Molecularly-thin anatase field-effect transistors fabricated through the solid state transformation of titania nanosheets

We demonstrate the field-effect transistor (FET) operation of a molecularly-thin anatase phase produced through solid state transformation from Ti_0.87O₂ nanosheets. A monolayer Ti_0.87O₂ nanosheet with a thickness of 0.7 nm is a two-dimensional oxide insulator in which Ti vacancies are incorporated, rather than oxygen vacancies. Since the fabrication method, in general, largely affects the film quality, the anatase films derived from the Ti_0.87O₂ nanosheets show interesting characteristics, such as no photocurrent peak at ∼2 eV, which is related to oxygen vacancies, and a larger band gap of 3.8 eV. The 10 nm thick anatase FETs exhibit superior transport characteristics with a maximum mobility of ∼1.3 cm² V^-1 s^-1 and a current on/off ratio of ∼10⁵ at room temperature. The molecularly-thin anatase FET may provide new functionalities, such as field-effect control of catalytic properties.