  Ionic liquid gating has been used to modify properties of layered transition
metal dichalcogenides (TMDCs), including two-dimensional (2D) crystals of TMDCs
used extensively recently in the device work, which has led to observations of
properties not seen in the bulk. The main effect comes from the electrostatic
gating due to strong electric field at the interface. In addition, ionic liquid
gating also leads to ion intercalation when the ion size of gate electrolyte is
small compared to the interlayer spacing of TMDCs. However, the microscopic
processes of ion intercalation have rarely been explored in layered TMDCs.
Here, we employed a technique combining photolithography device fabrication and
electrical transport measurements on the thin crystals of hexagonal TaSe2 using
multiple channel devices gated by a polymer electrolyte LiClO4/PEO. The gate
voltage and time dependent source-drain resistances of these thin crystals were
used to obtain information on the intercalation process, the effect of ion
intercalation, and the correlation between the ion occupation of allowed
interstitial sites and the device characteristics. We found a gate voltage
controlled modulation of the charge density waves and scattering rate of charge
carriers. Our work suggests that ion intercalation can be a useful tool for
layered materials engineering and 2D crystal device design.
