|M.Sc Student||Yamin Sivan|
|Subject||Synthesis and Characterization of Mechano-Optical Sensors|
Based on Polymeric Photonic Crystals
|Department||Department of Chemistry||Supervisors||Professor Moris Eisen|
|Professor Ester H. Segal|
|Full Thesis text|
Porous Si (PSi) is typically synthesized by anodic electrochemical etching of a single-crystal Si wafer. The resulting nanomaterials are characterized by tunable structural properties combined with unique optical properties. The fabrication of different PSi optical structures such thin films, microcavities, and photonic crystals (e.g., rugate filters) was demonstrated. These nanostructures have emerged as promising platforms for various applications including optical sensing/biosensing schemes, optical filters, and optoelectronic devices.
The main goals of this work are develop methodologies for fabricating polymeric photonic crystals by the replication of PSi templates and study the potential use of the resulting polymeric replicas as mechano-optical sensors. To achieve these goals, PSi rugate filters are first synthesized by electrochemical anodization of single-crystalline Si wafers. The resulting PSi nanostructures are characterized in terms of their optical properties and detailed morphology. In the next step, these PSi rugate filters are used as a template. Two replication methods are studied: (i) solution casting of a model polymer (polystyrene) onto the PSi, and (ii) in-situ free radical polymerization of styrene monomer within the PSi template. The resulting hybrids are optically characterized to determine the pore fill and the quality of replication. The effect of the following parameters on the replication process is examined: polystyrene molecular weight and its solution concentration, separation method of Si-bulk from the PSi-polymer hybrid (electropolishing vs. mechanical separation by liquid nitrogen). In the final step, the polystyrene replica is separated from the Si support and the PSi template is dissolved to obtain the free-standing replica which is characterized optically. The polymeric replicas are studied under tensile at a constant strain rate and their optical response is monitored perpendicular to replica surface during the mechanical test. The correlation between the mechanical input -strain, and the optical output - shift in photonic band gap peak position is established. Polymeric replicas, prepared by in-situ polymerization of styrene, show excellent correlation between the mechanical input and the optical response. Thus, for the first time, polymeric replicas prepared from PSi-based templates are successfully prepared and their feasibility as mechano-optical sensors is demonstrated.