Electronic structure of NiO

The effect of the withdrawal speed on properties of nickel oxide thin films

Nickel oxide thin films have been prepared by sol-gel dip-coating technique on glass substrate. It is shown that nickel oxide thin films have poly crystalline nature. Nickel oxide thin films exhibit high transmission (39–85%) in the wavelength range of 400–900 nm, strong absorption between 300 and 400 nm wavelengths and decrease of band gap values are in the range 3.69–3.27 eV with increase of withdrawal speed. High band gap at low withdrawal speed is because of the small average crystallite size, which decreases with increase in withdrawal speed. The SEM micrograph shows cubic crystallites and surface of thin films become dense, smooth and homogeneous with an increase in withdrawal speed. Assessment of nickel oxide deposition conditions provides gateway for effective and cheap solar cells.

A Study on the Thermodynamics of Grain Growth in R.F. Magnetron Sputtered NiO Thin Films

Postdeposition annealing of thin nickel films synthesized using R.F. magnetron sputtering technique is carried in this study. The XRD analysis indicates that annealing of the nickel films leads to the formation of nickel oxide with a preferential growth along (200) plane. The oxidation mechanism is observed with a phase transformation and results in polycrystalline NiO films. The surface morphology of the thin films was investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM) as a function of annealing temperature. The studies indicate the formation of well-defined grain boundaries due to agglomeration of nanocrystallites. The films annealed in the range 573–773 K are found to be porous. The optical transmission spectra of the films annealed at 773 K exhibit interference effects for photon energies below the fundamental absorption edge. The optical studies indicate the existence of direct interband transition across a bandgap of 3.7 eV in confirmation with earlier band structure calculations.