Adsorption Behavior Of Iron, Cobalt And Nickel Small-sized Clusters On Armchair Graphene Nanoribbons

The electronic properties of one-dimensional (1D) graphene nanoribbons(GNRs) are determined by the width of the ribbons and the atomic geometryalong the edges. By introducing defects, impurities and adsorbates, we cansignificantly change the electronic and magnetic properties of the GNRs.Specially, transition metal clusters adsorbed on GNRs will form different typesof structures, and significantly change the physical and chemical properties ofthe systems. Therefore, transition metal clusters adsorbed on the graphenenanoribbons could provide further potential applications in designing newmaterials for spintronic devices. In this thesis, the geometries and relatedproperties of Fen, Conand Nin(n=1-4) clusters adsorbed on armchair graphenenanoribbons (AGNRs) with different widths were theoretically investigated byusing density functional theory.In the first chapter, we mainly introduce graphene and graphene nanoribbon, including its experimental synthesis method and the latest progress. At the sametime, we describe the electronic properties of graphene nanoribbons withdifferent widths and edge structure. Finally, the research purpose andsignificance of this thesis are briefly presented. In the second chapter, weconcisely review the basic theoretical of density functional theory and theVienna ab-initio Simulation Packages (VASP). The third chapter and the fourthchapter mainly introduce our studies.In the third chapter, we systematically investigated the adsorption behaviorof Fen, Conand Nin(n=1-4) clusters on N=8armchair graphene nanoribbon(8-AGNR) and analyzed the structural stabilities, electronic and magneticproperties of Fen/AGNR, Con/AGNR and Nin/AGNR systems. We found that theFen/AGNR, Con/AGNR and Nin/AGNR systems have high stabilities and largemagnetic moments, the total magnetic moment of Fen/AGNR is lager than thoseof Con/AGNR and Nin/AGNR. Because of the1D structures of graphenenanoribbons，the most favorable adsorption sites for different-sized Fen, ConandNinare all at the edge of AGNR, and the clusters prefer to form two-dimensional or three-dimensional clusters rather than disperse to separatedadsorption sites. In addition, the edge structure of AGNR will have somedistortions due to the interaction between metal atoms and nearest-neighborcarbon atoms. Unlike AGNR non-magnetic semiconductor properties, thehalf-metal with-100%spin polarization was observed for the Fen/AGNRsystems when n=1-3, while the Fe4/AGNR system is a ferromagnetic (FM) semiconductor. For the Con/AGNR systems, only the system of Co singleadatom on AGNR exhibits half-metal electronic structure, but the Con/AGNR(n=2-4) systems remain FM semiconductor. Furthermore, Nin/AGNR systemsexhibit different states from those of Fen/AGNR and Con/AGNR. Theground-state Ni/AGNR was identified as a non-magnetic semiconductor, whileothe Nin/AGNR (n=2-4) are all half-metal. In addition, by changing themagnetic states of clusters, we found significant magnetoresistance effect in thesystems with half-metal.In the fourth chapter, considering the AGNRs with different widths havedifferent mirror symmetry, we chose the AGNR with N=9as model system tostudy the related properties of Fen, Conand Nin(n=1-4) clusters adsorbed onAGNR. The half-metal with-100%spin polarization was observed for theFen/AGNR systems when n=1-4. For Con/AGNR systems, we found that thesystems are half-metal, except for Co3/AGNR, which can exhibit FMsemiconducting behavior. For Nin/AGNR systems, we found that the Ni/AGNRsystem is non-magnetic semiconductor, while Ni3/AGNR and Ni4/AGNRsystems are half-metal with-100%spin polarization. More interestingly,Ni2/AGNR is also half-metal, but its spin polarization is+100%. These resultsshow that Fen/AGNR, Con/AGNR and Nin/AGNR have different electrical andmagnetic properties. Depending on the nature of clusters, the systems could beused to build functionalized nanodevices.