In this presentation, the molecular sensitivity of scattering-type near-field scanning optical microscopy (s-SNOM) will be demonstrated by imaging an organic thin film with thickness gradient that continuously vary from zero to over 200 nm on different substrates. We will then present recent s-SNOM experimental results that show phase separation and nanoscale pattern formation in thin films of blended polymers. The evolution of nanoscale domains and hierarchical patterns as a function of composition will be discussed. The results may help to understand the sensitivity of s-SNOM chemical imaging at the molecular “finger print” region of electromagnetic radiation and to realize the capability of the technique to resolve nanoscale domains and phase separation in multicomponent organic thin films.
We will present the manifestations of plasmon-molecule energy and electron transfer processes as observed surface enhanced Raman spectroscopy (SERS). We observe that in presence of intermediary surface ligands, the electron transfer channel is turned off. On the other hand, the presence of surface ligands facilitates plasmon to molecule energy transfer (plasmon pumped adsorbate intramolecular electronic excitation) by orienting the analyte molecules along the surface field vector as well as by prolonging the excited state lifetime. The adsorbate excitation appears to be followed by singlet to triplet intersystem crossing that leads to singlet oxygen generation that initiates N-demethylation reaction as demonstrated using the reactivity of methylene.
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