محمدرضا بنام

In this study, using density functional theory and Boltzmann equation, the thermoelectric properties of perfect and porous phosphorene nanosheets are calculated and compared at different temperatures including 100, 200 and 300 K. The results show that the maximum seebeck coefficient at 300 ° K for porous nanosheet is about twice the corresponding amount of the perfect one. A good thermoelectric material should have a high electrical conductivity as well as a low thermal conductivity. Although the electrical conductivity of the perfect sample is higher than that of the porous one at all studied temperatures, the electronic contribution of the thermal conductivity related to porous phosphorene is less than the thermal conductivity of the perfect one. At all studied temperatures, the maximum figure of merit (ZT) in porous phoephorene, is higher than the ZT in the perfect nanosheet. The results of this study indicate that two-dimensional porous phosphorene is a promising material for thermoelectric applications and even demonstrates a better performance than the perfect 2D-phosphoren.

In this paper, electronic properties of nano-sheets of silicon carbide, germanium carbide and tin carbide have been investigated. The calculations were performed based on the density functional theory (DFT) using full potential augmented plane wave (FP-LAPW) method. In our calculation we used GGA, LDA and TB-mBJ approximations for the exchange-correlation potential. Density of states calculations shows that the carbon p-orbitals have the highest contribution to the conducting and valance bands in the three nano-sheets. The band structure calculations show that the band gap in SiC, GeC and SnC nano-sheets is direct, direct and indirect, respectively. The band gaps calculated by the TB-mBJ approximation for these nano-sheets were obtained about 3.31, 2.93 and 1.38 eV, respectivly, which are significantly higher than the band gap calculated by the two other approximations. Therefore, due to the direct and relatively large energy bands, SiC and GeC nano-sheets can be considered in the nano electro-optic devices. The percentage of ionization of the bonds was investigated using Pauli's relation and electron density calculations. The results show that the type of the bonds is covalent and the percentage of ionization of the bonds in the SiC, GeC and SnC are 10, 7 and 8 percent, respectively.

Spin tunneling effect in Single Molecule Magnet Mn12 is studied by instanton calculation technique using SU(2) spin coherent state in real parameter as a trial function. For this SMM, tunnel splitting ( steps in hysteresis loop) arises due to the presence of a Berry phase in action, which causes interference between tunneling trajectories (instantons). In the analytical calculation, the assumption of the linearity of the instanton solution in term of applied magnetic field is used. It is observed that the number of quenching points of magnetic tunneling, the number of steps in hysteresis loop, are equal to the number of points obtained from numerical calculation. Of course, the position of the points (the magnitude of the field in which the tunneling amplitude is zero) is different.

The possibility of inserting an optical klystron on the storage ring of an Iranian Light Source Facility as a Synchrotron Radiation Free electron Laser for coherence harmonic generation in the soft x-ray spectrum has been studied. The study has been performed using the 3D FEL simulation code GENESIS 1.3 and in accordance with the available characteristic parameters of ISLF. Different potential schemes together with their output and characteristics are discussed.

Spin tunneling effect in Single Molecule Magnet Fe8 is studied by instanton calculation technique using SU(3) generalized spin coherent state in real parameter as a trial function. For this SMM, tunnel splitting arises due to the presence of a Berry like phase in action, which causes interference between tunneling trajectories (instantons). For this SMM, it is established that the use of quadrupole excitation (g dependence) changes not only the location of the quenching points, but also the number of these points. Also, these quenching points are the steps in hysteresis loops of this SMM. If dipole and quadrupole excitations in classical energy considered, the number of these steps equals to the number that obtained from experimental data.