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Nanoscale films for near infrared active plasmonic devices

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Title: Nanoscale films for near infrared active plasmonic devices
Authors: Braic, Laurentiu
Item Type: Thesis or dissertation
Abstract: As optoelectronic components become nano-dimensional, controlling the coupling between light and matter at the nanoscale has become a major technological challenge, as well as the subject of theoretical studies. The aim of this work is threefold. First, to assess the suitability of ferroelectric thin films - Barium Strontium Titanate (BST), and Strontium Barium Niobate (SBN), as active media for plasmonic devices. Second, to find suitable thin film electrodes for such devices, by exploring and optimizing the plasmonic behaviour of already known conductive materials, conductive oxides (Strontium Ruthenate - SRO), and transitional metal nitrides (Titanium nitride - TiN). Third, to optimize the deposition process of metallic (Silver – Ag) films, so as to improve their smoothness, and thus their suitability for plasmonic applications and lithography in general. SBN ceramic targets were sintered. SBN and BST films were deposited by PLD and ellipsometry and normal incidence reflectometry were used to examine their optical tunability. Ellipsometry was further used to measure the effects of the residual strain of the BST thin films on their optical properties. BST and SBN films were found to exhibit a birefringence under bias along the direction of growth. A residual strain variation along the films’ direction of growth was inferred from an observed non-linear change in the refractive index of BST films along that same direction. SRO and TiN films were fabricated using PLD and reactive magnetron sputtering, respectively. The effects of the deposition pressure upon structure, charge carrier concentration and mobility, and optical properties were studied using X-ray diffraction (XRD), Hall-effect measurements, and ellipsometry. The optical properties of SRO were explained based on electron concentration and structure. SRO was confirmed as a promising plasmonic material, for applications in the near infrared range and at elevated temperatures. The influence of the deposition temperature upon the optical properties of TiN films was shown. Films grown at high temperature (800oC) had quasi-metallic optical properties, while films grown at room temperature exhibited well defined plasmon bandwidth, between two distinct Epsilon-near-zero (ENZ) frequencies, which has been linked to the uniform oxidation of the samples). Finally, Ag thin films were deposited using magnetron sputtering, in an Ar/He atmosphere. The effect of the sputtering gas ratio on the films structure, morphology and reflectivity was studied using XRD, Atomic force microscopy (AFM) and visual-range normal incidence reflectometry. The addition of Helium to the sputtering atmosphere was found to reduce the roughness of Ag films and improve their reflectivity, due to the Penning effect present in the Ar-He plasma. The work undertaken has, by developing new plasmonic materials (SRO, oxidized TiN), and expanding the knowledge of the behaviour (BST) and fabrication (Ag) here has paved the way for the development of active plasmonic devices.
Content Version: Open Access
Issue Date: Sep-2015
Date Awarded: Mar-2016
URI: http://hdl.handle.net/10044/1/59245
DOI: https://doi.org/10.25560/59245
Supervisor: Petrov, Peter
Alford, Neil
Sponsor/Funder: Engineering and Physical Sciences Research Council
Funder's Grant Number: MMRE PS1228
Department: Materials
Publisher: Imperial College London
Qualification Level: Doctoral
Qualification Name: Doctor of Philosophy (PhD)
Appears in Collections:Materials PhD theses

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