Room-temperature highly sensitive and selective NH 3 gas sensor using vertically aligned WS 2 nanosheets.

Here, we report the room temperature (35 °C) NH 3 gas sensor device made from WS 2 nanosheets obtained via a facile and low-cost probe sonication method. The gas-sensing properties of devices made from these nanosheets were examined for various analytes such as ammonia, ethanol, methanol, formaldehyde, acetone, chloroform, and benzene. The fabricated gas sensor is selective towards NH 3 and exhibits excellent sensitivity, faster response, and recovery time in comparison to previously reported values. The device can detect NH 3 down to 5 ppm, much below the maximum allowed workspace NH 3 level (20 ppm), and have a sensing response of the order of 112% with a response and recovery time of 54 s and 66 s, respectively. On the other hand, a sensor made from nanostructures has a bit longer recovery time than a device made from nanosheets. This was attributed to the fact that NH 3 molecules adsorbed on the surface site and those trapped in between WS 2 layers may have different adsorption energies . In the latter case, desorption becomes difficult and may give rise to slower recovery as noticed. Further, stiffened Raman modes upon exposure to NH 3 reveal strong electron-phonon interaction between NH 3 and the WS 2 channel. The present work highlights the potential use of scaled two-dimensional nanosheets in sensing devices and particularly when used with inter-digitized electrodes, may offer enhanced performance.