Possible origin of the anomalous far-infrared absorption by small metal particles
Abstract
We carried out the far-infrared transmission measurements on the ligand stabilized Au55 particles dispersed in CsI. We found that the far-infrared absorption coefficient recovers the ω2-dependence (the same behavior as the classical electric dipole-like absorption) for frequencies above the crossover energy Ec=ℏ/2mea∼160 cm-1 (a=particle radius) while the absorption coefficient below Ec, which arises from the transitions of the electrons between the discrete energy levels, saturates to a value ∼4 cm-1 at ω∼Ec. Since Ec of the small metal particles (a>20 Å) studied in the past falls well below the lowest frequency typically accessible for the far-infrared spectroscopy (ω∼20 cm-1), we conclude that all the previously measured far-infrared absorption must have been an extension of the absorption of the quantum regime set at Ec, making the absorption measured in the typical far-IR window (20 cm-1<ω<120 cm-1) anomalously large when compared with the classical electric dipole absorption by the same size particles.
- Publication:
-
Solid State Communications
- Pub Date:
- December 2012
- DOI:
- 10.1016/j.ssc.2012.08.025
- Bibcode:
- 2012SSCom.152.2129K