Mechanism Of Electron-phonon Interaction In Nanoscale Electronic Devices

The electrical transport properties of a nanoscale device determine its applications in the fields of logical computing,sensor and energy-harvesting.Accurate study of the elec-trical transport properties of nanoscale devices is therefore important for the exploration and design of their applications.However,the effects of inelastic transport processes are ignored in many theoretical researches,and only the phonon-independent elastic transport processes are considered therein.In this dissertation,our theocratical researches show that the contribution of inelastic transport processes might be very strong sometimes,and significantly influence their transport properties.Thus,it may not be suitable to ignore the inelastic transport processes in some systems.The nonequilibrium Green’s function and the generalized lowest-order expansion method with consideration of electron-phonon interactions（EPIs）are used to investi-gate the spin-dependent electronic transport properties of ferromagnetic zigzag graphene nanoribbons.Results show that the consideration of EPIs will lead to a 4-5 orders of mag-nitude increase of the current in some bias regions when the spin polarizations of two electrodes are antiparallel.This results in the vanishing of the dual spin filtration effect and a narrowing of the effective bias region of giant magnetoresistance.The increases of the current mainly stem from first Born scattering process,and can be described by the Fermi’s golden rule,and may be a result of the breaking of the structural symmetry by the introduction of phonons.Based on the nonequilibrium Green’s function and density functional theory,a method to investigate the spin-dependent Seebeck effect（SDSE）with consideration of inelastic transport processes is presented.Results show that phonons with lower vibration energy may have more possibilities to contribute thermal drive inelastic currents and affect the SDSE properties.Consideration of inelastic processes may show both promotive or re-strictive corrections to the SDSE properties.A sample calculation in graphene nanorib-bons shows that the inelastic processes may contribute approximately two times the elastic current and will promote the SDSE of this sample device.We find that the main source of the large inelastic currents is coupling to the in-plane breathing mode.These results may be helpful for understanding of the physical process underlying the SDSE.The electrical transport properties of a single-molecule device were investigated us-ing the nonequilibrium Green’s function and density functional theory while taking inelas-tic processes into account.Ours results are in agreement with experimental data in which the height of the current plateau increased along with the temperature.It is found that this increase in the height of the current plateau is caused by inelastic resonant tunneling rather the decoherence mechanism of the quantum interference effect.And we find that some small steps and the tilt in the main current plateau are also responsible by the inelastic resonant tunneling processes.These results help us to understand the electrical transport mechanisms in single-molecule devices.A method,based on the nonequilibrium Green’s function and density functional the-ory,to investigate the differential conductance is presented.It is proved that the differ-ential conductance can be satisfactorily understood by the principle of inelastic resonant tunneling.Based on the equations,we provide the relationship between each peaks of dif-ferential conductance and their corresponding peaks of inelastic resonant tunneling.And the“sum effect”in differential conductance contour charts is proved by our method too.Based on this method,we investigate the differential conductance contour charts of C₆₀molecule device,and the results are in agreement with experimental data.