نشریه پژوهش سیستم های بس ذره ای
سال دهم شماره 4 (پیاپی 27، زمستان 1399)

In this paper, the electrical characteristics and resonant tunneling phenomenon in nanoscale double gate field effect Schottky transistor with InP (Indium Phosphide) as the channel material is investigated via non-equilibrium Green's function formalism. Unlike the conventional field effect transistor with doped source/drain, Schottky transistor possesses metallic source/drain regions and direct tunneling from source to channel is the main current mechanism of this device. The bandstructure of double gate device is calculated based on sp3d5s* tight binding approach employing thickness dependant two dimensional Hamiltonian. Reducing the channel thickness results in the increment of the carrier effective mass and shift of energy of subbands to higher values, in comparison with the related bulk values. In addition, by scaling down the channel thickness, gate control over the channel is enhanced that results in the improvement of the device electrical characteristics. Next, due to the increment of the effective Schottky barrier that is originated from quantum effects, a quantum well profile is created along the channel length from source to drain at low drain voltages. In this situation and for reduced values of temperature, resonant tunneling occurs in the proposed device. Different physical and structural parameters that may affect resonant tunneling are thoroughly investigated.

Austenitic stainless steel is widely used in the manufacture of reactor pressure vessels due to its mechanical properties and excellent resistance to corrosion in the water and vapor streams. Iron, nickel, and chromium are the main constituents of austenitic alloys. In this research, the role of nickel and chromium, as well as structural parameters on the stress-strain behavior of binary iron-nickel, iron-chromium, and ternary Fe-Ni-Cr alloys at different temperatures, were investigated by using molecular dynamics with two NVT and NPT ensembles. The simulation results show that the use of NVT ensemble leads to results with an error below 10% of the experimental data. Stress-strain curves of Fe-Cr, Fe-Ni, and Fe-Ni-Cr with different amounts of Ni and Cr indicate that increasing the amount of nickel and chromium will reduce Young's modulus. These results also show that Yield stress reduces by increasing Cr, while increases by increasing Ni. The effect of the size of the simulation box, the strain ratio and temperature on stress-strain behavior, Young's modulus, and Yield stress were also studied.

In this research, a hydrothermal method has been employed for synthesis of nanostructured MoS2 particles via the synthesis of MoO3. The structure of MoS2 samples was investigated by using a different precursors, such as DisodiumThiourea and Thioacetamide. Several investigation tools including FTIR, XRD, SEM, TEM, Raman and UV-Vis specteroscopy were used in order to characterize MoS2 nanostructures. XRD studies confirmed the hexagonal crystalline structure of samples. The FTIR spectra indicated the well-bonded MoS2 nanostructures. The size and the nearly uniform distribution of particles was detected by SEM and TEM. Photocatalytic activity of the MoS2 particles was checked by degration of Metylen Blue. Results showed the enhanced photocatalytic activity for the synthesized MoS2 with the molar ratio of 1:3 under UV irradiation.

In this paper, a combined biosensor from anti-resonant reflecting plasmonic waveguide (ARPWG) and Vernier-based microring resonator was designed. The Finite Difference Eigen solver method was used for ARPWG and two fundamental modes, including a pure mode and a bound surface plasmon polariton mode in the vicinity of the metal-dielectric interface, were obtained at the visible wavelengths by varying the refractive index of the superstrate layer. Then, the ARPWG applied in the four stage microresonator for achieving a free spectral range of 150 nm. The optical transfer function of this sensor was derived using the delay line signal approach and Mason rule. Lastly, the designed sensor was used for detection of Ecoli-O157 bacterium in drinking water. The sensitivity of 140.4 nm/RIU and 475.9 nm/RIU and the detection limit of 1.14 ×10-4 RIU and 3.36 ×10-5 RIU were realized for TMo and TM1 modes, respectively. The Advantages of the proposed sensor rather than conventional biosensors are in fast detection, high sensitivity and resolution, microscale size, low cost and the ability to integrate into the available electronics systems

In this paper, we consider the spin-1/2 Heisenberg chain with alternating exchange in presence of hexamer modulation of exchange on bonds. We studied the effect of uniform external magnetic field on the ground state phase diagram of this model using numerical Lanczos method. The ground state phase diagram consists of three gapless Luttinger Liquid(LL), two gapped plateau phases and a singlet spin phase. It is specified in the presence of additional modulation of exchange, the magnetization curve of system has two plateaus in magnetization diagram that are equal to and of the saturation value, respectively. Here, numerically we compute the entanglement entropy and the entanglement spectrum for a chain with finite number of particle. Numerical results shows that the singlet gapped phase exhibits four times degenerate and the first and second gapped plateau phases indicate two times degenerate.

Expansion of one-dimensional collisionless plasma into vacuum is studied in absence of magnetic field. In this paper, expansions of plasmas containing initial Maxwellian and modified Lorentzian (r,q) velocity distributions and the effect of q and r parameters on expansion are investigated and then compared by use of simulation of kinetic theory equations. In this simulation code, the electrons dynamic is determined by Vlasov equation and the ions dynamic obeys fluid equations. It is shown that the plasmas containing different initial velocity distributions for the electrons will be expand with different velocities. The results show that in the cases which initial electron distribution has more energy, then the ions will have more velocity.

We investigate the electronic and mechanical properties of pristine and fully hydrogenated AlN monolayer by first principles calculations. Two different states of hydrogen adsorption on AlN monolayer are considered: (I) adsorption of hydrogen atoms on Aluminum and Nitrogen atoms at the same side of AlN sheet (AlN-2H) and (II) adsorption of hydrogen atoms on Aluminum and Nitrogen atoms at the two opposite sides of AlN sheet (H-AlN-H). The hydrogenated AlN nanosheet is semiconductor and its energy band-gap changes relative to the pristine AlN sheet, so that, the band-gap values were obtained as 3 and 4.3 eV for H-AlN-H and AlN-2H, respectively. Based on the calculated electronic properties, density functional calculations in the harmonic elastic deformation range are performed to obtain the mechanical elastic constants of pristine and fully hydrogenated AlN monolayer. Energetically, compared with the pristine AlN, hydrogenation AlN is more stable. Also, by calculating the formation energy of the structures AlN-2H and H-AlN-H, the results indicate that the structure of H-AlN-H is more stable than AlN-2H. In particular, it is found that the in-plane stiffness of hydrogenated AlN is significantly smaller than that of pristine AlN, so that, the in-plane stiffness was obtained as 82 N/m for H-AlN-H.

In this paper, we consider quantum correlations (quantum discord and local quantum uncertainty) in a vertical quantum dot. Their dependencies on the magnetic field and temperature are presented in detail. It is noticeable that quantum discord and local quantum uncertainty behavior is similar to a large extent. In addition, the time evolution of quantum discord and local quantum uncertainty under dephasing and amplitude damping channels is investigated. It has been found that for some Belldiagonal states quantum discord is invariant under some decoherence in a finite time interval [Phys. Rev. Lett. 104, 200401 (2010)]. Also, our results show that quantum discord is invariant under dephasing channel for a finite time interval in a vertical quantum dot, while this phenomenon does not occur for local quantum uncertainty case

In this paper, we have studied the electronic structure of few two dimensional semiconducting nano-systems by suing three numerical methods meshless, finite element and finite difference. These methods .have been used to solve the two dimensional stationary Schrodinger equation w and the results have been compared. In order to solve the applied problems in the computational semiconducting quantum electronics, it is usually needed to solve the two dimensional stationary Schrodinger equation which have special numerical complexities. Evaluation of the energy eigenvalues is a challenging problem in this field of study. Here, by applying the methods on five applied examples we have shown that the eigenvalues converge to the exact values from lower bound in the finite difference method and converge to the exact values from upper bound in the finite element method. Therefore, in general applied problems under research, that we have not analytic eigenvalues and solutions, we are confidently able to find the upper and lower bounds of the eigenvalues. Finally, we have shown that in the mentioned examples, the meshless method has maximum accuracy among the investigated methods.

We study the kinks collisions up to five kinks and antikinks of the sinh-deformed φ^4 model numerically. In our simulations we observe reflection and bound state formation depending on the number of kinks and their initial conditions. The results show that the energy density at the point of collision is the maximum, which for odd (even) kinks appears in the form of potential energy density (kinetic energy density). The values of total energy density and elastic strain energy density of the φ^4 and sinh-deformed φ^4 models are almost the same, but the values of kinetic energy density in collisions of odd number of kinks and potential energy density in collisions of even number of kinks are different for these two models.

In statistical mechanics, the upper limit of entropy is very important for determining the final state of the system based on the Helmholtz variational principle. Hence many attempts have been made to calculate the entropy of the system, and a thermodynamic theory based on Renyi entropy has recently been presented that can describe new states in the thermodynamic system. The exact determination of entropy can not be done in many cases, and therefore approximate methods are used. An approximate solution often involves obtaining a high limit for entropy, which determines the final state of the system. This paper presents an upper limit for quantum entropy. For this purpose, the calculations are carried out in a separable Hilbert space with orthogonal bases. Using the Shanon definition of entropy, the upper limit is calculated for the relative entropy of two commutative operators.

Here using LAMMPS molecular dynamics (MD) software, we simulate polymer translocation in 2 dimensions. We do the simulations for weak and moderate forces and different pore diameters. Our results show that in both non-equilibrium and equilibrium initial conditions, translocation time will always increase by increasing binding energy and or increasing pore diameter. Moreover, scaling exponent of time versus force is -0.9531 in accordance to our predecessors. The comparison between equilibrium and non- equilibrium initial condition shows that the translocation time is very sensitive to the initial condition. Translocation time of the relaxed polymers for interaction energy of 8𝑘𝐵 𝑇 is smaller from the non- equilibrium case even in the small energy of 1𝑘𝐵 𝑇. Moreover, our simulation results show that the translocation velocity decrease by increasing the nanopore diameter from 3𝜎 to 5𝜎, where 𝜎 is the size of a monomer.