Gate-controlled multistate modulation in few-layer graphene via layer-by-layer ion intercalation

The simultaneous modulation of electric and optical properties in graphene is essential for advancing high-performance applications in optoelectronics. However, achieving in-situ control of multiple electric and optical states in graphene devices remains a challenge. Here we demonstrate a versatile and reversible electric-field control of organic-ion intercalation from bilayer to pentalayer graphene. Through simultaneous optical imaging and electric measurements, we reveal multiple physical states controlled by the layer-by-layer intercalation processes, resulting in both high transparency and high electric conductance with an increase in the number of intercalated layers. Raman spectroscopy demonstrates that the intercalated graphene maintains a high carrier concentration without lattice degradation. Moreover, Hall effect measurements reveal that the carrier density can reach approximately 1.5 × 10¹⁴ cm⁻² per layer. The ability to synchronously control the transparency and conductance states by adjusting the number of ion-intercalated layers highlights the potential of multistate modulation for the development of advanced optoelectronic devices in two-dimensional materials.