Controllable phase transition of two-dimensional ferromagnetic chromium telluride thin films grown by molecular beam epitaxy

Abstract Two-dimensional (2D) Cr (1+ δ ) Te 2 materials exhibit strong magnetic ordering and high Curie temperatures, making them attractive for various applications. It is crucial to achieve controllable synthesis for their successful integration into device technologies. In this study, we present the synthesis of phase-controllable 2D Cr (1+ δ ) Te 2 films on the Si (111) substrate via molecular beam epitaxy. The composition and phase transition of the as-grown Cr (1+ δ ) Te 2 films are characterized by using in-situ reflection high-energy electron diffraction, scanning tunneling microscopy, ex-situ X-ray photoelectron spectroscopy, X-ray diffraction, and theoretical calculations. At low growth temperatures, by carefully adjusting the film thickness from 2 to more than 3 layers, we achieve precise control over the phase of Cr (1+ δ ) Te 2 , from CrTe 2 to Cr intercalated Cr 2 Te 3 . At a relatively elevated growth temperature, it is demonstrated that the Cr (1+ δ ) Te 2 phase is independent of the film thickness, only Cr 2 Te 3 forms and its growth mode is thickness-dependent. These phase transitions at low growth temperatures and growth mode changes at elevated growth temperatures are attributed to interfacial effects and the phase stability of Cr (1+ δ ) Te 2 compounds. Additionally, we utilize scanning tunneling spectroscopy and computations to gain insights into the electronic properties of Cr 2 Te 3 . The magnetic measurements reveal that the 30-nm Cr 2 Te 3 film exhibits ferromagnetic behavior with a Curie temperature of about 180 K. Our work offers a robust method for the controllable growth of high-quality 2D Cr (1+ δ ) Te 2 films on Si substrates, providing an ideal platform for investigating their intrinsic properties and advancing the development of 2D magnet-based spintronics devices.