Thermodynamics and Kinetics in van der Waals Epitaxial Growth of Te

Abstract

Chemical vapour deposition (CVD) in tube furnace and molecular beam epitaxy (MBE) in vacuum chamber represent the most effective methods for the production of low-dimensional nanomaterials. However, the as-synthesized products always exhibit diverse morphologies and phases due to the varying thermodynamic and kinetic factors. A comprehensive investigation into these factors is thus imperative. Here, we employ tellurium (Te), a p-type semiconductor characterized by anisotropic properties, as a model system for van der Waals (vdW) epitaxy to elucidate the difference of kinetic and thermodynamic influences in CVD and MBE processes. From a thermodynamic perspective, the inherent structural anisotropy of Te crystal favors the growth of 1D nanowires. In CVD process, Te predominantly forms 1D structures at low substrate temperature (Tsub<473 K) due to substantial thermal mass and high deposition rate. At higher Tsub (>633K), diffusion takes over the dominance, resulting in the formation of kinetically controlled 2D Te nanoflakes. In MBE, the formation of 1D Te nanowires is impeded by kinetic limitations stemming from a limited deposition flux, yielding 2D Te films at low Tsub (120-300 K). Only at higher Tsub (400 K), when the MBE system reaches to a thermodynamic equilibrium, can 1D nanowires be synthesized. Our study reveals the distinct roles of thermodynamic and kinetic parameters in guiding the morphological evolution of Te nanostructures, and the findings provide a general framework for understanding the growth mechanism of other vdW epitaxial low-dimensional nanomaterials.