Herein, a facile fabrication process of ZnO-ZnFe2O4 hollow nanofibers through one-needle syringe electrospinning and the following calcination process is presented. The various compositions of the ZnO-ZnFe2O4 nanofibers are simply created by controlling the metal precursor ratios of Zn and Fe. Moreover, the different diffusion rates of the metal oxides and metal precursors generate a hollow nanostructure during calcination. The hollow structure of the ZnO-ZnFe2O4 enables an enlarged surface area and increased gas sensing sites. In addition, the interface of ZnO and ZnFe2O4 forms a p-n junction to improve gas response and to lower operation temperature. The optimized ZnO-ZnFe2O4 has shown good H2S gas sensing properties of 84.5 (S = Ra/Rg) at 10 ppm at 250 ∘C with excellent selectivity. This study shows the good potential of p-n junction ZnO-ZnFe2O4 on H2S detection and affords a promising sensor design for a high-performance gas sensor.

Interfacial and electrical properties of Al 2 O 3 /SiO 2 /Si were analyzed to determine the change in interfacial defects and suboxide density according to the thickness of the SiO 2 layer and to determine the effect on dipole and flat-band voltage. As the thickness of the SiO 2 layer increased (5/7/10 nm), the density of the suboxide present at the interface (2.23/3.23/4.73 × 10 14 atoms/cm 2 ) also increased, respectively. In addition, the slow state density, fixed oxide charge density, and interface state density calculated through the capacitance−voltage (C−V) curve all differ depending on the thickness of the SiO 2 layer and are further reduced by postmetallization annealing (PMA). The flat-band voltages (V FB ) of the SiO 2 /Si sample with thicknesses of 5, 7, and 10 nm before PMA are −1.27, −1.32, and −2.20 V, respectively, and further decreased after PMA (−0.64, −0.80, and −1.74 V). Consequently, it was demonstrated that there was a difference in interfacial defects and suboxides according to the thickness. In addition, it was confirmed that when the interfacial defects and suboxides were reduced, the oxide charge state density and oxygen diffusion decreased, and thus the dipole layer strength and V FB shift decreased.

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