Nanorod alignment in a liquid for polarized light emission
Begeleider(s): dr. ir. Mohammad Mohammadimasoudi


Almost all light sources (LEDs, phosphorescent lamps, sun) emit unpolarized light, while for some applications (displays, microscopy, car headlights) polarized light emitters would have a lot of benefits. The origin of polarized emission lies in the electrical dipole transitions that take place on the nano-scale. It is known that some long-shaped organic dye molecules and semiconductor nanorods emit photons that have an electric field component that is mainly along the long axis. If it is possible to align all dye molecules or nanorods on a substrate along the same axis, then the emission from that substrate will be polarized. Nanorods with a small (5 nm) CdSe dot in the core and a 50 nm long CdS shell are produced in the Physical Chemistry research group in the faculty of Sciences. These nanorods can be dispersed in a liquid and have a permanent electrical dipole moment. When an electric field is present in the liquid, the dipole moment (and the nanorod with it) tries to align with the field. This phenomenon can be used to align the nanords and obtain a polarized emitter.


The goal of this thesis is to define a procedure to align and fix the nanorods in a well-defined direction by applying a voltage between electrodes. The amplitude of the voltage should be sufficiently high to overcome the rotation due to the thermal (Brownian) motion. Once the nanorods are aligned, there are different possibilities to fix the orientiation: by evaporation of the liquid, by (UV induced) polymerization of the liquid or by reducing the temperature. The electrodes may be on one substrate, on two different substrates or on a probe. Testing the alignment can be done by observing the polarization of the photoluminescence. The plan is to try out different experimental setups and to try to obtain homogeneous regions with aligned nanorods that emit polarized light.