Controllable growth of two-dimensional NbSe2 flakes with irregular geometries under ion etching

Nanostructured NbSe2 has gained enormous interest in recent decades owning to its exotic properties and potential applications. Although two-dimensional (2D) NbSe2 structures have been successfully synthesized on various substrates, it remains a great challenge to prepare NbSe2 nanostructures with high edge-to-surface ratio, which is highly desirable for potential applications in catalysis. Here, we demonstrate that 2D NbSe2 with irregular geometries can be controllably grown on highly oriented pyrolytic graphite substrates via tuning the subtle balance between growth and ion etching. Atomic force microscopy, transmission electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy were employed to characterize the morphology and composition of the as-grown NbSe2 flakes. Our work highlights the important role of ion etching and paves the way for the growth of 2D materials with various geometries. •The direct synthesis of NbSe2 films with irregular edges is studied using molecular beam epitaxy methods.•The morphologies of the NbSe2 films are essentially affected by the delicate balance between film growth and Nb + ion etching.•Kink site of NbSe2 edges with higher free energy are more likely to break bonds and desorption under Nb + ion etching.•Nb + ion etching with high selectivity and precision is highly desirable for micro-machining technology.•NbSe2 flakes with irregular geometries is very promising for catalytic applications and micro-machining technology due to the high edge-to-surface ratio.