Impact of Substrate Effects on Sensing Performance in Electrodeposited Nanostructured Cu₂O Thin Films for LPG Detection

In this study, nanostructured Cu₂O thin films were synthesized by electrochemical deposition on various substrates, such as FTO, ITO, Ti, and Cu investigating their structural, electrical, and surface morphological characteristics, as well as their performance in sensing liquid petroleum gas (LPG). The Cu₂O films deposited with lactate solution of pH =10 exhibited polycrystalline growth on all substrates, with a notable preference for crystal orientation in the (111) plane. While on FTO and ITO substrates, the crystal growth exhibited a cubic-pyramidal shape, which transformed into tetrahedral shapes on Ti and Cu substrates. The grain size was found to vary from approximately 24 to 64 nm, with surface contact angles indicating moderate surface energy and wetting properties on FTO, ITO, and Ti substrates. Complex impedance spectroscopic measurements conducted on the film surfaces revealed a non-ideal capacitive behavior that increased in the order of Ti, ITO, FTO, and Cu respectively. Additionally, gas sensing evaluations were performed at 70°C, highlighting the highest LPG sensitivity of 11.3% on ITO substrates, and optimal gas sensing response and recovery times of 15-30 s on Ti substrates. Furthermore, the variation in carrier density before and after gas exposure indicated an increase in acceptor density with FTO exhibiting the most significant change of approximately 1×10¹⁹ cm^-2. These results underscore the substantial influence of the selected substrate on efficient gas sensing performance.