First-Principles Investigation On Molecular Electronic Devices With Phosphorene Nano-Electrodes

In the design and research of molecular electronic devices,the properties of the interface between the electrodes and the molecule,and the characteristics of the electrode materials themselves are very important to the transport properties of the molecular electronic devices.Metallic materials are used as electrodes in traditional molecular electronics.However,due to the factors such as difficult connection between metal materials and molecules,easy oxidation and uncertain lattice orientation,there are some problems,e.g.the experimental results are difficult to repeat and difficult to compare with the theoretical calculation results,which limit the development of molecular electronic devices and their researchIn recent years,graphene and other two-dimensional materials have been suc-cessfully prepared,which have the characteristics of flexibility,easy cutting,high mobility of carriers,easy adjustment of electronic structure and conductive edge state.It is possible to overcome some problems of the electrode made of metallic materials by using two-dimensional materials as the electrode of molecular elec-tronic devices.There are many researches on the molecular electronic devices of graphene nanoribbon.In this paper,we try to construct a molecular electron,ic device with zigzag phosphorene nanoribbons(zPNRs)as electrode materials,and study the connection mode between phosphorene and organic molecules,the electronic structure and electron transport properties of the molecularjunction sys-tem.We discuss the advantages and disadvantages of two-dimensional electrode materials and traditional metallic materials in the electron transport process,and intend to provide abundant alternative electrode materials for the construction and experimental exploration of new molecular junction.Based on the density func-tional theory(DFT)and the first principle calculation method of non-equilibrium Green's function(NEGF),the electronic transport properties of the molecular junction system composed of PNRs are studied from the energy band structure,local density of states(LDOS),molecular energy spectrum(MPSH)and transmis-sion spectrum,and the internal physical mechanism of the molecular device effect is further discussed,then some meaningful conclusions are obtained.The main research contents are as follows(1)Two half-infinite zPNRs are used as electrodes to form molecular junc-tion with benzene molecules,and discuss the influence of two different interface coupling modes on the transport properties.If the molecular and electrode are combined by two C-P bonds,there is a negative differential effect under low bias voltage.However,the current of the system increases slowly with the combination of single C-P bond.The negative differential effect of low bias voltage has certain significance for sensitive devices.We analyze the internal mechanism of negative differential effect by calculating transmission spectrum,LDOS and MPSH(2)The exponential transport law of the molecular junction of oligophenylene-linked(OPL)and oligoacene-linked(OGL)at the phosphorene electrode is studied We study the change of conductivity with the increase of molecular length which is composed of zPNRs electrodes and 1,2,3 OPL/OGL molecular.With the in-crease of molecular length at low bias voltage,the conductivity of the molecular junction of the zPNRs electrodes still conforms to the law of exponential decay,but the attenuation factors are different.It is found that the attenuation factors are directly related to the coupling strength of the electrodes and the molecular(3)We have constructed a single molecular field effect transistor formed by zPNRs electrode and OPL molecular to study the controllability of gate voltage on source and drain current.From the analysis of the transmission spectrum and the molecular energy spectrum of the central molecular,we find that the gate voltage can effectively control the energy level position of the molecules in the scattering region,thus could adjust the transport properties of the system.we focus on the transport mechanism of molecular devices with new phosphorene electrode materials,and find the negative differential effect and obvious gate regulationOur use of zigzag phosphorene nanoribbons(zPNRs)as electrode materials is novel,and we have found that the molecular junction of zPNRs electrode has low bias negative differential effect and obvious gate regulation effect,indicating that zPNRs electrode has a certain development potential.The results of this paper may provide a theoretical reference for the analysis and design of new multi-functional single-molecule devices.