Nanoscopic humidity-dependent adhesion behaviors of 2D materials

Abstract

Two-dimensional materials have gained significant attention in the research community due to their unique physicochemical and mechanical properties. Regarding their applications in devices irrespective of the involved length scale, interfacial adhesion plays an important role in nanoscopic single-asperity and macroscopic multi-asperity contacts. Therefore, this study aims at studying the adhesion behaviors of few-layered Ti3C2Tx, graphene oxide and WSe2 nano-sheets as a function of the adjusted relative humidity by atomic force microscopy. Reference experiments are conducted with graphite and silicon surfaces. The experimental results for graphene oxide and WSe2 nano-sheets show a monotonous increase of the adhesion force with increasing humidity. In contrast, silicon reference and bi-layered Ti3C2Tx nano-sheets show an increasing adhesion with increasing humidity before reaching a maximum value at a critical humidity followed by a pronounced decrease. Based upon the obtained adhesion and characterization data, the measured water adsorption behavior, and the existing knowledge for silicon regarding their superficial water structures, the observed experimental trends were connected with the respective surface groups of the nanomaterials and their ability to adsorb water on their surfaces.