Phase Tailoring of InSe Toward van der Waals Vertical Heterostructures via Selenization of γ-InSe Semiconductor.

The polymorphic nature of InSe leads to excellent phase-dependent physical properties including ferroelectricity, photoelectricity, and especially the intriguing phase change ability, making the precise phase modulation of InSe of fundamental importance but very challenging. Here, the growth of InSe with desired-phase is realized by temperature-controlled selenization of van der Waals (vdW) layered bulk γ-InSe. Detailed results of Raman spectroscopy, scanning electron microscopy (SEM), and state-of-the-art spherical aberration-corrected transmission electron microscopy (Cs-TEM) clearly and consistently show that β-InSe, 3R α-InSe, and 2H α-InSe can be perfectly obtained at ≈270, ≈300, and ≈600 °C, respectively. Further comprehensive atomic imaging analyses confirm that the seeding material, InSe, plays a critical role in the low-temperature epitaxial growth of vdW-layered InSe, and, more interestingly, β-InSe acts as an intermediate phase between 3R and 2H α-InSe transitions. This investigation not only provides a simple yet versatile strategy for the phase modulation of InSe, but also sheds light on the temperature-dependent phase evolution of InSe.