Molecular doping control at a topological insulator surface: F ₄-TCNQ on Bi₂Se₃

Recent electrical measurements have accessed transport in the topological surface state band of thin exfoliated samples of Bi₂Se₃ by removing the bulk n-type doping by contact with thin films of the molecular acceptor F₄-TCNQ. Here we report on the film growth and interfacial electronic characterization of F₄-TCNQ grown on Bi₂Se ₃. Atomic force microscopy shows wetting layer formation followed by 3D island growth. X-ray photoelectron spectroscopy is consistent with this picture and also shows that charge transferred to the molecular layer is localized on nitrogen atoms. Ultraviolet photoelectron spectroscopy shows a work function increase and an upward shift of the valence band edge that suggest significant reduction in carrier density at the Bi₂Se₃ surface.