Transition-Metal Chalcogenide, FeTe: Unveiling Molecular Mechanism of Phase-Selective Synthesis

Phase-selective chemical vapor deposition synthesis of two-dimensional (2D) transition-metal chalcogenides (TMCs) has garnered broad interest, yet its crucial dependence on the growth atmosphere is not understood. The chain of reactions transforming precursors into 2D crystals remains elusive. Focusing on iron telluride-a promising material for quantum and spintronic devices due to its phase-dependent topological superconductivity and magnetism-our first-principles calculation elucidates the phase-selective growth of tetragonal FeTe (t-FeTe), including its thermodynamic and kinetic shapes. We identify the FeTe₄Cl as the immediate precursor-a molecule reacting directly at the edge of the expanding crystal. Due to the stoichiometric mismatch of this gaseous precursor and the product-crystal, the growth mechanism through kink propagation requires an additional step-the edge cleaning, eliminating excess atoms after FeTe₄Cl attachment. Based on this, we further demonstrate that the experimental levers, namely Te-limited condition and H₂ supply, enable edge cleaning, thereby promoting nanosheet lateral, in-plane expansion and high t-FeTe phase purity. Conversely, in a Te-rich environment, off-plane nuclei become favored, biasing nucleation toward nonlayered phase (hexagonal h-FeTe). This work explains how the experimental atmosphere affects growth dynamics of t-FeTe and provides valuable guidelines for optimizing synthesis parameters of other TMCs.