Thema der Dissertation:
Development of a Phase-Sensitive Sum Frequency Generation Microscope for the Investigation of Molecular Structures at Interfaces
Development of a Phase-Sensitive Sum Frequency Generation Microscope for the Investigation of Molecular Structures at Interfaces
Abstract: Molecular assemblies at interfaces are vital in natural and industrial systems, including biological membranes and functionalized surfaces. Understanding their molecular structure, organization, and orientation is essential for progress in biophysics, materials science, and nanophotonics. However, characterizing molecular conformations and order at interfaces remains challenging. Of the available techniques, vibrational sum frequency generation (vSFG) microscopy stands out for its intrinsic sensitivity to non-centrosymmetric environments and its ability to detect molecular vibrations with sub-micron lateral resolution. Crucially, molecular orientation is encoded in the SFG signal, enabling fast, label-free, high-contrast imaging of chemical composition and orientational order. Despite these advantages, the inherently weak second-order signals in vSFG microscopy have limited its application mainly to systems exhibiting comparatively strong responses, such as thick films or metallic interfaces.
This thesis introduces a novel phase-resolved vSFG microscope designed to overcome limitations in sensitivity and spatial resolution. It uses a collinear beam geometry with a custom-drilled reflective objective for distortion-free sub-micron imaging. A paired-pixel balanced detection enhances signal-to-noise ratio by a factor of ~10, while interferometric time-domain scanning acquires pixel-wise phase-resolved vibrational spectra. The capabilities of the microscope are demonstrated by investigating chiral phospholipid monolayers, revealing micron-scale circular domains. Furthermore, azimuthally scanned hyperspectral imaging reveals highly curved in-plane molecular packing as part of a hierarchical spiral motif at the mesoscopic scale. Enantiomeric substitution experiments reveal deviations from mirror symmetry, providing insights into enantioselective interactions and homochirality. These results demonstrate the microscope’s potential for advancing molecular interfacial science through high-resolution, chemically specific imaging.
This thesis introduces a novel phase-resolved vSFG microscope designed to overcome limitations in sensitivity and spatial resolution. It uses a collinear beam geometry with a custom-drilled reflective objective for distortion-free sub-micron imaging. A paired-pixel balanced detection enhances signal-to-noise ratio by a factor of ~10, while interferometric time-domain scanning acquires pixel-wise phase-resolved vibrational spectra. The capabilities of the microscope are demonstrated by investigating chiral phospholipid monolayers, revealing micron-scale circular domains. Furthermore, azimuthally scanned hyperspectral imaging reveals highly curved in-plane molecular packing as part of a hierarchical spiral motif at the mesoscopic scale. Enantiomeric substitution experiments reveal deviations from mirror symmetry, providing insights into enantioselective interactions and homochirality. These results demonstrate the microscope’s potential for advancing molecular interfacial science through high-resolution, chemically specific imaging.
Zeit & Ort
04.06.2025 | 16:00
Hörsaal B (0.1.01)
(Fachbereich Physik, Arnimallee 14, 14195 Berlin)