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Proceedings Paper

Femtosecond electron injection from optically populated donor states into the conduction band of semiconductors
Author(s): Ralph Ernstorfer; Lars Toeben; Lars Gundlach; Silke Felber; Elena Galoppini; Qian Wei; Rainer Eichberger; Winfried Storck; Carsten Zimmermann; Frank Willig
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Paper Abstract

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.

Paper Details

Date Published: 4 December 2003
PDF: 11 pages
Proc. SPIE 5223, Physical Chemistry of Interfaces and Nanomaterials II, (4 December 2003); doi: 10.1117/12.507474
Show Author Affiliations
Ralph Ernstorfer, Hahn-Meitner-Institut (Germany)
Lars Toeben, Hahn-Meitner-Institut (Germany)
Lars Gundlach, Hahn-Meitner-Institut (Germany)
Silke Felber, Hahn-Meitner-Institut (Germany)
Elena Galoppini, Rutgers Univ. (United States)
Qian Wei, Rutgers Univ. (United States)
Rainer Eichberger, Hahn-Meitner-Institut (Germany)
Winfried Storck, Hahn-Meitner-Institut (Germany)
Carsten Zimmermann, Hahn-Meitner-Institut (Germany)
Frank Willig, Hahn-Meitner-Institut (Germany)

Published in SPIE Proceedings Vol. 5223:
Physical Chemistry of Interfaces and Nanomaterials II
Tianquan Lian; Hai-Lung Dai, Editor(s)

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