Transition Metal Doped First-principles Study Of Silicon Clusters

With the development of the nanotechnology, low-dimensional nanostructure materials play a critical role in the fundamental research and potential microelectronic devices. In recent years, clusters and nanowires or nanotubes have attracted intensive attentions and become an interesting subject as representatives of the low-dimensional nanostructure materials. As the bridge between microscopic atom or molecule and macroscopic condensed matter, the clusters exhibit various size-dependent properties so that people can design new materials by means of the building blocks of the clusters.Silicon-based materials have been the focus of extensive research due to their importance in microelectronic industry. New forms of Silicon-based low-dimensional nanomaterials have been considered. A number of studies have been carried out to the Si clusters. Researchers found that due to the existence of dangling bonds, the pure Si clusters exhibit chemical reactivity and the hollow Si cage structures are unsuitable to be as the building blocks of self-assembling materials. However, by doping some metal atoms into silicon clusters, the stability and properties of silicon clusters can be improved, new functional material can be developed. For those reasons, there is scientific significance and applied value to study semiconductors by mixing metal into silicon. We here use the first principle method based on the density functionaltheory to study 3d transition-metal- encapsulating Si₁₂ cage clusters, calculate thebinding energy of each atom (BE), HOMO-LUMO energy gap, the vertical ionization potential (VIP), the adiabatic electron affinity (AEA) and magnetic moment. The results imply that as the difference of the doping transition metal atoms, the valenceelectron increase gradually and the stability of SiuM clusters are changed. For theclusters Si₁₂Cr,Si₁₂Fe,Si₁₂V^- and Si₁₂Mn⁺ which satisfy the "18-electron rule" or the "20-electron rule", they are more stable than their neighbors, and we validate that when keeping to the Wigner-Witmer rule, the stability of Si₁₂M could be understood within an octet rule well. In the magnetism, the transition metal atoms have magnetic moments, however, when they are encapsulated into the Si₁₂ cage, the magneticmoments of most metal atoms are completely quenched and become to zero. We also have studied on Si₁₂M and Si₁₈M₂ (M = Cr, Mo, W) cluster and find that afteroptimizing structures, the most stable structures are the hexagonal prism and the hexagonal double prism structure respectively. We also calculate the bond length, the relational energies and magnetic moments of Si₁₂M and Si₁₈M₂ clusters, the Si₁₂Mclusters which have 18 electrons are stable. When doping two different metal atoms, we find that with the same electrons, the binding energy increase with the atomicradius increasing, the stabilities are stronger. In addition we find that Si₁₈M₂ (M =Fe, Ru, Os) with magic characters also have stronger stability. When self-assembled for Si₁₂Mo, it shows small binding energy, the interaction between these two clustersis weak, make these clusters attractive for cluster-assembled materials as building blocks.