The Nanoelectronic Phenomena And Corresponding Design Of Nano-functional Devices For Low-dimensional Carbon-and Silicon-based Structures

With the continuous development of device’s miniaturization and integration, the traditionalsilicon-based semiconductor device is approaching its limit. Meanwhile, due to the progress ofexperimental synthesis, more and more nano-materials and nano-structures emerge. Among them,carbon nano-structures, e.g., graphene and carbon nanotube, exhibit various geometries and uniqueelectrical features, considered to be the most promissing candidate for the next-generation nanodevices. Surprisingly, Si, also belonging to the carbon group, is recently found that it could form thegraphene-like structure, silicene. Besides, by doping with metal atoms, Si nanotube could bestabilized. These new structures make Si-based material may also play an important role in thenext-genaration device. Besides, they are compatible with the existing equipment and technology. Sofar, a variety of quantum phenomena in nano-structures have been discovered, which has been used todesign new devices. Using density functional theory combined with non-equilibrium Green function,we studied the transport of some typical carbon-and silicon-based nano-structures, as well as theircomposite structures, where a series of new electronic phenomena are discovered. Through analysis,we explained the physical mechanisms, and designed new nanoelectronic devices.The content of this thesis is as follows:Chapter1. Introduce the carbon and silicon nanostructures, nanoelectronics-related theory andfunctional application, and the content summary of this thesis.Chapter2. Introduce the theory and calculation methods, i.e., density functional theory, Landauertheory, and non-equilibrium Green function.Chapter3. The electronic transport of a recently synthesized nanotube-like fullerene D5h(1)-C90isstudied. One finds three negative differential resistance regions in the current-voltage curve, whichcould be modulated by the gate voltage. Further analysis shows that, the changes of both chargetransfer and molecule-electrode coupling, induced by both bias and gate voltages, are responsible forthe observed phenomena.Chapter4. The electronic transport properties of two-one-two dimensional carbon structures,graphene(benzene)-chain-graphene(benzene), are investigated. Switching behavior induced byconformational changes is observed. The spatial asymmetry of transmission channels between one-and two-dimensional carbon structures is found to be the physical mechanism behind, and it can beextended to metal systems. A kind of extremely-small pure-carbon logic operators and some other devices are proposed. As atomic motion could process information directly, the switching behaviorand those devices would be very useful in nanomechanics.Chapter5. We propose and investigate the transport of two pure-carbon systems,“partiallycontacted carbon nanotube and chain” and “partially hydrogenated zigzag graphene nanoribbon(ZGNR)”. For the former, it is found that the spin-polarized current can be achieved by partial contactbetween nanotube and chain, without using the dopants, ferromagnetic electrodes, and externalelectric field. Moreover, our results show that the device containing carbon nanotubes with largelength and diameter can produce the current with100%spin polarization. For the latter, it is foundthat, for ZGNR in ferromagnetic edge-coupling state, near-edge hydrogenation would suppress themagnetization on the edge of ZGNR, and lower down the transmission around Fermi energy to zeroexcept two peaks, which reside discretely on both sides of Fermi energy with opposite spins. Based onthis feature, we propose and demonstrate a three-terminal device, where the spin polarization of thecurrent can be modulated by the gate voltage (Vg) to vary from (almost)100%to-100%, which couldserve as a perfect electrically-controlled "pure-carbon" dual-spin filter. Moreover, a large range ofZGNR configurations are found to be suitable for the application of such a device.Chapter6. The spin-dependent electronic transport of Co(and Mn)-encapsulated Si nanotubescontacted with Cu electrodes. For the Co case, as the tube-length increases, a transition of thetransmission from spin-unpolarized to spin-polarized states is observed. The screening of electrodeson the magnetism of Co and the spin-asymmetric Co-Co interactions are the physical mechanismsbehind. For the Mn case, we find the spin-polarization of conductance could be modulated by the gatevoltage to vary from0to90%. Further analysis shows that, the modulation of electron transferbetween Si and Mn atoms by the gate voltage is the physical mechanism behind. Besides, the relationbetween temperature and spin current in silicene nanoribbon is investigated, where spin Seebeckeffect is observed. With the increase of the temperature difference between two electrodes, the spincurrent would first increase and then decrease. The modulation of transmission and Fermi distributionby temperature is found to be the the physical mechanism. Compared with the same effect ingraphene nanoribbon, the spin current in silicene is an order of magnitude larger. This is due to thelarger distance for the spin transmission peak away from the Fermi energy in graphene nanoribbon.Chapter7. The transport of helicene is studied, which exhibits the structural features of bothgraphene and bilayer graphene. With the increase of interlayer distance, the conductance exhibits “U”shape variation. This results from the competition between intra-layer and interlayer transport. Wefound the U shape variation of conductance is the intrinsic feature of helicene, being robust to theedge doping and electrode material. Chapter8. We propose and demonstrate a single-electron transistor (SET)-based nanopore sensorfor DNA sequencing. For nanopore sensors based on transverse electronic transport, the tunnelingcurrent generally exhibits a poor signal-to-noise ratio due to the weak coupling between the moleculeand electrodes. Instead of improving the coupling strength, we take full advantage of the weakcoupling feature by introducing SET to make the device operate in Coulomb blockade regime. Thecharge stability diagrams of the nucleobases within the SET-nanopore environment are found to bedistinctive for each molecule and, more importantly, independent of the nucleobase orientation, whichcan be served as electronic fingerprint for identification.Chapter9. Summary and outlook.