4 December 2003 Femtosecond electron injection from optically populated donor states into the conduction band of semiconductors
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Hot electron injection from the aromatic chromophore perylene into TiO2 was measured with transient absorption signals for different rigid anchor-cum-spacer groups revealing 15 fs as the shortest and 4 ps as the longest injection time. The energetic position of the donor orbital of the chromophore with respect to the conduction band edge was determined at about 0.8 eV employing ultraviolet photoelectron spectroscopy (UPS)and simple absorption spectroscopy.It is not clear in the case of rutile or anatase TiO2 whether unoccupied surface states are involved in the electron injection process as acceptor states. Since the surface reconstruction of TiO2 is difficult to control electron scattering between a well-defined surface state and isoenergetic unoccupied bulk states was studied with InP(100). Electron scattering was time-resolved employing two-color two-photon-photoemission (2PPE). Scattering from isoenergetic bulk states to the empty C1 surface state was found to occur with a 35 fs time constant, and the reverse process showed a time constant in the range of 200 fs. The latter was controlled by energy relaxation in bulk states, i.e. via the emission of longitudinal optical phonons in InP. In general, the injection of a hot electron from a molecular donor into electronic states of a semiconductor as to be distinguished from consecutive electron scattering processes between surface states and bulk states. Distinguishing between the different processes may become difficult, however,if the electronic interaction becomes large for a small chromophore directly attached to the semiconductor.
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Ralph Ernstorfer, Ralph Ernstorfer, Lars Toeben, Lars Toeben, Lars Gundlach, Lars Gundlach, Silke Felber, Silke Felber, Elena Galoppini, Elena Galoppini, Qian Wei, Qian Wei, Rainer Eichberger, Rainer Eichberger, Winfried Storck, Winfried Storck, Carsten Zimmermann, Carsten Zimmermann, Frank Willig, Frank Willig, } "Femtosecond electron injection from optically populated donor states into the conduction band of semiconductors", Proc. SPIE 5223, Physical Chemistry of Interfaces and Nanomaterials II, (4 December 2003); doi: 10.1117/12.507474; https://doi.org/10.1117/12.507474

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