Professor Ricardo Garcia, Instituto de Ciencia de Materiales de Madrid, CSIC, Madrid, Spain

Interfacial liquid water on graphite and 2D materials surfaces
Solid-water interfaces have a prominent role in a variety of fields such as surface science, geochemistry,  electrochemistry, energy storage or molecular and cell biology. Liquids near a solid surface form an interfacial layer where the molecular structure is different from that of the bulk. Yet the molecular-scale understanding of the interactions of liquid water with solid interfaces is unsatisfactory for the lack of high-spatial resolution methods. Here I will present an AFM-based method that provides atomic-scale resolution images of solid-liquid interfaces.

The presentation is divided in three sections. The first section is an introduction to the relevance of solid-liquid interfaces. The second section, presents the features and capabilities of  3D-AFM [1-3] to image with atomic resolution the three-dimensional interfacial structure of surfaces immersed in aqueous solutions. The third section reports the structure of interfacial water layers on different 2D materials from graphene to a few layer MoS₂ ; from hexagonal boron nitride to a few layer WSe₂. Those interfaces are characterized by the existence of a 2 nm thick region above the solid surface where the liquid density oscillates [4-6]. The distances between adjacent layers for graphene, few-layer MoS₂, h-BN and pentacene are ~0.50 nm. This value is larger than the one predicted and measured for water density oscillations (~0.30 nm). The experiments demonstrate that on extended hydrophobic surfaces water molecules are expelled from the vicinity of the surface and replaced by several molecular-size hydrophobic layers.

References
[1] D. Martin-Jimenez, E. Chacon, P. Tarazona, R. Garcia, Nat. Commun. 7, 12164 (2016).
[2] T. Fukuma and R. Garcia, ACS Nano 12 11785 (2018).
[3] S. Benaglia, et al. Phys. Rev. Lett. 15, 20574-20581 (2021).
[4] M.R. Uhlig, D. Martin-Jimenez and R. Garcia, Nat. Commun. 10. 2606 (2019).
[5] M.R. Uhlig, R. Garcia, Nano Lett.  21, 5593 (2021).
[6] M.R. Uhlig, S. Benaglia, R. Thakkar, J. Gomer and R. Garcia, Nanoscale 13, 5275 (2021).
[7]  R. Garcia, ACS Nano (2023).