Flexible Gas Sensor Based on the RF-Grown Fe2O3:ZnO/CNTs Material for Propylene Glycol Vapor Detection

Flexible electronic devices are increasingly in demand in the modern world. Among them, high-performance flexible sensors for the detection of vapors of industrially widespread propylene glycol (PG) are of interest. Herein, carbon nanotubes (CNTs) were grown using radio frequency (RF) magnetron sputtering and subsequently deposited by the electron beam deposition method onto a flexible sensor substrate. The sensor fabrication was complemented by introducing Fe₂O₃:ZnO nanograins and Pd catalyst particles onto the CNTs surface using RF and DC (direct current) sputtering techniques, respectively. The sensing materials were characterized by scanning electron (SEM) and transmission electron (TEM) microscopies and energy dispersive X-ray (EDX), electron energy-loss (EELS), X-ray diffraction (XRD), and Raman spectroscopies. The availability of CNTs and catalytic metal (Ni) was evident on the Si (100) substrate, revealing the hexagonal orientation of CNTs and the lattice interlayer spacing. The PGV (propylene glycol vapor) sensing behavior of the prepared sensor was investigated in detail using ultraviolet (UV) light combined with thermal heating in the range of 25–250 °C. The favorable sensitivities were registered at 150 °C with UV irradiation, where the sensor response values in the range 7–22 coincided with the PGV concentration range 1.5–60 ppm, respectively. The high performance of the sensor was confirmed with a short response (25 s) and recovery (87 s) times measured at a low detection limit concentration (1.5 ppm). The Fe₂O₃:ZnO/CNTs material embedded in the flexible polyimide substrate with high selectivity and response stability can be the best candidate for effective detection of PGV on any flexible surface.