Exploring asymmetrical depletion internal n-p heterojunctions engineered in gas-sensing CuFe2O4-CuO nanofibers

The designed n-p heterojunctions (HJs) have gained huge interest in improving the efficiency of sensing materials by promoting charge transportation across junctions, thereby increasing the depletion region at the interface. The process of charge migration through HJs is often theoretically explained by differences in their work functions; however, this has not been experimentally explored. In this work, two types of n-p HJs, including external CuFe2O4/CuO mixed nanofibers (NFs) and internal CuFe2O4-CuO composite NFs, were constructed by electrospinning. The sensor performances of these configurations were comprehensively evaluated at 0.1–1 ppm H2S and 1–10 ppm NO2 under 250 °C-450 °C. The gas selectivity of NF-based sensors towards various gases was evaluated. Results proved that the sensor based on the internal n-p CuFe2O4-CuO composite NFs significantly improved gas-sensing capabilities. On the contrary, the external n-p CuFe2O4/CuO mixed NFs exhibited lower efficiency than the pristine CuFe2O4 NFs. The cause of the gas-sensing properties of these materials was demonstrated using positron annihilation measurements. CuFe2O4 played a vital role in the change of electron configurations in the n-p HJs of the CuFe2O4-CuO composite NF, which also could be formed with more n-p HJs having extremely low-electron densities compared with CuFe2O4/CuO mixed NFs. The deep transfers of the conduction electrons and the holes in the internal CuFe2O4-CuO NFs were different, which produced an asymmetrically depleted region in the n-p HJs. This study contributed to the literature on the gas-sensing mechanism of metal oxide semiconductor-based n-p HJs. © 2025 Elsevier Ltd and Techna Group S.r.l.