Speakers
Description
Inhomogeneous molecular assemblies at interfaces play a critical role in both natural and industrial systems, with examples ranging from lipid rafts in biological membranes to lab-on-a-chip technologies. Investigating these assemblies at the molecular level, particularly their composition, arrangement, and packing structure, is a subject of great scientific interest. However, achieving such detailed characterization requires a technique that combines molecular recognition, orientational sensitivity, and high spatial resolution, ideally capable of probing monolayer-thick structures. Meeting all these requirements has remained a considerable challenge.
A technique that does satisfy the above requirements is vibrational sum-frequency generation (vSFG) microscopy as it gains access to molecular compositions through their characteristic vibrational resonances, is orientationally sensitive owing to its second-order selection rules, and can achieve sub-micron imaging resolution owing to its frequency upconversion. However, achieving such structural characterization with vSFG microscopy has so far been infeasible owing to the technical challenges of spatially mapping such weak signals, limiting its application to much thicker films or those on metal substrates where any in-plane signals are lost. In this contribution, we introduce a novel vSFG microscope design and imaging system which overcomes these limitations, yielding highly improved signal-to-noise ratios. We then demonstrate its ability to characterize heterogeneous structures by spatially mapping the molecular orientations and analyzing the packing structures within phase-separated monolayers of mixed chiral lipids.
