Berlin 2024 – scientific programme

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O: Fachverband Oberflächenphysik

O 4: New Methods: Experiments

O 4.3: Talk

Monday, March 18, 2024, 11:00–11:15, MA 005

Phase-Resolved, Wide-Field Sum-Frequency Generation Microscopy of Molecular Monolayers — •Ben John, Alexander Fellows, Tuhin Khan, Martin Wolf, and Martin Thämer — Fritz Haber Institut der MPG, Berlin, Germany

Inhomogeneous molecular assemblies at interfaces play an outstanding role in nature and industry e.g., in biological membranes, or lab-on-a-chip devices. Gaining experimental access to molecular compositions, arrangements, and packing is therefore of great scientific interest, however this has proven difficult. In particular, the elucidation of molecular conformations and the distribution of molecular orientations typically remains infeasible. Phase-Sensitive Vibrational Sum-Frequency-Generation (vSFG) microscopy can in principle yield such insight into molecular structures owing to its sensitivity to molecular directionality. However, vSFG microscopy still faces substantial technical obstacles, particularly its low signal-to-noise, which highly limits its application to either very thick films or those on metal substrates.

In this contribution, we introduce a novel vSFG microscope design and imaging system that overcomes these limitations. These technical advancements yield highly improved signal-to-noise ratios and a simplified experimental procedure, allowing for the first measurements of molecular monolayers on dielectric substrates. With measurements on phospholipid assemblies, we demonstrate that we can not only detect the molecular species in such monolayers but also characterize molecular compositions and fully determine the spatial distribution of their orientations.

Keywords: SFG Microscopy; Molecular Monolayers; Self Assembly; Nonlinear Imaging