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  Gundlach, L.; Ernstorfer, R.; Willig, F.: Escape dynamics of photoexcited electrons at catechol:TiO₂(110). Physical Review B 74 (2006), p. 035324/1-10

10.1103/PhysRevB.74.035324

Abstract:
Ultrafast electron escape dynamics following excitation of the interfacial charge transfer complex of catechol prepared on the rutile TiO2(110) surface was investigated with femtosecond two-photon photoemission (2PPE). Laser pulses were generated with two non-collinear optical parametric amplifiers operated simultaneously at a repetition rate of 150 kHz delivering a crosscorrelation function with 35 fs FWHM. Catechol was absorbed from solution. The experimental data were not depending on the choice between three different solvents. Photo-induced interfacial charge transfer was instantaneous and thus the rise of the signal was controlled by the crosscorrelation function. The energy distribution of the hot electrons generated at the surface was measured as 2PPE spectrum. The decay of the 2PPE signal was non-exponential with a first time constant below 10 fs, a dip in the 50 fs to 100 fs range, and a tail lasting for picoseconds. It was attributed to the release of the electrons from the surface and escape into the bulk of the semiconductor.