الفهرس | Only 14 pages are availabe for public view |
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. |