Enhanced gating efficiency in vertical mixed molecular transistors with deep orbital level

The advancement of molecular junction transistors relies heavily on precise modulation of molecular orbitals, yet this is hindered by a limited transmission window and reduced bias stability, which typically restricts the range of active channel molecules adopted to those with orbital levels near Fermi level of the contacts. In this study, we demonstrate an effective orbital gating of prototypical alkanethiol-based molecules with deeper orbital levels in vertical large-area mixed self-assembled monolayers (SAMs) configuration that offers enhanced electrical bias stability and gating efficiency. By using ion gel gating in Au-molecule-graphene junction, the channel conductance could be modulated notably according to a clear transition from direct tunneling to Fowler-Nordheim tunneling regime. The mixed SAM molecular transistors also showed a superior gating efficiency due to the suppressed field screening effect by the net molecular dipole. This work is expected to contribute toward developing reliable three-terminal molecular device platform extended to molecules with deep orbital levels.