Résumé
The optical properties of noble metal clusters are measured and compared in the size range 1.4–7 nm in diameter. The clusters of copper, silver and gold are produced by the same experimental technique, the deposition of preformed clusters in a transparent matrix. The size dependence is found to be different for the three metals. As the size decreases, the surface plasmon resonance is only slightly blue-shifted for silver, more strongly blue-shifted and damped for gold while this peak resonance vanishes for copper. We show that these results cannot be interpreted by a simple classical theory. Since ab initio calculations are not possible in this size range, we obtain a complete theoretical description of these optical properties through the same semi-quantal model for the three metals.