In situ reflection electron microscopy for investigation of surface processes on Bi2Se3(0001)

Abstract

The sublimation and van der Waals (vdW) epitaxy on Bi2Se3(0001) surface have been first visualized using in situ reflection electron microscopy. When Bi2Se3(0001) surface was exposed to a Se molecular beam (up to 0.1 nm/s) and heated to ∼400°C, we observed ascending motion of atomic steps corresponding to congruent Bi2Se3 sublimation. During the sublimation, grooves made by probe lithography act as sources of atomic steps: groove depth increases and generates atomic steps that move in the ascending direction away from the source. We used this phenomenon to create self-organized regularly-spaced zigzag atomic steps having 1 nm height on the Bi2Se3(0001) surface. The deposition of Bi (up to ∼0.01 nm/s) onto the Bi2Se3(0001) surface at constant Se flux (up to ∼0.1 nm/s) reversed the direction of the step flow, and vdW epitaxy was observed. The deposition of In and Se onto the Bi2Se3(0001) surface at ∼400°C led to the epitaxial growth of layered In2Se3. This vdW heteroepitaxy started with 2D island nucleation and, after 3–5 nm growth, continued with a screw-dislocation-driven formation of 3D islands. Ex situ Raman scattering measurements have shown that the grown 20-nm-thick In2Se3 film exhibits vibrational modes that originate from the β-In2Se3 crystal phase.