Water-Assisted Concerted Layer Growth of T_d-Phase WTe₂ for Nonlinear Hall Effect and Microwave Rectification

The T_d phase of tungsten ditelluride (WTe₂), a noncentrosymmetric transition metal dichalcogenide, hosts rich correlated phenomena, topological states, and nonlinear transport responses. However, the scalable synthesis of high-quality few-layer WTe₂ with precise layer control remains challenging. Here, we report a water-assisted chemical vapor deposition approach that deterministically grows monolayer to trilayer T_d-WTe₂ with controlled flake size and density. Moisture-mediated precursor liquefaction through salt-assisted intermediates enables vapor-liquid-solid growth and tunable layer numbers through a concerted layer growth mode. Transport studies reveal that trilayer WTe₂ exhibits a nonlinear Hall effect susceptibility of 1.1 μm·V^-1 at 10 K and 0.5 μm·V^-1 at 50 K, nearly an order of magnitude higher than that in bilayers, consistent with the calculated Berry curvature dipole enhancement. Layer-dependent microwave rectification further highlights the influence of topological band structure and interlayer coupling. These results establish layer-engineered T_d-WTe₂ as a promising platform for nonlinear quantum transport and high-frequency optoelectronic applications.