Functionalized CdS nanospheres and nanorods

Functionalized nanoparticles are discussed. Surfaces of CdS:Mn/ZnS core/shell nanospheres (Qdots) were converted from hydrophobic to hydrophilic by growth of a SiO₂ shell. The colloidal dispersion was stabilize by adding a surfactant with a negative surface charge, and a cell-penetrating-peptide, TAT, was attached through a primary amine group. The TAT functionalized Qdots were shown to pass the blood-brain-barrier and luminescence in the infused half of the brain.In addition, nanorods of S²⁻ rich CdS were synthesized by reaction of excess S with Cd precursors in the presence of ethylene diamine. The photoluminescence (PL) peak from the S²⁻ rich CdS nanorods was broad with a maximum at ∼710 nm, which was 40 nm longer in wavelength than the PL peak from Cd²⁺ rich CdS (∼670 nm) nanorods. The influence of surface electron or hole trap states on the luminescent pathway of CdS nanorods were used to explain these shifts in wavelength. Nanocrystals of Au with ∼2 nm diameters were grown on S²⁻ rich surfaces of CdS nanorods. Significant quenching of photoluminescence was observed from Au nanocrystals on CdS nanorods due to interfacial charge separation. Charge separation by Au nanocrystals on CdS resulted in enhanced UV photocatalytic degradation of Procion red mix-5B (PRB) dye in aqueous solution.     

Solvothermally synthesized europium-doped CdS nanorods: applications as phosphors

To exploit the photoluminescent behavior of CdS at nanoscale with different doping concentration of europium—a rare earth element, we report the synthesis of Eu-doped CdS nanorods by using low temperature solvothermal process by using ethylenediamine. The outcomes can have future applications as phosphors, photovoltaic cells, lasers, light emitting diodes, bio-imaging, and sensors. The doping was confirmed by electron dispersive spectroscopy supported by X-ray diffraction. From scanning electron microscopy and transmission electron microscopy analysis it was observed that the average diameter of the Cd_1−x Eu _x S nanorods is about 10–12 nm having lengths in the range of 50–100 nm. UV–Visible spectroscopy study was carried out to determine the band gap of the nanorods and the absorbance peaks showed blue shift with respect to the bulk CdS. The blue shift was also observed as the doping concentration of Eu increases. From photoluminescence (PL) studies at λ_ex = 450 nm, peaks at 528 and 540 nm were observed due to CdS, peak at 570 nm is due to defects related transitions, while the peak at 613 nm is due to Eu. As the doping concentration of Eu is increased the intensity of the luminescent peak at 613 nm is increased. Thermogravimetric analysis showed the nanorods are thermally stable up to 300 °C. The traces of impurities adsorbed on the nanorods were confirmed by Fourier transform infrared spectroscopy.     

TiO<Subscript>2</Subscript> Nanorod Arrays Sensitized with CdS Quantum Dots for Solar Cell Applications: Effects of Rod Geometry on Photoelectrochemical Performance

CdS quantum dot (QD) sensitized TiO₂ nanorod array (NRA) film electrodes with different rod geometries were fabricated via a solvothermal route followed by a sequentialchemical bath deposition (S-CBD) process. By controlling the solution growth conditions, the rod geometries, especially the tip structures, of the TiO₂ NRAs were tuned. The results indicated that the vertically aligned hierarchical NRAs possessed conically shaped tip geometry, which was favorable for film electrodes due to the reduced reflectance, enhanced light harvesting, fast charge-carrier separation and transfer, suppression of carrier recombination, sufficient electrolyte penetration and subsequent efficient QD assembly. CdS QD sensitized TiO₂ NRA film electrodes with tapered tips exhibited an enhanced photoelectrochemical (PEC) performance, a photocurrent intensity of 5.13 mA/cm² at a potential of 0 V vs. saturated calomel electrode, an open-circuit potential of −0.68 V vs. saturated calomel electrode and an incident photon to current conversion efficiency (IPCE) of 22% in the visible-light region from 400 to 500 nm. The effects of rod geometry on the optical absorption, reflectance, hydrophilic properties and PEC performance of bare TiO₂ and CdS QD sensitized TiO₂ NRA film electrodes were investigated. The mechanism of charge-carrier generation and transfer in these CdS QD sensitized solar cells based on vertically aligned TiO₂ nanorods is discussed.     

Preparation of Ru-loaded CdS/Al-HMS nanocomposites and production of hydrogen by photocatalytic degradation of formic acid

The composite of aluminum-substituted mesoporous silica (Al-HMS) molecular sieve coupled with CdS (CdS/Al-HMS) was prepared by template, ion exchange and sulfurization reactions. The result of low angle XRD patterns showed that the low content of 2.5 wt% CdS is incorporated inside Al-HMS channels. The results of diffuse reflectance UV-visible spectra and fluorescence emission spectra exhibited that the absorption edge and photoluminescence peak for CdS/Al-HMS are blue-shifted about 75 nm and 40 nm in comparison to bulk CdS, respectively. The activities of hydrogen production by photocatalytic degradation of formic acid were evaluated under visible light irradiation (λ ≥ 420 nm) and the CdS/Al-HMS loaded 0.07 wt% Ru showed the highest H₂ evolution at a rate of 3.7 mL h⁻¹ with an apparent quantum yield of 1.2% at 420 nm.     

Preparation and characterization of CdS/Si coaxial nanowires

CdS/Si coaxial nanowires were fabricated via a simple one-step thermal evaporation of CdS powder in mass scale. Their crystallinities, general morphologies and detailed microstructures were characterized by using X-ray diffraction, scanning electron microscope, transmission electron microscope and Raman spectra. The CdS core crystallizes in a hexagonal wurtzite structure with lattice constants of a=0.4140 nm and c=0.6719 nm, and the Si shell is amorphous. Five Raman peaks from the CdS core were observed. They are 1LO at 305 cm⁻¹, 2LO at 601 cm⁻¹, A₁-TO at 212 cm⁻¹, E₁-TO at 234 cm⁻¹, and E₂ at 252 cm⁻¹. Photoluminescence measurements show that the nanowires have two emission bands around 510 and 590 nm, which originate from the intrinsic transitions of CdS cores and the amorphous Si shells, respectively.     

Nucleation control for ZnO nanorods grown by catalyst-driven molecular beam epitaxy

We report a study of the annealing temperature and time on Ag catalyst size and density for subsequent growth of ZnO nanorods by catalyst-driven molecular beam epitaxy (MBE). Two different substrates (SiO₂ and SiN_X) for the Ag deposition were used and the thickness of the Ag held constant at 25 Å. Annealing between 600 and 800 °C produced Ag cluster sizes in the range 8-30 nm diameter on SiO₂ and 10-65 nm on SiN_X with a cluster density from 100 to 2500 mm⁻² for SiO₂ and 30 to 1900 mm⁻² for SiN_X. ZnO nanorods grown on these clusters show single-crystal, wurtzite-phase nature and strong band-edge photoluminescence at 380 nm. The nanorods can also be grown selectively on lithographically-patterned dielectric stripes with Ag clusters formed on top by e-beam evaporation and annealing.     

Anionic polymerization in Co and Fe doped ZnO: Nanorods,magnetism and photoactivity

The growth mechanism of Zn_1−xCo_xO (ZC) and Zn_1−xFe_xO (ZF) nanorods, and resulting magnetic and optical properties have been studied. The ZC and ZF nanorods were prepared by sol–gel synthesis route. X-ray diffraction results in polycrystalline phase with wurtzite structure of ZC and ZF nanorods. The transmission electron microscopy images show the formation of nanorods. The growth mechanism of nanorods is explained on the basis of agglomeration of Zn²⁺ with OH⁻ ions which is react with poly vinyl alcohol involve anionic polymerization of oriented growth. Magnetic measurement of ZC and ZF nanorods exhibit superferromagnetic behavior and the large value of saturation magnetization observed at room temperature. The magnetization below room temperature measurement confirms the origin of observed magnetism. Raman and photoluminescence spectra show good photoactivity. The observed Raman active modes show wurtzite structure belongs to C_6v symmetry group. Photoluminescence measurements of ZC and ZF nanorods exhibit ultraviolet peaks at 413.90 nm (∼3 eV) due to free exciton emission and at 546.31 nm (∼2.27 eV) due to transition from deep donor states which arises from oxygen vacancy.     

Shape and size transformation of gold nanorods (GNRs) via oxidation process: A reverse growth mechanism

The anisotropic shape transformation of gold nanorods (GNRs) with H₂O₂ was observed in the presence of “cethyl trimethylammonium bromide” (CTAB). The adequate oxidative dissolution of GNR is provided by the following autocatalytic scheme with H₂O₂: Au⁰ → Au⁺, Au⁰ + Auⁿ⁺ → 2Au³⁺, n = 1 and 3. The shape transformation of the GNRs was investigated by UV-vis spectroscopy and transmission electron microscopy (TEM). As-synthesised GNRs exhibit transverse plasmon band (TPB) at 523 nm and longitudinal plasmon band (LPB) at 731 nm. Upon H₂O₂ oxidation, the LPB showed a systematic hypsochromic (blue) shift, while TPB stays at ca. 523 nm. In addition, a new emerging peak observed at ca. 390 nm due to Au(III)-CTAB complex formation during the oxidation. TEM analysis of as-synthesised GNRs with H₂O₂ confirmed the shape transformation to spherical particles with 10 nm size in 2 h, whereas centrifuged nanorod solution showed no changes in the aspect ratio under the same condition. Au³⁺ ions produced from oxidation, complex with excess free CTAB and approach the nanorods preferentially at the end, leading to spatially directed oxidation. This work provides some information to the crystal stability and the growth mechanism of GNRs, as both growth and shortening reactions occur preferentially at the edge of single-crystalline GNRs, all directed by Br⁻ ions.     

Hydroxyethyl cellulose-assisted hydrothermal synthesis of Bi2S3 urchin-like colonies

Orthorhombic Bi₂S₃ with different morphologies was successfully synthesized by the acid-catalyst hydrothermal reactions of bismuth nitrate (Bi(NO₃)₃) and thiourea (NH₂CSNH₂) solutions containing different amounts of hydroxyethyl cellulose (HEC). Phase, morphologies, and optical properties were characterized by X-ray diffraction, selected area electron diffraction, scanning and transmission electron microscopy, and ultraviolet-visible spectroscopy. The products, hydrothermally synthesized in the HEC-free, 0.25 g HEC-added, 0.5 g HEC-added and 1.00 g HEC-added solutions, were respectively proved to be orthorhombic Bi₂S₃ irregular nanorods, complete urchin-like colonies of regular nanorods, incomplete urchin-like colonies of regular nanorods, and highly crystalline regular nanorods growing along the [001] direction. Tauc band gaps of the orthorhombic Bi₂S₃ nanorods, synthesized in the HEC-free, 0.25 g HEC-added, and 1.00 g HEC-added solutions were determined to be 3.0, 1.75 and 1.8 eV, respectively. Formation mechanism of orthorhombic Bi₂S₃ nanorods, synthesized in the HEC-free and HEC-added solutions, was also discussed at great detail.     

Architectures of YF<Subscript>3</Subscript>:Eu<Superscript>3+</Superscript> solid and hollow sub-microspheres: a facile arginine-assisted hydrothermal synthesis and luminescence properties

Solid and hollow YF₃:Eu³⁺ spheres assembled by nanorods have been successfully synthesized via a facile arginine-assisted hydrothermal method and followed by a subsequent heat-treatment process. The experimental results reveal that the as-prepared YF₃:Eu³⁺ spheres are composed of the nanorods with a diameter of 20–50 nm and a length of 200–500 nm, the morphologies of YF₃:Eu³⁺ have been changed from solid to hollow spheres assembled by nanorods. With increase of hydrothermal temperature and time, the diameter of YF₃:Eu³⁺ spheres can be controlled from 300 to 800 nm. The solid and hollow spheres show an intense orange red emission peak near 595 nm, corresponding to the ⁵D₀ → ⁷F₁ transition of Eu³⁺. The possible formation mechanism for the hollow spheres has been presented in detail. This amine acid-assisted method is very simple, economic and environmental friendly for organic-free solvent, which would be potentially used in synthesizing other hollow materials.     

An in-depth investigation of physical properties of Nd doped CdS thin films for optoelectronic applications

The different contents (0 wt.%, 1 wt.%, 3 wt.% and 5 wt.%) of Nd @CdS films were casted using spray pyrolysis deposition procedure. The preferential orientation of crystallites along (002) for all films was noted by XRD profiles. The mean crystalline size (D_avg), strain (ɛ_avg) and dislocation density (δ_avg) have also been evaluated using XRD results and discussed. The spherical shape morphology of nanoscale particles of Nd@CdS films were analyzed by FE-SEM, exhibits the increased grain sizes with Nd doping concentration. The optical band gaps (2.4–2.36 eV) were found to be decreased with increasing Nd doping content upto (3 wt.%) and increased at 5 wt.% The PL profile displays a stout intensity peak observed at 532 nm and week emission band at 638 nm. The dielectric constant, loss and loss tangent of pristine and Nd@CdS thin films were investigated by dielectric measurements. The optimum values of non-linear refractive index 1.06 × 10⁻¹⁰, 4.41 × 10⁻¹¹, 3.44 × 10⁻¹¹ and 1.85 × 10⁻¹⁰ were observed for Nd content varies from pristine to 5 wt.% respectively. Furthermore, optimum non-linear susceptibility values 7.31 × 10⁻¹², 1.079 × 10⁻¹², 4.53 × 10⁻¹³ and 1.36 × 10⁻¹¹ were observed for 0, 1, 3 and 5 wt.% of Nd contents respectively in CdS. Such type of characteristics of Nd doped CdS thin films can be useful for optical devices.     

Optical properties of cadmium sulfide nanocrystal film prepared by electrochemical synthesis at liquid-liquid interface

Dendritic nanocrystalline CdS film was deposited at liquid-liquid interface of surfactants and an electrolyte containing 4 mmol L⁻¹ cadmium chloride (CdCl₂) and 16 mmol L⁻¹ thioacetamide (CH₃CSNH₂) with an initial pH value of 5 at 15 °C by electrochemical synthesis. The nanofilm was characterized by transmission electron microscopy (TEM), field emission scanning electron microscope (FE-SEM), atomic force microscopy (AFM), ultraviolet visible (UV-vis) absorption spectroscopy and fluorescence spectroscopy. The surface morphology and particle size of the nanofilm were investigated by AFM, SEM and TEM, and the crystalline size was 30-50 nm. The thickness of the nanofilm calculated by optical absorption spectrum was 80 nm. The microstructure and composition of the nanofilm was investigated by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), showing its polycrystalline structure consisting of CdS and Cd. Optical properties of the nanofilm were investigated systematically by UV-vis absorption and fluorescence spectroscopy. A λ_onset blue shift compared with bulk CdS was observed in the absorption spectra. Fluorescence spectra of the nanofilm indicated that the CdS nanofilm emitted blue and green light. The nanocomposites film electrode will bring about anodic photocurrent during illumination, showing that the transfer of cavities produces photocurrent.     

Structure and magnetic properties of Zn<Subscript>0.9</Subscript>Co<Subscript>0.1</Subscript>O nanorods synthesized by a simple sol–gel method using metal acetylacetonate and poly(vinyl alcohol)

Room-temperature ferromagnetism was observed in Zn_0.9Co_0.1O nanorods with diameters and lengths of ∼100–200 nm and ∼200–1000 nm, respectively. Nanorods were synthesized by a simple sol–gel method using metal acetylacetonate powders of Zn and Co and poly(vinyl alcohol) gel. The XRD, FT-IR and SAED analyses indicated that the nanorods calcined at 873–1073 K have the pure ZnO wurtzite structure without any significant change in the structure affected by Co substitution. Optical absorption measurements showed absorption bands indicating the presence of Co²⁺ in substitution of Zn²⁺. The specific magnetization of the nanorods appeared to increase with a decrease in the lattice constant c of the wurtzite unit cell with the highest value being at 873 K calcination temperature. This magnetic behavior is similar to that of Zn_0.9Co_0.1O nanoparticles prepared by polymerizable precursor method. We suggest that this behavior might be related to hexagonal c-axis being favorable direction of magnetization in Co-doped ZnO and the 873 K (energy of 75 meV) being close to the exciton/donor binding energy of ZnO.     

Growth and characterization of pine-needle-shaped GaN nanorods by sputtering and ammoniating process

Pine-needle-shaped GaN nanorods have been successfully synthesized on Si(111) substrates by ammoniating Ga₂O₃/Nb films at 950 ^°C in a quartz tube. The products are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and field-emission transmission electron microscope (FETEM). The results show that the pine-needle-shaped nanorods have a pure hexagonal GaN wurtzite with a diameter ranging from 100 to 200 nm and a length up to several microns. The photoluminescence spectra (PL) measured at room temperature only exhibit a strong emission peak at 368 nm. Finally, the growth mechanism of GaN nanorods is also briefly explored.     

Synthesis of high quality and monodisperse CdS:Mn/ZnS and CdS:Mn/CdS core–shell nanoparticles

CdS:Mn²⁺/ZnS and CdS:Mn²⁺/CdS core–shell nanoparticles were synthesized in aqueous medium via chemical precipitation method in an ambient atmosphere. Polyvinylpyrrolidone (PVP) was used as a capping agent. The effect of the shell (ZnS and CdS) thickness on CdS:Mn²⁺ nanoparticles was investigated. Inorganically passivated core/shell nanocrystals having a core (CdS:Mn²⁺) diameter of 4 nm and a ZnS-shell thickness of ∼0.5 nm exhibited improved PL intensity. Optimum concentration of doping ions (Mn²⁺) was selected through optical study. For all the core–shell samples two emission peaks were observed, the first one is band edge emission in the lower wavelength side due to energy transfer to the Mn²⁺ ions in the crystal lattice; the second emission is characteristic peak of Mn²⁺ ions (⁴T₁ → ⁶A₁). The XRD, TEM and PL results showed that the synthesized core–shell particles were of high quality and monodisperse.     

Generation of CdS clusters using laser ablation: the role of wavelength and fluence

The formation of cationic clusters in the laser ablation of CdS targets has been investigated as a function of wavelength and fluence by mass spectrometric analysis of the plume. Ablation was carried out at the laser wavelengths of 1064, 532, 355, and 266 nm in order to scan the interaction regimes below and above the energy band gap of the material. In all cases, the mass spectra showed stoichiometric Cd _n S _n ⁺ and nonstoichiometric Cd _n S _n−1⁺, Cd _n S _n+1⁺, and Cd _n S _n+2⁺ clusters up to 4900 amu. Cluster size distributions were well represented by a log-normal function, although larger relative abundance for clusters with n=13, 16, 19, 34 was observed (magic numbers). The laser threshold fluence for cluster observation was strongly dependent on wavelength, ranging from around 16 mJ/cm² at 266 nm to more than 300 mJ/cm² at 532 and 1064 nm. According to the behavior of the detected species as a function of fluence, two distinct families were identified: the “light” family containing S₂⁺ and Cd⁺ and the “heavy” clusterized family grouping Cd₂⁺ and Cd _n S _m ⁺. In terms of fluence, it has been determined that the best ratio for clusterization is achieved close to the threshold of appearance of clusters at all wavelengths. At 1064, 532, and 355 nm, the production of “heavy” cations as a function of fluence showed a maximum, indicating the participation of competitive effects, whereas saturation is observed at 266 nm. In terms of relative production, the contribution of the “heavy” family to the total cation signal was significantly lower for 266 nm than for the longer wavelengths. Irradiation at 355 nm in the fluence region of 200 mJ/cm² has been identified as the optimum for the generation of large clusters in CdS.     

Optical and AFM study of electrostatically assembled films of CdS and ZnS colloid nanoparticles

CdS and ZnS semiconducting colloid nanoparticles coated with the organic shell, containing either SO₃⁻ or NH₂⁺ groups, were prepared using the aqueous phase synthesis. The multilayer films of CdS (or ZnS) were deposited onto glass, quartz and silicon substrates using the technique of electrostatic self-assembly. The films produced were characterized with UV-vis spectroscopy, spectroscopic ellipsometry and atomic force microscopy. A substantial blue shift of the main absorption band with respect to the bulk materials was found for both CdS and ZnS films. The Efros equation in the effective mass approximation (EMA) theoretical model allowed the evaluation of the nanoparticle radius of 1.8 nm, which corresponds well to the ellipsometry results. AFM shows the formation of larger aggregates of nanoparticles on solid surfaces.     

Synthesis and photoluminescence of single-crystal GaN nanorods prepared by sol-gel method

A new method was applied to prepare GaN nanorods. In this method, gallium oxide (Ga₂O₃) gel was firstly formed by a sol-gel processing using gallium ethanol, Ga(OC₂H₅)₃, as a new precursor. GaN nanorods were successfully synthesized after annealing of the Ga₂O₃ gel at 1000 °C for 20 min in flowing ammonia. The as-prepared nanorods were 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). Transmission electron microscopy (TEM) displayed that the GaN nanorods were straight and smooth, with diameters ranging from 200 nm to 1.8 μm and lengths typically up to several tens of microns. When excited by 280 nm light at room temperature, the GaN nanorods had a strong ultraviolet luminescence peak located at 369 nm and a blue luminescence peak located at 462 nm, attributed to GaN band-edge emission and the existence of the defects or surface states, respectively.     

Effect of intrinsic ZnO thickness on the performance of SnS/CdS-based thin-film solar cells

Tin monosulfide (SnS) has promising properties as an absorber material for thin-film solar cells (TFSCs). SnS/CdS-based TFSCs have the following device structure: SLG/Mo/SnS/CdS/i-ZnO/AZO/Al. The optimization of thickness of intrinsic zinc oxide (i-ZnO) for SnS-absorber layers and its impact on SnS/CdS heterojunction TFSCs has been investigated at different thicknesses ranging from 39 nm to 73 nm. With the increase in thickness of i-ZnO from 39 nm to 45 nm, the overall performance improved. The highest PCE of 3.50% (with V_OC of 0.334 V, J_SC of 18.9 mA cm⁻², and FF of 55.5%) was observed for 45 nm-thick i-ZnO layers. Upon a further increase in the i-ZnO thickness to 73 nm, the device performance deteriorated, indicating that the optimum thickness of the i-ZnO is 45 nm. The device performances were analyzed comprehensively for different i-ZnO thicknesses.     

Eu,Li doped CaWO4 nanorods: Synthesis,emission-decay curves and effective-refractive index

In the present paper, CaWO₄: Eu³⁺, Li⁺ nanorods have been successfully synthesized via an oleic acid (OA)-assisted solvethermal route. The transmission electron microscope (TEM) photograph shows that the CaWO₄: Eu³⁺, Li⁺ nanorods are monodisperse and uniform nanorods with average diameter of 26 nm. The optical properties of Eu³⁺ in CaWO₄ samples, including photoluminescence (PL) excitation spectra and luminescent decay curves, are investigated in detail. Due to the form of the nanorods, the relative contribution of CTB to the nanorods sample is greater than that to the bulk counterparts. The decay time of the ⁵D₀ level (ranging from 0.94 to 0.65 ms, depending on the filling factor of the nanorods) of the nanorods is longer than that of the bulk counterpart mainly due to the reduction in the size of the nanorods, which introduces an effective-refractive index smaller than the refractive index of CaWO₄.