مجله فیزیک کاربردی
سال دوازدهم شماره 3 (پیاپی 30، پاییز 1401)

In this paper, the electron transport through a zigzag single-walled carbon nanotube (SWCNT) junction consisting of zigzag SWCNT (central region) sandwiched between two semi-infinite metallic zigzag SWCNT leads to the presence of an applied uniaxial strain is numerically investigated. This study is based on a nearest-neighbor tight-binding approximation within the framework of a generalized Green’s function technique and relies on the Landauer-B¨utikker formalism. The results show that the electron transport properties of the system can be well controlled by modifying the uniaxial strain strength and length of the SWCNT junction. Besides, applying compressive strain is more effective than tensile strain in opening a band gap in the system. Furthermore, the current amplitude for the tensile strain is bigger than the compressive strain with the same absolute values of uniaxial strain strength. As the length of the intermediate region increases, the density of states in Fermi energy decreases, and the magnitude of the electron emission function in Fermi energy decreases to zero, leading to the transition of the metal to the semiconductor.

‎We present a theoretical interacting one-dimensional Bose-Einstein condensate (BEC) inside an optical cavity which is driven through of the fixed end mirrors. Under the Bogoliubov approximation and when the number of photons inside the cavity is not too large, the atomic field operator can be considered as a single-mode quantum field which is coupled to the radiation pressure of the intracavity field. In this way, the system behaves like an optomechanical system with an extra nonlinear term corresponding to the atom-atom interaction.We show that one of the best ways of tracing the effect of atomic interaction is to study the noise power spectrum of the field of the cavity. For this purpose, we study the light intensity spectrum of the cavity as well as the entanglement between the optical cavity and the BEC. We show how the pattern of the power spectrum of the cavity changes due to the nonlinear effect of atomic collisions. Furthermore, it is shown that due to the s-wave scattering frequency of the atom-atom interaction, one can measure the strength of interatomic interaction. Besides, we show how the atomic collisions affect the entanglement between subsystems and cooling behavior of the BEC atoms.

In this paper, using density functional theory combined with non-equilibrium Green's function, the effects of alligator-clip compounds on the electronic transport properties of benzene-based molecular devices are investigated. For this purpose, once a single Benzene molecule and once again two Benzene molecules with an acetylene spacer in between are considered as the central element of the molecular device between two gold electrodes. The spin polarization effects in the presence of Nickel and Iron anchors are studied. In the previous studies, other alligator-clip compounds such as Sulfur and organic molecular ones have been utilized. It is important to study the properties and behavior of different elements for the realization of high-performance molecular devices in the future. By utilizing Siesta and Transiesta codes, when excluding spin polarization effects, in all of the structures (except Nickel-Benzene), negative differential resistance is observed. It is an essential property that allows fast switching in certain types of electronic devices. However, when the spin polarization is considered, none of the combinations show the negative differential resistance feature. The I-V characteristics show that all of the combinations have linear behavior in low voltages no matter whether the spin polarization is considered or not. The voltage ranges from -2V to +2V are taken into account in order to investigate the probability of rectification.

In this research, we try to improve the performance of ultraviolet (UV) photodetector based on ZnO nanorods through decoration with Au nanoparticles. One-dimensional ZnO nanorods were grown on the quartz substrates by the vapor phase transport (VPT) method. Then, Au nanoparticles by depositing a thin nanometric Au layer with thicknesses 3, 6, 9, and 12 nm via sputtering technique and a heating process were coated on the ZnO nanorods. The morphology and structure of the samples were characterized by using a Scanning Electron Microscope (SEM) and X-ray diffractometer (XRD). The results showed formation of rather aligned ZnO nanorods with wurtzite hexagonal crystalline structure and preferred orientation along the c-axis which are coated with Au nanoparticles. The obtained data from measuring ultraviolet photoresponse shows that the decorated sample with 9 nm thick Au film possesses a higher on/off ratio (6.5), responsivity (568 ± 33 mA/W), and faster rise and decay times. In addition, with presence of Au nanoparticles, responsivity in the visible region (λ= 520 nm) increased from 6 ±0.5 mA/W to 19±1 mA/W. This improved detecting behavior results from Localized Surface Plasmons (LSPs) of the Au nanoparticles and the formation of localized Schottky barriers between Au nanoparticles and ZnO.

In this paper, electronic and structural properties such as lattice constant, energy band structure, and density of states of InP in bulk and nanowire are calculated. The calculations have been performed using the Pseudopotential method in the framework of density functional theory (DFT) with local density approximation (LDA), and generalized gradient approximation (GGA) by Quantum Espresso package. The results show a direct bandgap of 1.4 eV at the Γ point in the Brillouin zone and have not cut the Fermi level, with a good agreement with the available experimental results. Also, band structure in nanowires of about 1.49 eV was calculated, which shows an increased bulk state. The calculated results show good agreement with the available experimental results.

The Silver Gallium selenide crystal is more important than other crystals due to its intrinsic parameters. The transparency of the AGSe crystal is in the wavelength range of 10.06 microns, which uses the pulsed CO2 laser at atmospheric pressure (TEA) as the fundamental wavelength for the second harmonic generation. Therefore, the effect of parameters such as intensity, nonlinear crystal length, temperature and wavelength on the phase–mismatched and efficiency has been investigated. The coupled- wave equations are performed numerically by MATLAB software. The results indicate the existence of optimal length in the efficiency of the second harmonic generation in the crystal. In a crystal with a length of 1.05 cm, the efficiency reaches 80.35%. Also, the maximum efficiency of the second harmonic generation is 0.025W/cm2 (threshold intensity) and the crystal length is 0.5 cm. The results of modeling and numerical calculations in this work are in good agreement with the experimental results of others.