Graphene is one of the strongest, lightest and most conductive materials that have ever been
discovered. Graphene is stronger and stiffer than diamond, yet can be stretched by a quarter of its
length. Graphene properties are attractive for scientists and electrical engineers for great deal of
reasons. For example, it can provide us with circuits that are smaller and faster than what we have in
silicon or we can have many other useful devices like super small computers.
In this work, we have discussed a method in which we can control the charge transfer in graphene by
using an electric field existed by a kind of variable external bias perpendicular to the graphene surface.
This vertical electric field makes a rectangular barrier. The electrons go through the barrier in different
angles. By solving the Dirac equation in different areas, the components of the Dirac spinor can be
achieved. Finally, by applying the boundary conditions, we have evaluated the electronic transmission
coefficient and probability.
Our results show the complete transmission at the normal incident angle without being affected by the
barrier height or length. While as the incident angle increases from zero, we can observe different
values for the transmission probability including special angles at which we have resonances. Besides,
the transmission probability has an oscillatory behavior as a function of barrier length which is related
to quantum behaviors of the system. In addition, our calculations show that by manipulating the
adjustable electric barriers on graphene, it is possible to control angle-dependent electronic
transmission. In other words, we can control the electron transmission by manual tuning the external
gate voltage from zero to unit. This formalism can be used in designing graphene base nano electeronic
divices including field effect transistors.
Mechanical deformations cause to change the electronic properties in carbon nanotubes. In this paper, the uniaxial strain
and length effects have been investigated on the quantum conductance of (12,0) and (8,0) finite Zigzag Single Wall
Carbon Nanotubes (ZSWCNT) at Fermi energy, using the tight binding model and the Green's function technique. In the
absence of strain, all the finite ZSWCNTs are metal because of localization. Our probes show that by controlling the
uniaxial strain and carbon nanotube length, a metal-semiconductor transition occurs for (8,0) finite ZSWCNT under the
compressive strain condition and the length longer than 37 A<sup>0</sup>. However, under the all strain and length variations that
investigated conditions in this paper, the localization length is longer than the length of (12,0) finite ZSWCNT, so that it
remains metallic and the quantum conductance is non-zero.
Some exciting applications of the correspondence between the mechanical response and the electronic transport of the
carbon nanotubes are nano-electromechanical switch, sensor applications.
Graphene has recently attracted many attentions for some special properties. One of the most important
advantages of graphene is its very high electron mobility, which is essential to manipulate high-speed
next generation transistors and other nano-electronic devices. Besides, because of the thin layer of
carbon atoms in graphene, we can make ultra-small and extremely fast devices.
In this research, we have considered a monolayer graphene subjected to an electro-magneto static
field. By solving the Dirac equation analytically and finding the spin-dependent transmission
probability for electrons through the barrier constructed by the electro-magneto static field, we have
evaluated spin polarization in different conditions. Our results show there is no reduction in
transmission for electrons that vertically go through the barrier. In other words, we have unit
transmission probability at normal incidence, which is in complete accord with Klein paradox. In this
case, there is not any polarization. However, spin polarization can be seen by increasing the incident
In some special magnetic field strengths and incident angels, spin-filtering can be occurred, in which
only electrons with either spin-up or spin-down can pass through the barrier. Due to this fact, many
graphene-base spintronic devices can be exploited in the near future.
In this work, phonon dispersion relation of trilayer graphene with ABA stacking has been calculated by using forceconstant
model. In our calculation we have considered fifth nearest neighbors in plane of graphene and the interaction
between the nearest layers. By using the calculated phonon dispersion relation, phonon thermal conductivity of trilayer
graphene is investigated by Landaur theory at low temperatures. In force constant model, atoms are considered as a point
masses that move according to the classical mechanics laws. By formation of dynamical matrix and solving the secular
equation detD(k)=0 the eigen frequencies can be achieved. It can be seen that the degeneracy of the lowest acoustic
branch is splited into the three branches near the Briloan zone for trilayer graphene, which is due to weak van der waals
interaction between two layers. In addition, the phonon thermal conductivity increases by raising the number of layers.
Recently, one of the most significant topics in electronic devices is miniaturization. It has been a growing interest in
some mesoscopic systems such as quantum dots. The size of these quantum dots approaches to the atomic scale,
which contributes to interesting new behaviors. Understanding their properties is an important problem in the fields
of nano electronics. Here we study the transport properties of the single wall carbon nanotubes quantum dots.
Considering Carbon nanotube (2n,0)/1(n,n)/m(2n,0) quantum dot, we have investigated the effects of the
central cell size on the conductance of the system. By increasing the length of armchair carbon nanotube in metalmetal-
metal quantum dot m(12,0)/1(6,6)/m(12,0) , we have observed reduction in the conductance. In
semiconductor- metal- semiconductor quantum dots (8,0)/1(4,4)/m(8,0), increasing the length of armchair part
causes the scattering rate raising. For more than special length, due to the destructive and constructive interference
of the wave functions, the conductance gap oscillates near the Fermi energy. Therefore, by controlling on cell size
characteristics, it is possible to manipulate some efficient devices in nano-electronics.
We have considered a two dimensional narrow semiconductor ring with sectorial barriers that is threaded by
magnetic flux. Using numerical diagonalization techniques, we have presented the diagrams of the energy spectra
versus the magnetic flux. For a constant value of the barrier height, with enhancement of the number of barriers, the
energy levels shift to higher energies and the degeneracy of the system increases. We have also investigated the
behavior of the energy levels with the magnetic flux for different values of the barrier height. The fluctuation of the
energy levels decreases, as the barriers' height increases.
A new, simple and efficient method is presented for calculation of the ground and a few excited states of Hubbard chain
nanostructures. By using this method, the photoemission spectral function for organic charge transfer salt TTF-TCNQ, is
calculated. For a chain with maximum 70 sites the result is in good agreement with the previous works but there is a
difference for further number of sites in the chain, which is discussed in the text with all the specifics. We also show that
a source of errors in density matrix renormalization group method for a one dimensional chain is the deficiency of the
matrix product scheme for generating the desired states of the linear chain.
We use a tight-binding Hamiltonian for an infinite quantum wire with substitusional disorder of A and B atoms in a
uniform electric field and calculate the density of states by coherent-potential approximation method. The electric field
produces a little oscillation on the local density of states and by increasing the strength of the electric field the amplitudes
of the oscillations grow up and they becomes more localized too. Also, by increasing the strength of the electric field, the
range of the extension of the energy spread out. The density of states at E=0 versus a parameter which depends on electric
field, is calculated and it shows oscillating pattern too. The local density of states for the different sites is calculated and all
of them are similar except a shift which is proportional to the strength of the electric field.