The Electronic Transport Properties Of Carbon-based Molecular Devices

With the gradual miniaturization and high integration of electronic devices,molecular electronic devices have potential application in nanoelectronics and optoelectronic integration due to their unique properties,which have attracted widespread attention.At present,although great achievements have been made in the research of molecular electronic devices,there are still many problems need to be solved in terms of their properties and synthetic processes.These problems severely constrain development and practical application of molecular electronic devices.In our study,the effects of the number of benzene rings on the transport properties of polyaromatic hydrocarbon molecules(PAHs)were analyzed using first-principles non-equilibrium Green's functions(NEGF)and density functional theory(DFT),and the mechanism of the odd-even effect was analyzed.In addition,the electron transport properties of the combination of benzene and thiophene and the combination of benzene-thiophene molecules with side groups were analyzed.The influence of molecular combination structure and side groups on the transport properties of molecular devices was revealed,confirming that different molecular combinations produce unique properties and analyzing the mechanism of the side groups on transport behavior.Finally,we analyzed the transport properties of SimCn clusters,discussed the effect of the number of Si and C atoms on their properties,and analyzed the relationship between the width of zigzag graphene nanoribbons(ZGNR)and devices properties.The main research contents of this thesis are as follows:(1)PAHs with the different number of benzene rings were investigated.We found that PAHs show odd-even effect.This effect was strongly exhibited for narrow width PAHs,but decreased or even disappeared as the width of the PAHs was increased.PAHs with an odd number of rings exhibited poor transport properties while the even-rings PAHs showed excellent transport properties coupled with a negative differential resistance(NDR)effect.In addition,strong rectifying behavior was observed in molecular devices composed of three benzene rings.(2)The electron transport properties of the combination of benzene and thiophene molecular and molecules with different side groups were studied.The current,transmission spectrum,and state density of their structure were obtained.We have found that 3,6-(dithiophen-2-yl)benzene has better transport properties compared to 2,5-diphenylthiophene,and its properties can be regulated by side groups.Interestingly,2,5-diphenylthiophene system added by a thiophene has showed semiconductor behavior under a certain bias region.(3)The electron transport properties of SimCn clusters were investigated.It was found that the transport properties of SimCn show a decreasing tendency with the increase of the number of C and Si atoms.Interestingly,although C6 with a ring structure has good transport properties,Si9C6 with the same ring structure(C6)shows poor transport properties.Despite the poor transport capacity of C12 when adding an atom to it-C13 exhibits excellent transport performance.Besides,the transport properties of SimCn vary with the width of the graphene nanoribbons.These findings have important theoretical guiding significance for designing high-performance SimCn molecular devices.This paper is of great significance for deep understanding of the electronic transport properties of molecular devices,and provides theoretical guidance for the design and development of high-performance molecular switches,molecular sensors,and field-effect transistor devices.