Structural,optical and magnetic properties of cobalt-doped CdS dilute magnetic semiconducting nanorods

Nanostructures of dilute magnetic semiconductors (DMS) in which a part of host material is replaced by a magnetic dopant are the promising candidates for spintronic devices. Pure and cobalt-doped DMS nanorods of CdS have been synthesized by solvothermal method. The effect of doping as well as the size of synthesized nanorods on structural, optical, and magnetic properties has been investigated. Transmission electron microscopy confirms the nanorods' morphology with an average diameter between 7 and 11 nm. Structural study reveals the formation of single phase hexagonal wurtzite structure of CdS with P6₃mc space group. UV–visible absorption spectra confirms that the band gap of the synthesized nanorods lie in the visible region between 2.46 and 2.72 eV. Photoluminescence spectra show defects-free nature of synthesized nanorods. The hump of emission band, around 430 nm in Co-doped CdS nanorods, attributes to the direct transition from the energy states created in CdS. Magnetic study reflects the ferromagnetic character of synthesized nanorods with high magnetic saturation, 0.034, 0.041, 0.070 and 0.090 emu g⁻¹ for, respectively, pure, 5%, 10% and 15% Co-doped CdS nanorods. The observed ferromagnetism in the synthesized nanorods have been explained on the basis of F-center (sulfur vacancy) mediated exchange mechanism and indirect interaction among Co (II) centers.     

Ferromagnetism in Gd-doped CdS dilute magnetic semiconducting nanorods

Cd _x Gd_1?x S (x = 0–0.15) nanorods have been synthesized by solvothermal technique. X-ray diffraction study reveals that pure and Gd-doped CdS nanorods exhibits hexagonal wurtzite structure. Transmission electron microscopy reveals nanorods like morphology of synthesized CdS having 14 and 26 nm size of pure and 15 % doped CdS nanorods. UV–Visible absorption study confirms the blue shift in the energy band energy due to the quantum confinement effects. Photoluminescence spectra confirm the defect free nature of the synthesized nanorods with peaks emerging around 528 and 540 nm due to the green emission. The magnetic study shows that the pure and Gd-doped CdS nanorods exhibits ferromagnetic character and the magnetisation increased by five times from 0.074 to 0.422 emu/g upon Gd-doping.     

Optical and magnetic properties of copper doped ZnO nanorods prepared by hydrothermal method

Surfactant free ZnO and Cu doped ZnO nanorods were synthesized by hydrothermal method. The formation of ZnO:Cu nanorods were confirmed by scanning electron microscopy, X-ray diffraction and Raman analysis. Diffuse reflectance spectroscopy results shows that band gap of ZnO nanorods shifts to red with increase of Cu content. The orange-red photoluminescent emission from ZnO nanorods originates from the oxygen vacancy or ZnO interstitial related defects. ZnO:Cu nanorods showed strong ferromagnetic behavior, however at higher doping percentage of Cu the ferromagnetic behavior was suppressed and paramagnetic nature was enhanced. The presence of non-polar E ₂ ^high and E ₂ ^low Raman modes in nanorods indicates that Cu doping didn’t change the wurtzite structure of ZnO.     

Room temperature ferromagnetism in Tb-doped ZnO dilute magnetic semiconducting nanoparticles

Pure and Tb-doped ZnO nanoparticles have been synthesized by chemical co-precipitation method. The transmission electron microscopy study reveals the spherical morphology of synthesized nanoparticles with average particle size 14–18 nm. The effect of Tb-doping on structural, optical and magnetic properties has been studied. X-ray diffraction shows that pure and Tb-ZnO nanoparticles exhibit wurtzite structure having hexagonal phase with primitive unit cell. It further reveals that there is no effect of Tb-doping on the X-ray diffraction pattern up to 2 % doping, however, higher doping concentration result in accumulation of Tb on ZnO surface. Photoluminescence spectra reveal that the doping Tb in ZnO changes crystallographic structure generating non-radiative oxygen vacancies. Three emission peaks located around 423, 485 and 515 nm has been observed. Pure ZnO nanoparticles show diamagnetic character, however, Tb-doped ZnO nanoparticles exhibit room temperature ferromagnetism. The correlation between defects generated upon Tb-doping to the observed ferromagnetism, in the synthesized nanoparticles, has been reported.     

CdS:Mn nanorods: solvothermal synthesis and properties

Manganese (0.05-9 mol.%) doped CdS nanorods were synthesized via solvothermal route using ethylenediamine (En) and a mixture of En and water as the solvents. The diameters and the lengths of the doped CdS nanorods varied from 40-100 nm and 600-2500 nm, respectively, with change in the composition of the solvents. The broad photoluminescence (PL) emission from the undoped CdS nanorods centered at approximately 535 nm is found to be blue shifted to 516 nm with the incorporation of Mn in the CdS crystal structure. Also increase in the intensity of the PL was noticed in the Mn doped CdS nanorods for both the solvent systems. Maximum PL intensity was observed for 1 mol.% Mn in case of En system and for 0.5 mol.% Mn in case of En/water system, above which quenching occurred as a result of Mn-Mn clustering. EPR study revealed six-line hyperfine splitting for low Mn concentration in both solvent systems. Increase in the Mn concentration caused EPR signal broadening due to Mn-Mn clustering.     

Structural and magnetic properties of nanocrystalline Fe-doped SnO2

Single phase Sn_1?xFe_xO₂ (x = 0.1, 0.3 and 0.5) nanoparticles having size in the range 9–17 nm were prepared by a chemical route. XRD analysis of the samples confirmed the formation of cassiterite phase without any impurity. The nanocrystalline nature of the samples and their crystallinity were confirmed by TEM measurements. Raman and Mössbauer spectroscopy studies indicate structural disorder and vacancies in the nanostructures. M–H and M–T data recorded by a SQUID magnetometer show that the samples are essentially paramagnetic with a weak ferromagnetic component. Ferromagnetism is argued to be associated with the vacancies and defects present in the grain boundaries and interfaces of the nanoparticles.     

Optical properties of CdS sintered film

Chemical method has been used to prepare cadmium sulphide by using cadmium, hydrochloric acid and H₂S. The reflection spectra of covered and uncovered sintered films of CdS have been recorded by ‘Hitachi spectrophotometer’ over the wavelength range 300–700 nm. The energy band gaps of these films have been calculated from reflection spectra. It is found that the energy band gap of both films is same as 2.41 eV. It is indicated that energy band gap of these films does not change. This value of band gap is in good agreement with the value reported by other workers. The measurement of photocurrent has also been carried out using Keithley High Resistance meter/ Electrometer. This film shows the high photosensitivity and high photocurrent decay. Thus so obtained films are suitable for fabrication of photo detectors and solar cells.     

Optical and electrical properties of Te-substituted Sn-Sb-Se semiconducting thin films

Thin films of Sn₁₀Sb₂₀Se_70-XTe_X (0 ≤ X ≤ 14) composition were deposited using thermal evaporation technique. As-prepared films were amorphous as studied by X-ray diffraction. Surface morphology studies revealed that films have surface roughness ~ 2 nm and av. grain size ~ 30 nm. Optical band gap E_g showed a sharp decrease for initial substitution of Se with Te upto 2 at.%. A broad hump in the optical band gap is observed for further substitution of Se with Te. The trend of optical band gap variation with tellurium content has been qualitatively explained using band model given by Kastner. The dc-conductivity measurements showed thermally activated conduction with single activation energy for the measured temperature regime and followed Meyer-Neldel rule. The dc-activation energy has nearly half the value as that of optical band gap that revealed the intrinsic nature of semiconductor. The annealing below glass transition T_g led to decrease in optical band gap as well as dc-activation energy that might be related to increase of disorder in material with annealing.     

Preparation and magnetic properties of barium hexaferrite nanorods

The barium hexaferrite nanorods were successfully prepared by sol–gel technique combined with polymethylmethacrylate as template. The crystal structure, morphology and magnetic properties of BaFe₁₂O₁₉ with different shape were investigated with X-ray diffraction, field emission scanning electron microscope and vibrating sample magnetometry. The results show that diameters and lengths of magnetic nanorods are about 60 nm and 300 nm, respectively. The coercivity of rod-shaped BaFe₁₂O₁₉ is increased to 5350 Oe, in comparison with 4800 Oe with plate-shape. The formation mechanism of BaFe₁₂O₁₉ nanorods and reasons resulting in high coercivity are discussed.     

Fine-tuning the photoluminescence and photocatalytic properties of CdS nanorods of varying dimensions

CdS nanorods having different aspect ratio viz., 17 (length ∼170 nm and width ∼10 nm) and 28 (length ∼140 nm and width ∼5 nm) has been synthesized by solvothermal technique at different time intervals (2–10 h). The effect of aspect ratio, crystallinity, band gap energy, surface area and Au/Ag loading on the various photoactive properties of these CdS nanostructures are discussed here. The photocatalytic activity for salicylic acid oxidation under UV irradiation is gradually improved with the increasing crystallinity of CdS nanostructures, length (140 < 170 nm), exposed area (2358 < 5722 nm²) per particle and decreasing surface area (158 < 122 < 76 m²g⁻¹), surface to volume ratio (0.82 < 0.41 nm⁻¹) and aspect ratio (28 < 17). The deposition of 1–2 wt% Au (∼3.5 nm) and Ag (∼1.8 nm) nanoparticles onto CdS drastically quenched the emission and enhanced the photocatalytic activity.     

Cu-doping effect on structure and magnetic properties of Fe-doped ZnO powders

Fe-doped and Cu, Fe co-doped ZnO diluted magnetic semiconductors powders were synthesized by sol–gel method. The x-ray diffraction (XRD) results showed that Zn_0.97−xFe_0.03Cu_xO (x ≤ 0.02) samples were single phase with the ZnO-like wurtzite structure. X-ray photoelectron spectroscopy (XPS) showed that Fe²⁺ and Fe³⁺ existed in Zn_0.97Fe_0.03O, while Fe²⁺, Fe³⁺and Cu⁺, Cu²⁺ were found in Zn_0.95Fe_0.03Cu_0.02O. Both Zn_0.97Fe_0.03O and Zn_0.95Fe_0.03Cu_0.02O exhibited ferromagnetic performance at room temperature. But the Cu incorporation reduced the saturation magnetization of Fe-doped ZnO diluted magnetic semiconductors.     

Growth of semiconducting nanocrystals of CdS and ZnS

In this work, we report the study of growth of CdS as well as ZnS nanocrystals using in-situ small angle X-ray scattering (SAXS) technique, in presence of thio-glycerol as capping agent. We observe that the diameter of the nanocrystal is controlled between 1 and 3 nm by varying the temperature of the reaction. Further, the self-focusing of the size distribution can be observed and is more pronounced at higher temperatures reducing its relative width from 25% to 10%.     

Self-assembled stripe patterns of CdS nanorods

Sterically stabilized CdS nanorods, 3-5 nm in diameter with aspect ratios ranging from 4 to 15, were observed to self-align into networks of stripes several micrometers long when drop-cast from dispersions at submonolayer coverage. The stripes are two to three nanorods thick with nanorods assembled side-by-side with their long axes parallel to the stripe direction. Energetic forces between nanorods, such as van der Waals and dipole-dipole attractions, favor parallel nanorod alignment; however, we propose that pattern formation is kinetically limited, or mediated, by solvent evaporation.     

Photoelectrochemical performance of CdS nanorods grafted vertically aligned TiO2 nanorods

In this study, TiO₂ nanorods/CdS nanorods composite samples were successfully synthesized by grafting CdS nanorods on vertically aligned TiO₂ nanorods. A two-step hydrothermal method was used to prepare the samples. Some properties of the samples, such as morphological, structural, and optical properties were characterized by energy-dispersive X-ray detection, field emission scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and ultraviolet-visible spectroscopy. Moreover, photoelectrochemical properties were studied via current-voltage and photocurrent spectrum measurements. The results showed that CdS nanorods grafted on top of TiO₂ nanorods like a lawn. The amount grafted as well as the diameter and crystallinity of CdS nanorods increased first and then decreased as the grafting time increased, due to Ostwald ripening. Under the back-side illumination, the composite film with 2 h grafting time exhibited the highest photocurrent density which was almost twice of that of the pure TiO₂ nanorods.     

Optical properties of the gold nanorods tuned by lead sulfide

In this paper, the optical properties of gold nanorods (GNRs) tuned by lead sulfide (PbS) were studied. GNRs used in this work were synthesized by seed-mediated methods. Using electrostatic self-assembly methods, GNRs were modified by repetition of adsorbing oppositely charged polyelectrolyte. Then GNR-PbS nanostructure was fabricated by alternatively adsorbing Pb(2+) and S(2-) ions on the surface of polyelectrolyte-modified-GNRs. The formation of PbS nanocrystals on GNRs can effectively regulate their optical properties, including longitudinal surface plasmon resonance (LSPR) and fluorescence.     

Optical and magnetic properties of ZnCoO layers

Optical and magneto-optical properties of ZnCoO films grown at low temperature by Atomic Layer Deposition are discussed. Strong wide band absorption, with onset at about 2.4 eV, is observed in ZnCoO in addition to Co-related intra-shell transitions. This absorption band is related to Co 2+ to 3+ photo-ionization transition. A strong photoluminescence (PL) quenching is observed, which we relate to Co recharging in ZnO lattice. Mechanisms of PL quenching are discussed.