Near-threshold photoionization of germanium clusters in the 248-144 nm region: ionization potentials for Ge-n

We examine the photoionization thresholds of Ge, (n = 2 - 34) with a wide p hoton energy (5.0-8.6 eV) using a laser photoionization time-of-flight mass spectrometry. A high-output vacuum ultraviolet light generated with stimul ated Raman scattering is used as the ionization light source in the energy above 6.0 eV. A characteristic size dependence of ionization potential (IP) with a maximum at n = 10 is found for clusters smaller than 22 atoms. The rather high IP of Ge-10 in comparison with its neighbors is consistent with the results on the photodissociation study of Ge-n(+). We also find that I Ps decrease rapidly from n = 16 to 22, and then decrease at a much slower r ate for larger clusters. These features in IPs are similar to those of Si-n reported in our previous paper; except for the smaller IP gap of Ge, at n approximate to 20. We discuss these results on IPs in relation to their ele ctronic structure and stability.