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Vibrational Spectroscopy of Semiconductor Quantum Dots 31.01.2017 | 16:45 Uhr - 18:15 Uhr

Semiconductor nanocrystals (NCs) or quantum dots (QDs), e.g. colloidal CdSe NCs, are found in numerous applications, in particular as strong luminescent light emitters as their size dependent light emission can cover the entire visible spectral range. While the luminescence can be detected easily even for single QDs, recording the Raman spectrum of a single QD and thus determining its vibrational properties remains a challenge.

Here I use the example of CdSe quantum dots to introduce the main features observed in the Raman spectra and then to illustrate several approaches how the Raman response of the QDs can be enhanced and finally quasi-single QD Raman spectra obtained. Beginning with the enhancement via resonant excitation and utilizing interference enhanced Raman scattering this contribution will then focus on an investigation of resonant surface-enhanced Raman scattering (SERS) by optical phonons in colloidal CdSe NCs homogeneously deposited on arrays of Au nanoclusters using the Langmuir–Blodgett technique. SERS by optical phonons in CdSe NCs shows a significant enhancement factor which depends resonantly on the Au nanocluster size. SERS by optical phonons was also observed for CdSe NCs deposited on structures with a single Au dimer. A difference of the LO phonon energy is observed for CdSe NCs on different single dimers. This effect is explained as the confinement-induced shift which depends on the CdSe nanocrystal size and indicates that quasi-single NC Raman spectra can be obtained. Finally some Raman results for Cd-free QDs will be presented.

Referent/in

Prof. Dr. Dr. h.c. Dietrich R. T. Zahn, Technische Universität Chemnitz, Physics Department

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