In this paper,we analytically study vibration of functionally graded piezoelectric(FGP)nanoplates based on the nonlocal strain gradient theory.The top and bottom surfaces of the nanoplate are made of PZT-5H and PZT-4,...In this paper,we analytically study vibration of functionally graded piezoelectric(FGP)nanoplates based on the nonlocal strain gradient theory.The top and bottom surfaces of the nanoplate are made of PZT-5H and PZT-4,respectively.We employ Hamilton’s principle and derive the governing differential equations.Then,we use Navier’s solution to obtain the natural frequencies of the FGP nanoplate.In the first step,we compare our results with the obtained results for the piezoelectric nanoplates in the previous studies.In the second step,we neglect the piezoelectric effect and compare our results with those obtained for the functionally graded(FG)nanoplates.Finally,the effects of the FG power index,the nonlocal parameter,the aspect ratio,and the lengthto-thickness ratio,and the nanoplate shape on natural frequencies are investigated.展开更多
In the present work, we have studied electronic and optical properties of a lens-shaped quantum dot under an external magnetic field. For this goal, we have calculated the energy levels and wave functions using the fi...In the present work, we have studied electronic and optical properties of a lens-shaped quantum dot under an external magnetic field. For this goal, we have calculated the energy levels and wave functions using the finite element method(FEM) for different values of magnetic field. We have also studied effect of magnetic field on second harmonic generation(SHG) and third-harmonic generation(THG) in the lens-shaped quantum dot. In this regard, we have obtained an analytic expression for the SHG and THG by a compact density matrix approach and an iterative procedure. According to the obtained results, it is found that the presence of the magnetic field affects the symmetry of the system. The SHG and THG are decreased with increasing the magnetic field. The magnetic field has a great influence on the energy levels, wave functions, the SHG and THG in a lens shaped quantum dot.展开更多
In the present work,the optical properties of a GaAs quantum wire with equilateral triangle cross section are studied.For this purpose,we use analytical expressions for optical properties obtained by the compact-densi...In the present work,the optical properties of a GaAs quantum wire with equilateral triangle cross section are studied.For this purpose,we use analytical expressions for optical properties obtained by the compact-density matrix formalism.Here,we investigate the intersubband optical absorption coefficients and refractive index changes as a function of the triangle side(L) and the incident optical intensity(I).According to the obtained results,it is found that:(i) The total refractive index changes increase and shift towards lower energies when the triangle side increases.(ii) The total absorption coefficient decreases as the triangle side increases.Also,the resonance peak shifts towards lower energies by increasing the triangle side.展开更多
In this work, the simultaneous effects of electric field and impurity on the non-extensive entropy of a GaAs/Ga_(0.5) In_(0.5) As double cone-like quantum dot that is grown on a Ga As wet layer are studied. The system...In this work, the simultaneous effects of electric field and impurity on the non-extensive entropy of a GaAs/Ga_(0.5) In_(0.5) As double cone-like quantum dot that is grown on a Ga As wet layer are studied. The system is under an external electric field directed along the-x direction. First, we have solved the Schr¨odinger equation using the finite element method. Then, we have used the Tsallis formalism and calculated the entropy of the system for different temperatures, electric fields and impurity locations. It is found that the entropy decreases with increasing the electric field and temperature. Since the electric field directed along the-x direction, the entropy reduces when the impurity moves toward the left hand side.展开更多
In this work,the influence of strain on threshold energy of absorption in Silicon circular nanowires is investigated.For this purpose,we first have used the density functional theory(DFT) to calculate the electron and...In this work,the influence of strain on threshold energy of absorption in Silicon circular nanowires is investigated.For this purpose,we first have used the density functional theory(DFT) to calculate the electron and hole effective masses.Then,we have obtained absorption threshold energy with two different procedures,DFT and effective mass approximation(EMA).We have also obtained the band structures of Si nanowires both DFT and EMA.The results show that:i) the expansive strain increases the hole effective mass while compressive strain increases the electron effective mass,ii) the electron and hole effective masses reduce with decreasing the wire size,iii) the absorption threshold energy decreases by increasing strain for compressive and tensile strain and its behavior as a function of strain is approximately parabolic,iv) the absorption threshold energy(for all sizes) obtained using EMA is greater than the DFT results.展开更多
In this paper, we have studied electronic properties of a two-electron quantum dot using Tietz confining potential in the presence of an external magnetic field. In this regard, we have applied diagonalization procedu...In this paper, we have studied electronic properties of a two-electron quantum dot using Tietz confining potential in the presence of an external magnetic field. In this regard, we have applied diagonalization procedure of Hamilonian matrix. We have calculated singlet-triplet ground state transitions as a function of the magnetic field. The obtained results show that the dot size of the Tietz potential has an important role in the ground state transition. The singlet-triplet transition of the ground state shifts towards lower magnetic field when the quantum size increases. Our results yield much less transitions than that of previous results [R.G. Nazmitdinov, N.S. Simonovic, and M.J. Rost, Phys.Rev. B 65(2002) 155307].展开更多
文摘In this paper,we analytically study vibration of functionally graded piezoelectric(FGP)nanoplates based on the nonlocal strain gradient theory.The top and bottom surfaces of the nanoplate are made of PZT-5H and PZT-4,respectively.We employ Hamilton’s principle and derive the governing differential equations.Then,we use Navier’s solution to obtain the natural frequencies of the FGP nanoplate.In the first step,we compare our results with the obtained results for the piezoelectric nanoplates in the previous studies.In the second step,we neglect the piezoelectric effect and compare our results with those obtained for the functionally graded(FG)nanoplates.Finally,the effects of the FG power index,the nonlocal parameter,the aspect ratio,and the lengthto-thickness ratio,and the nanoplate shape on natural frequencies are investigated.
文摘In the present work, we have studied electronic and optical properties of a lens-shaped quantum dot under an external magnetic field. For this goal, we have calculated the energy levels and wave functions using the finite element method(FEM) for different values of magnetic field. We have also studied effect of magnetic field on second harmonic generation(SHG) and third-harmonic generation(THG) in the lens-shaped quantum dot. In this regard, we have obtained an analytic expression for the SHG and THG by a compact density matrix approach and an iterative procedure. According to the obtained results, it is found that the presence of the magnetic field affects the symmetry of the system. The SHG and THG are decreased with increasing the magnetic field. The magnetic field has a great influence on the energy levels, wave functions, the SHG and THG in a lens shaped quantum dot.
文摘In the present work,the optical properties of a GaAs quantum wire with equilateral triangle cross section are studied.For this purpose,we use analytical expressions for optical properties obtained by the compact-density matrix formalism.Here,we investigate the intersubband optical absorption coefficients and refractive index changes as a function of the triangle side(L) and the incident optical intensity(I).According to the obtained results,it is found that:(i) The total refractive index changes increase and shift towards lower energies when the triangle side increases.(ii) The total absorption coefficient decreases as the triangle side increases.Also,the resonance peak shifts towards lower energies by increasing the triangle side.
文摘In this work, the simultaneous effects of electric field and impurity on the non-extensive entropy of a GaAs/Ga_(0.5) In_(0.5) As double cone-like quantum dot that is grown on a Ga As wet layer are studied. The system is under an external electric field directed along the-x direction. First, we have solved the Schr¨odinger equation using the finite element method. Then, we have used the Tsallis formalism and calculated the entropy of the system for different temperatures, electric fields and impurity locations. It is found that the entropy decreases with increasing the electric field and temperature. Since the electric field directed along the-x direction, the entropy reduces when the impurity moves toward the left hand side.
文摘In this work,the influence of strain on threshold energy of absorption in Silicon circular nanowires is investigated.For this purpose,we first have used the density functional theory(DFT) to calculate the electron and hole effective masses.Then,we have obtained absorption threshold energy with two different procedures,DFT and effective mass approximation(EMA).We have also obtained the band structures of Si nanowires both DFT and EMA.The results show that:i) the expansive strain increases the hole effective mass while compressive strain increases the electron effective mass,ii) the electron and hole effective masses reduce with decreasing the wire size,iii) the absorption threshold energy decreases by increasing strain for compressive and tensile strain and its behavior as a function of strain is approximately parabolic,iv) the absorption threshold energy(for all sizes) obtained using EMA is greater than the DFT results.
文摘In this paper, we have studied electronic properties of a two-electron quantum dot using Tietz confining potential in the presence of an external magnetic field. In this regard, we have applied diagonalization procedure of Hamilonian matrix. We have calculated singlet-triplet ground state transitions as a function of the magnetic field. The obtained results show that the dot size of the Tietz potential has an important role in the ground state transition. The singlet-triplet transition of the ground state shifts towards lower magnetic field when the quantum size increases. Our results yield much less transitions than that of previous results [R.G. Nazmitdinov, N.S. Simonovic, and M.J. Rost, Phys.Rev. B 65(2002) 155307].
