2015/02/05 by Søren Ulstrup, J. Johannsen, Ulstrup, Søren +29 · 1 citation
Physics and Astronomy · #Force Microscopy Techniques and Applications #Spectroscopy and Quantum Chemical Studies #Surface and Thin Film Phenomena
paper · pdf · doi:10.48550/arxiv.1502.01933
In pump-probe time and angle-resolved photoemission spectroscopy (TR-ARPES)\nexperiments the presence of the pump pulse adds a new level of complexity to\nthe photoemission process in comparison to conventional ARPES. This is\nevidenced by pump-induced vacuum space-charge effects and surface\nphotovoltages, as well as multiple pump excitations due to internal reflections\nin the sample-substrate system. These processes can severely affect a correct\ninterpretation of the data by masking the out-of-equilibrium electron dynamics\nintrinsic to the sample. In this study, we show that such effects indeed\ninfluence TR-ARPES data of graphene on a silicon carbide (SiC) substrate. In\nparticular, we find a time- and laser fluence-dependent spectral shift and\nbroadening of the acquired spectra, and unambiguously show the presence of a\ndouble pump excitation. The dynamics of these effects is slower than the\nelectron dynamics in the graphene sample, thereby permitting us to deconvolve\nthe signals in the time domain. Our results demonstrate that complex\npump-related processes should always be considered in the experimental setup\nand data analysis.\n