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

TY - JOUR

T1 - Ramifications of optical pumping on the interpretation of time-resolved photoemission experiments on graphene

AU - Ulstrup, Søren

AU - Johannsen, Jens Christian

AU - Cilento, Federico

AU - Crepaldi, Alberto

AU - Miwa, Jill A.

AU - Zacchigna, Michele

AU - Cacho, Cephise

AU - Chapman, Richard T.

AU - Springate, Emma

AU - Fromm, Felix

AU - Raidel, Christian

AU - Seyller, Thomas

AU - King, Phil D. C.

AU - Parmigiani, Fulvio

AU - Grioni, Marco

AU - Hofmann, Philip

PY - 2015/4

Y1 - 2015/4

N2 - 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. (C) 2015 Elsevier B.V. All rights reserved.

AB - 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. (C) 2015 Elsevier B.V. All rights reserved.

KW - Graphene

KW - Time- and angle-resolved photoemission

KW - Space charge

KW - Hot electrons

KW - CARRIER MULTIPLICATION

KW - SPECTROSCOPY

KW - SURFACE

U2 - 10.1016/j.elspec.2015.04.010

DO - 10.1016/j.elspec.2015.04.010

M3 - Journal article

SN - 0368-2048

VL - 200

SP - 340

EP - 346

JO - Journal of Electron Spectroscopy and Related Phenomena

JF - Journal of Electron Spectroscopy and Related Phenomena

ER -