ELECTRON-TRANSFER DYNAMICS AT GAAS SURFACE QUANTUM-WELLS

Interfacial electron-transfer dynamics have been characterized for a h eterogeneous semiconductor-liquid junction. Molecular beam epitaxy was used to grow As-capped GaAs (100) surface quantum wells. Removal of t he As layer created a pristine, low defect, surface which was studied in situ in direct contact with an outer-sphere, ferrocene, redox coupl e using time-correlated single photon counting. The surface quantum we ll structure was used specifically to remove field-dependent transport effects from the photocarrier dynamics. Concentration-dependent decay profiles indicate that a significant fraction of electrons undergo el ectron transfer. A fit to the data gives an electron-transfer cross se ction of (2.4 +/- 0.8) x 10(-15) cm(2), which corresponds to charge tr ansfer in the adiabatic coupling regime. This work illustrates that th e electronic coupling between the solid state and molecular states at the surface can be sufficiently strong to produce adiabatic reaction c onditions even for weakly physisorbed outer-sphere accepters.