Morphological evolution and its correlation with optical and field emission properties in pulsed laser deposited ZnO nanostructures

Abstract The present report illustrates the effect of growth temperature on the morphological features, optical, and field emission properties (FE) of ZnO thin films deposited on Si substrate (100) through the pulsed laser deposition (PLD) technique. The as-deposited films have been characterized by employing various characterizations tools particularly X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), High- resolution TEM, etc., and confirms the successful deposition of the films. It demonstrates that as the growth temperature increases from ∼ 5000C to ∼ 8000C during 30 min, the spherical particle-like nanostructures transform into the truncated nanocones. Further, at a fixed deposition temperature of ∼ 8000C, and with enhancement in the growth time from ∼10 to 30 min, the nanoparticles get transformed into nanocones. Henceforth, the substrate temperature and growth time have been identified as determinant factors for the formation of these ZnO nanocones. XRD and TEM analysis suggest that the majority of nanocones have been aligned epitaxially with a preferred c-axis orientation on the Si substrates. Optical measurements reveal that the optical band gap of ZnO films exhibits a decreasing tendency from ∼3.26 to 3.22 eV with an increase in substrate temperature from ∼ 500 to 8000C. Subsequently, the field emission (FE) measurement of these aligned ZnO nanocones signifies a stable field emission with a low threshold field (2.40 V/μm) and a high field enhancement factor (∼2786). Their tapered morphologies and small tip diameters suggest as-deposited samples to be highly reproducible and henceforth as-deposited ZnO nanocones bearing excellent FE properties, through high-pressure PLD growth method without using any catalyst offer usage in various futuristic electronic applications.