CdSe Research Articles

Influence of Capping Ligands, Solvent, and Thermal Effects on CdSe Quantum Dot Optical Properties by DFT Calculations.

Cadmium selenide nanomaterials are very important materials in photonics, catalysis, and biomedical applications due to their optical properties that can be tuned through size, shape, and surface passivation. In this report, static and ab initio molecular dynamics density functional theory (DFT) simulations are used to characterize the effect of ligand adsorption on the electronic properties of the (110) surface of zinc blende and wurtzite CdSe and a (CdSe)33 nanoparticle. Adsorption energies depend on ligand surface coverage and result from a balance between chemical affinity and ligand-surface and ligand-ligand dispersive interactions. In addition, while little structural reorganization occurs upon slab formation, Cd···Cd distances become shorter and the Se-Cd-Se angles become smaller in the bare nanoparticle model. This originates mid-gap states that strongly influence the absorption optical spectra of nonpassivated (CdSe)33. Ligand passivation on both zinc blende and wurtzite surfaces does not induce a surface reorganization, and thus, the band gap remains nonaffected with respect to bare surfaces. In contrast, structural reconstruction is more apparent for the nanoparticle, which significantly increases its highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap upon passivation. Solvent effects decrease the band gap difference between the passivated and nonpassivated nanoparticles, the maximum of the absorption spectra being blue-shifted around 20 nm by the effect of the ligands. Overall, calculations show that flexible surface cadmium sites are responsible for the appearance of mid-gap states that are partially localized on the most reconstructed regions of the nanoparticle that can be controlled through appropriate ligand adsorption.

Nickel selenide nano-cubes anchored on cadmium selenide nanoparticles: First-ever designed as electrode material for advanced hybrid energy storage applications

The rational design and impressive performance of the desired electrode material are one of the top priorities in the field of the supercapacitor era. Chalcogenides are functional materials that attracted tremendous research due to their great electrochemical activity, non-toxicity, high theoretical capacities, low cost, high environmental safety, and tunable electronic configurations. Combining two different materials (compositing strategy) is a popular route to develop novel, robust, and highly efficient electrodes for high capacity, energy, and power delivery with good durability. Herein, for the first time, a high-performance hybrid supercapacitor is developed based on NiSe2, and CdSe and their composites, e.g., NiSe2/CdSe (denoted as CN-1, CN-2, and CN-3) via hydrothermal via ex-situ wet-chemical method. By changing the stoichiometry of the host compounds (e.g., NiSe2, CdSe), various nanocomposites take birth, such as; CN-1, CN-2, and CN-3. Notably, their capacitive performance was measured and compared in an aqueous alkaline media in KOH with three milli molar concentration. Subsequently, the CN-2 electrode displayed a good electrochemical energy storage performance of 358C/g capacity and lower overall resistance, which promotes the fast diffusion of electrolyte kinetics; hence, optimized electrochemical properties prove its importance for the fabrication of full cell development. More strikingly, the CN-2//AC hybrid supercapacitor revealed a high capacitance of 90 F/g, 40.5 Wh/kg energy density, and a maximum power of 7161.2 W/kg coupled with a high stability of 87.6 % (20 A/g) when repeatedly tested for long-term 15,000 cycling. The proposed method portrays a cost-effective and appealing runner for high-energy hybrid supercapacitors in future energy storage applications.

Architected Metal Selenides via Sequential Cation and Anion Exchange on Self-Organizing Nanocomposites.

Shape-preserving conversion reactions have the potential to unlock new routes for self-organization of complex three-dimensional (3D) nanomaterials with advanced functionalities. Specifically, developing such conversion routes toward shape-controlled metal selenides is of interest due to their photocatalytic properties and because these metal selenides can undergo further conversion reactions toward a wide range of other functional chemical compositions. Here, we present a strategy toward metal selenides with controllable 3D architectures using a two-step self-organization/conversion approach. First, we steer the coprecipitation of barium carbonate nanocrystals and silica into nanocomposites with controllable 3D shapes. Second, using a sequential exchange of cations and anions, we completely convert the chemical composition of the nanocrystals into cadmium selenide (CdSe) while preserving the initial shape of the nanocomposites. These architected CdSe structures can undergo further conversion reactions toward other metal selenides, which we demonstrate by developing a shape-preserving cation exchange toward silver selenide. Moreover, our conversion strategy can readily be extended to convert calcium carbonate biominerals into metal selenide semiconductors. Hence, the here-presented self-assembly/conversion strategy opens exciting possibilities toward customizable metal selenides with complex user-defined 3D shapes.

Effect of surface defects on photoluminescence properties of CdSe quantum dots in glasses

Cadmium selenide quantum dots (CdSe QDs) have shown great potential for applications in the visible range over the last few decades. Embedding CdSe QDs into inorganic glass matrix improves their stability, but complicates their surface conditions and deteriorates their optical properties. In this work, CdSe QDs with tunable and narrow band intrinsic photoluminescence (PL) are precipitated in silicate glasses by adjusting the heat-treatment temperatures. With the increase in heat-treatment temperature, PL peaks shift to long wavelength side with simultaneous reduction in full width at half maximum, while both PL quantum yields and lifetimes decrease. Ultrafast carrier dynamics analysis reveals that the above changes on PL properties are induced by the transformation of Cd2+-related to Se2--related surface defects during heat-treatment. Electron trapping by shallow Cd2+-related defects is responsible for the broad band defect emission, and hole trapping by Se2--related defects results in quenching of defect emission. These results uncover the relationship between surface defects of CdSe QDs and their PL properties, facilitating their applications towards light-emitting diodes (LEDs), backlight displays, and lasers.

Electrodeposition of Cadmium Selenide Based Photoanodes from TOMAC/Formamide Ionic Liquid System for Photoelectrochemical Water Splitting

The electrodeposition from room temperature ionic liquids (RTILs) has recently come up as a low-cost technique for the growth of II–VI semiconductor compounds and thin films, some promising alternatives to classical organic or inorganic solvents. As a relatively new field of study, only a few reports exist describing the growth mechanism of electrodeposition from RTILs, especially for CdSe films. In this paper, a new electrochemical method has been developed for the deposition of Cadmium Selenide thin layers onto indium doped tin oxide coated conducting glass (ITO) using an RTIL and an Organic solvent system (Tricaprylmethylammonium chloride/Formamide). Structural properties of prepared films have been investigated by X-ray diffraction (XRD) and micro-Raman analysis which reveal a pure cubic phase with the zinc-blende-type structure and typical peaks of nanostructured CdSe, respectively. Atomic force microscopy (AFM) analysis showed homogenous and smooth surface of the deposited films. UV-vis measurements demonstrated the presence of direct transition with a band gap energy around 1.68[Formula: see text]eV. The flat-band potential and carrier density values of CdSe thin film are [Formula: see text]0.667[Formula: see text]V and [Formula: see text][Formula: see text]cm[Formula: see text], respectively, as deduced from Mott–Schottky studies. The photoelectrochemical (PEC) behavior of the CdSe thin film exhibited an enhanced photocurrent density at about 0.35[Formula: see text]mA/cm2 vs. Ag/AgCl.

Photovoltaics literature survey (no. 182)

Photovoltaics literature survey (no. 182)

Heat transfer efficiency in planar and axisymmetric ternary hybrid nanofluid flows

Ternary hybrid nanofluids have been the focus of many recent studies due to their potential for improving the thermal and hydrodynamic characteristics of the fluid. This study investigates the thermal and hydrodynamic characteristics of ternary hybrid nanofluids consisting of silica, cadmium selenide quantum dots, and copper, immersed in ethanol for Hiemenz and Homann flows induced normal to the oncoming stagnation point flow. The flow is induced over an infinite plate in a porous medium, and is moving (at a constant velocity) towards/receding from normal stagnation point flow. The flow is driven due to porosity, magnetic effects, and Reynolds number, (where Reynolds number is proportional to the constant velocity of the moving plate). Moreover, Hiemenz's planar and Homann's axisymmetric flows normal to the stagnation point are considered. Heat transfer analysis is carried out by using Cattaneo-Christov theory with the effects of Ohmic heating, Roseland radiation (non-linear), and heat source/sink. The solutions are obtained through bvp4c routine in MATLAB. The numerical and asymptotic solutions are computed for the wall shear stress parameter. It is observed that the energy transport is augmented due to increment in the nanoparticle's concentration of Cadmium selenide quantum dots, however, velocity declines due to changes in drag force. An increase in Reynolds number generates more intense fluctuations in velocity near the wall, resulting in higher momentum transfer and amplified wall shear stress for Hiemenz and Homann flows.

SOĞURMA SPEKTROSKOPİSİ ve GEÇİRİMLİ ELEKTRON MİKROSKOPİ ile KADMİYUM SELENÜR KUANTUM NOKTALARININ OPTİK TESPİTİ

Quantum dots are tiny semiconductor nanocrystals. Their dimensions are between about 2 and 10 nm. They have attracted much attention due to their unique electronic and optical properties. These particles can be synthesized in a variety of ways. Synthesis methods of quantum dots can be classified into top-down and bottom-up. Top-down approach is a fragmentation process of bulk material. In contrast to top-down, quantum dots are constructed from atoms and molecules of the material at bottom-up procedure. Ball milling, optical lithography, laser ablation and arc-discharge are some top-down methods. However, chemical reduction, thermal decomposition, sol-gel and ultrasonic spray pyrolysis are bottom-up methods. In this study, chemical hot-injection synthesis method of cadmium selenide quantum dots which is a kind of bottom-up procedure will be explained. Cadmium selenide quantum dots have been grown in hot solvent at 259oC. Concentration of cadmium selenide quantum dots dispersed in toluene has been adjusted by observing their first exciton peak. First excitonic absorbance peak of cadmium selenide quantum dots has been measured at around 2.18 eV. Transmission electron microscope photo of these growth quantum dots has been shown. The average diameter of cadmium selenide quantum dots has been found to be approximately 3.48 nm. Lattice fringe spacing of cadmium selenide quantum dots has been measured as ~0.35 nm.

Size dependency of CdSe for light harvesting in quantum dots solar cell using COMSOL Multiphysics

A solar cell (SC) can increase its performance by applying a semiconductor nanoparticle into it, and the name became quantum dots solar cell (QDSC). A nanotube of titanium dioxide (TiO2) with various sizes of cadmium selenide (CdSe) quantum dots (QDs) was designed and simulated using COMSOL Multiphysics. This study is to identify the size of CdSe QDs that can harvest more light energy at 550 nm of wavelength through electric field distribution simulation. Following the result for CdSe QD that harvested highest at 550 nm of diameter size 3.0 nm, which matched the result of previous research, further study was done to look at the absorption percentage of this size. With the different structures of amorphous silicon SC, the maximum absorption value was 50.664% at 657 nm of wavelength and will increase to 52.819 % at 617 nm of wavelength when the 3 nm diameter size of CdSe is inserted. The presence of a certain size CdSe within an SC structure does improved the performance of SC.

OPTICAL CHARACTERIZATION of STEARIC ACID POWDER and ITS USE for THE SYNTHESIS of NANOPARTICLES

Fatty acids are found in the structure of triglycerides and phospholipids which have vital importance for the life. Stearic acid is an important member of the fatty acids. It is used in the manufacturing of various products such as soaps, detergents, and rubbers. It is valuable to provide a thermal and optical characterization database of stearic acid. In this study, a comprehensive database has been prepared by studying thermogravimetric analysis, X-ray powder diffraction, dispersive Raman and Fourier transform infrared spectroscopies of stearic acid. Its thermal decomposition temperature, X-ray diffraction angles and infrared vibrational modes have been determined. Stearic acid has been used at the synthesis of cadmium selenide quantum dots, bismuth nanoparticles and mixed copper/zinc nanocrystals. Hot-injection and one-pot synthesis methods have been utilized to synthesize these nanostructures. Their sizes, distributions, shapes, elemental compositions, and crystalline structures have been investigated by transmission electron microscopy and energy dispersive X-ray analysis. Mixed copper/zinc nanocrystals have also been examined by X-ray diffraction spectroscopy.

Epitaxial CdSe/PbSe Heterojunction Growth and MWIR Photovoltaic Detector

A novel Epitaxial Cadmium Selenide (CdSe) on Lead Selenide (PbSe) type-II heterojunction photovoltaic detector has been demonstrated by Molecular Beam Epitaxy (MBE) growth of n-type CdSe on p-type PbSe single crystalline film. The use of Reflection High-Energy Electron Diffraction (RHEED) during the nucleation and growth of CdSe indicates high-quality single-phase cubic CdSe. This is a first-time demonstration of single crystalline and single phase CdSe growth on single crystalline PbSe, to the best of our knowledge. The current-voltage characteristic indicates a p-n junction diode with a rectifying factor over 50 at room temperature. The detector structure is characterized by radiometric measurement. A 30 μm × 30 μm pixel achieved a peak responsivity of 0.06 A/W and a specific detectivity (D*) of 6.5 × 108 Jones under a zero bias photovoltaic operation. With decreasing temperature, the optical signal increased by almost an order of magnitude as it approached 230 K (with thermoelectric cooling) while maintaining a similar level of noise, achieving a responsivity of 0.441 A/W and a D* of 4.4 × 109 Jones at 230 K.

Oxygen Management to Avoid Photo-Inactive Cd(S,Se) for Efficient Cd(Se,Te) Solar Cells

Our previous work has demonstrated that the formation of a penternary cadmium chalcogenide Cd(O,S,Se,Te) region can significantly reduce the front interface recombination in Cd(Se,Te)-based thin-film solar cells. In this work, we have shown that oxygen management during the device fabrication is crucial to form this region. While both the CdS and CdSe layer depositions and the postdeposition CdCl2 treatment should be conducted in the presence of oxygen, the CdTe deposition should be conducted in an oxygen-free atmosphere. Improper oxygen management leads to low device performance due to the formation of a photoinactive Cd(S,Se) region and reduced absorber quality. Additionally, we investigated the carrier transport and collection properties in devices with photoinactive Cd(S,Se) and photoactive Cd(O,S,Se,Te) at the front interface to gain comprehensive understanding of the mechanisms that resulted in improved efficiencies approaching 20%.

Near-Infrared Emission from CdSe-Based Nanoplatelets Induced by Ytterbium Doping

Cadmium selenide (CdSe) nanoplatelets (NPLs) have attracted significant attention thanks to their favorable optical properties, including narrow emission linewidths, reduced Auger recombination, and a high absorption cross section. However, the photoluminescence (PL) quantum yield (QY) in the near-infrared (NIR) region is poor as compared to that in the visible region. Doping of metal ions is proven to be a successful strategy for inducing Stokes-shifted NIR emission. Here, we report the first account of the successful doping of ytterbium (Yb) into CdSe NPLs by a modified seeded-growth method. The successful incorporation of divalent Yb ions into CdSe NPLs resulted in an additional NIR emission apart from their excitonic emission. By optimizing the dopant concentration, we observed an impressive PL QY of ∼55% for these Yb-doped NPLs. Detailed elemental and optical characterizations were conducted to understand the emerging photophysical properties of these Yb-doped NPLs. These NIR-emitting lanthanide-doped CdSe NPLs might have applications in the next-generation bioimaging, night vision, and photodetection.

Effect of Variation of pH and Shell Thickness upon the Optical and Structural Characteristics of PVA Capped CdSe and CdSe/ZnO Nanoparticles

Poly-Vinyl Alcohol (PVA) capped Cadmium Selenide (CdSe) and Cadmium Selenide/Zinc Oxide (CdSe/ZnO) core/shell semiconductor/semiconductor nanoparticles have been synthesized using wet chemical precipitation method. The pH of each solution was varied ranging from 9.5 to 11.5. Particle size of the CdSe nanoparticles was estimated using Brus Equation. The results of UV-Visible spectroscopy of core CdSe samples show blue shifting of absorption edges in a range of 342-377 nm compared to that of the bulk CdSe 712 nm and red shifting of the absorption edges of the core /shell samples in a range (346-357) nm in comparison to the core sample, over which the shell is deposited. For CdSe core nanoparticles, the band gap values were found to be in the range of 3.70–3.90 eV, which is larger than the bulk CdSe of 1.74 eV. Also the band gap values for the core/shell nanoparticles were in the range of 3.75-3.80 eV. The positions of excitonic emission peak obtained from photoluminescence spectra for the core is around 323 nm and for the core/shell samples is around 324nm. The average crystallite size of the core/shell CdSe/ZnO sample was obtained from XRD spectra in the range of 62-69 nm and for the core CdSe sample it was of 11-31 nm. The core and the core/shell samples were more or less spherical as obtained from the SEM analysis. Some of the core nanoparticles were 3-8 nm in size whereas the core/shell nanoparticles were 20-50 nm in size as obtained from HRTEM analysis.

Kappa-carrageenan for benign preparation of CdSeNPs enhancing the electrochemical measurement of AC symmetric supercapacitor device based on neutral aqueous electrolyte

This study presents the development of an electrochemical supercapacitor with a cadmium selenide nanoparticles (CdSeNPs) electrode utilizing a straightforward and economical method based on kappa-carrageenan (κ-CGN). The structural, morphological, and optical characteristics of CdSeNPs were assessed. Activated carbon (AC) and green-prepared CdSeNPs were easily mixed to achieve excellent electrochemical properties. The nanoelectrode (AC@CdSe) was tested in an aqueous electrolyte of sodium sulfate (Na2SO4) with a concentration of 1 Molar. Specific capacitance (Csp) for the AC electrode and the AC@CdSe electrode at 1 A g−1 was calculated to be 103 and 480 F g−1, respectively. Besides, the symmetric supercapacitor AC@CdSe/AC@CdSe device has a high specific energy of 52 Wh kg−1 and a maximum specific power of 2880 W kg−1, with a specific capacitance of 115.5 F g−1. With a coulombic efficiency of between 82 % and 100 %, the device continues to maintain excellent capacitance after 10.000 cycles.

Hybrid Nanomat: Copolymer Template CdSe Quantum Dots In Situ Stabilized and Immobilized within Nanofiber Matrix

Fabrication and characterization of hybrid nanomats containing quantum dots can play a prominent role in the development of advanced biosensors and bio-based semiconductors. Owing to their size-dependent properties and controlled nanostructures, quantum dots (QDs) exhibit distinct optical and electronic characteristics. However, QDs include heavy metals and often require stabilizing agents which are toxic for biological applications. Here, to mitigate the use of toxic ligands, cadmium selenide quantum dots (CdSe QDs) were synthesized in situ with polyvinylpyrrolidone (PVP) at room temperature. The addition of PVP polymer provided size regulation, stability, and control over size distribution of CdSe QDs. The characterization of the optical properties of the CdSe QDs was performed using fluorescence and ultraviolet-visible (UV-Vis) spectroscopy. CdSe QDs exhibited a typical absorbance peak at 280 nm and a photoluminescence emission peak at 580 nm. Transmission electron microscopy (TEM) micrographs demonstrated that CdSe QDs having an average size of 6 ± 4 nm were obtained via wet chemistry method. CdSe QDs were immobilized in a blend of PVP and poly(L-lactide-co-ε-caprolactone) (PL-b-CL) copolymer that was electrospun to produce nanofibers. Scanning electron microscopy (SEM), thermal analyses and attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR) were used to characterize properties of fabricated nanofibers. Both pristine and hybrid nanofibers possessed cylindrical geometry and rough surface features, facilitating increased surface area. Infrared absorption spectra showed a slight shift in absorbance peaks due to interaction of PVP-coated CdSe QDs and nanofiber matrix. The presence of CdSe QDs influenced the fiber diameter and their thermal stability. Further, in vitro biological analyses of hybrid nanofibers showed promising antibacterial effect and decline in cancer cell viability. This study offers a simple approach to obtain hybrid nanomats immobilized with size-controlled PVP-coated CdSe QDs, which have potential applications as biosensors and antibacterial and anticancer cell agents.

Red CdSe/ZnS QDs' Intracellular Trafficking and Its Impact on Yeast Polarization and Actin Filament.

Quantum dots are nanoparticles (2-10 nm) that emit strong and tunable fluorescence. Quantum dots have been heavily used in high-demand commercialized products, research, and for medical purposes. Emerging concerns have demonstrated the negative impact of quantum dots on living cells; however, the intracellular trafficking of QDs in yeast cells and the effect of this interaction remains unclear. The primary goal of our research is to investigate the trafficking path of red cadmium selenide zinc sulfide quantum dots (CdSe/ZnS QDs) in Saccharomyces cerevisiae and the impact QDs have on yeast cellular dynamics. Using cells with GFP-tagged reference organelle markers and confocal microscopy, we were able to track the internalization of QDs. We found that QDs initially aggregate at the exterior of yeast cells, enter the cell using clathrin-receptor-mediated endocytosis, and distribute at the late Golgi/trans-Golgi network. We also found that the treatment of red CdSe/ZnS QDs resulted in growth rate reduction and loss of polarized growth in yeast cells. Our RNA sequence analysis revealed many altered genes. Particularly, we found an upregulation of DID2, which has previously been associated with cell cycle arrest when overexpressed, and a downregulation of APS2, a gene that codes for a subunit of AP2 protein important for the recruitment of proteins to clathrin-mediated endocytosis vesicle. Furthermore, CdSe/ZnS QDs treatment resulted in a slightly delayed endocytosis and altered the actin dynamics in yeast cells. We found that QDs caused an increased level of F-actin and a significant reduction in profilin protein expression. In addition, there was a significant elevation in the amount of coronin protein expressed, while the level of cofilin was unchanged. Altogether, this suggests that QDs favor the assembly of actin filaments. Overall, this study provides a novel toxicity mechanism of red CdSe/ZnS QDs on yeast actin dynamics and cellular processes, including endocytosis.

Investigations of dielectric properties of cadmium selenide thin films

Thin Films of different thickness of Cadmium Selenide (CdSe) were prepared by using thermal evaporation technique on a glass substrate, and investigation of dielectric properties as a function of frequency in the range up to 1 MHZ using Auto Lab Potentiostat/Galvanostat meter was conducted. Preliminary data for complex parameters i.e. complex dielectric constant (ε*), complex impedance (Z*), electric modulus (M*), tangent loss (δ) and conductivity (σ) has been calculated. All these properties are used to explore various processes that contribute to the dielectric spectroscopy investigation.

Binding Affinity of Monoalkyl Phosphinic Acid Ligands toward Nanocrystal Surfaces

We recently introduced monoalkyl phosphinic acids as a ligand class for nanocrystal (NC) synthesis. Their metal salts have interesting reactivity differences compared to metal carboxylates and phosphonates and provide a cleaner work-up compared to phosphonates. However, little is known about the surface chemistry of NCs with monoalkyl phosphinate ligands. Here, we probe the relative binding affinity of monoalkyl phosphinate ligands with respect to other X-type ligands. We perform competitive ligand exchange reactions with carboxylate and phosphonate ligands at the surface of hafnia, cadmium selenide, and zinc sulfide NCs. We monitor the ligand shell composition by solution 1H and 31P NMR spectroscopy. Using a monoalkyl phosphinic acid with an ether functionality, we gain an additional NMR signature, apart from the typical alkene resonance in oleic acid and oleylphosphonic acid. We find that carboxylate ligands are easily exchanged upon exposure to monoalkyl phosphinic acids, whereas an equilibrium is reached between monoalkyl phosphinates and phosphonates, slightly in the favor of phosphonate (K = 2). Phosphinic acids have thus an intermediate binding affinity between carboxylic acids and phosphonic acids for all the NCs studied. These results enable the sophisticated use of monoalkyl phosphinic acids for NC synthesis and for post-synthetic surface engineering.

Quantum vacuum fluctuations in inorganic compound CdSe

In the present work, we study the quantum vacuum fluctuations at finite temperature in the propagation of light in nonlinear optical media. We present nonlinear materials, that have the second-order electrical susceptibility tensor, and the fluctuating effective refractive index caused by fluctuating vacuum electric fields. Likewise, we study the fluctuations of the vacuum, which led to the contributions of thermal and mixed fluctuations being associated with a faithful test function to perform the calculations, in contrast to the Lorentzian distribution. We show the contribution of thermal and mixed fluctuations to time-of-flight fluctuations compared to the contributions of vacuum fluctuations. The result reveals a numerical estimate performed on cadmium selenide (CdSe) suggesting that the effects of fluctuations can cause uncertainty in time of flight due to quantum vacuum fluctuations in terms of thermal and mixed fluctuations.