Structural and electronic properties of nanosize semiconductor CeSin0/− (n = 4–20) material: A double-hybrid density functional theory investigation

https://doi.org/10.1016/j.comptc.2019.112635Get rights and content

Highlights

  • Structural evolution for global minimum CeSin0/− is explored.

  • The spectral information is reported.

  • The 4f electron of Ce atom in CeSin0/− does not participate in bonding.

  • HOMO-LUMO gap, relative stability and chemical bonding analyses is evaluated.

  • The superatom is assigned to be CeSi20.

Abstract

Structural evolution model, HOMO-LUMO gap, relative stability, magnetic moment and spectral property of nanosize CeSin0/− (n = 4–20) semiconductor material were performed by employing double-hybrid density functional scheme. Optimized geometries for CeSin displayed that the most stable structure is Ce-substituted for a Si in the ground state of Sin+1 with n ≤ 17; Ce atom as linker connects two small silicon subclusters with n = 17–19; and Ce atom is encapsulated into cage-like Si framework with ≥20. For anion, the most stable structure of CeSin is Ce-linked configuration with n = 8–18 excluded n = 9, and Ce atom is encapsulated into cage-like motif with n = 19–20. The spectral information was reported. The 4f electron of Ce atom in CeSin0/− does not participate in bonding, resulting the total magnetic moments of neutral and anionic CeSin0/− clusters are 2 and 1 μB, respectively. HOMO-LUMO gap, relative stability and chemical bonding analyses revealed that encapsulated configuration of CeSi20 is a “magic” cluster.

Introduction

Over the past few decades, metal atom, especially rare earth metal (REM) atom, doped semiconductor nanomaterials have attracted particular attention owing to the fact that they possess high temperature stability and conductivity, low thermal expansion coefficient and Schottky barrier heights, good oxidation resistance and corrosion resistance, and excellent magnetic performance, making they become particularly ideal device with applications as anode materials in Li-ion batteries, large scale integrated circuits, rectifying contacts, Ohmic contacts, optical source, and hard magnetic materials [1], [2], [3], [4], [5], [6]. It is known that doping semiconductor nanocluster with REM atoms as microcopic counterparts of nanomaterials can be utilized not only as a basic unit for designing novel nanostructured functional materials with controlled and variable properties, but also as a model system for studying localized effects in the condensed phase [7], [8], [9], [10], [11]. Accordingly, it is extremely important to explore the dominant growth patterns of REM-doped semiconductor nanoclusters in the transition from the molecular to the condensed phase, and to understand deep the interaction between each REM and semiconductor atoms.

Since Beck [4] found highly size-specific stability in metal-semiconductor binary compounds formed by a chemical reaction in a supersonic jet expansion in 1987, many experimental studies focused on the structures and properties of metal atom-doped semiconductor nanoclusters have been performed. For instance, MSin (M = Tb, Ho, Lu, Y, Sc, Ti, V, Zr, Nb, Hf, and Ta, 6 ≤ n ≤ 20) were probed by Koyasu et al. [7] using photoelectron spectroscopy (PES) and a chemical-probe scheme, and enhanced stabilities were observed in MSi12 (M = Sc, Y, Lu, Tb, and Ho) and in MSi16 (M = Sc, Y, Lu, Tb, Ho, Ti, Zr, and Hf). Grubisic et al. [6] presented the PES and prospect for magnetic moments of REMSin (3 ≤ n ≤ 13, REM = Ho, Gd, Pr, Sm, Eu, Yb) species. Atobe et al. [8] investigated the PES and geometries of MGen (M = Lu, Y, Sc, Ti, V, Zr, Nb, Hf, and Ta, 8 ≤ n ≤ 20) and MSnn (M = Y, Sc, Ti, Zr, and Hf), and found that the threshold energies of electron detachment exhibit local maxima at n = 16. Dr. Zheng and co-workers [12], [13], [14], [15] explored the structural and electronic properties of MSin (M = Ag, Au, Cr, and Nb, n ≤ 12) by using PES and single-hybrid density functional theory. Recently, Nakajima’s group developed a large-scale synthesis method and produced MSi16 (M = Ti and Ta) clusters in 100 mg scale [5], [16]. Stimulated by these experimental observations, some theoretical simulations by using single- or double-hybrid density functional theory have been carried out for introducing Si clusters with REM atoms including PmSin [17], SmSin [18], [19], EuSin [20], [21], TbSin [22], DySin [23], ErSin [24], TmSin [25], YbSin [26], [27], [28], and LuSin [29], [30] with small size n ≤ 13, and LaSin [31], [32], PrSin [33], [34], GdSin [35], [36], and HoSin [37], [38], [39], [40] with medium size n ≤ 21. The calculated results indicate that double-hybrid density functional scheme such as mPW2PLYP and B2PLYP predicted reliable the ground state structures and electronic properties such as adiabatic electron affinities (AEAs), vertical detachment energies (VDEs) and simulated PES.

Although there is some investigation on the structures and properties of REM-doped Si clusters, the study of the structures and properties of the Ce-doped Si nanoclusters are still lacking. Furthermore, it is vitally important and meaningful to see CeSin0/− from a standpoint of whole REM family because Ce atom has only one 4f electron. So here we have not only probed their structural evolution model, HOMO-LUMO gap, relative stability, magnetic moment and spectral property, but also compared them with those of other REMSin species reported previously.

Section snippets

Computational details

To search for the global minimum for neutral and negatively charged CeSin0/− (n = 4–20), three methods were employed to search their initial geometries. First, we adopted ABCluster program [41] combining with Gaussian 09 codes [42] to explore unbiased global search. In this process, we employed the ABCluster producing 300 isomers for each CeSin0/− (n = 4–20) at the PBE level with SMALL (SMALL: 6-31G for Si atoms and ECP 48MWB basis set [43] for Ce atoms) basis sets. Second, the substitutional

Lowest-Energy structure and isomers of CeSin.

The geometries for CeSin (n = 4–20) nanoclusters were illustrated in Fig. 1, where the relative energies and point group were also given. Table 1 summarized the electronic state, atomization energy (AE), and HOMO-LUMO energy gap (Egap) for the global minimum structure. The ground state of all neutral CeSin (n = 4–20) is inspected to be triplet. For CeSi4, both 4n1 and 4n2 can be viewed as replacing a Si atom at different positions of Si5 trigonal bipyramid [49], [50], [51] by a Ce atom,

Conclusions

The systematic isomer search for low energy structures of neutral and anionic cerium-doped Si clusters CeSin0/− (n = 4–20) were performed by employing an ABCluster global search technique combined with mPW2PLYP double hybrid density functional scheme. Structural evolution model, HOMO-LUMO gap, relative stability, magnetic moment and spectral property of nanosize CeSin0/− (n = 4–20) semiconductor material were confirmed. Optimized geometries for neutral CeSin displayed that the most stable

Declaration of Competing Interest

The authors declared that there is no conflict of interest.

Acknowledgments

This work was supported by the National Natural Science Foundation of China (Grant No. 21863007), and by Program for Innovative Research Team in Universities of Inner Mongolia Autonomous Region (Gran No. NMGIRT-A1603).

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