Investigation of NiO film by sparking method under a magnetic field and NiO/ZnO heterojunction

Abstract

Nickel oxide (NiO) film receives attention from the field of optoelectronics due to its wide band gap and high transparency. By using a sparking method, the deposition of the NiO film is facile and unique. However, the NiO film made by the sparking method indicates a porous surface with an agglomeration of its particles. In order to reduce the porousness of the NiO film, the assistance of a permanent magnet in the sparking apparatus is presented. Here, we report the investigation of the NiO film and the p-NiO/n-ZnO heterojunction deposited by the sparking method under a magnetic field. Our results demonstrate that the porosity of the NiO film was reduced by increasing the magnitude of a magnetic field from 0 mT to 375 mT. Furthermore, the crystallinity and the electrical properties of the NiO film are improved by the influent of a magnetic field. For heterojunction, the best device shows the rectification ratio of 95 and the ideality factor of 4.92. This work provides an alternative method for the deposition of the NiO film with promising applications in optoelectronic devices.

Improving the properties of Fe2O3 by a sparking method under a uniform magnetic field for a high-performance humidity sensor

“…12,13 Previously, we showed that an increase in the magnitude of a uniform magnetic eld reduces the porosity and improves the crystal structure as well as the electrical properties of a NiO lm. 14,15 Thus, a sparking method under a uniform magnetic eld could be employed to produce a Fe 2 O 3 lm and optimize its properties for humidity sensors.…”

Influence of Co concentration on properties of NiO film by sparking under uniform magnetic field

“…It is well known that the resistivity is inversely related to the crystallite size 40 . Our method provides the film with two orders of magnitude bigger crystallite size than the films deposited by the solution method due to the influence of the uniform magnetic field on the sparking method as mentioned in our previous report 19,39 . At the higher concentration than 0.1 M, the resistivity of the films increased.…”

“…This result can be interpreted that the bigger Co ions substitute Ni ions in the NiO lattice, causing the formation of defects in the crystal structure. In order to further study the crystallinity and defect of films, we use the following equation 19 :

Figure 1 ( a – e ) SEM images of 0 M, 0.05 M, 0.1 M, 0.15 M and 0.2 M Co-NiO films. ( f ) XRD spectra of samples on glass substrate.

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“…This shift can be interpreted that the Ni 2+ in the NiO lattice is substituted by Co 2+ , which reduces the band gap of the NiO film and increases the concentration of holes due to the Co 2+ having a lower number of electrons in 3d level (3d 7 ) than Ni 2+ (3d 8 ). To further verify the optical band gaps of the samples, we use Tauc’s relation expressed as 19 : where h is Planck's constant, ν is the photon's frequency, A is a proportionality constant, E g is the band gap, α is the absorption coefficient and n is equal to 2 or 1/2 for indirect and direct transitions. By deriving from Tauc’s relation as shown in Fig.…”

“…Their reports illustrate that the morphology of NiO films consists a lot of pores due to the agglomeration of NiO nanoparticles. To reduce the porousness of NiO films, the spark discharge was assisted by a uniform magnetic field, which reported by our previous work 19 . The effect of the uniform magnetic field on the spark discharge not only reduced the porous but also improved crystallinity of NiO films.…”