Nanocrystalline CdSe Research Articles

Shewanella oneidensis MR-1 respires CdSe quantum dots for photocatalytic hydrogen evolution

Living bio-nano systems for artificial photosynthesis are of growing interest. Typically, these systems use photoinduced charge transfer to provide electrons for microbial metabolic processes, yielding a biosynthetic solar fuel. Here, we demonstrate an entirely different approach to constructing a living bio-nano system, in which electrogenic bacteria respire semiconductor nanoparticles to support nanoparticle photocatalysis. Semiconductor nanocrystals are highly active and robust photocatalysts for hydrogen (H2) evolution, but their use is hindered by the oxidative side of the reaction. In this system, Shewanella oneidensis MR-1 provides electrons to a CdSe nanocrystalline photocatalyst, enabling visible light-driven H2 production. Unlike microbial electrolysis cells, this system requires no external potential. Illuminating this system at 530 nm yields continuous H2 generation for 168 h, which can be lengthened further by replenishing bacterial nutrients.

Studies on optical and electrical properties of PVA capped nanocrystalline CdSe thin film prepared by chemical bath deposition method

PVA-capped nanocrystalline CdSe thin films are deposited on chemically clean glass substrates by chemical bath deposition technique using Cadmium acetate [Cd(CH3COO)2.3H2O and Sodium Selenosulfate (Na2SeSO3) as Cd2+ and Se2- ions sources respectively. Polyvinyl Alcohol (PVA) is act as a capping agent. Films of five different molarities (0.1 M–0.50M) of same pH value 8 were prepared at room temperature 298 K. The characteristics of the prepared CdSe thin films are investigated in detail by measuring their optical and electrical properties. The band gap energy of 2.16–2.49 eV was determined from the optical absorption spectra. The optical band gap decrease with increase in molarities. The electrical conductivity measured using two co-planar Aluminium electrodes are found to increase with increase in temperature showing semiconducting nature of the films. The electrical conductivity at room temperature is found to be of the order of 10-4 Ω-1 cm-1 .

Effect of Intensity and Wavelength of Illumination on the Photoelectronic Properties of Nanocrystalline CdSe Thin Films

Photoelectronic properties of nanocrystalline CdSethin films prepared by chemical bath deposition (CBD) technique at room temperature are studied taking its molar concentration as a function. Structural analysis of the deposited thin films shows that change of molarity brings a variation in the crystalline sizes of the thin films. Such thin films show suitable photoelectronic properties for the construction of different optoelectronic devices. The photocurrents are observed to be significantly defect controlled in the visible range of wavelengths. The transport mechanism for the thin films is generally a doubly activated process and the photocurrent decay characteristics curves are found to exhibit 2 different decay times which actually correspond to 2 distinct trap levels. HIGHLIGHTS The photoelectronic properties of nanocrystalline CdSe thin films deposited by CBD method are studied From the XRD of the films diffraction peaks may be indexed to diffraction basically from the (111) plane of zincblende structure The optical band gap may be varied with the molarity of the solution used for deposition Photoelectronic properties are dependent of the intensity of different monochromatic illuminations Photocurrents for the films are basically controlled by the grain boundary defects Growth and decay of photocurrent are effectively governed by different kind of traps GRAPHICAL ABSTRACT

Assessing the dislocation density in CdSe nanocrystals from XRD peak profile analysis (XDPPA) assisted by first principles method

Nanocrystalline CdSe has been synthesized via a wet chemical technique followed by characterized using XRD and HRTEM. Classical (CWH) and modified Williamson Hall (MWH) techniques have been used for the determination of microstructures based on the X-ray diffraction peak profile analysis (XDPPA). Rietveld refinement of the experimental XRD pattern provides the refined full width at half maximum (FWHM) of CdSe nanocrystals. Here, the output structural information as obtained from the Rietveld refinement method has been fed into the Quantum Espresso (QE) code for the determination of elastic constants of CdSe using the first principles method. Both the FWHM and elastic constants are used in CWH and MWH analysis. Since the MWH method considers the strain anisotropy of the crystals, it can provide a better fit than the CWH method. In addition to this, the MWH method has been used to find out the dislocations character present in the CdSe nanocrystals. Dislocations are important because these are responsible for inducing strain in the nanocrystals.

Novel Metal Chalcogenide–Conducting Polymer Hybrid Material for Electronic Memory Devices

New hybrid (organic–inorganic) material based on nanocrystalline CdSe capped with EDTA and poly(O-toluidine) doped with camphor sulfonic acid (POT-CSA) is processed from solution and characterized in order to relate the device function (optical absorption, charge separation and transport properties) to active-layer properties and device parameters. POT/CdSe hybrid material has been synthesized using physical mixing method. X-ray diffraction (XRD) and scanning electron microscopy (SEM) are used to investigate the structural and morphological properties. The organic–inorganic composite system was applied as an active device component to demonstrate the electrical memory effects. The device exhibited a nonvolatile, resistive switching performance with a constant ON–OFF current ratio. The nonvolatile behavior was confirmed by applying a 2.5-V read pulse.

Surface and displacement damage engineering on CdSe nanocrystalline thin film by swift heavy Ag ions: A theoretical investigation by SRIM/TRIM package

Engineering of surface and structural properties of a sample by ion beam technology has got tremendous attention in recent times. Here, surface modification in CdSe nanocrystalline thin film due to 120 MeV Ag swift heavy ions (SHI) irradiation has been studied through Stopping and Range of Ions in Matter (SRIM)/Transport of ions in matter (TRIM) package in terms of sputtering yield and average surface binding energy. From this study, average range has been obtained as 1.6 μm and average surface binding energy as 1.7 eV. SHI deposits huge energy to the atomic lattice and that displaces the lattice atoms from their original positions, which has been utilized here to obtain displacement damage. The damage profile has been studied as a function of dpa, which shows that the maximum displacement damage peaks is at 1.5 μm for CdSe due to 120 Mev Ag ions irradiation.

Characterization of chemically deposited nanocrystalline CdSe thin films from transmittance spectra

Optical properties of nanocrystalline films of CdSe prepared by chemical bath deposition technique are studied as a function of molar concentration. Analyses of the transmittance spectra over 350–900 nm photon wavelengths of CdSe films indicates the existence of direct optical transition. A blue shift of absorption edge was observed which indicates a decrease in crystallite size. The optical band gap (Eg) was found to be in the range of 1.93–2.10 eV for as-prepared films. After annealing the band gap was found to decrease. The crystallite size was found in the range of 3.34–4.99 nm using the effective mass approximation model. Different optical parameters such as absorption coefficient, refractive index, extinction coefficient, optical conductivity, dielectric constants were determined from the transmittance spectra.

Morphology, Structure, and Optical Properties of Nanocrystalline CdSe Films Doped with Copper

Nanocrystalline CdSe films on a frosted glass substrate are synthesized via hydrochemical deposition with sodium selenosulfate using an additive of 5 × 10–4–10–3 mol/L copper(II) chloride. It is found that introducing copper(II) chloride into the reaction mixture accelerates the formation of solid phase CdSe and thins the cadmium selenide layer from 240 to 130–160 nm. It is established that doping with copper does not affect the cubic B3 structure (space group $$F\bar {4}3m$$ ) of the CdSe film, but 10−3 mol/L copper(II) chloride in the reactor reduces the period of the crystal lattice from 0.59967 to 0.59899 nm, due to the formation of supersaturated substitutional solid solution CuxCd1−xSe (x = 0.03). The band gap of the CdSe film, calculated according to light transmittance and diffuse reflectance, is 1.8 eV. Adding copper to the film lowers Еg to 1.6 eV. It is shown that doping with copper results in luminescence in the near-IR spectral range (680–780 nm) and changes conductivity from the n to the p type.

Facile fabrication of well-performing CdS/CdSe quantum dot sensitized solar cells through a fast and effective formation of the CdSe nanocrystalline layer

In this study a co-sensitization strategy is utilized for fabrication of a simple type of quantum dot sensitized solar cells (QDSCs) with high power conversion efficiency. A transparent layer of hydrothermally grown TiO2 nanocrystals (NCs) was sensitized with CdS and CdSe QDs layers and applied as the photoanode of the cells. The CdS layer was deposited through a successive ionic layer adsorption and reaction (SILAR) approach with optimized number of cycles. The CdSe nanocrystalline layer was also formed by a fast and effective chemical bath deposition (CBD) method for co-sensitization. The CBD time was altered in a short range of 6–15 min while the deposition was well-performed and quality of the CdSe layer was quite acceptable. The ZnS passivating layer was finally over-deposited and photoanodes were applied in conventional structure of QDSCs using polysulfide electrolyte and CuS counter electrodes. The CBD time was optimized to find the best bandgap energy/band edge positions and deposition amount of the CdSe layer for higher energy conversion efficiencies. The best photovoltaic performance was achieved for the QDSC with CdSe co-sensitizing layer deposited at 12 min of the CBD process. This optimized cell demonstrated the photovoltaic parameters of Jsc = 22.2 mA/cm2, Voc = 628 mV, and power conversion efficiency of 6.8%. This efficiency was increased about 172% compared to that of reference cell with just CdS QDs as the light sensitizing layer.

Synthetic Route of CdSe Nanocrystalline Films Fabricated by Substrate Vibration Assisted Drop Casting Method

Herein, we report a greener, non-toxic, cost effective and a modest scheme for the fabrication of excellent CdSe nanocrystals (NCs). Precursors for the present reaction are synthesized by the treatment of cadmium chloride (CdCl2) with 2-pyridyl selenolate (NaSeC5H4N) resulting a complex of the formula [(C5H4NSe)2Cd]. The complex is characterized by NMR (1H and 13C) and IR spectroscopies. The complex, [(C5H4NSe)2Cd] is found to be polymeric in nature, as indicated by its insolubility in solvents, and is further customized as a single-source pioneers for the preparation of colloidal CdSe NCs. Thermolysis of [(C5H4NSe)2 Cd] has been successfully carried out by hotinjection method using low-cost and harmless oleic acid (OA) as the coordinating solvent, thereby rejecting the need of air-sensitive and toxic solvents. Based upon dynamic light scattering (DLS) technique, the average size of colloidal CdSe NCs are determined using particle size analyzer. The average size of colloidal NCs comes out to be 6.3 nm. Thin films of colloidal CdSe NCs are deposited on glass substrate using drop-casting (DC) and ultrasonic substrate vibration assisted drop casting (SVADC) methods to study their use as workable materials for engineering devices. The films are characterized by ultraviolet-visible spectroscopy (UV-vis), photoluminescence (PL) studies, X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques.

CdSe films synthesized from chemical bath deposited Cd(O2)0.88(OH)0.24 precursor films immersed in a Se ionic solution

CdSe nanocrystalline thin films were synthesized with a method containing two stages. In the first stage Cd(O2)0.88(OH)0.24 precursor films with different deposition time were synthesized by Chemical Bath Deposition. In the second stage precursor films were transformed into CdSe films by immersion in a Se ionic solution. CdSe samples were characterized by x-ray diffraction, UV–vis, Raman spectroscopy, high resolution transmission electron microscopy, x-ray photoelectron spectroscopy and Secondary Ion Mass Spectrometry. CdSe samples crystallized in hexagonal wurtzite phase. Raman spectra showed the LO mode with higher order features. Cd and Se core levels obtained from measurements are in agreement with values for CdSe in bulk. Depth profile analysis confirms the presence of CdSe films on top of thicker Cd(O2)0.88(OH)0.24 precursor films.

Influence of trivalent bismuth doping on optoelectronic and microstructural properties of hydrophilic nanocrystalline cadmium selenide thin films

Doping is a prevalent technique for improving the optoelectronic properties of semiconductor thin films. Bismuth (Bi) doped nanocrystalline cadmium selenide thin films deposited on glass substrates were prepared by a chemical deposition method. The effect of different doping percentages of Bi has been investigated in detail. X-ray diffraction, high-resolution transmission electron microscopy, scanning electron microscopy, energy dispersive x-ray analysis, electrical techniques, optical absorption, photoluminescence, Raman spectroscopy, and water wettability measurement were used to characterize the films. X-ray diffraction showed the formation of a polycrystalline CdSe cubic phase with the preferential orientation (111). The optical band gap values decreased as the Bi doping concentration increased. The high optical band gap of the films up to 2.62 eV showed a strong blue shift. Films were luminescent with emission in the green region when they were excited with a UV source. The resistivity of the thin films was found to decrease with increase in Bi concentration. Surface morphology showed an almost uniform distribution of spherical grains. Water wettability analysis showed that the films were purely hydrophilic. Raman analysis confirmed the formation of nanocrystalline CdSe thin films.

Thickness dependent correlation between structural and optical properties of textured CdSe thin film

Nano-crystalline CdSe thin films of different thicknesses under sub-micron range were deposited on glass substrate via thermal evaporation route. A gradual deterioration in film crystallinity confirmed by XRD line profile analysis has been accompanied by a reduction in Cd to Se molar ratio as the film thickness decreases. A coordinated microstructural and crystallographic orientation distribution analysis explicitly demonstrated that CdSe tends to grow in nano-sized columns with hexagonal c-axis parallel to its growth direction on glass substrate. A thickness dependence of structural evolution was discussed in terms of aspect ratio of the columnar structure and dispersion in orientation of hexagonal (002) basal plane. The variation in the spectra of optical constants [n(λ), k(λ)] obtained from Swanepoel envelop method was interpreted in terms of crystallographic defects arising from stoichiometric disorder which was also accounted for the observed thickness dependent shifts in band gap and valence band split energy. The bathochromic shifts in dielectric and energy loss functions, optical conductivity, skin depth and cut-off energy were discussed in detail along with the variations in their spectral shapes in connection with the dispersion in the real and imaginary parts of complex refractive index, which might shed a new light upon holistic comprehension of thickness dependent optical properties of other chalcogenide semiconducting thin films.

Effect of Sm concentration on optical and electrical properties of CdSe nanocrystalline thin film

Abstract Present paper reports optical and electrical properties of samarium doped CdSe nanocrystalline thin film which was grown on a glass substrate by chemical bath deposition method (CBD). X-ray diffraction (XRD) analysis revealed that the deposited films were nanocrystalline with sphalerite cubic structure. The average crystallite size calculated from FWHM of XRD peaks was found to be 10.11 nm. The bandgap of the Sm doped CdSe nanocrystalline thin films was calculated to be 1.91 eV to 2.22 eV. The optical absorption edge of undoped (pure) and Sm doped CdSe films was obtained between 650 nm to 640 nm showing blue shift as compared to bulk CdSe. Sm doping further enhanced the photoconductivity of these films. The I-V characteristic confirmed the suitability of prepared films for photosensor applications.

Incorporation of tin in nanocrystalline CdSe thin films: a detailed study of optoelectronic and microstructural properties

Tin-doped nanocrystalline CdSe thin films were deposited onto glass substrate by simple chemical bath deposition technique. The films obtained were uniform and had good adherence to the substrate. The influence of Sn (0–5%) doping on the optical, photoluminescence, electrical, morphological, compositional and structural properties of the films was investigated. The optical absorption studies revealed that the optical band gap of the films varied from 2.62 eV for nano CdSe to 2.50 eV for 5% Sn:CdSe. These films are appropriate for application in different optoelectronics devices due to band gap tunability property. To analyze photoluminescence properties, the films were excited by UV (235 nm) and almost green spectrum was emitted by the films. It is observed that the low temperature resistivity of the thin films was in the range 107–104 Ω cm and also found to decrease with Sn concentration, as resulted from the dc two probe measurements. Activation energy was also calculated. Noticeable changes were observed in the optical and electrical properties of CdSe thin films due to the presence of Sn dopant. Surface morphology study using TEM/SEM showed almost uniform distribution of spherical grains. The elemental composition study using energy dispersive spectroscopy (EDAX) confirms the existence of the desired elements. X-ray diffraction pattern indicated that the formed structure is cubic with most prominent peak at (111). Some important structural parameters such as lattice constant, crystallite size, strain, dislocation density and number of crystallites per unit area were calculated and presented.

High-temperature thermodynamic properties of nanocrystalline CdSe thin film

ABSTRACTThe thermodynamic properties of the nanocrystalline CdSe (nc-CdSe) thin film were studied by in situ high-temperature X-ray diffraction measurement over the temperature range 288–1073 K. It is shown that nc-CdSe thin film has high thermal stability and no phase transformation up to 1002 K. Lattice parameter, thermal expansion coefficients along c-axis and crystal quality increased with the increase of temperature, but dislocation density and strain decreased with the increase of temperature. Surface effect and size effect are two of the most specific intrinsic properties of nc-CdSe thin films, both of which are of great significance to the thermodynamic properties. This work has provided a reliable basis for the research of nc-CdSe devices at high temperature.

The Effect of CdSe and InP Quantum Dots on the Interaction of ZnO with NO2 under Visible Light Irradiation

Nanocomposites based on nanocrystalline ZnO and CdSe and InP nanocrystals (quantum dots) have been synthesized by chemical precipitation and high-temperature colloidal synthesis. The microstructure parameters of the oxide matrix and the size of the CdSe and InP nanocrystals have been determined. A correlation was established between the spectral dependence of the photoconductivity of nanocomposites and the optical absorption spectra of quantum dots. The influence of CdSe and InP quantum dots on the interaction of ZnO with NO2 under visible light irradiation has been studied. It has been shown that the synthesized nanocomposites can be used to detect NO2 under illumination with green light without additional thermal heating.

Size-controlled synthesis of nanocrystalline CdSe thin films by inert gas condensation

Size, shape and structure are considered to have significant influence on various properties of semiconducting nanomaterials. Different properties of these materials can be tailored by controlling the size. Size-controlled CdSe crystallites ranging from ∼ 04 to 95 nm were deposited by inert gas-condensation technique (IGC). In IGC method, by controlling the inert gas pressure in the condensation chamber and the substrate temperature or both, it was possible to produce nanoparticles with desired size. Structure and crystallite size of CdSe thin films were determined from Hall–Williamson method using X-ray diffraction data. The composition of CdSe samples was estimated by X-ray microanalysis. It was confirmed that CdSe thin film with different nanometer range crystallite sizes were synthesized with this technique, depending upon the synthesis conditions. The phase of deposited CdSe thin films also depend upon deposition conditions and cubic to hexagonal phase transition was observed with increase in substrate temperature. The effect of crystallite size on optical and electrical properties of these films was also studied. The crystallite size affects the optical band gap, electrical conductivity and mobility activation of nanocrystalline CdSe thin films. Mobility activation study suggested that there is a quasi-continuous linear distribution of three different trap levels below the conduction band.

Investigation on microstructural and optical properties of nano-crystalline CdSe thin films

In this work, nano-crystalline CdSe thin films were deposited by thermal evaporation technique from CdSe nano-powders on glass substrates. The deposited films were characterized by using optical transmission measurements, and X-ray diffraction (XRD). X-ray line profile analysis revealed that the CdSe films are nano-crystalline and having a wurtzite (hexagonal) structure. These nano-crystalline CdSe films were preferentially oriented along the (002) plane with a c-axis perpendicular to the substrate surface. The crystallite size of these films varied from 16 to 36nm as measured from X-ray line broadening. The variation of film thickness had a great influence on the microstructural parameters, such as micro-strain, stacking-fault probabilities, and dislocation densities. The obtained results demonstrate that the micro-strain, dislocation density, and stacking fault probabilities decrease by increasing the film thickness. The estimated refractive indices of the films fitted well with Sellmeier dispersion formula over a spectral range, 200nm and 2500nm. The effective resonance absorption wavelengths were between 610 and 723nm. Optical parameters of nano-crystalline CdSe films were investigated extensively, and interpreted in the frame of Wemple-DiDomenico single oscillator model. These parameters provided valuable physical insights, such as the relationship between the ionicity of the CdSe films and microstructural parameters. The studied samples obviously had two distinct regions in Tauc plot, except for that sample CS04, due to the strong influence of strain and dislocations.

Effect of quantum confinement in CdSe/Se multilayer thin films prepared by PVD technique

Quantum confined nanostructures were prepared by depositing alternate CdSe and Se thin layers. The structural and optical characterizations of the prepared samples were carried out using X-ray diffractometer (XRD), Field emission scanning electron microscope (FE-SEM), UV–visible and photoluminescence spectrophotometers. XRD studies revealed that CdSe nanocrystals are polycrystalline in nature with hexagonal phase. The crystallite size of CdSe nanoparticles was found to be in the range of 8–14nm. FE-SEM images also confirmed that the embedded nanocrystalline CdSe particles are a few nanometers in dimension having a spherical morphology. The quantum confinement of charge carriers in the multilayer (ML) films is evident from the shifting of absorption edge to lower wavelengths in the UV–visible spectra. An increase in the energy band gap with decreasing thickness of the CdSe sub-layer has been ascribed to quantum confinement effect and the subsequent crystallite size calculated from Brus approximation method is ~3.5nm. Hence, the results indicate that the quantum confinement effect could be realized in CdSe nanocrystallites by ML stacking structure of CdSe and Se in appropriate thickness ratio.