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

Abstract.

We examine the photoionization thresholds of Ge _n (n=2-34) with a wide photon energy (5.0–8.6 eV) using a laser photoionization time-of-flight mass spectrometry. A high-output vacuum ultraviolet light generated with stimulated 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 Ge₁₀ in comparison with its neighbors is consistent with the results on the photodissociation study of Ge _n ⁺. We also find that IPs decrease rapidly from n=16 to 22, and then decrease at a much slower rate 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 _n at n≈20. We discuss these results on IPs in relation to their electronic structure and stability.