Photoionization profiles of metal clusters and the Fowler formula

TL;DR

This paper demonstrates that the Fowler theory effectively models the photoabsorption profiles of metal clusters, enabling accurate extraction of ionization potentials and internal temperatures, bridging atomic and bulk surface photoemission concepts.

Contribution

The study shows that the Fowler formalism can be applied to metal cluster photoionization, providing a simple, physical model that fits experimental data and extrapolates to bulk properties.

Findings

Fowler theory fits cluster photoabsorption profiles well

Ionization potentials extrapolate to bulk work function

Internal temperatures agree with expected evaporating cluster values

Abstract

Metal cluster ionization potentials are important characteristics of these "artificial atoms," but extracting these quantities from cluster photoabsorption spectra, especially in the presence of thermal smearing, remains a big challenge. Here we demonstrate that the classic Fowler theory of surface photoemission does an excellent job of fitting the photoabsorption profile shapes of neutral In_{n=3-34} clusters [Wucher et al., New J. Phys. 10, 103007 (2008)]. The deduced ionization potentials extrapolate precisely to the bulk work function, and the internal cluster temperatures are in close agreement with values expected for an ensemble of freely evaporating clusters. Supplementing an earlier application to potassium clusters, these results suggest that the Fowler formalism, which is straightforward and physical, may be of significant utility in metal cluster spectroscopy. It is hoped also that the results will encourage a comprehensive theoretical analysis of the applicability of bulk-derived models to cluster photoionization behavior, and of the transition from atomic and molecular-type to surface-type photoemission.