Synthesize and characterization of ZnSe based type I and type II heterostructure nanostructures

Nanostructured materials are of interest because they can bridge the gap between the bulk and molecular levels and leads to entirely new avenues for applications, especially in electronics, optoelectronics and biology. When a solid exhibits a distinct variation of optical and electronic properties with a variation of particle size <100 nm, it can be called a nanostructure, and is categorized as (1) two dimensional, e.g., thin films or quantum wells, (2) one dimensional, e.g., quantum wires, or(3) zero dimensional e.g., quantum dots. QDs can be sytnhesized in core or core/shell forms due to interest and generally are made from III-V and II-VI family or semiconductors in the periodic table. The small size of quantum dots (QDs) result in an observable quantum confinement effect, defined by an increasing bandgap accompanied by the quantization of the energy levels to discrete values. This effect is accompanied by an exaltation of the coulomb interaction between the charge carriers. Once an electron-hole pair is created by the absorption of a photon, they interact with each other by means of their opposite charges, forming a quasi-particle called "exciton". The total energy of an exciton indicates the color (wavelength) of the light emitted by the quantum systems. If these excitons are confined in the core, they are called Type I and if they seperetly move around core and shell they are called Type II semiconductors. The intermediate case, in which one charge carrier is localized to the core and the other is delocalized over the whole structure, is known as type-I1/2 or quasi type-II. ZnSe based core/shell QDs exhibit novel properties, making them attractive from both experimental and practical point of view. Semiconductor QDs, typically prepared as core/shell NCs, are a class of strained materials with novel properties. In core/shell NCs, lattice mismatch induced stress between core and shell affects the structural, electronic and optical properties such as core diameter, band offsets and exciton energy. In this thesis, the synthesis of ZnSe core and ZnSe/Cd(Zn)S core/shellZnSe/CdxZn1-xS core/ternary shell and ZnSe/Cd(Zn)S/Zn(Cd)S core/multishell NCs was aimed and the NCs characterized by UV-Vis, PL, HRTEM and XRD along with obtaining strain amount in interfacial layer and calculating capped core diameter theoretically after the compressive and tensile shell deposition. The ZnSe core and the other core/shell heterostructurs were synthezed in our nanosemlab with our equipments according to the latest techniques referenced in articles. The XRD analysis used for determining the atomic and molecular structure of the produced QDs and for characterization of optical properties UV-Vis, PL analysis were done. The induced interface strain from lattice mismatch between core and shell was calculated from continuum elastic theory and applied in effective mass approximation method to obtain the corresponding capped core diameter. The calculated results were compared with diameter of bare core TEM images to obtain the amount the core stretched or squeezed after deposition of tensile or compressive shells. The stretched and squeezed amount of the capped core found to be in proportion with lattice mismatch amount in the core/shell structure.