الفهرس 
1.1 Nano and NanotchnologyOnly 14 pages are availabe for public view
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Abstract
We have prepared different sizes of CdSe nanoparticles using two capping groups
(i.e. mercaptoasetic acid MAA, and 3-mercaptopropionic acid 3MPA) with different
amounts of capping molecules on their surface. Through Colloidal method, the
nanoparticles were prepared using different starting precursors and different ratios of
the starting reagents. We have characterized the prepared nanoparticles by Energy
Dispersive X-Ray (EDX), X-ray diffraction (XRD), UV-Vis optical absorption,
infrared spectroscopy and thermogravimetric analysis. The EDX analysis showed that
the extracted nanoparticles have different ratios of the constituent of the capping
molecule relative to CdSe core. X-ray and UV-Vis analysis revealed that there is a
graded diffusion of sulfur on the surface of the nanoparticles. The graded diffusion of
sulfur decreased for the rich selenium prepared samples. Infrared analysis proved the
coordination of thiol and carboxylate groups to the surface of the nanoparticles. On
the other hand, thermogravimetric analysis showed that the size of the nanoparticles
and amount of capping molecules have a high influence on the thermal degradation of
the nanoparticles. The prepared different sizes of CdSe nanoparticles capped by 3-
mercaptopropionic acid (3MPA) utilizing different cadmium sources and different
molar ratios of the starting precursors. The prepared nanoparticles possess different
Se/Cd ratios and different quantity of capping molecules as elucidated by energy
dispersive X-ray spectrums analysis are found to be size dependence. Infrared
analysis manifested that the two-function groups of 3MPA could coordinate to the
surface of the nanoparticles core. Optical analysis revealed that the quantity of
capping molecules coordinated to the surface of the nanoparticles have influence upon
the absorption and emission spectra. The obtained values of Eopt show a decrease
(4.3612 e V to 2.9185 e V) with increasing CdSe nanoparticle sizes ( 3.8 nm to 6.3 nm
for capping MAA) and (3.5931 e V to 2.1146 e V) with increase the size (3 nm to 4.5
nm for capping 3MPA). The dependence of Eopt on Se/Cd ratios (0.241 to 0.745 for
MAA and 0.148 to 0.671 for 3MPA) show the decrease of Eopt by increasing Se/Cd
ratios and this could be due to the decrease of the structural connectivity of the studied
samples. The photoluminescence of the sample with a lot of the capping molecules at
the surface of the nanoparticles displayed a band edge emission with narrow full
width at half maximum, in addition to a small Stokes shift with coupling constant
equal 1.2. Also the thermal analysis revealed that the coordination of capping
molecule to the surface of the nanoparticles influence on their thermal degradation.
We report a preparation of CdSe quantum dots in the presence of capping molecules
under ambient air and argon atmospheres. The growth of the quantum dots with
applying an equimolar ratio of precursor of Cd2+ and Se2− in the presence of a high
percentage of the mercaptoacetic acid as capping molecules is studied. EDX data
showed a graded diffusion of sulfur on the surface of CdSe quantum dots for the
sample prepared under argon atmosphere, while the sample prepared under ambient
air atmosphere the sulfur is not diffused into the CdSe core. In addition, the sample
prepared under air revealed a formation of oxides on the surface of the quantum dots.
On the other hand, we have studied the nature of capping and how the surface of the
quantum dots core is terminated for the prepared samples.