Fabrication of Thiol-Functionalized Ni-Doped ZnO Thin Films for Room-Temperature Ferromagnetism

Ferromagnetism in Ni-doped (3, 5, and 7 mol%) ZnO thin film has been enhanced by an approach that alters the electronic configuration of ZnO by surface functionalization (capping) with organic molecules. Dodecane thiol was used as a functionalization agent to enhance ferromagnetism in Ni-doped ZnO thin films grown by RF magnetron sputtering. The hexagonal wurtzite structure of ZnO was confirmed by X-ray diffraction analysis. The crystallite size decreases till 5 mol% Ni and then decreases further with the increase of Ni concentration. The pulsed laser emission intensity at 2.7 eV reveals the presence of oxygen vacancies, which actually mediate ferromagnetism in Ni
²⁺
-doped ZnO thin films. This green emission further shifted to 2.73 eV upon thiol capping. The saturation magnetization 6.70, 12.09, and 9.59 emu/cm
³
obtained for 3, 5, and 7 mol% Ni-doped ZnO thin films, respectively, is enhanced to 6.92, 13.24, and 11.27 emu/cm
³
by thiol functionalization. The presence of a Zn-S bond in the X-ray photoelectron spectroscopy spectrum reveals the formation of a surface layer between the Zn and S atoms, which could be the reason for the enhanced ferromagnetism.