Polymer assisted preferential growth of PbS and PbS:Mn nanorods: structural and optical properties

We report here the structural and optical properties of PbS and PbS:Mn nanorods (diameter 30–80 nm) grown in a polymer (polypyrrole) matrix. X-ray diffraction data of nanorods clearly reveals preferential growth of PbS nanorods with a strong lattice distortion from a bulk cubic to tetragonal one. The strain introduced lattice distortion is inherent to the growth process and strongly depends on polymer concentration. The polymer concentration is found to play an important role in controlling the structural properties. The effect of Mn²⁺ incorporation into PbS lattice shows no appreciable change in the structural properties. Optical absorption behaviors in such PbS and PbS:Mn nanorods are also reported. The absorption peak energy shows blue-shift with increase in Mn²⁺ concentration to some critical value beyond which red-shift is observed.     

Structural properties of Sm doped cerium oxide nanorods synthesized by hydrolysis assisted co-precipitation method

Cubic phase of 5% samarium doped cerium oxide nanoparticles was successfully synthesized by hydrolysis assisted co-precipitation method. The average grain sizes of the as-prepared and annealed (800 °C) samples were 12-16 nm respectively. The rod like morphology of the post annealed sample was revealed by transmission electron microscope (TEM). The nanoparticles exhibited the orange and red color emissions when excited at 330 nm. The as-prepared and annealed powders showed orange emission with maximum intensity at 574 nm which is the characteristic peak of the Sm³⁺ ion corresponding to the magnetic dipole transition between the ⁴G_5/2 and ⁶H_5/2 states. Size dependent luminous intensity was observed from photoluminescence studies.     

Crystallite, optical and photocatalytic properties of visible-light-driven ZnIn2S4 photocatalysts synthesized via a surfactant-assisted hydrothermal method

A series of ZnIn₂S₄ photocatalysts were synthesized via a surfactant-assisted hydrothermal method. The products were characterized with X-ray diffraction (XRD), UV-vis-near-IR diffuse reflectance spectra (UV-vis), photoluminescence spectra (PL) and field emission scanning electron microscope (FESEM). The results indicated that the CTAB-assisted ZnIn₂S₄ product had a wider band gap than the other three ZnIn₂S₄ products (CPBr-assisted, SDS-assisted and no-surfactant-assisted ZnIn₂S₄). The surfactant (especially CTAB) addition would greatly affect the crystal structure (i.e. d(0 0 6) along the c-axis) of ZnIn₂S₄. The photocatalytic activities of the as-prepared samples were evaluated by photocatalytic hydrogen production from water under visible light irradiation. The CTAB-assisted ZnIn₂S₄ product, with quantum yield (420 nm) determined to be 11.9%, had a much higher photocatalytic activity than the other three ZnIn₂S₄ products in our photocatalytic system. The energy conversion efficiency in the whole visible light region was determined to be 3.1% for the CTAB-assisted ZnIn₂S₄ photocatalyst.     

Effect of Ni-doping on optical and magnetic properties of solvothermally synthesized ZnS wurtzite nanorods

In this study we have reported the effect of Ni-doping on optical and magnetic properties of ZnS nanorods. The diameter and length of low temperature solvothermally synthesized, high quality nanorods are 10 and 50–300 nm respectively as revealed from transmission electron microscopy. From X-ray diffraction, the structure of Ni-doped nanorods was observed as wurtzite with lattice parameters, a = 3.83 and c = 6.26. The band gap of the undoped and doped samples was found to be blue shifted as compared to the bulk counterpart when analyzed with UV–visible spectroscopy. Quenching in photoluminescence spectra was observed in case of Ni-doped nanorods as compared to undoped counterpart. The magnetization as analyzed from vibrating sample magnetometer was found to increase with 1 and 5 % Ni-doping concentration, and decrease with further increase in Ni-doping concentration, i.e., with 10 % Ni-doping.     

Flower-like Se nanorods synthesized via carbamide-assisted hydrothermal routes

Flower-like Se nanostructures consisting of clusters of nanorods with width of 40–100 nm and length of several 100 nm have been synthesized via a carbamide-assisted hydrothermal method. The optimal clusters are composed of nanorods protruding from a central point. FESEM and TEM demonstrate the flower-like morphology. The X-ray diffraction (XRD) pattern shows that the as-prepared flower-like Se nanostructures are of hexagonal phase.     

Temperature dependent optical properties of PbS nanocrystals

A comprehensive study of the optical properties of PbS nanocrystals (NCs) is reported that includes the temperature dependent absorption, photoluminescence (PL) and PL lifetime in the range of 3-300 K. The absorption and PL are found to display different temperature dependent behaviour though both redshift as temperature is reduced. This results in a temperature dependent Stokes shift which increases from ～75 meV at 300 K with reducing temperature until saturating at ～130 meV below ～150 K prior to a small reduction to 125 meV upon cooling from 25 to 3 K. The PL lifetime is found to be single exponential at 3 K with a lifetime of τ(1) = 6.5 μs. Above 3 K biexponential behaviour is observed with the lifetime for each process displaying a different temperature dependence. The Stokes shift is modelled using a three-level rate equation model incorporating temperature dependent parameter values obtained via fitting phenomenological relationships to the observed absorption and PL behaviour. This results in a predicted energy difference between the two emitting states of ～6 meV which is close to the excitonic exchange energy splitting predicted theoretically for these systems.     

Size,morphology and optical properties of zirconia (ZrO<Subscript>2</Subscript>) nanostructures synthesized via the facile ionic surfactant-assisted solvothermal method

Zirconia (ZrO₂) nanostructures, assisted by various ionic surfactants were successfully achieved via the facile ionic surfactants-assisted solvothermal method with the average crystallite size of 7.09–15.22 nm. The spherical, cauliflower-petal and needle-like nanostructures were confirmed by SEM studies and possible growth mechanisms of the nanostructures were proposed. The increasing trends of the band gap energy confirm the quantum confinement effect for the prepared samples. The strong UV emission in photoluminescence of the prepared samples indicates the high purity, perfect crystallinity and is good candidate material for optoelectronic devices.     

Synthesis of cross-shaped PbS nanostructures by a surfactant-assisted reflux process

Cross-shaped PbS crystals composed of six pods were prepared by a reflux process using CTAB as the surfactant. Parameters affecting the morphology of PbS have been investigated systematically. Results reveal that various PbS structures including cubic, truncated octahedral, flower-shaped and dendritic crystals can be obtained by changing the sulfur and lead source, the solvent or the surfactant. The difference of the morphology was explained to be closely related to the change of the relative growth rate in the 〈100〉 direction to that in the 〈111〉 direction.     

The structural and optical properties of ZnO nanorods via citric acid-assisted annealing route

ZnO nanorods with diameters ranging from 25 to 88 nm and with length up to 1 μm were obtained via citric acid-assisted annealing route. The sample was characterized by X-ray diffraction, field-emission scanning electron microscopy (FE-SEM), Raman spectrometer, FTIR spectrophotometer, ultraviolet visible (UV–VIS) spectroscopy, and photoluminescence (PL) spectroscopy. It demonstrates that the sample is composed of ZnO with hexagonal structure and the ZnO nanorods are of excellent optical quality.     

Nonlinear optical properties of gold nanoparticles synthesized by ion implantation in sapphire matrix

Single crystal Al₂O₃ substrates have been implanted with 160-keV Au⁺ to a dose of 0.6 × 10¹⁷ or 1.0 × 10¹⁷ cm⁻², with a postimplantation annealing for 1 h at 800°C in air. The obtained composite layers were studied by the method of linear optical reflection; the nonlinear optical characteristics were determined by the RZ-scan technique using picosecond radiation pulses of an Nd:YAG laser operating at 1064 nm. The appearance of a characteristic surface optical plasmon resonance band in the linear reflection spectra was indicative of the formation of gold nanoparticles in a subsurface layer of ion-irradiated Al₂O₃. It is shown that the synthesized particles are responsible for the observed manifestations of nonlinear refraction. The composite layers were characterized by the nonlinear refractive index (n ₂) and the real part of the third-order nonlinear susceptibility (Reϰ ⁽³⁾).     

The formation of WO3 nanorods using the surfactant-assisted hydrothermal reaction

Monoclinic tungsten oxide (WO₃) nanorods were grown using the hydrothermal method on a seeded W foil. The seed layer was formed by thermal oxidation of W foil at 400°C for 30 min. Cetyltrimethylammonium bromide (CTAB) or hexamethylamine (HMT) was used in the reactive hydrothermal bath, along with sodium tungstate dihydrate (Na₂WO₄.2H₂O) and hydrochloric acid (HCl). The concentration of CTAB was varied from 0.01 M to 0.07 M and the concentration of HMT was varied from 0.01 M and 0.05 M. The result showed that CTAB-assisted hydrothermal reaction produced WO₃ nanorods with 4–7 nm diameter, and provided that CTAB concentration was less than 0.07 M. WO₃ nanorods could not be obtained when CTAB concentration was 0.07 M. Columnar structured WO₃ was produced with the presence of HMT in the hydrothermal bath. This was due to decomposition of HMT to form hydroxyl ions (OH^?) that inhibited the growth of nanorods. Cyclic voltammetry (CV) analysis showed better electrochromic property of WO₃ nanorods compared to columnar structured WO₃.     

Large scale hydrothermal synthesis of PbS nanorods

PbS nanorods with a diameter of 20-50 nm have been synthesized successfully by surfactant-assisted hydrothermal route. The product was over 90% yield according to the amount of Pb(CH₃CHOO)₂ used. Experiments showed that the concentration of N-cetyl-N,N,N-trimethyl- ammonium bromide (CTAB) and thiourea (Tu), reaction time and sulfur sources played important roles in the formation of the PbS nanorods. A reasonable mechanism for the formation of the PbS nanorods is also discussed.     

A chemical synthesized Al-doped PbS nanoparticles hybrid composite for optical and electrical response

Structural, morphological, optical and electrical investigations of pure and Al-doped lead sulfide (PbS) nanoparticles hybrid composite was synthesized by simple chemical route. The detail analysis of the nanoparticle morphology of hybrid composites through optical investigation, phase purity and crystalline size had been characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), ultraviolet spectroscopy (UV), photoluminescence (PL). The lower angle XRD results confirmed that the phase purity and average crystalline size of the pure and Al doped PbS nanoparticles were determined by using the Debye–Scherrer’s formula. The average grain sizes of the pure and the Al-doped PbS nanoparticles were calculated and found to be 22 and 16 nm respectively. Surface morphology analysis was carried out by using SEM and TEM analysis. The surface morphology of pure and Al doped PbS nanoparticles is without any pinholes or cracks and hence they appear to be densely packed with spherical shaped grains. The optical properties of pure and Al-doped PbS analyzed using UV–Vis. absorption spectroscopy and Photoluminiscence (PL) spectra. The band gap values for the pure and the Al-doped PbS nanoparticles were found to be 1.94 and 2.04 eV respectively. The dielectric properties of the Al-doped PbS nanoparticle composites typical response e.g. dielectric constant, dielectric loss, and AC conductivity were analyzed at various frequencies and temperatures.     

Synthesis and optical properties of single-crystalline GaN nanorods

Single-crystalline GaN nanorods were successfully synthesized on Si(1 1 1) substrates through ammoniating Ga₂O₃/Mo films deposited on the Si(1 1 1) substrate by radio frequency magnetron sputtering technique. The as-synthesized nanorods are confirmed as single-crystalline GaN with wurtzite structure by X-ray diffraction (XRD), selected-area electron diffraction (SAED) and high-resolution transmission electron microscopy (HRTEM). Scanning electron microscopy (SEM) displays that the GaN nanorods are straight and smooth with diameters in the range of 100-200 nm and lengths typically up to several micrometers. X-ray photoelectron spectroscopy (XPS) confirms the formation of bonding between Ga and N. The representative photoluminescence spectrum at room temperature exhibits a strong and broad emission band centered at 371.1 nm, attributed to GaN band-edge emission. The growth process of GaN nanorod may be dominated by vapor-solid (VS) mechanism.     

Magnetic properties of magnetite nanoparticles synthesized by forced hydrolysis

We report the synthesis of superparamagnetic nanoparticles of iron oxide in magnetite phase with diameters of approximately 15 nm. Nanoparticles of magnetite were synthesized by forced hydrolysis method, controlling the oxidation with a nitrogen atmosphere during the synthesis. Nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Mössbauer spectroscopy and vibrating sample magnetometry. Quantitative analysis of crystalline phases was done by performing Rietveld refinement of the XRD profiles. In order to obtain nanometers sizes of magnetite phase solely, the parameters of formation such a pH and molar concentration were analyzed and determined by an equilibrium thermodynamics model with the chemical computer code MINTEQA [Allison Geoscience Consultants, Inc., HydroGeoLogic, Inc., MINTEQA2 for Windows, Equilibrium Speciation Model. Ver 1.5(2003)].     

Preparation and photoluminescence properties of reverse type-I ZnO/PbS core/shell nanorods

ZnO/PbS one-dimensional core/shell nanorods have been fabricated by a two-step growth method. Photoluminescence properties of these samples with different shell thickness are studied in detail. The result reveals that the photoluminescence intensity of the ZnO/PbS core/shell nanorods changes with the increase of thickness of PbS shell. When the shell is very thin, the increase in photoluminescence intensity is attributed to the modification of surface defect state. When the shell becomes thicker, the formation of a reverse type-I band alignment between the core and shell is ascribed to be the factor resulting in the decrease in intensity of the photoluminescence properties.     

Nonlinear quantum optical computing via measurement

Abstract

We show how the measurement induced model of quantum computation proposed by Raussendorf and Briegel (2001, Phys. Rev. Letts., 86, 5188) can be adapted to a nonlinear optical interaction. This optical implementation requires a Kerr nonlinearity, a single photon source, a single photon detector and fast feed forward. Although nondeterministic optical quantum information proposals such as that suggested by KLM (2001, Nature, 409, 46) do not require a Kerr nonlinearity they do require complex reconfigurable optical networks. The proposal in this paper has the benefit of a single static optical layout with fixed device parameters, where the algorithm is defined by the final measurement procedure.     

Low-temperature growth and optical properties of Ce-doped ZnO nanorods

Ce-doped ZnO nanorod arrays were grown on zinc foils by a hydrothermal method at 180°C. The effects of Ce-doping on the structure and optical properties of ZnO nanorods were investigated in detail. The characterisation of the rod array with X-ray diffraction and X-ray photoelectron spectroscopy indicated that Ce³⁺ ions were incorporated into the ZnO lattices. There were no diffraction peaks of Ce or cerium oxide in the pattern. From UV-Vis spectra, we observed a red shift in the wavelength of absorption and decreased band gap due to the Ce ion incorporation in ZnO. The photoluminescence integrated intensity ratio of the UV emission to the deep-level green emission (I _UV/I _DLE) was 1.25 and 2.87, for ZnO and Ce-doped ZnO nanorods, respectively, which shows a great promise for the Ce-doped ZnO nanorods with applications in optoelectronic devices.     

Size-dependent optical and dielectric properties of nanocrystalline ZnS thin films synthesized via rf-magnetron sputtering technique

Nanocrystalline ZnS thin films have been synthesized by radio frequency magnetron sputtering technique on glass and Si substrates at a substrate temperature 300 K. X-ray diffraction and selected area electron diffraction studies confirmed the formation of nanocrystalline cubic phase of ZnS in the films, although the target material was hexagonal ZnS. The particle size, calculated from the XRD patterns of the thin films was found in the range 2.06-4.86 nm. TEM micrographs of the thin films revealed the manifestation of ZnS nanoparticles with sizes in the range 3.00-5.83 nm. UV-vis-NIR spectrophotometric measurements showed that the films were highly transparent (∼90%) in the wavelength range 400-2600 nm with a blue shift of the absorption edge. The direct allowed bandgaps have been calculated and they lie in the range 3.89-4.44 eV. The particle size, calculated from the shift of direct bandgap, due to quantum confinement effect lying in the range 3.23-5.60 nm, well support the TEM results. The room temperature photoluminescence spectra of the films showed two peaks centered around 315 and 450 nm. We assigned the first peak due to bandgap transitions while the latter was due to sulfur vacancy in the films. The composition analysis by energy dispersive X-rays also supported the existence of sulfur deficiency in the films. The dielectric property study showed high dielectric constant (85-100) at a higher frequency (>5 kHz).     

Thermal and optical properties of epoxy/zirconia hybrid materials synthesized via in situ polymerization

Epoxy/zirconia hybrid materials were synthesized from a bisphenol-A type epoxy resin, zirconium-tetra-n-propoxide and acetic acid via in situ polymerization. Acetic acid was used to control the hydrolysis and condensation reaction of the zirconium-tetra-n-propoxide. As a result, the zirconia produced by the in situ polymerization was uniformly dispersed into the epoxy matrix on a nano scale or less, and the hybrid materials exhibited an excellent optical transparency. With the increasing zirconia contents, the storage modulus in the rubbery region increased and the peak area of tanδ in the glass transition temperature region decreased. These results indicate that their heat resistance of the hybrid materials could be improved by hybridization with zirconia. Furthermore, the refractive indices of the hybrid materials were significantly improved with the increasing zirconia contents.