Influence of annealing temperature on the sensitivity of nickel oxide nanosheet films in humidity sensing applications

Abstract

Nickel oxide (NiO) nanosheet films were successfully grown onto NiO seed-coated glass substrates at different annealing temperatures for humidity sensing applications. NiO seed layers and NiO nanosheet films were prepared using a sol-gel spin coating and sonicated sol-gel immersion techniques, respectively. The properties of NiO nanosheet films at as-deposited, 300 ℃, and 500 ℃-annealed were examined by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), ultraviolet-visible (UV-vis) spectroscopy, and humidity sensor measurement system. The XRD patterns demonstrate that the grown NiO films have crystalline cubic structures at temperature of 300 ℃ and 500 ℃. The FESEM images show that the large porous nanosheet network spread over the layers as the annealing temperature increased. The UV-vis spectra revealed that all the nanosheet films have the average transmittance below than 50% in the visible region, with absorption edges ~ 350 nm. The optical band gap energy was evaluated in ranges of 3.39 to 3.61 eV. From the obtained humidity sensing results, it shows that 500 ℃-annealed film exhibited the best sensitivity of 257, as well as the slowest response time, and the fastest recovery time compared with others.

Annealing temperature dependency of structural, optical and electrical characteristics of manganese-doped nickel oxide nanosheet array films for humidity sensing applications

“…By comparing the same method and temperature from our previous work, 9 this highest sensitivity value has proved that Mn-doped NiO enhanced the sensitivity of the humidity sensor compared to undoped NiO ( S = 257). The list of sensitivity values for each sample is shown in Table 4, together with the response ( T r ) and recovery ( T c ) times.…”

“…In addition, the decrease in sensing performance also may be caused by the higher resistance due to the carrier scattering effect occurring at the grain boundaries. 33 By comparing the same method and temperature from our previous work, 9 this highest sensitivity value has proved that Mn-doped NiO enhanced the sensitivity of the humidity sensor compared to undoped NiO (S ¼ 257). The list of sensitivity values for each sample is shown in Table 4, together with the response (T r ) and recovery (T c ) times.…”

“…This condition shows that the crystallinity of the asdeposited sample is poor and the formation of NiO is still unfinished. 9 For this non-annealed situation, it can be said that the sample exhibits antiferromagnetic behaviour due to the synthesis occurring below the Néel temperature of approximately 523 K. 7 The high background noise from the XRD pattern could be attributed to the low crystallinity properties and thickness of the samples. [24][25][26] Figure 4(b) to (f) shows the XRD patterns annealed at different temperatures.…”

“…[5][6][7] Parimon et al reported NiO-based humidity sensors designed on seedless and seed-coated glass substrates with high sensitivities of 138 and 257, respectively. 8,9 In addition, the authors also successfully fabricated hierarchical NiO nanosheet/ nanoball-flower-like structure films for humidity sensors at low immersion temperatures with a highest sensitivity of 169. 10 However, these previous reports used single NiO compounds rather than heterostructures and composite techniques for the application of humidity sensors.…”