The Theoretical Investigation on the Structures,Electronic and Magnetic Properties of New SiC-or BN-based Low Dimensional Inorganic Nanomaterials

Author:Shen Xiao Peng

Supervisor:chen wei


Degree Year:2019





Successful preparation of graphene in experiments has aroused an upsurge in the research of low-dimensional nanomaterials.In view of the excellent optical,electrical and mechanical properties,graphene is considered to be a revolutionary material in the future and has a broad application in the next generation of electronic devices,energy storage and sprionics devices.As structural analogues of graphene,inorganic silicon carbide and boron nitride have also become new stars in the family of inorganic nanomaterials.Their superior properties have attracted extensive attention in experiment and theory.In this thesis,based on the density functional theory(DFT),we have constracted a series of new composite nanostructures by surface modification ofπ-conjugated chains with electron-donating/withdrawing groups,all-metal superhalogen Al13 and magnetic superhalogen MnCl3 on the low-dimensional silicon carbide(SiC)or boron nitride(BN)layer/nanoribbon,and further explore their electronic and magnetic properties.The findings are briefly summaried below:It is well known that the ground state of zigzag SiC nanoribbons(zSiCNRs)is energetically degenerate,with ferromagnetic(FM)and antiferromagnetic(AFM)configurations,somewhat preventing their practical application in multifunctional nanodevices.Here,a simple and effective strategy was proposed to modulate the electronic and magnetic properties of zSiCNRs via linkingπ-conjugated chains with electron-donating/withdrawing groups(-(CH=CH)n-NH2/NO2)on the surfaces of the nanoribbons.It is found that this type of covalent surface modification can evidently induce electron transfer between the zSiCNR substrate and conjugated chain by forming the typical donor–π–donor or donor–π–acceptor frameworks in the composite zSiCNR systems.Therefore,similar to applying an electric field,this can cause an evident change in the electrostatic potential of the substrate zSiCNRs,which can break the magnetic degeneracy of the zSiCNRs and endow these composite systems with either ferromagnetic metallicity or even ferromagnetic/antiferromagnetic half-metallicity.Moreover,all the studied systems also exhibit large negative formation energies,indicating their very high structural stabilities.These valuable findings can be advantageous for promoting the application of excellent SiC-based nanomaterials in multifunctional and spintronics nanodevices.Low-dimensional boron nitride(BN)nanomaterials have always been considered as an important member of the inorganic material family,but their wide band gap has seriously hindered their application in the field of electronic devices.Here,we propose to construct new composite nanomaterials by adsorbing superatom on the surface of BN nanomaterials,and modulae the electrical and magnetic properties.Superatom is a stable cluster consisting of many atoms,which can exhibit strong chemical bonds or closed electronic structures.As a typical hyperhalogen atom,Al13 has attracted extensive attention from experimental and theoretical researchers.On the basis of the first-principles computations,a new type of composite nanostructure(Al13@BN)can be constructed by depositing superhalogen Al13 on the surface of low-dimensional BN monolayer or nanoribbons(BNML/BNNRs).In view of the possible formation of an Al–N bond by a vacant p orbital of the Al atom receiving the lone pair of electrons of the N atom,the superhalogen Al13 can be stably adsorbed on the surface of these BN materials,and endow the composite Al13-BN with high structural stability.Moreover,it is revealed that independent of the chirality,ribbon width and adsorption site,introducing superhalogen Al13 can endow the BN-based composite systems with a magnetic ground state,and effectively narrow their robust wide band gaps.This can be advantageous for promoting the practical applications of excellent BN-based nanomaterials in multifunctional nanodevices.MnCl3 is another kind of important magnetic hyperhalogen atom.We constructed a new type of composite structure by depositing superhalogen MnCl3 on the surface of BNML/BNNRs.The DFT computations show that the superhalogen MnCl3 can be stably adsorbed on the surface of BNML/BNNRs,and result the increase in electrostatic potential in the BN substrate due to a charge transfer between BN and MnCl3parts.Regardless of dimension,chirality,ribbon width,adsorption site and coverage of MnCl3,adsorbing MnCl3 can endow these hybrid BN nanomaterials with a large magnetic moment,and significantly reduce the robust wide band gap of BN materials to the range of 0.0980.948 eV.These research results are helpful to promote the practical application of low-dimensional BN nanomaterials in multi-functional nanodevices fields.