OPTICAL-SPECTRA OF SIZE-SELECTED MATRIX-ISOLATED SILICON CLUSTERS

Size selected silicon clusters have been isolated in rare gas matrices and studied by optical absorption spectroscopy. The clusters were pro duced in a pulsed laser vaporization source, size selected with a quad rupole mass spectrometer and deposited at low energies into a co-conde nsed krypton matrix held at T<20 K. A comparison of the optical spectr a of ten atom wide bands (Si-25-Si35, Si35-Si45 and Si45-Si55) shows t he general size evolution of the optical properties. Single cluster si zes have also been isolated and show somewhat sharper spectra than the bands. The measured spectra show similarities to spectra calculated u sing Mie theory and bulk optical constants. Cluster-cluster agglomerat ion was studied by evaporating the inert gas matrix. The results sugge st that the clusters agglomerate into larger particles even under the mildest ''soft landing'' conditions.