CdSe thin films: morphological, optoelectronic and photoelectrochemical studies

Polycrystalline cadmium selenide (CdSe) thin films have been synthesized at room temperature by using chemical bath deposition method. The synthesized films were characterized by using X-ray diffraction (XRD), optical absorbance, electrical conductivity, scanning electron microscope, energy dispersive X-ray analysis, photoluminescence and photoelectrochemical (PEC) techniques. The film of 0.84 μm thickness, deposited on glass substrate showed uniform spherical morphology with an optical band gap of 1.99 eV. The XRD analysis confirmed presence of cubic structure. Scanning electron micrograph shows a typical spherical ball like morphology with large surface area, which is useful for absorption of large solar radiation. The conductivity measurements showed n type semiconducting nature of the film. A PEC cell device fabricated using ‘as deposited’ CdSe film as anode showed a stable conversion efficiency of 0.7 %.     

Structural,optical and photoconducting properties of sprayed CdSe films

CdSe films were grown by the pyrolytic decomposition of a mixture of aqueous solutions of selenourea (NH₂CSeNH₂) and CdCl₂·5H₂O. The effect of changes in the selenium-to-cadmium ion ratio on the photoconductivity was examined. The as-grown films had low resistance and showed poor photoconductivity gain. When the films were annealed in air the resistance as well as the gain increased appreciably. These changes have been attributed to chemisorption of oxygen. The samples with one part CdCl₂·5H₂O and one part NH₂CSeNH₂ were found to be the most photosensitive, the ratio of dark resistance to light resistance being of the order of 10⁵. The spectral response of the resistance of these films shows a dip in the region of 690 nm, which is in close agreement with the band gap determined from optical absorption measurements.     

Structural,optical and magnetic properties of cobalt-doped CdSe nanoparticles

Pure and Co-doped CdSe nanoparticles have been synthesized by hydrothermal technique. The synthesized nanoparticles have been characterized using X-ray diffraction (XRD), ultraviolet-visible spectroscopy (UV–Visible), photoluminescence spectroscopy (PL), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM) and superconducting quantum interference device (SQUID), at room temperature. From XRD analysis, pure and cobalt-doped CdSe nanoparticles have been found to be polycrystalline in nature and possess zinc blende phase having cubic structure. In addition to this, some peaks related to secondary phase or impurities such as cobalt diselenide (CoSe₂) have also been observed. The calculated average crystallite size of the nanoparticles lies in the range, 3–21 nm, which is consistent with the results obtained from TEM analysis. The decrease in average crystallite size and blue shift in the band gap has been observed with Co-doping into the host CdSe nanoparticles. The magnetic analysis shows the ferromagnetic behaviour up to 10% of Co-doping concentration. The increase of Co content beyond 10% doping concentration leads to antiferromagnetic interactions between the Co ions, which suppress the ferromagnetism.     

Structural, optical and photoelectrochemical properties of electrodeposited CdSe thin films

Cadmium Selenide thin films have been electrodeposited from an acidic bath using CdSO₄ as a cadmium source and SeO₂ as a selenium source at pH=3 on to stainless steel and fluorine-tin oxide coated glass substrates. The CdSe films have been characterized by X-ray diffraction, scanning electron microscopy and optical absorption. X-ray diffraction spectra showed that CdSe is polycrystalline with single hexagonal phase. The intensity of the (0 0 2) peak increases remarkably by annealing in nitrogen atmosphere. A microstructural study revealed that the films were uniform and well covered the substrate. Optical absorption studies showed that the bandgap of the CdSe is 1.70 eV. It is observed that the conductivity of the CdSe films increases by annealing in nitrogen atmosphere. The photoelectrochemical activities of CdSe films deposited on stainless steel and fluorine-tin oxide coated glass have been studied by using CdSe/ 1 M NaOH-1 M Na₂S-1 MS / C cell configuration and it is found that films deposited on stainless steel give better performance, photoelectrochemical (PEC) studies also reveal that the CdSe has n-type conductivity.     

Synthesis and size dependent optical studies in CdSe quantum dots via inverse micelle technique

Cadmium selenide quantum dots (CdSe QDs) were successfully synthesized without using trioctylphosphine (TOP). The XRD pattern showed zinc-blend phase of the CdSe QDs. The absorption and PL spectra exhibit a strong blue shift as the QDs size decreases due to the quantum confinement effect. In addition, the quantum efficiency of CdSe QDs with TOP capping is higher than CdSe QDs with oleic acid capping. TEM image shows a spherical shape, compact and dense structure of CdSe QDs. A good agreement between the Tauc's model and experimentally measured absorption spectra of CdSe QDs is achieved. The FTIR peak at ～1712 cm^?1 spectra confirms the influence of oleic acid as a capping agent.     

Structural,optical and electrical properties of Zn-doped SnO2 nanoparticles synthesized by the co-precipitation technique

Nanometric size Zn-doped SnO₂ particles with Zn concentration varying from 1 to 6 % were prepared using the co-precipitation method. X-ray diffraction patterns show for all samples a typical rutile-type tetragonal structure of SnO₂ without any additional peaks from spurious phases. These results together with transmission electron microscopy analyses have shown that the size of the nanoparticles decreases with Zn doping down to 4 nm. According to UV–visible absorption measurements this decrease of particle size is accompanied by a decrease of the band gap value from 3.34 eV for SnO₂ down to 3.28 eV for 6 % Zn doping. The electrical conductivity of the system has been investigated between 473 and 718 K, in the 200 Hz–5 MHz frequency range, by means of impedance spectroscopy. The temperature dependence of the bulk conductivity was found to obey the Arrhenius law with activation energies of 0.74 eV for SnO₂ and 0.69 eV for 6 % Zn doping.     

Structural,optical and electrical characterization of undoped ZnMgO film grown by spray pyrolysis method

Undoped Zn_1−X Mg _X O poly crystalline films were successfully grown by a spray pyrolysis method at 500 °C. The samples indicated high quality because (0002) orientation was strongly observed in the X-ray diffraction (XRD) pattern below Mg content X = 0.3. A lattice constant of c axis decreased linearly with increasing Mg content, indicating that the lattice constant of c axis followed Vegard’s law. It was deduced that Mg atoms could be successfully substituted in Zn site from lattice constants and optical bandgap.     

Structural and optical properties of nanocrystalline CdSe and Al:CdSe thin films for photoelectrochemical application

Nanocrystalline CdSe and Al:CdSe semiconductor thin films have been successfully synthesized onto amorphous and FTO glass substrates by spray pyrolysis technique. Aqueous solutions containing precursors of Cd and Se have been used to obtain good quality films. The optimized films have been characterized for their structural, morphological, wettability and optical properties. X-ray diffraction (XRD) studies show that the films are polycrystalline in nature with hexagonal crystal structure. Scanning electron microscopy (SEM) studies show that the film surface is smooth, uniform and compact in nature. Water wettability study reveals that the films are hydrophilic behavior. The formation of CdSe and Al:CdSe thin film were confirmed with the help of FTIR spectroscopy. UV–vis spectrophotometric measurement showed a direct allowed band gap lying in the range 1.673–1.87 eV. Output characteristics were studied by using cell configuration n- CdSe/Al:CdSe |1 M (NaOH + Na₂ + S)|C. An efficient solar cell having a power conversion efficiency of 0.38% at illumination 25 mW cm⁻² was fabricated.     

Stability studies of CdSe nanocrystals in an aqueous environment

In this paper, CdSe nanocrystal dissolution in an aqueous solution was studied. It was found that light is a key factor affecting the dissolution of nanocrystals. In the presence of light, the electrons generated from CdSe nanocrystals reduce water to hydrogen and hydroxide ions (OH-) while photo-generated holes oxidize CdSe to Cd2+ and elemental Se. The dissolution was accelerated in an acidic medium while moderate alkalinity (pH=10.3) can slow down the dissolution possibly due to precipitation of nanocrystals. This study has strong implications for the use of these crystals in aqueous environments (bioimaging and dye-sensitized solar cells).     

Ultrafast synthesis of CdTe/ZnSe semiconductor QDs by microwave method and investigation of structural,optical, and photocatalytic properties of CdTe/ZnSe QDs

Journal of Materials Science: Materials in Electronics - CdTe/ZnSe semiconductor quantum dots were synthesized by the ultrafast microwave method in an aqueous solution. X-ray diffraction results...     

锡硫化合物包覆的水溶性硒化镉量子点的制备与表征

以Na2S、Na2SnO3、稀盐酸及水合肼为原料成功合成了锡硫化合物(Metalchal cogenidometalates,MCCs)。该化合物在离子溶液中解离出SnS44-或Sn2S46-,这两种低聚阴离子因其电子空间结构特殊而具有配位作用,故能置换CdSe量子点表面原有的长链有机配体,从而实现量子点从有机相到无机相的转移。配体交换后的量子点可以较好地分散在水、氨水、水合肼和二甲亚砜等一系列极性溶剂中。我们分别用透射电子显微镜(TEM)、紫外吸收光谱(UV)、荧光发射光谱(PL)和红外吸收光谱(FTIR)表征了CdSe的分散性、光学性质及表面配体情况。     

Structural and optical properties of electron beam evaporated CdSe thin films

Thin films of cadmium selenide (CdSe) as a semiconductor is well suited for opto-electronic applications such as photo detection or solar energy conversion, due to its optical and electrical properties, as well as its good chemical and mechanical stability. In order to explore the possibility of using this in optoelectronics, a preliminary and thorough study of optical and structural properties of the host material is an important step. Based on the above view, the structural and optical properties of CdSe films have been studied thoroughly in the present work. The host material, CdSe film, has been prepared by the physical vapour deposition method of electron beam evaporation (PVD: EBE) technique under a pressure of 5 × 10⁻⁵ mbar. The structural properties have been studied by XRD technique. The hexagonal structure with a preferred orientation along the (0 0 2) direction of films has been confirmed by the X-ray diffraction analysis. The films have been analysed for optical band gap and absorbed a direct intrinsic band gap of 1·92 eV.     

Structural, morphological and optical properties of thermal annealed TiO thin films

Structural, morphological and optical properties of TiO thin films grown by single source thermal evaporation method were studied. The films were annealed from 300 to 520 °C in air after evaporation. Qualitative film analysis was performed with X-ray diffraction, atomic force microscopy and optical transmittance and reflectance spectra. A correlation was established between the optical properties, surface roughness and growth morphology of the evaporated TiO thin films. The X-ray diffraction spectra indicated the presence of the TiO₂ phase for the annealing temperature above 400 °C.     

Structural and electrical conductivity studies on undoped and copper-doped nanocrystalline zinc sulphide

Zinc sulphide (ZnS) and copper-doped zinc sulphide nanocrystallites (ZnS:Cu) of average size 4 and 3 nm, respectively, have been synthesized by chemical precipitation method. Structural and morphological studies using X-ray and high resolution transmission electron microscopy (HRTEM) measurements have confirmed hexagonal structure for the samples. Using impedance spectroscopy, the effect of grain interior and grain boundary regions on the electrical conductivity have been studied at various temperatures. In the high temperature region, the grain boundary contribution to conduction is found to be larger than that of the grain interior region. Further, the activation energies of charge carriers in both the grain interior and grain boundary regions have been determined. The conduction mechanism of copper-doped zinc sulphide nanocrystallites have been studied at various temperatures and the results are reported.     

Controlled synthesis of NiS nanoparticle/CdS nanowire heterostructures via solution route and their optical properties

In the present study, we have successfully synthesized the novel heterostructure of NiS nanoparticle (NP)/CdS nanowire (NW) through solution approach. The first step, CdS nanowires were synthesized by a convenient solvothermal route. Then, NiS nanoparticles were grown on the surface of CdS nanowires in a chemical solution of NiCl₂·6H₂O and anhydrous ethanol at 200 °C. The new catalyst-assisted growth mechanism of the NiS NP/CdS NW heterostructure has been tentatively discussed on the basis of experimental results. A detailed study of the effect of experimental parameters, such as reaction time, reaction temperature, and reaction solvent are also studied. The as-prepared products are characterized by field-emission scan electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), and their optical properties are measured by Raman spectra and PL spectra. Furthermore, using CdS nanowires and NiS NP/CdS NW heterostructure as examples, our study suggests that this general method can be employed for construction of other semiconductor heterostructures with novel properties.     

Structural, optical and electrical properties of undoped polycrystalline hematite thin films produced using filtered arc deposition

Thin films of α-Fe₂O₃ (hematite) were deposited using filtered arc deposition. The structural, optical and electrical properties of the films have been characterized. High-purity hematite films were produced, free from other iron oxide phases and impurities. The films exhibit preferred orientation, with the c-axis of the hexagonal structure aligned perpendicular to the substrate. The films have an upper uncertainty bound of the porosity of 15%, with a microindentation hardness of 17.5 ± 1 GPa and elastic modulus of 1235 ± 5 GPa. The indirect and direct band gap energies were found to be approximately 1.9 eV and 2.7 eV, respectively. The refractive index, and the extinction and absorption coefficients were determined from total reflectance and direct transmittance measurements. The thin films exhibit a high resistivity (≥ 10⁵ Ω cm) which indicates pure α-Fe₂O₃. An activation energy of 0.7 eV was calculated from an Arrhenius plot of the conductivity.