Electrochemical synthesis of Cu/ZnO nanocomposite films and their efficient field emission behaviour

The Cu/ZnO nanocomposite films have been synthesized by cathodic electrodeposition and characterized using X-ray diffractometer (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), photoluminescence (PL) and field emission microscope (FEM). The XRD pattern shows a set of well defined diffraction peaks, which could be indexed to the wurtzite hexagonal phase of ZnO. In addition, characteristic diffraction peaks corresponding to Cu and Zn are also observed. The SEM image shows formation of two-dimensional (2D) hexagonal sheets randomly distributed and aligned almost normal to the substrate. Uniformly distributed small clusters of Cu nanoparticles possessing average diameter of ∼25 nm, as revealed from the TEM image, are seen to be present on these 2D ZnO sheets. The selected area electron diffraction (SAED) image confirms the nanocrystalline nature of the Cu particles. From the field emission studies, carried out at the base pressure of ∼1 × 10⁻⁸ mbar, the turn-on field required for an emission current density of 0.1 μA/cm² is found to be 1.56 V/μm and emission current density of ∼100 μA/cm² has been drawn at an applied field of 3.12 V/μm. The Cu/ZnO nanocomposite film exhibits good emission current stability at the pre-set value of ∼10 μA over a duration of 5 h. The simplicity of the synthesis route coupled with the better emission properties propose the electrochemically synthesized Cu/ZnO nanocomposite film emitter as a promising electron source for high current density applications.