Interfacial Liquid Water on Graphite, Graphene and 2D Materials

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.<br/><br/>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 <b>three-dimensional</b> interfacial structure of surfaces immersed in aqueous solutions. The third section reports the structure of interfacial water layers on different <b>2D materials</b> 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 [4-8]. 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 <b>hydrophobic surfaces</b> <b>water</b> molecules are <b>expelled</b> from the vicinity of the surface and replaced by several molecular-size hydrophobic layers.<br/><br/><b>References </b><br/><br/>[1] D. Martin-Jimenez, E. Chacon, P. Tarazona, R. Garcia, Nat. Commun<i>. </i><b>7</b>, 12164 (2016).<br/>[2] T. Fukuma and R. Garcia, ACS Nano <b>12</b> 11785 (2018).<br/>[3] S. Benaglia, et al. Phys. Rev. Lett. <b>15</b>, 20574-20581 (2021)<br/>[4] M.R. Uhlig, D. Martin-Jimenez and R. Garcia, Nat. Commun. <b>10.</b> 2606 (2019).<br/>[5] M.R. Uhlig, R. Garcia, Nano Lett. <b>21</b>, 5593 (2021)<br/>[6] M.R. Uhlig, S. Benaglia, R. Thakkar, J. Gomer and R. Garcia, Nanoscale <b>13</b>, 5275 (2021)<br/>[7] D.M. Arvelo, M.R. Uhlig, J. Comer, R. Garcia, Nanoscale 14, 14178 (2022)<br/>[8] R. Garcia, ACS Nano 17, 51-69 (2023)