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Atomic-scale imaging excitons and plasmons at thin C60 films - P. Merino

Instituto Ciencia de Materiales de Madrid

LPS – salle S208a

Light at the nanoscale originate from two distinct mechanisms : excitons and plasmons.1 Excitons are a key concept for understanding the optoelectronic properties of quantum dots and molecular crystals.2 Plasmons dominate the optical response of metallic nanostructures.3 Here, I will present results on the scanning tunneling microscopy (STM) induced luminescence from thin C60 crystalline films grown on coinage metal surfaces and I will show that in this system both luminescence mechanisms coexist.1 Profiting from the atomically defined charge injection of the STM tip one can excite electroluminescence locally and map it down to the submolecular scale.3 I will show that the molecular orbital pattern visible in the photon maps enables an unambiguous discrimination between exciton recombination and the emission from tip-induced plasmons. I will demonstrate that the two types of luminescence are the result of two particular charge injection channels : holes injected into the valence band induce exciton generation,4,5 while electrons extracted from the conduction band cause plasmonic luminescence.1 The different dynamics of the two mechanisms permit controlling their relative contribution in the combined bimodal emission. Exciton recombination prevails for low charge injection rates, whereas plasmon decay outshines for high tunneling currents. The continuous transition between both regimes is described by a rate model characterizing emission dynamics on the nanoscale. This work provides the basis for developing blended exciton-plasmon light sources with advanced functionalities.
[1] P. Merino et al. Sci. Advances 4, eaap8349
[2] P. Merino et al. Nat. Commun.6, 8461 (2015)
[3] K. Kuhnke, et al. Chem. Rev. 117, 5174-5222 (2017)
[4] C. Grosse et al. Nano Letters 16, 2084-2089 (2016)
[5] C. Grosse et al. ACS Nano 11, 1230-1237 (2017)


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