Sharif Digital Repository

In this paper, some important circuit parameters of a monolayer armchair graphene nanoribbon (GNR) field effect transistor (GNRFET) in different structures are studied. Also, these structures are Ideal with no defect, 1SVGNRFET with one single vacancy defect, and 3SVsGNRFET with three SV defects. Moreover, the circuit parameters are extracted based on Semi Classical Top of Barrier Modeling (SCTOBM) method. The I-V characteristics simulations of Ideal GNRFET, 1SVGNRFET and 3SVsGNRFET are used for comparing with SCTOBM method. These simulations are solved with Poisson-Schrodinger equation self-consistently by using Non- Equilibrium Green Function (NEGF) and in the real space approach. The... 

A mechanochemical method was applied to prepare bismuth oxybromide (BiOBr) nanoplates using bismuth nitrate pentahydrate and potassium bromide for 15 (A15), 30 (A30) and 60 (A60) minutes. Scanning electron microscopy studies showed that all the products were comprised of nanoplates. Aggregated nanoplates along with microblocks were observed for A15 and A30 and the entire morphology was not homogenous. The morphology of A60 was uniform and consisted of thin and isolated nanoplates. Evaluation of the X-ray diffraction patterns showed that the purity and crystallinity of the products improved by increasing the milling time. The energy dispersive X-ray analysis confirmed the high purity of the... 

The local buckling behavior of perfect/defective and single/multi-walled carbon nanotubes (CNTs) under axial compressive forces has been investigated by the molecular dynamics approach. Effects of different types of defects including vacancy and Stone-Wales (SW) defects and their configurations on CNTs with different chiralities at room temperature are studied. Results show that defects largely reduce the buckling stress and the ratio of immediate reduction in buckling compressive stress of the defective CNT to the perfect one, but have little influence on their compressive elastic modulus. SW defects usually reduce the mechanical properties more than vacancy defects, and zigzag CNTs are... 

Despite the wide application ranges of TiO2, the precise explanation of the charge transport dynamic through a mixed crystal phase of this semiconductor has remained elusive. Here, in this research, mixed-phase TiO2 nanotube arrays (TNTAs) consisting of anatase and 0-15% rutile phases has been formed through various annealing processes and employed as a photoelectrode of a photovoltaic cell. Wide ranges of optoelectronic experiments have been employed to explore the band alignment position, as well as the depth and density of trap states in TNTAs. Short circuit potential, as well as open circuit potential measurements specified that the band alignment of more than 0.2 eV exists between the... 

Providing solar hydrogen as a clean energy resource is one of the human challenges for future. Controlling oxygen vacancies as well as surface morphology in metal oxide semiconductors enables developing PEC H2production in some understood ways. Here, the influence of simple change in annealing atmosphere, air and pure oxygen, on photoresponse of nanocrystalline WO3has been studied completely. Results revealed that such slight change in annealing procedure increases effective surface interface and donor density by 77 and 72%, respectively. These effects and also retarding recombination of photogenerated electro-hole pair resulted in photocurrent enhancement under solar like illumination more... 

We compare and contrast the physisorption behavior of imidazolium and butyltrimethylammonium based ionic liquids (ILs) on mono-vacant nitrogen and boron defective hexagonal boron nitride nanoflakes (h-BNNF) using M06-2X/cc-pVDZ level of theory. The presence of defects on the nanoflakes results in an increase in IL binding energy by ~ 1–27 kcal/mol partly due to the lowering of the energy band in the defective nanoflakes. Imidazolium based ILs adsorb energetically more favorably on h-BNNF-VB than on h-BNNF-VN while butyltrimethylammonium based ILs prefer to adsorb on h-BNNF-VN. Upon adsorption of imidazolium ILs on the nanoflakes, an increase in both HOMO and LUMO orbital energies is observed... 

In this work, V, Co-codoped TiO2(B) samples are synthesized through a hydrothermal method, and used as negative electrode materials for lithium ion batteries. The amount of dopants is varied in order to investigate their influence on electrochemical properties. The formation of V, Co-codoped TiO2(B) nanobelts with widths of 20 and 60 nm is demonstrated using X-ray diffraction, X-ray photoelectron spectroscopy, inductively coupled plasma–optical emission spectrometry and field-emission scanning electron microscopy analyses. In addition, the electrochemical properties of the samples are tested by cyclic voltammetry, charging/discharging, and cyclic performance techniques. Compared to other... 

High performance Fe-Gd-P tri-doped TiO2 nanoparticles (1 at% for each dopant) were successfully synthesized by a modified sol–gel method. Various analytical and spectroscopic techniques were carried out to determine the physicochemical properties of the prepared samples, including XRD, EDX, FESEM, BET, FTIR, XPS, PL, EIS and UV–Vis diffuse reflectance spectroscopy. The photocatalytic activities of prepared samples were evaluated by photo degradation of methyl orange (MO) and 4-chlorophenol (4-CP) as model pollutants under visible light irradiation. Effects of each dopant on different properties of TiO2 nanoparticles were investigated. Results show that Gd and P doping enhances TiO2 surface... 

Carbon nanotube (CNT)-reinforced polymer composites have attracted great attention due to their exceptionally high strength. Their high strength can be affected by the presence of defects in the nanotubes used as reinforcements in practical nanocomposites. In this article, a new three-phase molecular structural mechanics/finite element (MSM/FE) multiscale model is used to study the effect of CNT vacancy defects on the stability of single-wall (SW) CNT-polymer composites. The nanotube is modeled at the atomistic scale using MSM, whereas the interphase layer and polymer matrix are analyzed by the FE method. The nanotube and polymer matrix are assumed to be bonded by van der Waals interactions... 

Using the first-principles procedure of density-functional-theory within tight-binding approximation and nonequilibrium Green's function formalism, this paper reports on the impact of vacancy defects on the structural, electronic and transport properties of hydrogen-passivated graphene atomic sheet. After the introduction of vacancy defects in graphene atomic sheet passivated with hydrogen atoms, apart from increase in band gap, a suppression is noted in the intensity of transmission channels and density of states arising from the long array deformations of the graphene sheet and a corresponding shift of the Fermi level. This in turn decreases the conductance of the defected graphene atomic... 

Recently, aluminum titanate (Al2TiO5)-based nanostructures have been proved to serve as an efficient photocatalytic material with satisfactory photodegradation capacity. In this study, the citrate sol–gel method was used to synthesize these nanostructures and inspect the significant impacts of nitrogen-doping-originated crystalline defects on their photocatalytic performance in some details for the first time. The results indicated that the penetration of nitrogen atoms into AT crystal lattice, depending on the nitriding time and temperature, can induce a great deal of the residual stress and result in propagating the existing cracks and breaking down the particles. The XPS and FTIR results... 

In this paper, by using first-principle density functional theory (DFT) combined with non-equilibrium Green's function (NEGF), thermally induced spin current in zigzag and armchair Antimonene Nanoribbon (SbNR) is investigated. Also, we obtain higher spin current in Armchair nanoribbon (ANR) than zigzag nanoribbon (ZNR), because the start energy of transmission for ANR is closer to the Fermi level than ZNR. The results show that the device has a perfect spin Seebeck effect under temperature difference without gate voltage or bias voltage. For the ANR configuration, the competition between spin up holes and spin down electrons leads to negative differential behavior of charge current, which is... 

The relationship between unpaired electron delocalization and nearest-neighbor atomic relaxations in the vacancies of diamond has been determined in order to understand the microscopic reason behind the neighboring atomic relaxation. The Density Functional Theory (DFT) cluster method is applied to calculate the single-electron wavefunction of the vacancy in different charge states. Depending on the charge and spin state of the vacancies, at outward relaxations, 84-90% of the unpaired electron densities are localized on the first neighboring atoms. The calculated spin localizations on the first neighboring atoms in the ground state of the negatively charged vacancy and in the spin quintet... 

Carbon nanotubes are widely used in the design of nanosensors and actuators. Any defect in the manufactured nanotube plays an important role in the natural frequencies of these structures. In this paper, the effect of vacancy defects on the vibration of carbon nanotubes is investigated by using an atomistic modeling technique, called the molecular structural mechanics method. Vibration analysis is performed for armchair and zigzag nanotubes with cantilever boundary condition. The shift of the principal frequency of the nanotube with vacancy defect at different locations on the length is plotted. The results indicate that the frequency of the defective nanotube can be larger or smaller or... 

Single electron wavefunction of a vacancy in diamond lattice has been calculated in different symmetric configurations of the nearest neighbor (NN) atoms. We used ab initio density functional theory (DFT) and unrestricted Hartree-Fock (UHF) cluster methods. The variation of electron or spin localization on NN atoms have been investigated with respect to the lattice relaxation in the ground state of the neutral and negatively charged vacancy. Calculated variations are not symmetric with respect to the sign of the lattice relaxation. We obtain about 90% localization for electronic charge and spin density for the neutral and negatively charged vacancy, respectively. This is in good agreement... 

Because of the possibility of various types of vacancies in cementite due to its crystalline structure, the focus of this paper was only on vacancies. In this regard, the formation energies of single, two, three and four vacancies of over than 120 different cases were calculated using first-principles method. For the case of single vacancy, the results were in three values of ~1.63, 1.39 and 0.78 eV according to iron vacancies at general positions, iron vacancies located on mirror planes and carbon vacancies in the interstitial positions, respectively. The results for the case of two, three and four vacancies were between from 2.10 to 3.34 eV, from 3.92 to 5.10 eV and from 4.77 to 6.33 eV,... 

This study demonstrates the glucose-template assisted synthesis of hydrogen-treated Pt: TiO2/WO3 composites, and their round-the-clock photoactivity towards methanol (MeOH) degradation under light illumination and in dark. XRD indicated increasing rutile fraction in TiO2 as a function of template removal, WO3 crystallinity and H2 treatment process. The presence of oxygen vacancies in WO3 was confirmed by XPS. Lower recombination rate and higher surface area were observed in the optimized H2-Pt-G:TiO2/WO3 catalyst. The presence of oxygen vacancies and optical enhancements due to the synergistic interactions of the multi-system (TiO2, WO3 and Pt) extended the visible light absorption of the... 

Semiconductor-based photocatalysis is an efficient approach for degradation of organic pollutants. In this context, ZnO/g-C3N4 composite nanofibers containing carbonaceous species with different concentrations of g-C3N4 nanosheets (x = 0.25, 0.5, 1, 2, 10 wt%) noted as ZnO/carbon/(x wt%) g-C3N4 are prepared by electrospinning technique. For preparation of the composite nanofibers, bulk g-C3N4 is exfoliated to nanosheets, and then it is mixed with polyvinyl alcohol and appropriate zinc acetate content followed by electrospinning process. Thermal annealing of the as spun zinc acetate/poly(vinyl alcohol)/g-C3N4 nanosheets sample under N2 atmosphere leads to the formation of carbonaceous species... 

Carbon nanotubes (CNTs) are promising candidates for high-resolution mass nanosensors owing to their unique vibrational behavior. The structural characteristic (e.g. defect type and density) and working temperature have a significant effect on the natural frequency of CNT-based sensors. Herein, a stochastic approach based on novel finite element and molecular mechanics simulations is implemented to model the effect of temperature and structural characteristics of single-wall CNTs including defects (vacancy defect with different densities) and chirality (zigzag and armchair) on their vibrational behavior. The results show that the vacancy defects exert a significant deterioration of the... 

A novel method of oxide semiconductor nanoparticle synthesis is proposed based on high-voltage, high-current electrical switching discharge (HVHC-ESD). Through a subsecond discharge in the HVHC-ESD method, we successfully synthesized zinc oxide (ZnO) nanorods. Crystallography and optical and electrical analyses approve the high crystal-quality and outstanding optoelectronic characteristics of our synthesized ZnO. The HVHC-ESD method enables the synthesis of ZnO nanorods with ultraviolet (UV) and visible emissions. To demonstrate the effectiveness of our prepared materials, we also fabricated two UV photodetectors based on the ZnO nanorods synthesized using the subsecond HVHC-ESD method. The...