فهرست مطالب

Optoelectronical Nanostructures - Volume:3 Issue: 4, Autumn 2018

Journal of Optoelectronical Nanostructures
Volume:3 Issue: 4, Autumn 2018

  • تاریخ انتشار: 1397/09/18
  • تعداد عناوین: 7
|
  • Maryam Amoohadi *, Morteza Mozaffari, Abdolrasoul Gharaati , Mohammad Rezazadeh Pages 1-14
    In this study, Sendust (Fe85Si9.6Al5.4) nanostructure alloy was prepared by mechanical alloying and was characterized by X-ray diffraction. In addition, the alloy’s morphology and its distribution particle size were investigated by scanning electron microscopy method. The alloyed powders were insulated with 4wt% of three different insulating materials including polyvinyl alcohol, epoxy resin, and sodium silicate. Then, 0.5 wt% zinc stearate was added as a lubricant and the composites were formed at a pressure of 1600 MPa in a torodial die. These cores were annealed in Ar atmosphere at 350 to 450 ºC for 1 h. Some of the magnetic parameters of the as-milled and annealed samples were measured and compared with each other in the frequency range of 4 to 1000 kHz. The results showed that polyvinyl alcohol is not a suitable insulating agent for insulating this alloy. In addition, the real part of the initial magnetic permeability of the magnetic powder core insulated by sodium silicate in comparison with that insulated by epoxy resin is a bit smaller, but more reduction of the imaginary part of former results in an increase the Q-factor throughout measuring frequency range. The results show that annealing is more effective on improvement of the measured magnetic properties of the samples insulated with sodium silicate than that insulated with epoxy resin.
    Keywords: Soft Magnetic Composite Powder Cores, Epoxy Resin Insulator, Sodium Silicate Insulator, Magnetic Permeability, Q-Factor
  • Abbas Latifi, Seyyed Hamid Ahmadi *, Ali khanlarkhani, Manoochehr Fathollahi Pages 15-34
    Cylotrimethylenetrinitramine (RDX), with the chemical formula C3H6N6O6, is an energetic organic molecule used widely in military and industrial commodities of explosives. By stimulating RDX through exerting temperature or mechanical conditions such as impact or friction, decomposition reaction occurs at a very high rate. Molecular dynamics techniques and LAMMPS code with Reactive Force Field (ReaxFF) potential were employed to simulate initiation of RDX. Potential energy variations of the system were calculated over time for five different temperatures up to 100 ps. The products of decomposed system with respect to time were calculated at each stage of stimulation for different values of temperature and thermal initiation stimulation energy in NVT and NVE ensembles. The activation energy of decomposition was calculated 20.230 kcal.mol-1 through Arrhenius equation. The minimum required temperature to produce H2 with temperature decomposition was about 2500 K and production times for several conditions were calculated. The amount of nitrogen and hydrogen production were increased with raising temperature and reached the maximum value at 3000 K. The minimum impetus energy required to form the light species H2 is 66 kcal.mol-1.`
    Keywords: RDX, LAMMPS, Molecular Dynamics, Shock Wave, Simulation
  • Mahdi Zavvari *, Yashar Zehforoosh Pages 35-44
    Transition metal dichalcogenide (TMDC) materials are very important in electronic and optical integrated circuits and their growth is of great importance in this field. In this paper we present growth and fabrication of MoS2 (Molibdan DiSulfide) thin films by chemical bath method (CBD). The CBD method of growth makes it possible to simply grow large area scale of the thin layers of this material in lower temperatures (near room temperature) and atmosphere pressure in comparison to costly complicated growth methods. The results show the effect of growth temperature and time on the quality of layers and XRD measurements were performed for analysis of crystalline structure of layers. The results show that for the bath temperature of 60oC and for 75 min growth time, better quality of layers can be obtained with low intensity. The low intensity of XRD peaks belongs to poor crystalline structure of layers. For higher bath temperatures, the films lose their uniformity. The results were confirmed by SEM images.
    Keywords: Transition Metal Dichacogenide, Growth, Chemical Bath Deposition, Molybdenum Disulfide
  • hadi Rahimi * Pages 45-58
    In this paper, we explore the linear response of one dimensional quasiperiodic structure based on Fibonacci sequence composed of silicon dioxide, polystyrene and graphene materials. Here, a graphene monolayer is sandwiched between two adjacent layers. The numerical results are obtained by using the standard transfer matrix method. Due to the presence of graphene sheet in each structure, in the initial range of THz, an additional gap GPBG is induced which is absent in the case of without graphene. The amplitude of absorption peaks at the upper edge of the GPBG significantly enhances, when damping factor increases. The height of the absorption peak at the GPBG edge goes up as the temperature increases. At the GPBG edge, with increasing the thickness of graphene, the absorption peak rises and shifts to the lower frequencies. Moreover, we have realized that the amplitude of absorption peaks at the upper edge of the GPBG significantly enhance by increasing damping factor.
    Keywords: Graphene, Spectroscopy, Band gap, Quasiperiodic structures
  • Vahid Fallahi, Mahmood Seifouri * Pages 59-70
    Ring resonators have always been referred to as a highly flexible structure for designing optical devices. In this study, we have designed and simulation a four channel optical demultiplexer using square photonic crystal ring resonator. The square lattice constant for this purpose structure is used. The purposed structure has an average crosstalk, transmission coefficient, quality factor and channel spacing of -14.5 dB, 90%, 858 and 1.6 nm, respectively. To obtain the photonic band gap of the structure, the plane wave expansion (PWE) method has been used and the finite-difference time-domain (FDTD) method has been also used to analyze the optical behavior of the structure. The good results obtained from designing and simulating optical demultiplexer structure such as narrower channel spacing indicate the high flexibility of this structure and ring resonator for being used in designing optical devices as well as their suitability for being used in wavelength division multiplexing (WDM) systems.
    Keywords: Photonic Crystal, Ring Resonator, Demultiplexer, Wavelength Division Multiplexing (WDM), Plane Wave Expansion (PWE), Finite-Difference Time-Domain (FDTD)
  • Abdorreza Asrar*, Hossein Shahmirzaee Pages 71-80
    In this paper we have studied the effect of magneto-static field on propagation of thermal wave generated in metal by pulsed laser. In fact this interaction generate acoustic wave in different mechanisms. However, always the common mechanism in the interactions of laser pulse and metal is the thermo-elastic wave generation. Applying the suitable magneto-static field on the surface of interaction of laser pulse and metal can trap the propagation of thermal wave in thermo-elastic regime. The physical mechanism of trapping and experimental results have investigated in this paper. We obtained maximum reduction in 2D thermal wave propagation around in simulation and around 5.3% by metallography.
    Keywords: Thermal Wave, Metallography, Magnetic Field
  • Saman Salimpour, Hassan Rasooli Saghai * Pages 81-95
    Infrared photo detectors have vast and promising applications in military, industrial and other fields. In this paper, we present a method for improving the performance of an infrared photodetector based on an InSb substance. To achieve good performance at high temperatures, thermal noise and intrusive currents should be reduced. For this purpose, a five-layer hetero structure photodetector based on We introduce n+ InSb / n+ In1-xAlxSb / π InSb / p+ In1-xGaxSb / p+ InSb to improve the thermal performance in the mid-wavelength infrared (MWIR) range. With inserting of two thin layers from InAlSb and InGaSb on both side of the new (π) optical absorber created a barrier in the structure that prevents from entrance of diffusion currents and noise carriers at n+ and p+ regions into the active area. And also by reducing the density of unwanted carriers in the active layer, leads to decrease dark current, which is the main limiting factor for photodetectors’ performance based on InSb. Our proposed design reduced 49% dark current, increased 57% resistivity (R0) and increased 39% detectivity at 300K. Simulation of the structure was done using the SILVACO ATLAS software.
    Keywords: InSb Infrared Photodetector, High Temperature, Dark Current, Detectivity, Hetero Structure