XPS is carried out to study the elemental composition and valence states in ZnSnO
3/ZnO, and the results are shown in
Figure 3.
Figure 3a shows the full XPS spectrum of the ZnSnO
3/ZnO nanofibers;
thwe
researchers ccan observe that the obtained ZnSnO
3/ZnO nanofibers contain the elements Zn, Sn, C, and O. The peak at 284.8 eV corresponds to the spin-orbit peak of C 1s. The broad XPS spectrums of the Zn 2p range, Sn 3d, and O 1s range are shown in
Figure 3b–d. In the case of the Zn 2p spectrum, the Zn 2p peak can be distributed into two signals, as shown in
Figure 3b. The Zn-2p
3/2 and Zn-2p
1/2 signals are focused at 1021.1 eV and 1044.1 eV, respectively, which indicates that the chemical valence of Zn in the system is +2
[22]. As shown in
Figure 3c, the two peaks at 486.8 and 495.1 eV correspond to the Sn 3d
5/2 and Sn 3d
3/2 spin-orbit peaks, respectively. The bimodal spin-orbit shows a split value of approximately 8.3 eV, indicating the presence of Sn
4+ cations
[23]. The O 1s spectrum of the ZnSnO
3 and ZnSnO
3/ZnO is illustrated in
Figure 3d,e, which is deconvolved into three characteristic peaks by Gaussian fitting
[16][24][16,24]. The three fitting peaks are attributed to three essential oxygen species
[25], which are denoted as O
L, O
V, and O
C, respectively, corresponding to O
2− species in the lattice oxygen species, vacancy oxygen species (VO
S), and chemically adsorbed or dissociated oxygen species, respectively
[26]. The three characteristic peaks of O 1s in the ZnSnO
3 nanofibers are located at 530.06 eV, 531.65 eV, and 533.13 eV. In contrast, the distinct peaks of O 1s in the ZnSnO
3/ZnO nanofibers are located at 529.99 eV, 531.33 eV, and 532.27 eV, which can be ascribed to the three significant oxygen species, represented as O
L, O
V, and O
C, respectively
[17][27][17,27]. It must be pointed out that the gas-sensing properties may be highly dependent on the type of VO (vacancy oxygen) present on the semiconductor surface
[28]. The proportion of oxygen species in the obtained ZnSnO
3 and ZnSnO
3/ZnO nanofibers are shown in
Figure 3f and
Table 1. The results of
Figure 3f and
Table 1 clearly indicate that compared with the percentage of Ov of ZnSnO
3 nanofibers, that of ZnSnO
3/ZnO nanofibers is substantially larger.