4.6 Article

Effect of substrate temperatures on structural, optical and dispersion energy parameters of RF sputtered nickel oxide thin films

Journal

MATERIALS CHEMISTRY AND PHYSICS
Volume 294, Issue -, Pages -

Publisher

ELSEVIER SCIENCE SA
DOI: 10.1016/j.matchemphys.2022.127007

Keywords

Nickel oxide; Optical property; Sputtering; Thin film; Optoelectronic; Electrochromism

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Thin films of nickel oxide (NiO) were prepared by RF magnetron sputtering at different substrate temperatures, and the effects of temperature on their structural, morphological, optical, and vibrational properties were investigated. It was found that an increase in substrate temperature led to higher crystallinity and smoother surface morphology of the NiO films. The optical transmittance and bandgap of the films also varied with substrate temperature. The optical and dispersion energy parameters of NiO films were affected by temperature as well. The results suggest the potential application of NiO films in optoelectronic and electrochromic devices.
Thin films of nickel oxide (NiO) have been widely identified as a promising ion storage layer in electrochromic devices owing to their excellent electrochemical properties. There is, however, a lack of accurate description of their optical parameters, which are quite important to explore the optical and electrochromic characteristics of NiO. In the present investigation, nickel oxide (NiO) thin films have been deposited using radio frequency (RF) magnetron sputtering at different substrate temperatures (Tsub) viz. 100, 200 and 300 degrees C. The consequences of substrate temperature on the structural, morphological, optical, and vibrational properties were examined. The XRD pattern showed increased crystallinity with an increase in substrate temperature. Surface morphology revealed an ultrafine and smooth morphology. The average optical transmittance varied between 64% and 85%. Shrinkage in the energy bandgap was observed with the change in substrate temperature. The values of optical parameters like refractive index (n), extinction coefficient (k), the real part of the dielectric constant (epsilon 1), the imaginary part of the dielectric constant (epsilon 2), and porosity of NiO films were found to change with an increase in substrate temperature. The effect of substrate temperature on dispersion energy parameters (Eo and Ed) derived from the Wemple-DiDomenico model was calculated and discussed in detail. Room temperature photo-luminescence studies revealed peaks along 3.39 eV (365 nm) and 2.95 eV (420 nm) nm as a consequence of band -band PL phenomena for nickel oxide and defects. In the Raman spectrum, one predominant peak around 560 cm-1 corresponds to the one-phonon LO mode, and another minor peak at 1100 cm-1 owing to the two-phonon LO mode were observed, which arises from Ni-O vibrations. The observed results reveal the potential application of the NiO films in optoelectronic and electrochromic device applications.

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