Influence of the thermal reduction process on the tribological and conductive properties of single-layer graphene oxide

Graphene oxide (GO) can be intentionally modified by the reduction process to tune some of its physical properties. This allows the application of GO as a thin film interface in various technologies, especially MEMS devices. One of the key factors when considering GO as a nanocoating in MEMS is its ability to reduce friction and increase electrical conductivity. Here, we exemplify a simple adjustment of the friction and conductance of a single GO flake at the nanoscale by the thermal reduction process, which results in morphological, chemical, and structural changes. The core of this experimental work is based on atomic force microscopy (AFM), in particular AFM topography imaging, force spectroscopy, lateral force microscopy, and conductive AFM. Additional measurements were performed using optical microscopy, Fourier-transform infrared spectroscopy, Raman spectroscopy, and wetting angle measurements. The physical properties were measured as a function of the reduction temperature for isolated single-layer GO flakes. In our research, we have identified a temperature threshold at which structural and morphological changes occur. The conversion of the properties of GO as conductivity, thickness, adhesive, and friction force, as well as defect level was shown to occur at most at 130 °C. However, some effects start even at 100 °C. We have found a non-monotonic friction dependence as a function of the sliding velocity, close to our published results for fluoroalkylsilanes 1:Weiss M. et al. (2021), Tribology International, 162, 107133], which exhibits a characteristic friction minimum. It corresponds to the lowest possible energy dissipation in the system for a given sliding velocity and load. To extend the range of accessible sliding velocities and gain insight into the molecular details of the friction process, molecular dynamics simulations were performed. In conclusion, by controlling the thermal reduction process of GO, it is possible to influence the properties of the GO system, such as adhesion, friction, and electrical conductivity, which can enhance the performance of materials in various applications, including MEMS devices. • Graphene oxide (GO) is modified in thermal reduction process to tailor its properties. • Conductivity and nanotribological properties of GO depend on its reduction state. • GO – SiO x pair exhibit non-monotonic friction force versus sliding velocity dependence. • Several friction mechanisms can be distinguished. • Characteristic friction minimum dependent on the reduction temperature is observed.