Optically excited acoustic vibrations in quantum-sized monolayer-protected gold clusters.
We report a systematic investigation of the optically excited vibrations in monolayer-protected gold clusters capped with hexane thiolate as a function of the particle size in the range of 1.1-4 nm. The vibrations were excited and monitored in transient absorption experiments involving 50 fs light pulses. For small quantum-sized clusters (< or =2.2 nm), the frequency of these vibrations has been found to be independent of cluster size, while for larger clusters (3 and 4 nm), we did not observe detectable optically excited vibrations in this regime. Possible mechanisms of excitation and detection of the vibrations in nanoclusters in the course of the transient absorption are discussed. The results of the current investigation support a displacive excitation mechanism associated with the presence of finite optical energy gap in the quantum-sized nanoclusters. Observed vibrations provide a new valuable diagnostic tool for the investigations of quantum size effects and structural studies in metal nanoclusters.
Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109, USA.
Oleg
O
Varnavski
Guda
G
Ramakrishna
Junhyung
J
Kim
Dongil
D
Lee
Theodore
T
Goodson
D000162:Acoustics; D006046:Gold / Q000737:chemistry* / Q000528:radiation effects; D008027:Light; D046911:Macromolecular Substances / Q000737:chemistry; D008422:Materials Testing; D008968:Molecular Conformation; D049329:Nanostructures / Q000737:chemistry* / Q000528:radiation effects*; D036103:Nanotechnology / Q000379:methods*; D010316:Particle Size; D013499:Surface Properties; D014732:Vibration
D046911:Macromolecular Substances; D006046:Gold