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Interest in the two-dimensional MoS2material is consistently increasing because of its many potential applications, in particular in the next-generation nanoelectronic devices. By means of density functional theory computations, we systematically examined the effect of vertical electric field on the electronic structure of MoS2bilayer. The bandgaps of the bilayer MoS2monotonically decrease with an increasing vertical electric field. The critical electric fields, at which the semiconductor-to-metal transition occurs, are predicted to be in the range of 1.0–1.5 V/Å depending on different stacked conformations. Ab initio quantum transport simulations of a dual-gated bilayer MoS2channel clearly confirm that the vertical electric field continuously manipulates the transmission gap of bilayer MoS2.

Structural, electronic, and magnetic properties of the Fe-, Co-, Ni-, and V-intercalated graphene bilayer sandwich (denoted by C2|M|C2, M = Fe, Co, Ni, and V) and graphene on hexagonal boron nitride (h-BN) bilayer sandwich (denoted by C2|M|BN, M = Fe, Co, Ni, and V) are studied by using density functional theory method. We find that both the graphene bilayer and graphene-h-BN bilayer in all the C2|M|C2and C2|M|BN sandwiches favor AB stacking over AA stacking mode. The Fe, Co, and Ni atoms prefer to be located over the center of C–C bonds whereas V atoms prefer to be located above the C atoms on graphene, and they all prefer to be located above the N atoms on h-BN sheet, regardless of the stacking mode. The C2|Fe|C2, C2|Co|C2, C2|Fe|BN, and C2|Co|BN sandwiches of AB stacking are all ferromagnetic metals with the spin polarization of 86%, 67%, 65%, and 46% at the Fermi level, respectively. By contrast, both C2|Ni|C2and C2|Ni|BN sandwiches of AB stacking are nonmagnetic semiconductors with bandgaps of 0.64 and 0.23 eV, respectively, which provide a novel strategy of opening a bandgap of graphene. From the quantum transport calculation, we obtain a giant room-temperature magnetoresistance of ∼200% in the spin valve device based on AB stacking C2|Fe|C2sandwich.

We study the nonresonant Raman scattering of armchair and zigzag graphene nanoribbons (GNRs) using density functional perturbation theory. We find that, in both GNR types, the Raman spectrum is extremely polarized along the ribbon axis direction with the scattering intensity being over 102times greater than those of the other polarizations because of the geometrical confinement. Along the dominant polarization direction, the scattering intensity and frequency oscillate strongly with the ribbon width in the armchair GNRs, while the scattering intensity initially increases and then decreases with the ribbon width and the frequency monotonically changes with the ribbon width in the zigzag GNRs. Such a difference is closely associated with the different width dependences of band structure between the two types of GNRs.

We provide the first systematic ab initio investigation of the possibility to create a band gap in few-layer graphene (FLG) via a perpendicular electric field. Bernal (ABA) and arbitrarily stacked FLG remain semimetallic, but rhombohedral (ABC) stacked FLG demonstrates a variable band gap. The maximum band gap in ABC stacked FLG decreases with increasing layer number and can be fitted by the relationship Δmax= 1/(2.378 + 0.521N+ 0.035N2) eV. The effective masses of carriers over a wide range around the maximum band gap point in ABC stacked FLG are comparable with that in AB bilayer graphene under zero field. It is therefore possible to fabricate an effective field effect transistor operating at room temperature with high carrier mobility out of ABC stacked FLG.

We present the first transport property investigation of a-few-nanometer-long armchair graphene nanoribbon (AGNR) p–njunctions by using first-principles method. Intriguingly, family dependent rectification is observed. To be specific, traditional rectification effect in the forward direction is observed in the AGNR p–njunctions with 3nand 3n+ 2 widths, whereas reverse rectification effect is observed in the AGNR p–njunctions with 3n+ 1 width. The analysis of the spatial distribution of molecular projected self-consistent Hamiltonian eigenstates and the projected density of states give an insight into the observed results.

Using first-principles calculations, we explore the possibility of functionalized graphene as a high-performance two-dimensional spintronics device. Graphene functionalized with O on one side and H on the other side in the chair conformation is found to be a ferromagnetic metal with a spin-filter efficiency up to 54% at finite bias. The ground state of graphene semifunctionalized with F in the chair conformation is an antiferromagnetic semiconductor, and we construct a spin-valve device from it by introducing a magnetic field to stabilize its metallic ferromagnetic state. The resulting room-temperature magnetoresistance is up to 2200%, which is 1 order of magnitude larger than the available experimental values.

It has been well established that the electrical resistance of metal is insensitive to gate voltage and unsuitable for making field effect transistors. However, we find that telescoping pristine double-walled metallic carbon nanotubes are extremely sensitive to gate voltage with an on/off ratio up to 104based on the first principles quantum transport calculations. This remarkable feature is closely related to the antiresonances in the transmission spectra. Besides, robust negative differential resistance effects are also found in the same device.

Using density functional theory and nonequilibrium Green’s function method, we construct organometallic nanowires that consist of Fe or V atoms sandwiched between composite molecules (Cp*FeCp*, where Cp* is C5(CH3)5). For the first time, we demonstrate that half-metallicity, negative differential resistance, and sign-reversible high spin-filter capability can coexist remarkably in one organometallic nanowire (FeCp* wire). This renders FeCp* wire promising in electronics and spintronics.

We propose a novel single-molecule organic field effect transistor (FET) fabricated via covalent functionalization of an individual metallic single-walled carbon nanotube (SWCNT). The transfer characteristic of this FET is calculated by using ab initio quantum transport calculations. Because of the significantly reduced screening effect of the quasi-one-dimensional electrode and seamless connection between the electrode and scattering region, the optimized device shows an excellent overall performance over the experimental single-molecule organic field effect transistors. This renders functionalized metallic SWCNTs a promising candidate for a high-performance single-molecule organic field effect transistor.

Structural, electronic, and transport properties of Gd/Eu atomic chains encapsulated in single-walled carbon nanotubes (SWCNTs) are studied by using first-principles density functional theory and the nonequilibrium Green’s function method. We find that the linear single-atom Gd and Eu chains occupy an off-centered position when encapsulated in the (8,0), (10,0), and (6,6) SWCNTs and considerable electrons are transferred from the Gd and Eu chains to the SWCNTs. The resulting composites are all ferromagnetic metals, with the conductivity significantly larger than those of the pristine SWCNTs and the free-standing Gd/Eu linear single-atom atomic chains. The spin polarization of the finite Gd linear single-atom chain at the Fermi level is 67% when encapsulated in the (8,0) SWCNT from the quantum transport calculation.

We present for the first time the linearly polarized vibrational infrared spectra of edge-hydrogenated armchair and zigzag graphene nanoribbons (GNRs) through first-principles calculations. We find that there exists a prominent and width-insensitive peak in both GNRs for out-of-plane polarization, which can be used as a benchmark in measurements. In the major absorption regions of all polarizations, we observe noticeable differences between the two GNR types. In armchair GNRs, the spectra for in-plane polarization oscillate with the ribbon width, while in zigzag GNRs the dispersion relationship bears close resemblance with that of graphene. We also discover a special peak that reflects the mirror symmetry between the two edges of zigzag GNRs. Finally, the quenching of magnetism and oxygen-passivation are revealed to remarkably influence the infrared spectra. Our work provides a new insight into GNR fundamental property and is expected to help confront the current problem of edge structure and magnetism identification of GNRs.

We investigated the geometric and electronic properties and doping efficiency of phosphorus-doped zinc oxide nanowires along the [0001] direction using the first-principle calculation. For isolated point defects, the substitutional and vacancy defects prefer the edge of the nanowire, the Zn interstitial defects favor the tetrahedral site, and the most stable P and O interstitial defects have a dumbbell-like structure. A complex defect of PZn−2VZnis formed by the combination of a substitutional P at a Zn site (PZn) and two Zn vacancies (VZn), and it prefers the edge site. We found that PZndefects could be effective donors while VZnand PZn−2VZndefects could be effective acceptors. The PZndefects have low formation energies and high concentrations under the Zn- and P-rich conditions, and they can lead to n-type ZnO nanowires. The VZndefects have low formation energies and high concentrations under the O- and P-rich conditions. The VZndefects can greatly suppress the PZndefects. VZnand PZn−2VZndefects can lead to p-type ZnO nanowires under the O- and P-rich conditions.

We calculated the optical absorption spectrum response of single-walled carbon nanotubes under charge doping by using density functional theory. We find that the spectrum responses can be generally divided into two categories: one is similar to those obtained from the graphene zone-folding and rigid-band model, while the other deviates from the expectation and shows several special features. Our analysis reveals that the doping type and curvature effects play the primary role. Finally, we argue that the present results will probably prevail in more elaborate methods and other similar nanotubes.

We calculate the electronic structures of the fully bare and half-bare zigzag-edged boron nitride nanoribbons by using density functional theory. We find that the ground states of both the fully bare boron nitride nanoribbons and the boron nitride nanoribbons with a bare N edge and a H-terminated B edge are half-metallic. The alignment of the spin at the bare B edge is antiferromagnetic, while that at the bare N edge is ferromagnetic in the ground states of both the fully bare and half-bare zigzag-edged boron nitride nanoribbons. The H-terminated B or N edge of the half-bare zigzag-edged boron nitride nanoribbon exhibits no magnetism.

By using the density functional theory method, we calculate the 13C NMR isotropic chemical shifts of the semiconducting and semimetallic infinite single-walled carbon nanotubes (SWNTs). We find that the 13C chemical shifts of SWNTs with the diameter smaller than 1.4 Å can be classified into two distinct groups according to their electronic structures: the semiconducting group and the semimetallic group. The chemical shifts of the semiconducting group decrease monotonously with the increasing nanotube diameter, and are 0−12 ppm strikingly larger than those of their semimetallic counterparts in the typical diameter range (1.05 ± 0.2 nm) of SWNTs produced by the common high-pressure CO decomposition method (HiPCO). The chemical shifts of the two groups overlap around the diameter of 1.4 Å. Then the chemical shift of the semimetallic group becomes larger than that of the similar-sized semiconducting group as the diameter is larger than 1.4 Å. The chemical shifts of the four examined helical SWNTs are very close to those of the zigzag SWNTs with similar diameters and electronic structures.

We have investigated static and optical transverse and longitudinal screened polarizabilities of single-walled (SWBNNT) and multiwalled (MWBNNT) boron nitride nanotubes by using the density functional perturbation theory. The static and optical transverse and longitudinal screened polarizabilities of SWBNNTs all increase linearly with the radius and are smaller than those of similar-sized single-walled carbon nanotubes. The screened optical transverse polarizabilities of SWBNNTs are found to be about half that of the unscreened ones. In addition to the screened polarizabilities themselves, the ratio between the static and optical screened polarizabilities of SWBNNTs also exhibits anisotropy. In contrast to multiwalled carbon nanotubes, where the inner tube is almost completely shielded by the outer tube, in MWBNNTs, the inner tube is only partially shielded by the outer tube when a transverse electric field is applied.

With special topology differing from nanotubes, carbon nanoscrolls (CNSs) rolled up by a single graphene sheet show unique properties and have potential applications in hydrogen storage and energy storage. We studied various types of nanoscrolls by using first principle calculation. The minimum innermost radius of armchair-type nanoscrolls is achieved. The electronic structures of nanoscrolls are greatly related to chirality (n,m). Armchair nanoscrolls are metallic or semimeatllic depending on their sizes and those metallic ones have larger density of states at the Fermi level than metallic single-walled nanotubes (SWNTs). Zigzag nanoscrolls are semiconductors with energy gaps much smaller than corresponding zigzag SWNTs; moreover, they get small gaps at (16,0) and (19,0), while zigzag SWNTs have small gaps at (3n,0).