We investigated the layer-number-dependent work function of MoS₂ nanoflakes by using Kelvin probe force microscopy (KPFM) to measure the surface potential. The work functions of as-prepared 1- to 6-layer MoS₂ nanoflakes were 5.15–5.39 eV and increased with increasing layer number. After annealing, the work functions of the nanoflakes decreased to 0.1–0.2 eV due to elimination of absorbed molecules on the surface. However, the work function of the edge region of the annealed flakes was relatively larger than that of the internal region. The charge carrier trapping by adsorbed molecules due to the polarity and the hydrophilicity of MoS₂ may cause a reduction in the work function of the annealed flakes compared with that for MoS₂ exposed to air. The dependence of the obtained work function of MoS₂ nanoflakes on the number of layers is essential to the formation of metal contacts for fabricating future MoS2-based devices.

In this study, precise control over the thickness and termination of Ti₃C₂T_X MXene flakes is achieved to enhance their electrical properties, environmental stability, and gas-sensing performance. Utilizing a hybrid method involving high-pressure processing, stirring, and immiscible solutions, sub-100 nm MXene flake thickness is achieved within the MXene film on the Si-wafer. Functionalization control is achieved by defunctionalizing MXene at 650 °C under vacuum and H₂ gas in a CVD furnace, followed by refunctionalization with iodine and bromine vaporization from a bubbler attached to the CVD. Notably, the introduction of iodine, which has a larger atomic size, lower electronegativity, reduce shielding effect, and lower hydrophilicity (contact angle: 99°), profoundly affecting MXene. It improves the surface area (36.2 cm² g⁻¹), oxidation stability in aqueous/ambient environments (21 days/80 days), and film conductivity (749 S m⁻¹). Additionally, it significantly enhances the gas-sensing performance, including the sensitivity (0.1119 Ω ppm⁻¹), response (0.2% and 23% to 50 ppb and 200 ppm NO₂), and response/recovery times (90/100 s). The reduced shielding effect of the –I-terminals and the metallic characteristics of MXene enhance the selectivity of I-MXene toward NO₂. This approach paves the way for the development of stable and high-performance gas-sensing two-dimensional materials with promising prospects for future studies.