Fabrication and optical properties of Sb-doped CdS nanowires

Sb-doped CdS nanowires with an average diameter of 30 nm and lengths of up to 20-30 μm are fabricated by chemical vapor approach. The as-synthesized products have a single-crystal phase and grow along the <011> direction. The growth of Sb-doped CdS nanowires is suggested for Quasi-vapor-solid mechanism (QVSM). In particular, the PL spectra show enhancing emission peaks that strongly shift to long wavelength (up to 55 nm redshift) with a doping Sb where Sb-doped CdS nanowires are found to be responsible for the different characteristics. The PL mechanism is explained in detail.     

Synthesis and optical properties of CdS nanowires by a simple chemical deposition

CdS nanowires were prepared by a paired cell method, using highly ordered porous anodic alumina (PAA) membranes as templates. The morphology, structure, and composition of these nanowires were characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDS), and selected area electron diffraction (SAED) pattern. SEM images indicated that nanowires arrays are highly ordered and coincide with the contours of PAA. The EDS analysis, combined with HRTEM images and SEAD patterns, confirmed the formation of CdS. The formation and growth mechanism of CdS nanowires, as well as the optical properties, were also analyzed in details. The results indicated that the formation and growth of CdS nanowires experience from initial nuclei, nanoparticles, linear pearl-chain structures to final nanowires, attributed to electrostatic adsorption and ions diffusion. A strong emission with a maximum around 430 nm was observed from the synthesized CdS nanowires, which was attributed to the recombination of trapped electron/hole pairs. The absorption edge in UV–Vis spectrum of CdS/PAA nanoarrays showed a blue shift due to the quantum confinement effects. The technique can be used to fabricate other compound nanowires and newly light-emitting semiconductor materials.     

Annealing effects on the structural and optical properties of gallium oxide nanowires

We have prepared gallium oxide nanowires and investigated the effect of thermal annealing on the structural and optical properties. As-prepared and annealed nanowires, respectively, were found to be fully amorphous and amorphous with very small crystallites. Photoluminescence measurements indicated that both as-prepared and annealed nanowires under excitation at 250 nm showed two emission band at 364 and 466 nm but the relative peak intensities of UV and blue emission, respectively, increase and decrease by the thermal annealing.     

CdS/ZnO核壳结构纳米微粒的合成及其发射光谱研究

采用单分子前驱体热分解的方法合成了单分散CdS纳米晶,以CdS纳米晶作为核,在CTAB辅助下,对其表面进行修饰,荧光光谱表明CdS/ZnO核壳结构被成功合成。考查了温度对包覆的影响,结果表明,随着温度的升高晶体结晶越好,包覆越来越完全,ZnO包覆在CdS纳米晶的表面而掩盖了CdS纳米晶的缺陷,使得缺陷发光减弱而带隙发光增强。     

Effect of solvent-induced structural modifications on optical properties of CdS nanoparticles

We have investigated the effects of solvent used during synthesis on structural and optical properties of CdS quantum dots. Different methods of synthesis for the production of CdS quantum dots are presented. These are: (a) wet chemical co-precipitation in non-aqueous medium (i.e. methanol); (b) wet chemical co-precipitation in aqueous medium (deionized water) and (c) solid state reaction. It is demonstrated that the use of methanol as solvent leads to a strong enhancement of PL intensity of CdS quantum dots for use in optoelectronic devices. These products were characterized by X-ray powder diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM). The change in bandgap with size-quantization was investigated by UV-VIS absorption spectroscopy. CdS nanocrystals prepared in non-aqueous medium have narrow size distribution than those prepared in aqueous medium and solid state reaction. Phase transformation of CdS nanocrystals from a cubic to hexagonal structure was observed in methanol solution. The formation of CdS/Cd(OH)₂ nanostructure was also confirmed using X-ray diffraction pattern. This suggests that the strong enhancement of the PL intensity may have originated from the remarkable reduction of non-radiative recombination process, due to surface defects of quantum dots. The red shift of the Raman peaks compared to that for bulk CdS may be attributed to optical phonon confinement.     

Influence of substrates on the structural and optical properties of chemically deposited CdS films

Cadmium sulfide (CdS) films were chemically deposited on glass, polycarbonate (PC), polyethylene terephthalate (PET), and Si wafer. Effects of substrate types on the structural and optical properties of the films were investigated. There is a preferential orientation of the crystallites in the film grown on the glass along the c-axis (perpendicular to the plane of the substrate) producing a strong hexagonal (0 0 2) or cubic (1 1 1) peak, regardless of the presence of ITO coating. However, such preferential orientation decreases or disappears when the deposition was made onto PC or PET substrates. The crystallinity of CdS films on glass and Si is better than that of the other ones. The average transmittance of the films on PC and PET is about 50% and 55%, respectively, and increases up to 70% for glass substrate. The improvement of the transmittance was obtained from ITO-coated substrates.     

Using seed particle composition to control structural and optical properties of GaN nanowires

The morphology, structure, and optical properties of gallium nitride (GaN) nanowires grown using metal-organic chemical vapor deposition (MOCVD) on r-plane sapphire using gold and nickel seed particles were investigated. We found that different seed particles result in different growth rates and densities of structural defects in MOCVD-grown GaN nanowires. Ni-seeded GaN nanowires grow faster than Au-seeded ones, and they do not contain the basal plane stacking faults that are observed in Au-seeded GaN nanowires. We propose that stacking fault formation is related to the supersaturation and surface energies in different types of seed particles. Room temperature photoluminescence studies revealed a blue-shifted peak in Au-seeded GaN nanowires compared to the GaN near-bandgap emission. The blue-shifted peak evolves as a function of the growth time and originates from the nanowire base, likely due to strain and Al diffusion from the substrate. Our results demonstrate that seed particle composition has a direct impact on the growth, structure, and optical properties of GaN nanowires and reveal some general requirements for seed particle selection for the growth of compound semiconductor nanowires.     

A combined template and closed space sublimation approach to the synthesis of single-crystalline CdS nanowires and their optical properties

High-quality single-crystalline CdS nanowires about 40 nm in diameter have been successfully synthesized without any catalyst at ambient pressure by combining the closed space sublimation (CSS) technique with porous anodic alumina membrane (AAM) template method. Extensive characterizations of the nanowires have been carried out using scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Raman spectroscopy and UV-Visible absorption spectroscopy. A band gap of 2.38 eV is determined from the UV-Vis absorption spectrum obtained from the nanowire sample. Our facile technique may in principle also be used for synthesizing other one-dimensional (1D) materials with high vapor pressure and axial nanowire heterostructures.     

Electric field assisted growth of self-organized CdS films: size dependent structural and optical properties

This paper presents a systematic study of electric field assisted growth of self-organized cadmium sulphide (CdS) quantum dots (Q-CdS). CdS thin films of self-organized quantum dot like structure with different particle size have been successfully deposited simply by varying the concentration of surfactant in the reaction matrix. The model to describe the self-organization is also discussed. The size of CdS nanoparticles can be altered from 68 nm (corresponding to bulk) to 2 nm. The structural, optical, and morphological properties of Q-CdS films have been investigated. A blue shift has been observed in optical absorption and photoluminescence spectra. The strained growth of Q-CdS films has been observed. The microstructural strain calculated from peak broadening reveals an increase in strain with decreasing particle size. This study may provide a convenient method to deposit size selective and organized nanocrystalline semiconductor thin films.     

TiO2 nanowires sensitized with CdS quantum dots and the surface photovoltage properties

TiO₂ nanowires prepared by thermal annealing of anodized Ti foil were sensitized with CdS quantum dots (QDs) via chemical bath deposition (CBD). Microstructural characterizations by SEM, TEM and XRD show that the CdS nanocrystals with the cubic structure have intimate contact to the TiO₂ nanowires. The amount of CdS QDs can be controlled by varying the CBD cycles. The experiment results demonstrate that the surface photovoltage (SPV) response intensity was significantly enhanced and the surface photovoltage response region was also expanded obviously for the TiO₂ NWs sensitized by CdS QDs.     

Effect of Cr-doping on the structural and optical properties of CdS nanoparticles prepared by chemical precipitation method

Undoped and Cr doped CdS nanoparticles have been prepared by chemical precipitation method. X-ray diffraction analysis reveals that the undoped and Cr doped CdS nanoparticles exhibit hexagonal structure and the average particle size of the nanoparticles is in the range of 2.2–3.8 nm. The HRTEM studies show that the average particle size of undoped and Cr doped CdS nanoparticles is in the range of 2–3.7 nm. The compositional analysis results indicates that Cd, S and Cr are present in the samples. From the optical studies it is observed that the absorption edge of the prepared CdS and Cr doped CdS nanoparticles are shifted towards the shorter wavelength region (blue shift) when compared to that of bulk CdS and this shift is due to the quantum confinement effect present in the samples.     

Mg掺杂ZnO薄膜的结构及其光学性能研究

利用射频磁控溅射技术在(100)Si和玻璃衬底上沉积系列Mg掺杂ZnO(x=0~0.20)薄膜,XRD分析结果表明,Zn1-xMgxO薄膜均为六角纤锌矿结构,薄膜呈现出c轴择优生长特性,但随着x值的增加,晶格常数c逐渐减小。当x=0.20时,薄膜出现(100)面衍射峰,薄膜的c轴择优生长特性减弱。SEM分析表明,x=0.10时,薄膜表面平坦光滑,晶粒大小均匀,结构更加致密,结晶质量最佳。紫外可见光透射光谱表明,Mg的掺入提高薄膜在可见光范围内的透过率;同时增大了薄膜的禁带宽度;室温PL谱分析显示所有薄膜均出现了紫外发射峰和蓝光发射带,且紫外发射峰和蓝光发光带都随x值的增加而蓝移。     

Electrical and optical properties of vacuum-evaporated CdS films

1 m CdS films for the window layer of CdS/CulnSe₂ solar cells have been prepared by vacuum evaporation at various deposition conditions. Deposition rates were 0.73 and 3.3 nms^–1, and substrate temperature ranged from 50 to 225 C. The effect of the deposition conditions on the properties of CdS films was investigated by measuring electrical resistivity, optical transmittance and reflectance.The resistivity of the evaporated CdS films strongly decreased as substrate temperature decreased and the films with high deposition rate showed lower resistivity compared to the films with low deposition rate. Interestingly, the combination of high deposition rate and very low substrate temperature resulted in an increase of resistivity. The optical transmittance of CdS films increased as substrate temperature decreased and then decreased with further decrease in substrate temperature. The transmittance strongly depended on deposition rate at low substrate temperature (<100C), while it was independent of deposition rate at high substrate temperature (>100C). In particular, high transmittance can be extended to lower substrate temperature by reducing deposition rate. Low optical reflectance can be obtained by lowering substrate temperature. The results indicate that CdS films of low resistivity and high transmittance can be produced by vacuum evaporation at low substrate temperature and low deposition rate.     

Benzene-thermal synthesis and optical properties of CdS nanocrystalline

Solvent thermal process has been successfully applied to prepare nanocrystalline CdS via the reaction CdSO₄ with Na₂S₃ in benzene at 80–120 °C. It was found that solvent, temperature, and reactant have significant effect on crystal structure and particle size of CdS nanocrystalline. The results show that increasing of temperature and using of solvent of low dielectric constant are beneficial to prepare CdS nanocrystalline in hexagonal phase. The water content in the system not only induces the presence of cubic phase CdS nanocrystalline, but also leads to a particle size increase. The results demonstrate that both phase and particle size can be well controlled. As-prepared CdS nanocrystalline powders display obvious blue-shift characteristics.     

Structural and optical properties of Al-doped SnO2 nanowires

We report a facile thermal evaporation method for the syntheses of Al-doped SnO₂ nanowires using Al-doped SnO₂ nanoparticles as precursors. High-density, single-crystalline Al-doped SnO₂ nanowires were directly grown on the 6H-SiC substrates without any catalyst. X-ray diffraction patterns show that the Al dopants are incorporated into the rutile SnO₂ nanowires. The X-ray photoelectron spectra confirm the SnO₂ nanowires doped with 5 at.% Al. The photoluminescence spectra of the Al-doped SnO₂ nanowires exhibit that the large blue shift of the emission band can be observed in the Al-doped SnO₂ nanowires compared with undoped nanowires. The distortion of the crystal lattices caused by incorporation of Al atoms at the interstitials should be responsible for the large blue shift of the emission band.     

Photoluminescence and optical limiting properties of silicon nanowires

Si nanowires (SiNWs) have been produced by thermal vaporization on Si(111) substrate without catalysts added. The grown SiNWs have been characterized by Raman scattering, SEM, XRD, and electron diffraction and shown to be highly crystalline with only little impurities such as amorphous Si and silicon oxides. Photoluminescence (PL) study has illustrated that the Si band-to-band gap increases from 1.1 eV for bulk Si to 1.56 eV for the as-grown SiNWs due to quantum confinement effect. A strong PL peak at 521 nm (2.37 eV) is attributed to the relaxation of the photon-induced self-trapped state in the form of surface Si-Si dimers, which may also play an important role in optical limiting of SiNWs with 532-nm nanosecond laser pulses. With the observation of optical limiting at 1064 nm, nonlinear scattering is believed to make a dominant contribution to the nonlinear response of SiNWs.     

Synthesis and optical properties of ZnTe single-crystalline nanowires

Single-crystalline ZnTe nanowires with the zincblende structure have been synthesized on silicon (Si) substrates via a vapor phase transport method. The ZnTe (99.99%) powders were used as the source, and 10 nm-thick thermal evaporated gold (Au) film was used as the catalyst. The as-prepared ZnTe nanowires have diameters of 30-80 nm and lengths of more than 10 microm. The products were analyzed by X-ray diffraction, field emission scanning electron microscopy, and high-resolution transmission electron microscopy. Optical properties of these nanowires were investigated by room-temperature Raman scattering spectrum and temperature-dependent photoluminescence measurements. The results show that the as-prepared ZnTe nanowires are of high crystal quality.     

Influence of CTAB surfactant on structural and optical properties of CuS and CdS nanoparticles by hydrothermal route

Metal sulphide CuS and CdS nanoparticles capped with Cetyltrimethylammonium bromide (CTAB) were synthesized by hydrothermal method. Structural, morphological, chemical composition, optical and luminescent properties were evaluated by different analytical techniques. X-ray diffraction (XRD) analysis of the CTAB capped metal sulfide nanoparticles reveals the formation of hexagonal structure. High-resolution transmission electron microscopy (HRTEM) images show that the morphology of the capped copper sulphide samples consists of hexagonal structure and capped cadmium has spherical shape and also confirms the crystalline nature of the particles with distinct lattice fringes. In FTIR spectroscopy, the composition of the CTAB capped CuS and CdS nanoparticles have been confirmed. The analysis of photoluminescence (PL) and optical transition show a red shift due to the reduction of band gap energy and it is attributed to the low defects and high crystallinity. The optical studies indicate that CuS and CdS nanoparticles with CTAB can be suitable for optoelectronic devices and photovoltaic applications.     

Effect of the substrate temperature on the structural, optical and electrical properties of spray-deposited CdS:B films

Boron doped CdS films have been deposited by spray pyrolysis method onto glass substrate temperature in the range of 350–450 °C. And the effect of substrate temperature (T _s) on the structural, electrical and optical properties of the films were studied. The structural properties of boron doped CdS films have been investigated by (XRD) X-ray diffraction techniques. The X-ray diffraction spectra showed that boron doped CdS films are polycrystalline and have a hexagonal (wurtzite) structure. By using SEM analysis, the surface morphology of the films was observed as an effect of the variation of substrate temperature. The substrate temperature is directly related with the shift detected in the band gap values derived from optical of parameters and the direct band gap values were found to be in the region of 2.08–2.44 eV. The electrical studies showed that the film deposited at the substrate temperature 400 °C had high carrier concentration and Hall mobility and minimum resistivity. This resistivity value decreased with increase in temperature up to 400 °C indicating the semiconducting nature of B- doped CdS films. The lattice parameter, grain size, microstrain and dislocation densities were calculated and correlated with the substrate temperature (T _s ).