An investigation of the electrical behaviours of metallic, semiconducting and core-shell nanowires
Citation:
MANNING, HUGH, An investigation of the electrical behaviours of metallic, semiconducting and core-shell nanowires, Trinity College Dublin.School of Chemistry.CHEMISTRY, 2018Abstract:
From a device point of view, metallic nanowire networks provide a route to highly transparent, highly conductive, flexible, easy-to-fabricate and low-cost materials. The large-scale integration of these materials in commercial devices could revolutionise display, touch screen, as well as numerous emerging applications. To assess the true potential of metallic nanowire network systems, it is crucial to establish a complete understanding of their individual physical properties and how these properties affect performance of the network. This requires a part-to-whole consideration of the network, evaluating and characterising each aspect of the system, such as the ability of the nanowire to conduct electrical charge and the amount of electrical resistance at each of the nanowire junctions. Characterising these elements is a central goal of this thesis and critical to the development of high-performance transparent conductors based on metallic nanowire networks. In this work, experimentally reported literature data was matched with the optoelectronic performance described using an ab initio model derived from fundamental material properties, electrical equations and optical performance based on Mie scattering of light by small particles. The predictive power this model enables a material-by-design approach, whereby suitable systems can be prescribed for targeted technology applications.
A further goal of this research is to engineer the coating of Ag nanowires to add new and novel functionality. One highly desirable response is the memristive behaviour demonstrated by the semiconducting TiO2 material. We show that 1 ?m long individual TiO2 nanowire devices display a continuum of resistance levels when electrically stressed; rather than a singular high- or low-resistance state most commonly found in resistive switching materials. This dynamic generation of charge carriers causes a memristive behaviour and allows an arbitrary number of conductance states to be defined in the device. Through a combination of optical and voltage pulses is also shown that single nanowire devices can demonstrate an associative memory effect whereby a significant enhancement of the current response is observed when both stimuli are applied simultaneously.
The TiO2 element was incorporated into core-shell nanowires which combined a highly conductive Ag core with a TiO2 shell, shortening the active switching region to the nm scale. Ag nanowires are coated in sheaths of TiO2 of various crystalline qualities and contacted with both passive (Au) and active (Ag) electrodes to identify the ingredients necessary for engineering controllable resistive switching. It was found that a polycrystalline TiO2 shell and Ag electrodes allowed for controllable operation of bipolar and unipolar resistive switching regimes. The presence of both switching regimes is termed nonpolar resistive switching; this work demonstrates controllable nonpolar operation for the first time in a single nanowire system. The memory retention time could be selected by the magnitude of the current used to activate the device. This allowed for a short-term retention (up to 103 s) to be established in the bipolar state with long-term memory (> 106 s) demonstrated in the unipolar regime. ON/OFF ratios of 105 and 107 are demonstrated for bipolar and unipolar modes respectively. These results provide a foundation for engineering resistive switching behaviours for memory storage and hardware-based neuromorphic applications in core-shell nanowires.
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Grant Number
European Research Council (ERC)
Author's Homepage:
http://people.tcd.ie/manninhDescription:
APPROVED
Author: MANNING, HUGH
Advisor:
Boland, JohnPublisher:
Trinity College Dublin. School of Chemistry. Discipline of ChemistryType of material:
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Full text availableKeywords:
silver, titanium dioxide, core-shell, nanowire, resistive switching, memristive, junction, resistance, transparent, conductor, Mie theoryMetadata
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