| In recent years, molecular devices have elicited marvelous interest in experimental designs and theoretical predictions with the rapid development of nanomaterials. As the size of electronic devices scale down and the rapid development of microelectronics, molecular devices will possibly take the place of microelectronic devices in future. As we knows, all kinds of nanomaterials was the element of molecular devices design. The superior performances of low dimension nano-materials, including mechanics, electrics, magnetics, optics and thermal physics, in particular, electronic transport, play an important role during the development of electronic devices. However, nano-materials in the process of actual production and preparation, defects and impurities were inevitably introduced into the systems, and affected the performance of mechanical, electrical, optical and transport, which make the research more meaningful on low dimension nano-materials with defects and impurities.In this paper, we drilled down into the influence of different composite defects and impurities on some low dimension nano-materials by using the first principles method based on the density functional theory(DFT) and the non-equilibrium Green’s function(NEGF). Objects of study in this paper containing: carbon nanotubes(CNTs), graphene nanoribbons(GNRs), silicene nanoribbon(Si NRs). The research contents were as follows:The transport properties of spiral chiral single-walled carbon nanotubes(SWCNTs) containing nitrogen-vacancy complex defects were investigated. The calculated results showed the electronic transport properties of chiral SWCNTs were improved effectively by introducing pyrimidine complex defects with nitrogen atoms and vacancy defect, and observed obvious negative differential resistance effect and strong rectifying effect. Further studies showed that the changes of transport transmission coefficient on composite doping system in bias window lead to obvious rectifying effect of the device.The electronic structures and transport properties of chiral(8, 4) SWCNTs with carboxylated defect complexes and chiral(6, 3) SWCNTs with carboxylated boron-defect complexes were investigated.(i) For(8, 4) SWCNTs, results proved that both intrinsic defects and carboxylated defect complexes appeared defect states near the Fermi level. Among them, the strong electronic localization effect of intrinsic defect states put off the electrical conduction of SWCNTs. However, the complex defect states enhanced transport conductance of SWCNTs. For the investigation of electronic transport properties of(8, 4) SWCNTs devices with carboxylated defect complexes, results showed that the electronic conduction of devices were reduced by defect complexes under the bias, and appeared significantly negati ve differential resistance effect. Strong rectification effects was only observed when the monovacancy was oxidized by carboxyl group. This will provide valuable theoretical basis for the investigation of high performance molecular rectifiers.(ii) For(6, 3) SWCNTs, the structure with carboxylated boron-vacancy defect complex was more stable than others. Carboxylated boron-vacancy defect complex enhanced the electrical conduction ability of(6, 3) SWCNTs. Nevertheless, carboxylated boron-doped and boron-SW defect complexes had hindered the electronic transport channels of systems. And where the act depended entirely on the mutual coupling effects between molecular orbitals of carboxyl groups and boron-defect complexes. These tremendous properties suggested potential application of COOH-containing defect complexes in CNTs-based nanoelectronic devices.The electronic structure and transport properties of armchair graphene nanoribbons(a GNRs) with Si Nx dopants, which was formed by incorporating silicon(Si) and nitrogen(N) atoms in neighboring lattice points. Results showed that the systems with Si Nx dopants generated impurity states near the Fermi level, and impurity states moved down and associated with Fermi level with the N concentration increasing. Further results proved that impurity level was separate from the donor level, and have been perturbation effect of impurities. The obvious negative differential resistance effect was observed in a GNRs with Si Nx dopants, and the effect gradually weakened with the increase of N concentrations. This suggested that Si N x dopants with the low N concentration could regulated effectively electronic conductivity of a GNRs.The electronic band structures and transpo rt properties of AA-P2-doped armchair silicene nanoribbons(a Si NRs) with two quasi-adjacent substitutional phosphorus atoms incorporated in pairs of neighboring silicon atoms in the same sublattice A were investigated. The results showed that a Si NRs came t rue the transition between semiconductor and metal by different locations of AA-P2 dopants, which depended absolutely on the coupling effect between the Pz orbitals of silicon and phosphorus atoms. The symmetrical negative differential resistance behaviors can be found in such devices, and the symmetry weakened with the location of AA-P2 dopants from the center to the edge. More interesting, rectification effect was only observed when AA-P2 located at the edge of the diagonal doping in a Si NR.Then, based on the stable diagonal AA-P2-doped a Si NRs structures, we investigated that the electronic transport properties of AA-P2-doped a Si NRs devices connected with the asymmetric electrodes, in which the left lead was undoped a Si NR, the right was AA-P2-doped a Si NR. Results showed that the electronic transport properties were strongly dependent on the width of the ribbon and the position of the AA-P2 dopant. Obvious rectifying effect can be observed and can be modulated by changing the width of the ribbon or the position of the AA-P2 dopant. Further studies showed that the corresponding matching region between the energy bands of both electrodes and the coupling between the corresponding molecular orbitals and the bands of the electrode lead to rectifying effect of the device.The electronic transport and rectifying properties of molecular devices linked two zigzag-edge trigonal graphene terminated by fluorine(F) atoms and hydroxyl(-OH) groups. The calculated results proved that the molecular devices wit h F and-OH edge-terminated left TGNs(LTGNs) showed obvious rectifying behavior with different intensity and direction. The different location of zigzag-edge terminated by F and-OH in LTGNs results in the complete different rectifying directions. And that the chemical activity of the terminated atoms affected directly the rectification ratio of molecular devices. Further research showed that these can be unambiguously explained by the Schottky barrier originated from the edge-terminated atom-to-TGN charge transfer doping and these charge shifting between both TGNs. Findings were of importance for achieving a profound understanding and developing nanoelectronic devices on the TGN functionalized by edge modification.Then, the rectifying properties of molecular devices combined with two trigonal silicenes with vertex doped by aluminum(Al) and phosphorus(P) atoms. Results showed that the different configurations of vertex doping affected significantly the rectifying performance of molecular devices. Al-Si, Al-P doping configurations of devices showed the forward rectification, and the rectification ratio of Al-P system was larger than Al-Si system. On the contrary, Si-P system showed the reverse rectification. It suggested that the different vertex doped coul d control effectively the rectification of molecular junction device, and provide favorable conditions for molecular rectifier design. |
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