EXAFS Studies on the Size Dependence of Structural and Dynamic Properties of CdS Nanoparticles (original) (raw)
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The Journal of Physical Chemistry C, 2012
We show with the aid of first-principles electronic structure calculations that suitable choice of the capping ligands may be an important control parameter for crystal structure engineering of nanoparticles. Our calculations on CdS nanocrystals reveal that the binding energy of model trioctylphosphine molecules on the (001) facets of zincblende nanocrystals is larger compared to that on wurtzite facets. Similarly, the binding energy of model cis-oleic acid is found to be dominant for the (101̅ 0) facets of wurtzite structure. As a consequence, trioctylphosphine as a capping agent stabilizes the zincblende structure while cis-oleic acid stabilizes the wurtzite phase by influencing the surface energy, which has a sizable contribution to the energetics of a nanocrystal. Our detailed analysis suggests that the binding of molecules on the nanocrystalline facets depends on the surface topology of the facets, the coordination of the surface atoms where the capping molecule is likely to attach, and the conformation of the capping molecule.
CdS nanoparticles: structural and energetical correlations
Materials Chemistry and Physics, 2005
It is well known that the quantum confinement effects are closely related to the existence of different behavior for the same material composition. Due to the reduced size scale of the nanoparticles, the most part of their forming atoms are at the particle surface, which needs to be as stable as possible, to avoid phenomena such as dissolution and photodegradation. This way, methodologies for semiconductor nanoparticles obtention shall take into account the size, shape and energy of the final product. However, the relationship between these parameters is not yet clearly understood for nanometric systems, specially for those ones which are smaller than 20 nm. In this work, we present and discuss experimental and theoretical data obtained for nanoparticles of the semiconductor cadmium sulfide (CdS), in order to contribute for the understanding of the correlation between energetical and structural properties of nanometric systems in the quantum confinement regime.
Structural characterization of chemically synthesized CdSe nanoparticles
Physica E-low-dimensional Systems & Nanostructures, 2009
CdSe nanoparticles were prepared at room-temperature via direct reaction between Cd(NO 3) 2 and Na 2Se in the presence of cetyltrimethyl ammonium bromide (CTAB) used as a capping material. The nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-Visible absorption spectrum, Fourier transform infrared (FT-IR) spectroscopy, Raman scattering, differential scanning calorimetry (DSC), differential thermal gravimetric (DTG) and heat stage X-ray diffraction (HS-XRD). Analysis of the obtained data reveals the precipitation of defective zinc blende CdSe nanoparticles of size about 11 nm in diameter. A blue shift in the optical gap, from 1.71 to 1.82 eV, has been observed for the absorption spectrum of the synthesized CdSe nanoparticles, as an indication of quantum confinement effect. The zinc blende phase is enhanced upon annealing above the melting of Se (220 °C) as is transformed into a better order and stable wurtzite structure upon further heating. More than one melting point has been recorded for the CdSe nanoparticles referring to different ranges of particle sizes (7:25 nm). A value of 810 °C characterizes the melting point of the predominant size (11 nm) of the CdSe nanoparticles.
Applied Physics A, 2019
Cadmium sulfide (CdS) nanoparticles were prepared by hydrothermal method at 150 °C under different reaction times. It was found that hydrothermal method is an effective, quick, and eco-friendly method to synthesis CdS nanoparticles of hexagonal structure at lower temperature. X-ray peak profile analysis by Williamson-Hall analysis and size-strain plot was employed to estimate the crystallite size and lattice strain of the synthesized CdS nanoparticles and to investigate their effects on the peak broadening. The values of strain, stress and energy density were determined for all XRD peaks of wurtzite hexagonal phase of CdS, by applying various forms of Williamson-Hall procedure, such as UDM (uniform deformation model), USDM (uniform stress deformation model) and UDEDM (uniform deformation energy density model). The obtained results indicate that the crystallite size of CdS nanoparticles estimated from Scherrer equation, Williamson-Hall plots and size-strain plot, are nearly similar and in the range of 14-37 nm. CdS nanoparticles were also investigated using high-resolution transmission electron microscopy (HR-TEM), Fourier transform infra-red spectroscopy (FT-IR), and UV-visible and fluorescence spectroscopy. A dependence of the band gap and the nanoparticle size on the reaction time was reported.
Cadmium sulfide nanoparticles were synthesized with different sizes by chemical precipitation method. Transmission electron microscopy (TEM) and X-ray diffraction pattern (XRD) used to study the morphologies, distribution, and crystallinty of the CdS nanoparticles and to calculate the values of their sizes. The results indicated that the CdS were formed with cubic structure and the particle size decreases with increasing the Cd +2 ions. The Cd-S stretching vibration band appeared in the far infrared region at about 250 cm -1 and there is no effect of the particle sizes on the position of this band. Dependence of the blue shift and optical band gap on the quantum size effect was confirmed by UV-Visible spectroscopy. The dielectric properties are studied in the frequency range (2.5 KHz-5MHz) at different temperatures.
The Journal of Physical Chemistry C, 2007
We report orientation-specific, surface-sensitive structural characterization of colloidal CdSe nanorods with extended X-ray absorption fine structure spectroscopy and ab initio density functional theory calculations. Our measurements of crystallographically aligned CdSe nanorods show that they have reconstructed Cd-rich surfaces. They exhibit orientation-dependent changes in interatomic distances which are qualitatively reproduced by our calculations. These calculations reveal that the measured interatomic distance anisotropy originates from the nanorod surface.
Measurement of shell thickness in CdSe/CdS nanoparticles with X-ray absorption spectroscopy
Journal of Electron Spectroscopy and Related Phenomena, 2008
Using X-ray absorption spectroscopy at the Cd M-edge, we have investigated chemically prepared colloidal CdSe/CdS core/shell nanoparticles. The Cd 3d features originating from CdSe and CdS could be separated. From the intensity ratio of the CdSe and CdS contributions, we determined the core and shell thickness for two different sizes.
TURKISH JOURNAL OF CHEMISTRY, 2021
Cadmium dithiocarbamate and cadmium ethyl xanthate complexes were synthesized and characterized by microanalysis, Fourier transform infrared (FT-IR) spectroscopy and thermogravimetric analyses. The complexes were employed as molecular precursors for the fabrication of CdS nanoparticles in hexadecylamine (HDA) and oleylamine (OLA) at a temperature of 250 °C. Spherical and oval shaped particles with sizes ranging from 9.93 ± 1.89 to 16.74 ± 2.78 nm were obtained in OLA while spherical, oval and rod shaped particles with sizes ranging from 9.40 ± 1.65 to 29.90 ± 5.32 nm were obtained in HDA. Optical properties of the nanoparticles showed blue shifts as compared to the bulk CdS, with the OLA capped nanoparticles slightly more blue shifted than the corresponding HDA capped nanoparticles. Results of crystallinity patterns revealed hexagonal phase of CdS.
Structural and optical analysis of CdS nanocrystals prepared by low temperature thermolysis
Digest Journal of Nanomaterials and Biostructures
CdS nanoparticles were synthesized via low temperature thermolysis method using cadmium chloride and thiourea as cadmium and sulphur sources respectively. XRD analysis of nanocrystals prepared with three different synthesis times showed the crystalline nature, structure as well as particle size of the prepared CdS particles. From the peaks position of XRD spectra, the dependence of phase of CdS nanoparticles with the synthesis time has also been found. The absorption spectra enabled to visualize the blue shift in absorption onset. The bandgap of the prepared nanoparticles are found to be in the range 3.6-3.86eV. SEM, TEM and SAED images of CdS nanoparticles showed their morphology, particle size and crystallinity respectively. From the structural and SEM analysis it has been confirmed that phase change can be achieved by annealing the samples.