Optimization of WS2 layer thickness for enhanced performance in self-powered gas sensors

Abstract

• WS 2 thin films were grown by RF magnetron sputtering at 50, 150, and 250 nm. • FESEM confirmed WS 2 nanostructures (5–40 nm) with a uniform surface at 150 nm. • XRD showed improved crystallinity and lowest Urbach energy (74 meV) at 150 nm. • The 150 nm film had the optimal band gap (1.33 eV) and highest mobility (2.02 cm 2 /V·s). • The 150 nm film detected ethanol and ammonia with fast response in self-powered mode. The WS 2 thin films were deposited on glass substrates using RF magnetron sputtering using a tungsten sulfide target to study the effect of WS 2 layer thickness on the properties of the thin films. To analyze the morphological, structural, optical, electrical, and gas sensor characteristics of the thin films. The FESEM images indicated that samples have nanoparticles with 50, 150, and 250 nm thicknesses. The 50 and 250 nm and the sample of 150 nm have preferred orientations of (104) and (009), respectively. The 150 nm sample has a larger crystallite size than the other two samples and, as a result, has better crystallinity. Additionally, the Urbach energy calculation showed that the 150 nm sample had the lowest Urbach energy (74 meV), confirming better crystallinity and fewer crystal defects. The indirect band gap of the samples with increasing thickness is 1.89, 1.35, and 1.55 eV, respectively, which indicates that the 150 nm sample has the closest band gap value to the bulk state. Among the samples, the sample of 150 nm, which has better crystallinity and fewer crystal defects, has responded to the gas sensing of ethanol and ammonia in the self-powered mode. Measurements were performed at 500, 1500, and 2000 ppm and the recovery time for ethanol gas was 41.28 s.

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