Electron Transport In One-dimensional Systems Of Novel Materials

As the state-of-the-art technology,nanotechnology has been widely used in the field of semiconductor integrated circuits.It plays an irreplaceable role in realizing the miniaturization and functionalization of device circuits.With the advance of theories and technologies,nanomaterials keep developping in lower dimension.Since graphene was experimentally prepared,two-dimensional nanomaterials have attracted extensive attention and set off a huge research boom.The current two-dimensional materials include mainly graphene,molybdenum disulfide,black phosphorus and indium selenide.Quasi-one-dimensional nanoribbons of two-dimensional nanomaterials,due to the stronger quantum confinement and boundary effects therein,show more exotic physical properties indicating promising scientific value and application prospects.Electronic devices based on one-dimensional nanoribbons can effectively take advantage of nanoribbon edge characteristics,which provide a new approach for the functional design of nanodevices.Quantum transport simulations based on the combination of the first-principles density functional theory and the non-equilibrium Green's function do not require empirical parameters and experimental inputs to obtain the electronic structure and transport properties of nanomaterials.This method show great advantages in the early stages of exploration and research for electronic devices.With the help of software package,the method has been used in this thesis to study the electrical properties of graphene and indium selenide devices.Two parts are addressed as follows:(1)We have investigated systematically the electronic transport evolution through a phenylene rotor with an axis of atomic carbon chain(CPC)connected to two-fold symmetric electrodes of nonmagnetic zigzag graphene nanoribbons..The carbon chain of CPC filters out the ?-band electrons from the electrodes and the transport properties are characterized by the coupling between the ?*-band states of ZGNR and the HOMO-1,HOMO,and LUMO states of CPC.The intertwining of ? and ?* bands in ZGNR increases greatly the DOS around the Fermi levels of the electrodes and results in transmission peaks just inside the transport window.A parabolic I-V curve appears for small ? since the transmission peaks grow with bias Vb when the phenylene ring is almost coplanar to the ZGNR plane.For large ?,the transmission spectra are characterized by resonant transmission peaks at high energy,determined mainly by the bonding energies between the states in CPC and ZGNRs.They approach the edge of transport window as Vb increases and interact with other peaks there.Sharp current peaks and strong NDR phenomena appear in a large range of bias as the phenylene rotor rotates,indicating that the NDR might be manipulated efficiently via rotation angle in the device.(2)We have systematically investigated the electronic properties of In Se nanoribbons with Zigzag(Z),Armchair(A),or Klein(K)edges.The edges play a key role in determining the properties since electron states near the Fermi energy have big weight of edge atomic orbitals,which would be adjusted by the passivation hydrogen(H)atoms.Bare Z and K edges are conductive and magnetic.Strong edge-edge interaction may lead to the transition of n-HZZH nanoribbons from semiconductor to metal as width n increases.As a result,bare and H-passivated nanoribbons with Z and K edges are metallic except very narrow ones.n-AA and n-HAAH are nonmagnetic semiconductors with energy gaps narrower and wider,respectively,than that of In Se monolayer.Their gaps approach to each other in a zigzagged way as n increases,showing an even-odd behavior.The current-voltage curves of ZZ and KK nanoribbons are characterized by strong single-band NDR and spin polarization.These investigations have important reference value for the design of indium selenide nanoribbon electronic devices.