Van der Waals pressure and its effect on trapped interlayer molecules

TL;DR

This paper measures the high pressure exerted on molecules trapped between 2D crystals, revealing its ability to induce chemical reactions and alter material properties at the atomic scale.

Contribution

It provides direct measurements of interfacial pressure in van der Waals assemblies and demonstrates its impact on chemical reactions and material modifications.

Findings

Pressure of ~1.2 GPa measured via Raman spectroscopy

Trapped salts react with water to form oxides

Pressure influences chemical reactions at 2D interfaces

Abstract

Van der Waals assembly of two-dimensional (2D) crystals continue attract intense interest due to the prospect of designing novel materials with on-demand properties. One of the unique features of this technology is the possibility of trapping molecules or compounds between 2D crystals. The trapped molecules are predicted to experience pressures as high as 1 GPa. Here we report measurements of this interfacial pressure by capturing pressure-sensitive molecules and studying their structural and conformational changes. Pressures of 1.2 +/- 0.3 GPa are found using Raman spectrometry for molecular layers of one nanometer in thickness. We further show that this pressure can induce chemical reactions and several trapped salts or compounds are found to react with water at room temperature, leading to 2D crystals of the corresponding oxides. This pressure and its effect should be taken into account in studies of van der Waals heterostructures and can also be exploited to modify materials confined at the atomic interfaces.