Resonant Brillouin scattering by acoustoelectrically amplified phonons in CdSe

The dispersion of Brillouin scattering efficiency from the acoustoelectrically amplified phonon flux in CdSe has been measured in the range 1.37 to 1.65 eV. The dispersion curve shows enhancement and cancellation similar to those of GaAs, CdS and ZnO, and is in a good agreement with modified Loudon theory including exciton effects.     

Predicted new electromagnetic precursors and altered signal velocity in dispersive media

New optical precursors are predicted in media exhibiting “non-conventional” dispersion characteristics such as spatial dispersion, surface polaritons and surface plasmons. Numerical estimates are given for the exciton and surface polariton precursors in CdS, and surface plasmon in Al. The signal velocity increases in spatially dispersive media and is essentially constant throughout the “stop” gap. Measurement of these effects may provide new spectroscopic information regarding “non-conventional” dispersion.     

Preparation and characterization of nano cobalt oxide

A simple and general method has been proposed for preparing strong violet emitting CdS quantum dots, in which a ligand exchange strategy was applied to surface passivation and functionalization with good reproducibility. The resulting quantum dots showed a visible violet luminescence with emission peak centered near 423 nm and photoluminescence quantum yields reached over 30%. Additionally, different mercapto-compounds used as ligands can make different functionalized surfaces, favoring quantum dots dispersion in different media and their further applications. It was observed that the band edge emission has the main contribution to the bright violet luminescence.     

The enhanced photocatalytic activity of CdS/TiO2 nanocomposites by controlling CdS dispersion on TiO2 nanotubes

CdS/TiO₂ nanocomposites were prepared via a simple wet chemical method, and characterized through X-ray diffraction (XRD) and transmission electron microscopy (TEM). Their ability to degrade Acid Rhodamine B was investigated under visible light irradiation. The results indicate that CdS/TiO₂ nanocomposite with a mass ratio of 4:1(TiO₂:CdS) showed high photocatalytic activity and the CdS loaded on TiO₂ nanotube surface exhibited a hexagonal phase. The dispersion of CdS on TiO₂ nanotube surface had an important effect on the degradation efficiency of pollutant, which provides a strategy for practical industry application.     

Size effects on polaritons in thin crystals with perfect interference spectra

Size effects on polaritons in thin plane parallel CdS and CdSe crystals are discussed. For samples not thinner than 0.1 μm the measurements of transmittance and reflectance show the size quantization of the mechanical exciton dispersion and a shift of the resonance frequency of the exciton to the high-energy side with decreasing thickness. However no evidence for the alteration of the oscillator strength or other parameters has been obtained. This conclusion is in conflict with the recently published data taken on CdS samples. The stability of the polariton dispersion in our case is supported by the theoretical study of reflectance ignoring the effects of the finiteness of the exciton radius.     

Photoluminescence studies on nanostructured cadmium sulfide thin films prepared by chemical bath deposition method and annealed at different temperatures

Nanostructured cadmium sulfide (CdS) thin films have been prepared by chemical bath deposition (CBD) method and after post deposition annealing of the thin films at different temperatures, photoluminescence (PL) property has been studied. The effects of various photoexcitation wavelengths on the PL behaviour of different annealed films of CdS were studied by recording the PL spectra. The intensity of PL, the profile of the PL spectra and the effects of photoexcitation wavelength depend drastically on the temperature of the post deposition annealing of the thin films. The XRD patterns of the films show the presence of both the hexagonal and cubic phases (mixed phases). The emission peak arises from the surface defects of the CdS nanocrystalline thin films. Significant modification in the surface morphology of the CdS films upon annealing has been observed from the FESEM images. The morphology of the thin films is expected to influence the PL behaviour of the CdS thin films. The quantum size effect and size dependant PL have been observed.     

CdS quantum dot-sensitized ZnO nanorod-based photoelectrochemical solar cells

ZnO nanorods have been grown using ZnO seed layer onto ITO-coated glass substrates. CdS quantum dots have been deposited onto ZnO nanorods using simple precursors by chemical method and the assembly of CdS quantum dots with ZnO nanorod has been used as photo-electrode in quantum dot-sensitized solar cells. X-ray diffraction results show that ZnO seed layer, ZnO nanorods, and CdS quantum dot-sensitized ZnO nanorods exhibit hexagonal structure. The particle size of CdS nanoparticle is 5 nm. The surface morphology studied using scanning electron microscope shows that the top surface of the vertically aligned ZnO nanorods is fully covered by CdS quantum dots. The ZnO nanorods have diameter ranging from 100 to 200 nm. The absorption spectra reveal that the absorption edge of CdS quantum dot-sensitized ZnO nanorods shift toward longer wavelength side when compared to the absorption edge of ZnO. The efficiency of the fabricated CdS quantum dot-sensitized ZnO nanorod-based solar cell is 0.69% and is the best efficiency reported so far for this type of solar cells.     

Mechanism of fluorescence energy transfer in aqueous solution cadmium sulfide quantum dots

Cadmium sulfide (CdS) quantum dots (QDs) prepared by a convenient chemical method have been characterized using absorption, fluorescence, and photoluminescence excitation techniques. The photoluminescence excitation studies show that there is an electron transfer from the surface adsorbate (thiourea) to CdS QDs in aqueous solution. The excitation band with peak maximum at 5.8 eV is assigned to the electronic transitions in the chemisorbed thiourea, whereas the excitation band between 3.45 and 3.7 eV corresponds to the band-to-band transition within the nanocrystalline CdS host. The absorption spectroscopy of the CdS QD solutions shows a strong absorption peak which is generated from thiourea. The band-edge fluorescence of the CdS QDs has also been investigated. It is shown that the fluorescence property of the CdS QDs can be enhanced by adding cadmium chloride (CdCl₂) solution.     

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.     

Simplistic surface active agents mediated morphological tweaking of CdS thin films for photoelectrochemical solar cell performance

This study reports on the formation of cadmium sulfide (CdS) nanostructures with controlled morphology synthesized via a simple chemical route in surface active agent environment. The effect of organic surface active agents (surfactants) as sodium dodecyl sulfate (SDS), polyethylene glycol (PEG) and cetyltrimethylammonium bromide (CTAB) on structural, morphological, optical and photoelectrochemical properties of CdS thin films have been studied. Our results reveal that the organic surfactants play key roles in tweaking the surface morphology. A compact spongy ball like morphology was observed for the CdS samples grown without organic surfactants. The cauliflower's with nanopetals from the CTAB, whereas crowded star fish like morphology is observed in PEG-mediated growth. Water hyacinth like morphology is tweaked using SDS. Considering the importance of these nanostructures, the growth mechanism has been discussed in details. Additionally, the samples are photoelectrochemically (PEC) active and having a compact surface with a nanoporous structure twig helps in improved photoelectrochemical performance compared to that of CdS deposits from surfactant free solution. This is a simplistic way to tune the morphology using surfactants, which can be applied to other energy conversion applications.     

核/壳结构ZnS : Mn/CdS纳米粒子的制备及发光

利用溶剂热法制备了Mn离子掺杂的ZnS纳米粒子(ZnS : Mn),利用沉淀法对ZnS ∶ Mn纳米粒子进行了不同厚度的CdS无机壳层包覆。采用X射线衍射(XRD)、透射电子显微镜(TEM)、X射线光电子能谱(XPS)及光致发光(PL)光谱等手段对样品进行了表征。TEM显示粒子为球形,直径大约在14~18 nm之间。由XRD结果可以看出CdS壳层的形成过程受到了ZnS ∶ Mn核的影响,导致其结晶较差。XRD和XPS测量证明了ZnS : Mn/CdS的核壳结构。随着CdS壳层的增厚,样品的发光强度呈现一直减弱的现象。     

“Anomalous” spectral photoresistive field effect in CdS crystals caused by the screening of the electron-hole interaction

The changes observed in low-temperature (T = 77 K) near-band-edge photoconductivity spectra of CdS crystals in response to an external transverse electric field applied to the sample surface have been investigated. An analysis of the “anomalous” character of these changes for a number of crystals has revealed a significant role of the near-surface effects of screening of the electron-hole interaction in the formation of near-band-edge photoconductivity spectra of CdS crystals with a technological excess of cadmium near the surface. It has been shown that the depletion (enrichment) transverse electric field leads to a weakening (enhancement) of screening effects in the photoconductivity spectra of the CdS crystals.     

Surface photovoltage spectroscopy study of CdS thin films

The method of surface photovoltage spectroscopy has been applied to the study of the surface properties of thin CdS films deposited by vacuum evaporation. The energy spectrum of the surface states is obtained and their kinetic parameters are calculated. A comparison is made of the results obtained in air and in vacuum for non-recrystallized and recrystallized samples. The results for thin films are compared with the data on monocrystal CdS in the literature. It is assumed that the surface states established in the films are of a donor-like type.     

Asymmetric effect of (000$\bar{1}$) and (0001) facets on surface and interface properties of CdS single crystal

A different effect of (0001) and (000[`1]\bar{1}) crystal facets of the cadmium sulfide (CdS) wurtzite structure terminated with Cd and S atoms, respectively, was observed in respect to the properties of the crystal surface and interface with metal or organic semiconductor contacts. In addition to the different surface morphology, a bare CdS single crystal showed different features in photoluminescence from the Cd- and S-terminated surfaces. Different adhesive behavior of poly(3,4-ethylenedioxythiophene): poly(styrene sulfonic acid) (PEDOT:PSS) films in respect to the Cd- and S-terminated facets of the crystal has also been found. Photovoltaic properties of hybrid CdS/PEDOT:PSS heterojunctions have been shown to be sensitive in respect to the crystal facet used. Thin films of aluminum (Al) equally deposited onto the opposite crystal facets revealed much smaller sheet resistance on the sulfur facet than on the cadmium one, which has been assigned to the difference in both chemical interaction with the surface atoms and surface morphology. Current–voltage characteristics of an apparently symmetric Al/CdS/Al structure with Al electrodes deposited onto the opposite crystal facets showed asymmetric behavior depending on the bias direction applied to the Cd or S-terminated facet, with the barrier for electrons at the Al/S-terminated interface, respectively.     

On the frequency-dependence of the impedance of n- and p-type gallium arsenide electrodes

The impedance of n- and p-type GaAs electrodes has been studied as a function of applied voltage and of frequency. Simple frequency laws were found to exist for the series capacitance and resistance. To explain these laws, a distribution of time constants has been assumed, associated with dielectric relaxation phenomena in the double-layer at the semiconductor/electrolyte interface. This distribution was found to be independent of the distance from the crystal surface for n-type samples but to depend upon it for p-type specimens. An investigation on the role of the applied voltage in these frequency laws yielded additional evidence for the mathematical model which was originally introduced in a previous paper in order to explain similar laws observed at CdSe, CdS and TiO₂ electrodes. The frequency-dispersion of the p-type samples was found to be strongly influenced by an appropriate pretreatment of the surface, in contrast with the behaviour of the n-type specimens. In both cases, the experimental results indicate that the source of the frequency dispersion has to be sought in structural irregularities of the depletion region of the electrode. The possibility of determining the flat-band potential from frequency-dependent impedance data is discussed.     

Influence of P<Superscript>+</Superscript>-ZnTe back surface contact on photovoltaic performance of ZnTe based solar cells

In order to improve photovoltaic performance of solar cells based on ZnTe thin films two device structures have been proposed and its photovoltaic parameters have been numerically simulated using Solar Cell Capacitance Simulator software. The first one is the ZnO/CdS/ZnTe conventional structure and the second one is the ZnO/CdS/ZnTe/P⁺-ZnTe structure with a P⁺-ZnTe layer inserted at the back surface of ZnTe active layer to produce a back surface field effect which could reduce back carrier recombination and thus increase the photovoltaic conversion efficiency of cells. The effect of ZnO, CdS and ZnTe layer thicknesses and the P⁺-ZnTe added layer and its thickness have been optimized for producing maximum working parameters such as: open-circuit voltage V_oc, short-circuit current density J_sc, fill factor FF, photovoltaic conversion efficiency η. The solar cell with ZnTe/P⁺-ZnTe junction showed remarkably higher conversion efficiency over the conventional solar cell based on ZnTe layer and the conversion efficiency of the ZnO/CdS/ZnTe/P⁺-ZnTe solar cell was found to be dependent on ZnTe and P⁺-ZnTe layer thicknesses. The optimization of ZnTe, CdS and ZnTe layers and the inserting of P⁺-ZnTe back surface layer results in an enhancement of the energy conversion efficiency since its maximum has increased from 10% for ZnO, CdS and ZnTe layer thicknesses of 0.05, 0.08 and 2 µm, respectively to 13.37% when ZnO, CdS, ZnTe and P⁺-ZnTe layer thicknesses are closed to 0.03, 0.03, 0.5 and 0.1 µm, respectively. Furthermore, the highest calculated output parameters have been J_sc?=?9.35 mA/cm², V_oc?=?1.81 V, η?=?13.37% and FF?=?79.05% achieved with ZnO, CdS, ZnTe, and P⁺-ZnTe layer thicknesses about 0.03, 0.03, 0.5 and 0.1 µm, respectively. Finally, the spectral response in the long-wavelength region for ZnO/CdS/ZnTe solar cells has decreased at the increase of back surface recombination velocity. However, it has exhibited a red shift and showed no dependence of back surface recombination velocity for ZnO/CdS/ZnTe/P?+?-ZnTe solar cells.     

一维Mn2+掺杂CdS纳米晶体的水热合成及其发光性能

用水热方法合成了一维Mn2 掺杂CdS纳米晶体.产品分别用SEM,EDS,XRD,TEM,HRTEM和PL等技术进行了表征.结果表明,掺杂Mn2 完全替代了CdS晶格中Cd2 的位置,产品具有较好的结晶性.荧光光谱中,CdS纳米晶体表面缺陷态的发射峰被完全抑制,只能观察到单一的Mn2 的发射峰.     

Synthesis of poly-<Emphasis Type="Italic">p</Emphasis>-xylylene + CdS nanocomposites and studing of their surface structure

Thin-film polymeric nanocomposites based on a poly-p-xylylene matrix (PPX) and nanoparticles of cadmium sulfide (CdS) have been obtained using solid-phase cryochemical synthesis on optical quartz substrates. The optimal conditions for the formation of PPX + CdS nanostructured polymeric films have been determined. The topography and surface characteristics of PPX + CdS nanocomposites have been studied by scanning atomic force microscopy (AFM). The characteristics of the morphological and structural changes of the film surfaces have been found at different CdS nanoparticle concentrations. These changes point to a reorganization of the PPX + CdS polymeric matrix. It is shown that at 2–10 vol % CdS concentration, the elements of the surface’s structural organization are polymeric nanofibers, parallel to the substrate plane, and a small number of nanoglobules, locally positioned directly on the nanofiber surfaces. Ordering of the surface structure accompanied by the formation of a periodic surface relief in the shape of nanoglobules was observed at a CdS concentration of 13.5 vol %. A mechanism of the formation of nanostructured PPX + CdS films is proposed. Based on the AFM experimental data, one can assume that during co-condensation of a p-xylylene monomer, CdS nanoparticles initiate radical polymerization of the PPX matrix, when the substrate is heated from 77 K to 300 K. The type of surface structure (fibrillar, fibrillar + globular and globular) depends on the nanoparticle concentration in the polymeric matrix.     

Effect of corona discharge on cadmium sulphide and lead sulphide films

This paper describes the effect of corona discharge on cadmium sulphide (CdS) and lead sulphide (PbS) films prepared using the chemical route. The property of films before and after exposure to corona has been described in detail. The electronic properties of the CdS and PbS films have been studied by current-voltage (I-V), capacitance-voltage (C-V) measurements. The structural properties and surface morphology were studied by using X-ray diffraction and scanning electron microscopy before and after exposing to Corona discharge. The films displayed the change in surface morphology after exposure to the corona discharge. It has been found that the films showed an increase in resistivity after exposure. This change in property has been attributed to modification in surface states. Time-dependent recovery indicated that room temperature annealing is sufficient to regain the normal resistivity of the films. The experiment was carried with the aim of studying the effect of the interaction of corona discharge on the semiconductor films and its subsequent effects.     

Photovoltaic properties of a heterojunction based on copper phthalocyanine films on the surface of polycrystalline cadmium sulfide

The photovoltaic effect has been detected and studied in thin-film structures based on thermally deposited 200-nm-thick copper phthalocyanine (CuPc) films on the surface of polycrystalline CdS. The structures under study demonstrate the linear current-voltage characteristics at external electric fields to 3.5 × 10⁴ V/cm. Two components of the photovoltage of different signs have been revealed when the sample is illuminated in the wavelength range from 350 to 700 nm. The first component has the positive sign on the CuPc film side and is observed when using the radiation with a wavelength lesser than 500 nm, i.e., in conditions of predominant absorption of the radiation in the CdS layer. The second component has the negative sign on the CuPc film side and is observed when using the radiation with a wavelength in the range from 500 to 570 nm, corresponding to the spectral region of the absorption edge of the CuPc films. The dependences of the photovoltage on the radiation intensity studied in the range from 5 × 10¹² to 10¹⁴ photons cm^?2 s^?1 are different in the cases of the two detected components. Mechanisms of generation of the photovoltage components associated with a change in the band bending during photogeneration of charge carriers in the region of space charge in CdS and a change in conditions of the charge transfer in the interfacial CuPc/CdS region during the radiation absorption in the CuPc film have been proposed.