Search for: vacancy-defects
0.008 seconds

    Effect of defects on the local shell buckling and post-buckling behavior of single and multi-walled carbon nanotubes

    , Article Computational Materials Science ; Volume 79 , November , 2013 , Pages 736-744 ; 09270256 (ISSN) Eftekhari, M ; Mohammadi, S ; Khoei, A. R ; Sharif University of Technology
    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... 

    Pull-in behaviors of carbon nanotubes with vacancy defects and residual stresses

    , Article Journal of Computational and Theoretical Nanoscience ; Vol. 11, issue. 1 , 2014 , pp. 153-159 ; ISSN: 15461955 Fakhrabadi, M. M. S ; Rastgoo, A ; Ahmadian, M. T ; Sharif University of Technology
    The paper deals with investigation of the effects of vacancy defects on the pull-in behaviors of the carbon nanotubes. The influences of single, double and triple vacancies in different peripheral and longitudinal positions are studied. The results reveal that the vacancy defects drastically reduce the pull-in charge because they weaken the nanostructure. Moreover, the effects of residual stresses on the pull-in and vibrational properties of the carbon nanotubes are scrutinized. The influences of the angular deviations from the parallel positions of the CNT and ground plate during the fabrication process are also reported. Copyright  

    Fracture analysis of monolayer graphene sheets with double vacancy defects via MD simulation

    , Article Solid State Communications ; Volume 151, Issue 17 , 2011 , Pages 1141-1146 ; 00381098 (ISSN) Ansari, R ; Motevalli, B ; Montazeri, A ; Ajori, S ; Sharif University of Technology
    Carbon nanostructures such as carbon nanotubes (CNTs) and graphene sheets have attracted great attention due to their exceptionally high strength and elastic strain. These extraordinary mechanical properties, however, can be affected by the presence of defects in their structures. When a material contains multiple defects, it is expected that the stress concentration of them superposes if the separation distances of the defects are low, which causes a more reduction of the strength. On the other hand, it is believed that if the defects are far enough such that their affected areas are distinct, their behavior is similar to a material with single defect. In this article, molecular dynamics... 

    Modeling comparison of graphene nanoribbon field effect transistors with single vacancy defect

    , Article Superlattices and Microstructures ; Volume 97 , 2016 , Pages 28-45 ; 07496036 (ISSN) Nazari, A ; Faez, R ; Shamloo, H ; Sharif University of Technology
    Academic Press  2016
    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... 

    Improving ION / IOFF and sub-threshold swing in graphene nanoribbon field-effect transistors using single vacancy defects

    , Article Superlattices and Microstructures ; Volume 86 , October , 2015 , Pages 483-492 ; 07496036 (ISSN) Nazari, A ; Faez, R ; Shamloo, H ; Sharif University of Technology
    Academic Press  2015
    Graphene nanoribbon field effect transistors are promising devices for beyond-CMOS nanoelectronics. Graphene is a semiconductor material with zero bandgap and its bandgap must be changed. One of the opening bandgap methods is using graphene nanoribbons. By applying a defect, there is more increase on band gap of monolayer armchair graphene nanoribbon field effect transistor. So, by applying more than one defect, we can reach to much more increase in bandgap of graphene nanoribbon field effect transistors (GNRFET). In this paper, double-gated monolayer armchair graphene nanoribbon field effect transistors (GNRFET) with one single vacancy (1SV) defect (so-called 1SVGNRFET)are simulated and... 

    Manipulation of structural, electronic and transport properties of hydrogen-passivated graphene atomic sheet through vacancy defects: First-principles numerical simulations based on density-functional-theory along with tight-binding approximation

    , Article Materials Research Express ; Volume 6, Issue 8 , 2019 ; 20531591 (ISSN) Sattar, A ; Irfan, M ; Iqbal, A ; Shahid, F. A ; Junaid Amjad, R ; Usman, A ; Mahmood, H ; Latif, H ; Imran, M ; Akhtar Ehsan, S ; Akhtar, M. N ; Akbar, N ; Sharif University of Technology
    Institute of Physics Publishing  2019
    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... 

    Effect of vacancy defects on the fundamental frequency of carbon nanotubes

    , Article 3rd IEEE International Conference on Nano/Micro Engineered and Molecular Systems, NEMS 2008, Sanya, 6 January 2008 through 9 January 2008 ; 2008 , Pages 1000-1004 ; 9781424419081 (ISBN) Pirmoradian, M ; Ahmadian, M. T ; Asempour, A ; Tajalli, S. A
    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... 

    Vibrational behavior of defective and repaired carbon nanotubes under thermal loading: A stochastic molecular mechanics study

    , Article Mechanics of Materials ; Volume 163 , 2021 ; 01676636 (ISSN) Payandehpeyman, J ; Moradi, K ; Zeraati, A. S ; Hosseinabadi, H. G ; Sharif University of Technology
    Elsevier B.V  2021
    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... 

    Investigating the effect of carbon nanotube defects on the column and shell buckling of carbon nanotube-polymer composites using multiscale modeling

    , Article International Journal for Multiscale Computational Engineering ; Volume 7, Issue 5 , 2009 , Pages 431-444 ; 15431649 (ISSN) Montazeri, A ; Naghdabadi, R ; Sharif University of Technology
    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...