Enhanced and Tunable Absorption Characteristics of Au-nanoparticle Loaded ZnO Nanorods Grown by Hydrothermal Technique

In this work we report materials growth, optical characterization and finite-difference time domain (FDTD) based numerical analysis to study the enhancement and tuning of absorption characteristics of gold nanoparticle loaded ZnO nanorods grown by hydrothermal technique. Scanning electron microscopy imaging confirms that nearly vertically oriented, ordered array of ZnO nanorods can be grown on glass substrates if prior to hydrothermal growth, a seed layer of Al-doped ZnO (AZO) is deposited onto the substrate using drop-casting technique. Optical spectroscopy confirms absorption enhancement of the array with increasing size of gold-nanoparticles attached to the ZnO nanorods. Numerical results obtained from FDTD analysis of the three-dimensional photonic structure confirm that the reduced transmittance observed at ~550 nm is owing to the absorption enhancement caused by plasmonic resonance of the Au-nanoparticles. The simulation results also show that absorption characteristics of such arrays can be conveniently tuned from visible to near-infra-red wavelengths by controlling diameter and areal density of the nanorods. This study also suggests future scopes of research in this area regarding further enhancement and tuning of absorption characteristics of nanoparticle loaded ZnO nanorods grown on an AZO seeded substrate by hydrothermal technique.