الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
Recently semiconductor nanocrystals or quantum dots (QDs) have attracted a great deal of scientific interest, because of the sensitivity of their optical and non-radiative properties to their size, shape, structure and composition. In this work, a group of samples of heterostructured semiconductor nanocrystals was prepared via a two-step method of organometallic synthesis. First, we prepared nanocrystals of CdTe which served as the core material, and then we subsequently over grew a shell of four different thicknesses of CdSe in a second step.
All prepared samples were characterized using HRTEM to determine their size distribution and crystal structure. The UV-Vis optical absorption and photoluminescence spectroscopy has been measured to the prepared samples. It was found that type-II quantum dots of CdTe/CdSe core/shell could be achieved with shell thickness larger than 2 ML for a core size of 34 Å.
We have employed the Photoascoustic spectroscopy (PAS) to study the optical and thermal properties of those samples. Photoacoustic technique is a photothermal detection technique. It is proved to be a powerful tool to study the optical and thermal properties of such material in a non-destructive manner without particular sample treatment.
A complete theoretical treatment of the PAS technique is presented which includes the solution of the heat diffusion equation in the sample and surrounding media in case of front illumination, then, the temperature distribution within the PA cell and the production of the PA signal are introduced. Finally, the PA signal is separated into two measurable quantities amplitude and phase which are complicated expressions and can be simplified in case of thermally thick samples.
The thermal parameters (effusivity, diffusivity, and conductivity) were determined for CdTe core and CdTe/CdSe core/shell samples using the PA technique and compared to that of the corresponding bulk values. It is found that there is a remarkable decrease in the thermal parameters compared to their bulk counterparts.
Keywords: nanotechnology, photoacoustic spectroscopy, core/shell nanocrystals, type-II quantum dots.