The controlled synthesis of few‐layer vertically oriented MoS2 flakes for high‐performance NO2 gas sensor applications is introduced. The density and the thickness of MoS2 nanosheets are controlled by varying the heating rate of the chemical vapor deposition process. Herein, it is confirmed that the nanoflakes of about three layers are obtained under the heating rate of 5 °C using powders of MoO3 and S as precursors without using any catalyst. This is very advantageous because no catalyst is used, there is no need of buffer layer at the bottom of the MoS2 thin‐film flacks, thus omitting the leakage current when measuring the electrical signal and enhancing the gas sensing performance. Gas sensing measurements demonstrate that the interconnected vertically oriented MoS2 nanoflakes have a good response value of 20.1% to 0.5 ppm NO2 at room‐temperature (RT), and 1.73% at 150 °C. The sensor shows full recovery characteristic at a measured temperature of 150 °C with response and recovery time of about 15 and 100 s, respectively. The sensor also exhibits good selectivity with the ignorable response to SO2, H2, NH3, H2S, and a low detection limit of 42 ppb.

The current work reports a direct synthesis of multi-layer MoS2 nanodots by a chemical vapor deposition method. The morphological, structural and optical properties of the growing MoS2 are investigated by field emission scanning electron microscopy (FESEM), Raman and Photoluminescence (PL) spectroscopy, respectively. High magnification FESEM image reveals a layer of MoS2 nanodots with the average size of about 10 nm. Resonance Raman data exhibits the two active E12g and A1g modes corresponding to in-plane variation of Mo and S atoms centered at 383.3 cm-1 and to out of plane variation of S atoms located at 407.1 cm-1, respectively. The spacing between two peaks is about 23.8 cm-1, which can be used to evaluate the number of MoS2 layer. The Raman spectrum also indicates any intensity enhancement of the A1g peak compared to the E12g peak. This result is elucidated through the quantum confinement effect. The PL emission shows a pronounced peak at 505 nm that is significant blue shift compared to single MoS2 layer. The interpretation of this phenomena is discussed in detail.