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 ).     

The local crystal structure and electronic band gap of β-sialons

The electronic properties of β-Si₃N₄ and β-sialons (β-Si_6?z Al _z O _z N_8?z ) solid solutions were characterized using a combination of X-ray emission spectroscopy (XES), X-ray absorption spectroscopy (XAS), and density functional theory (DFT). The electronic structure measurements reveal a single bonding environment for both the Si and Al atoms, which corresponds to a specific nonrandom structural arrangement of the Al–O solute atoms into nanotube-like clusters or channels, running parallel to the c-axis of the β-Si₃N₄ host structure. Compared to an arrangement of alternating Si–N and Al–O slabs (“Dupree model”), lower total energy and overall better agreement to the experimentally observed electronic features confirm this “Al–O nanotube” model for β-sialon originally proposed by Okatov to be closer to the true chemical topology of the β-Si_6?z Al _z O _z N_8?z solid solution series. The β-sialons are shown to be wide band gap semiconductors with the band gap reduction arising from the O p-states moving toward the Fermi level. This band gap reduction provides the ability for direct band gap transitions, which is very important for practical applications. In contrast to the previous observations, both measurement and theory indicate a linear dependence of band gap energy with composition z. The experimental (theoretical) electronic band gaps of β-Si_6?z Al _z O _z N_8?z with z = 0.0, 2.0, and 4.0 as determined by XAS/XES (DFT) are 7.2 ± 0.2 (5.88), 6.2 ± 0.2 (3.45), and 5.0 ± 0.2 (2.39) eV, respectively. The considerable discrepancy between experimental and theoretical values is attributable to the shortcomings of DFT, which often underestimates the electronic band gap energy.     

Sol-gel synthesis,structural and enhanced photocatalytic performance of Al doped ZnO nanoparticles

In this research ZnO and Zn_1?x Al_xO (x = 1, 3, 5, 7% mol) nanoparticles were synthesized by sol-gel method. The effect of Al concentration on the structure, morphology, absorption spectra and photocatalytic properties investigated by using X-ray, TEM, EDS and UV–Vis spectrophotometer approaches. Hexagonal, spherical and rod-like structure was achieved as the dominant structure for undoped nanoparticles, low and high concentrations of doped Al, respectively. Photocatalytic activity of nanoparticles was measured by degradation of methyl orange as a pollutant under radiation of ultraviolet (UV). The experimental test results indicate that the best photocatalytic performance is at of 5% of Al. Furthermore, the doped ZnO nanoparticles have more activity in visible area compared with undoped nanoparticles. The absorption amount in this area increases by raising the Al concentrations. Furthermore, the band gap of the particles decreases from 3.22 eV to 2.93 eV by increasing Al percentage.     

Nano-Ag doping induced changes in optical and electrical behaviour of PVA films

Hybrids of nano-Ag and PVA films prepared via sol-gel method have been characterized through XRD, TEM, UV-vis spectroscopy and I-V measurements. The change in optical band gap value and room temperature dc conduction behaviour of undoped and nano-Ag doped PVA films have been studied. The value of optical band gap has been found to be reduced from 4.92 eV (for undoped PVA) to 3.93 eV on doping 1.32% (by wt.) nano-Ag in PVA. This decrease in optical band gap and observed increase in conduction can be correlated to the formation of the charge transfer complexes within the polymer network on dispersing nano-Ag in it. Current-voltage behaviour suggests that Poole-Frenkel mechanism is primarily responsible for the observed conduction for both undoped and nano-Ag doped PVA films.     

Quantum confinement effect of CdS nanoparticles dispersed within PVP/PVA nanocomposites

Nanocomposite films of CdS nanoparticles within PVP/PVA blend were prepared. The prepared films were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy, Ultraviolet–visible spectroscopy (UV–vis), transmission electron microscopy (TEM) and photoluminescence (PL) spectra. The amount of Cd⁺ used strongly influenced the size of the CdS nanoparticles, which was confirmed by XRD, UV–vis absorption spectra, PL emission spectra and TEM images. Smaller sized CdS nanoparticles were formed in higher content of cadmium. The results of XRD indicate that CdS nanoparticles were formed with hexagonal phase in the polymeric matrix. PL and UV–vis spectra reveal that nanocomposite films shows quantum confinement effect. Optical band gap and particle size were calculated and is in agreement with the results obtained from TEM data. The direct energy band gap was increased up to 2.86 eV.     

Photoconductivity of n-type semiconductor nanoparticle-doped poly(N-vinylcarbazole) films

TiO₂, CdS and ZnS nanoparticles that disperse stably in organic solvents are synthesized. Poly(N-vinylcarbazole) films doped with the n-type semiconductor nanoparticles are prepared with a cast method. The films exhibit a transient photocurrent when irradiated by a light pulse and act such as a diode when AC voltage is applied under continuous illumination. The transient photocurrent response and diode-like properties are significantly different depending on the kind of the nanoparticles and their amounts. The films doped with TiO₂ and CdS nanoparticles increase the transient photocurrent at lower doped amounts, which is remarkable for TiO₂-doped films. Time of flight analysis of the transient photocurrent shows that mobility of hole in PVK increases with increase in the amount of CdS and TiO₂. From the studies on the diode-like properties, the current increase at lower dopant concentration is concluded to be due to increase in the amount of holes by an electron transfer from PVK to the photo-excited nanoparticles. At higher doping with CdS nanoparticles, main charge carrier of the films is found to change from holes to electrons.     

Studies on optical absorption and photoluminescence of thioglycerol-stabilized ZnS nanoparticles

ZnS quantum dots of size 3 nm are prepared at 303 K using ZnSO₄ and Na₂S₂O₃ precursors with thioglycerol as stabilizing agent. Cd²⁺ doped ZnS were prepared by varying doping concentration from 1 to 8 wt.%. ZnS quantum dots were mixed with CdS quantum dots of size 4 nm in the 3:1, 2:1, 1:1, 1:2, 1:3 and 1:4 M ratio. The nanoparticles were characterized by UV–vis, photoluminescence (PL), XRD and high-resolution TEM measurements. The XRD pattern, high-resolution TEM image and SAED pattern reveal that the nanoparticles are in well-crystallized cubic phase. The band gap of ZnS has increased from the bulk value 3.7 to 4.11 eV showing quantum size effect. Excitonic transition is observed at 274 nm in UV absorption and PL emission at 411 nm. Doping with Cd²⁺ red-shifts both UV and PL spectral bands and enhances the PL band of ZnS nanoparticles. Mixing CdS and ZnS quantum dots in different molar ratios shows red-shift of the band edge in the CdS/ZnS hybrid system. In the 1:1 hybrid system of CdS/ZnS nanoparticles, PL band is red-shifted and the intensity is almost doubled with respect to that of CdS nanoparticles.     

Effect of aluminum doping on the properties of PEC cells formed with CdS:Al films

Aluminum doped and undoped CdS films were prepared by chemical bath deposition technique and the photoelectrochemical (PEC) properties have been studied by forming doped CdS/NaOHNa₂SS/C junction. Better results are obtained with 0.1 wt% Al doped CdS films. These results are discussed with the help of the optical and transport properties of the Al doped CdS films.     

CdS nanoparticles grown in a polymer matrix by chemical bath deposition

Nanocrystallites of CdS have been grown by chemical bath deposition within the pores of poly(vinyl alcohol) (PVA) on glass and Si substrates. The CdS-PVA composite films are transparent in the visible region. XRD and TEM diffraction patterns confirmed the nanocrystalline CdS phase formation. TEM study of the film revealed the manifestation of nano CdS phase formation and the average particles size was varied in the range 5-12 nm. UV-vis spectrophotometric measurement showed high transparency (nearly 80% in the wavelength range 550-900 nm) of the films with a direct allowed band gap lying in the range 2.64-3.25 eV. Particle sizes have also been calculated from the shift of band gap with respect to that of bulk value and were found to be in the range 3.3-6.44 nm. The high dielectric constant (lies in the range 120-250 at high frequency) of PVA/CdS nanocomposite compared to that of pure PVA (-28) has been observed. The dielectric constant decreases with increase of dispersibility of the CdS nanoparticles within PVA. The nanocrystalline PVA/CdS thin films have also showed field emission properties with a turn-on field of approximately 6.6 V/microm, whereas only PVA thin film and bulk CdS on PVA have shown no field emission.     

CdS thin films doped with metal-organic salts using chemical bath deposition

CdS thin films doped with metal-organic salts were grown on glass substrates at 90 °C by the chemical bath deposition technique. Metal-organic salts such as zinc acetate, chromium acetylacetonate, ammonium fluoride, aluminum nitrate, tin acetate and indium acetate were used. The chemical bath was prepared with cadmium acetate, ammonium acetate, thiourea and ammonium hydroxide. In the case of un-doped films, the S/Cd ratio was varied by changing the thiourea in the range 1-12. The best optical, structural and electrical properties were found for S/Cd = 2. The doped films were prepared by always keeping the ratio S/Cd constant at 2. The band gap (E_g) of doped and un-doped films was evaluated from transmittance spectra, where films with lower sulfur concentration exhibited higher E_g. X-ray analysis showed that both un-doped and doped films were polycrystalline with preferential orientation along the (111) direction and with the zincblende structure in all cases. The dark electrical results showed that CdS doped with Zn (1 at.%) exhibited the lowest resistivity values of 10 Ω cm.     

Growth of CdS nanoparticles in Y- and Z-type Langmuir–Blodgett thin film using 1,3-bis-(p-iminobenzoic acid)indane

Cadmium sulphide (CdS) nanoparticles were formed in 1,3-bis-(p-iminobenzoic acid)indane by exposing Cd²⁺ doped Y- and Z-type multilayered Langmuir–Blodgett (LB) films to H₂S gas. The growth of CdS nanoparticles were monitored by UV–visible spectroscopy measurements. It was observed that CdS nanoparticles in both Y- and Z-type LB films cause a blue-shift in absorption spectra. The surface morphology of LB films were characterized with atomic force microscopy DC electrical measurements were carried out for these LB films grown in a metal/LB film/metal sandwich structures with and without CdS nanoparticles. By analyzing I–V curves and assuming Schottky conduction mechanism the barrier height was found to be as 1.25 and 1.17?eV for Y-type unexposed and exposed samples; 1.18 and 1.25?eV for Z-type unexposed and exposed samples, respectively.     

Storage modulus and glass transition behaviour of CdS/PMMA nanocomposites

The storage modulus and glass transition temperature (T _g) of CdS/PMMA nanocomposites have been evaluated as a function of concentration of CdS nanoparticles. CdS particles have been synthesised via chemical route using cadmium acetate, thiourea and dimethylformamide. The solution-based processing has been used to prepare PMMA composites with CdS nanoparticles at different filler concentration. Size and shape of CdS nanoparticles in PMMA have been determined with the help of small angle X-ray scattering and transmission electron microscope measurements. Dynamical mechanical analysis was carried out on the CdS/PMMA nanocomposites to study storage modulus and tan?δ. It is observed that CdS nanoparticles enhance the storage modulus and T _g for composites. The storage modulus and T _g show the maximum value of 6?wt.% of CdS nanoparticles embedded PMMA composite. The results indicate that the 6?wt.% of CdS nanoparticles in PMMA matrix provides more stability to the composite over the other composites.     

Synthesis of CdS Nanoparticles by Hydrothermal Method and Their Effects on the Electrical Properties of Bi-based Superconductors

Cadmium sulfide (CdS) nanoparticles were synthesized by hydrothermal process and have been characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), and energy-dispersive x-ray spectroscopy (EDXS) system. The effect of added CdS nanoparticles on the superconducting properties and flux pinning capability in (Bi,Pb)₂Sr₂Ca₂Cu₃O_y system (denoted as (Bi,Pb)-2223) has been reported. Hydrothermal method is an effective route to synthesize CdS nanoparticles with good crystallinity and having average grain size of about 12 nm. Then, small amounts (0–0.4 wt%) of nanosized CdS particles were added to Bi-2233 samples using a solid-state reaction route. The transport critical current densities and the electrical resistivity ρ(T, H) were performed using the four-probe technique. The results show that samples sintered by small amount of CdS nanoparticles (≤?0.3 wt%) exhibit the higher critical current densities and energy pinning in applied magnetic fields compared to free added sample. Consequently, the addition of CdS could introduce effective pinning centers which account for the improvement in superconducting properties in the Bi-2223 materials.     

Optical properties of titanium dioxide nanoparticles/3-(2-benzothiazolyl)-7-N,N-diethylaminocoumarin/polymethyl methacrylate composite films

3-(2-benzothiazolyl)-7-N,N-diethylaminocoumarin organic laser dye-polymethyl methacrylate (PMMA) composite films doped with inorganic titanium dioxide (TiO₂) particles are fabricated by spin-coating technique. TiO₂ nanoparticles exhibit a strong influence on optical properties of the organic laser dye/PMMA composite films. The refractive index and absorbance (absorption intensity) of organic laser dye/PMMA composite film with micro- and nanoparticles of TiO₂ are reduced, compared to those without TiO₂ particles. The organic laser dye/PMMA composite film with TiO₂ nanoparticles has the lowest refractive index and absorbance values. Photoluminescence intensities of all systems exhibit a maximum peak around the excitation wavelength, close to that of the organic laser dye, at 450 nm and the minimum around the excitation wavelength of 350 nm. Photoluminescence intensity of the organic laser dye/PMMA composite film with TiO₂ microparticles is always the lowest at all excitation wavelengths. However, the photoluminescence intensity of the organic laser dye/PMMA composite film with TiO₂ nanoparticles has the highest value at excitation wavelengths of 330 and 380 nm, while the photoluminescence intensity of composite film without TiO₂ particles is more than that with nanoparticles at other excitation wavelengths.     

The role of the surface ligand in the optical properties of CdS quantum dots in poly(vinyl alcohol) matrix

The synthesis and characterization of CdS nanoparticles prepared in poly(vinyl alcohol) (PVA) in situ, to produce a series of CdS/PVA nanocomposite films, is described in this paper. The role of 2-mercaptoethanol as the surface ligand for the nanoparticles has been investigated. Different molar concentrations of the cadmium precursor have also been evaluated, aiming at the preparation of stable aqueous colloidal systems and polymeric films. UV–visible (UV–Vis) and photoluminescence spectroscopies together with scanning electron microscopy and transmission electron microscopy have been used for characterization of the growth kinetics and the relative stability of CdS nanocrystals in the polymeric matrix. The results clearly indicate the formation of hexagonal CdS nanoparticles embedded in the PVA matrix. PVA was not effective in stabilizing colloidal CdS nanoparticles against aggregation. However, it leads to a displacement of the first optical transition of CdS due to compressive deformation effect. The combination of PVA with 2-mercaptoethanol as surface ligands had a strong effect on the optical properties of the resulting embedded CdS nanoparticles.     

Preparation of alumina films by the sol-gel method

This review describes our study on preparation of alumina films by a sol-gel process and their several applications that have been investigated since 1986. Alumina films were prepared from alkoxide or inorganic salt. Both as-prepared alumina films were transparent in ultraviolet, visible and near infrared regions. The alumina from inorganic salt (inorganic alumina) was structureless even after annealed at 300–700°C in air, while the alumina from alkoxide (alkoxide alumina) was in pseudo-boehmite at an annealing temperature lower than 400°C and was in - or -type at 400–700°C. Both alumina films became opaque after annealed at temperatures above 1000°C. The inorganic alumina film annealed at 800°C showed a gas permeability that was influenced by physico-chemical properties of penetrant and alumina. Composite films of alumina and poly(vinyl alcohol) (PVA) were hydrophilic but insoluble in water, and removal of PVA from the composite films by annealing at 600°C led to formation of transparent alumina films. Such properties enabled us to use a counter diffusion method for fabricating -Fe₂O₃-doped alumina films. Alumina films doped with organic dyes such as laser dyes, hole-burning dyes and non-linear optical dyes, which were fabricated by gelation of dye-added alumina sol, exhibited laser emission, hole-spectra and second- or third-harmonic generation properties, respectively. Hydrogenation of alkene was catalyzed by Ni nanoparticles doped alumina films that were prepared by gelation of Ni²⁺ solution-added alumina sol and annealing the Ni²⁺-doped alumina gel in hydrogen gas. Nonlinear optical properties were observed for alumina films doped with CdS, Au and Ag nanoparticles, which were fabricated by gelation of Cd²⁺, HAuCl₄ and AgNO₃ solution-added alumina sols and annealing the Cd²⁺-doped alumina gel in H₂S gas and the Ag⁺- and Au³⁺-doped alumina gels in H₂ gas. Rare earth metal ion-doped alumina films, which were prepared by gelation of rare earth metal ion solution-added alumina sol and annealed the ion-doped alumina gel, exhibited not only normal luminescence but also up-conversion emission, energy transfer type luminescence and long lasting luminescence.     

Performance of CuIn1 − xGaxSe2/(PVD)In2S3 solar cells versus gallium content

The present work studies the influence of the Ga content (x = Ga / (Ga + In)) in the absorber on the solar cell performance for devices using (PVD)In₂S₃-based buffers. Input to the hypothesis of the relative conduction band positions can be found in the evolution of the device parameters with x. For experiments with x between 0 and 0.5 devices using (PVD)In₂S₃-based buffers are compared to reference devices using (CBD)CdS. Both buffers give similar cell characteristics for narrow band gap absorbers, typically E_gCIGSe < 1.1 eV. However, the parameters of the cells buffered with (PVD)In₂S₃ are degraded when the absorber gap is widened whereas (CBD)CdS reference devices are only slightly affected. Consequently, the solar cell efficiency is similar for both buffer layers at the lower x values and increases with x only in the case of (CBD)CdS. These evolutions are coherent with the existence of a conduction band cliff at the CIGSe/(PVD)In₂S₃ interface.     

Ab-initio electronic structure,optical, dielectric and bonding properties of lizardite-1T

The structural, electronic, optical, dielectric and bonding properties of lizardite-1T [Mg₃Si₂O₅(OH)₄] are investigated using plane wave pseudopotential density-functional theory (DFT) method taking the generalized gradient approximation (GGA) as the exchange–correlation energy functional. The structural properties are consistent with the earlier experimental and theoretical results. The direct electronic band gap at the Γ-point is estimated to be 3.34 eV, which is less than the optical band gap of ～4.0 eV measured from the fundamental absorption edge. A remarkable optical anisotropy is observed in the optical spectra. The dielectric properties are consistent with previous theoretical calculations. Analysis of Mulliken charge and bonding population shows the coexistence of covalent and ionic bonding in the lizardite-1T and the results are also consistent with previous theoretical calculations and experimental results.     

Synthesis of high-luminescent cadmium sulfide nanocrystallites by a novel single-source precursor route

Highly luminescent cadmium sulfide nanocrystallites have been successfully produced by the thermolysis of a novel single-source precursor, cadmium O, O′-dialkyldithiophosphates, which were dissolved in oleic amine. The microstructure and morphology of the as-prepared CdS nanoparticles were characterized using X-ray diffraction, transmission electron microscopy and high resolution transmission electron microscopy. It was found that the as-prepared CdS nanoparticles show a narrow size distribution and high crystallinity. The optical properties of these samples were examined by UV-visible and photoluminescence spectroscopy. Not only an intensive red-light-emitting luminescence phenomenon derived from the solution of the CdS nanocrystallites can be observed easily at room temperature, the band gap of CdS nanocrystallites can also be tailored by changing the length of substituted alkyl chain of single-source precursors.     

Photoluminescence and energy transfer investigation from SiO2: Tb,Au inverse opals to rhodamine-B dyes

Energy transfer has attracted extensive attention due to its widespread applications in medical diagnostics, DNA analysis and lighting devices. There are few reports on the energy transfer from rare earth ions to dyes. In the present work, the SiO₂:Tb inverse opals with and without Au nanoparticles were prepared, and the organic rhodamine-B (RhB) dyes were filled into the voids of SiO₂:Tb inverse opals. Non-radiative and radiative energy transfer processes from the SiO₂:Tb inverse opals to the RhB were observed. The influence of Au nanoparticles and photonic band gap on the energy transfer from SiO₂:Tb inverse opals to the RhB was investigated. The Au nanoparticles enhanced energy transfer was observed due to the surface plasmon resonance effects of the Au nanoparticles. When the emission peaks from the SiO₂:Tb inverse opal is overlapped with the photonic band gap, the emission suppression of the SiO₂:Tb inverse opal as well the emission enhancement of the RhB dyes were obtained, which is attributed to improved energy transfer caused by the photonic band gap. The steady state rate equations were used to explain enhancement of energy transfer caused by the photonic band gap.