Low-temperature synthesis of 2D MoS₂on a plastic substrate for a flexible gas sensor

Abstract

The efficient synthesis of two-dimensional molybdenum disulfide (2D MoS2) at low temperatures is essential for use in flexible devices. In this study, 2D MoS2 was grown directly at a low temperature of 200 °C on both hard (SiO2) and soft substrates (polyimide (PI)) using chemical vapor deposition (CVD) with Mo(CO)6 and H2S. We investigated the effect of the growth temperature and Mo concentration on the layered growth by Raman spectroscopy and microscopy. 2D MoS2 was grown by using low Mo concentration at a low temperature. Through optical microscopy, Raman spectroscopy, X-ray photoemission spectroscopy, photoluminescence, and transmission electron microscopy measurements, MoS2 produced by low-temperature CVD was determined to possess a layered structure with good uniformity, stoichiometry, and a controllable number of layers. Furthermore, we demonstrated the realization of a 2D MoS2-based flexible gas sensor on a PI substrate without any transfer processes, with competitive sensor performance and mechanical durability at room temperature. This fabrication process has potential for burgeoning flexible and wearable nanotechnology applications.

Flexible Sensors—From Materials to Applications

“…Devices based on SiNMs were shown to withstand bending radii down to 5 mm for a strain of 0.025% [217]. Similarly to graphene, transition metal dichalcogenides (TMDs), namely MoS 2 [234][235][236][237][238][239][240][241][242], WS 2 [243][244][245][246], and WSe 2 [247][248][249], were employed in the fabrication of flexible sensors due to their mechanical and electrical properties when scaled down to a single or few 2D crystalline layers. Among these materials, MoS 2 is the most widely used due to its widespread availability [250].…”

“…Based on the methods developed for the deposition of graphene, MoS 2 has been implemented in flexible substrates using mechanical [239], and chemical exfoliation [234,241,254,255]. In addition, other methods such as CVD on SiO 2 followed by transfer of the nanoflakes [235][236][237], PECVD [256], sulfurisation of Mo film [257], and more recently the direct hydrothermal growth of MoS 2 on aluminium foil were researched [238]. In flexible sensors, TMDs are mostly used as sensitive layers in gas sensors, and multiple reviews can be found on the subject [250,258,259].…”

Recent Progress in Chemiresistive Gas Sensing Technology Based on Molybdenum and Tungsten Chalcogenide Nanostructures

“…Lee et al prepared MoS 2 film by sulfurizing a thin layer of Mo and used it for sensing ammonia in concentration range of 2–30 ppm with an empirical limit of detection of 300 ppb 160. Zhao et al used a CVD technique with precursors like Mo(CO) 6 and H 2 S to grow MoS 2 film both on hard (SiO 2 ) and soft (polyimide) substrate at low temperature (i.e., 200 °C) for ammonia and NO 2 sensor 161. A comparative performance of flexible sensor towards NO 2 and NH 3 showed much better results toward NO 2 gas (a response of ≈300% at 5 ppm) as compared to NH 3 (a response of only 5% at 5 ppm) gas.…”

H2S detection at low temperatures by Cu2O/Fe2O3 heterostructure ordered array sensors

“…One strategy to realize accurate measurements at low temperatures is based on the nanostructure design of 2D metal oxide nanostructures. 7,8 However, progress in the eld of functionalized nanostructure design has not conformed to expectations and the structural design of high-performance sensing materials at low temperatures (even below the freezing point) still remains a challenging task.…”