Highly Responsive Pd-Decorated MoO₃ Nanowall H₂ Gas Sensors Obtained from In-Situ-Controlled Thermal Oxidation of Sputtered MoS₂ Films

Abstract

Among transition metal oxides, MoO3 is a promising material due to its layered structure and different oxidation states, making it suitable for different device applications. One of the methods used to grow MoO3 is radio frequency magnetron sputtering (RFMS), which is the most compatible method in industry. However, obtaining nanostructures by RFMS for metal oxides is challenging because of compact morphology film formation. In this study, α-MoO3 with vertical nanowalls is obtained by a two-step process; deposition of magnetron-sputtered MoS2 vertical nanowalls and postoxidation of these structures without changing the morphology. In situ transmittance and electrical measurements are performed to control the oxidation process, which shed light on understanding the oxidation of MoS2 nanowalls. The transition from MoS2 to α-MoO3 is investigated with partially oxidized MoS2/MoO3 samples with different thicknesses. It is also concluded that oxidation starts from nanowalls perpendicular to the substrate and lasts with oxidation of basal planes. Four different thicknesses of α-MoO3 nanowall samples are fabricated for H2 gas sensors. Also, the effect of Pd deposition on the H2-sensing properties of sensors is deeply investigated. An outstanding response of 3.3 × 105 as well as the response and recovery times of 379 and 304 s, respectively, are achieved from the thinnest Pd-loaded sample. Also, the gas-sensing mechanism is explored by gasochromic measurements to investigate the sensor behaviors under the conditions of dry air and N2 gas as the carrier gas.

The versatile family of molybdenum oxides: synthesis, properties, and recent applications

“…By increasing the doping concentration, the optimum operating temperature was decreased by about 40 • C, and at the same time, they improved the sensitivity response. Also, Mobtakeri et al [197] studied Pd-decorated MoO 3 vertical nanowalls for H 2 gas sensors (figure 15). In this work, they investigate the influence of the nanowall thickness and the effect of Pd deposition.…”

“…(a) Schematic illustration of the MoO 3 gas sensor. (b) Dynamic responses and (c) response and recovery times for 1000 ppm H 2 concentration at 100 • C of MoO 3 samples grown during different times (Z 0.5 , Z 2.5 , Z 7.5 , and Z 30 , corresponding to 30 s, 2.5 min, 7.5 min, and 30 min growth time with thicknesses of 40, 115, 370, and 1440 nm, respectively) (Reproduced from[197]. CC BY 4.0).…”

ZIF-67/BiOCl nanocomposites for highly efficient detection of NO2gas at room temperature

“…For this purpose, the two-dimensional (2D) laminate material has gained much attention due to its unique architectural properties, large specic surface area, and excellent electrical conductivity. [8][9][10][11] Bismuth oxychloride (BiOCl) is one of the important members of the 2D material family, which exhibits a layer-by-layer structure of [X-Bi-O-Bi-X] and is stacked together by intra-layer covalent bonding and inter-layer van der Waals forces. 12 It has been successfully used in catalysis, exhaust gas treatment, and water purication due to its unique structural, optical, electrical, and physicochemical properties.…”

Controlling crystallites orientation and facet exposure for enhanced electrochemical properties of polycrystalline MoO3 films

“…And indeed, previous studies have proven that α-MoO 3 exhibits anisotropy, particularly in catalytic properties 13 . Moreover, this material is also commonly investigated as an electrode material for batteries and electrochemical capacitors 14 , 15 , but also for photocatalysts 16 , electrochromic films 17 , and gas sensing materials 18 . Hence, it is reasonable to develop methods of MoO 3 deposition that enable the control of crystals orientation and exposure of specific crystal facets on the same type of polycrystalline substrate.…”