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From two-dimensional electron gas to localized charge: Dynamics of polaron formation in organic semiconductors

Electronic transport in organic semiconductors is mediated by localized polarons. However, the dynamics on how delocalized electrons collapse into polarons through electron-nuclear interaction is not well known. In this work, we use time- and angle-resolved photoemission spectroscopy to study polaron formation in titanyl phthalocyanine deposited on Au(111)surfaces. Electrons are optically excited from the metal to the organic layer via the image potential state, which evolves from a dispersive to a nondispersive state after photoexcitation. The spatial size of the electrons is determined from the band structure using a tight-binding model. It is observed that the two-dimensional electron wave collapses into a wave packet of size ∼3 nm within 100 fs after photoexcitation.

Physical Review B 91, 041201 (2015)

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Authors: 
Ti Wang*, Claudiu Caraiani*, G. William Burg*, and Wai-Lun Chan* KU Authors*