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Investigations into the electrical properties of hybrid memristor devices containing surface modified zinc oxide nanorods

Gardner, Benjamin

Authors

Benjamin Gardner



Contributors

Neil T. Kemp
Supervisor

Abstract

This thesis focusses on improving the fabrication and electronic switching properties of hybrid memristor devices that have been developed in the nanophysics group at the University of Hull. The devices consist of vertically aligned semiconducting ZnO nanorods embedded within an organic polymer (Polymethyl-methacrylate) matrix. They are made using a novel ultra-fast microwave fabrication technique, which provides a simple and cost effective route to the fabrication of devices in large numbers and on lightweight and flexible substrates.

The primary aim of this work was to improve the resistance on/off ratio in the memristors by modifying the ZnO surface stoichiometry. The nanorods high surface area to volume ratio is expected to be important in the switching since it has been shown that the mobility of defects at surfaces of transition metal oxides is much higher than in the bulk. Thus it is possible that either oxygen vacancies and/or zinc interstitials confined on the surface of the ZnO shuttle up and down along the lengths of the nanorods to mediate the switching. Investigations are focussed on the modification of the nanorod surface through oxygen plasma treatment as well as studying changes in the electrical performance of the nanorods by changing the nanorod diameter.

Investigations into the effects of exposing the nanorods to an oxygen plasma showed increased resistance of both the high and low resistive states (HRS/LRS) of devices. Energy Dispersive X-Ray spectroscopy results indicated that a likely cause of the increased resistance is increased oxygen in the nanorod surface, producing a more stoichiometric (ZnO2) and resistive material.

Attempts at manipulating the overall surface stoichiometry through changes in the surface area to volume ratio, implemented by changing the nanorods diameter, was not successful with the approach used in this work. This was because the nanorod diameter could not be significantly modified through the technique of changing the annealing temperature of the nanocrystal seed layer. This was unexpected as it has been previously reported that the nanorod diameter can be varied between 40nm and 350nm by annealing the seed layer at temperatures between 150°C and 500°C respectively.

It is worth noting throughout the investigations that the use of low incidence X-ray diffraction measurements on the thin-films proved to be a quick and reliable way to confirm nanorod alignment and growth along the C axis.

Citation

Gardner, B. (2016). Investigations into the electrical properties of hybrid memristor devices containing surface modified zinc oxide nanorods. (Thesis). University of Hull. Retrieved from https://hull-repository.worktribe.com/output/4218124

Thesis Type Thesis
Deposit Date Jun 1, 2016
Publicly Available Date Feb 23, 2023
Keywords Physics
Public URL https://hull-repository.worktribe.com/output/4218124
Additional Information Department of Physics and Mathematics, The University of Hull
Award Date Jan 1, 2016

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Copyright Statement
© 2016 Gardner, Benjamin. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright holder.




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