Triboelectrification and Unique Frictional Characteristics of Germanium-Based Nanofilms

In this study, germanium arsenide (GeAs) is investigated as a promising nanomaterial for application in triboelectric nanogenerators and green energy harvesting. The mechanical and electrical properties of mechanically exfoliated GeAs on silica substrates are evaluated through friction force microscopy and Kelvin probe force microscopy, respectively. First, it is observed that the surface potential/work function of GeAs varied with thickness. Second, thickness-dependent friction on GeAs films is found. However, the variation of friction with GeAs thickness followed an inverse trend typically observed for most other 2D material systems: larger friction is measured on thicker GeAs films. The higher friction is attributed to the higher surface potential of thicker GeAs, resulting from the accumulation of electrons on the GeAs surface that also resulted in higher adhesion between GeAs surface and the tip. Finally, history-dependent friction is observed and resulted from a continual increase in the friction force as the surface is scanned and originated from the triboelectrification of the surface. The dynamic triboelectrification behavior of thick GeAs during the scanning process is further verified and visualized by a serial experiment, where the GeAs is tribo-electrified through scanning and gradually de-electrified/discharged upon ceasing the scan. The thinner germanium arsenide (GeAs) is found to have a lower surface potential, reduced surface adhesion, and consequently lower surface friction, aligning with an inverse thickness-dependent friction trend observed in most other 2D material systems. Meanwhile, GeAs undergoes triboelectrification during scanning, manifested by an increase in surface adhesion and friction. The accumulated charge gradually discharges upon ceasing the scan.image