X-ray absorption spectroscopic studies on ZnO/Au hybrid thin films
K. Saravanan1*, S.H. Hsieh1, H.T. Wang2, W.F. Pong1
1Department of Physics, Tamkang University, Tamsui, Taiwan
2Department of Physics, National Tsinghua University, Hsinchu, Taiwan
* presenting author:Kothalamuthu Saravanan, email:saravananmsc05@gmail.com
Semiconductor/metal hybrid plasmonic devices have made major advances in the past few years. However, there are still many challenges in the fundamental understanding and devising applications of these hybrid structures. In the present work, ZnO/Au hybrid films have been studied using X-ray absorption spectroscopic studies. ZnO films with different thickness (20, 50 and 150 nm) were prepared with and without Au film (5nm) using pulsed laser deposition method on quartz substrates. 20 nm ZnO/Au/Qz film has shown enhanced photoluminescence (PL) emission in comparison with ZnO film directly deposited on quartz (ZnO/Qz). X-ray absorption near edge structure (XANES) at the O K-edge and Zn L3,2-edge spectra show that the features of Zn L3,2-edge are found to be same in all the samples. However, the intensity of the O K-edge XANES spectra varies depending on ZnO film thickness and the presence of Au film. The main features located at 533.7, 538.5, 542, 544.5 eV, respectively, are correspond to the transition of electrons from 1s to hybridized orbitals of O 2p and Zn 4sp unoccupied states. In thick film, the intensity of main feature in ZnO/Au/Qz is slightly higher than ZnO/Qz. However, the enhancement increases with the decrease of film thickness. The enhanced intensity may due to more unoccupied states introduced in ZnO which are hybridize with O 2p orbital in the close vicinity of Au NPs, which results and enhanced PL emission in the thinnest film. XANES with additional UV laser excitation of the samples show interesting enhanced intensity in the presence of Au film, which indicates that the surface plasmon resonance (SPR) of Au nanoclusters has strong influence on the optical properties of these hybrid films. X-ray photoelectric spectroscopic studies on these film show slight increase of O 1s peak intensity in the presence Au film, whereas the Zn 3d valence band features are same in all the films. In this work, the optical and structural properties of the ZnO/Au hybrids and the effect of SPR on the optical properties will be discussed in detail with the help of synchrotron radiation based X-ray absorption spectroscopic measurements.

Keywords: Surface plasmon resonance, ZnO, Au nanoparticles, Photoluminescence, X-ray absorption spectroscopy