Probing the valence orbitals of transition metal–silicon diatomic anions: ZrSi, NbSi, MoSi, PdSi and WSi

Abstract

Evolution of electronic properties and the nature of bonding of the 4d-transition metal silicides (ZrSi, NbSi, MoSi and PdSi) are discussed, revealing interesting trends in the transition metal-silicon interactions across the period. The electronic properties of select transition metal silicide diatomics have been determined by anion photoelectron imaging spectroscopy and theoretical methods. The electron binding energy spectra and photoelectron angular distributions obtained by 2.33 eV (532 nm) photons have revealed the distinct features of these diatomics. The theoretical calculations were performed at the density functional theory (DFT) level using the unrestricted B3LYP hybrid functional and at the ab initio unrestricted coupled cluster singles and doubles (triplets) (UCCSD(T)) methods to assign the ground electronic states of the neutral and anionic diatomics. The excited electronic states were calculated by the DFT (TD-DFT)/UB3LYP method. We have observed that the valence molecular orbital configuration of the ZrSi and NbSi anions are significantly different from that of the MoSi and PdSi anions. By combining our experimental and theoretical results, we report that the composition of the highest occupied molecular orbitals shift from a majority of transition metal s- and d-orbital contribution in ZrSi and NbSi, to mainly silicon p-orbital contribution for MoSi and PdSi. We expect these observed atomic scale transition metal-silicon interactions to be of increasing importance with the miniaturization of devices approaching the sub-nanometer size regime.

Study on Structural Evolution, Thermochemistry and Electron Affinity of Neutral, Mono- and Di-Anionic Zirconium-Doped Silicon Clusters ZrSin0/-/2- (n = 6–16)

“…There are many such example. For instance, at the CCSD(T) level, the LanL2DZ basis set for Si atom predicted the ground state of ZrSi was to be triplet state, but 6-311+G(3df,3pd) basis set for Si atom predicted to be singlet state [1].…”

“… a The relative energy, AEA, VDE, and D 0 is in eV. The AEA and VDE were calculated based on the 2 ∑ + ground state of anionic ZrSi - ; b The data taken from [1]; c The data taken from [25]; d The data taken from [24]. …”

“…Transition metal (TM) silicides as novel functional materials have been extensively utilized in diverse fields such as aerospace, microelectronic device manufacturing, optical instruments, magnetic material, and the chemical industry because of their oxidation resistance, high-temperature stability, and low electrical resistivity [1,2]. For example, in the early 1960s platinum silicide was successfully used to improve the rectifying characteristics of diodes [3].…”

“…Composite coatings including molybdenum silicide can be used for protection of missile nozzles and aero engine blades [5]. Zirconium silicide is an ideal device with significant potential applications as anode materials in Li-ion batteries, protective coating on zirconium-alloy fuel cladding in light water reactors, heating elements for electrical furnaces, and also can be incorporated into the semiconductor industry as large scale integrated circuits, Schottky barriers, Ohmic contacts, and rectifying contacts due to the fact that interfaces of zirconium and silicon have good lattice matching, sharp interfaces, low Schottky barrier heights, high conductivity, and excellent thermal stability [1,2,6,7,8]. Therefore, a large amount of research on zirconium silicides was carried out in the past few decades.…”

“…On the experimental aspect, Koyasu et al investigated the equilibrium configurations, electronic structures, and properties of MSi n (M = Zr, Sc, Y, Lu, Ti, Hf, V, Nb, and Ta, n = 6–20) by means of anion photoelectron spectroscopy (PES) and their reactivity to H 2 O adsorption, presented their AEAs and vertical detachment energies (VDEs), and discussed the cooperative effect between their geometric and electronic structures [22,23]. Recently, bond dissociation energies, valence orbitals, AEAs, and VDEs of ZrSi have been measured by using resonant tow-photon ionization spectra and photoelectron imaging spectroscopy, respectively [1,24,25].…”