ONLINE - Ph.D. Thesis Defense: Substrate-enhanced and subsurface infrared near-field spectroscopy of organic layers
CIC nanoGUNE Seminars
- Speaker
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Lars Mester, Nanooptics Group
- When
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2021/01/18
12:00 - Place
- Online webinar
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**Substrate-enhanced and subsurface infrared near-field spectroscopy of
organic layers**
Lars Mester
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
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ONLINE - Ph.D. Thesis Defense: Substrate-enhanced and subsurface infrared
near-field spectroscopy of organic layers on Jan 18, 2021 11:00 AM CEST: