Effect of cadmium doping on gas sensitivity for CdxNi1−xFe2O4 thin films prepared via pulsed laser deposition on silicon substrate

Abstract

In this study, nanostructured Cd_xNi_1−xFe₂O₄(0 ≤ x ≤ 0.9) thin films were deposited on silicon substrates using pulsed laser deposition (PLD), and their structural, optical, and gas-sensing properties were thoroughly examined. X-ray diffraction analysis indicated that the samples possess a single-phase inverse spinel structure, with the average crystallite size decreasing from 13 nm (x = 0) to 8 nm (x = 0.9). The average grain size of Cd increased from 62.95 to 98.74 nm, as shown by atomic force microscopy, and the maximum surface roughness was 6.1 nm at x = 0.7. Optical measurements, which are associated with enhanced electronic polarizability, demonstrated improved UV photon absorption. Gas-sensing tests for 70 ppm NO₂ revealed a substantial increase in sensitivity, reaching a maximum of 145% at an optimal operating temperature of 200 °C, with the fastest response time of 4.7 s at x = 0.9 and a recovery time of approximately 21 s. These findings unequivocally demonstrate that well-controlled Cd doping significantly enhances the surface reactivity and electronic transport of Cdxni1-xfe2o4 thin films, making PLD-grown compositions highly competitive and effectively adjustable candidates for NO2 detection.