Influence Of SW Defect,Edge Modification And Heterojunction On Transport Properties Of Zigzag Silicene Nanoribbons

With the successful preparation of graphene in recent years,nanomaterials have aroused a enthusiasm among scientists from various countries.The application of nanomaterials to practical electronic devices is an important research topic.Silicon is the backbone of the microelectronics industry.The study of Silicon-based nanomaterials will have more significant importance to its practical use in micro electronics industry.The two-dimensional material,silicene,is well compatible with existed silicon-based technologies,and has become one of the most suitable candidate materials that can be applied to modern micro-nano devices.At present,the preparation of silicene is difficult,its stability is not so strong.All these disadvantanges make the experimental research on silicene-based electronic devices very difficult.However,The first principles study of silicene-based electronic devices can provide a certain solution for exploring the properties of silicene nanoribbon et al and improves the research efficiency significantly.Therefore,using density functional theory combined with first-principles methods of non-equilibrium Green's function,we studied the effects of SW defects,edge modification and heterojunctions on the transport properties of zigzag silicene nanoribbons,including the geometry,electromagnetic and thermal properties of silicene nanoribbons.Additionally,the inherent mechanism of some intrigue properties such as negative differential resistance(NDR)and spin polarization are researched in detail.The major research details and results of this paper are listed below:Firstly,the two-electrode model of the zigzag silicene nanoribbons(ZSiNRs)with or without stone-wales defect are simulated.Their optimized lattice structure and electrical transport performance are calculated using the density functional theory combined with the non-equilibrium Green function method.Including the conductivity of the molecular Junction,the current-voltage characteristic curve,the electron state density of the frontier molecular orbital and thermal conductivity are studied in detail,respectively.We found that the binding energy of silicene nanoribbons with stonewales defect is significantly lower than that of graphene and silicene,indicating that these defects in silicene nanoribbons have relatively higher stability as in graphene and silicene.The NDR behavior can be observed both in the perfect silicene nanoribbons and the SWdefected ones.The SW-defected silicene nanoribbons have a better rectifying effect than the perfect ones at high bias voltage From the analysis of the frontier molecular orbital electron state density spectrum(MPSH),the NDR behavior stems from the decrease of the frontier molecular orbital electron state density,which is caused by the increase of external bias voltage.The thermal transport properties of SW-defected SiNRs under different sizes are also involved in our research by calculating the thermal conductivity of SiNRs and the transmission of simulated heat flux using the non-equilibrium simulation(NEMD).Our study reveals the mechanism of the negative differential resistance of the silicene nanoribbons in a certain bias voltage range;the influence of Stone-Wales defects on the rectification in the zigzag silicene nanoribbons as well as on the thermal conduction of silicene nanoribbons.Secondly,the effects of edge-modified by transition metals Mn and Co on the spin filtering efficiency and electronic conductivity of the zigzag silicene nanoribbons are investigated,the performance of two kinds of nanodevices was discussed.By applying the first principle caculation,the effect of Mn passivation on the single edge of silicene nanoribbons were studied.By caculating its magnetic and transport properties,we found that when the doped silicene nanoribbons are in the spin-up states,more electron tunnel transmission channels are opened,higher transmission coefficients appear,while the spin-down state channel seems to be suppressed,which indicates a relatively good spin filtering property.On the other hand,the energy of the doped silicene nanoribbons under AFM coupling is 0.56 meV lower than that of FM coupling ones,showing that the introduction of Mn atoms makes the zigzag silicene nanoribbons more inclined to be in the anti-ferromagnetic States.The results of energy band calculations also demonstrate that the silicene nanoribbons with manganese modified edges have semi-metal properties which could be a good candidate of Nano electronic devices.As for Co atom doping ones,the total energy of the unit cell in ferromagnetic state is lower than that in antiferromagnetic state,which indicates that the ground state of cobalt doped silicene nanoribbons is ferromagnetic state.The calculation also shows that the spin filtering efficiency can reach nearly 100% within the limited bias range.Thirdly,a ZAZ silicene nanoribbon Heterojunction model with zigzag-armchair is constructed based on the silicene nanoribbon.Differential conductivity,transmission spectrum and electron state density spectrum of frontier molecular orbitals at different widths are calculated.The result shows that the differential conductivity of the three systems are reduced in accordance with the order of 5-ZAZ>4-ZAZ>3-ZAZ.Interestingly,NDR phenomena can only be observed in some bias voltages of 3-ZAZ SiNRs.The study of the mechanism illustrates that the NDR behavior originates from the joint action of LUMO of the frontier molecular orbital and the inhibition of the increase of bias pressure.The transport properties of heat in silicene and arsenene heterostructure nanoribbons are also investigated.It is found that the thermal conductivity of the heterojunction decreases with the increase of the temperature of the system,and almost keep unchanged with the mutative length of the nanoribbons.Which means the thermal transport properties of this system is insensitive to the influence of the size.These properties may be very useful in dsesigning some nano electronics device which has high demands to the stability of thermal conductance.Our results may provide some theoretical support for the potential application of two-dimensional nanostructured molecular junction devices with heterojunctions.