In operando synthesis of an ultrathin dielectric based on crystalline gallium oxide

Abstract Dielectric materials are essential in modern science and technology, but their miniaturization represents a challenge. Herein, we synthesize a dielectric based on atomically thin crystalline gallium oxide (Ga 2 O 3 ) on conducting graphene. The oxide is obtained via the direct oxidation of a two-dimensional semiconductor (gallium selenide, GaSe) grown by molecular beam epitaxy on graphene and is probed in real time during the oxidation by near-ambient pressure X-ray photoelectron spectroscopy. The oxide possesses (i) a clean, atomically abrupt interface with graphene; (ii) a wide band gap (4.5 eV) with a weakly dispersed valence band; (iii) large conduction and valence band offsets ( >1.5 eV) relative to the Dirac cone of graphene; and (iv) a large break down electric field, as probed locally by conductive atomic force microscopy. The direct oxidation of the semiconductor enables the integration of conducting and insulating building blocks for scalable nanoelectronics. Also, it provides a general route for synthesizing oxides from a variety of metal-based two-dimensional semiconductors.