Photoelectron spectroscopy of negatively, charged clusters of aluminum, copper, silver, and gold reveals electronic shell structure and electron energy band development. Photodetachment experiments on Au$\sb6\sp-$ also suggests that an image-bound state of the anion exists at the detachment threshold.
Al$\sb{\rm x}$, Cu$\sb{\rm x}$, Ag$\sb{\rm x}$, and Au$\sb{\rm x}$ all show closed shells in their electron affinities for clusters with x $<$ 21. The electron affinities of Au$\sb{\rm x}$ for 20 $<$ x $<$ 60 have three spherical shells at x = 20, 34, and 58, all of which are dramatically manifested in dips of 1.2, 0.65, and 0.75 eV when compared to their adjacent lower mass neighbors. The photoelectron spectra of Ag$\sb{\rm x}\sp-$, 30 $<$ x $<$ 58, have cleanly resolved peaks that are a result of level structure in the density-of-states and they are predicted by the Nilsson-Clemenger formalism of shell theory. Copper clusters in the same size range show similar behavior although not as pronounced.
The onset of the 3d-band in copper is monotonically increasing with cluster size and at Cu$\sb{410}$ the band is only 0.6 eV from its bulk value. The monotonic increase is a result of the expanding sphere of charge that induces a dipole as the electron leaves the vicinity of the cluster. Sharp features in the 3d-band onset are very similar to bulk photoemission spectra and suggest that these structures are beginning to show crystalline character.
The induced dipole also causes at least one weakly bound state to exist for Au$\sb6\sp-$ at the detachment threshold. Photodetachment spectroscopy shows a 30 cm$\sp{-1}$ phase shift between the 1- and 2-photon ejected electrons. The phase shift may be due to a sequence congestion of vibrational states between the ground and image-bound electronic states of Au$\sb6\sp-$.
| Identifer | oai:union.ndltd.org:RICE/oai:scholarship.rice.edu:1911/16397 |
| Date | January 1990 |
| Creators | Taylor, Kelly J. |
| Contributors | Smalley, Richard E. |
| Source Sets | Rice University |
| Language | English |
| Detected Language | English |
| Type | Thesis, Text |
| Format | 98 p., application/pdf |
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