مجله فیزیک کاربردی
سال دهم شماره 3 (پیاپی 22، پاییز 1399)

Platinum is an expensive material that is widely used in dye sensitized solar cells (DSSCs) due to its excellent electrocatalytic and conduction features. In order to achieve economical affordability in DSSCs, we require to introduce new lower cost materials to replace the current expensive component. In this research, we propose the composite of low-cost carbon black and tin selenide materials to replace the platinum in DSSCs’ counter electrodes. We study different ratios of carbon black and tin selenide composites and find out the optimized ratio which is later used in fabrication of DSSCs. Our best DSSC showed an efficiency of ~5% that is comparable to the cells fabricated from platinum counter electrodes. The results of this paper, can pave the way for economic feasibility of DSSCs.

In this study, we surveyed the possibility of nanometer scale lithography in ambient condition using a scanning tunneling microscope. Optimized parameters for this purpose have been determined. The study will be hopefully an initiative step toward further progress in manufacturing nano-bio chips and nano-bio electromechanical systems utilized for diagnosis and treatment purposes in medical areas. Tests showed that the scanning tunneling microscope lithography yielded the same result in each test and thus it was reproducible. Using STM microscopy, nanostructures were first created in the form of protruding points on the surface. Then we created linear structures, more complex forms, and finally we were able to write some words.  Nanostructures were created on gold surfaces by tungsten, gold, platinum-palladium tips. It is found that the voltage used in lithography is effective on creating nanostructures, and also on the size of nanostructures, so that with increasing voltage, the size of nanostructures increases too. The speed of tip is also another important factor that can affect nanostructures size and their continuity. Time interval between consecutive pulses influences on the nanostructures integration and its value should be specified based on conditions and purposes of lithography. The size of nanostructures ranged between 20 and 150 nm. Tip geometry, humidity and temperature are also likely to be influential factors that require further studies to investigate their effects.

All optical decoders play a key role in the design and implementation of all optical processing systems. Switching speed, power and structural dimensions are the most important parameters that should be considered in the design of all optical devices. In this research, by using two nonlinear resonance cavities based on photonic crystals, a structure for design and implementing an all optical decoder is presented. Nonlinear resonance cavities are created by adding nonlinear rods made of contaminated glass inside the cavity. The proposed structure has one activation port, one input port and two output ports. If the activator port is off, both outputs will be off regardless of the status of the input port situation. In design of this structure, we need an activator input port and a control input. The activator input port is connected directly to the main waveguide using a side waveguide. The control input of the decoder, which is the same as the main input port of the decoder 1 to 2, is connected to the main waveguide by means of an optical power divider. Also to improve the efficiency of the light transmission from the activator port to the main waveguide, two point defects with a radius of 60 nm have been installed at the junction of the input waveguides to the main waveguide. In the designed structure, the maximum delay time is 5 ps.

In today’s world, the nations perceive the valuable position the archeological and historical monuments have in the culture and civilization of their nations. In order to know a historical monument, its raw materials must first be characterized. By identifying the raw materials, suitable protection and restoration methods can be suggested for that monument. With increasing the awareness of the destructive effects of the use of chemical and toxic substances on the objects, the environment and users, the replacement or minimum use of these harmful materials in the treatment and protection of valuable and rare objects is a priority. Cold plasma due to its features such as low temperature and high energy, in addition to a wide range of applications in various fields, since 1979, has attracted the attention of specialists in conservation and restoration of cultural and historical objects.

Coronal loops ExtremeUltraViolet (EUV) images provide us a lot of information about the structure of the chromospheres, the transition zone, the corona and the solar magnetic field. These structures are constantly moving and changing and the collected information from these images are too much such that in SDO reach to 1.6 TeraByte of data per day. This huge amount of information and images should be reduced and processed and this needs the development of the automated analysis tools of the solar images data. Especially investigation of the coronal loops needs exact extraction of them from the received images. In this paper we introduce and investigate the image processing methods, recognition and extraction of the coronal loops in active regions. We express the introductions regarding to trace patterns and features in digital images and present the recent studies about image processing methods and pattern recognition in solar physics. Afterwards we extract the coronal loops and develop the required techniques for that. These data, related tools and extended codes will be effective in various analysis of the coronal loops interactions.

The spin-1/2 XY chain model in the presence of a transverse magnetic field is considered. The ground state phase diagram consists of two gapped ferromagnetic and the paramagnetic phases. These two phases are separated from each other by the quantum critical point, a neighborhood of which, is known as the quantum critical region. First, using the fermionization approach the Hamiltonian is diagonalized and the spectrum is obtained. Then, using energy spectrum of the system, free energy and thermodynamic quantities such as entropy, specific heat, magnetic expansion coefficient and Grüneisen ratio are calculated and the behavior of these quantities is studied in the quantum critical region. Results show that the different behavior of the specific heat in the critical region is related to the work in the isothermal process. Moreover, the Grüneisen ratio is always independent of the temperature in the critical quantum regions.