| Summary: | Recently, a monolayer of SnTe was discovered to be a two-dimensional ferroelectric with an in-plane polarization, and, most dramatically, it exhibits a significant enhancement of the ferroelectric phase transition temperature compared to its bulk counterpart. This phenomenon is due to a structural phase transition from bulk-like α/β-SnTe, a topological crystalline insulator, to layered γ-SnTe as the thickness is decreased to a few atomic layers. A detailed understanding of the growth mechanism and phase distribution of ultrathin SnTe films are of great interest for potential applications. Here, we report detailed studies of the molecular beam epitaxial growth and in situ scanning tunneling microscopy characterization of ultrathin SnTe films on graphene substrates. By varying the growth conditions, SnTe can be prepared as either a continuous film or in the form of large rectangular plates. The rate of nucleation of SnTe was found to be highly sensitive to the substrate temperature. The coexistence and competition between the β and γ phases formed at room temperature was studied, and the phase diagram with respect to the average thickness of SnTe and the substrate temperature during growth is drawn.
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