LITERATURE REVIEW

LITERATURE REVIEW

              Zhang et al. (2008) have fabricated Ni-doped ZnO nanocrystals have been by using a simple chemical Vapor-deposition method. Such one-dimensional nanoscale nanocombs arrays may indicate a new way to assemble semiconductor nanowires into ordered. Microstructure analyses and RTPL measures indicate Ni2+ substitute into ZnO lattice at Zn2+ site and show doping influences the light emission behaviour result in a slightly blue shift emission. The simple friendly environment doping technique can be applied to fabricate other semiconductors nanocombs or Nano cantilevers and may be applicable on large scale applications in nanotechnology.

              Chauhan et al. (2011) reported that method of chemical co-precipitation to prepare nano crystals of undoped and nickel doped ZnO. The crystalline structure was determined by XRD while optical properties and band gap were determined by UV-visible spectra. XRD result shows that the prepared samples are in hexagonal wurtzite phase. By controlling the reaction temperature the particle size can be adjusted. The average size of nanoparticle depends on temperature and amount of nickel doping. The size increases as temperature is increased and decreases as the percentage doping of nickel metal is increased. The strongest absorption peak observes at 260 nm, which is blue shifted from the absorption edge of bulk ZnO (365 nm). The band gap value of prepared undoped and nickel doped ZnO nanoparticles decreases when annealing temperature increases from 300 to 800oC. Optical absorption measurements indicate red shift in the absorption band edge upon Ni doping.

              Straumal et al. (2011) reported that the ferromagnetism properties of pure ZnO at room temperature with post oxidation annealing in air. ZnO nanoparticles annealed at different temperature showed clear hysteresis loops at room temperature. Different techniques such as selected area electron diffraction, x-ray diffraction, and x-ray photoelectron spectroscopy measurements indicate that all the samples possess a typical wurtzite structure without other impurity phases. Defects existing in fabricated samples were observed by the results of the Raman spectra. It is found that ferromagnetism decreases with increasing particle size of nanoparticles. It is also found that the ferromagnetism of ZnO nanoparticles improves after annealing in vacuum condition and decrease after annealing in a rich-oxygen atmosphere which confirm that the oxygen vacancies play an important role for ferromagnetism behaviour in the ZnO nanoparticles.

              Saleem et al. (2012) reported that the transparent ZnO thin films were deposited on glass substrate by a multi-step sol-gel technique by increasing the molar concentration from 0.35 to 0.65 M. The structural, morphological and optical properties were investigated. It is reported that the structural and optical properties were improved by changing sol-gel molar concentration. XRD results exhibited that a hexagonal wurtzite structure with (002) plane after annealing at 400˚C for 1hour in air ambiance. The grain size and the thickness of the films depend on sol-gel concentration and changes from 15.3 to 19.7 nm and 266 to 295 nm respectively when the sol concentration increases from 0.35 M to 0.65 M. SEM result of ZnO thin film indicates that the small grains made a smooth surface with fine structure and the grain become more uniform and bigger in size. When the sol concentration changes from 0.35 to 0.65 the average transmittance of the samples are 83 to 95% in the visible wavelength range from 400 to 800 nm while band gap energies are found to be 3.307 to 3.227 eV.

              Gopala et al. (2010) reported that Ni-doped nanoclusters have different microstructure having no change in a hexagonal wurtzite structure. XRD measurements reveal that average crystalline size decreases from 37.5 to 26.6 nm for x = 0 to 0.05. The change in lattice parameters, micro-strain, shift of XRD peaks and the blue shift of energy gap from 3.18 to 3.33 eV (DEg = 0.15 eV) for Ni from 0.0 to 0.02 and red shift of Eg from 3.33 to 3.14 eV (DEg = 0.19 eV) for Ni from 0.02 to 0.05 showed the substitution of Ni2 ions into ZnO lattice. FTIR spectra showed that the presence of functional groups and the chemical bonding. The shift of NBE UV emission between 374 and 395 nm, the shift of green band emission between 517 and 531 nm, the change in intensity and the broadening effect in the photoluminescence spectroscopy indicates the substitution of Ni2+ ions into the ZnO.

              Vijayaprasath et al. (2014) reported that pure and Ni doped ZnO nanoparticles are synthesis by co precipitation method. Rod shaped structure of Ni doped ZnO was observed by XRD. Ferromagnetic behaviour was observed at room temperature. VSM showed the diamagnetic behaviour of pure ZnO and 3% Ni doping in ZnO makes the samples as weak ferromagnetic at room temperature. The d-spacing of samples matches with standard data. The XRD pattern of Ni doped ZnO are same as that of pure ZnO, showing small amount of Ni doping did not change the ZnO structure.

              Kulkarni et al. (2015) reported that zinc oxide is a semiconductor material with the energy gape of 3.37 eV has the unique properties and large excitation energy at almost room temperature enables is to be used in electronics and optoelectronics. Most importantly it is transparent, environment friendly and very much non-toxic. Due to above reasons the ZnO NPs were synthesized by sol-gel method using NaOH and zinc acetate as initial materials with distilled water as a solvent. The synthesized nanoparticles were subjected to the different characteristics to investigate the structure, morphology and other properties by using XRD, SEM and EDAX. The optical properties have been studies using UV visible spectrophotometer. FTIR analysis has been opted for the confirmation of ZnO NPs.

            Raja et al. (2014) reported that Ni-doped ZnO nanoparticles (Zn1-xNixO, where x = 0.00, 0.02, 0.04, 0.05, 0.06 and 0.08) were synthesized by the chemical co-precipitation method. The sample are characterized by using X-Ray Diffraction (XRD), Energy Dispersive X-ray spectroscopic analysis (EDX), UV–Visible absorption (UV-V),Photoluminescence Spectroscopy(PL) and Vibrating Sample Magnetometer (VSM) to investigate the structural, optical and magnetic properties. XRD results show that the lattice constants of Zn1-xNixO, of x > 0.0 are slightly larger than the ones of pure ZnO and both pure and doped ZnO samples exhibit hexagonal wurtzite structure. There is no additional peak appear corresponding to secondary phases of Ni in ZnO. The presence of Ni is confirmed by EDX data and UV-Vis spectroscopy indicate that Ni ions exist in octahedral crystal field in the divalent valence state with no change in the wurtzite crystal structure of ZnO. It is also consider that the observed red shift in the optical absorption band edge and PL spectra with Ni-doping in ZnO may be due to the sp-d exchange interactions between the band electrons and the localized d-electrons of the Ni2+ ions, thus Ni2+ ions substitute Zn2+ ions in the crystal lattice. Ni-doped ZnO show distinctly hysteresis loops at room temperature, indicating the ferromagnetic behaviour of the samples investigated by VSM. Magnetic properties of ZnO nanoparticles are due the defects states of ZnO.

              Parihar et al. (2018) reported that nanotechnology deals with materials at Nano size. At this level surface to the volume ratio has large value. Due to this the intrinsic properties of materials vary. Due to large band width and high excitation potential the zinc oxide nanoparticles attracted the researcher today. This large band width and high potential capability it is used in the electronics and optoelectronics. The zinc oxide nanoparticles have different magnetic and structural properties from the bulk matter making it significantly important to be used in different fields. Our aim of study is to study comprehensively the properties of the Ni-ZnO nanoparticles.

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