Hydrogen Sensing Mechanism of WS<sub>2</sub> Gas Sensors Analyzed with DFT and NAP-XPS
Tomoya Minezaki,
Peter Krüger,
Fatima Ezahra Annanouch,
Juan Casanova-Cháfer,
Aanchal Alagh,
Ignacio J. Villar-Garcia,
Virginia Pérez-Dieste,
Eduard Llobet,
Carla Bittencourt
Affiliations
Tomoya Minezaki
Department of Materials Science, Graduate School of Science and Engineering, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba-shi 263-8522, Chiba, Japan
Peter Krüger
Department of Materials Science, Graduate School of Science and Engineering, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba-shi 263-8522, Chiba, Japan
Fatima Ezahra Annanouch
Departament d’Enginyeria Electronica, Universitat Rovira i Virgili, Països Catalans 26, 43007 Tarragona, Spain
Juan Casanova-Cháfer
Chimie des Interactions Plasma Surface, CIRMAP, Université de Mons, Place du Parc 23, 7000 Mons, Belgium
Aanchal Alagh
Departament d’Enginyeria Electronica, Universitat Rovira i Virgili, Països Catalans 26, 43007 Tarragona, Spain
Ignacio J. Villar-Garcia
ALBA Synchrotron Light Source, Carrer de la Llum 2-26, 08290 Cerdanyola del Vallès, Spain
Virginia Pérez-Dieste
ALBA Synchrotron Light Source, Carrer de la Llum 2-26, 08290 Cerdanyola del Vallès, Spain
Eduard Llobet
Departament d’Enginyeria Electronica, Universitat Rovira i Virgili, Països Catalans 26, 43007 Tarragona, Spain
Carla Bittencourt
Chimie des Interactions Plasma Surface, CIRMAP, Université de Mons, Place du Parc 23, 7000 Mons, Belgium
Nanostructured tungsten disulfide (WS2) is one of the most promising candidates for being used as active nanomaterial in chemiresistive gas sensors, as it responds to hydrogen gas at room temperature. This study analyzes the hydrogen sensing mechanism of a nanostructured WS2 layer using near-ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS) and density functional theory (DFT). The W 4f and S 2p NAP-XPS spectra suggest that hydrogen makes physisorption on the WS2 active surface at room temperature and chemisorption on tungsten atoms at temperatures above 150 °C. DFT calculations show that a hydrogen molecule physically adsorbs on the defect-free WS2 monolayer, while it splits and makes chemical bonds with the nearest tungsten atoms on the sulfur point defect. The hydrogen adsorption on the sulfur defect causes a large charge transfer from the WS2 monolayer to the adsorbed hydrogen. In addition, it decreases the intensity of the in-gap state, which is generated by the sulfur point defect. Furthermore, the calculations explain the increase in the resistance of the gas sensor when hydrogen interacts with the WS2 active layer.
