WIDTH OF CLUSTER PLASMON RESONANCES - BULK DIELECTRIC FUNCTIONS AND CHEMICAL INTERFACE DAMPING

The damping of collective electron resonances in clusters which develo p into plasmon polaritons at larger sizes is investigated for free, su pported, and embedded neutral metal clusters. Embedding of free 2 nm A g clusters of 2-nm diameter into a SiO2 matrix leads to an increase of the width of the resonances by more than a factor of 3. The optical s pectra are compared with the Mie theory using size-effect-modified die lectric functions of the solid state. The results corroborate the assu mption that the widths of the resonances strongly depend on chemical i nterface effects. The results are briefly discussed with regard to lim ited-mean-free-path and quantum-size-effect theories and a recent appr oach by Persson. It is demonstrated that the widths of the spectra of supported and embedded clusters have to be interpreted with care since true intrinsic size effects of the clusters appear to be less effecti ve than previously believed and can be obscured by the chemical interf ace damping.