title: Ionization energies and structures of lithium doped silicon clusters.
abstract: We report on a combined experimental and theoretical study of the ionization energies and structures of small lithium doped silicon clusters, SinLim with n = 5-11 and m = 3-6. Photoionization efficiency curves are measured in the 4.68-6.24 eV range and subsequently compared with calculated values of both vertical and adiabatic ionization energies for the lowest energy isomers obtained using density functional theory at the B3LYP/6-311+G(d) level. The evolution of the cluster geometries and ionization energies is studied as a function of the number of silicon and lithium atoms along the SinLi3 (n = 5-11) and Si8Lim (m = 1-6) series, respectively. For most studied sizes good agreement is found between the experimental and the calculated ionization energies for the lowest-energy isomer. In the SinLi3 (n = 5-11) series, positively charged lithium atoms surround a negatively charged silicon framework and mainly act as electron donors. Upon sequential lithium addition along the Si8Lim (m = 1-6) series, the Si8 framework deforms from a rhombic (m = 0, 1) over a tetracapped tetragon (m = 1-4) to a square antiprism (m = 4-6) structure. Subsequent addition of lithium implies the addition of excess electrons to the silicon framework, which is reflected in a decrease of the ionization energy with increasing lithium content. This decrease is non-monotonous and odd-even alternations, reflecting the higher stability of clusters with an even number of electrons, are observed. In addition, post-threshold features in the experimental photoionization efficiency curves of SinLi3 (n = 8-11) may be related to the computed density of states of the corresponding lowest energy isomers.
authors.affiliation: Laboratory of Solid State Physics and Magnetism, KU Leuven, B-3001 Leuven, Belgium. Peter.Lievens@fys.kuleuven.be.
authors.forename: Jorg
authors.initials: J
authors.lastname: De Haeck
authors.forename: Soumen
authors.initials: S
authors.lastname: Bhattacharyya
authors.forename: Hai Thuy
authors.initials: HT
authors.lastname: Le
authors.forename: David
authors.initials: D
authors.lastname: Debruyne
authors.forename: Nguyen Minh
authors.initials: NM
authors.lastname: Tam
authors.forename: Vu Thi
authors.initials: VT
authors.lastname: Ngan
authors.forename: Ewald
authors.initials: E
authors.lastname: Janssens
authors.forename: Minh Tho
authors.initials: MT
authors.lastname: Nguyen
authors.forename: Peter
authors.initials: P
authors.lastname: Lievens