Erbium Nanowires On Silicon Surface: A First-principles Study

Silicon materials are the cornerstones of the modern semiconductor industry,and silicon materials dominate the semiconductor materials for various applications.With increasing requirements for information processing efficiency as well as information storage density in semiconductor materials,the size scale of integrated circuit design architectures continues to shrink,with today’s interconnect sizes being less than 10nanometers.Incorporating nanoscale components into integrated circuits will require interconnects of a similar scale,and technologies such as self-assembled nanowires will become even more compelling below these scales.By inducing surface reconstruction through adsorption of different metallic elements on the silicon surface to form structures such as nanodots,nanorings,and nanowires,not only can a range of interesting physical phenomena be explored,but also have great applications in the fields of nanoelectronics and spintronics.In recent years,the formation of nanostructures on silicon surfaces induced by rare-earth metals(REM)has attracted great interest because of their promising electronic device applications.Among the various kinds of reconstructions induced by REM on silicon surfaces,of particular interest and attraction are REM nanowires grown on Si(001)surface by self-organization which are characterized by one-dimensional(1D)linearity.In this thesis,we have performed a detailed ab initio study on the Er nanowire on clean Si(001)surface.Firstly,we investigated the structural stability of the bulklike and the double-core odd-membered ring(5-7-5)structure of Er on the Si(001)surface.We found that the double-core odd-membered ring(5-7-5)structure is one of the most stable surface structures at lower coverage and has the lowest total energy in the ferromagnetic(FM)ground state.We also calculated the total energy as a function of the total magnetic moment in the double-core odd-membered ring(5-7-5)structure by fixing the magnetic moment to obtain the correct FM ground state.Then we calculated the electronic properties for the stable Er nanowire on Si(001)surface with double-core odd-membered ring(5-7-5)structure.The total magnetic moment of the double-core odd-membered ring(5-7-5)structure is about 8.20μ_B,which is mostly all contributed by Er-4f orbital electrons.The magnetic moment at each Er site is about 2.04-2.06μ_B.The calculated electronic band structures and band-decomposed charge density distributions show that the highest occupied state is mainly contributed by the Er-4f orbits,and the lowest unoccupied state is contributed by the p-orbits of the buckled Si dimer on the Si(001)surface,which are surface states.In general,the surface structure of the double-core odd-membered ring(5-7-5)structure exhibits the properties of an indirect bandgap semiconductor with a small indirect surface band gap of about 0.13 e V.Finally,we investigated the surface bonding and electron transfer in the double-core odd-membered ring(5-7-5)structure.By analyzing the electron localization function(ELF)maps,we found that each Er atom on the(5-7-5)Si-rings is ionically bonded to the four nearest Si atoms,with each Er atom providing two electrons,and a total of four Er atoms corresponding to eight Si atoms in the whole structure.The bonding behavior due to these electron transfers indicated that the hanging bonds of the Si atoms on the(5-7-5)Si-rings are completely saturated by the Er atoms,which means that the double-core odd-membered ring(5-7-5)structure is thermodynamically stable in the FM ground state.