Study Of Charge Transport,AC Response,and Mobility Properties In DNA Molecules

As we known,scientists have studied the field of molecular electron-ics for more than 40 years.Recently,with the breakthrough of experi-mental techniques and the development of theoretical methods,scientists have actually obtained the chance to explore the conductance properties of single-molecule junctions.As the traditional silicon material,molecular electronic devices are likely to become one main candidate of components of the future semiconductor industry.As a research branch of molecular electronics,DNA molecules have frequently been brought to the center of hot topics.By now,DNA molecule has attracted a lot of attentions from worldwide researchers due to its good self-assembling ability.In this dissertation,we will study properties of charge transport,ac response and polaron mobility of DNA molecules.In the first chapter,we briefly cover the development history of molec-ular electronics,including the introduction of the corresponding important experiments and theories.With regard to the main topics of this dis-sertation,we also outline the recent advancements related to the DNA molecules,and discuss the pros and cons for two main transport computa-tional models of the DNA molecules:the one-dimensional model and the two-channel model.In the second chapter,we first derive the general expressions of time-dependent current,time-independent current and transmission coefficient in a mesoscopic system.Then,taking advantage of landauer formula,we obtain the transport current through DNA molecular junction with-in the non-equilibrium Green's function approach.We make a detailed discussion about the I-V characteristics of DNA sequences?GC?N_GCand?GC?1?T A?N_{T A}?GC?3.We find that,by using a gate voltage to adjust the highest occupied molecular orbital?HOMO?in DNA,the conduc-tivity of sequence?GC?N_GCcan increase rapidly where the bias voltage is low.For DNA sequence?GC?1?T A?N_{T A}?GC?3,our work also shows the phenomenon of a weak distance dependent conductance,which is ob-served by a pioneering experiment.However,distinguished from thermal-ly induced hopping of charges explained by the experiment,the intrinsic physics mechanism of this phenomenon we propose is that discrete quan-tum well states in the T A base pairs dominate the quantum tunnelling process.In the third chapter,we study the ac response of the above mentioned DNA sequences?GC?N_GCand?GC?1?T A?N_{T A}?GC?3 under light illumina-tion.First,we derive formulas for the real and imaginary parts of the ac conductance of DNA molecule.By calculation,we find the suppression phenomenon in ac conductances'real parts of the left and right lead of DNA sequences at certain frequencies.In fact,the conductance suppres-sion can be attributed to the excitation of electrons in the DNA sequences to the Fermi surface of metal electrodes due to ac potential,or to the excitation of electrons in deep energy levels of DNA sequences to partially occupied energy levels in the transport window.Based on the one-dimensional model for electronic transport along D-NA,we investigate the polaron mobility in DNA molecule with the effect of electron-vibration coupling in the fourth chapter.By analyzing depen-dence of the DNA polaron mobility on temperature,lengths and sequences of DNA molecule,it is obvious that our results are qualitatively consis-tent with the previous polaron mobility of the three-dimensional organic crystal case in despite of two different approximation approaches.Finally,in the fifth chapter,we sum up the whole content of this dissertation and give some insights into the future works.