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Letter
Plasmonic Metal-to-Semiconductor Switching in Au nanorod-ZnO nanocomposite films Fei Wu, Limei Tian, Ravindra K. Kanjolia, Srikanth Singamaneni, and Parag Banerjee ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/am402309x • Publication Date (Web): 02 Aug 2013 Downloaded from http://pubs.acs.org on August 4, 2013
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ACS Applied Materials & Interfaces
Plasmonic Metal-to-Semiconductor Switching in Au nanorod-ZnO nanocomposite films Fei Wu1, Limei Tian1, Ravindra Kanjolia2, Srikanth Singamaneni1, Parag Banerjee1* 1
Department of Mechanical Engineering and Materials Science, One Brookings Drive,
Washington University in St. Louis, St. Louis, MO – 63130. 2
SAFC Hitech, 1429 Hilldale Ave, Haverhill, MA – 01832.
*Corresponding Author, email:
[email protected] Abstract: We demonstrate conductivity switching from a metal to semiconductor using plasmonic excitation and charge injection in Au-nanorod (AuNRs)-ZnO nanocomposite films. ZnO films 12.6, 20.3 and 35.6 nm were deposited over AuNRs using atomic layer deposition. In dark condition, the films transitioned from metallic to semiconducting behavior between 150 K200 K. However, under sub-band gap, white light illumination, all films behaved as semiconductors from 80 K – 320 K. Photoresponse (light/dark conductivity) was strongly dependent on thickness of ZnO; being 94.4 for AuNR–12.6 nm ZnO and negligible for AuNR– 35.6 nm ZnO. Conductivity switching and thickness dependence of photoresponse were attributed to plasmonically excited electrons injected from AuNRs into ZnO. Activation energies for conduction were extracted for these processes. Key Words: Plasmon Enhancement, Atomic Layer Deposition, Au Nanorods, Temperature Dependent Conductivity, Photoresponse, ZnO
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Introduction:
Photon management using plasmonics is a new method to trap and absorb light inside various semiconductor thin films and nanostructures.1-4 Shape-controlled Au nanostructures have been extensively studied, owing to their localized surface plasmon resonance (LSPR) in the visible and near infrared parts of the electromagnetic (EM) spectrum.1, 5-7 Recently8-9 it has been shown using a layered combination of Au nanoparticles (NPs) and TiO2 film, that light absorption and resultant photoresponse can be made to map the spectral behavior of the plasmon resonance in the AuNPs rather than the fundamental absorption mode (3.3 eV) of the TiO2 thin film. Thus, this approach decouples a film’s ability to absorb light (governed by its band gap, Eg ~ 3.3 eV) from its optoelectronic response. Further, increased light absorbance while lowering film thicknesses has provided a promising way to improve photocurrent responses and overall 1 ACS Paragon Plus Environment
ACS Applied Materials & Interfaces
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efficiencies of energy harvesting devices such as photocatalytic, photoelectrochemical and dyesensitized solar cells.4, 8,
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In this letter, we report on the temperature dependent (80 K-320 K) conductivity behavior of Au nanorod (AuNR)-ZnO nanocomposite films under dark and sub-band gap (
