We have designed and manufactured a flanged coaxial line as a sample holder for measuring the electromagnetic interference (EMI) shielding efficiency (SE) of planar materials in broadband frequency ranges up to 18 GHz. Connecting the samples holder to a vector network analyzer $\text{(50\hspace{0.17em}}\mathrm{MHz}⩽\mathrm{M}\text{⩽13.5\hspace{0.17em}}\mathrm{GHz}\mathrm{),}$ we measured the $S$ (scattering)-parameters and the EMI SE of copper (Cu) as a highly conducting material and emeraldine salt form of polyaniline (PAN–ES) as an intermediately conducting one. The measured EMI SEs of the materials from 50 MHz to 13.5 GHz were compared with those obtained from the conventional ASTM D4935-99 method and theoretical simulation using dc conductivity. We observed that the EMI SEs measured by using both experimental techniques agree with each other in the common frequency range $\text{(50\hspace{0.17em}}\mathrm{MHz}\text{∼1.5\hspace{0.17em}}\mathrm{GHz}\mathrm{).}$ The EMI shielding characteristics of samples such as the contribution of absorption and reflection to total EMI SE were analyzed through the measured $S$ parameters.

Hexagonal molybdenum diselenide (MoSe₂) multilayers were grown by chemical vapor deposition (CVD). A relatively high pressure (>760 Torr) was used during the CVD growth to achieve multilayers by creating multiple nuclei based on the two-dimensional crystal growth model. Our CVD-grown multilayer MoSe₂ thin-film transistors (TFTs) show p-type-dominant ambipolar behaviors, which are attributed to the formation of Se vacancies generated at the decomposition temperature (650 °C) after the CVD growth for 10 min. Our MoSe₂ TFT with a reasonably high field-effect mobility (10 cm²/V · s) exhibits a high photoresponsivity (93.7 A/W) and a fast photoresponse time (τ_rise ~ 0.4 s) under the illumination of light, which demonstrates the practical feasibility of multilayer MoSe₂ TFTs for photodetector applications.

Layered semiconductors with atomic thicknesses are becoming increasingly important as active elements in high-performance electronic devices owing to their high carrier mobilities, large surface-to-volume ratios, and rapid electrical responses to their surrounding environments. Here, we report the first implementation of a highly sensitive chemical-vapor-deposition-grown multilayer MoSe₂ field-effect transistor (FET) in a NO₂ gas sensor. This sensor exhibited ultra-high sensitivity (S = ca. 1,907 for NO₂ at 300 ppm), real-time response, and rapid on–off switching. The high sensitivity of our MoSe₂ gas sensor is attributed to changes in the gap states near the valence band induced by the NO₂ gas absorbed in the MoSe₂, which leads to a significant increase in hole current in the off-state regime. Device modeling and quantum transport simulations revealed that the variation of gap states with NO₂ concentration is the key mechanism in a MoSe₂ FET-based NO₂ gas sensor. This comprehensive study, which addresses material growth, device fabrication, characterization, and device simulations, not only indicates the utility of MoSe₂ FETs for high-performance chemical sensors, but also establishes a fundamental understanding of how surface chemistry influences carrier transport in layered semiconductor devices.