Development of a Novel, Polymer-Free, Wet CVD-Graphene Transfer Method and its Application to SERS Surfaces and TERS Probes

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)

Abstract

Raman spectroscopy is a powerful optical technique which provides highly discriminatory chemical information in a non-destructive manner. The weak nature of the response can be overcome through the use of metallic nanoparticles, which enhance the signal via localised surface plasmons. This process is termed surface-enhanced Raman spectroscopy, SERS. Minimal sample preparation is required, which means that measurements can be made in seconds. Despite the huge potential of SERS, current substrates which offer the best sensitivities may suffer from irreproducible signals, high fluorescent backgrounds, and/or metal oxidation under ambient conditions. The aim of this project was to add monolayer graphene to metallic SERS-active surfaces in order to improve their properties. This required the development of a wet, polymer-free graphene transfer method, and extensive optimisation of factors such as the etchant composition, and the cleaning and transfer of the free-floating graphene. The best results were obtained with an 0.1 M ammonium persulfate etchant containing 0.1% isopropanol, where a manual spoon scooping method was used to move graphene to a cleaning solution prior to deposition on the final substrate. This method was used to transfer graphene to not only SERS surfaces, but also for the first time to tip-enhanced Raman spectroscopy (TERS) probes, where benefits similar to those gained in graphene-SERS (G-SERS) analysis were anticipated. The success of the coating was assessed by scanning electron microscopy (SEM), atomic force microscopy (AFM), Raman spectroscopy and peak fitting. Graphene could be clearly seen adhering to our SERS surfaces, however it was cracked and torn. TERS measurements of a graphene coated SPM probe also showed indications of graphene peaks present, suggesting the coating of the apex was likely to have been successful. This is the first time that graphene-TERS tip coating has been reported, and with further proof of concept has the potential to revolutionise the production and commercial availability of these probes.
Date of Award2024
Original languageEnglish
Awarding Institution
  • Glasgow Caledonian University
SupervisorMahesh Uttamlal (Supervisor), Aleix Garcia Guell (Supervisor) & Sheila Smith (Supervisor)

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