Transport Properties Of Organometallic Metal-benzene Complexes

Recently,Moore’s Law is going to be invalid,since Very Large Scale Integration（VLSI）is likely to reach its limit of miniaturization.Meanwhile,the Molecular Electronics has developed fast since it can be a great solution to this global problem.The development of molecular materials and theoretical researches have attracted a great deal of interests from scientists.Low-dimensional materials,especially the Topological Insulator materials like graphene,have attracted great attentions.Many experimental and theoretical studies have been carried out on one-dimensional materials like carbon chain,and muti-decker-cyclopentadienyl complexes,as well as on some two-dimensional materials like graphene and stanene.Organometallic Metal-Benzene Complexes[M_n（Bz）_m,（M=Sc-Co）]have been synthesized in early experiments.As low-dimensional materials,they have complex structures and rich properties and therefore sufficient theoretical studies are in need.We investigated electrical,magnetic and thermal properties of M_n（Bz）_m using the density functional theory and nonequilibrium Green’s function techniques.In our investigations,seven transition metal atoms from Sc to Co are used as a part of M（Bz）₂,and we develop junction models by sandwiching the molecules between two gold nanowire leads.In this work,we investigated two different lead-molecule-lead junctions,as T-shaped and H-shaped junctions.The molecular properties were calculated using an ab initio method from the GAMESS program and the properties of molecular junction were calculated by ATOMISTIX-TOOLKIT（ATK）program.Firstly,we investigate the molecular junction model,in which Fe（Bz）₂ is coupled between two Gold nanowire leads.As the Fe（Bz）₂molecular has two spin states,high-spin and low-spin,the calculations of the two sulfur atoms anchoring Fe（Bz）₂complex reveal high energy gap between the high-spin s=1 state and low-spin s=0 state.It is found that the asymmetrical T-shaped contact junction still has two spin states,while the H-shaped contact junction only has the low-spin state.By calculating the transport properties of two different shaped junctions in different spin states,it is found that the current curve of H-shaped junction is spin-independent while the T-shaped junction displays the spin-polarized current characteristics.Meanwhile,for the T-shaped junction,the molecular junction in high-spin state has a good spin-filter effect and Seebeck effect.Also,we found that the high-spin state shows a smaller total current than the low-spin one.By further analyzing these conclusions,we found that the d_xy and d_yz electrons lead the transport process,and effect the transport properties of different contact types in different spin states.Then,the remaining transition metal atoms are taken into consideration.The calculations show that the magnetism of the molecular varies with the change of different metal atoms.Then,we calculate the transport properties of two different contact type junctions.The H-shaped junctions have high symmetric contact structures,and the spin-filtering effects are observed in H-shaped junctions when the central molecules have magnetic moments.Although there is no spin-crossover effect in the M（Bz）₂ for the remaining metal atoms（except Fe）,varying degrees of spin Seebeck effect can be observed.Meanwhile,negative differential resistance（NDR）effects can be seen when the atomic numbers of metal atoms are less than 25（Mn）.In summary,we investigate the transport properties for a series of Organometallic Metal-Benzene Complexes[M_n（Bz）_m（M=Sc-Co）].Our findings strongly suggest that the Organometallic Metal-Benzene Complexes are promising materials for application in spintronics and thermo-spintronicdevices.