Nguyen N. Hieu

Effect of electric field on the electronic and magnetic properties of a graphene nanoribbon/aluminium nitride bilayer system

The effect of an external electric field on the electronic and magnetic properties of the heterostructure of zigzag graphene nanoribbons (ZGNRs) placed on an aluminium nitride nanosheet (AlNNS) is studied using density functional theory (DFT). DFT calculations show that the local magnetic moments and total magnetization of the edge carbon atoms in the 4-ZGNR/AlNNS with a spin up electron subsystem are strongly dependent on a transverse electric field. We can control the band gap of the 4-ZGNR/AlNNS by using an external electric field. We established the critical values of the transverse electric field providing for semiconductor–metal phase transition in spin down electron configuration, which opens up potential opportunities for applications in spintronics devices. The effect of an external electric field (both amplitude and direction) on the effective charge and formation of the interface state energy is also studied and discussed.

Uniaxially deformed (5,5) carbon nanotube: Structural transitions

The Kekule structure of the ground state of (5,5) armchair carbon nanotube is revealed by semiempirical molecular orbital calculations. This structure has bonds with two different bond lengths, differing by 0.003 nm. The ground state has tripled (compared to undistorted case) translational period due to Peierls distortions. Two first order structural phase transitions controlled by the tension are predicted at zero temperature. These transitions correspond to 5% and 13% elongations of a uniaxially deformed (5,5) nanotube. The narrow gap semiconductor to metal transition is predicted at 5% elongation of the nanotube.

Electric field and substrate–induced modulation of spin-polarized transport in graphene nanoribbons on A3B5 semiconductors

In this work, we present the density functional theory calculations of the effect of an oriented electric field on the electronic structure and spin-polarized transport in a one dimensional (1D) zigzag graphene nanoribbon (ZGNR) channel placed on a wide bandgap semiconductor of the A3B5 type. Our calculations show that carrier mobility in the 1D semiconductor channel of the ZGNR/A3B5(0001) type is in the range from 1.7×104 to 30.5×104 cm2/Vs and can be controlled by an electric field. In particular, at the critical value of the positive potential, even though hole mobility in an one-dimensional 8-ZGNR/h-BN semiconductor channel for spin down electron subsystems is equal to zero, hole mobility can be increased to 4.1×105 cm2/Vs for spin up electron subsystems. We found that band gap and carrier mobility in a 1D semiconductor channel of the ZGNR/A3B5(0001) type depend strongly on an external electric field. With these extraordinary properties, ZGNR/A3B5(0001) can become a promising materials for application...

Linear and nonlinear magneto-optical properties of monolayer phosphorene

We theoretically study the magneto-optical properties of monolayer phosphorene under a perpendicular magnetic field. We evaluate linear, third-order nonlinear, and total absorption coefficients and relative refractive index changes as functions of the photon energy and the magnetic field, and show that they are strongly influenced by the magnetic field. The magneto-optical absorption coefficients and relative refractive index changes appear in two different regimes: the microwave to THz and the visible frequency. The amplitude of intra-band transition peaks is larger than that of the inter-band transitions. The resonant peaks are blue-shifted with the magnetic field. Our results demonstrate the potential of monolayer phosphorene as a new two-dimensional material for applications in nano-electronic and optical devices as a promising alternative to graphene.

First-principles study of the structural and electronic properties of graphene/MoS2 interfaces

In this paper, we study the structural and electronic properties of graphene adsorbed on MoS2 monolayer (G/MoS2) with different stacking configurations using dispersion-corrected density functional theory. Our calculations show that the interaction between graphene and MoS2 monolayer is a weak van der Waals interaction in all four stacking configurations with the binding energy per carbon atom of −30 meV. In the presence of MoS2 monolayer, the linear bands on the Dirac cone of graphene at the interfaces are slightly split. A band gap about 3 meV opens in G/MoS2 interfaces due to the breaking of sublattice symmetry by the intrinsic interface dipole, and it could be effectively modulated by the stacking configurations. Furthermore, we found that an n-type Schottky contact is formed at the G/MoS2 interface in all four stacking configurations with a small Schottky barrier about 0.49 eV. The appearance of the non-zero band gap in graphene has opened up new possibilities for its application in electronic device...

Dispersion-Corrected Density Functional Theory Investigations of Structural and Electronic Properties of Bulk MoS2: Effect of Uniaxial Strain

Strain-dependent structural and electronic properties of MoS2 materials are investigated using first principles calculations. The structural and electronic band structures of the MoS2 with relaxed unit cells are optimized and calculated by the dispersion-corrected density functional theory (DFT-D2). Calculations within the local density approximation (LDA) and GGA using PAW potentials were also performed for specific cases for the purpose of comparison. The effect of strain on the band gap and the dependence of formation energy on strain of MoS2 are also studied and discussed using the DFT-D2 method. In bulk MoS2, the orbitals shift towards the higher/lower energy area when strain is applied along the z/x direction, respectively. The energy splitting of Mo4d states is in the range from 0 to 2 eV, which is due to the reduction of the electronic band gap of MoS2.

Magnetically operated nanorelay based on two single-walled carbon nanotubes filled with endofullerenes Fe@C20

Structural and energy characteristics of the smallest magnetic endofullerene Fe@C20 were calculated using the density functional theory. The ground state of Fe@C20 was found to be a septet state, and the magnetic moment of Fe@C20 was estimated to be 8 Bohr magnetons. The characteristics of an (8,8) carbon nanotube with a single Fe@C20 inside were studied with a semiempirical approach. The scheme of a magnetic nanorelay based on cantilevered nanotubes filled with magnetic endofullerenes was examined. This nanorelay is turned on as a result of bending of nanotubes by a magnetic force. The operational characteristics of such a nanorelay based on (8,8) and (21,21) nanotubes fully filled with Fe@C20 were estimated and compared to the ones of a nanorelay made of a (21,21) nanotube fully filled with experimentally observed (Ho3N)@C80 with the magnetic moment of 21 Bohr magnetons. The room-temperature opera- tion of (21,21) nanotube-based nanorelays was demonstrated.

Electronic energy band structure of uniaxially deformed (5,5) armchair carbon nanotube

Semiempirical molecular orbital calculations of the (5,5) armchair carbon nanotube give the Kekule structure in its ground state with two essentially different bonds (the bond lengths difference is 0.003 nm). This is a result of the Peierls distortions leading to tripled (compared with undistorted case) translational period. When the armchair nanotube is elongated, two first order deformational structural phase transitions are predicted. The first one at the elongation of 5% leads to doubling of a translational period (instead of tripling at smaller elongations). The second one at the elongation of 13% leads to the quinoid type structure. The dependence of the electronic energy-band structure of the (5,5) carbon nanotube on elongation is investigated using the tight binding approximation. The transition from narrow-gap semiconductor to metal is predicted at the elongation of 5%, indicating that the uniaxially deformed armchair carbon nanotube at greater elongation (more than 5%) remains metallic at all temperatures.

Effect of Peierls transition in armchair carbon nanotube on dynamical behaviour of encapsulated fullerene

The changes of dynamical behaviour of a single fullerene molecule inside an armchair carbon nanotube caused by the structural Peierls transition in the nanotube are considered. The structures of the smallest C20 and Fe@C20 fullerenes are computed using the spin-polarized density functional theory. Significant changes of the barriers for motion along the nanotube axis and rotation of these fullerenes inside the (8,8) nanotube are found at the Peierls transition. It is shown that the coefficients of translational and rotational diffusions of these fullerenes inside the nanotube change by several orders of magnitude. The possibility of inverse orientational melting, i.e. with a decrease of temperature, for the systems under consideration is predicted.

Interwall conductance in double-walled armchair carbon nanotubes

Abstract The dependence of the interwall conductance on distance between walls and relative positions of walls are calculated at the low voltage by Bardeen method for ( n , n ) @ ( 2 n , 2 n ) double-walled carbon nanotubes (DWCNTs) with n = 5 , 6 , … , 10 . The calculations show that interwall conductance does not depend on temperature (for T ⩽ 500 K ) and current-voltage characteristic is linear. The conductance decreases by 6 orders of magnitude when the interwall distance is doubled. Thus, depending on the interwall distance, DWCNTs can be used as temperature stable nanoresistors or nanocapacitors.