Artist’s rendering of silver clusters capped with organic ligand molecules. |
Center
for Nanoscale Materials (CNM) users from the Ecole Polytechnique
Federale de Lausanne in Switzerland, working with the CNM Nanophotonics
Group at Argonne National Laboratory, have demonstrated the existence of long-lived charge-separated
states in silver clusters. The clusters, synthesized chemically in
solution, consist of exactly 44 silver atoms and are stabilized by
exactly 30 organic molecules.
Thus,
the clusters exist at the boundary between the quantum-mechanical
regime of small molecules and the classical regime of metal
nanoparticles. Time-resolved optical measurements carried out at the CNM
established that absorption of a photon by a cluster is followed very
quickly—within a few picoseconds—by the separation of positive and
negative charges within the cluster. The charges remain separated for a
long time, as much as 300 nanosec. The stable charge-separated state,
together with the fact that the clusters absorb light over a wide range
of wavelengths, mean that the clusters represent a new and promising
class of materials for solar energy applications.
Long-lived charge-separated states in ligand-stabilized silver clusters
