Significant enhancement in the cold emission characteristics of chemically synthesized super-hydrophobic zinc oxide rods by nickel doping

Abstract

The current article presents a huge enhancement in the field emission characteristics of zinc oxide (ZnO) micro/nanorods by nickel doping. The synthesis of pure and nickel-doped zinc oxide (ZnO) micro/nanorods was done by a simple low-temperature chemical method. Both the as-prepared pure and doped samples were analyzed by X-ray diffraction and electron microscopy to confirm the proper phase formation and the developed microstructure. UV-vis transmittance spectra helped in determining the band gap of the samples. Fourier-Transform Infrared Spectroscopy (FTIR) spectra showed the different bonds present in the sample, whereas X-ray Photoelectron Spectroscopy (XPS) confirmed the presence of nickel in the doped sample. Photoluminescence (PL) spectra showed that after doping, the band-to-band transition was affected, whereas defect-induced transition had increased significantly. After the nickel doping, contact angle measurement revealed a significant decrease in the sample's surface energy, leading to a remarkably high water contact angle (within the superhydrophobic region). Simulation through ANSYS suggested that the doped sample has the potential to function as an efficient cold emitter, which was also verified experimentally. The cold emission characteristics of the doped sample showed a significant improvement, with the turn-on field (corresponding to J = 1 μA cm⁻²) reduced from 5.34 to 2.84 V μm⁻¹. The enhancement factor for the doped sample reached 3426, approximately 1.5 times higher compared to pure ZnO. Efforts have been made to explain the results, given the favorable band bending as well as the increased number of effective emission sites.