טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentKloper Viktoria
SubjectColloidal Synthesis of CdTe Semiconductor Nanocrystals
with Bright Luminescence
DepartmentDepartment of Chemistry
Supervisor Professor Efrat Lifshitz


Abstract

In recent years, there has been an increase of interest in the scientific and a technological aspect of semiconductor Quantum Dots (QDs). These materials exhibit unique chemical and physical properties. One of the fabrication techniques of a semiconductor QDs is a chemical colloidal synthesis based on a hot injection method. High-quality colloidal semiconductor nanocrystals are nanometer sized single crystalline fragments of the corresponding bulk crystals, which have well-controlled size and size distribution and are dispersible in desired media. There is growing interest in nanocrystallin inorganic colloidal semiconductor materials, in large part due to their markedly different properties with respect to their bulk counterpart, and the promise of exploiting these properties for manufacturing useful, marketable devices.

In this project highly luminescent CdTe nanocrystals were synthesized by the reaction of Cadmium oxide (CdO) and metallic Tellurium (Te) in a mixture of oleic acid and trioctylphosphine using a non coordinating solvent. Fairly narrow particle size distributions have been obtained by using the “hot injection” technique to separate nucleation and growth stages of the NCs. A series of nearly monodisperse crystalline CdTe nanoparticles with zinc blende lattice and mean particle sizes between 3 nm and 4 nm were isolated without size-selective precipitation techniques. The particles show strong band edge photoluminescence tunable in the visible spectral range from green to red and have been characterized by powder X ray diffraction (XRD), high resolution transmittance electron microscopy (HRTEM), absorption and luminescence spectroscopy. A photoluminescence quantum efficiency of up to 85% is observed at room temperature without any farther surface passivation. More over, the CdTe NCs fabricated by this method were found to possess very high chemical and spectroscopic stability over a period of time of two years.

The CdTe NCs synthesized by a newly developed colloidal method are compared to CdTe NCs synthesized in alternative surfactant mixtures. In addition, CdTe tetra-pod shape NCs are synthesized and their growth conditions are compared to those of the spherical particles.