| In recent years,with the rapid development of nanoscience and nanotechnology,more and more high-quality two-dimensional nano-materials were proposed or found.In particular,graphene was successfully prepared in 2004 and set off a new climax in condensed matter physics and materials science with its novel characteristics.It was considered to be very likely to replace the traditional silicon material and became the first choice for the preparation of nanoelectronic devices in the future.However,the zero bandgap characteristic of graphene and the band spin-degenerate phenomenon caused by zero net magnetic moment in the ground state,thus limiting its practical application.Therefore,the purpose of this paper was to study the physical properties of graphene and graphene-like(such as BN monolayer)which are modulated by physical methods(tailoring,stress,applied electric field,etc.)and chemical methods(edge modification,doping,etc.)and to obtain the structural model that satisfies the functional requirements of the device.All of our computational simulations used the first-principles principle based on the density functional theory and non-equilibrium Green’s function.This paper focuses on the modification of electronic and magnetic properties of low-dimensional nanomaterials by chemical modification,which tries to provide theoretical reference for the design and preparation of nanoelectronic devices and magnetic devices.The main research contents are as follows:Firstly,the ordered doping is carried out for the armchair graphene nanoribbon(AGNRs),mainly B atoms,N atoms and BN molecules are selected and single row doping is considered.Our simulation calculations show that the AGNRs may be a metal or a semiconductor depending on B or N atom-doping positions,and the calculated atom-projected density of states(atom-PDOS)indicates that B or N impurity atoms can induce the new lowest conduction band(LCB)or the highest valence band(HVB).More interestingly,as compared with the intrinsic AGNR device,the current in the B-or N-doped AGNR device with the most energetically favorable state is extremely small,completely different from a macroscopic Si semiconductor with p-type or n-type doping,which always leads to a significant increase in current.Also shown is that the doping with BN molecules generally increases the bandgap of the AGNR regardless of the doping position,but the size of these bandgaps depends on the doping positions.The current in the BN-doped AGNR device is also decreased greatly in comparison with that for the intrinsic AGNR device.The organic molecule deposited between gaphene electrodes to form a molecular device has been demonstrated experimentally.Motivated by this case,devices consisting of the polyphenylene molecule bonded covalently with armchair-edged graphene nanoribbon(AGNR)electrodes are constructed and the selective doping with N atom is considered theoretically.Our modeling calculations show that such devices hold the nonlinear and doping-site-dependent transport properties,prominently with multipeak NDR(negative differential resistance)effect.And,for a peculiar doping site,a very large NDR can be observed,which could be attributed to interactions of the molecular core and doped AGNR electrodes,namely,these hybridized wave functions hold distinctly different delocalization in different benzene rings of the polyphenylene molecule when the applied bias is altered.Also shown is that this large NDR is robust regarding the length increasing and rotation of molecule.Finally,the structural and magneto-electronic properties and electric field-mediated effects for zigzag boron nitride nanoribbons(ZBNNRs)terminated with typical transition metal(TM)atoms(TM-ZBNNRs)are investigated systematically,in which TM atoms are always connected to different sublattices on both sides.Our work demonstrates that ZBNNRs form strong bonds with all studied termination atoms.The strong interactions and large orbital hybridizations of TM atoms to the ribbon make the magnetic anisotropy enhanced significantly,favorably to stabilize magnetism.The spin-split features for such hybridized structures can occur in most of the magnetic configurations,leading to a large magnetic moment.Higher spin polarization can be found in the ferromagnetic(FM)state.In particular,spin polarization exceeding 90%at the Fermi level can be achieved for Fe-ZBNNRs when an in-plane transverse electric field is applied.These results might be of interest from the prospects of both fundamental science and its potential applications. |
