"ONLINE - Ph.D. Thesis Defense: Substrate-enhanced and subsurface infrared near-field spectroscopy of organic layers"
Who: Lars Mester, Nanooptics Group
Place: Online webinar
Date: Monday, 18 January 2021, 11:00
Substrate-enhanced and subsurface infrared near-field spectroscopy of organic layers
Nanooptics Group, CIC nanoGUNE
Infrared nanospectroscopy based on Fourier transform infrared near-field spectroscopy (nano-FTIR) is an emerging nanoanalytical tool with large application potential for label-free chemical characterization of organic and inorganic composite surfaces. However, there are many open questions and challenges related to nano-FTIR. On the one hand, the detection of thin organic layers is still challenged by weak nano-FTIR signals, when the organic layer is placed on standard substrates such as CaF2. On the other hand, the potential capability of nano-FTIR for subsurface material analysis is still largely unexplored terrain. In this thesis, it is first demonstrated that a significant enhancement of the nano-FTIR signal from a thin organic layer is obtained by placing the organic layer on highly reflecting substrates such as silicon or gold. An even further signal enhancement is demonstrated by exploiting polariton-resonant tip-substrate coupling and surface polariton illumination of the nano-FTIIR probing tip. A signal enhancement of up to nearly two orders of magnitude is achieved on a polaritonic quartz substrate, as compared to the standard IR substrate CaF2. Secondly, it is demonstrated that nano-FTIR spectroscopy of subsurface organic layers is possible, revealing that nano-FTIR spectra from thin surface layers differ from that of subsurface layers of the same material. Furthermore, various peak characteristics are studied and a simple and robust method for distinguishing surface from subsurface layers is established, without the need of theoretical modelling. The obtained results are critically important for boosting the sensitivity of nano-FTIR to ultra-thin organic layers and for interpreting nano-FTIR spectra of multilayer samples, particularly to avoid that geometry-induced spectral peak shifts are explained by chemical effects.
Supervisor: Rainer Hillenbrand
Please access to the following link for ONLINE - Ph.D. Thesis Defense: Substrate-enhanced and subsurface infrared near-field spectroscopy of organic layers on Jan 18, 2021 11:00 AM CEST: