arXiv subjects

Bohayra Mortazavi

Publications and source records attributed to Bohayra Mortazavi.

At least 55 records · Page 3Linked to original sources

arXiv2018

Theoretical Investigation: 2D N-Graphdiyne Nanosheets as Promising Anode Materials for Li/Na Rechargeable Storage Devices

N-graphdiyne monolayers, a set of carbon-nitride nanosheets, have been synthesized recently through the polymerization of triazine- and pyrazine-based monomers. Since the two-dimensional nano-structures are mainly composed of light-weight nonmetallic elements including carbon and nitrogen, they might be able to provide high storage capacities for rechargeable cells. In this study, we used extensive first principle calculations such as electronic density of states, band structure, adsorption energy, open-circuit voltage, nudged-elastic band and charge analyses to investigate the application of the newly fabricated N-graphdiyne monolayers as the anode material for Li/Na/Mg ion batteries. Our calculations suggest that while Mg foreign atoms poorly interact with monolayers, Li and Na adatoms illustrate outstanding anodic characteristics for rechargeable storage cells. Electronic density of states calculations indicate that the insertion of Li/Na into the novel N-graphdiyne materials enhances the electrical conductivity of nanosheets. Adsorption energy and open-circuit voltage calculations predict that the nanosheets can provide a high storage capacity spectrum of 623-2180 mAh/g which is higher than that for most recently discovered 2D materials (e.g. phosphorene, borophane, and germanene involve Li binding capacities of 433, 504, and 369 mAh/g, respectively) and it is also significantly greater than the capacity of commercial anode materials (e.g. graphite contains a capacity of 372 mAh/g). This study provides valuable insights about the electronic characteristics of newly fabricated N-graphdiyne nanomaterials, rendering them as promising candidates to be used in the growing industry of rechargeable storage devices.

physics.comp-ph↗

arXiv2018

First-principles investigation of Ag-, Co-, Cr-, Cu-, Fe-, Mn-, Ni-, Pd- and Rh-hexaaminobenzene 2D metal-organic frameworks

In the latest experimental advances, Ni-, Co- and Cu-HAB MOFs were synthesized in 2D forms, with high electrical conductivities and capacitances as well. Motivated by these experimental advances, we employed first-principles simulations to explore the mechanical, thermal stability and electronic properties of single-layer Ag-, Co-, Cr-, Cu-, Fe-, Mn-, Ni-, Pd- and Rh-HAB MOFs. Theoretical results reveal that Co-, Cr-, Fe-, Mn-, Ni-, Pd- and Rh-HAB nanosheets exhibit linear elasticity with considerable tensile strengths. Ab-initio molecular dynamics results confirm the high thermal stability of all studied nanomembranes. Co- and Fe-HAB monolayers show metallic behavior with low spin-polarization at the Fermi level. Single-layer Ag-, Cu-, Cr-, and Mn-HAB however yield perfect half-metallic behaviors, thus can be promising candidates for the spintronics. In contrast, Ni-, Pd- and Rh-HAB monolayers exhibit nonmagnetic metallic behavior. The insights provided by this investigation confirm the stability and highlight the outstanding physics of transition metal-HAB nanosheets, which are not only highly attractive for the energy storage systems, but may also serve for other advanced applications, like spintronics.

physics.comp-ph↗

arXiv2018

N-, P-, As-triphenylene-graphdiyne: Strong and stable 2D semiconductors with outstanding capacities as anodes for Li-ion batteries

Since the first report of graphdiyne nanomembranes synthesis in 2010, different novel graphdiyne nanosheets have been fabricated. In a latest experimental advance, triphenylene-graphdiyne (TpG), a novel two-dimensional (2D) material was fabricated using the liquid/liquid interfacial method. In this study, we employed extensive first-principles simulations to investigate the mechanical/failure, thermal stability, electronic and optical properties of single-layer TpG. In addition, we predicted and explored the properties of nitrogenated-, phosphorated- and arsenicated-TpG monolayers. Our results reveal that TpG, N-TpG, P-TpG and As-TpG nanosheets can exhibit outstanding thermal stability. These nanomembranes moreover were found to yield linear elasticity with considerable tensile strengths. Notably, it was predicted that monolayer TpG, As-TpG, P-TpG and N-TpG show semiconducting electronic characters with direct band-gaps of 1.94 eV, 0.88 eV, 1.54 eV and 1.91 eV, respectively, along with highly attractive optical properties. We particularly analyzed the application prospect of these novel 2D materials as anodes for Li-ion batteries. Remarkably, P-TpG and N-TpG nanosheets were predicted to yield ultrahigh charge capacities of 1979 mAh/g and 2664 mAh/g, respectively, for Li-ions storage. The acquired results by this work suggest TpG based nanomembranes as highly promising candidates for the design of flexible nanoelectronics and energy storage devices.

physics.comp-ph↗

arXiv2018

Anisotropic mechanical properties and strain tuneable band-gap in single-layer SiP, SiAs, GeP and GeAs

In this investigation, we conducted density functional theory simulations to explore the mechanical responses of single-layer GeP, GeAs, SiP and SiAs. In particular, we explored the possibility of band-gap engineering in these 2D structures through different mechanical loading conditions.First-principles results of uniaxial tensile simulations confirm anisotropic mechanical responses of these novel 2D structures, with considerably higher elastic modulus, tensile strength and stretchability along the zigzag direction as compared with the armchair direction. Notably, the stretchability of considered monolayers along the zigzag direction was found to be slightly higher than that of the single-layer graphene and h-BN. The electronic band-gaps of energy minimized single-layer SiP, SiAs, GeP and GeAs were estimated by HSE06 method to be 2.58 eV, 2.3 eV, 2.24 eV and 1.98 eV, respectively. Our results highlight the strain tuneable band-gap character in single-layer SiP, SiAs, GeP and GeAs and suggest that various mechanical loading conditions can be employed to finely narrow the electronic band-gaps in these structures.

physics.comp-ph↗

arXiv2018

Hydrogenation and defect formation control the strength and ductility of MoS2 nanosheets: Reactive molecular dynamics simulation

Two-dimensional (2D) molybdenum disulfide (MoS2) has attracted significant attention because of its outstanding properties, suitable for application in several critical technologies like, solar cells, photocatalysis, lithium-ion batteries, nanoelectronics, and electrocatalysis. Similar to graphene and other 2D materials, the physical and chemical properties of MoS2 can be tuned by the chemical functionalization and defects. In this investigation, our objective is to explore the mechanical properties of single-layer MoS2 functionalized by the hydrogen atoms. We moreover analyze the effects of different types of defects on the mechanical response of MoS2 at the room temperature. To investigate these systems, we conducted reactive molecular dynamics simulations using the ReaxFF forcefield. We demonstrate that an increase in the hydrogen adatoms or defects contents significantly affects the critical mechanical characteristics of MoS2, elastic modulus, tensile strength, stretchability and failure behavior. Our reactive molecular dynamics results provide useful information concerning the mechanical response of hydrogenated and defective MoS2 and the design of nanodevices.

physics.comp-ph↗

arXiv2018

N-Graphdiyne two-dimensional nanomaterials: Semiconductors with low thermal conductivity and high stretchability

We conducted density functional theory (DFT) and molecular dynamics simulations to explore the mechanical/failure, thermal conductivity and stability, electronic and optical properties of three N-graphdiyne nanomembranes. Our DFT results of uniaxial tensile simulations reveal that these monolayers can yield remarkably high stretchability or tensile strength depending on the atomic structure and loading direction. Studied N-graphdiyne nanomembranes were found to exhibit semiconducting electronic character, with band-gap values ranging from 0.98 eV to 3.33 eV, based on the HSE06 estimations. The first absorption peak suggests that these 2D structures can absorb visible, IR and NIR light. Ab initio molecular dynamics results reveal that N-graphdiyne 2D structures can withstand at high temperatures, like 2000 K. Thermal conductivities of suspended single-layer N-graphdiyne sheets were predicted to be almost temperature independent and about three orders of magnitude smaller than that of the graphene. The comprehensive insight provided by this work highlights the outstanding physics of N-graphdiyne 2D nanomaterials, and suggest them as highly promising candidates for the design of novel stretchable nanodevices.

physics.comp-ph↗

arXiv2018

Boron-graphdiyne: superstretchable semiconductor with low thermal conductivity and ultrahigh capacity for Li, Na and Ca ions storage

Most recently, boron-graphdiyne, a π-conjugated two-dimensional (2D) structure made from merely sp carbon skeleton connected with boron atoms was successfully experimentally realized through a bottom-to-up synthetic strategy. Motivated by this exciting experimental advance, we conducted density functional theory (DFT) and classical molecular dynamics simulations to study the mechanical, thermal conductivity and stability, electronic and optical properties of single-layer B-graphdiyne. We particularly analyzed the application of this novel 2D material as an anode for Li, Na, Mg and Ca ions storage. Uniaxial tensile simulation results reveal that B-graphdiyne owing to its porous structure and flexibility can yield superstretchability. The single-layer B-graphdiyne was found to exhibit semiconducting electronic character, with a narrow band-gap of 1.15 eV based on the HSE06 prediction. It was confirmed that the mechanical straining can be employed to further tune the optical absorbance and electronic band-gap of B-graphdiyne. Ab initio molecular dynamics results reveal that B-graphdiyne can withstand at high temperatures, like 2500 K. The thermal conductivity of suspended single-layer B-graphdiyne was predicted to be very low, ~2.5 W/mK at the room temperature. Our first-principles results reveal the outstanding prospect of B-graphdiyne as an anode material with ultrahigh charge capacities of 808 mAh/g, 5174 mAh/g and 3557 mAh/g for Na, Ca and Li ions storage, respectively. The comprehensive insight provided by this investigation highlights the outstanding physics of B-graphdiyne nanomembranes, and suggest them as highly promising candidates for the design of novel stretchable nanoelectronics and energy storage devices.

physics.comp-ph↗

arXiv2018

2D Hydrogenated graphene-like borophene as a high capacity anode material for improved Li/Na ion batteries: A first principles study

Fast-growing electronics industry and future energy storage needs have encouraged the design of rechargeable batteries with higher storage capacities, and longer life times. In this regard, two-dimensional (2D) materials, specifically boron and carbon nanosheets, have garnered enthusiasm due to their fascinating electronic, optical, mechanical and chemical properties. Recently, a hydrogen boride (HB) nanosheet was successfully fabricated showing remarkable stability and superior physical properties. Motivated by this experimental study, we used first principle electronic structure calculations to study the feasibility of this nanosheet to serve as an anode material for Li/Na/Ca/Mg/Al ion batteries. Most active adsorption sites for single adatoms were evaluated and next adatoms were gradually inserted into the anode surface accordingly. The charge transfer, electronic density of sates, storage capacity, structural stability, open-circuit potential and diffusion energy barriers were explored. Our theoretical study predicts that HB shows outstanding electrode properties for Li and Na ion batteries. The intercalation of both Li and Na adatoms into the HB monolayer can lead to a high identical storage capacity of 1133.8 mAh/g which is promising compared to the capacities of the traditional anode materials; such as graphite (372 mAh/g) and TiO2 (200 mAh/g), and other 2D materials; such as germanene (369 mAh/g), stanene (226 mAh/g), and phosphorene (432.8 mAh/g) nanosheets. These results may open a new horizon for the design of rechargeable batteries with higher storage capacitates.

physics.app-ph↗

arXiv2018

Mechanical responses of two-dimensional MoTe2; pristine 2H, 1T and 1T' and 1T'/2H heterostructure

Transition metal dichalcogenides (TMD) are currently among the most interesting two-dimensional (2D) materials due to their outstanding properties. MoTe2 involves attractive polymorphic TMD crystals which can exist in three different 2D atomic lattices of 2H, 1T and 1T', with diverse properties, like semiconducting and metallic electronic characters. Using the polymorphic heteroepitaxy, most recently coplanar semiconductor/metal (2H/1T') few-layer MoTe2 heterostructures were experimentally synthesized, highly promising to build circuit components for next generation nanoelectronics. Motivated by the recent experimental advances, we conducted first-principles calculations to explore the mechanical properties of single-layer MoTe2 structures. We first studied the mechanical responses of pristine and single-layer 2H-, 1T- and 1T'-MoTe2. In these cases we particularly analyzed the possibility of engineering of the electronic properties of these attractive 2D structures using the biaxial or uniaxial tensile loadings. Finally, the mechanical-failure responses of 1T'/2H-MoTe2 heterostructure were explored, which confirms the remarkable strength of this novel 2D system.

physics.comp-ph↗

arXiv2018

Borophene hydride: a stiff 2D material with high thermal conductivity and attractive optical and electronic properties

Two-dimensional (2D) structures of boron atoms so called borophene, have recently attracted remarkable attention. In a latest exciting experimental study, a hydrogenated borophene structure was realized. Motivated by this success, we conducted extensive first-principles calculations to explore the mechanical, thermal conduction, electronic and optical responses of borophene hydride. The mechanical response of borophene hydride was found to be anisotropic in which it can yield an elastic modulus of 131 N/m and a high tensile strength of 19.9 N/m along the armchair direction. Notably, it was shown that by applying mechanical loading the metallic electronic character of borophene hydride can be altered to direct band-gap semiconducting, very appealing for the application in nanoelectronics. The absorption edge of the imaginary part of the dielectric function was found to occur in the visible range of light for parallel polarization. Finally, it was estimated that this novel 2D structure at the room temperature can exhibit high thermal conductivities of 335 W/mK and 293 W/mK along zigzag and armchair directions, respectively. Our study confirms that borophene hydride benefits an outstanding combination of interesting mechanical, electronic, optical and thermal conduction properties, promising for the design of novel nanodevices.

physics.comp-ph↗

arXiv2018

Edge-Grafted Molecular Junctions between Graphene Nanoplatelets: Applied Chemistry to Enhance Heat Transfer in Nanomaterials

The edge-functionalization of graphene nanoplatelets (GnP) was carried out exploiting diazonium chemistry, aiming at the synthesis of edge decorated nanoparticles to be used as building blocks in the preparation of engineered nanostructured materials for enhanced heat transfer. Indeed, both phenol functionalized and dianiline-bridged GnP (GnP-OH and E-GnP, respectively) were assembled in nanopapers exploiting the formation of non-covalent and covalent molecular junctions, respectively. Molecular dynamics allowed to estimate the thermal conductance for the two different types of molecular junction, suggesting a factor 6 between conductance of covalent vs. non-covalent junctions. Furthermore, the chemical functionalization was observed to drive the self-organization of the nanoflakes into the nanopapers, leading to a 20% enhancement of the thermal conductivity for GnP-OH and E-GnP while the cross plane thermal conductivity was boosted by 150% in the case of E-GnP. The application of chemical functionalization to the engineering of contact resistance in nanoparticles network was therefore validated as a fascinating route for the enhancement of heat exchange efficiency on nanoparticle networks, with great potential impact in low-temperature heat exchange and recovery applications

cond-mat.mtrl-sci↗

arXiv2018

Carbon ene-yne graphyne monolayer as an outstanding anode material for Li/Naion batteries

Recently "carbon ene-yne" (CEY), a novel full carbon two-dimensional (2D) material was successfully synthesized by the solvent-phase reaction. Motivated by this experimental effort, we conducted extensive first-principles density functional theory simulations to explore the application prospects of CEY as an anode material for Mg, Na and Li-ion batteries. To simulate the ionic intercalation process in an anode electrode, the adatoms coverage was gradually increased. We then employed Bader charge analysis to evaluate the charge transfer between the adatoms and the CEY nanosheet and finally to report the theoretical storage capacity of the anode. We particularly studied the evolution of adsorption energy, electronic density of states and open-circuit voltage with respect to adatoms coverage. The diffusion of an adatom over the CEY surface was also investigated by using the nudged elastic band method. Remarkably, our results suggest CEY as a promising anode material containing the highest theoretical charge capacities among 2D materials studied so far, with ultrahigh capacities of 2,680 mAh/g and 1,788 mAh/g for Li and Na-ion batteries, respectively. The provided insight by this study highlights the CEY as a novel full carbon material with properties, highly desirable for the application as anode material in the next generation rechargeable ion batteries.

cond-mat.mtrl-sci↗

arXiv2018

Mechanical, optoelectronic and transport properties of single-layer Ca2N and Sr2N electrides

Electride materials offer attractive physical properties due to their loosely bound electrons. Ca2N, an electride in the two-dimensional (2D) form was successfully recently synthesized. We conducted extensive first-principles calculations to explore the mechanical, electronic, optical and transport response of single-layer and free-standing Ca2N and Sr2N electrides to external strain. We show that Ca2N and Sr2N sheets present isotropic elastic properties with positive Poisson's ratios, however, they yield around 50% higher tensile strength along the zigzag direction as compared with armchair. We also showed that the strain has negligible effect on the conductivity of the materials; the current in the system reduces by less than 32% for the structure under ultimate uniaxial strain along the armchair direction. Compressive strain always increases the electronic transport in the systems due to stronger overlap of the atomic orbitals. Our results show that the optical spectra are anisotropic for light polarization parallel and perpendicular to the plane. Interband transition contributions along in-plane polarization are not negligible, by considering this effect the optical properties of Ca2N and Sr2N sheets in the low frequency regime significantly changed. The insight provided by this study can be useful for the future application of Ca2N and Sr2N in nanodevices.

physics.comp-ph↗

arXiv2017

Theoretical realization of Mo2P, a novel stable 2D material with superionic conductivity and attractive optical properties

Mo2P as a new member of the advancing two-dimensional (2D) materials family has been theoretically identified in this study. We conducted extensive density functional theory calculations to explore the crystal structure, dynamical stability, mechanical response, electronic structure and optical properties. Mo2P was found to be metallic with the Fermi energy locating at the d bands of transition metal Mo. A high reflectivity of ~100% at low energies less than 1 eV was observed, introducing Mo2P as a potential candidate for photonic and optoelectronic applications such as transmitting electromagnetic waves devices. Our calculations confirm that the novel 2D structure is dynamically stable and can withstand at high temperatures including 1000 K. Mo2P was found to yield high tensile strength and elastic modulus of 12 GPa.nm and 56 GPa.nm, respectively. We particularly evaluated the application of Mo2P as an anode material for Li and Na-ion rechargeable batteries.

cond-mat.mtrl-sci↗

arXiv2017

Adsorption of Metallic, Metalloidic, and Nonmetallic Adatoms on Two-Dimensional C3N

Two-dimensional polyaniline with a C3N stoichiometry, is a newly fabricated material that has expected to possess fascinating electronic, thermal, mechanical and chemical properties . The possibility of further tuning the C3N properties upon the adsorption of foreign adatoms is thus among the most attractive researches. We carried out extensive ab-initio density functional theory (DFT) simulations to investigate the adsorption of various elements including nonmetallic, metalloidic and metallic elements on the C3N monolayer. While pristine C3N acts as a semiconductor with an indirect electronic band gap; the functionalization with nonmetallic and semimetallic elements leads to a p-type doping and induces metallic behavior to the monolayer. On the other hand, metallic adsorption depending on the adatom size and the number of valence electrons may result in semiconducting, half-metallic or metallic properties. Whenever metallic foreign atoms conduct metallic characteristics, they mostly lead to the n-type doping by electron donation to the surface. Moreover, adsorption of transition metals could enhance the magnetic behavior of the monolayer due to the contribution of d electronic states. These results suggest that C3N illustrates viable electronic-magnetic properties which could be promising for semiconducting, nanosensores and catalytic applications.

physics.comp-ph↗

arXiv2017

Electronic, optical and thermal properties of highly stretchable 2D carbon Ene-yne graphyne

Recently, a new carbon-based two-dimensional (2D) material, so called "carbon Ene-yne" (CEY), was successfully synthesized. In this work, we examine electronic, optical and thermal properties of this novel material. We studied the stretchability of CEY via density functional theory (DFT) calculations. Using the PBE and HSE06 functionals, as well as the G$_0$W$_0$ method and the Bethe-Salpeter equation, we systematically explored electronic and optical properties of 2D CEY. In particular, we investigated the change of band-gap and optical properties under uniaxial and biaxial strain. Ab-initio molecular dynamics simulations confirm that CEY is stable at temperatures as high as 1500 K. Using non-equilibrium molecular dynamics simulations, the thermal conductivity of CEY was predicted to be anisotropic and three orders of magnitude smaller than that of graphene. We found that in the visible range, the optical conductivity under high strain levels is larger than that of graphene. This enhancement in optical conductivity may allow CEY to be used in photovoltaic cells. Moreover, CEY shows anisotropic optical responses for x- and y- polarized light, which may be suitable as an optical linear polarizer. The comprehensive insight provided by the present investigation should serve as a guide for possible applications of CEY in nanodevices.

cond-mat.mtrl-sci↗

arXiv2017

Graphene or h-BN paraffin composite structures for the thermal management of Li-ion batteries: A multiscale investigation

The reliability and safety of lithium-ion batteries can be affected by overheating issues. Phase change materials like paraffin due to their large heat capacities are among the best solutions for the thermal management of batteries. In this investigation, multiscale modelling techniques were developed to explore the efficiency in the thermal management of rechargeable batteries through employing the paraffin composite structures. A combined atomistic-continuum multiscale modelling was conducted to evaluate the thermal conductivity of paraffin reinforced with graphene or hexagonal boron-nitride nanosheet additives. In addition, heat generation during a battery service was simulated using the Newman's electrochemical model. Finally, three-dimensional heat transfer models were constructed to investigate the effectiveness of various paraffin composite structures in the thermal management of a battery system. Interestingly, it was found that the thermal conductivity of paraffin nanocomposites can be enhanced by several times but that does not yield significant improvement in the batteries thermal management over the pure paraffin. The acquired findings can be useful not only for the modelling of nanocomposites but more importantly for the improvement of phase change materials design to enhance the thermal management of rechargeable batteries and other electronic devices.

physics.comp-ph↗

arXiv2017

Anomalous strain effect on the thermal conductivity of borophene: a reactive molecular dynamics study

Borophene, an atomically thin, corrugated, crystalline two-dimensional boron sheet, has been recently synthesized. We investigate mechanical properties and lattice thermal conductivity of borophene via reactive molecular dynamics simulations. We performed uniaxial tensile strain simulations at room temperature along in-plane directions, and found 2D elastic moduli of 188 N/m and 403 N/m along zigzag and armchair directions, respectively. The anisotropy is attributed to the buckling of the borophene structure along the zigzag direction. We also performed non-equilibrium molecular dynamics to calculate the lattice thermal conductivity. We predict room-temperature lattice thermal conductivities of $75.9 \pm 5.0$ W/m-K and $147 \pm 7.3$ W/m-K, respectively, and estimate effective phonon mean free paths of $16.7 \pm 1.7$ nm and $21.4 \pm 1.0$ nm for the zigzag and armchair directions. The anisotropy is attributed to differences in the density of states of low-frequency phonons, with lower group velocities and possibly shorten phonon lifetimes along the zigzag direction. We also observe that when borophene is strained along the armchair direction there is a significant increase in thermal conductivity along that direction. Meanwhile, when the sample is strained along the zigzag direction there is a much smaller increase in thermal conductivity along that direction. For a strain of 8\% along the armchair direction the thermal conductivity increases by a factor of 3.5 (~250\%), whereas for the same amount of strain along the zigzag direction the increase is only by a factor of 1.2 (~20\%). Our predictions are in agreement with recent first principles results, at a fraction of the computational cost. The simulations shall serve as a guide for experiments concerning mechanical and thermal properties of borophene and related 2D materials.

cond-mat.mtrl-sci↗