Abstract
Tungsten disulfide (WS(2)) is attractive for the development of chemiresistive sensors due to its favorable band gap, as well as its mechanical strength and chemical stability. In this work, we elaborate a procedure for the synthesis of thin films consisting of vertically and/or horizontally oriented WS(2) nanoparticles by sulfurizing nanometer-thick tungsten layers deposited on oxidized silicon substrates using magnetron sputtering. According to X-ray photoelectron spectroscopy and Raman scattering data, WS(2) films grown in an H(2)-containing atmosphere at 1000 °C are almost free of tungsten oxide. The WS(2) film's thickness is controlled by varying the tungsten sputtering duration from 10 to 90 s. The highest response to nitrogen dioxide (NO(2)) at room temperature was demonstrated by the film obtained using a tungsten layer sputtered for 30 s. The increased sensitivity is attributed to the high surface-to-volume ratio provided by the horizontal and vertical orientation of the small WS(2) nanoparticles. Based on density functional calculations, we conclude that the small in-plane size of WS(2) provides many high-energy sites for NO(2) adsorption, which leads to greater charge transfer in the sensor. The detection limit of NO(2) calculated for the best sensor (WS(2)-30s) is 15 ppb at room temperature and 8 ppb at 125 °C. The sensor can operate in a humid environment and is significantly less sensitive to NH(3) and a mixture of H(2), CO, and CO(2) gases.