Ni-doped ZnO Thin Films Research Articles

Characteristics of Nickel-doped Zinc Oxide thin films prepared by sol–gel method

Transparent and conductive high preferential c-axis oriented Ni-doped ZnO (NZO) thin films as a function of Ni content have been prepared by sol–gel method using zinc acetate and nickel acetate as starting material, anhydrous ethanol and 2-methodxyethanol as solvent. The NZO thin films with a dopant ratio (0.2, and 0.4 mol%) have a preferred orientation in the (002) direction. However, when the Ni doping ratio exceeds 0.6 mol%, films possessed a non-textured polycrystalline structure. The electric and optical properties of the Ni doped ZnO films were found to be strongly dependent on the Ni contents. The lowest resistivity value was 4.8×10−4 Ω cm, which was obtained in the 0.2 mol% Ni-doped ZnO thin film. The improvement of the electrical and optical properties of NZO films may be related to the both increase in the concentration of oxygen vacancies and free carries of Ni ions. The average optical transmittance values of the 0.2 mol% Ni-doped NZO thin films were more than 91.2% in the visible range.

Influence of structure characteristics on room temperature ferromagnetism of Ni-doped ZnO thin films

The influence of structure characteristics on the ferromagnetism of Ni-doped ZnO (ZnO:Ni) thin films prepared by pulsed laser deposition has been investigated by magnetization and resistivity measurements. Structural and optical absorption analyses revealed that Ni has been incorporated into ZnO lattice as Ni2+ substituting for Zn2+ ions and the microstructure of the films becomes more inhomogeneous with increasing Ni content. The room temperature ferromagnetic (FM) behavior only occurs when Ni content is not high and the saturation magnetic moment per Ni atom decreases with increasing Ni content. No FM signal was detected for the film with 7at.% Ni content. Interestingly, the carrier density decreases with the increase of Ni doping from 1to5at.%, whereas an increase of carrier density is observed for 7at.% doped film, which indicates that carrier density alone cannot account for the FM property in ZnO:Ni films. All the results demonstrated that the microstructure of ZnO:Ni films gets more deteriorated with increasing Ni content and it is unfavorable for the long-range FM order in the ZnO:Ni films.

Nanostructured zinc oxide gas sensors by successive ionic layer adsorption and reaction method and rapid photothermal processing

Undoped and Sn, Ni-doped nanostructured ZnO thin films were deposited on glass substrates using a successive ionic layer adsorption and reaction (SILAR) method at room temperature. The SILAR deposited zinc oxide films have been rapid photothermal processing (RPP) at various temperatures to study the effect of annealing on the sensing properties. Structural, electrical and sensing properties were investigated by means of X-ray diffraction (XRD), Energy Dispersive X-ray spectroscopy, scanning electron microscopy, electrical resistivity, and sensitivity measurements. Microstructures of the deposited films were studied for different concentrations of dopants and zinc-complex solution and temperatures. The results of influence of growth processes, doping, and RPP on phase structure, surface morphology, particles size and resistivity values are presented and discussed. The average grain size determined from XRD patterns was 240, 220 and 265 Å for ZnO, Sn–ZnO and Ni–ZnO films, respectively. Moreover, electrical characterization of the sensors prepared from SILAR deposited nanostructured zinc oxide thin film has been carried out. The variation in resisitivity of the ZnO film sensors was obtained with doping and post-deposition rapid photothermal processing in vacuum and N 2 ambient. Electrical resistivity measurements showed semiconducting nature with room temperature resistivity 1.5 × 10 5, 6.1 × 10 2, 70 Ω cm for as-deposited ZnO, 4 at.% Ni–ZnO and 4 at.% Sn–ZnO, respectively. These values decreased to 1 × 10 4, 2 × 10 2, 30 Ω cm for RPP annealed films. The types of doping and temperatures of RPP were found to have an important role in determining the sensitivity and resolution of the NO 2, NH 3 ZnO-based sensors. While the nanostructured ZnO sensor showed higher ammonia sensitivity than that of NO 2, an enhanced NO 2 sensitivity was noticed with the ZnO films doped with 4 at.% Sn and higher NH 3 sensitivity was obtained by 4 at.% Ni doping of zinc oxide thin films.

Nitrogen oxides and ammonia sensing characteristics of SILAR deposited ZnO thin film

Abstract Pure and Sn, Ni doped ZnO thin films were deposited on glass substrates using a novel successive ionic layer adsorption and reaction (SILAR) method at room temperature. Microstructures of the deposited films were optimized by adjusting growth parameters. The variation in resistivity of the ZnO film sensors was performed with rapid photothermal processing (RPP). The effect of rapid photothermal processing was found to have an important role in ZnO based sensor sensitivity to NO 2 , NH 3 . While the undoped ZnO film surface exhibited higher NH 3 sensitivity than that of NO 2 , an enhanced NO 2 sensitivity was noticed for the ZnO films doped with Sn and higher NH 3 sensitivity was obtained by Ni doping.

Doping concentration dependence of room-temperature ferromagnetism for Ni-doped ZnO thin films prepared by pulsed-laser deposition

High-quality Ni-doped ZnO thin films of single phase with preferred c-axis growth orientation were formed on Si (100) substrates by pulsed-laser deposition at room temperature. The films exhibited room-temperature ferromagnetic behaviors with saturation magnetic moment per Ni atom of 0.37μB,0.26μB,0.25μB and 0.21μB for the Ni concentration of 1, 3, 5, and 7 at. %, respectively. The decrease of ferromagnetism with doping concentration demonstrates that ferromagnetism observed at room temperature is an intrinsic property of Ni–ZnO thin films, not from any secondary phase.