Ramifications of optical pumping on the interpretation of time-resolved photoemission experiments on graphene

Søren Ulstrup, Jens Christian Johannsen, Federico Cilento, Alberto Crepaldi, Jill A. Miwa, Michele Zacchigna, Cephise Cacho, Richard T. Chapman, Emma Springate, Felix Fromm, Christian Raidel, Thomas Seyller, Phil D.C. King, Fulvio Parmigiani, Marco Grioni, Philip Hofmann

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Abstract

Abstract In pump-probe time and angle-resolved photoemission spectroscopy (TR-ARPES) experiments the presence of the pump pulse adds a new level of complexity to the photoemission process in comparison to conventional ARPES. This is evidenced by pump-induced vacuum space-charge effects and surface photovoltages, as well as multiple pump excitations due to internal reflections in the sample-substrate system. These processes can severely affect a correct interpretation of the data by masking the out-of-equilibrium electron dynamics intrinsic to the sample. In this study, we show that such effects indeed influence TR-ARPES data of graphene on a silicon carbide (SiC) substrate. In particular, we find a time- and laser fluence-dependent spectral shift and broadening of the acquired spectra, and unambiguously show the presence of a double pump excitation. The dynamics of these effects is slower than the electron dynamics in the graphene sample, thereby permitting us to deconvolve the signals in the time domain. Our results demonstrate that complex pump-related processes should always be considered in the experimental setup and data analysis.
Original languageEnglish
Pages (from-to)340–346
JournalJournal of Electron Spectroscopy and Related Phenomena
Volume200
Early online date23 Apr 2015
DOIs
Publication statusPublished - Apr 2015

Keywords

  • Hot Electrons
  • Graphene
  • Time- and Angle-Resolved Photoemission
  • Space Charge

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