Manipulation of Vanadium Oxide Characteristics for Applications: Resistive switching & Reflectance Anisotropy Spectroscopy
Citation:
Murtagh, Oisín, Manipulation of Vanadium Oxide Characteristics for Applications: Resistive switching & Reflectance Anisotropy Spectroscopy, Trinity College Dublin.School of Physics, 2022Download Item:
Abstract:
This thesis deals with the study of vanadium dioxide, vanadium pentoxide and the mixed 4+ and 5+ valence vanadium oxide phases, or Wadsley phases. Thin films (VO2) and single crystals (V2O5) are examined. Vanadium dioxide is of particular interest to novel future electronic applications due to a large and accessible metal-insulator transition (MIT). The aim of this work is to enable the use of vanadium oxides through the physical understanding of their properties, and leveraging this understanding to manipulate the material's properties to enable novel and useful applications. Specifically, manipulation of VO2's resistive switching is explored via (i) the application of pulsed voltage signals and (ii) through the forming of VO2 from the reduction of V2O5 single crystals.
In this thesis, three main studies are carried out. First, vanadium dioxide thin film devices are fabricated that exhibit a voltage-driven metal insulator transition. It is found that the intrinsic hysteresis of this transition is due to Joule heating in the low resistance phase, and that the hysteresis width can be changed by applying pulsed voltage signals of different lengths. Computer simulation via Python is leveraged to confirm the Joule heating effect through modelling of the sample temperature.
In the second study, it is found that V2O5 crystals, when annealed in vacuum, form a surface layer composed of Wadsley phases and VO2. This layer exhibits a VO2-like MIT which undergoes an electric-field-driven MIT at a very low field of 425 V/m. This is found to be due to Joule heating in the surface layer, which shows a low resistance. Analysis of crystals annealed at four different temperatures at different time intervals is presented to illustrate how V2O5 evolves over continuous vacuum annealing. Vanadium oxide phases V6O13, V4O9 and VO2(B) are all identified to be present in this evolution. Transmission electron microscopy is used to identify the geometry of the phases present in the surface layer after annealing.
In the third study, the optical anisotropy of pristine and annealed V2O5 crystals is studied using reflectance anisotropy spectroscopy (RAS). The RAS spectrum of the V2O5(010) surface is presented, along with RAS features of V6O13 and V4O9. This is achieved through analysis of four samples annealed at different temperatures. Comparisons of x-ray diffraction, resistance and RAS measurements allows particular features to be identified and matched to particular phases. The effect of the VO2 MIT on RAS measurements is characterised. Computational modelling via Python is used to simulate and confirm V2O5 and V6O13 RAS measurements.
Sponsor
Grant Number
The Naughton Foundation
Author's Homepage:
https://tcdlocalportal.tcd.ie/pls/EnterApex/f?p=800:71:0::::P71_USERNAME:MURTAGHODescription:
APPROVED
Author: Murtagh, Oisín
Sponsor:
The Naughton FoundationAdvisor:
Chvets, IgorPublisher:
Trinity College Dublin. School of Physics. Discipline of PhysicsType of material:
ThesisAvailability:
Full text availableMetadata
Show full item recordLicences: