Size and temperature dependence of the plasmon absorption of colloidal gold nanoparticles

The size and temperature dependence of the plasmon absorption is studied fo r 9, 15, 22, 48, and 99 nm gold nanoparticles in aqueous solution. The plas mon bandwidth is found to follow the predicted behavior as it increases wit h decreasing size in the intrinsic size region (mean diameter smaller than 25 nm), and also increases with increasing size in the extrinsic size regio n (mean diameter larger than 25 nm). Because of this pronounced size effect a homogeneous size distribution and therefore a homogeneous broadening of the plasmon band is concluded for all the prepared gold nanoparticle sample s. By applying a simple two-level model the dephasing time of the coherent plasmon oscillation is calculated and found to be less than 5 fs. Furthermo re, the temperature dependence of the plasmon absorption is examined. A sma ll temperature effect is observed. This is consistent with the fact that th e dominant electronic dephasing mechanism involves electron-electron intera ctions rather than electron-phonon coupling.