Ph.D Thesis


Ph.D StudentYifat Nakibli
SubjectElectrophoretic Deposition of CdTe Nanotetrapods
DepartmentDepartment of Chemical Engineering
Supervisor Professor Tsur Yoed
Full Thesis textFull thesis text - English Version


Abstract

Over the last decade numerous research groups have devoted their efforts to finding synthesis routs for uniform, high yield reproducible nanoparticle structures with a great variety of morphologies, sizes and composition. This field has reached impressive abilities in fabrication of unique self-assembled shapes. To date, semiconductor nanoparticles of a wide variety of different shapes have been reported. Semiconductor nanoparticles obtain unique size dependable properties, known as the quantum size effect, such as the excitonic absorption band, the radiative lifetime of the electronic excitation, the melting temperature, and the character of the kinetics of chemical processes on their surfaces.

Nanotetrapods are an example for an elongated complex morphology. This unique structure has a shape similar to an sp3 hybridization of the carbon atom, having a core with four arms growing from it. Finding a way to link between the nanotetrapods and the bulk, thereby exploiting its unique properties, was the goal standing in the base of this research. The fact that the symmetry of this shape obligates it to lay with three arms on a surface and the fourth arm facing away from the surface, led us to search for a high yield, simple and cheap deposition method. Out of several techniques investigated the electrophoretic deposition (EPD) of the CdTe nanotetrapods was found to be the most promising one to start with. 

High anodic and low cathodic yields observed during the deposition experiments suggested two main mechanisms: electrophoretic deposition resulting from interaction between the applied field and net charge, and dielectrophoresis resulting from interaction between the dipole moments of the tetrapod and field gradients. Nanorods where examined too, since they provide a simpler model to investigate the dipole effect in the dielectrophoretic process. The nanorods showed similar behavior to the tetrapods, only to a higher extent, as expected.

This work provides a detailed study of the electrophoretic deposition mechanism of CdTe nanotetrapods, including the effect of several parameters such as electrode type, electric field and electrode configuration on the deposition yield. EPD holds the advantage of allowing deposition on a wide variety of electrode architectures with relatively rough metal surfaces. Furthermore, it offers a simple, high yield and controllable way for deposition. In our case, the electrode roughness gave rise to field gradients and enhanced the deposition yield. We propose that this enhanced yield and the cathodic deposition mentioned above are due to dielectrophoresis.