Study On The Transport Properties Of Transition Metal Complexes Embedded In Graphene And Dichalcogenide Compounds

The excellent electrical,optical,magnetic properties,and wide application ranges of graphene and transition metal dichalcogenides?TMDs?have stimulated great research enthusiasm.The novel two-dimensional?2D?materials formed by surface functionalization,covalent doping,strain engineering,stacking or intercalation have broadened their applications.Among them,the study of covalently embedded transition metal complexes is favored,but few studies have reported that porphyrin molecules are covalently embedded in graphene nanoribbon?GNR?and transition metal complexes are intercalated between TMDs interlayer.In this paper,the above two complexes are investigated using the first-principles calculation method combining density functional theory?DFT?and non-equilibrium Green function?NEGF?,and the results reveal their potential applications in magnetic devices,optoelectronic devices and spin filters.The research contents are as follows:Firstly,one-dimensional?1D?composite systems Fe PP-GNR are formed by covalently embedding iron porphyrin?Fe PP?molecules into GNR and the transport properties of the planar structures?labeled p?and their wrinkled isomers?labeled w?are investigated.The effects of the embedding positions of Fe PP,the embedding concentrations of Fe PP,and the compressive strain on the properties are comprehensively examined.It is found that the compounds embedded with high concentrations of Fe PP tend to favor ferromagnetic?FM?ground states while the compounds with low embedding concentrations of Fe PP tend to prefer antiferromagnetic?AFM?ground states.The phenomenon of spin polarization becomes more and more obvious with the increase of strain intensity?and the magnetic moment increases with the increase of?.Embedding high concentration of Fe PP makes the systems have higher conductivity,while complexes with the low embedding concentrations of Fe PP exhibit significant negative differential resistance?NDR?effects.The magnetic properties,electronic structures,and transport properties of the composite systems can be tuned by strain,the embedding positions and concentrations of Fe PP.Secondly,Fe PP-GNR monolayers with different sizes adopt four stacking modes to form composite bilayer systems m AA,m AB,m AA',and m AB',and their transport properties are investigated,where m=1,2,3,and 4 reflects the sizes of the nanoribbons from small to large.It is found that all systems exhibit FM ground states,and the m=1,2,and 3 systems are metallic and the m=4system is semiconducting.The typical metallic m=1 system and semiconducting m=4 system are selected for in-depth study.As a result,all the eight systems have large magnetic moments and the carrier transport mainly depends on the Fe-Fe interaction in bilayer systems.All the systems exhibit polarized transport properties,the current of the spin-down state is higher than that of the spin-up state,the conductivities of systems are affected by both the stacking types and the sizes of the nanoribbons.Most of the spin filtering efficiency?SFE?of 1AB,1AB',and 1AA'systems is greater than 80%within the bias from-1.0?1.0 V,especially the SFE of 1AA'system is close to 100%.All m=4 systems show significant NDR effects,and 4AB'system also shows the current flip phenomenon.Finally,the transport properties of the novel intercalation compounds PdCl₂/Pt Cl₂-MX₂?M=Mo,W;X=S,Se?formed by covalently embedding PdCl₂/Pt Cl₂ groups into the bilayer space of MX₂ are investigated.It is found that the Pd/Pt tend to adopt the planar tetradentate coordination mode of PdCl₂X₂/Pt Cl₂X₂.The intercalations of PdCl₂/Pt Cl₂ groups enhance the chance of electron-hole recombination in the systems,and their derived VBM and CBM are shielded well by the MX₂ bandgap,which is beneficial to improve the fluorescence quantum yield.Nevertheless,the conductivities of the composite systems are slightly lowered down than MX₂ owing to the embedding of PdCl₂/Pt Cl₂ exerts a trap effect on the carrier transport.The transport properties show obvious anisotropy,and the conductivity of the zigzag system is higher than that of the armchair system.The results of photocurrent effect?PGE?are contrary to the conductivity,and the armchair system exhibits much higher photoresponse comparing with the zigzag system.For a given MX₂,the PdCl₂ induce higher photoresponse than the Pt Cl₂.Furthermore,the photoresponse intensity can be tuned by the polarization angle?and photon energy,and the photoresponse on/off switches can be designed.