جستجوی مقالات مرتبط با کلیدواژه « Bandgap » در نشریات گروه « فنی و مهندسی »

In this work, an attempt was made to prepare thin layers of nanostructured cadmium selenide (CdSe) based on a simple solution method of chemical bath deposition (CBD), which commercially has an accessible precursor. In the chemical solution bath layering method, manufacturing factors play a significant role and determine the characteristics of the final product. In this research, the effect of an important factor, the concentration of primary solutions of selenium and cadmium ions, which is one of the most important factors in the formation of cadmium selenide, and it will be observed that the change in the concentration of these metal and non-metal ions strongly affects the type of electronic structure of the material. In comparison with the sputtering methods, in the chemical solution deposition method, there is a high control in the formation of solid deposits with different combinations of metal and non-metal binary compounds. Changing the selenide ionconcentration changes the size of the energy band gap. It has been observed that the energy gap increases with the increase of selenide non-metal ion concentration.

Every year around the world, earthquakes and other seismic waves cause damage to civil infrastructures. The most harmful waves for civil infrastructure are surface waves, as this study focused on it. Therefore, this study aims to investigate the behavior of resonators as an approach to reducing surface seismic waves based on both infinite and finite lattices for the proposed resonator. To this end, first, an infinite lattice is evaluated using the Bloch-Floquet theory by modeling the smallest repetition of the considering lattice. The dispersion relation of the considered resonator is obtained by an eigenfrequency analysis for each wave vector in the first irreducible Brillouin zone. Then, the bandgap for surface waves is defined using the sound line concept, a common approach in solid-state physics to find the pure surface modes of the dispersion relation for resonators. The sound line concept is used to distinguish between the pure surface and other waves, such as body waves. In Bloch-Floquet theory, the lattice is assumed to have an infinite number of unit cells; however, in real applications, the lattice needs to have a finite number of unit cells. Therefore, the accuracy of the bandgap obtained for the infinite lattice is evaluated by considering a finite lattice model in both frequency and time domains to consider a more realistic case. The results show that the considered resonator has a notable surface wave bandgap. Moreover, the results of the finite lattice conform well to the results of the infinite lattice in both frequency and time domains. The proposed resonator is made of concrete and has a height of six meters, and the unit cell constant is considered two meters. The obtained bandgap is between 14 and 21 Hz, confirmed by a finite model in both frequency and time domains. As a result, the proposed resonator can reduce surface seismic waves efficiently.

Microtubules, polymer tubes stretched from the cell nucleus to the cell membrane, are the major parts of the cytoskeleton that provide the mechanical rigidity, organization, and shape retention for the cytoplasm of eukaryotic cells. These structures play a key role in some cellular processes such as cell division, intracellular transport, and the internal organization of cells. In all the above applications, the network structure of microtubules is the main reason for the importance of in-depth studies of their mechanical properties. In this paper, the propagation of elastic waves in periodic networks based on two-dimensional fractal microtubules of fixed mass-center triangles is analyzed. This study begins with the selection of a suitable beam model for a microtubule and examines the dynamic behavior of microtubules by creating periodic structures. To obtain dispersion curves, finite element models of microtubules and their networks are developed, and the bandgap equations are calculated based on Bloch's theory. The results show that depending on the topology of the selected unit cells as well as the considered periods, it is possible to design a frequency gap in specific ranges for the application of low and high-frequency bio-filters. This study helps researchers control or absorb some unwanted vibrations using periodic structures, and thanks to their better biocompatibility, these networks can be used in next-generation nanomechanical devices such as implantable biosensors.

Ultrasonication in liquids is one of the most important approaches to exfoliate 2D materials. Here we described some experiments based on Liquid Phase Exfoliation of Molybdenum Disulfide (MoS2) powder in the water-ethanol solution without any additives. It is reported that MoS2 as a prototype 2D Transition Metal Dichalcogenide, has a bandgap that increases with decreasing layer thickness. There are some factors that affect the average band gap energy value (and the thickness of the exfoliated flakes). In this study, 2D nanoflakes of Molybdenum Disulfide (MoS2) were produced using an ultrasonic probe in various solutions. Because of the key role of surface tension in the exfoliation process, and also to reduce the negative effects of chemical residues on the environment, we used a binary solution consisting of water and ethanol with the ratio determining based on the Connors-Wright equation. Our findings from UV-Visible spectroscopy show that the best efficiency, i.e. the minimum thickness of MoS2 nanoflakes, is obtained for the solution with the mentioned solution. The FESEM and TEM images, and the XRD pattern confirmed that we obtained the few-layers of MoS2.

In this paper, the performance of Cadmium Telluride (CdTe) solar cells, which are second generation or thin film solar cells, has been simulated using SCAPS software. The purpose of this paper is to improve the efficiency of the CdTe solar cell. The primary structure of the solar cell consists of Ni, CdTe, CdS, and n-ZnO-Al layers. Therefore, adding a thin layer of tin (SnS) of 0.4 μm to the absorbing layer (CdTe) leads to the creation of a backscattering or an auxiliary electrical field in the direction of the main field, between the adsorbent layer and the buffer layer (CdS). Therefore, adding the layer reduces the recombination of carriers at longer wavelengths by the auxiliary field, and leads to an improvement in the primary structure of the cadmium-telluride solar cell from the values of η=19.09 %, FF= 85.14%, JCS= 25.77 mA/cm2, VOC = 0.87 V to η=22.98 %, FF= 85.99%, JCS= 32.51 mA/Cm2, VOC = 0.82 V.