Amir A. Farajian

Wright State University, Dayton, Ohio, United States

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Publications (83)174.29 Total impact

  • Tim H. Osborn · Amir A. Farajian
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    ABSTRACT: Applications based on silicene as grown on substrates are of high interest toward actual utilization of this unique material. Here we explore, from first principles, the nature of carbon monoxide adsorption on semiconducting silicene nanoribbons and the resulting quantum conduction modulation with and without silver contacts for sensing applications. We find that quantum conduction is detectably modified by weak chemisorption of a single CO molecule on a pristine silicene nanoribbon. This modification can be attributed to the charge transfer from CO to the silicene nanoribbon and the deformation induced by the CO chemisorption. Moderate binding energies provide an optimal mix of high detectability and recoverability. With Ag contacts attached to a ∼1 nm silicene nanoribbon, the interface states mask the conductance modulations caused by CO adsorption, emphasizing length effects for sensor applications. The effects of atmospheric gases—nitrogen, oxygen, carbon dioxide, and water—as well as CO adsorption density and edge-dangling bond defects, on sensor functionality are also investigated. Our results reveal pristine silicene nanoribbons as a promising new sensing material with single molecule resolution.
    Nano Research 06/2014; 7(7). DOI:10.1007/s12274-014-0454-7 · 6.96 Impact Factor
  • Kirti K. Paulla · Ahmed J. Hassan · Cory R. Knick · Amir A. Farajian
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    ABSTRACT: Adsorption of functional groups on graphene nanoribbons has fundamental impacts on their applications in areas as diverge as energy storage, nanoelectronics, drug delivery, and sensors. To reveal adsorption geometries, energy barriers, and room temperature rate constants for assessing reaction kinetics, we study interactions of NO2 molecules with ultra-narrow (1 nm) hydrogen terminated armchair graphene nanoribbons (AGNRs), using first principles. We show that formation of hydrogen bonded NO2 at the edge and physisorbed NO2 at the center are processes without barriers, whereas chemisorption at center or edge are activated processes. Nonbonding and weak sp3 hybridization at the edge of AGNR are shown to be more favorable than center adsorptions, revealing increased reactivity compared to graphene. Resultant modulations of quantum transport are calculated for sensing extremely low gas concentrations. Detectable current decrease is predicted for two hydrogen-bonded or chemisorbed molecules. We discuss possible measures to enhance sensitivity of GNRs for detecting extremely low concentrations of nitrogen dioxide and similar molecules.
    RSC Advances 01/2014; 4(5):2346. DOI:10.1039/c3ra46372a · 3.84 Impact Factor
  • Kirti K. Paulla · Amir A. Farajian
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    ABSTRACT: We study detection of CO and CO2 gas molecules by change in quantum conductance of armchair graphene nanoribbons (AGNR) with a width of 1 nm. Quantum conductance modulations are calculated by using the second-order Møller–Plesset (MP2) method and density functional theory (DFT) for geometry optimization and a hybrid approach for electronic structure calculations. We determine stable and metastable physisorption orientations of gas molecules with varying concentrations. Our MP2-calculated binding energies relate 8.33% and 16.33% surface coverages of CO and CO2, respectively, to 1.72 × 104 and 497 ppm. With such concentrations, adsorption of molecules results in conductance characteristics shifts on the order of few meV. As the concentrations detected in experiments are much less, other mechanisms including substrate and/or carrier gas doping as well as adsorption on defects or electrodes may contribute toward gas sensing using graphene plates. We also discuss temperature effects and propose possible methods for improving gas detection by GNRs.
    The Journal of Physical Chemistry C 06/2013; 117(24):12815–12825. DOI:10.1021/jp312711s · 4.77 Impact Factor
  • Kirti K Paulla · Amir A Farajian
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    ABSTRACT: We study the electronic and magnetic structures of bilayer graphene nanoribbons (BGNRs) beyond the conventional AA and AB stackings, by using density functional theory within both local density and generalized gradient approximations (LDA and GGA). Our results show that, irrespective of the method chosen, stacking arrangements other than the conventional ones are most stable, and result in significant modification of BGNR characteristics. The most stable bilayer armchair and zigzag structures with a width of ∼1 nm are semiconducting with band gaps of 0.04 and 0.05 eV, respectively. We show mechanical shift evolution of magnetic states and the emergence of magnetization upon mechanical deformation in bilayer zigzag GNRs. Band gap dependence on mechanical shift can be used to design accurate nanosensors.
    Journal of Physics Condensed Matter 03/2013; 25(11):115303. DOI:10.1088/0953-8984/25/11/115303 · 2.35 Impact Factor
  • Tim H. Osborn · Amir A. Farajian
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    ABSTRACT: We explore the adsorption characteristics and stability of lithium on silicene from first principles. Our work shows that lithium adsorption could provide a unique method for isolating a stable silicene-based material while inducing a bandgap. We explore the energetics, temperature dependent dynamics, phonon frequencies, and electronic structure associated with lithium chemisorption on silicene. Our results predict the stability of completely lithiated silicene sheets (silicel) in which lithium atoms adsorb on the atom-down sites on both sides of the silicene sheet. Stability is confirmed by molecular dynamics simulations conducted at elevated temperatures and real phonon frequencies for all k-values. Upon complete lithiation, the band structure of silicene is transformed from a zero-gap semiconductor to a 0.368 eV bandgap semiconductor. This new, uniquely stable, two-atom-thick, semiconductor material could be of interest for nanoscale electronic devices.
    The Journal of Physical Chemistry C 10/2012; 116(43):22916–22920. DOI:10.1021/jp306889x · 4.77 Impact Factor
  • A. A. Farajian · B. I. Yakobson · H. Mizuseki · Y. Kawazoe
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    ABSTRACT: The electronic transport through bent single-wall carbon nanotubes is studied. Using a four-orbital per atom tight-binding model, the relaxed configurations of a (10, 0) semiconducting nanotube at different bending angles are first obtained. The optimized structures are then used in calculating conductance and current–voltage characteristics of the systems. These results are used to establish a correspondence between the mechanical deformation and transport properties, with potential applications in, e.g., nanoswitches. The source of the switching behavior is explained in terms of the localized states within the bent region.
    International Journal of Nanoscience 11/2011; 03(01n02). DOI:10.1142/S0219581X04001900
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    ABSTRACT: Silicene, a silicon equivalent of graphene, is a newly synthesized nanostructure with unique features and promising potential. Using density functional theory, the geometries and energetics of partially hydrogenated silicene (hydrogenation ratios between 3.1 and 100 atom%) are calculated. We find that the hydrogenation energy increases with the hydrogenation ratio, reaching 3.01 eV/H for complete hydrogenation. Molecular dynamics simulations reveal the stability of the adsorption configurations. Our results show that partial and patterned hydrogenation, achievable through exposing silicene to hydrogen gas with various densities and/or masking techniques, provide the attractive possibility of metal/semiconductor/insulator functionality within the same silicon nanosheet.Graphical abstractView high quality image (110K)Highlights► Density functional geometries and energetics of partially hydrogenated silicene. ► Stability assessment via molecular dynamics simulations. ► Possibility of engineering silicene’s electronic and transport properties. ► Metal/semiconductor/insulator functionality within the same silicon nanosheet.
    Chemical Physics Letters 07/2011; 511(1-3):101-105. DOI:10.1016/j.cplett.2011.06.009 · 1.99 Impact Factor
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    Narjes Gorjizadeh · Yoshiyuki Kawazoe · Amir A. Farajian
    Physics and Applications of Graphene - Theory, 03/2011; , ISBN: 978-953-307-152-7
  • Ahmed Hassan · Cory Knick · Amir Farajian
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    ABSTRACT: Graphene nanoribbons have the potential of being used as the functional part of nanoelectronic gas sensors. This study focuses on the changes induced in the conduction of graphene nanoribbons upon adsorption of NO2. Both chemisorption and physisorption situations, i.e., NO2 adsorption with and without chemical bond formation, are studied. We use ab initio electronic structure calculations with MP2 correlation energy in order to optimize the structures of graphene nanoribbons, with hydrogen-terminated edges, in presence of NO2. Subsequently, quantum conductance calculations are performed using Green's function implementation of the Landauer's approach. We explain different conductance modulation patterns in terms of charge transfer and dipole interactions. The results clarify some of the basic functionality issues of nanoelectronic-based gas sensors.
  • Narjes Gorjizadeh · Amir A Farajian · Yoshiyuki Kawazoe
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    ABSTRACT: The effect of electron-phonon (e-ph) interaction on the conductance of carbon chains is investigated by a non-equilibrium Green's function technique combined with a four-orbitals-per-atom tight-binding Hamiltonian. The optimized structure of the chain is found to be the semiconducting polyyne type (···-C≡C-C≡C-···). Our results show that the conductance of a carbon chain attached to two fixed contacts decreases due to e-ph interaction, and this reduction is stronger for longitudinal phonon modes which decrease the hopping energy between carbon atoms. Study of individual phonon modes reveals that emission of longitudinal phonons is stronger than that of transverse modes at room temperature, while absorption of transverse phonons is dominant. Conductance at finite temperature is also studied by considering the overall phonon effects; this shows that the reduction of the conductance is stronger at higher temperatures. The results are explained on the basis of the unique features of the carbon chain band structure.
    Journal of Physics Condensed Matter 02/2011; 23(7):075301. DOI:10.1088/0953-8984/23/7/075301 · 2.35 Impact Factor
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    ABSTRACT: Direct ultrasonication of graphite particles dispersed in water, in the presence of a surfactant, is a promising way to produce pristine nanoscale graphene platelets (NGPs) without graphite intercalation or oxidation. We investigate possible exfoliation mechanisms, specifically those involving sodium dodecylbenzenesulfonate (SDBS) surfactant, and compare their corresponding energies. The model includes interlayer van der Waals interactions and a force-field approach capable of treating charged surfactant and solvent. Our calculations reveal the significant role of SDBS in liquid-phase NGP production, through a locking mechanism that prevents restacking.
    The Journal of Physical Chemistry C 11/2010; 114(49). DOI:10.1021/jp1071378 · 4.77 Impact Factor
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    ABSTRACT: Oscillation mechanism of carbon nanotubes (CNTs) under various external electric fields is investigated by performing first principles molecular dynamics (MD) calculations on closed and open ended CNTs. From MD calculations we observe that in addition to the strength of the induced dipole moment temperature chirality and moment of inertia of a CNT affect its oscillation frequency We propose a procedure to discriminate CNTs with different moments of inertia and/or chiralities based on their different oscillation frequencies The implication of our results in the process of nanotube insertion into biological cells where the existing field across the cell membrance facilitates CNT penetration is also discussed (C) 2010 The Japan Society of Applied Physics
    Japanese Journal of Applied Physics 11/2010; 49(11):5103. DOI:10.1143/JJAP.49.115103 · 1.06 Impact Factor
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    L. C. Lew Yan Voon · E. Sandberg · R. S. Aga · A. A. Farajian
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    ABSTRACT: The structural and electronic properties of the hydrides of silicene and germanene have been studied using ab initio calculations. The trend for the M–H ( M = C , Si, and Ge) bond lengths, and corresponding bond energies, is consistent with the atomic size trend, and comparable to those of MH <sub>4</sub> hydrides. Band structures were also obtained for the buckled configuration, which is the stable form for both silicene and germanene. Upon hydrogenation, both silicane (indirect gap) and germanane (direct gap) are semiconducting.
    Applied Physics Letters 11/2010; 97(16-97):163114 - 163114-3. DOI:10.1063/1.3495786 · 3.52 Impact Factor
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    ABSTRACT: The structural configurations and electronic properties of polythiophene-cyclodextrin (PT-CD) inclusion complexes have been investigated by a combined quantum mechanics and molecular mechanics method. The results show that the structure of n-type PT in CDs has a quinoidlike form. In the cases of β-cyclodextrins and cross-linking α-cyclodextrins the electronic structure of polythiophene is almost the same as that of polythiophene in free space. The dopants are located outside the CDs, and hence for realization of a doped polymer chain it is important to control the separation distance between CDs, which can be easily achieved in the case of a molecular nanotube of cross-linking α-CDs.
    Molecular Crystals and Liquid Crystals 07/2010; 406(1):1-10. DOI:10.1080/744818981 · 0.58 Impact Factor
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    ABSTRACT: We calculate the quantum transport of a nanoelectronic gas sensor for various adsorption orentations of the gas molecules. The nanosensor employs electronic transport properties of a carbon nanotube exposed to NO2 molecules. The calculations are based on ab initio electronic structures, combined with the Green's function formulation of Landauer's transport theory. Our results show that different energetically equivalent orientations of the NO2 molecules result in different details of transport characteristics. The main features of transport modulation, however, are the same for all the orientations. Implications for nanotube-based gas sensors are discussed.
  • Ed Sandberg · Lok Lew Yan Voon · Rachel Aga · Amir Farajian
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    ABSTRACT: The structure, stability and electronic properties of nanosheets of group-IV elements were studied using density-functional theory. The nature of bonding with hydrogen was investigated by analyzing the electron density distribution and by calculating the binding energy.
  • Tim H. Osborn · Amir A. Farajian · Lok C. Lew Yan Voon · Rachel Aga
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    ABSTRACT: The energies and temperature-dependent dynamics of hydrogen chemisorption on a silicon nanosheet were studied using density functional theory and molecular-dynamics (MD) simulations. Energy calculations were performed by utilizing generalized-gradient approximation with the Perdew-Burke-Ernzerhof exchange correlation functional. The adsorption energies of hydrogen on the silicon nanosheet were calculated for different hydrogenation ratios corresponding to weight percents between 0 and 3.59 %. The preferred adsorption configurations were determined based on these energy calculations. MD simulations revealed the stability of adsorption configurations, and possible transitions between them, at different temperatures.
  • Narjes Gorjizadeh · Amir A Farajian · Yoshiyuki Kawazoe
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    ABSTRACT: The quantum conductance of graphene nanoribbons that include vacancy and adatom-vacancy defects is studied for both armchair and zigzag edge structures. The conductance is calculated by using the Green's function formalism combined with a tight-binding method for the description of the system. Our results reveal that, owing to the localized states that appear near the defect sites, the conductance of the defected nanoribbons generally decreases. We show that details of the conductance reduction depend on the structure of the defect, its distance from the ribbon edges, and the ribbon width. While some defect structures cause the conductance of the ribbon to vanish, some other defects have no effect on the conductance at the Fermi energy.
    Nanotechnology 02/2009; 20(1):015201. DOI:10.1088/0957-4484/20/1/015201 · 3.67 Impact Factor
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    ABSTRACT: We investigate electronic and magnetic properties of graphene nanoribbons whose edges are doped by s-, p-, and d-type atoms. The edges of the ribbon are chemically active and can accommodate appropriate dopants to obtain different electronic and magnetic properties, all with the same geometrical structure of the ribbon. Dopings by Mg and B turn the semiconducting armchair ribbon into a metal, while Fe and Mn change it into a ferromagnet with a large magnetic moment. Doping of zigzag ribbon and implications for transport characteristics are also discussed. Our results suggest that the present structures are suitable for nanoelectronic and spintronic applications.
    Physical Review B 10/2008; 78(15). DOI:10.1103/PhysRevB.78.155427 · 3.74 Impact Factor
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    ABSTRACT: We theoretically investigate the polarization, aggregation, and yield stress in carbon nanotube suspensions under an electric field. The nanotubes are modeled as solid rods with hemispherical ends. An exact numerical approach, which includes self-consistent Coulomb interactions within classical electrostatics, is employed to derive nanotube surface charge densities. Two essential nanotube characteristics, i.e., large aspect ratios and end contributions, are included together. The reliability of the model is demonstrated by comparing the calcu-lated emerging yields against experimental data. The onsets of system parameters can be used to control the phase transition in nanotube suspensions.
    Physical review. B, Condensed matter 05/2008; 77(20). DOI:10.1103/PhysRevB.77.205432 · 3.66 Impact Factor

Publication Stats

1k Citations
174.29 Total Impact Points

Institutions

  • 2008–2014
    • Wright State University
      • Department of Mechanical and Materials Engineering
      Dayton, Ohio, United States
  • 1998–2011
    • Tohoku University
      • Institute for Materials Research
      Japan
  • 2007–2008
    • Rice University
      • Department of Mechanical Engineering and Materials Science
      Houston, Texas, United States
  • 2001–2002
    • National Institute of Advanced Industrial Science and Technology
      Tsukuba, Ibaraki, Japan