Electron Transfer without Overcoming a Barrier
In the recently accepted paper in Physical Review Letter, Hrvoje Petek and his colleagues investigate the coherent electron transfer from an interface state that forms upon chemisorption of Ag nanoclusters onto graphite to a σ symmetry interlayer band of graphite. Interfacial charge transfer is a fundamental process in heterogeneous and plasmonically enhanced catalysis. The charge transfer, however, is thought to be restrained by an interfacial potential barrier, such as a Schottky barrier at a metal-semiconductor interface. With optical excitation, the interfacial charge transfer can also be efficiently completed by coherent dipole coupling between the donor and acceptor bands. In this study Petek and his colleagues advance the time-resolved multidimensional multiphoton photoemission spectroscopy technique to not only pump the donor band and probe the acceptor band, but also directly image the coherent polarization dynamics between them. They discover a direct resonant electron transfer channel where two-photon absorption couples a donor interface state formed by electron delocalizing from Ag clusters to graphite and the acceptor state, which is the unoccupied interlayer band of graphite. Such electron transfer can be driven instantaneously by two photon absorption and is completed within the electron-hole dephasing time of ~10 fs.