Thickness-dependent decoupling charge transport and NH₃sensing in multilayer MoS₂transistors

Thickness is a critical yet often overlooked degree of freedom governing both charge transport and surface reactivity in two-dimensional (2D) semiconductors. Here, we elucidate the thickness-dependent coupling between carrier transport and NH₃sensing in multilayer MoS₂field-effect transistors with controlled layer numbers. The field-effect mobility exhibits a pronounced nonmonotonic evolution, increasing from 0.13 cm^-2V^-1s^-1(6 layers) to a maximum of 20.1 cm^-2V^-1s^-1at ∼21 layers before decreasing at larger thicknesses, reflecting the competition between interfacial Coulomb scattering, dielectric screening, and interlayer transport limitations. In stark contrast, the NH₃sensing response shows a monotonic decrease with increasing thickness, with the 6-layer device delivering a response as high as 466.17% at 160 ppm. This inverse correlation arises from the progressive decoupling of surface adsorption from bulk transport due to enhanced electrostatic screening and reduced participation of inner layers. By directly linking thickness-dependent scattering physics with surface charge-transfer modulation, this work establishes a unified framework for understanding and engineering the trade-off between transport efficiency and sensing sensitivity in multilayer MoS₂. These findings highlight thickness as a key design parameter for optimizing 2D semiconductor devices across electronic and sensing applications.