Sung-Hyuk Her

In two-dimensional transition-metal dichalcogenides (TMDCs), the local electrostatic field of the chalcogen p -orbitals dictates the crystal field splitting of the transition metal d -orbitals, stabilizing diverse electronic states from semiconducting and semimetallic to exotic topological phases. On-demand substitution of the lattice chalcogens is therefore an efficient route to tuning TMDC electronic phases. Here, we custom-molded van der Waals (vdW) heterostructures by layer-by-layer vapor-phase chalcogen substitution starting from p -type WSe ₂ multilayers into which we locally inscribed insulating WO _x , n -type WS ₂ , and semimetallic WTe ₂ . This spatially precise conversion seamlessly integrated distinct electronic phases, both vertically and laterally, into modular vdW semiconductor heterostructures that are otherwise inaccessible. As a demonstration, we integrated WO _x /WSe ₂ local gate stacks to build ultrascaled metal oxide–semiconductor field effect transistors (MOSFETs), achieving an unprecedented subthreshold swing at subnanometer equivalent oxide thickness.

Two-dimensional (2D) and one-dimensional (1D) materials are anticipated to serve as functional devices due to their unique structural characteristics and high surface area. However, unlike conventional three-dimensional (3D) materials, their applications are limited by impurity-involved transfer processes and the formation of metastable, inhomogeneous heterostructures. To address these challenges, recent approaches have focused on inducing phase transitions by concentrating high-energy beams, aiming to achieve stable heterophase homojunctions [ 1]. We achieved the vertical growth of the one-dimensional semiconductor material, trigonal tellurium, on the metallic two-dimensional material NiTe₂ through an electron beam-induced phase transition. The metastable trigonal tellurium, which does not typically grow at room temperature and atmospheric pressure, achieves a stable junction on NiTe₂ due to the strain induced by the substrate [ 2]. Also, we controlled the growth of trigonal tellurium at the nanoscale using STEM (Scanning Transmission Electron Microscopy) and analyzed the deformation mechanism at the atomic scale. Our results, demonstrating the formation of stable heterojuctions through high-energy beam irradiation, are expected to serve as a foundation for phase transitions in multidimensional materials.