Probing the interactions in graphene oxide/MoS2 and reduced graphene oxide/MoS2 nanoarchitectures using multimodal scanning probe microscopy

Scanning probe microscopy (SPM) encompasses a versatile set of characterization techniques that reveal different properties and characteristics of materials. Herein, we demonstrate the potential of combining different SPM modes to understand the interactions (and their properties) between the components in two-dimensional/two-dimensional nanoarchitected thin films: graphene oxide (GO)/molybdenum disulfide (MoS2) and reduced graphene oxide (rGO)/MoS2. The films were prepared through the liquid-liquid interfacial route and analyzed by atomic force microscopy in topographic and phase contrast images, Kelvin probe force microscopy, lateral force microscopy and peak force microscopy. It was shown that the presence of oxygenated surface groups, the occurrence of structural defects and the surface electrical potential significantly affect the morphology and properties of the films. Due to their effective electrostatic interaction, the very small MoS2 flakes are uniformly distributed over the rGO flakes, whereas in an opposite way, they tend to agglomerate in the GO sheets. As a result, the GO/MoS2 film exhibits Young's modulus of 30 GPa, which is lower than that of the film containing neat GO (78 GPa), due to the increase in both deformation (2.6 nm) and adhesion (7.2 nN). Otherwise, the stiffness increases from 15 GPa to 25 GPa from neat rGO to the rGO/MoS2 nanocomposite, in which it was observed that the presence of MoS2 increases friction and promotes n-type doping. Based on the different SPM modes, it was possible to correlate the structural and morphological characteristics with some mechanical and electrical properties of bi-component thin films, and probe the specific interactions between the components.