Our latest work on the molecular structure of water at the interface to air is now published in Science Advances. This work by Alex and Louis Lehmann (Netz group, FU Berlin) probes the vibrational bending mode using our SFG/DFG technique. The analysis of the spectra confirms previous indications that the SFG signal of the bending mode is dominated by electric quadrupolar transitions but also reveals the desired purely dipolar spectrum for the first time. Comparison to calculated spectra from simulations shows almost perfect quantitative agreement. Furthermore, a detailed analysis of the depth-dependent nonlinear signals uncovers a pronounced layering in molecular arrangements of water molecules with alternating tilt and in particular molecular twist angles. These findings offer a revised picture of the structural particularity of interfacial water by showing that the common structural analysis in terms of “pointing up or down” [more...]

This work by Alvaro is now published in JACS. In this paper the depth-dependent structural anisotropy of water at charged interfaces is investigated using our depth-resolved vibrational spectroscopy (SFG/DFG). The measured data allows for the first time to accurately isolate the spectroscopic signal from the first water layers in direct contact with the surface charges (bonded interfacial layer, BIL) and compare it to the signals from water in the layers below (diffuse layer, DL). Our analysis shows a remarkable change in structural anisotropy at the transition from DL to BIL by 2 orders of magnitude while the spectral analysis reveals that the anisotropy in both regions is clearly dominated by an anisotropic orientational molecular distribution without any notable changes in the hydrogen-bond structure.
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Álvaro successfully defended his thesis on SFG/DFG spectroscopy at aqueous interfaces and obtained his PhD. Congratulations! Thank you for your successful work over the last years and all the best for your future career!

This paper by Niclas Müller and Alex Fellows is now published in Advanced Materials. The work is the result of joint efforts together with the group of Alex Paarmann, the Theory Department, and external collaborators. In this work, h-BN monolayer flakes are imaged by probing in-plane phonons using our phase resolved SFG microscope. The combination of SFG imaging and sample rotation reveals the location of the crystallographic axes in individual h-BN flakes and allows for the determination of the edge terminations.
Link to publication

Debojyoti joined our group. He is a Postdoc and will be working on our spectroscopy project focussing on the development of doubly resonant SFG/DFG. Welcome!

Ben successfully defends his PhD thesis on the development of the SFG microscope. Congratulations and all the best for your future career!

At the DPG Spring-Meeting in Regensburg Alex and I organized a Focus Session on Chemical Imaging. This was an exciting session with lots of interesting contributions.

After two very successful years as a Postdoc in our group Alex now started his own group (Nonlinear Chemical Imaging Group) at our institute. Congratulations!
The two groups will be working closely together on the nonlinear spectroscopy and microscopy projects.