Tuning Stoichiometry and Structure of Pd-WO3−x Thin Films for Hydrogen Gas Sensing by High-Power Impulse Magnetron Sputtering

Abstract

By tuning the deposition parameters of reactive high-power impulse magnetron sputtering, specifically the pulse length, we were able to prepare WO3−x films with various stoichiometry and structure. Subsequently, the films were annealed in air at moderate temperature (350 °C). We demonstrate that the stoichiometry of the as-deposited films influences considerably the type of crystalline phase formed in the annealed films. The appropriate sub-stoichiometry of the films (approx. WO2.76) enabled crystallization of the monoclinic phase during the annealing. This phase is favorable for hydrogen sensing applications. To characterize the sensory behavior of the films, the tungsten oxide films were decorated by Pd nanoparticles before annealing and were assembled as a conductometric gas sensor. The sensory response of the films that crystallized in the monoclinic structure was proven to be superior to that of the films containing other phases.

Three-Layer PdO/CuWO4/CuO System for Hydrogen Gas Sensing with Reduced Humidity Interference

“…It is worth noting that the approximately 30 nm height of the islands (Figure 6) excludes these islands from being formed by PdO because there is simply not enough material for it. Interestingly, the appearance of the Pd particles in the dark zone is similar to that observed on 2 Pd/ 100 W-O films synthesized at similar parameters (published in our previous work [17]).…”

“…Along with the demands for better performance, novel approaches have been employed such as the formation of heterojunctions by combining more than one MOS [5][6][7], the addition of catalytic metal particles onto MOS (Pt, Pd, Rh, etc.) [8][9][10][11], MOS nanostructuring [12][13][14][15], and MOS doping or the formation of ternary MOS [16,17]. Ternary oxides such as Zn 2 SnO 4 [18], ZnWO 4 [16,19], NiWO 4 [20], and CuWO 4 [21,22] are attractive candidates for the research in this field.…”

Hydrothermal synthesis of hierarchical microstructure tungsten oxide/carbon nanocomposite for supercapacitor application

“…The main diffraction peaks at 23.0°, 23.9°, 28.7°, 33.5°, and 34.0° could be attributed to the (002), (110), (102), (112), and (200) planes of tetragonal WO 3 , aligning with COD No. 1521532 34 , 35 . However, this attribution may not be absolute, and a pseudo-phase consisting of orthorhombic and tetragonal phases would also be likely, as observed from previous work 13 , 34 .…”

Pulse length dependence of a reactive high power impulse magnetron (HiPIMS) discharge

“…There is an ongoing challenge to further enhance the energy-influx during film deposition making use of so-called bipolar pulsing, a positively biased anode, and the use of an external anode [13][14][15]. Another approach is to vary the employed pulse length which influences ion composition and ion energy during the discharge and thus affects the deposition rate, the composition, and other properties of deposited thin films [16][17][18][19][20][21][22][23][24][25][26][27][28]. An alternative approach was employed by Magnus et al [29] varying the pulse frequency and, hence, the time between two subsequent pulses.…”