential applications in future optoelectronic nanodevices. Raman measurement of as-synthesized GeO₂ nanowires was made at room temperature.     

The effect of zinc ions on the fluorescence spectra of (La, Zn)OF:Sm powder phosphors

This paper reports the fluorescence properties of a new series of (La, Zn) OF:Sm³⁺ powder phosphors. The measured fluorescence spectra were analyzed by computing the color coordinates and relative fluorescence intensity ratios (ED/MD). A bright yellowish-orange color was observed from these powder phosphors under a UV-source due to the confirmation of the transitions ⁴G_5/2→⁶H_5/2, ⁴G_5/2→⁶H_7/2, and ⁴G_5/2→⁶H_9/2. Scanning electron microscopic studies were performed to understand the average grain size of the synthesized powder phosphors.     

In situ scanning electron microscope electrical characterization of GaN nanowire nanodiodes using tungsten and tungsten/gallium nanoprobes

A lithography-free technique for measuring the electrical properties of n-type GaN nanowires has been investigated using nanoprobes mounted in a scanning electron microscope (SEM). Schottky contacts were made to the nanowires using tungsten nanoprobes, while gallium droplets placed in situ at the end of tungsten nanoprobes were found to be capable of providing Ohmic contacts to GaN nanowires. Schottky nanodiodes were fabricated based on single n-type nanowires, and measured current–voltage (I–V) results suggest that the Schottky nanodiodes deviate from ideal diodes mainly due to their nanoscopic contact area. Additionally, the effect of the SEM electron beam on the I–V characteristics was investigated and was found to impact the transport properties of the Schottky nanodiodes, possibly due to an increase in carrier density in the nanodiodes.     

Structural and spectroscopic studies of thin film of silver nanoparticles

We report the deposition of thin film of silver (Ag) nanoparticles by wet chemical method. The as-synthesized Ag nanoparticles have been characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), X-ray energy dispersive spectroscopy (EDS), field emission transmission electron microscopy (FETEM) and high-resolution TEM (HRTEM), UV-vis spectroscopy and thermogravimetric-differential thermal analysis (TG-DTA) respectively. FESEM image indicates that the silver film prepared on the quartz substrate is smooth and dense. XRD pattern reveals the face-centered cubic (fcc) structure of silver nanoparticles. EDS spectrum indicates that samples are nearly stoichiometric. From TEM analysis, it is found that the size of high purity Ag nanoparticles is ranging from 10 to 20 nm with slight agglomeration. Absorption in UV-vis region by these nanoparticles is characterized by the features reported in the literature, namely, a possible Plasmon peak at ∼403 nm. Optical absorbance spectra analysis reveals that the Ag film has an indirect band structure with bandgap energy 3.88 eV. TGA/DTA studies revealed that a considerable weight loss occurs between 175 and 275 °C; and the reaction is exothermic.     

Effect of low-energy electron irradiation on the cathodoluminescence of multiple quantum well (MQW) InGaN/GaN structures

The effect of low-energy electron-beam (e-beam) irradiation on the InGaN-related cathodoluminescence in multiple quantum well (MQW) InGaN/GaN light-emitting diode (LED) structures has been studied. It is shown that the e-beam exposure leads to an increase of emission intensity and to a formation of new blue-shifted emission bands. The changes observed were explained by the enhancement of In diffusion stimulated by excess carrier recombination.     

Short time and low temperature mineralization of ZnO nanorod-bunches from solution using cetyl trimethyl ammonium bromide

The low temperature mineralization of zinc oxide nanorod bunches from zinc precursor solution mixed with the cationic surfactant Cetyl Trimethyl Ammonium Bromide is reported. Five different combinations of zinc precursor and surfactant ratios are chosen and their properties are compared using the average particle size, lattice parameter ratio (c/a$c/a$) of hexagonal ZnO from X-ray diffraction, the morphologies from SEM, TEM and their optical characteristics by using optical absorption spectroscopy spectrometry. A surfactant lowers the surface tension of the solution, and forms a thermodynamically ordered and a disordered phase wherein, ordered phase seeds the growth of the ZnO nanostructures. A peculiar circular structure called ‘micelle’ is formed by the surfactant. The heads, located on the peripheries of the micelle, are the ordered phase in the solution, and are the original nucleation sites of the Zinc Oxide nanostructures. This fashion of nucleation is the reason for the ‘arms of the wheel-like’ morphology consisting of nanorod bunches. Out of the five combinations experimented, the 3:1, 3:2, 1:1 ratios show nearness in the standard c/a$c/a$ value. The photoluminescence spectrum shows UV emission in the region of 380 nm and weak blue emission. The UV–VIS–NIR spectrum has exhibited a characteristic UV-absorption.     

Real-time manipulation of gold nanoparticles inside a scanning electron microscope

The forces needed to overcome static friction and move 150 nm diameter Au nanoparticles on an oxidized Si substrate were measured in Normal and Shear oscillation modes inside a scanning electron microscope (SEM) in real time. The experimental setup consisted of a quartz tuning fork (QTF) mounted onto a high-precision 3D nanomanipulator used with a glued silicon or tungsten tip as a force sensor. Static friction was found to range from tens of nN to several hundred nN. Large variations in static friction values were related to differences in particle shape. Kinetic friction tended to be close to the detection limit and in most cases did not exceed several nN. The influence of thermal treatment in reducing the static friction of nanoparticles was considered.     

Characteristics of SiOx nanowires synthesized via the thermal heating of Cu-coated Si substrates

We have demonstrated the growth of SiO_x nanowires by the simple heating of the Cu-coated Si substrates. We have applied X-ray diffraction, scanning electron microscopy and transmission electron microscopy techniques to characterize the structure of the samples. The as-synthesized SiO_x nanowires had amorphous structures with diameters in the range of 20–80 nm. The thickness of the Cu layer affected the resultant sample morphology, favoring the nanowire formation at smaller thickness. Photoluminescence spectra of the nanowires exhibited blue emission. We have proposed the possible growth mechanism.     

Exploring electro-optic effect of impurity doped quantum dots in presence of Gaussian white noise

We explore the profiles of electro-optic effect (EOE) of impurity doped quantum dots (QDs) in presence and absence of noise. We have invoked Gaussian white noise in the present study. The quantum dot is doped with Gaussian impurity. Noise has been administered to the system additively and multiplicatively. A perpendicular magnetic field acts as a confinement source and a static external electric field has been applied. The EOE profiles have been followed as a function of incident photon energy when several important parameters such as electric field strength, magnetic field strength, confinement energy, dopant location, relaxation time, Al concentration, dopant potential, and noise strength possess different values. In addition, the role of mode of application of noise (additive/multiplicative) on the EOE profiles has also been scrutinized. The EOE profiles are found to be adorned with interesting observations such as shift of peak position and maximization/minimization of peak intensity. However, the presence of noise and also the pathway of its application bring about rich variety in the features of EOE profiles through some noticeable manifestations. The observations indicate possibilities of harnessing the EOE susceptibility of doped QD systems in presence of noise.     

Thioglycolic acid (TGA) assisted hydrothermal synthesis of SnS nanorods and nanosheets

Nanorods and nanosheets of tin sulfide (SnS) were synthesized by a novel thioglycolic acid (TGA) assisted hydrothermal process. The as prepared nanostructures were characterized by X-ray diffraction (XRD) study, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). XRD study reveals the formation of well-crystallized orthorhombic structure of SnS. Diameter of the SnS nanorods varied within 30-100 nm. High-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) patterns identify the single crystalline nature for the SnS nanocrystals. The mechanism for the TGA assisted growth for the nanosheets and nanorods have been discussed.     

The influence of hydrogen on the growth of gallium catalyzed silicon oxide nanowires

In this paper, we report that amorphous silicon oxide nanowires can be grown in a large quantity by chemical vapor deposition with molten gallium as the catalyst in a flow of mixture of SiH₄, H₂ and N₂ at 600 °C. Meanwhile, when we grow these nanowires under the same conditions but without H₂, octopus-like silicon oxide nanostructures are obtained. The reasons and mechanisms for the growth of these nanowires and nanostructures are discussed. Blue light emission is observed from SiO_x nanowires, which can be attributed to defect centers of high oxygen deficiency. These SiO_x nanowires may find applications in nanodevices and reinforcing composites.     

Reflux synthesis of Co3O4 nanoparticles and its magnetic characterization

Co₃O₄ nanoparticles have been prepared for the first time via reflux method, as an alternative low-temperature high-yield process, starting from one single precursor. A plausible mechanism is suggested for the synthetic process. XRD, TEM, FTIR and VSM were used for the structural, morphological, spectroscopic, and magnetic characterization of the product respectively. X-ray diffraction line profile fitting showed that average particle size of the sample is 28 nm. Morphology of the synthesized powder was observed to be thin nanosheets with a thickness of 2-3 nm based on SEM and TEM analyses. Magnetic measurements showed a deviation of the Neel temperature from the bulk value which is attributed to the finite size effects. A loop shift with an enhanced coercivity is observed in the field-cooled hysteresis loops. The opening of the hysteresis loop reveals the existence of the spin-glass like surface spins of the Co₃O₄ nanoparticles.     

Surface morphology and step fluctuations on Ag nanowires

Silver nanowires fabricated using a wet-chemical synthesis have been characterized in UHV using scanning tunneling microscopy. The nanowires have a faceted structure with a high density of steps at the facet boundaries. Monolayer height steps are easily imaged, and have measurable temporal fluctuations at room temperature. Measurement of the step time correlation functions shows that the steps fluctuate via periphery diffusion, with a hopping time constant of 0.10-0.24 s. The symmetry of islands on the facets and the quantitative step characteristics are both consistent with (1 0 0) oriented facets, in agreement with previous TEM characterization.