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. 1. Introduction Nickel oxide (NiO) is considered as a model p-type semiconductor. It is a wide bandgap ( ) transition metal oxide, with a cubic rock-salt structure and antiferromagnetic properties below its Neel temperature 523？K. Transparent conducting nickel oxide films have potential advantages for use as active layers in flat panel displays and gas sensor devices. There has been an increasing interest in developing nanostructured films due to their broad range of applications as catalysts, electrochromic display devices, and fuel cells [1–5]. P-type conducting thin films are required for the fabrication of many optoelectronic devices, which make use of hole injection [6]. Nickel oxide, as one of the relatively few p-type metal oxides, has got considerable attention because of its stable wide bandgap and excellent chemical stability [7]. Recent studies have shown that NiO thin films can make attractive sensing materials in gas like hydrogen and humidity detection devices [8]. There are several reports on nickel oxide thin film preparation by physical vapor deposition [9], electron beam evaporation [10], dip coating [11], sputtering [12–14], spray pyrolysis, chemical vapor deposition, sol gel, and pulsed laser deposition [15]. R.F. magnetron sputtering has been used extensively to fabricate high surface area thin films, having large potential in the region of gas sensing [16]. Attempt has been made in this study to prepare NiO films by postdeposition annealing of R.F. magnetron sputtered thin nickel films and to understand the
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