  Layer number-dependent band structures and symmetry are vital for the
electrical and optical characteristics of two-dimensional (2D) transition metal
dichalcogenides (TMDCs). Harvesting 2D TMDCs with tunable thickness and
properties can be achieved through top-down etching and bottom-up growth
strategies. In this study, we report a pioneering technique that utilizes the
migration of in-situ generated Na-W-S-O droplets to etch out one-dimensional
(1D) nanotrenches in few-layer WS$_2$. 1D WS$_2$ nanotrenches were successfully
fabricated on the optically inert bilayer WS$_2$, showing pronounced
photoluminescence and second harmonic generation signals. Additionally, we
demonstrate the modulation of inkjet-printed Na$_2$WO$_4$-Na$_2$SO$_4$
particles to switch between the etching and growth modes by manipulating the
sulfur supply. This versatile approach enables the creation of 1D nanochannels
on 2D TMDCs. Our research presents exciting prospects for the top-down and
bottom-up fabrication of 1D-2D mixed-dimensional TMDC nanostructures, expanding
their use for photonic and optoelectronic applications.
