Triboelectrification of Two-Dimensional Chemical Vapor Deposited WS at Nanoscale.

Triboelectric properties of chemical vapor deposited WS nanoflakes have been characterized in nano-range by atomic force microscopy (AFM) and Kelvin force microscopy (KFM). The triboelectric process is dependent on the thickness of WS nanoflakes, and it is sensitive to the adsorbates like water molecules, as well as transferred Pt from the tip on the sample. The density of tribo-charge can be modified by applying various biases to the conductive Pt-coated tip during the frictional process. Tunneling of the tribo-charge into the gap between WS and the underlying substrate results in a long lifetime, which is about 100 times longer than conventional triboelectric charges. Moreover, we observe a positive correlation between the layer number and resistance to charge dissipation. Our finding can become the driving force for a new category of two-dimensional (2D) WS triboelectrically controllable nanodevices.