Insight into the underlying competitive mechanism for the shift of the charge neutrality point in a trilayer-graphene field-effect transistor

Layer-number modulation in graphene has become a recent focus of research due to the superior degree of freedom that can be achieved in terms of magic-angle, wettability, superconductivity, and superlattices. However, the intrinsic transport of multilayer graphene is indistinguishable in atmospheric adsorbates and supporting environment, and its underlying charge transfer mechanism has not yet been thoroughly determined. In this study, a shift in the charge neutrality point of trilayer graphene (TLG) is demonstrated to be regulated by three governing factors: oxygen gas (O2), water molecules (H2O), and thermally activated electrons. Absorbed O2 ​induces a high work function in semimetallic TLG, while H2O is not an evident dopant but can strengthen binding against O2 ​desorption. A simplified model is developed to elucidate the competitive mechanism and charge transfer among these two dopants (O2, H2O) and thermal electrons, and the model is demonstrated by work function regulation and Bader charge transfer based on density functional theory calculations. This study provides a strategy to explore transport modulation of multilayer graphene in the fields of ballistic transport and low power consumption of graphene field-effect transistors.