Photoelectron Spectroscopy of Lanthanide−Silicon Cluster Anions LnSi_n⁻ (3 ≤ n ≤ 13; Ln = Ho, Gd, Pr, Sm, Eu, Yb): Prospect for Magnetic Silicon-Based Clusters

Abstract

Photoelectron spectroscopy was utilized to study a variety of LnSi(n)(-) cluster anions (Ln = Yb, Eu, Sm, Gd, Ho, Pr; 3 <or= n <or= 13). For a particular size n, the measured valence electronic transitions of all these systems fall into either one of two categories, reflecting the influence of the different oxidation states of the lanthanide atoms involved. In one, the spectra of YbSi(n)(-) and EuSi(n)(-) are nearly identical to each other, while in the other the spectra of GdSi(n)(-), HoSi(n)(-), and PrSi(n)(-) are essentially identical. SmSi(n)(-) clusters exhibit an intermediate behavior with smaller clusters resembling the former category and larger clusters resembling the latter category. In the intermediate size range, 7 <or= n <or= 10, for SmSi(n)(-) both categories appear to be present, with one matching the EuSi(n)(-)-like systems and the other HoSi(n)(-)-like clusters. The distinction between LnSi(n)(-) categories strongly correlates with the oxidation state of the particular lanthanide as usually found in its compounds. On the basis of this observation, we conclude that, among the Ln-silicon clusters studied herein, Yb, Eu, and in case of Sm, sizes n >or= 10, adopt a nominal +2 oxidation state while Ho, Pr, Gd, and in case of Sm, sizes n <or= 7, exhibit a nominal +3 oxidation state. Furthermore, dramatic increases in adiabatic electron affinity values observed at n = 10 for the Ln(III)Si(n) series and at n = 12 for the Ln(II)Si(n) series were attributed to an inherent electronic stabilization of those particular clusters, rather than to the lanthanides' encapsulation. The observed limited effect of f-electrons on the valence electronic structure and thus on bonding in LnSi(n)(-) clusters may leave these electrons available for inducing magnetism. Consequently, Ln@Si(n) clusters may hold promise as building blocks of silicon-based cluster materials with magnetic properties.

Structural determination of niobium-doped silicon clusters by far-infrared spectroscopy and theory

“…[6][7][8][9][10][11][12] Different from carbon clusters that usually show sp 2 hybridization, bonding in pure silicon clusters occurs through sp 3 hybridization and thus they are more chemically reactive due to the existence of unsaturated dangling bonds on the clusters' surface, making them less suitable as nanoscale building blocks. 13 However, it has been found that silicon clusters can be stabilized by doping with transition metal (TM) atoms, [14][15][16] and by now a great number of studies, both experimentally [17][18][19][20][21][22][23][24][25][26][27][28][29] and theoretically, [30][31][32][33][34][35][36] have explored the structures and electronic properties of TM-doped silicon clusters for their potential use in silicon-based nanomaterials. In fact, doping silicon clusters with appropriate transition metal atoms [37][38][39][40][41] can reduce the number of dangling bonds on the cluster surface or even fully saturate them via pd hybridization, and thereby change the geometrical structures and chemical reactivities compared to pure silicon clusters.…”

“…In fact, doping silicon clusters with appropriate transition metal atoms [37][38][39][40][41] can reduce the number of dangling bonds on the cluster surface or even fully saturate them via pd hybridization, and thereby change the geometrical structures and chemical reactivities compared to pure silicon clusters. Accordingly, novel physical and chemical properties of transition-metal doped silicon clusters, e.g., size-specific stability, 30,42 magnetic, 17,28,37,39,43 and optical properties, 44 open up many new and exciting applications, for instance, for silicon-based nano-devices in optoelectronics, tunable lasers, and sensors.…”

“…37,47 Silicon clusters doped with a lanthanide atom retaining a partially filled 4f shell, such as Si n Ln À (Ln = Ho, Gd, Pr, Sm, Eu, Yb), have been suggested as magnetic silicon-based nanomaterials. 17 Interestingly, the fully TM-encapsulated silicon clusters, TM@Si 16 (TM = Ti and Zr), are also predicted to exhibit luminescence in the visible range, making them attractive for optoelectronic applications, 44 and the neutral TiSi 16 cluster has a closed-shell electron configuration with a large gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). 18 The isoelectronic TaSi 16 + has been recently reported to form stable heterodimers with C 60 upon deposition from the gas phase.…”

Geometric structure and electron spectrum of YSi n − clusters (n = 6–17)

“…The modern level of experimental methods does not allow us to obtain information on the geo metric structure of insulated clusters, while the theo retical methods often give contradictory results [3][4][5]. At the same time, the experimental investigation of the electron structure of the clusters is possible, and there are the publications in which the results of studying the electron energy spectrum of anion clusters by the method of photoelectron spectroscopy are presented [6][7][8]. However, no information on the structure of clusters detected in the experiment is contained in these publications; therefore, combining the results of computer simulation of stable structures with the results of photoelectron spectroscopy can become the effective method of determining the actual geometric structure of clusters.…”

Geometrical and electronic structure of the Ba-doped Sin (n=1–12) cluster: A density functional study

“…By taking the time-consumption into account, the basis sets labelled GENECP are the combinations of pseudopotential with basis sets LANL2DZ and full electrons basis sets 6-311+G(d), which are employed for the Ba and Si atoms, respectively. To search the lowest-energy structures, a large number of previous optimized Si n and XSi n geometries [17][18][19][20][21][22][23][24] are considered as our initial structures. Then, we constructed many structures by placing one Ba atom at each possible sites on the basis of initial structures, i.e., Ba-capped, Basubstituted, and Ba-encapsulated patterns.…”