Theoretical Study Of The Electronic Structures And Transport Properties Of C/Si Copolymerization Conductive Polymer Materials

Recently,carbon-based and silicane-based one-dimensional nanomaterials have draw continiuous attention because of their application prospect.The conductive polymer materials with ?-conjugate system,such as polyethylene,polypyrrole,polyferrocenophane,polythiophene make their polular application in electronic components or transistor due to their advantages of excellent thermal,mechanical,electrical peroerties and high tenacity.However,these kinds of conductive polymer materials have not good stability.Silicon-alkyl one-dimensional nanomaterials have good stability with domain ?-conjugate system of silicon chain,but their electrical conductivity is weaker than carbon-based conductive polymer materials.Therefore,the researchers have gradually put focus on carbon-based and silicane-based copolymerization of one-dimensional nanomaterials,thus poly?phenyl silane?,polyvinylsilance,polyferrocenophane-silane and copolymer of silane and thiophene have been synthesized.This kind of new nano-materials is studied on mechanical,thermal,optical characteristics,but the theoretical researches the electronic structure and transport properties are less.In this paper,the electronic structure and transport properties,the relationship between the structure and the performance of two kinds of C/Si copolymerization polymer materials are theoretically researched.These work will provide theoretical references for the development of C/Si copolymer conductive polymer materials.Firstly,the structures of the two series of copolymerized polymer materials were optimized,and two-probe devices were established according to the structural characteristics.Secondly,the transport properties of a series of ?-? conjugated nanowires[?SiH₂?_x?CH=CH?_y]_n?n = 2-4 & ?,x = 2-4,y = 1-4?using non-equilibriumGreen? s function?NEGF?formalism with the density functional theory?DFT?were studied.It was found that the silanylene moiety length x,the ethenylene moiety length y,and the whole molecular length n played important roles in governing the transport properties of the nanowires:?1?the conductivity tended to be decreased with increasing the silanylene moiety length x;?2?length increase of the ethenylene moiety y was not always favorable to enhancing conductivity;?3?the zero-bias conductance was exponentially decayed with the whole molecular length n.Further analysis indicated that the conductivities well correlated with the transmission spectra and the topology of the HOMO and LUMO states.Finally,silicon bridge-tuned electronic structures and transport properties of polymetallocenes,([V?Cp?₂?SiH₂?_n]_m?n=1-3,m=?,Cp= cyclopentadienyl?,were studied using the density functional theory?DFT?and non-equilibrium Green? s function?NEGF?methods.As the silicon bridge was lengthened,the V-V ferromagnetic?FM?coupling was weakened,while the antiferromagnetic?AFM?coupling was strengthened.Polymetallocenes [V?Cp?₂?SiH₂?₁]_m and[V?Cp?₂?SiH₂?₂]_m favored the FM ground state,while [V?Cp_?2?SiH₂?₃]_m prefered the AFM ground state.Each V atom in the FM state of [V?Cp?₂?SiH₂?₁]_m and[V?Cp?₂?SiH₂?₂]_m has a magnetic moment of ³.0 ?B.The transport properties of[V?Cp?₂?SiH₂?₁]_m,[V?Cp?₂?SiH₂?₂]_m and [V?Cp_?2?SiH₂?₃]_m were in good agreement with their electronic structures.Their conductivities followed the sequence [V?Cp_?2?SiH₂?₃]_m > [V?Cp?₂?SiH₂?₂]_m > [V?Cp?₂?SiH₂?₁]_m.For[V?Cp?₂?SiH₂?₁]_m and [V?Cp?₂?SiH₂?₂]_m,the spin-down state had slightly higher conductivity than the spin-up state.Polymetallocenes [V?Cp?₂?SiH₂?₁]_m and[V?Cp_?2?SiH₂?₃]_m systems both displayed evident negative differential resistance?NDR?behavior,while [V?Cp?₂?SiH₂?₂]_m could not.This difference may originated from the orientation of the two V?Cp?2 units,which was V-shaped for[V?Cp?₂?SiH₂?₁]_m and c?odd number of SiH₂ units?lead to ioniclike inter-quantum dot coupling,and parallel for [V?Cp?₂?SiH₂?₂]_m?even number of SiH2 units?to,lead to covalent-like interquantum dot coupling.In addition,the conductivity of [V?Cp?₂?SiH₂?₁]_m,[V?Cp?₂?SiH₂?₂]_m and [V?Cp_?2?SiH₂?₃]_m was sensitive to the current direction because of the asymmetric coupling between the scattering region and two electrodes.Compared the bandgaps of [V?Cp?₂?SiH₂?_n]_m and [?SiH₂?_x?CH=CH?_y]_n,we knowed that the conductivity of [?SiH₂?_x?CH=CH?_y]_n was higher than that of[V?Cp?₂?SiH₂?_n]_m.In addition,[V?Cp?₂?SiH₂?₁]_m and [V?Cp_?2?SiH₂?₃]_m had obvious a negative differential resistance effect.however,all the [?SiH₂?x?CH=C H?y]n system had not negative differential resistance effect.This work showed that the specific function of new C/Si copolymerization nano conductive polymer materials could be designed through the combination of different carbon and silicon alkyl structure units.