Localized Energy Band Bending in ZnO Nanorods Decorated with Au Nanoparticles.

Luca Bruno,Giorgia Franzò,Mario Scuderi,Francesco Priolo,Vincenzina Strano,Salvo Mirabella

doi:10.3390/nano11102718

Luca Bruno, Giorgia Franzò + Show 4 more

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https://doi.org/10.3390/nano11102718

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Abstract

Surface decoration by means of metal nanostructures is an effective way to locally modify the electronic properties of materials. The decoration of ZnO nanorods by means of Au nanoparticles was experimentally investigated and modelled in terms of energy band bending. ZnO nanorods were synthesized by chemical bath deposition. Decoration with Au nanoparticles was achieved by immersion in a colloidal solution obtained through the modified Turkevich method. The surface of ZnO nanorods was quantitatively investigated by Scanning Electron Microscopy, Transmission Electron Microscopy and Rutherford Backscattering Spectrometry. The Photoluminescence and Cathodoluminescence of bare and decorated ZnO nanorods were investigated, as well as the band bending through Mott–Schottky electrochemical analyses. Decoration with Au nanoparticles induced a 10 times reduction in free electrons below the surface of ZnO, together with a decrease in UV luminescence and an increase in visible-UV intensity ratio. The effect of decoration was modelled with a nano-Schottky junction at ZnO surface below the Au nanoparticle with a Multiphysics approach. An extensive electric field with a specific halo effect formed beneath the metal–semiconductor interface. ZnO nanorod decoration with Au nanoparticles was shown to be a versatile method to tailor the electronic properties at the semiconductor surface.

Highlights

Zinc oxide (ZnO) is an n-type semiconductor attracting great attention due to its physical and chemical properties [1,2]
ZnO nanorod decoration with Au nanoparticles was shown to be a versatile method to tailor the electronic properties at the semiconductor surface
We systematically investigated the decoration of ZnO NRs with Au NPs and its effect on position and population of electronic energy bands

Summary

Introduction

Zinc oxide (ZnO) is an n-type semiconductor (band gap of 3.2–3.4 eV, large excitonicbinding energy of 60 meV) attracting great attention due to its physical and chemical properties [1,2]. A controlled improvement of performance needs a microscopic understanding of ZnO surface states and deep levels, especially in low-dimensional nanostructures where the significant surface-to-bulk ratio significantly impacts electronic energy band bending. The surface decoration of semiconductor nanostructures with metallic nanoparticles (NPs) usually leads to an improvement of their catalytic and electrical properties [10,11,12,13,14]. The formation of nano-Schottky junctions at the metal–semiconductor interface leads to the creation of a strong electric field directed toward the surface and to a significant modification of the ZnO NRs energy band profiles [15,16,17,18,19].

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