Fig. 2

a XRD pattern shows the α-NiS nanosphere films at different annealing temperatures (300, 400, and 500 °C). The top view images of the α-NiS films were annealed at b 300, c 400, and d 500 °C for 4 h. Inset: the EDS spectra were in the inset of b–d. e The images showed that XRD patterns (top left), FE-SEM images (top right, 3 h; bottom left, 6 h), and EDS spectra (bottom right) of the α-NiS films at different annealing times (3 and 6 h). f The curves showed the record about temperature and humidity measurements in our laboratory for preservation testing of conditions