The application of an electric field can be a new technique to control the electronic properties of two-dimensional materials. In a conventional double-gate structure, an ionic liquid is used in the top gate to produce a large electric field successfully. However, the material in the bottom gate has been restricted to solid dielectrics, which limits the applicable electric field. In this study, we combine the direct electron transfer and electrostatic gating to produce a large electric field. Bilayer graphene (BLG), which exhibits a band gap under a perpendicular electric field, was placed on electron-donating self-assembled monolayers with an amino end group (NH2-SAMs). As the NH2-SAMs were prepared on SiO2/Si substrates, the electron density of the BLG was increased further by applying a positive bottom gate voltage through the SiO2 dielectric. Additionally, a negative top gate voltage was applied with an ionic gel to produce an upward electric field. The transport gap in the BLG was evaluated based on the temperature dependence of the minimum conductivity at the charge neutrality point of the BLG. Comparing the results obtained from the BLG without the NH2-SAMs, we found that the NH2-SAMs donated electrons whose sheet density was 3.9 × 1012/cm2, or in other words, they produced an additional electric displacement field of 0.72 V/nm without a significant reduction of the mobility. Furthermore, we successfully evaluated the actual carrier density controlled by the top gate voltage based on a simple capacitor model. The combination of the two methods to accumulate carriers offers a unique opportunity to explore a novel electronic property by enhancing the controllability of the electric field and the carrier density.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films