Isfahan University of Technology,
The Physics Society of IranIranian Journal of Physics Research1682-695712120191126Effect of uniaxial strain on the current of (6,6) finite armchair carbon nanotubeEffect of uniaxial strain on the current of (6,6) finite armchair carbon nanotube18955FASEFaizabadiZKargarJournal Article20191126 In this paper, the uniaxial strain effect on the electronic properties of (6,6) finite armchair carbon nanotube was investigated by using the Green function technique and Landure-Buttiker formula. It was found that, in (6,6) finite carbon nanotube with 3q and 3q+1 length, where q is a certain integer, the current was induced by the application of a suitable tensile strain and compressive strain in low voltage, respectively. The current of (6,6) finite carbon nanotube with 3q-1 length was decreased by loading the uniaxial strain. According to the results semiconductor-metal transition in (6,6) finite carbon nanotube and vice versa is observed by applying uniaxial strain. In this paper, the uniaxial strain effect on the electronic properties of (6,6) finite armchair carbon nanotube was investigated by using the Green function technique and Landure-Buttiker formula. It was found that, in (6,6) finite carbon nanotube with 3q and 3q+1 length, where q is a certain integer, the current was induced by the application of a suitable tensile strain and compressive strain in low voltage, respectively. The current of (6,6) finite carbon nanotube with 3q-1 length was decreased by loading the uniaxial strain. According to the results semiconductor-metal transition in (6,6) finite carbon nanotube and vice versa is observed by applying uniaxial strain.https://ijpr.iut.ac.ir/article_955_824015afe82513c3b859e933f71a8c65.pdfIsfahan University of Technology,
The Physics Society of IranIranian Journal of Physics Research1682-695712120191126Comparison of fractal and CMR models to investigate ionic conductivityComparison of fractal and CMR models to investigate ionic conductivity914956FAMRShoar Abouzari0000-0001-8287-4008Journal Article20191126 A simple equivalent circuit to explain the electrical response of an ionic conductor is a parallel circuit consisting of an electrical resistance and a capacitor. Impedance semicircle of such a circuit is exactly a semicircle, but the impedance semicircle of experimental data is a depressed one. To explain this deformed shape of semicircle, usually CPE (constant phase element) is used in equivalent circuit instead of the capacitor. There are just a few theoretical researches about this element, which explain the deformed shape b y fractals based on the surface roughness. The present work investigated the surface roughness and rejected its influence on the shape of impedance semicircle by using experimental data. An equivalent circuit is offered for ionic conductors based on the CMR “Concept of Mismatch and Relaxation” model. A simple equivalent circuit to explain the electrical response of an ionic conductor is a parallel circuit consisting of an electrical resistance and a capacitor. Impedance semicircle of such a circuit is exactly a semicircle, but the impedance semicircle of experimental data is a depressed one. To explain this deformed shape of semicircle, usually CPE (constant phase element) is used in equivalent circuit instead of the capacitor. There are just a few theoretical researches about this element, which explain the deformed shape b y fractals based on the surface roughness. The present work investigated the surface roughness and rejected its influence on the shape of impedance semicircle by using experimental data. An equivalent circuit is offered for ionic conductors based on the CMR “Concept of Mismatch and Relaxation” model.https://ijpr.iut.ac.ir/article_956_87e6da4bf1ac24534115ab327829eae0.pdfIsfahan University of Technology,
The Physics Society of IranIranian Journal of Physics Research1682-695712120191126The ground state energy of 3He droplet in the LOCV frameworkThe ground state energy of 3He droplet in the LOCV framework1519957FAMModarresSMotahariARajabiJournal Article20191126 The (extended) lowest order constrained variational ((E) LOCV) method was used to calculate the ground state energy of liquid helium 3 (3He) droplets at zero temperature. Different types of density distribution profiles, such as the Gaussian, the Quasi-Gaussian and the Woods-Saxon were used. It was shown that at least, on average, near 20 3He atoms are needed to get the bound state for 3He liquid droplet. Depending on the choice of the density profiles and the atomic radius of 3He, the above estimate can increase to 300. Our calculated ground state energy and the number of atoms in liquid 3He droplet were compared with those of Variational Monte Carlo (VMC) method, Diffusion Monte Carlo (DMC) method and Density Functional Theory (DFT), for which a reasonable agreement was found. The (extended) lowest order constrained variational ((E) LOCV) method was used to calculate the ground state energy of liquid helium 3 (3He) droplets at zero temperature. Different types of density distribution profiles, such as the Gaussian, the Quasi-Gaussian and the Woods-Saxon were used. It was shown that at least, on average, near 20 3He atoms are needed to get the bound state for 3He liquid droplet. Depending on the choice of the density profiles and the atomic radius of 3He, the above estimate can increase to 300. Our calculated ground state energy and the number of atoms in liquid 3He droplet were compared with those of Variational Monte Carlo (VMC) method, Diffusion Monte Carlo (DMC) method and Density Functional Theory (DFT), for which a reasonable agreement was found.https://ijpr.iut.ac.ir/article_957_7c71f3ac4d9bdc97f58805d8e3deb76f.pdfIsfahan University of Technology,
The Physics Society of IranIranian Journal of Physics Research1682-695712120191126Structural deformations in liquid crystals with dispersed magnetic nano-colloidsStructural deformations in liquid crystals with dispersed magnetic nano-colloids2128958FASShoarinejadDNaseriJournal Article20191126 The stable colloidal dispersions of magnetic nano-particles in nematic liquid crystals are called ferronematics. Their behaviour in magnetic fields depends on various parameters such as anchoring energy, magnetic anisotropy, and shape and volume fraction of the particles. In the present paper, the threshold field is obtained for these colloidal nematics. Then, the influence of magnetic anisotropy, cell thickness, magnetic moment, and volume fraction of the particles are discussed . It is found that due to the influence of some effective parameters, the threshold field changes when compared to pure nematic liquid crystals. The obtained results are consistent with the reported experimental results. The stable colloidal dispersions of magnetic nano-particles in nematic liquid crystals are called ferronematics. Their behaviour in magnetic fields depends on various parameters such as anchoring energy, magnetic anisotropy, and shape and volume fraction of the particles. In the present paper, the threshold field is obtained for these colloidal nematics. Then, the influence of magnetic anisotropy, cell thickness, magnetic moment, and volume fraction of the particles are discussed . It is found that due to the influence of some effective parameters, the threshold field changes when compared to pure nematic liquid crystals. The obtained results are consistent with the reported experimental results.https://ijpr.iut.ac.ir/article_958_b71370cb1a4d8d4719b29ea9cc64973c.pdfIsfahan University of Technology,
The Physics Society of IranIranian Journal of Physics Research1682-695712120191126Large and small solar coronal mass ejectionsLarge and small solar coronal mass ejections2936959FANAlipour RadHSafariJournal Article20191126 The large and small Coronal Mass Ejections (CMEs) and mini-CMEs are observed by the Extreme Ultra Violet Imager (EUVI) on the Solar Terrestrial Relation Observatory (STEREO). These eruption events are usually associated with dimming and wave-like brightenings. Here, the images of the full sun on 26 Apr 2008 with STEREO spacecraft (behind) with the cadences of 10 minutes and 150 seconds and pixel size of 1.59 arcsecond in pass band 195 and 171 Å were analyzed. The velocities of the large and small wave-like brightening were 221 km.s-1 and 6 km.s-1, respectively. The zernike moments of events and non-events were computed and these features were fed to the Support Vector Machine (SVM) classifier. Using this method, 697 mini-CMEs on three different regions of solar corona were detected. The number of mini-CMEs was increased when the CMEs occurred. The average velocity of mini-dimmings was 13.8 km.s-1. The large and small Coronal Mass Ejections (CMEs) and mini-CMEs are observed by the Extreme Ultra Violet Imager (EUVI) on the Solar Terrestrial Relation Observatory (STEREO). These eruption events are usually associated with dimming and wave-like brightenings. Here, the images of the full sun on 26 Apr 2008 with STEREO spacecraft (behind) with the cadences of 10 minutes and 150 seconds and pixel size of 1.59 arcsecond in pass band 195 and 171 Å were analyzed. The velocities of the large and small wave-like brightening were 221 km.s-1 and 6 km.s-1, respectively. The zernike moments of events and non-events were computed and these features were fed to the Support Vector Machine (SVM) classifier. Using this method, 697 mini-CMEs on three different regions of solar corona were detected. The number of mini-CMEs was increased when the CMEs occurred. The average velocity of mini-dimmings was 13.8 km.s-1.https://ijpr.iut.ac.ir/article_959_9e297f0dedfa1e5f45861d02d10904c3.pdfIsfahan University of Technology,
The Physics Society of IranIranian Journal of Physics Research1682-695712120191126Electronic transport through a ladder nanostructure in the presence of network defectsElectronic transport through a ladder nanostructure in the presence of network defects3743960FAMMardaaniHRabaniAMazloom ShahrakiJournal Article20191126 The present research studied the electronic transport of an ideal infinite ladder nanostructure in the presence/absence of network defects by using Green’s function method at the tight-binding approximation. The network defects can be simulated by considering a finite ladder which is connected via two contacts to two similar infinite ladders. The results showed that the hopping energy of rungs determines the overlapping region of the ladder conductance channels. By increasing hopping energy of rungs, the allowed energy region of the ladder increases, while the overlapping region shrinks and eventually vanishes. Creation of branched bonds in the center ladder leads, through the system, to a harder electron tunneling. Moreover, the closer electron energy to the system gap edges leads to a better tunneling. The present research studied the electronic transport of an ideal infinite ladder nanostructure in the presence/absence of network defects by using Green’s function method at the tight-binding approximation. The network defects can be simulated by considering a finite ladder which is connected via two contacts to two similar infinite ladders. The results showed that the hopping energy of rungs determines the overlapping region of the ladder conductance channels. By increasing hopping energy of rungs, the allowed energy region of the ladder increases, while the overlapping region shrinks and eventually vanishes. Creation of branched bonds in the center ladder leads, through the system, to a harder electron tunneling. Moreover, the closer electron energy to the system gap edges leads to a better tunneling.https://ijpr.iut.ac.ir/article_960_4feef3d37ac9070e6281d8942b877f99.pdfIsfahan University of Technology,
The Physics Society of IranIranian Journal of Physics Research1682-695712120191126The electronic conductance of polypyrrole (PPy) molecular wires and emergence of Fano resonance phenomenaThe electronic conductance of polypyrrole (PPy) molecular wires and emergence of Fano resonance phenomena4550961FAMMardaani0000-0002-6268-5311MMardaaniSAnsaryJournal Article20191126In this paper, we studied the electronic conductance of a polypyrrole polymer, which is embedded between two semi-infinite simple chains by using Green’s function technique in tight-binding approach. We first reduced the center polymer to a one dimensional chain with renormalized onsite and hopping energies by renormalization method. Then, we calculated the system conductivity as a function of incoming electron energy, polymer length and contact hopping terms. The results showed that by increasing polymer length and decreasing contact hopping energies, the conductance decreases in the gap regions. This means that for larger gaps, the electron tunneling happens with more difficulty. Moreover, at the resonance area, due to the existence of nitrogen atom in the polymer cyclic structure, the Fano resonance will emerge. Furthermore, the polymer can behave like a metallic chain by variation of the value of nitrogen on-site term.In this paper, we studied the electronic conductance of a polypyrrole polymer, which is embedded between two semi-infinite simple chains by using Green’s function technique in tight-binding approach. We first reduced the center polymer to a one dimensional chain with renormalized onsite and hopping energies by renormalization method. Then, we calculated the system conductivity as a function of incoming electron energy, polymer length and contact hopping terms. The results showed that by increasing polymer length and decreasing contact hopping energies, the conductance decreases in the gap regions. This means that for larger gaps, the electron tunneling happens with more difficulty. Moreover, at the resonance area, due to the existence of nitrogen atom in the polymer cyclic structure, the Fano resonance will emerge. Furthermore, the polymer can behave like a metallic chain by variation of the value of nitrogen on-site term.https://ijpr.iut.ac.ir/article_961_d8ba1445a57f3b27a6cc82d67f73283d.pdfIsfahan University of Technology,
The Physics Society of IranIranian Journal of Physics Research1682-695712120191126The effect of gate voltage on the electrical transport properties in the contacts of C60 to carbon nanotube leadsThe effect of gate voltage on the electrical transport properties in the contacts of C60 to carbon nanotube leads5157962FAAAShokriSHNikzadJournal Article20191126 In this paper, we examined the effect of gate voltage, bias voltage, contact geometries and the different bond lengths on the electrical transport properties in a nanostructure consisting of C60 molecule attached to two semi-infinite leads made of single wall carbon nanotubes in the coherent regime. Our calculation was based on the Green’s function method within nearest-neighbour tight-binding approximation. After the calculation was of transmission, the electrical current was obtained by the Landauer-Buttiker formula. Next, the effect of the mentioned factors was investigated in the nanostructure. The application of the present results may be useful in designing devices based on molecular electronics in nanoscale. In this paper, we examined the effect of gate voltage, bias voltage, contact geometries and the different bond lengths on the electrical transport properties in a nanostructure consisting of C60 molecule attached to two semi-infinite leads made of single wall carbon nanotubes in the coherent regime. Our calculation was based on the Green’s function method within nearest-neighbour tight-binding approximation. After the calculation was of transmission, the electrical current was obtained by the Landauer-Buttiker formula. Next, the effect of the mentioned factors was investigated in the nanostructure. The application of the present results may be useful in designing devices based on molecular electronics in nanoscale.https://ijpr.iut.ac.ir/article_962_f36e7f30a0a2449bf934b5fbf43f02c1.pdfIsfahan University of Technology,
The Physics Society of IranIranian Journal of Physics Research1682-695712120191126The effect of Lanthanum vacancy on structural, electrical and magnetic properties of La1-xMnO3+Î´ manganiteThe effect of Lanthanum vacancy on structural, electrical and magnetic properties of La1-xMnO3+Î´ manganite5966963FAAHosseinzadehPKameliHSalamatiBAslibeikiJournal Article20191126 In this investigation, the effect of Lanthanum vacancy on the structural, electrical and magnetic properties of La1-xMnO3+δ manganite (x=0, 0.05) was studied. Decreasing La3+ amount in samples led to creation of some Mn4+ cations. By increasing the Mn4+content in atomic structure of samples, double exchange interaction was strengthened. Results of Ac magnetic susceptibility measurements indicated that both samples (x=0, 0.05) have spin glass-like behavior at low temperatures. Electrical transport measurements showed a decrease in resistivity of samples, which can be attributed to variation in Mn3+ to Mn4+ ratio and different kinds of magnetic interactions in the samples. Furthermore, it was shown that fast cooling (FC) is an appropriate method in controlling the oxygen of samples. The samples prepared by FC method showed similar properties with stoichiometric La1-xMnO3. In this investigation, the effect of Lanthanum vacancy on the structural, electrical and magnetic properties of La1-xMnO3+δ manganite (x=0, 0.05) was studied. Decreasing La3+ amount in samples led to creation of some Mn4+ cations. By increasing the Mn4+content in atomic structure of samples, double exchange interaction was strengthened. Results of Ac magnetic susceptibility measurements indicated that both samples (x=0, 0.05) have spin glass-like behavior at low temperatures. Electrical transport measurements showed a decrease in resistivity of samples, which can be attributed to variation in Mn3+ to Mn4+ ratio and different kinds of magnetic interactions in the samples. Furthermore, it was shown that fast cooling (FC) is an appropriate method in controlling the oxygen of samples. The samples prepared by FC method showed similar properties with stoichiometric La1-xMnO3.https://ijpr.iut.ac.ir/article_963_a2a223b216b0ed22f19e5e3060d1aee5.pdfIsfahan University of Technology,
The Physics Society of IranIranian Journal of Physics Research1682-695712120191126Study of nuclear level densities for exotic nucleiStudy of nuclear level densities for exotic nuclei6775964FAMNasri Nasrabadi0000-0002-8706-727XMSepianiJournal Article20191126Nuclear level density (NLD) is one of the properties of nuclei with widespread applications in astrophysics and nuclear medicine. Since there has been little experimental and theoretical research on the study of nuclei which are far from stability line, studying NLD for these nuclei is of crucial importance. Also, as NLD is an important input for nuclear research codes, hence studying the methods for calculation of this parameter is essential. Besides introducing various methods and models for calculating NLD for practical applications, we used exact spectra distribution (SPDM) for determining NLD of two neutron and proton enriched exotic nuclei with the same mass number.Nuclear level density (NLD) is one of the properties of nuclei with widespread applications in astrophysics and nuclear medicine. Since there has been little experimental and theoretical research on the study of nuclei which are far from stability line, studying NLD for these nuclei is of crucial importance. Also, as NLD is an important input for nuclear research codes, hence studying the methods for calculation of this parameter is essential. Besides introducing various methods and models for calculating NLD for practical applications, we used exact spectra distribution (SPDM) for determining NLD of two neutron and proton enriched exotic nuclei with the same mass number.https://ijpr.iut.ac.ir/article_964_97868457d93d4701101c5529d727a65a.pdfIsfahan University of Technology,
The Physics Society of IranIranian Journal of Physics Research1682-695712120191126Fabrication and size control of Ag nanoparticlesFabrication and size control of Ag nanoparticles7783965FAMFarbod0000-0002-9774-705XMRBatvandiJournal Article20191126 The objective of this research was to fabricate Ag nanoparticles and control their sizes. Colloidal Ag nanoparticles with particle size of 30 nm were prepared by dissolving AgNO3 in ethanol and through the chemical reduction of Ag+ in alcohol solution. To control the nanoparticle size, different samples were fabricated by changing the AgNO3 and stabilizer concentrations and the effects of different factors on the shape and size of nanoparticles were investigated. The samples were characterized using SEM and EDX analysis. The results showed that by increasing the AgNO3 concentration, the average size of nanoparticles increases and nanoparticles lose their spherical shape. Also, we found that by using the stabilizer, it is possible to produce stable nanoparticles but increasing the stabilizer concentration caused an increase in size of nanoparticles. Fabrication of nanoparticles without using stabilizer was achieved but the results showed the nanoparticles size had a growth of 125 nm/h in the alcoholic media. The objective of this research was to fabricate Ag nanoparticles and control their sizes. Colloidal Ag nanoparticles with particle size of 30 nm were prepared by dissolving AgNO3 in ethanol and through the chemical reduction of Ag+ in alcohol solution. To control the nanoparticle size, different samples were fabricated by changing the AgNO3 and stabilizer concentrations and the effects of different factors on the shape and size of nanoparticles were investigated. The samples were characterized using SEM and EDX analysis. The results showed that by increasing the AgNO3 concentration, the average size of nanoparticles increases and nanoparticles lose their spherical shape. Also, we found that by using the stabilizer, it is possible to produce stable nanoparticles but increasing the stabilizer concentration caused an increase in size of nanoparticles. Fabrication of nanoparticles without using stabilizer was achieved but the results showed the nanoparticles size had a growth of 125 nm/h in the alcoholic media.https://ijpr.iut.ac.ir/article_965_a6e1427b6460764e8b1b619ed92e948b.pdfIsfahan University of Technology,
The Physics Society of IranIranian Journal of Physics Research1682-695712120191126Investigation of (111) wafers and comparison with (100) substratesInvestigation of (111) wafers and comparison with (100) substrates8589966FAABahariJournal Article20191126 In the last decade, Si(100) has been used as a suitable substrate in field effect transistors. Some issues such as leakage current and tunneling current through the ultrathin films have been increased with shrinking the electronic devices – particularly, field effect transistors – to nanoscale, which is threatening more use of Si(100). We have thus demonstrated a series of experiments to grow ultrathin films on both Si(100) and Si(111) substrates and studied their nanostructural properties to see the possibility of replacing Si(100) with Si(111). The obtained results indicate that Si(111) substrate with silicon nitride film on top is desirable. In the last decade, Si(100) has been used as a suitable substrate in field effect transistors. Some issues such as leakage current and tunneling current through the ultrathin films have been increased with shrinking the electronic devices – particularly, field effect transistors – to nanoscale, which is threatening more use of Si(100). We have thus demonstrated a series of experiments to grow ultrathin films on both Si(100) and Si(111) substrates and studied their nanostructural properties to see the possibility of replacing Si(100) with Si(111). The obtained results indicate that Si(111) substrate with silicon nitride film on top is desirable.https://ijpr.iut.ac.ir/article_966_2e05be5450c4048e2951659c2efad797.pdf