Unit:
Κατεύθυνση Φυσική των Υλικών (ΒΑΣΙΚΗ ΦΥΣΙΚΗ)Library of the School of Science
Author:
Papadakis Dimitrios
Supervisors info:
Βλάσης Λυκοδήμος, επίκουρος καθηγητής, τμήμα Φυσικής, ΕΚΠΑ
Νικόλαος Στεφάνου, καθηγητής, τμήμα Φυσικής, ΕΚΠΑ
Εμμανουήλ Συσκάκης, επίκουρος καθηγητής, τμήμα Φυσικής, ΕΚΠΑ
Original Title:
Ενίσχυση σκέδασης Raman σε φωτονικούς κρυστάλλους TiO2 τροποποιημένους με νανοκολλοειδή οξειδίου γραφενίου
Translated title:
Enhanced Raman scattering in TiO2 photonic crystals functionalized by graphene oxide nanocolloids
Summary:
Surface enhanced Raman scattering (SERS) has been established as a highly sensitive analytical technique with unprecedented resolution in the identification of minute amounts of analytes reaching the level of single molecule detection and imaging. Despite the marked progress in the field, fabrication of low cost, recyclable and biocompatible SERS substrates based on the local field and radiation enhancement generated by the localized surface plasmon resonance (LSPR) of coinage metals has been a key challenge for the implementation of practical SERS applications. The development of dielectric nanostructures with suitably modified morphology and electronic properties has been attracting particular research interest as a promising means to alleviate the major shortcomings of conventional metallic SERS substrates, especially in applications where ultrasensitive detection is not a prerequisite.
In this work, surface modified TiO2 photonic crystals by graphene oxide nanocolloids (nanoGO) were explored as efficient, plasmon-free SERS substrates. TiO2 photonic crystals in the form of inverse opals for three different diameters with photonic gaps (stop bands) of 435, 502, και 646 nm were applied for the detection of methylene blue as model analyte at variable laser excitations of 488, 514, 633 και 785 nm. The best performance was observed for the photonic crystal with 435 stop band at 488 and 514 nm due to the close match of the laser excitation with the slow photon spectral region. In that case, slow light propagation results in multiple light scattering at the nanocrystalline titania walls, where the analyte molecues are adsorbed, leading to the effective extension of the path length of incident photons and the Raman amplification. Additional contribution was identified by the chemical interaction of the analyte molecules with the semiconducting substrate. Surface functionalization of the TiO2 photonic crystals with nanoGO sheets resulted in a marked increase of the SERS performance by one order of magnitude indicative of significant synergy. This enhancement can be related to the increased adsorption of the analyte molecules by means of surface oxygen groups and π-π interactions on the substrate and the interfacial charge transfer between GO and the analyte-TiO2 system. Optimal combination of these mechanisms resulted in a limit of detection reaching 710-7 Μ at 514 nm, one of the lowest reported in the literature for SERS detection of MB on dielectric substrates, paving the way for the development of efficient self-cleaning dielectric SERS by means of their photocatalytic properties.
Main subject category:
Science
Keywords:
Raman Spectroscopy, SERS effect, photonic crystals, titanium dioxide, graphene oxide
