EAS Doctoral Proposal Defense by Misbah ul Ain
SENG 106
Dr. Wei-Shun Chang
wchang2@umassd.edu
Abstract:
Chirality plays a fundamental role in biological and chemical systems, and the ability to detect and characterize chiral signals at the nanoscale is of considerable importance for applications ranging from biosensing to enantioselective catalysis. Plasmonic nanostructures can strongly enhance chiroptical responses, and these responses depend on the geometry, orientation, and coupling between individual particles. Current measurement methods have important limitations in resolving this response. Ensemble circular dichroism (CD) spectroscopy averages the response over many structures, which can hide variations within a sample. Single-particle measurements can resolve differences between individual particles, but they generally treat each particle as a single object and do not provide spatial information within extended structures. This becomes particularly challenging for periodic nanostructure arrays and self-assembled systems, where the structures can appear as continuous features under a microscope and may contain significant local variations in geometry and optical response. This dissertation addresses this limitation by developing a dark-field hyperspectral circular differential scattering (CDS) mapping technique that measures chiroptical response with both spatial and spectral resolution. The first aim develops and validates the instrument itself, using achiral gold nanorods and nanorod dimers spanning a range of inter-particle separations to confirm that spatial CDS mapping recovers results consistent with single-particle measurements. The second aim applies the platform to periodic helicoid nanoparticle arrays to investigate spatial variations in chiroptical response associated with different optical modes, including localized plasmon resonances and collective surface lattice resonances. The third aim extends the method to self-assembled gold nanorod-fibril structures, where variations in nanorod packing and orientation arise from the assembly process. Spatially resolved CDS measurements will be used to relate local structure to the resulting chiroptical response. Together, these studies will establish a method for spatially and spectrally resolved characterization of chiroptical response in complex plasmonic and nanophotonic systems. The resulting measurements will allow the relationship between local structure, plasmonic coupling, and chiroptical response to be examined in systems that are difficult to characterize using conventional ensemble or single-particle measurements.
ADVISOR(s): Dr. Wei-Shun Chang, Department of Chemistry and Biochemistry (wchang2@umassd.edu)
COMMITTEE MEMBERS:
- Dr. Jongping Hsu, Department of Physics
- Dr. Maricris L. Mayes, Department of Chemistry and Biochemistry
- Dr. Shuowei Cai, Department of Chemistry and Biochemistry
NOTE: All EAS Students are ENCOURAGED to attend.